WO1998033063A1

WO1998033063A1 - Device for determining composition and structure of objects

Info

Publication number: WO1998033063A1
Application number: PCT/US1998/001365
Authority: WO
Inventors: O. V. Komardin; A. F. Lawrence; P. I. Lazarev
Original assignee: Quanta Vision
Priority date: 1997-01-24
Filing date: 1998-01-23
Publication date: 1998-07-30
Also published as: JP2000512764A; AU5929198A; CN1216109A; AU6039798A; EP0898704A1; WO1998033062A1

Abstract

The invention relates to a device for determining the composition and internal structure of an object. The device includes a source of radiation which can penetrate the object and at least one unit for forming radiation from the radiation source into a plurality of weakly divergent beams. Each beam is positioned so it can be incident on the object. A separation device defines a first component and a second component in at least one of the beams after the at least one beam has passed through the object. The first component includes primarily radiation scattered over small angles by the object. The second component includes primarily radiation which was not scattered on passing through the object. The device also includes at least one first detector configured to register at least a portion of the radiation in the first component of the at least one beam and at least one second detector configured to register at least a portion of the radiation in the second component of the at least one beam. A processing system receives first signals from the at least one first detector and second signals from the at least one second detector. The processing system processes the first and second signals to create an image of the internal structure of the object.

Description

DEVICE FOR DETERMINING COMPOSITION AND STRUCTURE OF

OBJECTS

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to devices for determining compositions and structures of objects opaque to visible light using radiation scattered by small angles while passing through the object. More particularly, this invention relates to a device for determining the composition and structure of an object such as luggage.

Description of Related Art

The known devices for obtaining an object's internal structure are generally based on absorption radiography. Absorption radiography generally includes recording the intensity distribution of radiation transmitted through an object (US4,651,002, G01T/161, 17.03.87; US4,549,307, G3B41/16, 22.10.85).

Changes in the intensity of the radiation result from different degrees of radiation absorption by different parts of the object. The radiation passed through an object is known to scatter. This radiation scattering is a "parasitic" phenomenon which results in background and damages the image contrast. It has been proposed to offset the effects of scatter by recording the scattered radiation separately and subtract the scattered radiation intensity from the overall signal obtained when the object is X-rayed (US4,651,002). Since the integral scattering picture is measured, the relative positions of the collimation lattice and the filter lattice are not finely adjusted. Accordingly, the filter is implemented as a mobile element and the scattering is measured for large angles.

In U.S. patent number 4,549,307, it is proposed to use special lids forming spots on the object surface in which only the scattered radiation is recorded. The background level over the entire image is determined by approximation and then subtracted from the overall absorption signal to obtain a higher-contrast image.

Devices based strictly on absorption radiography may face additional challenges. If the object of interest contains substances only weakly differing in absorbing properties, the parts of the obtained image corresponding to such substances may be practically indistinguishable. Consequently, it will not be possible to obtain an image with the desired contrast. Approaches other than absorption radiography have attempted to address this problem.

A method has been proposed for identifying crystalline and poly- crystalline substances based on Bragg reflection from the crystal structure of the object (GB,2,299,251, G01N23/207,1996). The energy spectrum distribution of the polychromatic radiation reflected at a certain angle from the crystal structure of the substance will be characteristic for each substance and hence allows the substance to be identified using an available database. The collimator of the proposed device allows the device to record the energy spectrum for each separate region of the object that the radiation passes through. This method was proposed for identifying explosives in luggage. However, its use is limited to detecting objects with crystalline or polycrystalline structure.

Devices for visualizing an object's internal structure have been described by measuring X-ray refraction at the boundaries between parts of the object with different electronic densities (SU.1402871, G01N23/06,1987, RU,2012872, G01N23/02, 1994). These boundaries can cause X-ray to deflect up to three angular seconds. Single crystals were used in those inventions to both collimate the incident radiation and filter the radiation deflected due to refraction. One drawback of that method and device results from its small aperture ratio. The small aperture ratio results from the single crystal reflecting the incident radiation according to the Bragg law. For every wavelength, the radiation is reflected at a certain angle within the deflection interval equal to the angular interval of the Bragg reflection which is about ten angular seconds. This means that a small fraction of the source radiation energy is used for X-raying the object.

The single crystal discussed above has been replaced with aperture lattices in order to overcome the above drawbacks (WO96/17240, G01N23/04, 1996). A first lattice positioned before the object acts as a collimator forming the incident flux as a series of narrow, weakly diverging beams. A second lattice positioned between the object and a detector acts as a scattering radiation filter. To ensure the required resolution for detecting inhomogeneities in the analyzed object, the opaque regions of the collimator lattice should be made no more than 0.05-0.1 mm wide. The specified lattices should be positioned with respect to each other in such a way that the penetrating radiation flux in the absence of the analyzed object would not fall onto the detector. Since the object is immobile with respect to the detector, the positions and sizes of the X-rayed parts of the object will be determined by the frequencies of spatial positions of the detecting rays. Further, the dimensions of the collimation lattice should encompass the entire object. As a result, aperture lattices can complicate the adjustment of the device and can increase the device cost.

It has also been suggested to record the spectra of coherent radiation scattered by angles within 1°-12° relative to the incident beam direction. This technique has been applied to identifying objects in biological tissues and explosives in luggage (US,4751772, G01N 23/201, 1988, US, 4754469, G01N 23/201 1988, US, 4956856, G01N 23/201, 1980, US, 500 8911, G01N23/201, 1991, US, 5265144, G01N23/201, 1993). A large part of the elastically scattered radiation is located within those angles if the X-ray energy is sufficiently small. The energy spectra of the elastically scattered radiation (unlike the inelastically scattered Compton radiation) is identical to the spectrum of the primary beam. Further, the elastically scattered radiation has a characteristic angular dependence with a pronounced maximum in the angular interval 1 to 19 degrees. The maximum position depends on both the X-rayed substance and the energy of the incident radiation. Since the intensity distribution of the coherently scattered radiation for small scattering angles depends on the molecular structure of the object substance, substances with the same absorbance (which cannot be discriminated by conventional absorbance X-ray analysis) can be discriminated by the intensity distribution of the angular scattering of coherent radiation characteristic for each substance.

In the specified patents, a narrow collimated beam of monochromatic or polychromatic radiation is used to analyze the object. The intensity of the coherently scattered radiation is measured using a detecting system resolving both the energy and the coordinate (scattering angle). U.S. patent numbers

4,751,722 and 4,754,469, propose using the known principles of computer tomography to obtain the object image using small-angle scattering. The described devices have relatively low sensitivities since the coherent radiation cross-section is small in the specified angular range. As a result, high radiation doses are required to X-ray the object.

U.S Patent number 5,265,144 proposes using many circularly positioned detecting elements for recording the radiation scattered at each particular angle, to increase the sensitivity. However, since the object is X-rayed using a narrow beam with small divergence, the small aperture ratio problem remains causing these types of devices to have low sensitivity.

The radiation flux in the described devices is scattered on different materials it encounters when it passes through the object. As a result, the resultant scattering curves will be superpositions of several curves resulting from different materials contained in the object. This superimposition complicates the process of identifying a substance from known scattering curves. This problem can be solved with small-angle computer tomography (4,751 ,722). However, small-angle computer tomography can require a large number of objects X-raying from different angles (0 to 360 degrees) which is expensive and not always feasible.

For the above reasons there is a need for a device and method which which can obtain a radiation absorption distribution over the volume of an object and discern different substances which have similar absorptions. The device and method should also be able to obtain the substance distribution over the volume of an object. There is also a need for a device which can construct a less costly device with a higher aperture ratio. A need also exists for a device which provides an image of an object's internal structure (a topographic projection) while being simple to produce and operate and while enhancing image quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device and method which can obtain a radiation absorption distribution over the volume of an object and discern different substances which have similar absorptions. Another object of the present invention is to provide a device and method which can discern the distribution of substances which make up an object.

Yet another object of the present invention is to provide a device and method which can provide an image of the radiation absorption distribution over the volume of an object.

One more object of the present invention is to provide a device and method which can provide an image of the distribution of substances which make up an object. An object of the invention is to provide a device and method which X- rays an object at different angles to determine the distribution of absorption factors in the object.

Another object of the invention is to provide a device and method which obtains the small-angle scattering curves for an object.

Yet another object of the invention is to provide a device and method which X-rays an object at different angles to determine a distribution of absorption factors and a distribution of small-angle scattering curves over an object. One more object of the invention is to provide a device and method for obtaining the small-angle coherent scattering intensity distribution of radiation over an object.

Another object of the invention is to provide a device and method for obtaining an image of the small-angle coherent scattering intensity distribution of radiation over an object such that each point on the image reflects the diffraction properties of the material which makes up the corresponding point in the object.

A further object of the invention is to provide a device and method for obtaining an image of the small-angle coherent scattering intensity distribution. The image carries information about the molecular structure of the materials composing the object.

An object of the invention is to provide a device and method which can discern the distribution of the substances which comprise an object over the volume of the object. Another object of the invention is to provide a low cost device and method for discerning the composition and structure of an object.

Another object of the invention is to provide a device and method which uses an increased aperture ratio for discerning the composition and structure of an object. Another object of the invention is to provide a device and method which uses a high aperture ratio for discerning the composition and structure of an object.

One more object of the invention is to provide a device and method which provides an image of an object's internal structure while being simple to produce and operate and while enhancing image quality.

Even another object of the invention is to provide a device and method which provides a topographic image of an object's internal structure while being simple to produce and operate and while enhancing image quality. The above objects can be achieved with a device for determining the composition and internal structure of an object. The device includes a source of radiation which can penetrate the object and at least one unit for forming radiation from the radiation source into a plurality of weakly divergent beams. Each beam is positioned so it can be incident on the object. A separation device defines a first component and a second component in at least one of the beams after the at least one beam has passed through the object. The first component includes primarily radiation scattered over small angles by the object. The second component includes primarily radiation which was not scattered on passing through the object. The device also includes at least one first detector configured to register at least a portion of the radiation in the first component of the at least one beam and at least one second detector configured to register at least a portion of the radiation in the second component of the at least one beam. A processing system receives first signals from the at least one first detector and second signals form the at least one second detector. The processing system processes the first and second signals to create an image of the internal structure of the object.

The above objects can also be achieved with a device for determining the composition and internal structure of an object. The device includes a source of radiation which can penetrate the object and at least one unit for forming radiation from the radiation source into a plurality of weakly divergent beams. Each beam is positioned so it can be incident on the object. A separation device defines a component in at least one beam after the at least one beam has passed through the object. The component includes primarily radiation scattered over small angles by the object. At least one detector is configured to register at least a portion of the radiation in the component. A processing system receives signals from the at least one first detector, the processing system configured to process the signal so as to create an image of the internal structure of the object. Similarly, the processing system can process the signal to discern the nature of the substances making up the object.

The above objects can also be achieved with a device for determining the composition and internal structure of an object. The device includes a source of radiation which can penetrate the object a unit for forming the radiation flux in the direction of the analyzed object. The unit includes a first collimator system and a second collimator system. The first collimator system is configured to form weakly divergent beams from the radiation source. The second collimator system includes at least one collimator which can form a number of weakly divergent beams from the radiation source, the beams being oriented at different angles to the object. The device also includes a first system for obtaining an image of the object based on radiation absorbed by the object including at least one detector configured to detected the radiation which has not been scattered by the object. The device also includes a second system for obtaining an image of the object based on radiation scattered by the object over small-angles. The second system includes a plurality of detectors and a spatial filter at least partially positioned between the detectors and the unit for forming radiation flux, the filter screens the detectors from radiation transmitted through the object without being scattered over small angles.

The above objects can also be achieved with a device for determining composition and internal structure of an object. The device includes a source of radiation and a unit for forming the radiation in the direction of the object. The unit includes a series of multislit collimators configured to form weakly diverging beams from the radiation source. The collimators are oriented so the beams form different angles of incidence with the object. An imaging system obtains at least one image of the object based on radiation absorbed by the object and on radiation scattered by the object over small-angles. The imaging system includes a raster of slits with detectors positioned to receive radiation passing through the slits, each detector is coupled with a processing system configured to discriminate between detectors receiving radiation scattered at small angles from radiation transmitted through the object without scattering.

The above objects can also be achieved with a device for analyzing an internal structure of an object. The device includes a radiation source and a collimator for forming at least one weakly diverging beam incident on the object. At least one detector registers the radiation produced by the source. A filter is positioned opposite the object from the radiation source. The filter includes a structure complementary to the collimator in which filter regions coπesponding to the transparent regions of the collimator include a material opaque to the penetrating radiation. As a result, the opaque regions of the filter substantially screen the transparent regions of the collimator allowing at least a portion of a radiation scattered by the object over small-angles scattered radiation to be registered on the detector.

The above objects can also be achieved with a device for analyzing an internal structure of an object. The device includes a radiation source forming a plurality of narrow and weakly diverging beams incident on the object. A spatial filter is positioned opposite of the object from the source. The filter substantially separates radiation scattered by the object over small angles from radiation which has not been scattered and allow at least a portion of each type of radiation to pass through openings. At least one first registering element receives radiation which has passed through the openings and is composed primarily of scattered radiation. At least one second registering element receives radiation which has passed through the openings and is composed primarily of direct radiation. A processing system is coupled with the registering elements and includes logic to at least partially process the scattered radiation independent of the direct beam radiation.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic diagram is shown for a device with a separate registration system for the radiation absorption measurements and the radiation scatter measurements.

Figure 2 is a block diagram showing the scheme for data processing and output.

Figure 3 is a schematic of a device which combines the registration system for the radiation absorption measurements and radiation scatter measurements.

Figure 4 is a sideview of one embodiment of a spatial filter.

Figure 5 is a schematic of an embodiment registration system for radiation scatter measurements. Figure 6 is a cross section of a fan beam obtained when the collimator is manufactured from an opaque material with slit-shaped transparent regions.

Figure 7 is a cross section of a collimator including a block of opaque material with transparent channels.

Figure 8 is a sideview of the relative position of the collimator and the filter for weakly divergent fan shaped beams.

Figure 9 is a schematic of an embodiment of a device including a filter with the registering elements placed in the slits.

Figure 10 illustrates an embodiment of a device which converts radiation passing through the object into luminous radiation. Figure 11 is a schematic of a luggage control facility.

Figure 12, is a sideview of the embodiment of Figure 11 along the aπow labeled B in Figure 11.

Figure 13A is a sideview of a slitless collimator. Figure 13B is a sideview of a plate in a slitless collimator including an unpolished band.

DETAILED DESCRIPTION

To determine the absorption factors, the object (which, e.g., can be luggage checked for explosives) is scanned by several flat fan-shaped beams of penetrating radiation from a single source directed at various angles as different as much as possible one from another. The scanning can be performed by either moving the optical elements of the device (collimator, spatial filter, and detector), or by moving the object itself. In the luggage control device, it is more practical to move the object. The thickness of each beam is selected from the required resolution of the device; i.e., by selecting the dimensions of the area occupied in the object by the substance to be identified. The width of each of the flat beam in the direction perpendicular to that of scanning should be such that the beam would encompass the entire analyzed object.

The intensity of the radiation transmitted through the object for each beam is recorded using a coordinate-sensitive detector. The latter can be a system of detecting elements positioned parallel to the plane of the incident beam. In that direction, the dimensions of the revealed inhomogemeties will be determined by the spatial resolution of the coordinate-sensitive detector.

When the object is moved, each of the beams will successively scan the entire object. The intensity of the radiation transmitted through the object at a certain angle will depend on absorption factors of the substances crossed by the beam. From the values of attenuation for beams crossing the same object cell at different angles, the average absorption factor can be determined for the substances filling that cell. The values of the measured intensities of the radiation transmitted through the object will be transfeπed into the data processing system where the distribution of the absorption factor will be calculated over the entire object volume. The object will then be represented as a three-dimensional matrix consisting of elementary cells such that absorption factors remain the same within each cell; i.e., each of the cells is considered to be filled with one substance only. From the obtained absorption factor distribution, average atomic numbers can be determined for the substance filling each cell. Since different substances can have close absorption factors, the object image obtained in this mode of X-raying may not be sufficient to discriminate between substances having close absorption factors.

To discriminate between substances having close absorption factors, coherent small-angle scattering (SAS) is used. Each individual substance has its unique scattering curve, so, for every substance, the small-angle scattering intensity can be measured at several angle points lj=l(θj), and an approximate scattering curve can be obtained. The more the detectors i.e. the larger the number of angles at which the scattered radiation intensities are measured, the more exact is the curve approximation. Scattering curves of substances of interest can be entered into a database. By comparing the obtained approximate curve with those in the database, the substance can be identified.

Data obtained can be a superposition of scattering curves from different substances within the section of the object the radiation beam passes through. The superposition of scattering curves can present difficulties in discerning what substances the beam has passed through. To isolate the scattering curve related to a single substance it is necessary to obtain small-angle intensity distributions for several angles of incidence of the radiation onto the object. Preferably the each angle of incidence differs as much as possible from each other. To obtain small-angle intensity distributions for each incidence angle, a SAS system is used consisting of a collimator, spatial filter and coordinate-sensitive detector. Each collimator forms a series of narrow, weakly diverging beams from a single source. The object can be moved so it successively passes through each SAS systems. As a result, each system forms an object image in the small-angle contrast for a particular angle of incidence. Processing the small-angle scattering curves for different scanning angles yields a distribution of scattering properties characterizing the structure of the substances composing the object over the entire object volume.

The small-angle scattering intensity is measured in each cell at several different angles and the corresponding approximate scattering curve is constructed to allow the substance in the cell to be identified by comparison with the scattering curves of known substances.

The accuracy of the approximation will be higher when the coherent scattering intensities are measured over a large number of angles. The range of the measured small-angle scattering can be limited to the angle region in which the major part of the coherently scattered radiation is located, namely, the so-called central diffraction peak region. This region may be from 5 angular seconds to 1 degree depending on the wavelength used and the structural properties of the material. Recording small-angle scattering in the central peak region increases the intensity of the recorded radiation.

When calculating the radiation scattering curves for each cell, allowance should be made for the fact that they are obtained at non-identical conditions because of differences in absorption of the primary beam before it reaches the particular cell, and attenuation of the primary beam on the way from the cell to the detector. This allowance is made using the previously determined absorption factors. Then the scattering curves obtained for each cell are averaged. Substances are identified for each cell, first, for absorption factor, and then the molecular structure of the substances is refined using the reduced small angle scattering curves. The overall number of different SAS systems used in the device is determined by the complexity of the analyzed object. Suitable objects include, but are not limited to, luggage in an airport security system. The overall number of items present in a typical suitcase can be approximately. To determine absorption factors of the substances, four analyzing beams can be used 40° apart from each other. The SAS systems will then be positioned in the spaces between the individual beams. The overall spread of the system will be approximately 120°.

When the absorption factor data indicates that a particular substance being sought is not present within a particular cell, that cell can be excluded from SAS considerations. For instance, if the device is being used to search luggage for explosives, regions occupied by metals, ceramics, etc., can be excluded from SAS considerations. These exclusions can considerably simplify and accelerate the procedure of obtaining normalized SAS data for each cell determined to be of interest from absorption data. These exclusions can also serve to increase the rate of identifying substances in cells of interest.

Accordingly, the data processing and storage system will contain object images in two forms: that of absorption factors, and that of small-angle scattering curves, over the entire object volume. By combining those two types of images, the data processing system will output the three-dimensional internal structure image of the object, with identification of the substances composing the object, onto the display screen.

One embodiment of the device contains a source of penetrating radiation, a registration system for radiation absorbed in the analyzed object, a registration system for radiation scattered by small angles, and a device for moving the object.

The source includes, but is not limited to, any industrially produced X- ray radiation source which provided the intensity of radiation necessary to penetrate the object. The focal spot dimensions of the source depend on the collimator/spatial filter system employed in the particular device.

The registration system for radiation absorbed by the object can include a collimator for forming weakly divergent beams, a number of slits positioned behind the objects and eliminating background radiation to improve the image contrast, and a number of coordinate-sensitive detectors each of which records the intensity of the transmitted radiation for a separate beam and is spatially resolving along the direction parallel to the plane of the incident beam. The dimensions of each collimator slit determine the width and angular divergence of the beam and should be such that the size of the incident beam on the object is less than the mimmal size of a particular substance being sought in the object. Otherwise, the substance might not be discriminated from the surrounding medium. Preferably, the size of the beam projection in the direction perpendicular to the scanning direction should be no less than one of the object dimensions.

The radiation transmitted through the object is recorded, for each beam, by a coordinate-sensitive detector during the whole period of object scanning. The measured value of the intensities of the transmitted radiation for different angles of beam incidence onto the object are transfeπed into the data procession system where the object image is constructed from intensity values of the transmitted radiation in the form of absorption factor distribution over three-dimensional matrix elementary cells into which object is divided. The measuring system for the small-angle scattering from the object can use penetrating radiation from the same source. It can include blocks positioned at different angles to the object. Each block can include a collimator, a spatial filter, and a two-coordinate position-sensitive detector. The collimator can be positioned between the source and the object forms the beam falling onto the object consisting of at least one naπow weakly diverging beams.

The collimator is a regular, periodic structure consisting of regions transparent to the radiation alternating with opaque regions. The lines of the surfaces forming the opaque regions should converge at the focal spot of the source for each collimator to increase the energy efficiency of the device. Accordingly, the radiation reaching different slits of the collimator may be emitted by different parts of the source focal spot. Suitable transparent regions include, but are not limited to, slits and circular orifices. In the case of circular orifices the detecting elements can be mounted in capillary tubes or deep inside intersecting plates made of material opaque to penetrating radiation. Further, the circular orifices can be positioned in a hexagonal pattern. The shape and position of the transparent regions can be determined by the nature of objects being analyzed. The lines of the surfaces which form the transparent region should converge at the source's focal spot to enhance the energy efficiency of the device. As a result, the radiation reaching different collimator transparent regions may originate from different parts of the source's focal spots thus enabling use of powerful wide-focus sources. The collimator should form beams with a divergence of 2γ in order to register radiation scattered in the small-angle range, to ensure that beams of the primary flux scattered by angle α fall outside the primary flux in the registration area. The collimator structure period prevent neighboring beams from overlapping each other in the detector plane and should ensure detection of beams scattered angles up to β (α and β are angle values determining the small-angle range, with α typically of 5 angular seconds or more, and β up to 1 degree.).

The collimator input and output should be placed apart a distance larger than the collimator cross dimensions. The collimator can be designed as alternating plates opaque to the radiation with gaps between the plates. Alternatively, the collimator can be two diaphragms. One diaphragm can have at least one slit at the input and another diaphragm can have a plurality of at the output. Similarly, a collimator having radiation-transparent channels with circular apertures can be implemented either as a capillary twist, or as two diaphragms, the input with at least one orifice, and the output one with many orifices.

To form beams of micron- or submicron-thicknesses and divergence of a few angular minutes, a slitless collimator can be used. A slitless collimator is based on the X-ray transmission effect at the border of two flat polished plates, with repeated complete internal reflection (CIR). Such collimators have high aperture ratios and can obtain beams l-2μm wide.

The slitless collimator is implemented as a set of metal or glass plates with polished surfaces stacked on top of each other without gaps, and pressed together under high pressure. The length of the plates in the direction of X-rays propagation should allow complete absorption of the part of the beam not passing along the boundary between the plates (the working plane).

For perfectly flat and smooth plates, the effective width of a channel along which the X-rays will propagate in a slitless collimator, is determined by the penetration depth of the radiation into the medium upon CIR, which is from tens to hundreds of Angstroms.

Practically, this value depends on the polishing quality and flatness of the plates, and conditions of their pressing. The divergence 2γ of the beam passed through a slitless collimator is equal to the input aperture angle of the collimator but cannot exceed twice the CIR critical angle, 2Θ. The input aperture angle is determined as

2δ = f/ D where f is the focus size of the X-ray tube along the direction perpendicular to the collimator working plane; D is the distance from the tube focus to the collimator input. A modified slitless collimator can be used to obtain extremely naπow (with divergences less than ten angular seconds) high-intensity X-ray beams. A slitless collimator can include a stack of the polished-surfaced plates pressed together, but unpolished bands are made on the reflecting surfaces perpendicular to the X-ray path, and located at such distances from the device input and output as to be able to completely absorb the beams. The X-ray beam divergence is decreased for such a design because after the beams have passed through the input boundary of the polished surfaces according to CIR, the beams proceeding at larger angles fall onto the unpolished regions of the surfaces and get absorbed by them because CIR does not happen on unpolished surfaces. However, the beams proceeding at smaller angles do reach the collimating device output because they do not fall on the unpolished surfaces.

To isolate the radiation scattered by the analyzed object at small angles, a spatial filter is positioned before the coordinate-sensitive detector. The spatial filter is a structure similar to the collimator in which the regions corresponding to the transparent regions of the collimator are manufactured of a material opaque to the penetrating radiation and arranged in such a way that the opaque regions of the filter screen the transparent regions of the collimator. The dimensions of the channels (or slits) and the structure period of the collimator as well as the dimensions of the transparent regions of the collimator should ensure that only the small-angle scattered radiation is recorded on the position-sensitive detector. Accordingly the spatial filter is aπanged to screen direct beams formed by the collimator but transmits the radiation scattered at small angles. The spatial filter should be correlated with the collimator design. For instance, a linear raster should be coπelated with a linear collimator. Similarly, a raster with round orifices and a hexagonal unit should be correlated with a collimator using tightly packed cylindrical transparent sections.

The collimator forms beams penetrating separate areas of the object. As a result, in order to obtain an accurate image of the entire object, it is necessary to ensure passage of the entire object through each of the beams. This can be ensured with a conveyor which moves the object through each of the registration systems. Similarly, this can be accomplished by moving the registration sources past the object. In each case the movement should be with a speed which provides the detectors with sufficient exposure time.

The detecting device for recording the small-angle scattering can be a two-coordinate position-sensitive X-ray element which can be a charge-coupled device, photodiode matrix, a luminescent screen, X-ray film, etc. In one embodiment the detecting device registers information from all rays simultaneously. The detector sensitivity can affect the power required by the radiation source and the speed the object can be scanned at.

From the position-sensitive detector, the signal gets into the data processing system which forms the object's image from small-angle scattering which is then compared to the image obtained from radiation absorption. Small-angle scattering curves obtained for individual cells are compared with the small angle scattering curves of known substances. The small angle scattering curves of known substances can be stored in data processing system to allow the computer to automatically make the comparisons.

In another embodiment of the device every fan-shaped beam is directed to the object at a definite angle, both the radiation transmitted without absorption and the intensity distribution of small-angle scattering are recorded simultaneously. As in the above-described embodiment, a series of narrow weakly diverging beams is formed from a single source of penetrating radiation using a collimator. Radiation is recorded using detecting elements (e.g., a bar of charge-coupled elements, or X-ray range photodiodes) positioned deep inside a raster of slits made of plates opaque to the radiation. The plate thickness is selected so as to eliminate the influence of the radiation scattered by the given recording element on the neighboring elements. The depths and widths of gaps between the plates is determined by the requirement for the individual detector to register radiation falling onto it at a specific angle. The dimensions of each recording element should be at least twice as small as the projection of a separate beam onto the registration plane. Each detector is connected to the data processing system separating the radiation scattered by the object from that of the direct beam. Two images then appear on the display screen: one coπesponds to radiation absorption by the object, and the other to small- angle scattering. Both the absorption factors and the small-angle scattering curve are measured for each beam at exactly the same angle of incidence of radiation onto the object. The beams passed through the object without scattering and the beams scattered at small angles follow almost the same path within the object, so there is no need to specifically allow for such a difference while processing the measurement results.

Another emboidment of the device includes a penetration radiation source, a slit collimator forming the incident flux as a number of small, weakly diverging beams, and a registering spatial filter positioned behind the object.

Such a spatial filter is implemented as a slit raster made of plates opaque to the radiation, with the registering elements placed in the slits. The widths of the plates are selected so as to make sure the primary radiation scattered on the detector material does not affect the neighboring registering elements. The depths and widths of the gaps between the plates are determined from the condition that each individual detector should register radiation falling on it under a definite angle. The dimensions of each registering elements should be at least twice smaller than the projection of an individual ray on the registration plane. Each of the detectors is connected to the information processing system allowing to separate the radiation scattered by the object from the direct beam radiation. Then two images appear on the monitor: one image coπesponds to the small- angle contrast of the object, the other to the absorption contrast. As shown in Figure 1, the device includes source 1 of penetrating radiation. A suitable source 1 includes, but is not limited to, an X-ray tube. The source 1 is directed at the analyzed object 2 moved using the conveyor 3. Collimators 4, 5 are positioned between the analyzed object 2 and the source 1. The collimators 4, 5 form weakly divergent beams which are incident on the object. The collimator 4 of the registration system for the transmitted radiation is blocks of material opaque to penetrating radiation, with slit-shaped transparent regions 6. The slit axes are oriented along lines converging at a point coinciding with the focal spot of the source of penetrating radiation (the X-ray tube focus), and positioned at angles to the conveyor plane as much as possible different from each other. The slit width should be selected so the beam size in that direction is less than the size of a substance sought within the object. Suitable substances being sought include, but are not limited to explosives. In the direction perpendicular to the latter one, the collimator should be able to form beams covering the entire object. The radiation transmitted through the object is recorded using coordinate-sensitive detectors 7 positioned parallel to the collimator slits 6. Before each detector 7, a series of slits 8 is positioned improving the signal/noise ratio for the recorded intensity of the transmitted radiation. The coordinate resolution of the detector 7 determines the spatial resolution in the direction perpendicular to that of the object motion. In the SAS registration system, the radiation flux falling on the object is formed using a collimator 5 as a number of narrow weakly diverging beams.

Each of the specified collimators 5 has regions alternating transparent 9 and opaque 10 to penetrating radiation, with the regions forming channels. The channel axes are oriented along directions 11 converging at a point coinciding with the focus of the radiation source. The axes of each of the collimators 5 also converge at the source focus and are positioned at various angles relative to the conveyor plane, the angles are preferably as different as possible from each other. In the path of the radiation transmitted through the object, spatial filters 12 are placed including the transparent 13 and the opaque 14 regions. The spatial filter 12 is designed to isolate the coherent radiation scattered at small angles and the radiation scattered at large angles. The collimator 5 and the spatial filter 12 are positioned in such a way that the opaque regions 14 of the filter screen the regions 9 of the collimator transparent to penetrating radiation, and only the radiation scattered by the object at small angles is transmitted through the transparent regions 13.

The dimensions of the transparent regions (in this case, the widths and the depths of the slits), the structure period (distance between slits) of the collimator, and the dimensions of the transparent regions of the spatial filter should be selected in such a way as to ensure that the radiation scattered at small angles by the analyzed object in a specific angular range is recorded by the position-sensitive detector 15.

Each detector 15 is a two-coordinate position-sensitive element ensuring resolution sufficient to build a small-angle scattering curve for each of the object cells. The device operates in the following way. Before the object 2 crosses the registration system for radiation absorption, detectors 7 measure the radiation intensities of the primary beams formed by collimators 4 in the absence of the object 2. The measured values are transfeπed into the measurement result processing system 16 (Figure 2). When the object 2 is moved by the conveyor 3, it first enters the registration system for radiation absorption consisting of the source 1, collimators 4, slits 8, and detectors 7. While the object is moved through the registration system for radiation absorption, detectors 7 record the transmitted .radiation crossed the object 2 at various angles. The measured intensity values of the transmitted radiation are transfeπed to the measurement result processing system 16. The system 16 calculates the ratios of the measured intensity values of the transmitted radiation in the presence of those objects to those in the absence of the object, and builds a matrix of absorption factors distributed over the object volume. The object 2 is then moved through the small-angle measurement system consisting of the same source 1, collimators 5, two-coordinate detectors 15, and spatial filters 12 selecting only radiation scattered at small angles (up to a few degrees) positioned before each of the detectors. When the object is absent, radiation does not reach detectors 15 which then record only the background intensity.

The values of small-angle scattering intensity recorded by the detectors 15 when the object 2 passes the system reach the SAS data processing system 17 into which the data on absorption factor distribution over the volume of the object 2 are also transfeπed from the system 16.

The values of the absorption factor distribution over the object volume can be found when reduced small-angle scattering curves are calculated in the system 17. The system 17 for processing the data obtained from the different small- angle scattering systems constructs the object image from the scattered radiation in the form of a matrix of small-angle scattering curve distributed over the volume.

In the block 18, images of the object 2 obtained for absorption and for small-angle scattering are compared, and the data obtained are compared to an available atlas of small-angle scattering curves. Based on comparison results, three-dimensional image of the object is formed on the video display screen 19 with the substances composing the object identified.

Another embodiment of the device presented in Figure 3 contains the source 1 of penetrating radiation. The collimators 20 form naπow weakly diverging fan-shaped beams directed on the object 2 which is moved using the conveyor 3. The collimators 20 are oriented with respect to the analyzed object

2 in such a way as their axes are inclined to the direction of object motion at angles. The angles preferably differ as much as possible from each other. The scattered radiation 21 and the radiation 22 transmitted without scattering is recorded using linear coordinate-sensitive detectors 12 placed in the raster slits 24. The raster 24 (Figure 4) is implemented as a system of plates 25 opaque to penetrating radiation, with bars of linear detectors registering radiation placed in the gaps between them. The thickness of the plates is selected so as to eliminate the influence of radiation scattered on the material of the detector 23, on the neighboring elements. The length and width of the slots between the plates is selected according to the requirement for each individual detector to record radiation falling onto it at a specific angle. Signals will be transfeπed to the data processing system via two independent channels, one of which will be connected to the detectors recording radiation intensity distribution caused by different absorbance factors of the materials composing the object, and the second to the detectors recording the radiation scattered at small angles. The read data will be processed by a computing unit, and then transfeπed to the video display screen.

A small-angle topography device illustrated in Figure 5 contains a penetrating radiation source 31 and a diaphragm 32 with an orifice 33. A part of the penetrating radiation 34 is selected by the diaphragm 32 and directed to the analyzed object 5. Between the analyzed object 35 and the diaphragm 32, the collimator 36 is located containing alternating regions transparent 37 and opaque 38 to the penetrating radiation. In the path of the radiation passed through the object 39, the spatial filter 40 is positioned having transparent 41 and opaque 42 regions. The purpose of the spatial filter 40 is selecting the coherent radiation scattered under small angles as well as absorbing the direct radiation and radiation scattered under large angles. The collimator and spatial filter are aπanged so the opaque regions of the filter screen the transparent regions of the collimator, so the detector registers background scattering intensity signal in the absence of the object. When the object is placed into the device, the radiation scattered by the object creates a signal on the detector.

The distribution picture of small-angle scattered radiation obtained on the coordinate-sensitive detector carries information about the object's structure and is determined by the scattering ability of the substances contained in the analyzed object. Since every substance has a unique small-angle scattering curve, this method allows substances present in the object to be identified upon comparison with the scattering curves of known substances included in a database.

As seen from Figure 6, the device can be implemented so as the collimator 36 illuminates, by radiation, only a part (a separate band) of the object 35 at each moment of time. To obtain data on the structure of the entire object, it is necessary to scan it in the radiation field. One can perform scanning either by moving the optical elements of the device relative to the object, or by moving the object itself. Motion of the object 35 can be achieved with the drive 44 (Figure 5) rocking the lever 45 hinge-fixed at one end, connected to the object 35 and the detector 43 by the hinged traction bars 46 and 47, respectively. To observe the image scale of the internal structure of the object 35 obtained on the detector 43, it is desirable that the synchronous displacements of the object 35 and the detector 43 were proportional to the distance from the diaphragm 32 to the object and to the detector respectively.

In Figure 7, one of the possible implementations of the collimator and the spatial filter are shown. The collimator 36 is implemented by the block 48 made of material opaque to the radiation, with transparent channels 49. The channel axes are oriented along lines 50 converging at the point 51 coinciding with the source focus, or to the orifice 33 of the diaphragm 32 (Figure 5).

The spatial filter 40 matching the described collimator 36 is also the block 52, but it is made of a material transparent to the radiation. The channels

53 made in the block 52 are filled with a material opaque to the radiation such as tin, tungsten, titanium, lead etc. The channel axes 53 are also oriented along lines 50 converging at the same point 51. The blocks 48 and 52 described here for the collimator 36 and the filter 40 can be manufactured using stereo-lithography. To manufacture the block 48 for the collimator 36, a plate is used made of a polymer transparent to penetrating radiation, and inclined projections are made in it (which form the channels 49). The space inside the plate between the projections is then filled with a layer of material opaque to the penetrating radiation, e.g. tungsten powder.

When the block 52 for the spatial filter 40 is manufactured, through inclined channels 53 are made in a plate made of a polymer transparent for the penetrating radiation, which are then filled with a material opaque to the penetrating radiation, e.g. lead or tungsten. The dimensions of the channels (in this case, their depths and diameters), the collimator structure period (the distance between the collimator channels), and dimensions of the transparent regions of the block 52 (spatial filter 40) should be selected so as only the radiation coπesponding to small-angle scattering of the analyzed object 35 is registered on the position-sensitive detector 43 (Figure 5).

One other implementation of the collimator is shown in Figure 8. In this implementation, the collimator 36 is made of a set of plates 54 positioned parallel to each other with gaps 55 between them, and are manufactured from the material opaque to the penetrating radiation, e.g. tungsten or lead. The plate thickness is determined from the condition of absorption of the penetrating radiation by the material of the plate. The plate length should be such as to cover the entire projection of the analyzed object in the given direction.

The spatial filter 40 also consists of a set of plates 56 made of a material opaque to the penetrating radiation, e.g. tungsten or lead. The gaps 57 between the plates form slits transparent to the radiation.

The thickness of the plates 56 along the direction of radiation propagation is also selected from the condition of radiation adsorption. The length of the plate 56 should cover the entire projection field of the object while its width should be sufficient to cover the transparent region i.e. the collimator gap 55, so that all the regions transparent to the penetrating radiation (the collimator gaps 55) should be screened by the absorbing plates 56 of the spatial filter 40. When the collimator is implemented as a set of plates, the radiation flux from the source can be formed using the diaphragm 58 having one or several regions transparent to the radiation, in the shapes of slits 59. The diaphragm slits 59 should be parallel to the collimator gaps 55 and the filter gaps 57. The presence of several slits in the diaphragm 58 allows increased illumination of the analyzed object 35 and an increased object scanning rate.

In Figure 9, the spatial filter 40 therein is implemented as a set of plates 60 opaque to the penetrating radiation with gaps between the plates containing bars of radiation-registering detectors 61. The plate thickness is set to exclude the impact of the primary radiation scattered in the material of the detector 61 onto the neighboring registering elements. The width and length of the gaps between the plates are set from the condition of registering, by each detector, of the radiation falling onto that detector under a specific angle. Then, the radiation passed through the object 35 without scattering and the radiation scattered by the object 35 will be registered in two independent channels 62 and 63. In the channel 62, the contrast will be registered resulting from the differences in absorption coefficients of the materials composing the object 35, while the channel 63 will register the small-angle contrast. The information obtained is processed by the computing unit 64, and the image obtained is transfeπed to the display 65. As a result, two images of the object's internal structure will appear on the display screen, complementing each other, one in direct, the other in scattered radiation.

The small-angle topography device can have one more implementation somewhat different from that shown in Figure 5. This device (Figure 10) contains the penetrating radiation source 66 and the diaphragm 68 positioned in the path of the radiation flux 67, with the diaphragm having several slits 69 forming the radiation flux 70 in the direction of the object 35. Between the diaphragm 69 and the object 35, the diaphragm 71 is placed forming many naπow weakly-diverging beams directed to the analyzed object. Behind the object, the spatial filter 72 is positioned implemented as a set of parallel plates

73, with the gaps between the plates forming many slits 74. Those slits are specifically implemented in that a phosphor is deposited onto the surface of each plate. The plates 73 of the filter 72 are located in the shadowed areas of the penetrating radiation flux 74, the areas brought about by the diaphragm 71, and the phosphor present on the surface of the plates 73 transforms the penetrating radiation scattered by the object 35 into the luminous one. The luminous radiation then passes through the optical system comprising the concave minor 75 and the collecting lens 76, and is registered by the detector 76 on which the intensity distribution of the radiation scattered by the obj ect 35 can be observed.

Accordingly, it is possible to obtain two images of the internal structure of the analyzed object - in the scattered radiation on the detector 77, and in the direct radiation passed through the analyzed object on the detector 78.

This allows to obtain more complete information about the object's internal structure.

In Figs. 11 and 12, a possibility is shown for use of the proposed device in a luggage control facility.

Using the conveyor 79, the analyzed object 35 is moved between the penetrating radiation source 80 (e.g. an X-ray tube) and the detector 81. The X- ray radiation passes through the collimator 82 forming many naπow, weakly diverging X-ray radiation beams. The obtained beams further pass through the analyzed abject moving along the conveyor 79, and then through the filter 83 detaining the non-scattered part of the radiation. The coherent radiation scattered under small angles reaches the detector 81. At each moment of time, the detector registers a fragment of the internal structure image of the object as a separate band. The specified fragments are recorded by the computing unit 84, into which the information about the object displacement is simultaneously entered. The computing unit 84 is connected to the input of the detector 81, and the drive 85 of the conveyor 79. From the two received signals (the fragment of the object's internal structure, and the object displacement coordinate), the computing unit generates the complete image of the object's internal structure, and transfers the image to the video screen 86.

In Figure 12, relative positions are shown of the conveyor 79, the radiation source 80, the collimator 82, the spatial filter 83, the detector 81, and the analyzed object 35. In the described luggage control facility, different designs of the proposed small-angle topography device shown in Figs. 8, 9, or 10, can be used.

Figure 13 A illustrates a slitless collimator. A set of metal or glass plates 87 with polished surfaces 88 are stacked on top of each other without gaps, and pressed together under high pressure.

Figure 13B is a sideview of a plate used in a modified slitless collimator used to obtain extremely naπow (with divergences less than ten angular seconds) high-intensity X-ray beams. An unpolished band 89 is made on the reflecting surfaces perpendicular to the X-ray path, and located at such distances from the device input and output as to be able to completely absorb the beams. The X-ray beam divergence is decreased for such a design because after the beams have passed through the input boundary of the polished surfaces according to CIR, the beams proceeding at larger angles fall onto the unpolished regions of the surfaces and get absorbed by them because CIR does not happen on unpolished surfaces. However, the beams proceeding at smaller angles do reach the collimating device output because they do not fall on the unpolished surfaces. The foregoing description of a prefeπed embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

CLAIMSWhat is claimed is:

1. A device for determining composition and internal structure of an object, comprising: a source of radiation which can penetrate the object; a facility for moving the object relative to the source; at least one unit for forming radiation from the source into a plurality of weakly divergent beams, each beam positioned so it can be incident on the object; a separation device defines a first component and a second component in at least one beam after the beam has passed through the object, the first component includes primarily radiation scattered over small angles by the object, the second component includes primarily radiation which was not scattered on passing through the object; at least one first detector is configured to register at least a portion of the first component of the at least one beam; at least one second detector is configured to register at least a portion of the second component of the at least one beam; a processing system for receiving first signals from the at least one first detector and second signals form the at least one second detector, the processing system configured to process the first and second signals so as to create data signals providing information which indicates the internal structure of the object.

2. The device of claim 1, wherein the unit is a collimator.

3. The device of claim 2, wherein the collimator includes regions transparent to the radiation alternating with regions opaque to the radiation.

4. The device of claim 1, wherein the unit is a slitless collimator.

5. The device of claim 1, wherein the separating device is a filter configured to screen the at least one first detector from the radiation in the second component.

6. The device of claim 5, wherein the filter includes regions which are opaque to the radiation and regions which are transparent to the radiation, the opaque regions are positioned to screen the at least one first detector from the radiation in the second component.

7. The device of claim 1, wherein the at least one first detector is position sensitive.

8. The device of claim 1 , wherein the at least one first detector is two dimensional coordinate sensitive.

9. The device of claim 1 , wherein the at least one second detector is position sensitive.

10. The device of claim 1 , wherein the at least one second detector is two dimensional coordinate sensitive.

11. A device for determining composition and internal structure of an object, comprising: a source of radiation which can penetrate the object; a facility for moving the object relative to the source; at least one unit for forming radiation from the radiation source into a plurality of weakly divergent beams, each beam positioned so it can be incident on the object; a separation device for defining a component in at least one beam after the beam has passed through the object, the component includes primarily radiation scattered over small angles by the object; at least one detector configured to register at least a portion of the radiation in the component of the at least one beam; a processing system for receiving signals from the at least one first detector, the processing system configured to process the signal so as to create an image of the internal structure of the object.

12. The device of claim 11, wherein the unit is a collimator.

13. The device of claim 12, wherein the collimator includes regions transparent to the radiation alternating with regions opaque to the radiation.

14. The device of claim 11 , wherein the unit is a slitless collimator.

15. The device of claim 11 , wherein the separating device is a filter configured to screen the at least one first detector from the radiation in the second component.

16. The device of claim 15, wherein the filter includes regions which are opaque to the radiation and regions which are transparent to the radiation, the opaque regions are positioned to screen the at least one first detector from the radiation in the second component.

17. The device of claim 11 , wherein the at least one detector is position sensitive.

18. The device of claim 11 , wherein the at least one detector is two dimensional coordinate sensitive.

19. A device for determining composition and internal structure of an object, comprising: a source of radiation which can penetrate the object; a facility for moving the object relative to the source; at least one unit for forming radiation from the radiation source into a plurality of weakly divergent beams, each beam positioned so it can be incident on the object; a separation device for defining a component in at least one beam after the beam has passed through the object, the component includes primarily radiation scattered over small angles by the object; at least one detector configured to register at least a portion of the radiation in the component of the at least one beam; a processing system for receiving signals from the at least one first detector, the processing system configured to process the signal so as to discern the nature of the substances making up the object.

20. A device for determining composition and internal structure of an object, comprising: a source of radiation which can penetrate the object; a facility for moving the object relative to the source; a unit including a first collimator system and a second collimator system, the first collimator system configured to form a plurality of weakly divergent beams from the radiation source, the second collimator system including at least one collimator configured to form a plurality of weakly divergent beams from the radiation source, at least two of the beams being oriented at different angles to the object; a first system including at least one first detector for receiving radiation which primarily has passed through the object without being absorbed or scattered, the first system configured to receive first signals from the at lest one first detector and obtain an image of the object based on the first signals; and a second system including at least one second detector and a spatial filter, the filter configured to screen the at least one detector from radiation transmitted through the object without being scattered over small angles, the second system configured to receive second signals from the at least one second detector and provide an image of the object based on the second signals.

21. The device of claim 20, wherein the collimator includes regions transparent to the radiation alternating with regions opaque to the radiation.

22. The device of claim 20, wherein the collimator is a slitless collimator.

23. The device of claim 20, wherein the filter includes regions which are opaque to the radiation and regions which are transparent to the radiation, the opaque regions are positioned to screen the at least one second detector from unscattered radiation.

24. The device of claim 20, wherein the at least one second detector is position sensitive.

25. The device of claim 20, wherein the at least one second detector is two dimensional coordinate sensitive.

26. A device for determining composition and internal structure of an object, comprising: a source of radiation; a unit including multislit collimators configured to form weakly diverging beams from the radiation source, the said collimators oriented so the beams form different angles incident with the object; an imaging system configured to obtain at least one image of the object based on radiation absorbed by the object and on radiation scattered by the object over small-angles including a raster of slits with detectors positioned to receive radiation passing through the slits, each detector coupled with a processing system configured to discriminate between detectors receiving radiation scattered at small angles from radiation transmitted through the object without scattering.

27. The device of claim 26, wherein the dimensions of each detector exposed to radiation which has not been scattered by the object is at least twice smaller than the projection of a separate beam on a registration plane.

28. A device for analyzing an internal structure of an object, comprising: a radiation source; a collimator for forming at least one weakly diverging beam incident on the object; at least one detector configured to register the radiation produced by the source; and a filter positioned on an opposite side of the object from the radiation source, the filter including a structure complementary to the collimator in which filter regions co╧Çespond to the transparent regions of the collimator and include a material opaque to the penetrating radiation so the opaque regions of the filter substantially screen the fransparent regions of the collimator allowing at least a portion of a radiation scattered by the object over small-angles scattered radiation is registered on the detector.

29. The device of claim 28, wherein the collimator includes a plate opaque to the penetrating radiation in which transparent channels are made, with the channel axes converging at the focus of the radiation source, and the spatial filter includes a plate transparent to the radiation having regions opaque to the radiation in the shapes of rods screening the channels transparent to the penetrating radiation of the collimator.

30. The device of claim 28, wherein the collimator is includes a set of plates, with the gaps between the plates forming a system of slits fransparent to the penetrating radiation, the planes of the slits crossing in the line passing through the radiation source.

31. A device for analyzing an internal structure of an object, comprising: a radiation source forming a plurality of na╧Çow and weakly diverging beams incident on the object; a spatial filter positioned on an opposite side of an object from the source and configured to substantially separate radiation scattered by the object over small angles from radiation which has not been scattered and allow at least a portion of each type of radiation to pass through openings; a first at least one registering element configured to receive radiation which has passed through the openings and is composed primarily of scattered radiation; a second at least one registering element configured to receive radiation which has passed through the openings and is composed primarily of direct radiation, and a processing system coupled with the registering elements and including logic to at least partially process the scattered radiation independent of the direct beam radiation.