Radiographic apparatus and radiation detection signal processing method

Abstract

Corrected X-ray detection signals are obtained by removing lag-behind parts through a recursive computation based on initial values determined from lag signal value (step T2). Thus, the lag-behind parts can be removed by taking into consideration lag signal values remaining at a starting point of the recursive computation. The lag signal values are dependent on the characteristic of an FPD (flat panel X-ray detector). By removing the lag-behind parts, with the lag signal values taken into consideration, the lag-behind parts are removed from X-ray detection signals with increased accuracy, without being influenced by the characteristic of the FPD.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.

FIG. 1 is a block diagram showing an overall construction of a fluoroscopic apparatus according to the invention;

FIG. 2 is a plan view of an FPD used in the fluoroscopic apparatus;

FIG. 3 is a schematic view showing a state of sampling X-ray detection signals during X-ray radiography by the fluoroscopic apparatus;

FIG. 4 is a flow chart showing a procedure of an X-ray detection signal processing method according to the invention;

FIG. 5 is a flow chart showing a recursive computation process for time lag removal in the X-ray detection signal processing method;

FIG. 6 is a view showing a state of radiation incidence;

FIG. 7 is a view showing time lags corresponding to the radiation incidence of FIG. 6; and

FIG. 8 is a view showing a time lag situation where a lag (i.e. a lag-behind part) in radiography overlaps fluoroscopy.

Claims

1. A radiographic apparatus for obtaining radiographic images based on radiation detection signals, comprising: radiation emitting means for emitting radiation toward an object under examination;radiation detecting means for detecting radiation transmitted through the object under examination; andsignal sampling means for taking radiation detection signals from the radiation detecting means at predetermined sampling time intervals;said apparatus obtaining radiographic images based on the radiation detection signals outputted from the radiation detecting means at the predetermined sampling time intervals as radiation is emitted to the object under examination;said apparatus further comprising:time lag removing means for removing lag-behind parts from the radiation detection signals by a recursive computation, on an assumption that a lag-behind part included in each of said radiation detection signals taken at the predetermined sampling time intervals is due to an impulse response formed of a single exponential function or a plurality of exponential functions with different attenuation time constants; andinitial value determining means for determining initial values for the recursive computation based on lag signal values remaining at a starting point of the recursive computation;wherein said time lag removing means is arranged to obtain corrected radiation detection signals by removing the lag-behind parts from the radiation detection signals through the recursive computation based on the initial values determined by the initial value determining means.

2. A radiographic apparatus as defined in claim 1, wherein said time lag removing means is arranged to perform the recursive computation for removing the lag-behind part from each of the radiation detection signals, based on the following equations A-C: Xk=Yk−Σn=1N[Snk]  ATn=−Δt/τn   BSnk=exp(Tn)·{αn·[1−exp(Tn)]·exp(Tn)·Sn(k—1)}  C

3. A radiographic apparatus as defined in claim 2, wherein each residual rate γn is set to satisfy conditions of the following equation E: Σn=1 N [γn]≦1, 0≦γn   E

4. A radiographic apparatus as defined in claim 3, wherein equation E is set to satisfy conditions of Σn=1 N [γn]=1   E′

5. A radiographic apparatus as defined in claim 3, wherein equation E is set to satisfy conditions of Σn=1 N [γn]<1   E″

6. A radiographic apparatus as defined in claim 1, wherein said radiation detecting means is a flat panel X-ray detector having numerous X-ray detecting elements arranged longitudinally and transversely on an X-ray detecting surface.

7. A radiographic apparatus as defined in claim 1, wherein said apparatus is a medical apparatus.

8. A radiographic apparatus as defined in claim 7, wherein said medical apparatus is a fluoroscopic apparatus.

9. A radiographic apparatus as defined in claim 7, wherein said medical apparatus is an X-ray CT apparatus.

10. A radiographic apparatus as defined in claim 1, wherein said apparatus is for industrial use.

11. A radiographic apparatus as defined in claim 10, wherein said apparatus for industrial use is a nondestructive inspecting apparatus.

12. A radiation detection signal processing method for taking, at predetermined sampling time intervals, radiation detection signals generated by irradiating an object under examination, and performing a signal processing to obtain radiographic images based on the radiation detection signals outputted at the predetermined sampling time intervals, said method comprising the steps of: removing lag-behind parts from the radiation detection signals by a recursive computation, on an assumption that a lag-behind part included in each of said radiation detection signals taken at the predetermined sampling time intervals is due to an impulse response formed of a single exponential function or a plurality of exponential functions with different attenuation time constants;determining initial values for the recursive computation based on lag signal values remaining at a starting point of the recursive computation, when performing the recursive computation; andobtaining corrected radiation detection signals by removing the lag-behind parts through the recursive computation based on the initial values.

13. A radiation detection signal processing method as defined in claim 12, wherein the recursive computation for removing the lag-behind part from each of the radiation detection signals is performed based on the following equations A-C: Xk=Yk−Σn=1N[Snk]  ATn=−Δt/τn   BSnk=exp(Tn)·{αn·[1−exp(Tn)]·exp(Tn)·Sn(k—1)}  C

14. A radiation detection signal processing method as defined in claim 13, wherein each residual rate γn is set to satisfy conditions of the following equation E: Σn=1 N [γn]≦1, 0≦γn   E

15. A radiation detection signal processing method as defined in claim 14, wherein equation E is set to satisfy conditions of Σn=1 N [γn]=1   E′

16. A radiation detection signal processing method as defined in claim 14, wherein equation E is set to satisfy conditions of Σn=1 N [γn]<1   E″

17. A radiation detection signal processing method as defined in claim 12, wherein the recursive computation for removing the lag-behind part from each of the radiation detection signals is performed based on the following equations A-C: Xk=Yk−Σn=1N[Snk]  ATn=−Δt/τn   BSnk=exp(Tn)·{αn·[1−exp(Tn)]·exp(Tn)·Sn(k—1)}  C

18. A radiation detection signal processing method as defined in claim 12, wherein the recursive computation for removing the lag-behind part from each of the radiation detection signals is performed based on the following equations a-c: Xk=Yk−Σn=1N{αn·[1−exp(Tn)]·exp(Tn)·Snk}  aTn=−Δt/τn   bSnk=Xk—1+exp(Tn)·Sn(k—1)   c

19. A radiation detection signal processing method as defined in claim 12, wherein the recursive computation for removing the lag-behind part from each of the radiation detection signals is performed based on the following equations a-c: Xk=Yk−Σn=1N{αn·[1−exp(Tn)]·exp(Tn)·Snk}  aTn=−Δt/τn   bSnk=Xk—1+exp(Tn)·Sn(k—1)   c