CN1276870A - CT target detection using surface normals - Google Patents

Abstract

CT (120) baggage (112) inspection with a throughput on order of 700 bags (112) per hour is achieved by excluding unrelated data from reconstruction. By using a threshold, calibration 'air scans' can be performed with objects such as the system conveyor (110) in the field of view. The scanner identifies object shape to better detect sheet explosives. The system compensated for dark currents and temperature dependent current offsets.

Description

Utilize the surface normal CT target detection

Invention field

Relate generally to Computerized chromatographic X-radiography of the present invention (CT) scanner, and be particularly related to the luggage scanning system of using the CT technology.

Background of invention

As everyone knows, before luggage is emplaned, can adopt multiple X-ray luggage scanning system that luggage is detected, with existing of explosive substance and other prohibited items in detection luggage or the chest.The common technology of Measuring Object density is to use the x-ray irradiation object, and the radiation that Measuring Object absorbed, and the size of institute's absorbed radiation can correspondingly indicate the density of object.Because a feature of many explosive substances is that they are in the density range different with other article that can find in luggage, therefore, are fit to adopt the X-x-ray apparatus that explosive substance is surveyed.

The most X-ray luggage scanning systems that adopt are " line sweep instrument " type at present, it comprises a fixing X-ray source, a fixing line detector array, and one at luggage when the scanner, in order to the conveying belt of transmission luggage between X-ray source and detector array.X-ray source produces an X-beam, and this X-beam passes luggage, is partly decayed by luggage, and is detected the device array subsequently and receives.Measure interim at each, detector array produces the integration data of representing the luggage planar section density that the X-beam passed, and these data are used to form one or more grid strokes of a two dimensional image.When conveying belt transmission luggage passed through static X-ray source and detector array, scanner produced the two dimensional image of representing luggage density.Usually, this density image is shown by operating personnel, to be used for analysis.

Known, the X-ray source technology of employing double energy can provide the out of Memory about the object chemical property except density.Use the technology of double energy X-ray source to comprise the absorption characteristic of Measuring Object to the X-ray of two kinds of different-energy levels.These are measured except the density that can indicate object, can also refer to illustrate the atomic number of object.For example, at Alvarez, " energy in the X-ray computer tomo camera work is selected image reconstruction " (Phys.Med.Biol.1976 of people such as Robin, Vol.21, No.5,733-744) and U.S. Patent No. 5,132, in 998, this double energy x-ray technology of selecting image reconstruction about the energy of X-ray CT image has been described respectively.

A kind of recommended use of this double energy technology is as baggage scanner, to be used for surveying existing of luggage explosive substance.A popular feature of explosive substance is that its atomic number is in the known range, thereby is suitable for adopting the double energy X-ray source to survey.Be entitled as the pending U.S. Patent Application series No.08/671 of " improved double energy power supply " (Attorney Docket No.ANA-094), in 202, a kind of such double energy source has been described, this patent has been transferred to the assignee identical with the present invention, and here all is incorporated herein by reference.

The plastics explosive substance is owing to its plasticity and can make the geometric configuration that is difficult to survey, thereby has proposed a special challenge for the luggage scanning system.The weight that great majority can significantly endanger the explosive substance of an airplane are at least 1 pound, and its length and width and height are also enough greatly, thereby regardless of the orientation of explosive substance in luggage, can be detected by X-ray scanning system at an easy rate.Yet plastics explosive substance that is enough to endanger an airplane can be made the minimum and thin slice of the relative thin that size on two other direction is relatively large of in one direction size.Because be difficult to see in image explosive substance (particularly when object be placed with thin slice when being parallel to the direction of X-beam by system the time), therefore, detection plastics explosive substance may be difficult.

Therefore, the detection to suspicious luggage needs wholwe-hearted especially operating personnel.This specific demand to notice will cause operating personnel extremely tired, and the dispersion of tired and any notice all might cause suspicious duffel bag not to be detected by system.

Therefore, for designing a kind of better baggage scanner, made a large amount of effort.For example, at United States Patent(USP) Nos. 4,759,047 (people such as Donges); 4,884,289 (people such as Glockmann); 5,132,988 (people such as Tsutsui); 5,182,764 (people such as Peschmann); 5,247,561 (Kotowski); 5,319,547 (people such as Krug); 5,367,552 (people such as Peschmann); Among 5,490,218 (people such as Krug) and German patent DE 31 503 06 A1 (HeimannGmbH), similar design has been described respectively.

As at United States Patent(USP) Nos. 5,182,764 (people such as Peschmann) and 5,367,522 people such as () Peschmann (with call in the following text ' 764 He ' No. 552 patent) described in like that, at least a by business development in these designs is and at following being referred to as " no phantom machinery " (Invision Machine).This no phantom machinery comprises the CT scanner of a third generation type, and this scanner generally includes and is fastened on respectively in an annular table or the dish along an X-ray source and an X-ray detector system on the diametric relative both sides.Described dish is rotatably installed in the frame support part, thus the X-ray begin to pass from X-ray source in the opening that is placed on dish object and when arriving detector system, dish can be in operation continuously around a turning axle rotation.

Detector system can comprise a linear detector array, and it is arranged to circular-arcly be arranged in a unique sequence with one, and the center of curvature of circular arc is positioned at the focus of X-ray source (promptly being positioned at X-ray source and X-ray from its point that sends).X-ray source produces an X-ray fan-ray beam or a fan-beam that is sent by focus, and it passes a flat image field, is detected device then and receives.CT scanner comprises one by X, Y and the defined coordinate system of Z axle, and wherein, when the rotation of coiling turning axle, each coordinate axis intersects each other at the rotation center place of dish and is vertical mutually.This rotation center is commonly referred to and " waits " center ".The Z axle is determined that by turning axle X and Y-axis are then determined by the flat image place, and be positioned at wherein.Therefore, fladellum is defined in point source (being focus) and is subjected to determined spatial volume between the detector receiving surface of detector array of X-beam irradiation.Because the size of receiving plane on the Z-direction of principal axis of the linear array of detector is less relatively, so fladellum is thinner relatively on this direction.Each detector produces the output signal that a representative projects the X-transmitted intensity on the detector.Because the X-ray partly weakened by all substances on its road, thus the output signal representative that each detector produced be placed on the density of all substances in the image fields between X-ray source and this detector.

Along with the rotation of dish, detector array is periodically sampled, and in each measured at interval, each detector in the detector array produced the output signal of representative density of the part of scanned object in this interval.In arbitrary measurement at interval, the set of all output signals that all detectors produce in unique sequence detector array is called one " projection ", and when projection produced, the angular range of dish (with the respective corners orientation of X-ray source and detector array) was called " projected angle ".On each projected angle position, be called as increasing gradually of " ray " by X-raypath receiving surface zone from a point source to detector on xsect of focus to each detector, because the area of detector receiving surface is greater than the area of any xsect of the object that ray passed, therefore, it is considered to be the density measurements of having amplified.

When disk ring rotated around the object that is scanned, corresponding to a plurality of projected angles, scanner produced a plurality of projections.Utilize known algorithm, can produce the CT image of a target object by all data for projection of on each projected angle position, collecting.This CT image has been represented the density of a two dimension " section " of object, and this section is passed by fladellum during by different projected angle in disc spins.The resolution of CT image partly depends on the width in each detector receiving surface zone in the fladellum plane, here, the width of detector is defined in measured size on the direction identical with the Width of fladellum, and the length of detector is defined as along being parallel to scanner turning axle or Z-axle measured size on the direction perpendicular to fladellum here.

The speed that important design considerations is the scanner scanning luggage and articles of baggage scanner.As the utility device of arbitrary main airports, baggage scanner should be able to be with a large amount of baggages of very fast speed (for example, being about per hour 700 baggages or faster) scanning.For reaching this speed, scanner must be to scan the baggages of an average-size per approximately 5 seconds or smaller again speed scans.Therefore, the problem that no phantom machine exists is, ' 764 and ' No. 552 patents described in the scanner of type need be with the relative data that produce a monolithic CT image than the long time (for example, spiral turn around needs about 0.6 to 2.0 second).In addition, for each image, the beam section of passing baggages is thin more, and the resolution of image is good more, therefore, only is the plastics explosive substance of several millimeters thick for detecting, and CT scanner should provide the image with sufficiently high resolution.Need 0.6 to 2.0 second if produce the data of each slice CT image, the average length of supposing baggages is about 70cm, so, per hour pass through under the situation of 700 baggages desirable, because baggages must move and stop on each scanning position, a traditional CT baggage scanner only can produce average about two to three CT images for each baggages.Obviously, in the stipulated time of distributing to a reasonably quick throughput, can not scan whole baggages.Only can produce two to three CT images to each baggages and will stay multiple articles and be not scanned, thereby accurate or complete scanning can not be provided.

Summary of the invention

The invention provides a kind of luggage scanning system, this system has overcome the shortcoming in the prior art basically.Luggage scanning system of the present invention can not need operating personnel's intervention when scanner is passed through in the luggage transmission, per hour make an appointment with and can scan 700 baggages.

On the one hand, the invention provides a kind of apparatus and method in the CT scanner, be adapted to the size of each scanned object (for example every luggage), thereby improved the throughput of scanner greatly by the data reconstruction window that makes scanner.At this on the one hand, the present invention makes the reconstruct window be adapted to the size and the position of baggages in the scanner field of view, this reconstruct window determined by scan-data be reconstructed, with the number of the pixel that produces an image.CT machine scanning field of view is to produce the scan-data by the object of scanner.Size and the position thereof of object in the visual field is determined.Utilize the size and the position of target object, two parts pixel in the visual field is identified out.First's pixel is by reconstruct, and with the image of generation target object, and the second portion pixel that is identified needn't reconstruct.

Therefore, of the present invention this on the one hand, only those are provided about the pixel (being first's pixel) of the information of the baggages that are scanned and have handled when the image reconstruction.The pixel (being the second portion pixel) that those and baggages have nothing to do is refused reconstruct.Irrelevant pixel may comprise that those are positioned at the position below the baggages induction system, and contiguous and be positioned at the position of baggages top.Do not provide the pixel that relates to baggages information by giving up those effectively, the treatment capacity during reconstruct has reduced significantly, thereby has shortened reconstitution time, and the scanning throughput that has improved baggages.

In one embodiment, the size of the baggages in the visual field and position can be determined by the border of surveying baggages.This can utilize known boundary alignment method in the prior art, determines that by the analysis scan data object boundary is achieved.In one embodiment, parallel data for projection is analyzed to determine the border.In another embodiment, scanner comprises a standalone sensor, in order to survey the border of baggages.This sensor can be an acoustic sensor, such as the detector of a high-frequency ultrasonic scope, perhaps can be an optical sensor, and it can comprise one or more optical devices such as laser, light emitting diode, or infrared eye.Any one of these methods returned the data on expression baggages border, and these data can be in order to the center of indication baggages, thereby and indicates its position in scanner field of view.

In one embodiment, be identified as the pixel that has nothing to do with baggages and refuse reconstruct, and all pixels relevant with baggages are by reconstruct, to produce the complete image of baggages.This method can provide complete image (regardless of its size) for each baggages, and the scanning throughput that has been improved.Yet because the change in size wide range of baggages, therefore, the throughput of its treatment capacity and baggages is difficult to monitor and control.May have such situation, promptly the throughput of baggages can reduce, when for example scanner will be handled large quantities of special big baggages continuously.So, in another embodiment, for the overall dimension of reconstruct window has been set a upper limit.To can be accomplished this point by the maximum pixel number of reconstruct by setting one.This maximum pixel window can adapt to baggages sizing, position and volume really, thereby in predefined pixel reconstruction scope, can produce baggages image as well as possible.This method can be guaranteed the scanning throughput of baggages is maintained on the controllable level in the effective image that produces baggages.

By the irrelevant pixel of baggages of omitting from the image reconstruction process process and being analyzed, adaptability reconstruct window of the present invention provides obvious superiority.For example, eliminated obvious unnecessary data processing process, thereby shortened reconstitution time, and, increased the throughput of baggages according to of the requirement of busy commercial airport to the baggages throughput.

On the other hand, the invention provides a kind of system and method, in order in a CT system, to implement calibration or " sky " scanning, system is edited according to the variation that responds in indivedual detectors.Owing to be difficult to from the visual field of baggage scanner, remove barrier (as conveyer system) usually, therefore be difficult to according to implementing empty scanning at an easy rate in the same way as of the enterprising line space scanning of traditional CT machine.Scanner of the present invention can compensate the barrier that is present in the visual field when realizing empty calibration scan.

In one embodiment, calibration is to be undertaken by the mode of at first carrying out a visual field scanning under barrier is present in situation in the visual field and gathering out whole group data.Set a calibration threshold value, and each detector is selected the ken data that exceed threshold value, in order to calculate the calibration deviation value of this detector.The value that is lower than threshold value is rejected.In one embodiment, threshold setting gets enough high, thereby any data value that can draw above the Fujian value all is the conclusion of not passing the radioactive ray of barrier in the visual field, so it can suitably be used for empty calibration.For each detector, can be used for calculating the clearancen calibration value for this detector from the selected data value in the ken of not being obstructed.In one embodiment, get the mean value of selected value, to calculate empty calibration value.So, empty calibration value in the scanning of subsequently actual object as a standard, so that the response change between the detector is compensated.

By empty scan calibration data are put on the threshold value, can identify the data relevant with the raypath of not being obstructed.This can carry out the calibration of having leisure under the situation of not removing barrier from the visual field.This point is particular importance in baggage scanner, because in baggage scanner, scanning is carried out continuously, therefore causing removing from the visual field barrier (as conveyer) is extremely difficult to carry out sky scanning between baggages.Yet this method also is very favourable in the Medical CT field.Though to a certain extent, removing a patient table from a Medical CT scanning machine, remove conveyer than from baggage scanner comparatively convenient,, needn't removing patient table, can to carry out the empty scanning of Medical CT also will be a kind of significant improvement to Medical CT.Therefore, empty scanning of the present invention provides very big superiority in the Medical CT field.

On the other hand, the invention provides a kind of method and apparatus, be used for from the CT view data of an object of three dimensions, identifying a for example target object of tablet.As everyone knows, the plastics explosive substance can be made into chip shape, because the thickness of explosive substance thin slice may be less than the resolution of conventional CT scans instrument, this thus sheet explosive substance adopts traditional CT technology to be difficult to detect.In the present invention, can analyze, whether be a tablet with the shape of determining target object, and whether may be a plastics explosive substance the view data of a target object.

In apparatus and method of the present invention, whether by near the view data the evaluating objects body surface, can analyze target object is a tablet.The target object of being analyzed is determined by its border or surface in three dimensions.On each point of all points in target object surface, calculate a surface normal, and turned back in the target object by projection.On the many points in the line that returns by the surface normal projection, can form the CT data of target object, and obtain the density of target object.Can adopt interpolation method to calculate the data that each is put.Set a ultimate range of target approach object, and produce density up to maximum distance apart.Ultimate range is chosen as the maximum ga(u)ge of expecting greater than tablet.

After producing all density, for each normal, produce the distance of a target approach object, decay in this distance density.Usually, if density is decaying less than maximum distance apart, then this density measurements may represent to have a thin target object to exist, and it may be a tablet.And when still not having appreciable decay to take place up to maximum distance apart, show that then target object is thicker than a tablet.

The attenuation distance that calculates can be compiled a distribution plan, for example a bar chart (histogram).Subsequently, can analyze, to determine the shape of target object this bar chart.The peak value that occurs bar chart at the attenuation distance place less than ultimate range can show that the major part of target object has the thickness that equals attenuation distance.This can be used for indicating a tablet.And can show that at the peak value that bar chart appears in maximum distance apart the major part of target object has the thickness bigger than the expection thickness of a tablet.This can be used for indicating target object is not a tablet.

Adopt the method for the target object of surface normal and bar chart identification chip shape that the superiority that is better than other identification tablet method is provided.For example, in an existing method, the shape of target object is analyzed with the ratio of its volume by calculating its surface area.High ratio shows a thin target object, for example a tablet.Yet the not really accurately part of this method is that it only calculates a numerical value to whole object, and it is uncertain that this numerical solution gets up.Some has big surface area and the less relatively target object of volume may be designated as chip shape mistakenly.Contrast with it, the present invention can analyze on many points around whole target object.By the thickness distribution that spreads all over whole target object is carried out statistical study, can obtain the more accurate conclusion of target object shape.

On the other hand, the present invention proposes the apparatus and method that afford redress for " dark current " in the CT system (being the electric current that detector is produced) when not having the X-ray, particularly, the detector dark current is compensated with variation of temperature.According to the present invention, carry out a calibration operation, to characterize out dark current with variation of temperature.Utilize this variation, produce one group of detector deviation value.Each deviation value is that a specific temperature has been determined dark current or departed from electric current.In one embodiment, each detector is produced one group of deviation value.In another embodiment, one group of deviation value is used for all detectors.When subsequently actual scanning is carried out in a target object or zone, utilize deviation value to adjust the data-signal that detector produces.Scanning this regional in, the temperature of detector is detected.For each detector, will with current detection to the corresponding deviation value of temperature be applied on the signal that detector produces, adjusting density, thereby compensated temperature variant detector dark current by the detected target object of detector.

In one embodiment, during calibration variation of temperature be by will depart from-data point of right-temperature is fitted in one group of parametric equation and is described.In another embodiment, this variation is described by a constant coefficient Taylor series polynomial expression.This coefficient can be drawn by the minimum mean-square error analytic approach.

By being applied in the detector data with departing from of changing of temperature, luggage scanning system of the present invention can provide than the more accurate dark current compensation of existed system.Since as a rule, the luggage scanning system is running continuously, thereby under the luggage scanning circumstance, temperature effect is than even more important under medical environment.Therefore, by keep the quality of generation image and the ability of system's detection of a target article, just become very important with departing from of changing of temperature.So the present invention is by using temperature variant departing from, thereby provide more accurate CT baggage scanner.

Brief description of the drawings

In conjunction with the accompanying drawings, by the following more detailed explanation that preferred embodiment is done, aforementioned and other purpose of the present invention, characteristic and superiority will be more obvious.In each accompanying drawing, identical reference number is represented identical parts.Accompanying drawing needn't be drawn in proportion, and it focuses on illustrating principle of the present invention.

Fig. 1 is the skeleton view according to a luggage scanning system of the present invention.

Fig. 2 is the cross sectional end view of system shown in Figure 1.

Fig. 3 is the xsect radial view of system shown in Figure 1.

Fig. 4 is the schematic electric and mechanical block scheme of an embodiment of baggage scanner of the present invention.

Fig. 5 is the view field image synoptic diagram of baggage scanner of the present invention, shows to be in the visual field, is positioned at baggages on the transmission system.

Fig. 6 is the schematic chart that is superimposed upon the baggage scanner of the present invention visual field on the cartesian coordinate system.

Fig. 7 is the simplified schematic block scheme of an embodiment of luggage scanning system of the present invention, and it utilizes sensor to discern the border of baggages.

Fig. 8 A is the synoptic diagram of geometric configuration of radiographic source, detector array and the visual field of a conventional CT scans instrument.

Fig. 8 B is in the single pass of visual field shown in Fig. 8 A, the synoptic diagram of a data-signal that single detector obtained.

Fig. 9 A is the synoptic diagram of geometric configuration of an embodiment of baggage scanner of the present invention.

Fig. 9 B is in the single pass of visual field shown in Fig. 9 A, the synoptic diagram of a data-signal that single detector obtained.

Figure 10 is the synoptic diagram of the three dimensional CT image of an objective object.

Figure 11 is the density profile along the CT imaging surface normal of a thin target object and a thick target object.

Figure 12 A is the bar chart of the density decay distance of a thin target object.

Figure 12 B is the bar chart of the density decay distance of a thick target object.

The detailed description of accompanying drawing

Fig. 1, skeleton view, end cross-sectional view and the radial cross-section view of the luggage scanning system 100 that 2 and 3 show according to the present invention is respectively constructed.This system provides detection of a target object such as the sheet explosive substance that has strengthened) ability that exists, and can be regardless of their orientation.This system also provides fast and CT luggage scanning completely, thereby system can be scanned baggages reliably in the mode of relative high speed and high probability ground detection of a target object.System 100 comprises an induction system 110, is used for carrying luggage or chest 112 continuously along direction shown in the arrow 114, makes it the center pit by CT scan system 120.Induction system 110 comprises the conveying belt of motor driven, in order to support luggage.Among the figure, induction system 110 is represented as has many independent transportation sections 122; Yet, also can adopt the induction system of other form.CT scan system 120 comprises that one places the annular table in the frame support 125 or coils 124, and in order to rotate around a turning axle 127 (as shown in Figure 3), this turning axle is preferably the direct of travel 114 that is parallel to luggage 112.Can be by any suitable driving mechanism around turning axle 127 driving-discs 124, for example, adopt one to be with 116 and motor-driven system 118, perhaps, can adopt other suitable driving mechanism, as authorize the U.S. Patent No. 5 that is entitled as " X-tomographic scanning system " (Attorney DocketNo.ANA-30CON) of GilbertMcKenna in Dec 5 nineteen ninety-five, 473, described in 657 like that, this patent is transferred to assignee of the present invention, and here all is introduced into as a reference.Turntable 124 has been determined a center pit 126, and induction system 110 is carried luggage 112 by this hole.

System 120 comprises an X-ray tube 128 and a detector array 130, and detector array 130 is arranged in the platform 124 along diametric relative both sides.Detector array 130 can be a two-dimensional array, as described in the pending U.S. Patent Application that is entitled as " the regionally detecting device array that is used for computed tomography scanning system " (Attorney Docket No.ANA-137), this application and the application proposed on same, and here all were introduced into as a reference.System 120 also comprises in order to receive and to handle 134 and X-ray tubes of a data acquisition system (DAS) control system 136 of the information that is produced by detector array 130, with thinking that X-ray tube 128 provides power and controls its operation.System 120 also preferably has a computer system (not shown), in order to the signal of deal with data acquisition system 134 output, and produces and is used for the required signal of operation and control system 120.Computer system also can comprise a monitor, comprises the information of the image that is produced in order to demonstration.Since it is particularly useful can also refer to illustrate its atomic number except the density of directing object aspect to be used for the double energy x-ray technology of energy-selection reconstruct of X-ray CT image, therefore, X-ray tube control system 136 can adopt the X-ray tube control system of double energy, for example at the serial No.08/671 of the U.S. Patent application of above introducing, the X-ray tube control system of the double energy described in 202 is although this is not intended that the invention be limited to the control system of the type.System 120 also comprises protection screen 138, and this protection screen can be made by lead, for example, propagates beyond frame 125 in order to prevent radioactive ray.

In one embodiment, X-ray tube 128 produces a pyramidal X-beam 132 (being commonly called " conical beam "), and this beam passes a three-dimensional plot image field, by the conveying of induction system 110, makes luggage 112 from wherein passing through.Conical beam 132 is detected device array 130 later on and receives passing the luggage that is arranged in the picture field, and array 130 produces the signal of expression luggage 112 expose portion density.Therefore, beam has been determined a scan volume space.Platform 124 is around its turning axle 127 rotations, so carry continuously when passing center pit 126 by induction system 110 at luggage 112, make X-ray source 128 and detector array 130 around luggage with the circular arc orbiting motion, thereby produce a plurality of projections corresponding to a plurality of projected angles.

Utilize known mode, at first gathered from the signal of detector array 130, and handling with the CT scan signal processing technology by the computer system (not shown) subsequently by data acquisition system (DAS) 134.Treated data can show on monitor, and/or also can further be analyzed by computer system, to determine existing of suspicious object.For example, the data of being gathered can be used for determining whether these data mean to have to have sheet explosive substance density the article of (when adopting the double energy system, also comprising molecular weight) exist.If this data, can demonstrate such article to the monitor of operating personnel or system by suitable mode is detected, for example, can on the screen of a monitor 140, show, send alarm that can hear or visual, and/or a kind of automatic pop-up device is provided, in order to suspicious baggages are shifted out from conveying belt, so that do further to check, or conveying belt stopped, thereby suspicious baggages can be examined and/or shift out.

As mentioned above, detector array 130 can be the two-dimensional array detector, and it can provide the scan-data of X and Y direction, and the scan-data of Z-direction.Between each measurement zone, a plurality of detector row of array 130 produce data from a plurality of respective projection, and an individual regions of while luggage scanning 112.It is the function of desired resolution of scanner and throughput that the size of detector row and number preferably are chosen as, and desired resolution of scanner and throughput are the speed of rotation of universal stage 124 and the function of speed of induction system 110 conversely.Be chosen as at platform 124 rotations one whole circle in the required time these parametric optimizations, induction system 110 just pushed away luggage 112 forward, thereby in the once rotation of platform, the body region that detector array 130 is scanned is continuous, and the body region not overlapping (or overlapping) that detector array 130 is scanned during with the rotating of platform next time.

Induction system 110 (is preferably constant speed) continuously luggage and articles 112 is carried by CT scan system 120, simultaneously platform 124 luggage and articles by the time rotate continuously with constant rotational speed Lee's article that detour.In this way, 120 pairs of whole luggage and articles of system are implemented the three-dimensional CT scan of a spirality.A part of data and the screw reconstituted algorithm that is provided by array 130 preferably is provided luggage scanister 100 at least, so that produce the three-dimensional CT image of whole luggage and articles when luggage and articles process system.In one embodiment, system's 100 logarithms are executed a kind of section reconstruct (NSR) of spiraling factually, as the pending U.S. Patent Application series No.08/831 that proposes on April 10th, 1997, described in 558 like that, this application is entitled as " slice CT of spiraling image reconstruction apparatus and method " (Attorney Docket NO.ANA-118), and here is introduced into as a reference.Thereby system 100 provides a complete CT scan to each baggages, rather than the CT scan of selected portion in the luggage and articles only is provided, and does not need a prescreen equipment.Because two-way detector array 130 can make system in each rotary course of platform 124, scan the relative article in each baggages simultaneously, so system 100 also provides quick scan function than many parts.

Fig. 4 is the mechanical/electrical block scheme of an embodiment of luggage scanning system 100 of the present invention.The frame of scanner 100 comprises two critical pieces, promptly coils 124 and the framework (not shown).Dish 124 is a rotary part, and it is loaded with a part, supply unit and the data linked set of X-x-ray apparatus, detector assembly 130, data acquisition system (DAS) (DAS) 134, high-voltage power supply and monitor/control device.Described frame supported total system 100, and it includes luggage loading and unloading induction system 110.Dish 124 connects ball bearing chuck mechanical connection on framework by a diclinic.Dish 124 can rotate with constant rate of speed by a belt that is driven by DC servo motor 505.Frame also comprises the X-ray protection screen that is positioned on dish and the frame assembly.

In one embodiment, baggage conveyor system 110 comprises a single conveying belt that drives with constant rate of speed, and to satisfy specific throughput needs, the needs of this throughput comprise the demand of per hour handling 675 baggages in one embodiment.Conveying belt can be driven by a high moment of torsion, low speed device, so that constant speed is provided under the condition that load changes.A kind of graphitic carbon epoxide resin material of low decay can be used as the conveyer base part under the X-ray.The total length of conveyer should be designed to hold the baggages of three average lengths.Around conveyer a passage is set, to satisfy the security needs of box X-ray system.

In one embodiment, 208 volts, three-phase, 30 amperes input electric energy are as the primary power that can provide to total system.This input electric energy can be provided by the on-site airport of system.Electric energy is carried by a series of framework brush by framework, and these framework brushes can form continuous tight the contact with the becket on being bound up on dish 124.The low-tension supply 501 of dish on 124 provides electric energy for DAS134, X-ray cooling system and various monitor/control computer and electron device.Low-tension supply on the framework provides electric energy for reconstruction computer and various monitor/control electron device.Conveying belt motor 503, frame motor 505, the electric energy of high-voltage power supply and X-ray cooling medium pump can be directly by the primary power supply.

High-voltage power supply provides electric energy for X-ray tube 128.Power supply can provide two voltages at the cathode/anode two ends, and it can be modulated into the frequency of 540Hz.Drive waveforms can be sine wave.This power supply also can be X-ray silk electric energy is provided.The electric current of power supply all can keep substantial constant constant for two kinds of voltages.

The X-x-ray apparatus comprises bipolar, a fixed anode X-ray tube 128, heat-exchange system 507, collimator 509, protection screen, X-radiation transducers and an adjustment/installing plate.It is the conical beam of 61 ° of segment angles of 6 ° that collimator can provide scattered band.Heat-exchange system 507 comprises pump, radiator, fan and a water supply pipe.Heat-conduction liquid can be high dielectric oil.An available adjustment plate will be managed 128 and will be connected on the dish 124 complexity and time when changing with the minimizing place.Can comprise an X-radiation transducers, so that X-radiographic density feedback to be provided.

Double energy x-ray irradiation luggage, the part of X-ray is passed and is shone on the detector assembly 130.Detector assembly 130 can be made up of scintillater, photodiode, installation substrate, anti-scatter and a mechanical erection column.Can also comprise a post well heater that has temperature sensor 521.Detector assembly 130 can carry out the analog-converted that converted to visual photon and then be converted to electric current by the X-ray.Anti-scatter can be made by the material of high atomic number, and with the X-ray at angle, shine amount of scatter radiation on the scintillater with minimizing.Scintillater is made by enough thick cadmium tungstate crystal, thereby can almost completely absorb all X-rays.Scintillater is converted to visual photon with the X-ray.Crystal all sides except that the bottom all can be enclosed with optical reflectors.Therefore, visual photon can be passed by the crystal bottom.Photodiode can be bonded in the crystal bottom with optically clear adhesive.Photodiode is launched electric current, and this electric current is the logarithm mode along with the decay of the X-ray of baggages to be reduced.Photodiode can be connected on the ceramic substrate, and the size of substrate can be designed to place several detectors.This electric substrate available wire welding be connected to a P.e.c. that has a connector that is connected with DAS 134 with epoxy resin on.But mechanical connection is on erection column subsequently for each probe substrate, and this post has fan beam radius and projection on the Z direction.But this post rigidity subsequently is fastened on the dish 124.

DAS 134 can sample to detector current, and the voltage that amplifies is multiplexed to one group of 16 analog-digital converter, and numeral output is multiplexed in the serial data link 511 of non--contact.DAS 134 can be by the angle location triggered of dish 124.

Non--contact link 511 and 513 with high-speed figure DAS data transmission to image reconstruction processor 515, and with lower speed monitor/control signal coil and the framework control computer between transmit to and fro.Data link 511 can be based on a RF transmitter and receiver.Host-host protocol can be to transmit the TAXI that reaches 350 megabit per seconds ^TMControl link 513 can be based on wireless lan technology, and it can comprise and is installed in framework and coils roughly the same PCMCIA plate mutually in the computing machine.Plate can have transmitter and receiver electron device, and Ethernet (Ethernet) card of energy mock standard.So, for a point-to-point network has been set up in lower speed monitor and control communication.

For different high and low energy, image reconstructor all will become the two dimensional image of one group of baggages section from the digital line Integral Transformation of DAS 134.Can carry out CT reconstruct by a spiral-taper-beam solution.Reconstructor can include embedded software, a high speed D S outlet, an array processor, the spinner based on DSP, and one is returned the projector, video memory, UART control interface and a SCSI output interface that is used for view data based on ASIC.Array processor can carry out data correction and interpolation.Reconstructor can be autonomous type, and the image based on baggages information that receives via the UART interface can be transmitted to the framework computing machine.

Monitor and control system can be based on the embedded control system of PC.All subsystems are all monitored, to obtain crucial status information.This system is the may command kinematic system also, can detect luggage information, may command environment (for example temperature, humidity etc.), position, angle that can detection dish 124 and start DAS and HVPS.This system also can have an optical signal and keyboard interface, to be used for engineering diagnosis and control.In addition, can also comprise that is used for an on-the-spot control panel that uses.

CT baggage scanner of the present invention has the ability that can make the image reconstruction window be adapted to baggages to be scanned, to improve the luggage throughput of system.Before reconstruct baggages image, system of the present invention can identify needs reconstruct with pixel that produces the target object image and the pixel that does not need reconstruct.The pixel of reconstruct is those pixels relevant with the density of the baggages that scanning.Refuse reconstruct with the pixel that baggages are irrelevant, and rejected effectively.The pixel that weeds out comprises the pixel in zone below the conveying belt, and near the baggages and top pixel.By from reconstruction processing, omitting a considerable amount of pixels, the time decreased of processing, consequently, the throughput of luggage has increased.

Fig. 5 is the synoptic diagram of scanner field of view 350, in order to self-adapting reconstruction window of the present invention to be described.Shown in visual field 350 include conveying belt 110, be placed with on it one high for h, widely be the baggages 112 of w.Also comprise zone 351, the zone 352 above the baggages 112 and the zone, opposite flank 353 of baggages 112 below the conveying belt 110 in the visual field.These zones 351,352 and 353 are scanned by system of the present invention, and therefrom collect scan-data.Yet, since baggages 112 not in these zones, these regional image pixels are to the not contribution of the information that relates to baggages, thereby they are disallowable in the image reconstruction process of baggages.

Fig. 6 is for being superimposed upon x, the diagrammatic representation of the baggage scanner of the present invention visual field on the y cartesian coordinate system.The image of the baggages 112 that just are being scanned can be regarded as by a rectangular pixels array 357 and produced.Baggages can be counted as having N wide and M pixel height of pixel, and each pixel has the size p (usually by millimeter) of equal height and width.Therefore, the wide w of baggages 112 can be provided by w=Np, and the high h of baggages 112 can be provided by h=Mp.By the actual height and width of the baggages determining to be scanned, need the number of the pixel 357 of reconstruct to calculate by N * M.Need the locations of pixels of reconstruct also can be placed on coordinate x by center with baggages ₀, y ₀Locate and be determined.

By the border of location baggages 112, can determine high h, wide w and x ₀, y ₀As shown in Figure 6, the end of baggages and top are respectively by coordinate y ₁And y ₂Provide, the left side of baggages and the right are respectively by coordinate x ₁And x ₂Provide.Center 354 is by x ₀, y ₀Mark, wherein x ₀=(x ₂-x ₁)/2 and y ₀=(y ₂-y ₁)/2.High h is by h=y ₂-y ₁Provide, and wide w is by w=x ₂-x ₁Provide.Pixel columns N and number of lines of pixels M can utilize known Pixel Dimensions p to be determined by wide w and high h respectively.

According to the height of determined baggages, wide and position, total number of pixels N * M will calculate as described above.In one embodiment, the pixel of total number is by reconstruct, to produce the image of baggages.In another embodiment, for guaranteeing can to receive and controllable baggages throughput, the reconstruct of pixel is limited in the reconstructed pixel of a predetermined maximum number.The required baggages throughput of system is used to determine the maximum reconstructed number of pixels of each baggages.In one embodiment, this maximum pixel number is set at 25,000.The required total number of pixels N * M of reconstruct baggages image compares with the default pixel limit.If N * M is less than this limit, then N * M pixel is by reconstruct.Yet,, the window of this special baggage items bag of reconstruct is adjusted into the optimum reconstruct window that meets this limit if N * M surpasses this limit.

As mentioned above, derive high, wide, center and Pixel Dimensions N and M by the boundary position of the baggages in the scanner field of view.The border determine to adopt any in the some kinds of possibility methods.In one embodiment, analysis scan data itself are to determine boundary position x ₁, x ₂, y ₁, y ₂This can realize by the mode of checking the parallel projection data that produced by scan-data.In another embodiment, a discrete sensor on the scanning machine is used to survey the border of baggages.

Fig. 7 is the simplified block diagram of an embodiment of luggage scanning system 100 of the present invention, has wherein used in order to determine the discrete sensor on baggages border.System 100 shown in Figure 7 includes CT scanner 120, and is carrying the belt system 110 of baggages 112 by scanner 120.One or more sensors 360 that are installed on the scanner 120 have been adopted, in order to when baggages 112 enter scanner 120, to detect its border.Sensor 360 can comprise one or more laser instruments and optical receiver, to survey the border.Perhaps, sensor 360 can comprise the combination of infrared eye and/or light emitting diode and photo-detector, with detection boundaries.In addition, sensor 360 can comprise the high frequency ultrasound converter, detects the border of baggages 112 as boundary detector.

The output of sensor is transported in the sensor output processing circuit 370 of handling output quantity, to determine the border of baggages.The detector signal that detector produced in the scanner 120 is sent in the data acquisition system (DAS) (DAS) 134, the output of 134 pairs of detectors of this data acquisition system (DAS) (DAS) is handled, and produce corresponding signal, be transported to simultaneously in the disposal system 364.Disposal system 364 also receives the output of the sensor treatment circuit 370 that comes self-identifying baggages border.Disposal system 364 produces graph data from detector data, to produce the image of baggages 112.

CT luggage scanning system of the present invention also provides the function of calibration system, makes it to make compensation to the variation of different explorer responses.This calibration is to realize by the visual field of system being carried out primary calibration or " sky " scanning.In a traditional Medical CT system, when carrying out sky scanning, all barriers as the estrade that the patient uses, are all removed from the visual field.Carry out the complete scan of a visual field subsequently, and the data that detector collects are analyzed.In baggage scanner, in scanner of the present invention, the barrier in the visual field (as belt system) is to be not easy to move to carry out sky scanning.System of the present invention allows not remove in the visual field and carries out sky under the situation of barrier and scan.

Fig. 8 A and 8B show traditional empty scanning process.Fig. 8 A has schematically shown the layout of traditional CT scanner.Scanner comprises a source 204 and detector array 202, and they rotate along the counter clockwise direction shown in the arrow 206 around a rotation center 203 simultaneously.Source 204 and detector array 202 can be regarded as around rotation center and turn over a series of ken v.On each ken v, collect a series of sample s corresponding to the detector in the array 202.Usually, the visual field comprises a circular window 200, and this window is translucent for the X-ray from source 204.

Fig. 8 B is the synoptic diagram of the data-signal in the whole ken v scope that is obtained by a single detector or sample s.As shown in the figure, owing to from the visual field, removed barrier, and because window 200 is circular, thereby on the whole ken, present constant density, to put it briefly, each detector received data-signal on all kens is a constant.In a traditional sky scanning, each detector in the array 202 obtains a data set shown in Fig. 8 B.For each detector calculates a calibration factor, thereby when being applied in these factors on the detector, its response is equal to.At this ideally, because the data-signal of each detector does not become with the ken, therefore, the calibration factor of each detector that calculates is irrelevant with the ken.That is, the calibration factor that is applied on the data of being gathered by a detector is identical on each ken of detector image data.Consequently, only independently calibration factor is relevant with one for each detector.Yet in fact, the response of detector is not accurately irrelevant with the ken.Because the influence of gravitation and other effect, in fact the line of drawing among Fig. 8 B is not flat.Thereby calibration factor is relevant with the ken.Therefore, for each detector, need calculate the calibration factor of each ken, thereby need a big correction card, this need expend sizable storage space.

Fig. 9 A schematically shows the scanning layout of luggage scanning system 100 of the present invention.Shown in Fig. 9 A, its layout is different with the conventional in layout shown in Fig. 8 A.In baggage scanner 100, belt system 110 is positioned at the visual field, and is left a barrier in the visual field when empty calibration scan.In addition, the circular port of machine hole 126 in neither conventional machines.Contrast with the circular window 200 in traditional scanning system, machine of the present invention also can comprise a non-circular window 220.These factors combine, once producing an explorer response that depends on the ken in the empty scanning process, its result is shown in Fig. 9 B, wherein, show when in the visual field of baggage scanner of the present invention, carrying out once empty calibration scan the data-signal curve that on all ken v, is produced by a single detector or sample s.Be appreciated that the curve shape shown in Fig. 9 B only represented a uneven explorer response that depends on the ken, it does not accurately represent the real response of arbitrary detector.

For carrying out effective empty calibration scan, wish only to use those rays not pass the ken of barrier.In the present invention, the data about each detector shown in Fig. 9 B are analyzed, and selected the ray data that is not stopped, to be used to calculate the calibration adjusted value of detector by barrier.In one embodiment, this is by a detector signal threshold value T is set, and data value is handled with respect to the position that T falls according to data value.Threshold value T can be provided with like this, and the data value of threshold value T can be considered to be produced by the ray that is not obstructed that passes the visual field so that be higher than.Subsequently, can only utilize those data values that surpass threshold value T to calculate calibration factor.

For example, shown in Fig. 9 B, the data value that is produced in two kens 223 and 225 scopes exceeds threshold value T.These kens be considered to by the ray that is not obstructed pass given detector sample s the visual field produced.Therefore, only utilize the data value that is produced in these two FOV (Field of View) to calculate the calibration factor of this detector.In one embodiment, the data value that is higher than threshold value T is averaged, and determine the calibration factor of this detector or sample s with this mean value.This will cause determining a single calibration factor for this detector, and this single calibration factor can be used for all data that this detector collects on all kens.That is to say that calibration is irrelevant with the ken.

Therefore, although because the existence of barrier in the visual field, the response of detector is relevant with the ken, the difference of the ken and the ken of not being obstructed is come because the present invention will be obstructed, consequently, for detector produces a calibration factor that has nothing to do with the ken.This adjusts aspect the data value at the storage calibration factor with when scanning the realistic objective object subsequently, has saved a large amount of storage spaces and computing time.

In actual scanning, scan-data is the calibration factor that each detector was calculated by standardization to draw under empty calibration scan situation.For each projection of each ken and sample, can be according to P _VS=ln (A _VS/ D _VS) calculate standardized value, wherein, P _VSBe the data for projection when specific ken v and the detector sample s, A _VSFor at ken v and the punctual resulting calibration factor of sample colonel s, D _VSBe the real data of on ken v, being gathered by detector sample s.What should be noted that is, as mentioned above, in one embodiment, A on all ken v _VSBe identical.

Threshold value T can calculate with multiple diverse ways.In one approach, maximum data value (representing with reference number 227 in Fig. 9 B) can multiply by a constant factor, to calculate threshold value T.Preferably, this factor is to be slightly less than 1 mark, for example 0.95.Select so high relatively threshold value that a kind of high confidence level is provided, that is, when calculating calibration factor, only use those data values relevant with the ray that is not obstructed.

The present invention also is included in the three dimensional CT graph data of target object, detects the apparatus and method of target object (particularly sheet target object) shape.The hypothetical target object is determined that by border or an outside surface each pixel in the image has been represented the density of target object on this pixel simultaneously.Figure 10 is the synoptic diagram of the three dimensional CT image of a target object 300.For ease of explanation, target object 300 illustrates with two dimensional form.Yet, should be appreciated that the present invention is applicable to the objective object.

According to the present invention, a series of point 302 is discerned and analyzed along target object 300 surfaces.Determine this surperficial pixel in the given three dimensions, adopt as calculating this surface graded method and can on any given position, determine a surface normal vector N.Put 302 places at each, can determine a surface normal vector N.For each normal vector N, a normal direction line 304 throws back in the target object 300.Can determine the series of points 306 along normal direction line 304 subsequently, simultaneously, the density value from target object CT data is endowed each data point 306.Determine density for putting 306 places at each, can between pixel value, insert interpolate value along normal direction line 304.Set a maximum ga(u)ge T _MAX, to determine the ultimate range along normal direction line 304, the data point 306 on this normal direction line will be calculated.Maximum ga(u)ge T _MAXShould be chosen as expection maximum ga(u)ge greater than tablet.

Determine and analyze along the Density Distribution of the each point 306 of normal direction line 304.Figure 11 is data point 306 sample distribution in both cases along normal direction line 304.In a kind of distribution (with 310 expressions), target approach object 300 outwards and exceed maximum ga(u)ge T _MAX, density p is a constant relatively.In with 312 distributions of representing, density function is at certain distance T _RPlace's decay.This attenuation distance T _RExpression target object 300 is corresponding to the thickness at surface normal line 304 places.Therefore, at this specific surface normal N place, target object 300 is thinner relatively.In the place that does not have decay, shown in curve 310, target object is thicker relatively at corresponding point 302 places.In fact, its at least with predefined maximum ga(u)ge T _MAXEqually thick.

Go up many positions 302 along target object 300 surfaces and repeat this step, and distribution is as shown in figure 11 analyzed, thereby give each surface normal N with a T _RValue.T _RValue can be along curve, the respective value of the point when decay takes place density, as shown in figure 11.Perhaps, T _RValue can be calculated by the mean value about the curve 312 of surface normal N.When distribution does not decay, shown in curve 310, T _RCan be made as maximum ga(u)ge T _MAX

Subsequently, can produce about all T _RBar shaped (statistical distribution) figure of value, for example, shown in Figure 12 A and 12B.Figure 12 A illustrates a bar chart, and wherein, target object 300 can be confirmed as a tablet.In this example, T _MAXBe set at 10mm, and the peak value in the bar chart occurs in about 4mm place.This shows along in the each point 302 on surface, the pad value T of most of point _RBe at the 4mm place.Because most thickness is lower than maximum of T basically _MAXThereby can draw target object 300 is the conclusion of a tablet.

For analyzing this bar chart, can set a threshold value T.If the peak value of curve surpasses this threshold value, shown in Figure 12 A, can conclude that so this peak value indicates a tablet, this tablet has for example thickness of 4mm along transverse axis at the peak value place.Curve is at T _MAXThe small rise of (10mm) locating shows that a considerable amount of measuring positions locate its thickness and exceed maximum ga(u)ge T _MAXThis mainly is owing to the thin edge metering along tablet, thereby trends towards indicating the high density that extends to the target object vertical-depth.But, statistically see, in the rise of the peak value at 4mm place far above the 10mm place, thereby, indicated a tablet.

It is not the bar chart that is produced under the situation of tablet that Figure 12 B is illustrated in target object 300.Shown in Figure 12 B, at maximum ga(u)ge T _MAX(10mm) locate bar chart and a peak value occurs, the major part of its expression measurement result has shown a thickness that surpasses the tablet maximum ga(u)ge of expection.Therefore, can conclude that target object 300 is not a tablet.Clip T _MAXThe method of the distribution at place has reduced the processing time, and has eliminated the problem of calculating corresponding to the surface normal along tile edges.

In one embodiment, statistical study can be carried out on a processor automatically.Search peak on bar chart automatically.By comparing with a data with existing set or database, utilize the position and the shape of peak value, whether can determine target object is a tablet.

CT scan of the present invention system also has the electric current ability of (or " departing from " in brief) that departs from that compensation depends on " dark current " detector of temperature.Dark current is to close at X-ray source, i.e. the electric current that is produced by detector when detector does not receive the X-ray.In the scanning of common target object, this residual or spacing current causes the error of the scan-data that is obtained.Dark current also depends on temperature (varying with temperature), and has nothing in common with each other between detector except that causing error.Can adjust the compensation that dark current is departed from, thereby reduce its inexactness.

In the present invention, can calculate depart from (value) that depends on temperature for each detector.In one embodiment, before actual scanning, carry out a kind of calibration operation, to characterize out the dependence that departs from temperature.In calibration operation, in the detector temperature circulation change, measure the electric current that detector sends.Obtain many data points of many detectors, promptly depart from the relation of (value) and temperature.In one embodiment, obtain the data point of each detector.In another embodiment, only used a subclass of all detector data points.Subsequently, these mean values that depart from (value) are used in each detector.

After obtaining depending on the sign of temperature, can carry out actual scanning process.Near detector, dispose temperature sensor, when scanning, to detect the temperature of detector.Current Temperatures is relied on function with the temperature of storage compare, be applied to departing from the data that from scan detector, obtain (value) to draw.In one embodiment, under the situation that X-ray source is closed, between baggages, periodically scan.These periodic dark current scannings are at known temperature T ₁Carry out down.Subsequently, when carrying out actual scanning, detect temperature T ₂Dark current is scanned temperature T ₁With current scanning temperature T ₂Difference when being applied in calibration operation the resulting temperature that stores rely on the function, be applied to suitably departing from the detector data (value) to determine.

For explaining that temperature of the present invention relies on deflection function, make that x is that the temperature of an individual passage being analyzed relies on and departs from.The dependence that departs from temperature can be provided by following taylor series expansion:

X (T) ≈ α ₀+ α ₁T+ α ₂T ², (1) wherein T is the temperature of passage, α _i, I=0,1,2, be constant.

α _iValue utilize calibration operation to determine.The temperature dependence calibration that departs from often is not needs, and perhaps only annually, or wealth need carry out in the detector of replacing an inefficacy.During calibration, the temperature of detector changes, thereby carries out the measurement of bias under the many temperature in having represented scanner typical operation scope.Make x _iFor in temperature T _iThe time measure depart from, I=0 wherein, 1 ..., N-1, N is for measuring number of times.The representative value of N is 5.α _iValue utilize the estimation of following minimum mean-square error:

Make that C is α _iMatrix, as: $C=\left[\begin{array}{c}{\mathrm{\α}}_0\\ {\mathrm{\α}}_1\\ {\mathrm{\α}}_2\end{array}\right]---\left(2\right)$ Matrix C can by

C=A ^-1B (3) obtains, wherein $A=\left[\begin{array}{c}<x_i,1>\\ <x_i,T_i>\\ <x_i,{{\mathrm{<figure-callout\; id="2"\; label="T\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">T</figure-callout>}}_i}^2>\end{array}\right]---\left(4\right)$ With $B=\left[\begin{array}{ccc}<\mathrm{1,1}>& <T_i,1>& <{{\mathrm{<figure-callout\; id="2"\; label="T\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">T</figure-callout>}}_i}^2,1>\\ <\mathrm{1,1}>& <T_i,T_i>& <{{\mathrm{<figure-callout\; id="2"\; label="T\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">T</figure-callout>}}_i}^2,T_i>\\ <\mathrm{1,1}>& <T_i,{{\mathrm{<figure-callout\; id="2"\; label="T\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">T</figure-callout>}}_i}^2>& <{{\mathrm{<figure-callout\; id="2"\; label="T\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">T</figure-callout>}}_i}^2,{{\mathrm{<figure-callout\; id="2"\; label="T\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">T</figure-callout>}}_i}^2>\end{array}\right]---\left(5\right)$ Wherein $<{\mathrm{\&alpha;}}_i,{\mathrm{\&beta;}}_i>=\underset{i=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_i{\mathrm{\&beta;}}_i-----\left(6\right)$

In the scanner course of work, departing from periodically of detector measured.Under common operational circumstances, per hour depart from measurement once.Make T ₁Temperature when departing from for measurement.And make x (T ₁) departing from when being this first temperature.Behind the certain hour, the temperature of detector will be T in scanning process ₂Deviation value x (T under this second temperature ₂), can obtain by formula (1), promptly

x(T ₂)≈x(T ₁)+α ₁(T ₂-T ₁)+α ₂(T ₂ ²-T ₁ ²) (7)

In fact, under situation, only the little subclass of detector sum D is carried out the measurement of detector temperature with D detector.Make that N is the number of temperature reading, its value is 5 usually.Temperature reading is recorded by temperature sensor, for example, and 5 temperature sensors 521 as shown in Figure 4.Make d _iFor carrying out thermometric detector, I=0 wherein, 1 ..., N-1, in addition, wherein N is the number of temperature reading.Make T _DiFor at detector d _iThe temperature of gained is measured at the place.The temperature T at detector j place _j(j=0 wherein, 1 ..., D-1) can carry out the quadratic polynomial estimation by N reading.The parametric form of temperature relation formula is:

T _j=β ₀+ β ₁J+ β ₂j ², (8) are β wherein _iBe constant, it can be calculated by following minimum mean-square error and try to achieve:

Order $F=\left[\begin{array}{c}{\mathrm{\&beta;}}_0\\ {\mathrm{\&beta;}}_1\\ {\mathrm{\&beta;}}_2\end{array}\right]---\left(9\right)$ Matrix F can be obtained by following formula:

F=D ^-1E (10) wherein $D=\left[\begin{array}{c}<T_{\mathrm{di}},1>\\ <T_{\mathrm{di}},d_i>\\ <T_{\mathrm{di}},{{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">d</figure-callout>}}_i}^2>\end{array}\right]---\left(11\right)$ With $E=\left[\begin{array}{ccc}<\mathrm{1,1}>& <d_i,1>& <{{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">d</figure-callout>}}_i}^2,1>\\ <1,d_i>& <d_i,d_i>& <{{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">d</figure-callout>}}_i}^2,d_i>\\ <1,{{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">d</figure-callout>}}_i}^2>& <d_i,{d_i}^2>& <{{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">d</figure-callout>}}_i}^2,{{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="A9881002000421.png"\; state="\{\{state\}\}">d</figure-callout>}}_i}^2>\end{array}\right]---\left(12\right)$ Detector d _iTemperature can utilize thermopair and resistance temperature detector (RTD) to measure.

Though show especially with reference to its preferred embodiment and described the present invention, those skilled in the art should understand, and can make various changes in the form and details, and not break away from by the defined the spirit and scope of the present invention of following claim.

Claims (40)

1. the method for a calibration calculations machine X-tomographic (CT) scanning system, described CT scan system comprises a radiographic source and a detector array, this detector array passes the ray of CT scan system visual field in order to reception, and generation and the received relevant signal of ray of detector, described signal is in order to produce the scan-data about visual field scanning, and described method comprises:

Carry out the calibration scan of visual field, think that each detector in the detector array produces the calibration scan data;

Be calibration threshold value of calibration scan data setting;

For each detector, select to surpass the calibration scan data value of calibration threshold value; With

Utilize selected calibration scan data value to calculate the detectors calibrate value of each detector, described detectors calibrate value is used for the scan-data that calibration detectors is gathered in scanning subsequently.

2. method according to claim 1 is characterized in that, the calibration scan of visual field is to have under the situation of a barrier to carry out in the visual field.

3. method according to claim 2 is characterized in that, described barrier comprises that the moving target object makes it the conveyor by the CT scan system.

4. method according to claim 1 is characterized in that, for each detector in the array is set a calibration threshold value.

5. method according to claim 1 is characterized in that, the setting of calibration threshold value should make selected calibration scan data value relevant with the ray that does not pass the visual field with being obstructed.

6. method according to claim 1 is characterized in that, for the step of each detector calculating detector calibration value comprises: the calibration scan data value of selecting for each detector is averaged.

7. a computing machine X-tomographic (CT) scanning system comprises:

A radiographic source is used so that radiation exposure passes the visual field of CT scan system;

A detector array, in order to receiving described ray, and generation and the received relevant signal of ray of detector, the scan-data of described signal when producing visual field scanning;

Be used to carry out the device of visual field calibration scan, think that each detector in the detector array produces the calibration scan data;

Device for calibration scan data setting calibration threshold value;

The device that surpasses the calibration scan data value of calibration threshold value for each detector selection; With

Utilize selected calibration scan data value to be the device of each detector calculating detector calibration value, described detectors calibrate value in scanning subsequently in order to scan-data that calibration detectors collected.

8. CT scan according to claim 7 system is characterized in that, the calibration scan of visual field is to have under the situation of a barrier to carry out in the visual field.

9. CT scan according to claim 8 system is characterized in that, barrier comprises that being used for the moving target object makes it conveyor by the CT scan system.

10 CT scan according to claim 7 systems is characterized in that, are that each detector in the array is set a calibration threshold value.

11. CT scan according to claim 7 system is characterized in that the setting of calibration threshold value should make selected calibration scan data value relevant with the ray that does not pass the visual field with being obstructed.

12. CT scan according to claim 7 system is characterized in that, is used to the device of each detector calculating detector calibration value to comprise the device that the selected calibration scan data value of this detector is averaged.

13. in a kind of CT scan system, has a radiographic source, be used to radiate the ray that passes a zone, and detector array, in order to be received in scanning during this zone from this regional ray, and produce the detector signal of the ray that representative received, and the method for the electric current that the ray that a kind of compensation is produced by detector and received with detector is irrelevant, described method comprises:

Change the temperature of detector;

The measurement electric current that detector produced in the detector temperature change procedure;

Characterize out electric current with the variation of temperature situation;

Utilize electric current with variation of temperature, produce one group of detector offset signal, when scanning this zone, to be applied on the detector signal that is produced;

Scan this zone, to produce detector signal;

Detect the temperature of detector; With

To be applied on the detector signal corresponding to the detector offset signal of detected temperatures, so that electric current is compensated.

14. method according to claim 13 is characterized in that, each detector in the detector array is endowed a corresponding offset signal.

15. method according to claim 13 is characterized in that, characterizes electric current and comprises with variation of temperature described variation is fitted in the parametric equation.

16. method according to claim 13 is characterized in that, characterizes electric current and comprises with variation of temperature and utilize the detector offset signal to produce a kind of least square method estimation.

17. a CT scan system comprises:

A radiographic source is with so that ray passes a zone;

A detector array, in order to be received in scanning during this zone from this regional ray, and produce the detector signal of the ray that representative received; With

Be used to compensate the device of the irrelevant electric current of the ray that produced and received with detector by detector, the described device that is used for offset current comprises:

Change the device of detector temperature;

The device of the electric current that measurement is produced when detector temperature changes;

Characterize out the device of electric current with temperature change;

Utilize electric current to produce the device of one group of detector offset signal with variation of temperature;

Scan this zone to produce the device of detector signal;

Detect the device of detector temperature; With

To put in the detector signal corresponding to the detector offset signal of measured temperature, with the device that electric current is compensated.

18. CT scan according to claim 17 system is characterized in that each detector in the detector array is endowed a corresponding offset signal.

19. CT scan according to claim 17 system is characterized in that, is used for characterizing the temperature variant device of electric current and comprises the device that described variation is fitted to a parametric equation.

20. CT scan according to claim 17 system is characterized in that, is used to characterize the temperature variant device of electric current and comprises the device that utilizes the detector offset signal to produce a least-squares estimation.

21. in a target object CT view data in 3-D view space, survey the method for a target object, comprising:

On many points on target object surface, calculate perpendicular to target object surface and extend into normal in the target object;

On the many points on the normal of each target approach object, determine the density of target object by the CT view data; With

Utilization produces and represents the thickness reading of target object at each normal place along the density of each normal.

22. method according to claim 21 is characterized in that, also comprises:

Produce the thickness profile data relevant with each normal; With

Distributed data is analyzed, to determine the shape of target object.

23. method according to claim 22 is characterized in that, distributed data analyzed, and whether be tablet to determine target object.

24. method according to claim 22 is characterized in that, produces a kind of distributed data and comprises: the thickness bar chart that produces a thickness relevant with described normal.

25. method according to claim 1 is characterized in that, also comprises setting entering and will being determined the ultimate range of the target object of its density, wherein, this ultimate range is relevant with the greatest expected thickness of measured target object.

26. in the 3-D view space, survey the device of a target object in the CT view data of a target object, comprising:

Be used at many points, calculate perpendicular to target object surface and extend into the device of the normal in the target object along the target object surface;

Be used for determining the device of the density of target object by the CT view data at the many points on the normal of each target approach object; With

Be used to utilize density, produce and represent the device of target object at the thickness reading at each normal place along each normal.

27. device according to claim 26 is characterized in that, also comprises:

Be used to produce the device of the thickness distribution situation relevant with each normal; With

Be used for distribution situation is analyzed, to determine the device of target object shape.

28. device according to claim 27 is characterized in that, the described device that is used to analyze determines whether place's target object has the shape of tablet.

29. device according to claim 27 is characterized in that, the device that is used to produce distribution situation comprises the device of the thickness bar chart that is used to produce the thickness relevant with normal.

30. device according to claim 29 is characterized in that, also comprises the device that is used for analyzing thickness bar chart peak value, to determine whether target object has the shape of tablet.

31. in a kind of CT scan machinery, a kind of method of handling about the scan-data of a target object in the CT scan machinery visual field, many image pixels have been determined in described visual field, these image pixels can be by scan-data reconstruct, to produce the image of visual field, described method comprises:

The visual field is scanned, thought that the visual field produces scan-data;

The size of detection of a target object;

The position of target object in the detection viewing field; With

First and second portion in the visual field are identified in the size of the target object that utilization detects and position, and described first will be by reconstruct, to produce the image of target object; Described second portion in producing the target object image process not by reconstruct.

32. method according to claim 31 is characterized in that, also comprises the first in the reconstruction visual field, to produce the image of target object.

33. method according to claim 31 is characterized in that, the size of detection of a target object comprises the border of detection of a target object from the scan-data of visual field.

34. method according to claim 31 is characterized in that, the position of the target object in the detection viewing field comprises the border of detection of a target object from the scan-data of visual field.

35. method according to claim 31 is characterized in that, first and second parts of identification visual field comprise sets a boundary to the number of pixels of need reconstruct.

36. a device that is used for handling the CT scan data of the target object in CT scan machinery visual field, many image pixels have been determined in described visual field, and these pixels can be by scan-data reconstruct, and to produce a view field image, described device comprises:

The device that is used for scanning field of view is to produce the scan-data of visual field;

Be used for the size of detection viewing field target object and the device of position; With

The size of the target object that utilization detects and position, the device of first and second parts of identification visual field, described first will be by reconstruct when producing the image of target object, and described second portion is refused reconstruct when producing the image of target object.

37. device according to claim 36 is characterized in that, also comprises the first that is used for reconstruction visual field, to produce the device of target object image.

38. device according to claim 36 is characterized in that, is used for the size of detection of a target object and the device of position and comprises from the device of the scan-data detection of a target object boundary of visual field.

39. device according to claim 36 is characterized in that, the device that is used for detection of a target object size and position comprises the sensor in order to detection of a target object boundary.

40. device according to claim 36 is characterized in that, the device that is used to discern first and second parts of visual field comprises the device of the number of pixels of need reconstruct being set a boundary.

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