Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part I: Studies on Image Quality Using Dual Source CT

다국어 초록 (Multilingual Abstract)

Objective: To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT.
Materials and Methods: Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung.
Results: Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP.
Conclusion: IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.

다국어 초록 (Multilingual Abstract)

Objective: To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT.
Materials and Methods: Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung.
Results: Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP.
Conclusion: IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.

참고문헌 (Reference)

1 AAPM, "the Measurement, Reporting, and Management of Radiation Dose in CT" American Association of Physicists in Medicine 2008

2 Mulkens TH, "Use of an automatic exposure control mechanism for dose optimization in multi-detector row CT examinations: clinical evaluation" 237 : 213-223, 2005

3 Kalra MK, "Techniques and applications of automatic tube current modulation for CT" 233 : 649-657, 2004

4 Lasio GM, "Statistical reconstruction for x-ray computed tomography using energy-integrating detectors" 52 : 2247-2266, 2007

5 Prasad SR, "Standard-dose and 50%-reduced-dose chest CT: comparing the effect on image quality" 179 : 461-465, 2002

6 Mayo JR, "Reduced radiation dose helical chest CT: effect on reader evaluation of structures and lung findings" 232 : 749-756, 2004

7 Ravenel JG, "Radiation exposure and image quality in chest CT examinations" 177 : 279-284, 2001

8 Prakash P, "Radiation dose reduction with chest computed tomography using adaptive statistical iterative reconstruction technique: initial experience" 34 : 40-45, 2010

9 Rothenberg LN, "Radiation dose in CT" 12 : 1225-1243, 1992

10 황혜전, "Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part II: Assessment of Radiologists’ Preferences Using Dual Source CT" 대한영상의학회 13 (13): 720-727, 2012

11 Takahashi M, "Low-dose spiral computed tomography of the thorax: comparison with the standard-dose technique" 33 : 68-73, 1998

12 Dinkel HP, "Low-dose multislice CT of the thorax in follow-up of malignant lymphoma and extrapulmonary primary tumors" 13 : 1241-1249, 2003

13 Yamada T, "Low-dose CT of the thorax in cancer follow-up" 51 : 169-174, 2004

14 Kyriakou Y, "Intensity distribution and impact of scatter for dual-source CT" 52 : 6969-6989, 2007

15 Wildberger JE, "Individually adapted examination protocols for reduction of radiation exposure in chest CT" 36 : 604-611, 2001

16 Lell MM, "High-pitch spiral computed tomography: effect on image quality and radiation dose in pediatric chest computed tomography" 46 : 116-123, 2011

17 Xu J, "Electronic noise modeling in statistical iterative reconstruction" 18 : 1228-1238, 2009

18 Schenzle JC, "Dual energy CT of the chest: how about the dose?" 45 : 347-353, 2010

19 Gregor J, "Computational analysis and improvement of SIRT" 27 : 918-924, 2008

20 Pontana F, "Chest computed tomography using iterative reconstruction vs filtered back projection (Part 2): image quality of low-dose CT examinations in 80 patients" 21 : 636-643, 2011

21 Pontana F, "Chest computed tomography using iterative reconstruction vs filtered back projection (Part 1): evaluation of image noise reduction in 32 patients" 21 : 627-635, 2011

22 Mayo JR, "CT of the chest: minimal tube current required for good image quality with the least radiation dose" 164 : 603-607, 1995

23 Yu L, "Automatic selection of tube potential for radiation dose reduction in CT: a general strategy" 37 : 234-243, 2010

24 McNitt-Gray MF, "AAPM/RSNA Physics Tutorial for Residents: topics in CT. Radiation dose in CT" 22 : 1541-1553, 2002