[Multi-facility Survey on Accuracy and Calibration Method for Dose Area Product Meter of Angiography Systems].

In many facilities, the displayed dose of dose-area product (DAP) is used for the dose management of interventional radiology. In this study, we investigated the measured dose at the patient entrance reference point (interventional reference point) and the displayed dose on each angiography systems. Also, we investigated the calibration method of each DAP. The errors of the measured dose and the displayed dose were less than 35%, but that dispersion was wide between the systems. The calibration methods varies according to a system. And even in the same manufacturer, the calibration methods were different. Therefore, to use the displayed dose of DAP for patient dose management, we need to compare that with the measured dose regularly. The differences of calibration methods induce the wide dispersion of the errors of the measured and the displayed dose. So the standardization of the calibration method in each manufacturer is expected.

[Measurement of Head and Neck Exposure in CT Guided IVR].

In April 2011, the International Radiological Protection Committee recommended that "The equivalent dose of the crystalline lens should not exceed 20 mSv/year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv". Based on this recommendation, it is predicted that the equivalent dose limit of our crystalline lens can be lowered in the near future. Therefore, it is important to grasp the current situation of radiation exposure. The purpose of this study is to measure the crystalline lens of surgeons by focusing on the CT-fluoroscopy guided interventional radiology's (IVRs). We also examined whether the exposure dose of the crystalline lens can be correctly evaluated by measuring the unequal exposure dose of the neck, which is usually used for the unequal exposure measurement. Results of the analysis of 200 CT-fluoroscopy guided IVR procedures showed that the unequal exposure dose of the neck was significantly correlated with the exposure dose of the crystalline lens which was measured near the left eye ball (R=0.83). However, the exposure dose of the crystalline was 33% lower than those of the neck. Therefore, although the individual dosimeter worn on the neck can be used as the useful index of the exposure dose of the crystalline lens, the results can be overestimated.

[Construction of a System That Links Treatment RIS Terminals and Smartphones to Facilitate Radiation Therapy Operations].

Confirmation of patient information is required to ensure the safety of radiation therapy. The purpose of this study was to construct a system that facilitates radiation therapy operations by linking a radiation therapy information system to a smartphone. By linking a smartphone to a radiation therapy operation support system, without using a PC terminal, we were able to input information about the patient's position and fixation into images taken with a smartphone. In addition, patient information could be directly linked into the radiation therapy information system. In addition, patient information could be verified in the irradiation room by synchronizing the smartphone with the radiation therapy support system. The questionnaire was highly evaluated in terms of radio reception, usability, visibility and barcode reading. In this study, by linking a smartphone to a radiotherapy information system, it was possible to construct a system that facilitates radiotherapy operations by checking and registering patient information at hand.

[The protocol of dose reduction in liver perfusion computed tomography].

Cerebral perfusion computed tomography (CT) has been widespread, but abdominal perfusion CT has not been very popular because there has been a problem with regard to the limit of irradiation range and respiratory effects. Recently, it became easy to perform perfusion of abdominal organs because the use of multi detector row CT (MDCT) has been extensive. Along with it, the number of hospitals that perform liver perfusion CT has increased. However, patient dose of the liver perfusion CT is very high, making it very important to reduce patient dose. We created the virtual data that reduced the number of irradiation by partly reducing the data obtained on the liver perfusion CT. We compared the analysis results of all data with that of the partly reduced. It is possible to reduce the patient dose by reducing the number of irradiation because there was no significant difference in the analysis results.

[Influence of different movement systems on image quality: comparison of the sliding gantry CT system and the sliding table CT system].

The combination of angiography and CT angiography (CTA) is increasingly being used for the diagnosis and treatment of hepatic cancer. Recently, a CT system with sliding gantry was developed to optimize patient safety and to shorten transfer time between the angiography and CTA tables. As the CT gantry itself undergoes considerable movement in sliding over the patient table, it was considered necessary to evaluate this system regarding the precision of movement and any possible effect on image quality. Therefore, in this preliminary study, we compared image quality between the sliding gantry CT (SGCT) system and the sliding table CT (STCT) system. Comparative analysis revealed that there was no significant difference in image noise, low contrast resolution, modulation transfer function (MTF) , or precision in gantry or table movement. It was also noted that although the effective slice thickness for the SGCT system was 1-4% thinner than the STCT system it had no influence on image quality. It was thus concluded that the sliding movement of the gantry does not influence the quality of images obtained with this CT system.

Changes in liver perfusion and function before and after percutaneous occlusion of spontaneous portosystemic shunt.

PURPOSE: To evaluate changes in liver perfusion after occlusion of spontaneous portosystemic shunt and to analyze mechanisms of liver profile improvement. MATERIALS AND METHODS: Liver function changes and portal venous and hepatic arterial blood flow were evaluated using perfusion CT before and after shunt occlusion in 23 patients who underwent percutaneous occlusion of spontaneous portosystemic shunt because of gastric varices (n = 15) or hepatic encephalopathy (n = 8). RESULTS: Portal venous blood flow was significantly higher at 1 week (278.7 ml/min, 92.7-636.7, p = 0.012), 1 month (290.0 ml/min, 110.1-560.1, p < 0.001) and 3 months (299.6 ml/min, 156.7-618.5, p = 0.033) after shunt occlusion than the baseline (220.9 ml/min, 49.5-566.7). Hepatic arterial liver blood flow became lower than the baseline (132.3 ml/min, 47.9-622.3) after shunt occlusion, but a significant decrease was observed only at 1 month later (107.9 ml/min, 45.8-263.6 p = 0.027). Serum albumin concentration became significantly higher than the baseline (3.4 mg/dl, 1.9-4.5) at 1 month (3.8 mg/dl, 2.3-4.3, p = 0.018) and 3 months (3.9 mg/dl, 2.6-4.3, p = 0.024) after shunt occlusion. CONCLUSION: Shunt occlusion increases portal venous blood flow and decreases hepatic arterial blood flow, thereby improving the liver profile.

[Study of spatial resolution in three-dimensional rotational angiography].

In interventional radiology (IVR) of cerebral aneurysms, it is important to understand the form and physical relationships between the cerebral aneurysm and the surrounding vessels. However, because the vessels in the head area are highly complex, it can be difficult to comprehend the structure using conventional angiography. Therefore, three-dimensional rotational angiography (3D-RA) has been used in recent years. This article discusses studies of the spatial resolution of 3D-RA. We reconstructed 3D-RA of an acrylic slit phantom (slit widths: 0.5, 0.75, 1.0, 1.5 mm) and examined spatial resolution by visual evaluation and profile curves. When the slit phantom was arranged to avoid the effect of beam hardening, the spatial resolution of 3D-RA was found to be as high as 0.75 mm. When the slit phantom was placed orthogonal to the rotational axis of the C-arm, the spatial resolution of 3D-RA was decreased because of the cone angle effect of X-rays. However, it was considered within the allowable range for clinical study. Consequently, 3D-RA is valuable in IVR.

[Evaluation of gantry tilt correction in multi detector-row CT: effect on multi-planar reconstruction images].

In multi-slice CT, the scanning center of each line multiple-row detector array is shifted in the Y-axis direction by the tilting of the gantry. Correction of this effect is necessary when CT images are reconstructed. Correction of table feed is necessary as well. These corrections are possible with the Somatom Plus4 Volume Zoom. The use of multi-planar reconstruction (MPR) images has been increasing rapidly in the area of clinical diagnosis. Therefore, we examined the influence of MPR images according to gantry tilt. For each gantry tilt, the spatial resolution of MPR images was almost the same even though scanning pitch was changed. When the gantry was tilted, the full width at half maximum (FWHM) of the section sensitivity profile (SSP) was about 10% to 20% wider than that when the gantry was not tilted. The spatial resolution of MPR images is more affected by whether or not the gantry is tilted than by the angle of tilt. Gantry tilt correction is useful to obtain images without artifact for metal and artificial teeth; however, deterioration in spiral resolution cannot be avoided.