Nobukazu Tanaka

Investigation of optimum anti-scatter grid selection for digital radiography: physical imaging properties and detectability of low-contrast signals

Our aim in this study was to evaluate the effect of the grid variations on the imaging performance for a computed radiographic system under identical exposure condition. Digital radiographies using a 20-cm Lucite phantom were performed without grid and with grid ratios of 5:1, 8:1, 10:1, 12:1, and 14:1. The scatter fraction, the incident dose to the image receptor, the Wiener spectrum (WS), and the noise-equivalent quanta (NEQ) were measured. Visibility of low-contrast signals was evaluated using a contrast-detail phantom. The scatter fractions decreased considerably with an increase in the grid ratio. On the other hand, the WSs were increased (the noise property deteriorated) as the grid ratio increased due to a decreased incident dose to the image receptor under the identical exposure condition. The NEQs were improved as the grid ratio increased. The high grid ratios provided higher low-contrast detectability compared to the low grid ratios. Our results indicated that the removal of scattered radiation was very effective in improvement of the NEQ in the digital system under the identical exposure condition.

Detectability of simulated pulmonary nodules on chest radiographs: Comparison between irradiation side sampling indirect flat-panel detector and computed radiography

OBJECTIVE To compare the detectability of simulated pulmonary nodules on chest radiographs between an irradiation side sampling indirect flat-panel detector (ISS-FPD) and computed radiography (CR). MATERIALS AND METHODS This study was an observer performance study. Simulated pulmonary nodules of 8 mm in diameter were superimposed on an anthropomorphic chest phantom. Chest radiographs were acquired under 2 exposure levels (4 and 3.2 mAs) with the ISS-FPD and the CR. Six thoracic radiologists evaluated all 40 images (10 patterns × 2 different exposure doses × 2 different systems) for the presence or absence of a lesion over each of 12 defined areas on a 3-megapixel monochrome liquid-crystal display. Receiver operating characteristic (ROC) curves were obtained for observation in predefined 480 areas. A jackknife method was used for statistical analysis. Differences with a P value of <0.05 were considered significant. RESULTS The analysis of the observer detection of simulated pulmonary nodules showed larger areas under the ROC curve (AUC) by the ISS-FPD than by the CR. There was a statistically significant difference between the two systems at 3.2 mAs (P=0.0330). CONCLUSION The ISS-FPD was superior to the CR for the detection of simulated pulmonary nodules at 3.2 mAs.

Effect of readout direction in the edge profile on the modulation transfer function of computed radiographic systems by use of the edge method.

We investigated the effect of the readout direction of the edge profile obtained by the edge method on the presampled modulation transfer function (MTF) in various computed radiographic (CR) systems. There were no differences in the MTFs derived from two edge profiles in the sub-scanning direction of four CR systems used in this study. On the other hand, the MTFs measured at a readout direction from the low (edge) to the high (direct exposure) exposure region were higher than those measured at a readout direction from the high to the low exposure region in the laser-beam scanning direction for three of the four CR systems. Although this phenomenon depends on the CR system, it is important to understand and indicate both MTFs at the two edge profiles in the laser-beam scanning direction for accurate assessment of the resolution property.

Detectability of simulated interstitial pneumonia on chest radiographs: comparison between irradiation side sampling indirect flat-panel detector and computed radiography.

OBJECTIVE To compare the detectability of simulated interstitial pneumonia on chest radiographs between an irradiation side sampling indirect flat-panel detector (ISS-FPD) and computed radiography (CR). METHODS Simulated interstitial pneumonia findings (ground-glass opacity, reticular opacity and honeycomb lung) were superimposed on an anthropomorphic chest phantom. Chest radiographs were acquired under three exposure levels (4.0, 3.2 and 2.0 mAs) with an ISS-FPD and with CR. 5 thoracic radiologists evaluated 72 images for the presence or absence of a lesion over each of 6 areas. A total of 1296 observations were analysed in a receiver-operating characteristic analysis. A jackknife method was used for the statistical analysis. RESULTS The areas under the curves (AUCs) for the detection of simulated honeycomb lung obtained with the ISS-FPD were significantly larger than those obtained with CR at all exposure conditions. For the detection of simulated ground-glass opacity and reticular opacity, there were no significant differences between the two systems. In addition, the AUCs for the detectability of simulated honeycomb lung obtained with the ISS-FPD at all exposure levels were significantly larger than those obtained with CR at 4 mAs. CONCLUSION The ISS-FPD was superior to CR for the detection of simulated honeycomb lung. Provided that the chosen model is representative of interstitial pneumonia, the use of an ISS-FPD might reduce a patients exposure dose during the detection of interstitial pneumonia. ADVANCES IN KNOWLEDGE The ISS-FPD has shown its advantage compared with CR in the detection of honeycombing, one sign of interstitial pneumonia.

Imaging Properties of Digital Magnification Mammography

Imaging properties of magnification mammography with a computed radiography (CR) system were measured to investigate the potential utility under the conditions of a matched average glandular dose (AGD). The AGD in each magnification mammography was matched to that of conventional contact mammography with 4 cm breast thickness. A dedicated mammographic unit with nominal focal spot sizes of 0.1 mm and 0.3 mm, molybdenum anode and 0.03 mm molybdenum filter, was used in this study. The magnification factor varied from 1.2 to 1.8, including contact radiography. The basic physical imaging parameters were evaluated by measuring scatter fraction, modulation transfer function (MTF) including geometric unsharpness of focal spot and presampled MTF of detector, and noise power spectrum (NPS) for the various magnification factors. In the no grid technique, the scatter fraction of the magnification radiography decreases considerably with increasing magnification factor, and was comparable to magnification radiography in the grid technique. The MTF of magnification mammography improved with an increasing magnification factor. The resolution properties of the digital magnification mammography depend upon focal spot size, pixel size, and magnification factor. The noise level for the digital magnification radiography was significantly increased. This result was caused by the reduced entrance exposure to the phantom, and thus reduced incident radiation to the detector.

Dose reduction in general radiography for adult patients by use of a dual-side-reading photostimulable phosphor plate in a computed radiography system

Abstract Our purpose in this study was to evaluate the potential of dose reduction in general radiography for adult patients by use of a dual-side-reading (DSR) photostimulable phosphor plate in a computed radiography system. The image quality and low-contrast detectability in terms of the contrast-detail diagram of the DSR system with use of the X-ray beam quality of the RQA 5 defined by the International Electrotechnical Commission 61267 were compared with those of a conventional single-side-reading (SSR) system. The radiographic noise of the DSR system was lower compared to that of the SSR system under the same exposure conditions. Although there were no statistical differences in low-contrast detectabilities between the SSR system and the DSR system under the same exposure levels, the DSR system showed superior detectability compared to the SSR system. We conclude that the DSR system for general radiography has the potential to reduce the patient dose.

SU‐E‐I‐188: Potential for Dose Reduction in An Indirect Flat Panel Detector System Employing Irradiation Side Sampling

Purpose: To investigate possibility of dose reduction for a newly developed indirect flat panel detector(FPD)system employing irradiation side sampling (ISS), physical imaging properties were measured and compared with those of a conventional computed radiography(CR)system. Method and Materials:The FPDsystem employing ISS (CALNEO MT, Fuji Film) and the CRsystem (FCR PROFECT CS, Fuji Film) including the imaging plate (ST‐VI, Fuji Film) were used in this study. The Wiener spectrum (WS), the presampled modulation transfer function(MTF), and the detective quantum efficiency (DQE) for both systems were measured. To evaluate image quality of the detector for chest radiography, the RQA 9 in the International Electrotechnical Commission (IEC) 62220‐1 was used. Results: The WS of the FPDsystem showed considerably lower than that of the CRsystem at every spatial frequency. The WS of the FPDsystem with a 50 % dose reduction of the CRsystem was almost identical to that of the CRsystem. The presampled MTF of the FPDsystem was comparable to that of the CRsystem. The DQE of the FPDsystem obtained at zero spatial frequency was almost twice than that of the CRsystem. Conclusion: The radiographic noise property and the detection efficiency of the new ISS FPD were significantly superior to those of the conventional CRsystem. It is expected that the use of the new ISS FPDsystem for chest radiography can reduce the patient skin dose by 50 % compared with the conventional CRsystem.

SU‐GG‐I‐155: Physical Imaging Properties and Detectability of Simulated Microcalcifications of Digital Magnification Mammography with Matched Incident Exposure

Purpose: To improve the image resolution over that obtainable with contact radiography, digital magnification mammographies under the same incident exposure conditions with contact mammography were performed. Method and Materials: Magnification radiographies of 1.2 – 1.8 times in addition to contact radiography were performed with the same incident exposure in combination with focal spot sizes of 0.1 mm and 0.3 mm, with and without grid techniques. A computed radiography system (FCR PROFECT CS, Fuji Film), including the imaging plate (HR‐BD, 50 μm pixel pitch, Fuji Film), was used in this study. Basic imagingproperties, namely; scatter fractions, total modulation transfer functions (MTFs) at object plane and the noise power spectra (NPSs) were measured. Visibilities of contrast‐detail mammography (CDMAM) phantom and simulated microcalcification images were evaluated by using a contrast‐detail curve and a free‐response receiver operating characteristic (FROC) analysis, respectively. Results: Scatter fractions decreased considerably as the magnification factor increased for the no‐grid technique. In the grid technique, scatter fractions for all magnification techniques were comparable. The total MTFs at object plane improved significantly for magnification technique with a combination of 0.1 mm focal spot size compared with conventional contact technique. However, the total MTFs with a combination of 0.3 mm focal spot size slightly improved or were comparable. The NPSs degraded with an increase of the magnification factor compared with contact radiography due to the maintained incident dose to object. Observer performance tests indicated that the magnification techniques using the 0.1 mm focal spot size provided higher detectability than the contact technique. Conclusion: It is expected that the use of digital magnification mammography under the same incident exposure conditions with contact mammography improved the detectability of microcalcifications.