Purpose: X-ray film or computed radiography (CR) system has been employed in clinical setting, and these devices are gradually replaced by portable flat-panel detector (FPD) systems. They may be employed to measure the beam width instead of the traditional CR system. In this study, we estimated the accuracy of beam width measured by the portable FPD system. Method: A CR cassette and FPD were placed at the isocenter, and the pixel values were measured in a single axial CT scanning at a tube potential of 80 kVp, tube currents of 10–40 mA (5 mA steps), and tube rotation time of 0.5 s. Then, the FPD was sandwiched between 0.5 mm copper plate and 2 mm lead plate to avoid the pixel saturation and artifact from the FPD electronic substrates. The beam widths were measured at selected nominal beam widths (40, 80, 120 and 160 mm) using a double exposure technique (tube currents of 10 and 20 mA). Result: Log-linear relationships for two systems were obtained between the pixel value and radiation exposure for parameters less than or equal to 12.5 mAs. A test for the equivalence with confidence intervals showed that the measurement accuracy of the CR and FPD systems was equivalent. Conclusion: The portable FPD system could be utilized for the measurement of the CT beam width as well as CR system.
Purpose: A virtual monochromatic image (VMI) is acquired from two different types of polychromatic energy X-rays, not a monochromatic X-ray. The effective energy of monochromatic X-ray does not vary in passing through the patient’s body. On the other hand, beam hardening effects are seen in images because of the change of polychromatic X-ray energy. The purpose of the present study was to evaluate the beam hardening improvement effect of VMI using a phantom with a bone mimicking ring. Method: We used a water equivalent electron density phantom with a hole in the center for inserting various measurement materials (i.e. fat, two types of bone with differing densities, contrast medium, blood, and water). Then, the CT numbers of each measurement materials were obtained from single energy CT (SECT) images and VMIs, respectively. Also, an additional bone-mimetic ring was used to obtain the CT numbers for evaluation of beam hardening effect. The CT number change rates were calculated from the obtained CT numbers with and without beam hardening effect. Result: The rate of CT number, change of VMI was significantly lower than that of SECT for all measured materials. Conclusion: In this study, VMI minimized changes in CT numbers due to the beam hardening effect and showed a higher beam hardening reduction effect.
The aims of this study were to elucidate signal pattern of cerebral aneurysm clip in brain magnetic resonance angiography (MRA) using non-contrast enhanced ultra-short echo time (UTE) sequence and to explore effective utilization of this novel technique for patients, who underwent cerebral aneurysm clipping. The clip was embedded in homemade phantom and scanned using UTE sequence. We investigated characteristic features of the artifacts derived from the clip. Besides, we compared the volume of signal loss between conventional time-of-flight (TOF) and UTE-MRA in 50 patients with the cerebral aneurysm clip. In phantom study, the clip was delineated as signal void area fully surrounded by high signal on original images. On reconstructed short-axial views for the clip, four-leaf clover pattern of artifact was observed when clip was arranged orthogonal to the static magnetic field. On the other hand, this artifact disappeared when the clip was arranged in parallel with the static magnetic field. The volume of signal loss in clinical cases was significantly reduced in UTE-MRA (P < 0.05): 1.30, 0.52–2.77 cm3 for TOF; 0.84, 0.28–1.74 cm3 for UTE (median, range). The scan time for UTE-MRA was 2 minutes and 52 seconds. To understand the characteristic feature of the artifacts from the clip could contribute to define vascular structure in image interpretation. Adding UTE-MRA to routine protocol is useful approach for follow-up imaging after cerebral aneurysm clipping with clinically acceptable prolongation of the scan time.
Purpose: In this study, we evaluated the stability and reliability of absorbed dose-to-water for an HDR 192Ir sandwich setup phantom method by comparing measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol. Methods: The sandwich setup phantom was designed with a dedicated device for two ion chamber measurements of absorbed dose-to-water for a mHDR-v2r 192Ir brachytherapy source is presented. To test the reliability of sandwich setup phantom of measurements with absorbed dose-to-water, we were compared with values based on AAPM TG-43 protocol and evaluated temporal variations of the measurement, intra-rater reliability. Results: The measured doses at sandwich setup phantom agreed within 1.0% with AAPM TG-43 protocol. In all measurement fractions, the temporal variations of measurement value were less than 1.0%, and the intra-rater reliability were 0.94% or more. Conclusions: The measurement value obtained by the absorbed dose-towater had good reliability, and sandwich setup phantom is potentially useful and convenient for daily dose management of 192Ir sources in clinics.
Specific binding ratio (SBR) is mainly used as a quantitative index of dopamine transporter scintigraphy, although it was reported that standardized uptake value (SUV) is useful for clinical diagnosis in recent years. The aim of this study is to evaluate whether xSPECT is useful for SUV in dopamine transporter scintigraphy. xSPECT is a recently developed, high-resolution image reconstruction technique that transforms single photon emission computed tomography (SPECT) to a computed tomography (CT) coordinate system. Furthermore, low-penetration high-resolution (LPHR), which there has been no previous physical evaluation report was also evaluated. The radioactive concentration of the image with xSPECT is automatically calculated by the periodic sensitivity calibration and one volume sensitivity calibration. In the case of images with conventional reconstruction methods as filtered back projection (FBP) and ordered subset expectation maximization (OSEM), the calibration factor related to the photon count and radioactive concentration was calculated from measuring a cylinder phantom filled with Iodine-123. Radioactive concentrations of the SUV factor were measured by SPECT data acquisition with the striatal phantom in various conditions. Radioactive concentrations with conventional reconstruction methods had a lower value (for example, with FBP it was 7.53 kBq/ml, with OSEM it was 7.22 kBq/ml) compared to the actual measurement value, although that with xSPECT (12.45 kBq/ml) got close to the actual measurement value (14.68 kBq/ml). LPHR showed an approximation to low-energy high-resolution (LEHR) in terms of spatial resolution and scatter fraction estimated from energy windows. The quantitative accuracy of radioactive concentration was the highest under xSPECT.
The purpose of this study is to compare the detectability of diseases the new image processing and the conventional image processing by receiver operating characteristic (ROC) analysis and to show the usefulness of the new image processing. Radiographs with and without nodular cancer models in the chest phantom were used for observation samples. Totally 200 radiographs were evaluated by 10 radiological technologists (each readers had over 20 years or under 4 years of experience). The mean area under the curve (AUC) calculated from the over 20 years group was 0.754 for the new processing and 0.771 for the conventional processing (p value=0.651, 95% confidence interval=−0.084/0.049 (lower bound/upper bound)). On the other hand, the average AUC calculated from under 4 years group was 0.819 for the new processing and 0.678 for the conventional processing (p value= 0.041, 95% confidence interval=0.019/0.262 (lower bound/upper bound)). New image processing provides high detectability in less than 4 years group compared to conventional processing.
Japanese Diagnostic Reference Levels (DRLs) were released as “Japan DRLs 2015” from Japan Network for Research and Information on Medical Exposure (J-RIME) in June 2015. In “Japan DRLs 2015”, DRLs in angiography and interventional procedures are set at a fluoroscopic dose rate of 20 mGy/min at the interventional reference point using a phantom. In order to achieve optimization with DRLs, then it need to be revised regularly. Therefore, we (research group to examine the effect of Japan DRLs 2015 and the necessity of additional items in angiography and vascular interventions) examined the effects of “Japan DRLs 2015” on angiography and interventional procedures. And we also investigated for DRLs revision in the future. As a result, it turned out that it is important to create DRLs in medical procedures that can be effectively used in clinical settings.