[Evaluation of Refocus Flip Angle for Three-dimensional Proton Density-weighted Turbo Spin-echo Imaging in Cerebrovascular Black Blood MRA and Comparison with Three-dimensional Time-of-flight MRA].

The three-dimensional time-of-flight (3D-TOF), which is currently the most common acquisition technique of intracranial magnetic resonance angiography (MRA), may result in poor branch visualization due to reduced blood flow velocity. Proton density-weighted volume isotropic turbo spin-echo acquisition (PDVISTA) is less susceptible to these factors and has been reported to be useful in assessing cerebral vasospasm after subarachnoid hemorrhage. In this study, we investigated the effect of refocus flip angle (RFA) for PDVISTA on the contrast between blood vessels and background brain tissue using flow velocity phantom and clinical images, assuming the usefulness of PDVISTA in daily clinical practice. The phantom experiments showed that the contrast ratio significantly improved with decreasing RFA; however, considering the signal-to-noise ratio, RFA 80° was determined as optimal for clinical use. Visual assessment was performed on PDVISTA (RFA 80°) and conventional 3D-TOF MRA clinical images, which suggested the superiority of PDVISTA over 3D-TOF in the delineation of peripheral branches of cerebral vessels. The results suggest that PDVISTA is useful not only for subarachnoid hemorrhage patients but also in daily clinical practice.

[Display Performance of X-ray Image Output from DICOM-embedded Printer to Paper-based Hard Copy Print: Comparison with X-ray Image on LCD].

PURPOSE: We have been using a paper-based hard copy print (paper print) system of X-ray images, in which digital imaging and communications in medicine (DICOM) data can be directly output on papers from medical imaging systems or from a picture archiving and communication system (PACS) server, and they are utilized as patient referral materials or for preoperative planning. The purpose of this study was to compare the display performance of X-ray images on the printed paper and that on the liquid crystal display (LCD). METHODS: We measured contrast response to verify consistency of image appearance on both display systems. The contrast resolution was assessed by a CDRAD phantom. The spatial resolution was assessed by an X-ray test chart. RESULTS: The contrast response of the paper printer was not concordant with the grayscale standard display function (GSDF). The difference between the measured contrast response and the ideal GSDF on the paper was large in the high-density area. The low-contrast resolution on the paper was inferior to that on the LCD. The spatial resolving power on the paper was superior to that on the LCD. CONCLUSION: The display performance of the paper printer for X-ray images was clarified. X-ray images printed on the paper should be used carefully taking account of their characteristics of display performance.

[Influence of Image Reconstruction Method on Image Quality in Digital Breast Tomosynthesis].

PURPOSE: Digital breast tomosynthesis (DBT) imaging uses two types of image reconstruction. methods, i.e., filtered back projection (FBP) method and an iterative reconstruction (IR) method. Although the effect of the difference in the image reconstruction method on the image quality has been reported, these studies were performed using different apparatus or conditions. In this study, we examined the effect of image reconstruction on the image quality using the same equipment under the same conditions. METHOD: We measured reflection artifact, sharpness, signal detection ability, and granularity using DBT-photographed images by both the FBP and the IR methods. RESULT: Although the difference between the two methods was subtle for granularity, IR was found to be superior to FBP in all items tested. CONCLUSION: This study suggested the clinical usefulness of IR over FBP.

[Construction and usefulness of the dose management system using DICOM radiation dose structured report (Dose SR) in angiography].

The International Commission on Radiological Protection recommends diagnostic reference levels (DRL) in each radiological examination for justification and optimization of patients' dose in medicine. The aim of our study was to propose the dose management system by utilizing dose information in diagnostic X-ray radiation dose structured report (Dose SR) in The Digital Imaging and Communications in Medicine to optimize radiation dose in institutions. Our dose management system is able to organize dose information obtained from various angiography systems and CTs. It is possible to provide this information to operators for justification and optimization of patient dose. Our system would be useful for the estimation of organ dose and could be used for the determination of local DRL (LDRL) for each radiological practice. In addition, the optimization became possible to compare LDRL with national DRL.

[Optimization of histogram analysis for pediatric digital chest radiography using flat panel detector system].

Optical density of the lung area in pediatric digital chest radiography using an indirect flat panel detector (FPD) system were changed enormously by the influence of such factors as the size of lung area, gas of retroperitoneum, and so on. Our purpose in this study was to improve the stability of lung density on output images by means of optimizing histogram analysis. Chest images of a lung phantom were taken at various X-ray tube voltages and processed using a half-type region of interest (ROI) for the lung area. The shape of the histogram obtained by two different calculation methods including frequency distribution and cumulative relative frequency were compared, and digital chest images of 110 clinical cases in our hospital were classified into three age-groups (under 6 years old, over 6 years old and under 13 years old, and over 13 years old) and their histograms were analyzed. In conclusion, it was important that to analyze the histograms of age-groups, a cumulative relative frequency histogram should be used because the influence of X-ray tube voltage was lower than the frequency distribution histogram, and stabilized lung density under 6 years old could be obtained if the value of the imaging parameter for lung density from default was 90% to 85% or 80% because the distribution of lung area and its center value were significantly lower than in those over 13 years old.