653 ノート Code No. 522 DR DQE 1 國友博史 4 服部真澄 2 小山修司 5 岡田陽子東出林 1 了 6 則夫 3 市川勝弘 7 澤田道人有限会社緒言 digital radiography: DR d

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1 653 ノート Code No. 522 DR DQE 1 國友博史 4 服部真澄 2 小山修司 5 岡田陽子東出林 1 了 6 則夫 3 市川勝弘 7 澤田道人有限会社緒言 digital radiography: DR detective quantum efficiency: DQE DQE DR q X signal-to-noise ratio: SNR 1, 2 SNR DQE DR X Investigation of Measurement Accuracy of Factors Used for Detective Quantum Efficiency Measurement in Digital Radiography Hiroshi Kunitomo, 1 Shuji Koyama, 2 Ryo Higashide, 1 Katsuhiro Ichikawa, 3 Masumi Hattori, 4 Yoko Okada, 5 Norio Hayashi, 6 and Michito Sawada 7 1 Department of Central Radiological Technology, Nagoya City University Hospital 2 Radiological Sciences, Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine 3 Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University 4 Department of Radiology, Tokai Memorial Hospital 5 Department of Radiological Technology, Anjo Kosei Hospital 6 School of Radiological Technology, Gunma Prefectural College of Health Sciences 7 Mutsuda Shoukai Corporation, Ltd. Received September 17, 2013; Revision accepted May 29, 2014 Code No. 522 Summary In the detective quantum efficiency (DQE) evaluation of detectors for digital radiography (DR) systems, physical image quality indices such as modulation transfer function (MTF) and normalized noise power spectrum (NNPS) need to be accurately measured to obtain highly accurate DQE evaluations. However, there is a risk of errors in these measurements. In this study, we focused on error factors that should be considered in measurements using clinical DR systems. We compared the incident photon numbers indicated in IEC with those estimated using a Monte Carlo simulation based on X-ray energy spectra measured employing four DR systems. For NNPS, influences of X-ray intensity non-uniformity, tube voltage and aluminum purity were investigated. The effects of geometric magnifications on MTF accuracy were also examined using a tungsten edge plate at distances of 50, 100 and 150 mm from the detector surface at a source-image receptor distance of 2000 mm. The photon numbers in IEC coincided with our estimates of values, with error rates below 2.5%. Tube voltage errors of approximately ±5 kv caused NNPS errors of within 1.0%. The X-ray intensity non-uniformity caused NNPS errors of up to 2.0% at the anode side. Aluminum purity did not affect the measurement accuracy. The maximum MTF reductions caused by geometric magnifications were 3.67% for 1.0-mm X-ray focus and 1.83% for 0.6-mm X-ray focus. Key words: detective quantum efficiency (DQE), measurement accuracy, incident photon numbers, normalized noise power spectrum (NNPS), modulation transfer function (MTF) *Proceeding author

2 International Electrotechnical Commission IEC 2003 IEC IEC DQE 3 5 IEC 6 DQE presampled modulation transfer function MTF normalized noise power spectrum NNPS DQE(u) Dobbins Siewerdsen X 7, 8 NNPS DR 9, IEC presampled MTF 13, 14 15, 16 presampled MTF X DQE(u) 1. 方法と使用機器 X IEC 1 μgy mm -2 μgy -1 X NNPS NNPS presampled MTF IEC IEC RQA5 4 X X X Philips OPTIMS50 SRO2550 Siemens AXION Luminos drf Luminos UD150B DK-85 UD150L DK-85 Radcal X5-6 Fig. 1 a X 2000 mm 99.5 IEC 7.1 mmal Fig. 1 a 73 kv X Fig. 1 b RAMTEC413 CdTe 0.1 mm 0.05 mm X CdTe 2000 mm 40 ma 20 μgy/s X X X electron gamma shower Ver.5 17 EGS5 Fig. 1 c X 2000 mm 1.0 cm X kev 0.03

3 655 Fig. 1 Setup for measurement and calculation of photon number. (a) Geometry for defined X-ray beam quality (RQA5; International Electrotechnical Commission), (b) Geometry for measurement of X-ray spectrum, (c) Geometry for Monte Carlo simulation K air=ψ (μ tr/ρ) air 1 K air Ψ(µ tr/ρ) air (µ tr/ρ) air (µ en/ρ) air 2 K air Ψ( E ) ( µ / ρ) en 2 air 3 K Ψ( E ) ( μ / ρ) air en air μgy 3, 5 IEC mm -2 μgy RQA5 X AXION Luminos drf RQA5 73 kv kv RAMTEC413 X mm 0.2 mm RQA5 IEC H A 1050 RAMTEC NNPS X NNPS X IEC

4 656 source-image receptor distance SID 1500 mm NNPS mm 3, 5 X SNR SNR 2 NNPS NNPS X X X UD150B DK-85 Konica Minolta flat panel detector FPD AeroDR0.175 mm SID 1500 mm RQA5 73 kv 40 μc/kg mm 64 N=64 X ±179 mm 64 region of interest ROI NNPS 22 mm 128 NNPS NNPS RQA5 RQA5 73 kv kv C/kg NNPS X 20 NNPS exposure NNPS exposure NNPS 12, 21 NNPS RQA5 73 kv exposure NNPS NNPS RQA mm exposure NNPS MTF X computed radiography CR X 22, 23 X Philips SRO mm 0.6 mm CR Konica Minolta Regius μm IEC 1 mm SID 2000 mm d mm line spread function LSFpresampled MTF X CR IEC RQA5 MTF α 4 d α = fs l d 4 fs l α d 0 mm f MTF p(f) 5 sin( αfπ) p( f ) = 5 αfπ 2. 結果 IEC 4 X Table 1 IEC

5 657 Table 1 Calculation data of photon number using EGS5 and error rate with photon numbers of mm -2 µgy -1 at RQA5 X-ray equipment Tube voltage (kv) Photon number (mm -2 μgy -1 ) Difference from IEC (%) Philips OPTIMS50/SRO2550 Siemens AXION Luminos drf Shimadzu UD150B/DK-85 Shimadzu UD150L/DK-85 Table 2 Calculation data of photon number: variation in tube voltage/purity of aluminum filter X-ray equipment Tube voltage Purity of Aluminum filter Photon number Difference from IEC (kv) (%) (mm -2 μgy -1 ) (%) Siemens AXION Luminos drf RQA5 73 kv Table 2 IEC 73 kv RQA5 73 kv Table NNPS X NNPS Fig. 2 NNPS 1.47 cycles/mm X Fig cycles/mm IEC SID 1500 mm mm Fig. 2 The error ratio of NNPS above 1.47 cycles/mm by the X-ray quantum number distribution to NNPS value at the center of the irradiated field exposure NNPS Fig. 3

6 658 Fig. 3 Error in NNPS from RQA5 due to variation in tube voltage. Fig. 4 Exposure NNPS due to difference in purity of aluminum filter. exposure NNPS -5 kv +6 kv ± exposure NNPS Fig NNPS MTF CR X 1.0 mm 1.49 mm 1.15 mm 0.6 mm mm mm MTF Fig. 5 MTF Fig. 6 MTF MTF MTF cycle/mm MTF Fig. 5 Result of presampled MTF from two focal spot sizes. 2.0 cycles/mm MTF Table mm 3 cycles/mm 考察 3-1 IEC RQA5

7 659 a b Fig. 6 Influence of presampled MTF on geometric magnification. (a) Large focal spot, (b) Small focal spot Table 3 Comparison of theoretical values and measured values in MTF reduction rate due to geometric magnification and blurring with effective focal spot size (a) Large focal spot Object-to-detector distance (mm) Spatial frequency Theoretical Measured Theoretical Measured Theoretical Measured (mm -1 ) value value value value value value (b) Small focal spot Object-to-detector distance (mm) Spatial frequency Theoretical Measured Theoretical Measured Theoretical Measured (cycles/mm) value value value value value value X IEC +2.5 Fig. 7 7 IEC RQA5 Table 2 IEC IEC

8 660 Fig. 7 X-ray energy spectra for two different beam collimation sizes. 3-2 NNPS IEC SID 1500 mm NNPS mm NNPS 2 IEC mm RQA5 NNPS ±1.0 exposure NNPS IEC DQE 3-3 MTF DR 5 10 cm SID 1500 mm 2000 mm SID cm 3.75 cm 7.50 cm cm 7.3 cm 1.0 cycle/mm cycles/mm 6.69 MTF 1.0 cycle/mm cycles/mm 2.81 MTF MTF X 2000 mm DQE MTF MTF 5 DQE 10 DQE DQE MTF 4. 結論 X DQE 4 X IEC FPD RQA5 ±5 kv NNPS 1 NNPS IEC X DQE MTF 23 DQE

9 661 参考文献 1 Dainty JD, Shaw R. Image Science. New York: Academic Press, Cunningham IA. 2, Applied linear-systems theory. Handbook of Medical Imaging Vol. 1. SPIE Press, Bellingham, 2000: International Electrotechnical Commission: Medical electrical equipment-characteristics of digital X-ray imaging devices part1: Determination of detective quantum efficiency, ed.1.0, International Electrotechnical Commission: Medical electrical equipment-characteristics of digital X-ray imaging devices Part 1-2: Determination of the detective quantum efficiency-detectors used in mammography, ed.1.0, International Electrotechnical Commission: Medical electrical equipment-characteristics of digital X-ray imaging devices Part 1-3: Determination of the detective quantum efficiency Detectors used in dynamic imaging, International Electrotechnical Commission: Medical diagnostic X-ray equipment-radiation conditions for use in the determination of characteristics, ed Dobbins JT, Ergun DL, Rutz L, et al. DQE(f) of four generations of computed radiography acquisition devices. Med Phys 1995; 22(10): Siewerdsen JH, Antonuk LE, el-mohri Y, et al. Signal, noise power spectrum, and detective quantum efficiency of indirect-detection flat-panel imagers for diagnostic radiology. Med Phys 1998; 25(5): Neitzel U, Günther-Kohfahl S, Borasi G, et al. Determination of the detective quantum efficiency of a digital x-ray detector: comparison of three evaluations using a common image data set. Med Phys 2004; 31(8): Samei E, Flynn MJ. An experimental comparison of detector performance for direct and indirect digital radiography systems. Med Phys 2003; 30(4): ; 66(7): Dobbins JT, Samei E, Ranger NT, et al. Intercomparison of methods for image quality characterization. II. Noise power spectrum. Med Phys 2006; 33(5): Morishita J, Doi K, Bollen R, et al. Comparison of two methods for accurate measurement of modulation transfer functions of screen-film systems. Med Phys 1995; 22(2): Samei E, Ranger NT, Dobbins JT 3rd, et al. Intercomparison of methods for image quality characterization. I. Modulation transfer function. Med Phys 2006; 33(5): presampled MTF 2008; 64(4): Buhr E, Günther-Kohfahl S, Neitzel U. Accuracy of a simple method for deriving the presampled modulation transfer function of a digital radiographic system from an edge image. Med Phys 2003; 30(9): Hirayama H, Namito Y, Bielajew AF, et al. The EGS5 CODE SYSTEM, SLAC Report number: SLAC-R Haba T, Kondo S, Hayashi D, et al. Accuracy validation of incident photon fluence on DQE for various measurement conditions and X-ray units. Radiol Phys Technol 2013; 6(2): H X Samei E, Flynn MJ. An experimental comparison of detector performance for direct and indirect digital radiography systems. Med Phys 2003; 30(4): Z4704 X X 2004; 60(8):

07_学術.indd

07_学術.indd Arts and Sciences computed radiography CRpresampled MTF Measurement of presampled MTFs with computed radiography (CR) by contrast method using smoothed square-wave. 1 16813 1, 2 1 1 1 2 Key words: contrast

653 ノート Code No. 522 DR DQE 1 國友博史 4 服部真澄 2 小山修司 5 岡田陽子 東出林 1 了 6 則夫 3 市川勝弘 7 澤田道人 有限会社 緒言 digital radiography: DR d

653 ノート Code No. 522 DR DQE 1 國友博史 4 服部真澄 2 小山修司 5 岡田陽子東出林 1 了 6 則夫 3 市川勝弘 7 澤田道人有限会社緒言 digital radiography: DR d