CN102855603B - Method and device for adaptive interpolation - Google Patents
Method and device for adaptive interpolation Download PDFInfo
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Abstract
The invention relates to the field of medical equipment, in particular to a method for adaptive interpolation. The method includes: sampling positions of an X-ray bulb tube by a position sensor to obtain rotational speed information of the X-ray bulb tube; setting an interpolation coefficient according to the rotational speed information to enable an angle interval between two times of continuous film reading to be unchanged; and calculating projection angle of the X-ray bulb tube during each film reading according to the interpolation coefficient by using a formula shown as follows: Alpha Nu=Xi(t)*360, wherein the Xi(t) refers to the interpolation coefficient, the t refers to time point of a certain film reading, the Alpha(Nu)refers to the projection angle of the X-ray bulb tube during the film reading, and the av refers to the projection angle of the X-ray bulb tube at the time point t. The invention further provides a device for adaptive interpolation. Compared with the prior art, the method and the device for adaptive interpolation can lower product cost and improve imaging quality and accuracy rate of projection angle calculation.
Description
Technical field
The present invention relates to field of medical device, particularly a kind of adaptive interpolation method and device.
Background technology
In X ray computer fault imaging (Computed Tomography, CT) equipment, two kinds of methods are usually had to measure or calculate the projection angle of X-ray bulb.One is set time triggering method, detector (DMS, Data measurement system) read tablet (namely reading gathers X-ray projection data) in interval of delta t at a fixed time in the method.In this time interval Δ t, the anglec of rotation of X-ray bulb is called angle intervals
its integration being X-ray tube angular velocity of rotation ω in interval time t, wherein angular velocity omega=v/r, v is rotary speed, and r is the radius of machine frame hole.Rotary speed v is changeless in theory, so the angle intervals between twice read tablet
it should be a constant.But, absolute balance can not be kept due to frame in rotary course and stablize, and the friction between the rotating part of frame and stationary part can change along with temperature, so rotary speed is not changeless, and then the angle intervals between twice read tablet also changes, this change can affect CT image quality, as produced artifact etc.When the change of rotary speed exceedes threshold value, picture quality will become very poor.
The another kind of method measuring or calculate actual projection angle is fixed position triggering method, and in the method, detector is in the fixed angle position read tablet of X-ray tube.In theory, need measurement image rebuild needed for whole projection angles, otherwise can cause image blurring or picture quality is very poor.As in high-end CT equipment, utilize the position sensor of rack-mounted more than 1000 to the angle position of X-ray bulb of sampling, so detector can just carry out a read tablet every 360 °/1000=0.36 °, this mode considerably reduces differential seat angle, thus significantly improves image quality.But owing to being provided with a large amount of position sensors and complicated signal collecting and controlling system, product cost is also very high, so cannot for low side CT equipment.
Cross in order to workinprocess cost and seek a suitable equalization point between image quality, prior art proposes a kind of method combined with set time triggering method by position sensor, and it adopts the method for linear interpolation or quadratic interpolation to generate the projection angle of each read tablet.But this method interpolation accuracy rate and be limited to the improvement of image quality, unless still used a large amount of position sensors.
Application number is that 201110145184.7 applications for a patent for invention disclose a kind of time triggered apparatus and method for keeping sweep spacing constant, this application needs the firmware (firmware) and the control system that change CT equipment, as programmable interval timer still needs to spend certain cost.The application is then without the need to changing the firmware of CT equipment.
Summary of the invention
The object of the present invention is to provide a kind of adaptive interpolation method and device, the projection angle of X-ray bulb during to calculate each read tablet, and the object that makes the angle intervals between twice continuous read tablet substantially constant was originally realized with lower one-tenth, improve the accuracy rate that projection angle calculates, obtain higher image quality.
In view of this, the present invention proposes a kind of adaptive interpolation method, and described method comprises: sample in the position of position sensor to X-ray bulb, to obtain X-ray bulb rotating speed data; Set an interpolation coefficient according to described rotating speed data, remain unchanged to make the angle intervals between twice continuous read tablet; The projection angle of X-ray bulb: α when calculating each read tablet according to described interpolation coefficient by following formula
v=ξ (t) * 360, wherein ξ (t) is interpolation coefficient, and t is the time point of certain read tablet, and α (v) is the projection angle of X-ray bulb during this read tablet, α
vfor the projection angle of X-ray bulb when time point t.Thus when not changing and increasing equipment firmware, keep the angle intervals of X-ray bulb between twice continuous read tablet substantially constant with lower cost.
According to one embodiment of present invention, the step of described setting interpolation coefficient comprises: the fundamental curve obtaining described interpolation coefficient; Obtain a regulation coefficient according to described rotating speed data, and change the frequency of described fundamental curve with this regulation coefficient.
According to another embodiment of the invention, the step of described acquisition fundamental curve comprises: the fundamental curve obtaining described interpolation coefficient according to a known variables relevant with angle intervals.
According to still a further embodiment, described known variables is the variable that frame gravity causes.
According to still another embodiment of the invention, described fundamental curve is a sine curve.
According to still another embodiment of the invention, described sinusoidal initial phase and amplitude are fixing, and frequency can adjust according to described gantry rotation rate information.
According to still a further embodiment, described method comprises further: carry out read tablet according to described projection angle, to obtain X-ray projection data.
The present invention also provides a kind of adaptive-interpolation device, and described device comprises: a position sensor, for sampling to the position of X-ray bulb, to obtain X-ray bulb rotating speed data; An interpolation coefficient assignment component, for setting interpolation coefficient according to described rotating speed data, remains unchanged to make the angle intervals between twice continuous read tablet; One projection angle computation module, the projection angle of X-ray bulb: α during for calculating each read tablet according to described interpolation coefficient by following formula
v=ξ (t) * 360, wherein, ξ (t) is described interpolation coefficient, and t is the time point of certain read tablet, and α (v) is the projection angle of X-ray bulb during this read tablet, α
vfor the projection angle of X-ray bulb when time point t.Thus when not changing and increasing equipment firmware, keep the angle intervals of X-ray bulb between twice continuous read tablet substantially constant with lower cost.
According to one embodiment of present invention, described interpolation coefficient assignment component comprises: stuck-module, for storing the fundamental curve of described interpolation coefficient; Variable module, for obtaining a regulation coefficient according to described rotating speed data, and changes the frequency of described fundamental curve with this regulation coefficient.
According to one embodiment of present invention, described device comprises further: a read tablet assembly, for carrying out read tablet according to described projection angle, to obtain X-ray projection data.
As can be seen from such scheme, because the present invention can, when not changing and increasing equipment firmware, keep the angle intervals of X-ray bulb between twice continuous read tablet substantially constant, to improve image quality with lower cost; Meanwhile, the present invention only needs a position sensor to the rotating speed data of frame of sampling, and compares fixed position triggering method, can the structure of reduced data acquisition system control circuit board greatly, reduces the cost of data collecting system.In addition, the present invention can also improve the accuracy rate calculating projection angle.
Accompanying drawing explanation
Embodiments of the invention will be described in detail by referring to accompanying drawing below, make clearer above-mentioned and other feature and advantage of the present invention of those skilled in the art, in accompanying drawing:
Fig. 1 is the schematic diagram that the present invention obtains interpolation coefficient.
Fig. 2 a be angle intervals between twice continuous read tablet obtaining of adaptive interpolation method of the present invention and actual angle interval compare schematic diagram.
Fig. 2 b is the schematic diagram of difference after normalized of the projection angle that obtains of adaptive interpolation method of the present invention and actual projection angle.
When Fig. 3 a is employing 2 position sensors, the angle intervals obtained of adaptive interpolation method of the present invention and linear interpolation, quadratic interpolation method compare schematic diagram.
When Fig. 3 b is employing 24 position sensors, the angle intervals obtained of adaptive interpolation method of the present invention and linear interpolation, quadratic interpolation method compare schematic diagram.
Fig. 4 is the schematic diagram of adaptive-interpolation device of the present invention.
Detailed description of the invention
For making the object, technical solutions and advantages of the present invention clearly, the present invention is described in more detail by the following examples.
The invention provides a kind of adaptive interpolation method and device, with the object that the angle intervals originally realizing X-ray bulb between maintenance twice continuous read tablet with lower one-tenth is substantially constant.Here, the time interval Δ t between twice continuous read tablet is constant, and its angle intervals can be corrected through adaptive interpolation method of the present invention.Adaptive interpolation method of the present invention can be configured in the software of equipment and go, so just without the need to changing or increase the firmware of equipment, thus cost-saving.
Be specifically described for CT equipment below.
As stated in the Background Art, the formula of the linear interpolation adopted in prior art is:
Wherein, the sampling time point of adjacent two position sensors is t
1, t
2, corresponding projection angle is α
t1(v), α
t2(v).Because the time interval between twice continuous read tablet is fixing, so t
2-t
1=Δ t, t are the time point of certain read tablet, are known quantities, and available like this formula (1) calculates α (v).
The formula of the quadratic interpolation mentioned in prior art is:
Wherein, in an initial condition, t
1≤ t≤t
2≤ t
3, under other conditions, t
1≤ t
2≤ t≤t
3.The sampling time point of adjacent three position sensors is t
1, t
2, t
3, corresponding projection angle is α
t1(v), α
t2(v), α
t3(v).Because the time interval between twice continuous read tablet is fixing, so
And t is known, available like this formula (2) calculates α (v).
Such as when there being 24 position sensors, the angle intervals of adjacent two position sensors is 360 °/24=15 °, and the swing circle of X-ray bulb is 0.48s, then Δ t=0.48/24=0.02s; Get α
t1(v)=15 °, α
t2(v)=30 °, α
t3(v)=45 °, t
1=0.02s, t
2=0.04s, t
3=0.06s, then can obtain the projection angle of the read tablet when moment such as t=0.03s or 0.05s according to the interpolation method of formula (1) or (2).But the accuracy rate of above-mentioned linear interpolation or quadratic interpolation method interpolation is lower, also limited to the improvement of image quality, and except the position sensor that non-usage is a large amount of, but this can improve the cost of product.This point will illustrate in Fig. 3 a and Fig. 3 b.
For reducing product cost, projection angle when namely can obtain each read tablet with less position sensor, and make the difference of this projection angle and actual projection angle less, the present invention proposes a kind of adaptive interpolation method, and its following formula (3) calculates projection angle during each read tablet:
α
v＝ξ
1(t)α
t1(v)+ξ
2(t)α
t2(v)，t
1≤t≤t
2(3)
Wherein ξ
1(t), ξ
2t () is interpolation coefficient.
Two position sensors are only needed to obtain t in formula (3)
1the projection angle α of sampling time point
t1(v) and t
2the projection angle α of sampling time point
t2(v).
Consider from the angle reducing product cost, the position sensor number of adaptive interpolation method of the present invention can reduce to one from two, in this case, and t in formula (3)
1=0, t
2=T (rotational time), α
t1(v)=0, α
t2(v)=360 °, so formula (3) just develops into following formula (4):
α
v＝ξ(t)*360，0≤t≤T (4)。
Formula (3) and (4) middle interpolation coefficient ξ
1(t), ξ
2t () and ξ (t) are different from the linear interpolation coefficient in formula (1), also quadratic interpolation coefficient in formula (2) is different from, the difference of interpolation coefficient difference projection angle and actual projection angle that adaptive interpolation method of the present invention is obtained is less just, and the demand of reduction to position number of sensors.
Fig. 1 is the schematic diagram that the present invention obtains interpolation coefficient.It comprises the steps:
Step 101, samples with the position of position sensor to X-ray bulb, to obtain X-ray bulb rotating speed data.Such as, the rotational time T that current X-ray bulb rotates a circle required is got.
Step 102, obtains the fundamental curve of interpolation coefficient.This fundamental curve can be obtained according to a known variables relevant with angle intervals.
As described in the background art, be not changeless in the rotary speed of CT scan mid frame, rotary speed can be analyzed to four components: the variable that the variable that constant baseline speed component, gravity cause, friction cause and stochastic variable.The variable that wherein gravity causes is a sine curve and is predictable in each swing circle, once assemble frame, the sinusoidal amplitude of the variable that gravity causes and initial phase just no longer change, unless maintenance needs to ressemble frame.In use, the variable that gravity causes can be measured and record again simultaneously.After more than 100 times rotate, the variable caused that rubs also can regard a near-sinusoidal as, though it is measurable unlike the variable that gravity causes, but measurable.A position sensor can be utilized to obtain X-ray bulb to rotate a circle required rotational time, due to the difference of rotational time quite little (as being no more than 0.2%) between twice continuous rotation, so can carry out with the rotational time of a week in X-ray tube the variable that estimated friction causes.Sometimes, the variable caused that rubs also can regard that the amplitude of the variable that gravity causes changes as.In above-mentioned four components, the variable that gravity causes and variable the having the greatest impact to image quality that cause of rubbing, and stochastic variable on image quality affect variable that phase force of gravity causes and the variable that causes of rubbing just relative much little on the impact of image quality.Accordingly, the impact of the change of rotary speed on image quality only can need be reduced to minimum along with rotary speed synchronously changes by interpolation coefficient.
According to one embodiment of present invention, the variable that interpolation coefficient can cause according to frame gravity sets, so described fundamental curve is a sine curve, and its initial phase and amplitude are changeless.
Step 103, sets described interpolation coefficient according to one with the look-up table of described rotating speed data.
Described look-up table comprises a stuck-module and a variable module.Wherein store the fundamental curve of described interpolation coefficient in stuck-module, it just write in advance before product consigns to client, and can not change, unless write by CT service engineering Shi Zaici.Look-up table can be incorporated in the software systems of CT equipment.
Variable module obtains a regulation coefficient according to the rotational time T that position sensor obtains, and changes the frequency of described fundamental curve with this regulation coefficient, and this part can write at any time.
Because the time interval between twice continuous read tablet is constant, so the change of rotational time T can cause read tablet number of times to change, that is, when rotational time is longer, read tablet increased frequency, when rotational time is shorter, read tablet number of times reduces.This change shows as change of frequency on sine curve.This change causes image quality poor just.Therefore adaptive interpolation method of the present invention just adjusts the frequency of this fundamental curve by a regulation coefficient, substantially constant to ensure the angle intervals between twice continuous read tablet.As sinusoidal frequency very fast (f1), an available regulation coefficient a1 being less than 1 is multiplied by this frequency, substantially constant to ensure the angle intervals between twice continuous read tablet; As sinusoidal frequency comparatively slow (f2), an available regulation coefficient a2 being greater than 1 is multiplied by this frequency, substantially constant to ensure the angle intervals between twice continuous read tablet, namely
Wherein f0 is the frequency of described fundamental curve.
Step 104, calculates the projection angle of each read tablet by formula (4) according to the interpolation coefficient obtained.
Further, adaptive interpolation method of the present invention comprises:
Step 105, carries out read tablet according to described projection angle, to obtain X-ray projection data.
Fig. 2 a be adaptive interpolation method of the present invention obtain angle intervals between twice continuous read tablet and actual angle intervals compare schematic diagram.Wherein, abscissa is the read tablet number of times in a swing circle, the longitudinal axis is angle intervals, chain line be hypothesis actual angle interval variation curve (as, sine component amplitude of variation is 5%, and random element is 1%), solid line is the angle intervals change curve that adaptive interpolation method of the present invention obtains, the angle intervals change curve of itself and actual measurement is matching substantially, and angle intervals is about about 0.3 degree.
Fig. 2 b is the schematic diagram of difference after normalized of the projection angle that obtains of adaptive interpolation method of the present invention and actual projection angle.Wherein, abscissa is the read tablet number of times in a swing circle, and the longitudinal axis is the projection angle difference after normalization.Can find out in Fig. 2 b that the difference of employing adaptive interpolation method projection angle of the present invention and actual projection angle is very little after normalization, within the difference range of ± 0.01.Wherein normalized projection angle difference is defined as:
(angle intervals that actual angle interval-adaptive interpolation method obtains)/(360 °/each read tablet total degree rotated).
When Fig. 3 a is employing 2 position sensors, the angle intervals obtained of adaptive interpolation method of the present invention and linear interpolation, quadratic interpolation method compare schematic diagram.Wherein abscissa is the read tablet number of times in a swing circle, ordinate is angle intervals, chain line is that (sine component amplitude of variation is 5% to the actual angle interval variation curve supposed, random element is 1%), solid line is the angle intervals change curve that adaptive interpolation method of the present invention obtains, dotted line is the angle intervals change curve that linear interpolation obtains, and dotted line is the angle intervals change curve that quadratic interpolation obtains.In Fig. 3 a visible linear interpolation and quadratic interpolation and actual angle interval variation curve widely different, the angle intervals change curve that adaptive interpolation method of the present invention obtains then can matching actual angle interval variation curve well.
When Fig. 3 b is employing 24 position sensors, the angle intervals obtained of adaptive interpolation method of the present invention and linear interpolation, quadratic interpolation method compare schematic diagram.Wherein abscissa is the read tablet number of times in a swing circle, ordinate is angle intervals, chain line is that (sine component amplitude of variation is 5% to the actual angle interval variation curve supposed, random element is 1%), solid line is the angle intervals change curve that adaptive-interpolation obtains, dotted line is the angle intervals change curve that linear interpolation obtains, and long dotted line is the angle intervals change curve that quadratic interpolation obtains.Visible in Fig. 3 b, after the quantity of position sensor is increased to 24, linear interpolation and quadratic interpolation reduce than Fig. 3 a greatly with actual angle interval variation curve difference out-phase, and the angle intervals change curve that adaptive interpolation method of the present invention obtains is still basically identical with Fig. 3 a, still can matching actual angle interval variation curve well.It can thus be appreciated that compare linear interpolation and quadratic interpolation method, the sensitiveness of adaptive interpolation method of the present invention to the number of position sensor reduces greatly.
In addition, compare linear interpolation and quadratic interpolation method, adaptive interpolation method of the present invention also reduces greatly to the sensitiveness that rotary speed amplitude changes.
The present invention also provides a kind of adaptive-interpolation device 1, and as shown in Figure 4, device 1 comprises:
A position sensor 11, for sampling to the position of X-ray bulb, to obtain X-ray bulb rotating speed data.
An interpolation coefficient assignment component 12, for setting interpolation coefficient according to described rotating speed data, remains unchanged to make the angle intervals between twice continuous read tablet.Wherein said interpolation coefficient assignment component comprises:
Stuck-module, for storing the fundamental curve of described interpolation coefficient;
Variable module, for obtaining a regulation coefficient according to described rotating speed data, and changes the frequency of described fundamental curve with this regulation coefficient.
Described fundamental curve and illustrating in the method for aforementioned acquisition interpolation coefficient by the frequency that regulation coefficient changes described fundamental curve, repeats no more here.
One projection angle computation module 13, the projection angle of X-ray bulb during for calculating each read tablet according to described interpolation coefficient by formula (4).
Further, device 1 also comprises: a read tablet assembly 14, for carrying out read tablet according to described projection angle, to obtain X-ray projection data.
Can make in the process rotated a circle in X-ray tube with adaptive approach of the present invention and device as seen, the size of the angle intervals between double read tablet is substantially equal, thus minimize the change of angle intervals, the artifact in CT image can be reduced, make low side CT equipment without the need to just can image quality be improved by the extra correction firmware that increases, can product cost be saved.In addition, owing to only needing a position sensor, the structure of reduced data acquisition system control circuit board greatly.
The present invention relates to field of medical device, particularly a kind of adaptive interpolation method.Described method comprises: sample in the position of position sensor to X-ray bulb, to obtain X-ray bulb rotating speed data; Set an interpolation coefficient according to described rotating speed data, remain unchanged to make the angle intervals between twice continuous read tablet; The projection angle of X-ray bulb: α when calculating each read tablet according to described interpolation coefficient by following formula
v=ξ (t) * 360, wherein ξ (t) is interpolation coefficient, and t is the time point of certain read tablet, and α (v) is the projection angle of X-ray bulb during this read tablet, α
vfor the projection angle of X-ray bulb when time point t.The present invention also provides a kind of adaptive-interpolation device.Method and apparatus of the present invention reduces product cost compared to existing technology, improves the accuracy rate of image quality and projection angle calculating.
The above instrument is preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, and any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (8)
1. an adaptive interpolation method, described method comprises:
Sample in the position of position sensor to X-ray bulb, to obtain X-ray bulb rotating speed data;
Set an interpolation coefficient according to described rotating speed data, remain unchanged to make the angle intervals between twice continuous read tablet;
The projection angle of X-ray bulb when calculating each read tablet according to described interpolation coefficient by following formula:
α
v＝ξ(t)*360，
Wherein ξ (t) is interpolation coefficient, and t is the time point of certain read tablet, α
vfor the projection angle of X-ray bulb when time point t;
The step of described setting interpolation coefficient comprises:
Obtain the fundamental curve of described interpolation coefficient;
Obtain a regulation coefficient according to described rotating speed data, and change the frequency of described fundamental curve with this regulation coefficient.
2. method according to claim 1, is characterized in that, the step of described acquisition fundamental curve comprises: the fundamental curve obtaining described interpolation coefficient according to a known variables relevant with angle intervals.
3. method according to claim 2, is characterized in that, described known variables is the variable that frame gravity causes.
4. method according to claim 3, is characterized in that, described fundamental curve is a sine curve.
5. method according to claim 4, is characterized in that, described sinusoidal initial phase and amplitude are fixing, and frequency can adjust according to described gantry rotation rate information.
6. method according to claim 1, is characterized in that, described method comprises further:
Read tablet is carried out, to obtain X-ray projection data according to described projection angle.
7. an adaptive-interpolation device, described device comprises:
A position sensor, for sampling to the position of X-ray bulb, to obtain X-ray bulb rotating speed data;
An interpolation coefficient assignment component, for setting interpolation coefficient according to described rotating speed data, remains unchanged to make the angle intervals between twice continuous read tablet;
One projection angle computation module, the projection angle of X-ray bulb during for calculating each read tablet according to described interpolation coefficient by following formula:
α
v＝ξ(t)*360，
Wherein, ξ (t) is described interpolation coefficient, and t is the time point of certain read tablet, α
vfor the projection angle of X-ray bulb when time point t;
Described interpolation coefficient assignment component comprises:
Stuck-module, for storing the fundamental curve of described interpolation coefficient;
Variable module, for obtaining a regulation coefficient according to described rotating speed data, and changes the frequency of described fundamental curve with this regulation coefficient.
8. device according to claim 7, is characterized in that, described device comprises further:
One read tablet assembly, for carrying out read tablet according to described projection angle, to obtain X-ray projection data.
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|---|---|---|---|---|
| US6169778B1 (en) * | 1998-03-24 | 2001-01-02 | Siemens Aktiengesellschaft | Computed tomography device |
| CN101327127A (en) * | 2007-06-21 | 2008-12-24 | 上海西门子医疗器械有限公司 | Method and apparatus for acquiring projected angle in image reconstruction |
| CN101496726A (en) * | 2008-01-28 | 2009-08-05 | 上海西门子医疗器械有限公司 | Method and apparatus for acquiring projected angle in image reconstruction |
| CN102805633A (en) * | 2011-05-31 | 2012-12-05 | 上海西门子医疗器械有限公司 | Self-adaptive time triggering device and method for keeping scanning interval invariant |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6169778B1 (en) * | 1998-03-24 | 2001-01-02 | Siemens Aktiengesellschaft | Computed tomography device |
| CN101327127A (en) * | 2007-06-21 | 2008-12-24 | 上海西门子医疗器械有限公司 | Method and apparatus for acquiring projected angle in image reconstruction |
| CN101496726A (en) * | 2008-01-28 | 2009-08-05 | 上海西门子医疗器械有限公司 | Method and apparatus for acquiring projected angle in image reconstruction |
| CN102805633A (en) * | 2011-05-31 | 2012-12-05 | 上海西门子医疗器械有限公司 | Self-adaptive time triggering device and method for keeping scanning interval invariant |
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