SCATTER RADIATION CORRECTION IN RADIOGRAPHY AND COMPUTED TOMOGRAPHY EMPLOYING FLAT PANEL DETECTOR

• US 20080080663A1
• Filed: 09/28/2007
• Published: 04/03/2008
• Est. Priority Date: 09/29/2006
• Status: Active Grant

• Current Assignee: Siemens Healthineers AG (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Ruehrnschopf, Ernst-Peter, Haerer, Wolfgang
• Granted Patent: US 7,860,208 B2
• Time in Patent Office: Days
• US Class Current: 378/7
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: G06T 2207/10081 Computed x-ray tomography [CT]
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 2207/30004 Biomedical image processing
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening

Abstract

In a method for correction of scatter radiation errors in radiography and computer tomography, using flat panel detectors, initially an estimation of a scatter radiation distribution S_cor(y,z) is undertaken, and a standard correction term δp_cor is subsequently calculated. Noise filtering of the standard correction term δp_cor with F(δp_cor) is implemented and subsequently the noise-filtered standard correction term F(δp_cor) is added to the logarithmized measured total projection data p_s. The noise filtering can be implemented adaptively dependent on a previously-determined local noise variance. The method can be implemented in a radiography system and/or by a computer for generation and/or processing of projective and/or tomographic exposures, with a memory containing program codes causing the computer in operation to execute the steps of the method.

Claims

1. A method for correction of scatter radiation errors in radiography and computed tomography using flat panel detectors, comprising the steps of:

estimating a scatter radiation distribution S_cor(y,z);

automatically electronically calculating a standard correction term δ

p_cor;

automatically electronically noise filtering the standard correction term δ

p_cor with F(δ

p_cor); and

automatically electronically adding the noise-filtered standard correction term F(δ

p_cor) to the logarithmized measured total projection data p_s.

2. A method according to claim 1 comprising calculating the standard correction term δ

p_cor with the equation;

δ

p_cor=−

ln(1−

S_cor/P_s),

wherein P_s is the normalized total intensity distribution including scatter radiation.

3. A method according to claim 1 comprising calculating the standard correction term δ

p_cor with the equation;

δ

p_cor=p_cor−

p_s,

wherein p_cor=−

ln(P_s−

ln(1−

S_cor/P_s), p_s is to the logarithmized total projection data, and P_s is the normalized total intensity distribution including scatter radiation.

4. A method according to claim 1 comprising estimating the scatter radiation distribution S_cor(y,z) by measurement thereof.

5. A method according to claim 1 comprising the estimating the scatter radiation distribution S_cor(y,z) by calculation thereof.

6. A method for correction of scatter radiation errors in radiography and computed tomography using flat panel detectors comprising the steps of:

estimating a scatter radiation distribution S_cor(y,z);

automatically electronically calculating a standard correction term δ

p_cor;

automatically electronically determining a local noise variance;

automatically electronically adaptively determining a local noise filter mask size;

automatically electronically adaptively noise filtering the standard correction term δ

p_cor with Φ

(δ

p_cor); and

automatically electronically adding the noise-filtered correction term Φ

(δ

p_cor) to the logarithmized measured total projection data p_s.

7. A method according to claim 6 comprising implementing the adaptive noise filtering dependent on a previously determined local noise variance.

8. A method for correction of scatter radiation errors in radiography and computed tomography using flat panel detectors, comprising the steps of:

estimating a scatter radiation distribution S_cor(y,z);

automatically electronically calculating a standard correction term δ

p_cor;

automatically electronically determining a local noise variance;

automatically electronically determining a local noise growth term;

when said growth term reaches a predetermines size automatically electronically implementing an adaptive noise correction by adaptively determining a local noise filter mask size, adaptively noise filtering the standard correction term δ

p_cor with Φ

(δ

p_cor), and adding the noise-filtered standard correction term Φ

(δ

p_cor) to the logarithmized, measured total projection data p_s; and

automatically electronically implementing a non-adaptive noise correction when the noise growth term has not reached said predetermined size, by adding a noise filtering the standard correction term δ

p_cor with F(δ

p_cor), and adding the noise-filtered standard correction term F(δ

p_cor) to the logarithmized, measured total projection data p_s.

9. A method according to claim 8 comprising calculating the noise growth term with the equation

(S/P)*σ

(p_s)*√

{square root over (I₀)},

wherein S is the normalized scatter radiation distribution, P is the normalized primary radiation distribution, σ

(p_s) is the interference ratio due to scatter radiation and I₀ is the unattenuated intensity distribution without a subject in the beam path of radiation in which said flat panel is disposed.

10. A method according to claim 8 comprising calculating the noise growth term with the equation

11. A method for correction of scatter radiation errors in radiography and computed tomography using flat panel detectors, comprising the steps of:

estimating a scatter radiation distribution S_cor(y,z);

automatically electronically calculating a standard correction term δ

p_cor;

automatically electronically segmenting an uncorrected projection image p_s(x,y);

automatically electronically determining a local noise variance;

automatically electronically implementing a segment-dependent determination of a local noise filter mask size;

automatically electronically implementing segment-dependent noise filtering of the standard correction term δ

p_cor with Φ

(δ

p_cor); and

automatically electronically adding the noise-filtered correction term Φ

(δ

p_cor) to the logarithmized, measured total projection data p_s.

12. A method according to claim 11 comprising implementing segment-dependent noise filtering at least partially as an adaptive noise variance-dependent noise filtering.

13. A radiography system comprising:

an x-ray imaging system comprising an x-ray source that emits a radiation beam onto a flat panel radiation detector, to acquire tomographic data from a subject in a scan having a scatter radiation distribution F_cor(y),(z) associated therewith; and

an imaging computer that generates an image from the tomographic data and automatically corrects scatter radiation errors by estimating said scatter radiation distribution S_cor(y,z), automatically calculating a standard correction term δ

p_cor;

automatically noise filtering the standard correction term δ

p_cor with F(δ

p_cor), and automatically adding the noise-filtered standard correction term F(δ

p_cor) to the logarithmized measured total projection data p_s.

14. A radiographic system according to claim 13 wherein said imaging computer calculates the standard correction term δ

p_cor using the equation;

δ

p_cor=−

ln(1−

S_cor/P_s),

wherein P_s is the normalized total intensity distribution including scatter radiation.

15. A radiographic system according to claim 13 wherein said imaging computer calculates the standard correction term δ

p_cor using the equation;

δ

p_cor=p_cor−

p_s,

wherein p_cor=−

ln(P_s−

ln(1−

S_cor/P_s), p_s is to the logarithmized total projection data, and P_s is the normalized total intensity distribution including scatter radiation.

16. A radiographic system according to claim 13 wherein said imaging computer estimates the scatter radiation distribution S_cor(y,z) based on a measurement thereof.

17. A radiographic system according to claim 13 wherein said imaging computer estimates the scatter radiation distribution S_cor(y,z) by calculation thereof.