熊本大学学術リポジトリ Kumamoto University Repositor Title CT 検査における被ばく線量最適化のための低線量 CT 画像 シミュレーション技術の開発 Author(s) 竹永, 智美 Citation Issue date 2016-03-25 Type URL Thesis or Dissertation http://hdl.handle.net/2298/34662 Right
[ ] computed tomography (CT) CT CT CT ( CT ) CT CT CT [ ] CT CT filtered backprojection (FBP) CT CT CT FBP CT modulation transfer function (MTF) MTF American college of radiology disk edge-spread function (ESF) logistic curve-fitting i
ESF ESF disk MTF [ / ] MTF CT MTF MTF CT MTF noise power spectrum standard deviation [ ] CT CT CT ii
... i... iii... v... vi 1... 1.1... 1.2... 2 CT... 2.1... 2.2 NPS... 2.3 MTF... 3 CT MTF... 3.1... 3.2... 3.2.1... 3.2.2 MTF... 3.2.2.1 Disk... 3.2.2.2 logistic curve-fitting ESF... 3.2.2.3 Double logistic curve-fitting ESF... 3.2.3 MTF... 3.2.4... 3.3... 3.4... 3.5... 4 CT... 4.1... 4.2... 4.2.1 CT... iii
4.2.2... 4.2.3... 4.2.4... 5 CT... 5.1... 5.2... 5.2.1... 5.2.2... 5.3... 5.4... 5.5... 6 CT... 6.1... 6.2... 6.2.1... 6.2.2... 6.3... 6.4... 6.5... 7......... iv
CT CT v
ACR American college of radiology CT computed tomography DFOV display field of view ESF edge spread function FBP filtered back projection FFT fast Fourier transform HU Hounsfield unit LSF line spread function MTF modulation transfer function NEQ noise equivalent quanta NPS noise power spectrum QA ROI SD quality assurance region of interest standard deviation vi
1 1 1.1 2007 The New England Journal of Medicine Brenner Computed Tomography - An Increasing Source of Radiation Exposure [1] computed tomography (CT) Brenner 1980 300 CT 2006 6200 CT 1.5-2.0% CT Pearce CT 10 [2] Mathews CT CT 24 CT [3] 2011 3 11 CT 20 ( ) 20 9 1 200 2015 4 20 2013 CT 10 CT CT CT
1 X CT CT CT CT CAD [4] [5] [6] CT CT CT CT
1 [7-12] [7-9] CT CT CT CT CT CT CT CT standard deviation (SD) noise power spectrum (NPS) modulation transfer function (MTF) MTF 2 quality assurance (QA) MTF MTF American college of radiology (ACR) [13] MTF edge spread function (ESF) [14] ESF MTF [15]
1 CT ESF MTF
1 1.2 7 1 2 CT NPS MTF 3 MTF logistic curve fitting MTF 4 5 6 7
2 CT 2 CT 2.1 CT CT NPS 2 2.2 3 MTF MTF 2 2.3
2 CT 2.2 NPS CT CT CT X [16] Computed radiography flat panel detector X NPS CT NPS Radial Frequency [17, 18] [19, 20] 2 [21] 3 2 X NPS Radial Frequency 2 NPS X Y NPS NPS 3 [22] 3 Radial Frequency Radial Frequency Fig. 2.1 NPS region of interest (ROI) (Fig. 2.1a) ROI cupping CT 2 ROI (Fig. 2.1c) Fig. 2.1b Fig. 2.1c CT 2 fast Fourier transform (FFT) (Fig. 2.1d) NPS NPS NPS, ROI ROI 2 ACR 3 NPS
2 CT ROI 128 128 16 ROI ROI X +64 pixel +128 pixel NPS Fig. 2.2 NPS NPS ROI Fig. 2.1 Summary of the radial frequency method for measurement NPS. (a) ROI for NPS measurement, (b) 3D surface plot of ROI, (c) 3D surface plot of ROI after subtraction of 2D fitting image, (d) the power spectrum of (c).
2 CT 1000 +0 +64 +128 100 NPS [mm 2 ] 10 1 0.0 0.2 0.4 0.6 0.8 1.0 Spatial frequency [cycles/mm] Fig. 2.2 Comparison of NPSs obtained from different distance from the isocenter.
2 CT 2.3 MTF CT MTF MTF CT MTF MTF MTF MTF 2 FFT 2 FFT Fig. 2.3 Z CT MTF Fig. 2.3a-c ROI 0 ( ) (Fig. 2.3d) 2 FFT (Fig. 2.3e)0 MTF MTF MTF MTF MTF MTF MTF, ROI ROI 2 0 MTF MTF MTF CT MTF
2 CT, 1 (2.3) 0.15-0.2 mm [23] MTF CT MTF MTF Fig. 2.3 Summary of the wire method for measurement MTF. (a) ROI for MTF measurement, (b) 3D surface plot of ROI, (c) 3D surface plot of ROI after subtraction of 2D fitting image, (d) 3D surface plot of ROI after zeroing, (e) the power spectrum of (d).
3 CT MTF 3 CT MTF 3.1 MTF CT [24-27]QA [13] MTF CT [28] MTF MTF [29, 30] ACR MTF [15, 29, 30] MTF ACR ESF line spread function (LSF) ESF [27 31] Richard ACR disk MTF [29] ESF CT ESF ESF MTF Wilson 4 disk MTF [30] ESF Savitzky Golay smoothing filter [32] ESF [33] MTF Friedman ACR 3 disk MTF [15] axial z MTF MTF MTF MTF
3 CT MTF CT MTF ACR disk MTF logistic curve-fitting disk disk disk
3 CT MTF 3.2 3.2.1 ACR [13] (model 464 Gammex-RMI Middleton WI) 64 CT (Brilliance Philips Healthcare Cleveland OH) Table 3.1 Axial (type C) filtered back projection (FBP) MTF display field of view (DFOV) 120 kv 250mm 3 3.2.3 MTF Fig 3.1 ACR 1 3 1 Fig 3.1a 3 3 MTF 25 mm 3 (bone) CT 955 120-95 Hounsfield unit (HU) solid water CT 0 HU 3 Fig 3.1b CT 0 HU solid water 200 mm disk MTF 1 disk MTF Table 3.1 Acquisition parameters used for the MTF measurement Parameter Value scan type axial tube voltage [kv] 120 tube current [ma] 100, 200, 300 slice thickness [mm] 0.625, 1.25, 2.5, 5.0 pixel size [mm 2 ] 0.488 0.488 time per rotation [sec] 1.0
3 CT MTF (a) (b) Fig. 3.1 Axial slice images of the ACR phantom; (a) the first module containing three different solid inserts with a diameter of 25 mm and one air cavity (lower right), and (b) the third module containing uniform solid water with a diameter of 200 mm. 3.2.2 MTF disk MTF 3.2.2.1 Disk ACR 1 3 disk ROI disk [34] ROI disk Disk CT disk ROI CT disk CT 3.2.2.2 logistic curve-fitting ESF oversampled ESF ROI disk
3 CT MTF (Fig. 3.2) Fig. 3.3 1 10 (rebinning) ESF logistic ESF Logistic 4 [35] disk Fig. 3.3 fitted ESF rebinned ESF Logistic curve-fitting rebinned ESF fitted ESF LSF fitted ESF LSF LSF FFT MTF MTF MTF z cm
3 CT MTF 1.2 1.0 normalized CT value 0.8 0.6 0.4 0.2 0.0-0.2 0 5 10 15 20 25 Distance from the center of the disk [mm] Fig. 3.2 The oversampled ESF with normalized pixel values. 1.2 normalized CT value 1.0 0.8 0.6 0.4 0.2 rebinned ESF fitted ESF 0.0-0.2 0 5 10 15 20 25 Distance from the center of the disk [mm] Fig. 3.3 The logistic curve-fitting for the rebinned ESF with one-tenth pixel size.
3 CT MTF 3.2.2.3 Double logistic curve-fitting ESF FBP ESF ESF (3.2) logistic 3 3.2.2.2 logistic double logistic curve-fitting 3.2.3 MTF CT disk MTF ACR 1 bone disk 1 3 disk MTF CT X disk MTF disk CT MTF Disk 2 disk disk
3 CT MTF [36] Disk disk bone disk MTF 1 25 mm bone disk 200 mm solid-water MTF disk 3.2.4 MTF - (3.5) disk - MTF ACR disk bone disk ESF double logistic curve-fitting [37 38]
3 CT MTF 3.3 logistic curve-fitting MTF curve-fitting MTF Fig. 3.4 disk 100 ma 0.625 mm ACR 1 bone Logistic curvefitting ESF 16 ESF Fig. 3.4 logistic curve-fitting MTF logistic curve-fitting MTF MTF Fig. 3.5a b Fig. 3.5a 0.625 mm 100 200 300 ma CT MTF 100 200 300 ma SD 29.0 20.6 16.9 HU Fig. 3.5b 100 ma 0.625 1.25 2.5 5.0 mm MTF 0.625 1.25 2.5 5.0 mm SD 29.0 21.7 15.7 11.3 HU Fig. 3.5a b MTF CT 955 120-95 HU bone disk MTF Fig. 3.6 100 ma 0.625 mm MTF 50% ( ) bone 0.385 0.004 0.366 0.030 0.372 0.044 cycles/mm ( SD) bone 4.9% Disk bone disk disk MTF 100 ma 0.625 mm CT ACR Fig. 3.7 disk MTF CT [39] 1 25 mm bone 3 200 mm solidwater disk MTF Fig. 3.8 100 ma 0.625 mm disk disk MTF disk
3 CT MTF MTF disk MTF Fig. 3.9 bone disk 100 ma 0.625 mm - disk - 30 mm double logistic curve-fitting ( (3.3) ) MTF 1.2 1.0 0.8 with curve-fitting without curve-fitting MTF 0.6 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] Fig. 3.4 Comparison of MTFs obtained from the circular edge method with and without the logistic curve-fitting technique.
3 CT MTF 1.2 1.0 (a) MTF 0.8 0.6 100mA 200mA 300mA 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] 1.2 1.0 (b) 0.625 mm MTF 0.8 0.6 1.25 mm 2.5 mm 5.0 mm 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] Fig. 3.5 Comparison of MTFs measured by changing acquisition parameters; (a) tube currents, and (b) slice thickness.
3 CT MTF 1.2 1.0 Bone Acrylic 0.8 Polyethylene MTF 0.6 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] Fig. 3.6 Comparison of MTFs measured from different disk images of bone, acrylic, and polyethylene inserts. 1.2 1.0 0.8 0 mm 31 mm MTF 0.6 62 mm 100 mm 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] Fig. 3.7 Comparison of MTFs measured for various distances from the isocenter to the disk center.
3 CT MTF 1.2 1.0 0.8 diameter of 25 mm diameter of 200 mm MTF 0.6 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] Fig. 3.8 Comparison of MTFs obtained from disk images with two different diameters, 25 and 200 mm. 1.2 1.0 0.8 Wire method Circular edge method with Eq. (3.3) MTF 0.6 0.4 0.2 0.0 0.0 0.5 1.0 1.5 spatial frequency [cycles/mm] Fig. 3.9 Comparison of MTFs obtained by the wire method and circular edge method with Eq. (3.3).
3 CT MTF 3.4 CT MTF MTF LSF ESF logistic curve-fitting MTF Fig. 3.4 logistic curve-fitting MTF (3.2) (3.3) ROI ESF ESF logistic curve-fitting CT Fig. 3.5 MTF LSF ESF logistic curve-fitting CT MTF Fig. 3.6 MTF disk MTF MTF disk disk ESF MTF MTF CT disk MTF Disk -disk disk disk (3.5) CT [39] MTF Fig. 3.7 disk disk MTF disk MTF (Fig. 3.8) disk disk disk MTF
3 CT MTF disk disk MTF disk MTF (3.3) MTF double logistic curve-fitting double logistic curve-fitting MTF (3.2) (3.3) logistic FBP ESF CT MTF logistic curve-fitting
3 CT MTF 3.5 CT MTF logistic curve-fitting MTF CT CT MTF disk MTF MTF CT MTF
4 CT 4 CT 4.1 CT CT X 250-350 [40 41]CT CT [7-12] CT CT CT CT FBP CT FBP CT CT [7-9] CT [10-12] 2 CT CT [7-9] CT CT CT CT 2 CT CT
4 CT CT Britten CT [10] CT Li CT (GE Noise Addition Tool, GE Healthcare, Waukesha, WI, USA) [11] CT GE CT Kim CT [12]CT CT noise equivalent quanta (NEQ) CT NEQ Kim CT Kim CT CT
4 CT 4.2 4.2.1 CT Fig. 4.1 CT ( 4 4.2.3) ( 4 4.2.4) CT CT CT CT CT Fig. 4.1 Summary of the simulation scheme 4.2.2 [39]
4 CT ( ) X X ( ) (4.1) (4.2) CT X X 4.2.3 (4.3) CT CT (4.3) Ram-Lak FBP Ram-Lak Ram-Lak FBP SD CT
4 CT CT ROI SD (4.3) SD CT (4.4) SD (4.3) CT X X 4.2.4 FBP NPS CT NPS CT NPS Ram-Lak NPS NPS CT 128 128 ROI 2 FFT [17]
5 CT 5 CT 5.1 CT CT 5.2 5.2.1 CT ACR (model 464, Gammex-RMI, Middleton, WI, USA) Catphan (CTP486, The Phantom Laboratory, Salem, NY, USA) TOS (Toshiba Medical Systems Corporation, Otawara, Japan) 64 CT (Brilliance; Philips Healthcare, Cleveland, OH, USA) Table 5.1 (type C) FBP axial DFOV 120 kv 350 mm Fig. 5.1 3 Table 5.1 Acquisition parameters used for low-dose CT image simulation Parameter Value scan type axial tube voltage [kv] 120 tube current [ma] 100, 200, 300 slice thickness [mm] 0.625, 1.250, 2.500, 5.000 pixel size [mm 2 ] 0.684 0.684 time per rotation [sec] 1.0
5 CT (a) (b) (c) Fig. 5.1 CT images of the phantoms used in this study: (a) The third module of the ACR phantom, (b) CTP 486 image uniformity module of the Catphan phantom, and (c) TOS phantom. The background material is water-equivalent. 5.2.2 CT 200 300 ma 100 200 ma ACR Catphan TOS CT MTF NPS MTF CT MTF ACR 25 mm TOS 40 mm Catphan
5 CT 200 mm disk NPS 128 128 ROI 2 FFT 0.625 mm
5 CT 5.3 (4.3) 300 mas 100 mas ACR CT 0.00032 mas CT Ram-Lak NPS Fig. 5.2 0.6 Enhancement Factor 0.4 0.2 estimated reconstruction filter Ram-Lak Filter 0.0 0.0 0.2 0.4 0.6 Spatial Frequency [cycles/mm] Fig. 5.2 The estimated reconstruction filter used for the low-dose simulation in this study. ACR Catphan TOS 100 mas CT 300 mas Fig. 5.3 128 128 ROI CT SD Table 5.2 CT SD
5 CT (a) Fig. 4.4 (b) (c) (d) (e) (f) Fig. 5.3 Demonstration of low-dose simulation for Catphan and TOS phantoms: (a), (b) real high-dose CT images (300 mas), (c), (d) real low-dose CT images (100 mas), (e), (f) simulated low-dose images (100 mas).
5 CT Table 5.2 Comparison of noise in terms of standard deviation for Catphan and TOS phantoms. High-dose and low-dose correspond to 300 mas and 100 mas, respectively. The noise model and the reconstruction filter were determined from an ACR phantom. Phantom High-dose image (HU) Low-dose image (HU) Simulated low-dose image (HU) Catphan 15.1 ± 0.2 26.7 ± 0.3 27.5 ± 0.2 TOS 50.7 ± 0.5 89.5 ± 0.7 89.8 ± 0.6 Fig. 5.4 CT CT MTF Fig. 5.4a 5.4b Catphan TOS MTF CT 300 mas 100 mas 200 mas 200 mas 100 mas 3 MTF TOS MTF MTF MTF Catphan TOS CT CT Fig. 5.5a 5.5b Catphan TOS NPS MTF CT 200 mas 300 mas CT 100 mas NPS 100 mas NPS Catphan TOS CT Fig. 5.6a, 5.6b 300 mas 100mAs
5 CT 1.0 real 100 mas CT image real 200 mas CT image (a) real 300 mas CT image simulated 100 mas from 200 mas simulated 100 mas from 300 mas simulated 200 mas from 300 mas MTF 0.5 0.0 0.0 0.5 1.0 1.5 Spatial frequency [cycles/mm] 1.0 real 100 mas CT image real 200 mas CT image (b) real 300 mas CT image simulated 100 mas from 200 mas simulated 100 mas from 300 mas simulated 200 mas from 300 mas MTF 0.5 0.0 0.0 0.5 1.0 1.5 Spatial frequency [cycles/mm] Fig. 5.4 Comparison of MTFs measured from real CT images and simulated images. (a) Catphan phantom, and (b) TOS phantom.
5 CT 1000 (a) 100 NPS [mm 2 ] real 100 mas CT image 10 real 200 mas CT image real 300 mas CT image simulated 100 mas from 200 mas simulated 100 mas from 300 mas simulated 200 mas from 300 mas 1 0.0 0.2 0.4 0.6 Spatial frequency [cycles/mm] 10000 (b) 1000 NPS [mm 2 ] 100 real 100 mas CT image real 200 mas CT image 10 real 300 mas CT image simulated 100 mas from 200 mas simulated 100 mas from 300 mas simulated 200 mas from 300 mas 1 0.0 0.2 0.4 0.6 Spatial frequency [cycles/mm] Fig. 5.5 Comparison of NPSs measured from real CT images and simulated images. (a) Catphan phantom, and (b) TOS phantom.
5 CT 3.5E-04 parameter c [mas] 3.0E-04 2.5E-04 2.0E-04 1.5E-04 1.0E-04 (a) ACR Catphan TOS 5.0E-05 0.0E+00 0.00 1.25 2.50 3.75 5.00 Slice Thickness [mm] 3.5E-04 parameter c [mas] 3.0E-04 2.5E-04 2.0E-04 1.5E-04 1.0E-04 (b) simulated 100 mas from 200 mas simulated 100 mas from 300 mas simulated 200 mas from 300 mas 5.0E-05 0.0E+00 0.00 1.25 2.50 3.75 5.00 Slice Thickness [mm] Fig. 5.6 Relationship between slice thickness and parameter c of the noise model. (a) Effect of reference phantoms. (b) Effect of exposure doses when an ACR phantom was used as a reference phantom.
5 CT Fig. 5.7 ACR 300 mas 100 mas Fig. 5.7a ACR 0.625 mm Fig. 5.7b 300 mas 100 mas 0.625 mm Fig. 5.7c 0.6 (a) Enhancement Factor 0.4 0.2 0.625 mm 1.250 mm 2.500 mm 5.000 mm RL Filter 0.0 0.0 0.2 0.4 0.6 Spatial Frequency [cycles/mm]
5 CT 0.6 (b) Enhancement Factor 0.4 0.2 200 mas 100 mas 300 mas 100 mas 300 mas 200 mas RL Filter 0.0 0.0 0.2 0.4 0.6 Spatial Frequency [cycles/mm] 0.6 (c) Enhancement Factor 0.4 0.2 ACR Catphan TOS RL Filter 0.0 0.0 0.2 0.4 0.6 Spatial Frequency [cycles/mm] Fig. 5.7 Effects of various factors on the reconstruction filter. (a) Effect of slice thickness for low-dose simulation of 100 mas from 300 mas with the reference ACR phantom. (b) Effect of exposure doses with slice thickness of 0.625 mm and the reference ACR phantom. (c) Effect of reference phantoms for low-dose simulation of 100 mas from 300 mas with the slice thickness of 0.625 mm.
5 CT 5.4 CT Fig. 5.3 SD (Table 5.2) NPS (Fig. 5.5) Fig. 5.4 MTF MTF TOS MTF TOS ACR Fig. 5.6 Fig. 5.7 CT CT CT (4.3) 2 35 cm CT SD 5 [9] 500 mas (50-450 mas) Frush 25 cm SD 2% [7] 120 mas () CT 40-100 mas () CT SD Catphan 3% TOS 1%
5 CT Table 5.1 CT
5 CT 5.5 CT CT CT MTF NPS 2 CT
6 CT 6 CT 6.1 4 CT 5 2 MTF NPS MTF NPS Žabić 88 mas CT 11 mas CT 11 mas CT [9] [7, 8] CT
6 CT 6.2 6.2.1 CT CT CT (50 mas) CT 5 CT 64 CT (Brilliance Philips Healthcare Cleveland OH) (type C) FBP DFOV 120 kv 5.0 mm 250 mm ACR 51-151 2 50 mas 105-339 mas CT 50 mas 2 CT 6 415 6.2.2 5 50 mas 50 mas Fig. 6.1 ROI SD
6 CT Fig. 6.1 ROIs for SD measurement. They are within LV, fat, liver, spleen, and aorta.
6 CT 6.3 Fig. 6.2 CT 1 (50 mas) (322 mas) SD Table 6.1 SD Table 6.1 Error of standard deviation within each ROI. ROI location CASE 1 CASE 2 CASE 3 CASE 4 CASE 5 average LV 0.2% 6.0% 4.7% 8.4% 7.8% 5.4% Fat 13.3% 8.6% 6.9% 15.9% 3.8% 9.7% Liver 9.2% 3.1% 2.2% 1.4% 2.7% 3.7% Spleen 2.9% 4.4% 1.4% 9.2% 1.5% 3.9% Aorta 8.3% -4.2% 1.0% 3.4% 2.0% 3.8%
6 CT Fig. 6.2 Demonstration of low-dose simulation for a clinical CT image: (a) Real high-dose CT image (322 mas), (b) real low-dose CT image (50 mas), (c) simulated low-dose image (50 mas).
6 CT 6.4 Fig. 6.2 CT CT 5 1 SD
6 CT 6.5 CT CT
7 7 CT CT MTF MTF CT ESF logistic curve-fitting CT MTF NPS CT
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