[Effect of Reducing Fluoroscopy Pulse Rates on Visibility of Devices and Radiation Dose in Percutaneous Coronary Intervention].

The goal of our study was to clarify the effect of low pulse rate fluoroscopy applying in percutaneous coronary intervention (PCI) on devices' visibility and radiation dose. Four types of fluoroscopy conditions combined with two pulse rates (7.5 and 15 pulses/s) and two types of adaptive temporal filters (ATFs) (weak and strong) were used. Samples for visibility evaluation were acquired with moving phantom and devices such as stent, balloon, and guidewire. Trailing artifacts and the visibility of stent were evaluated by Scheffe's method of paired comparisons. Incident air kerma (Ka,r) and kerma area product (PKA) in the clinic were obtained under two fluoroscopic pulse rate conditions (7.5 and 15 pulses/s). As a result, in 7.5 pulses/s fluoroscopy, trailing artifacts were decreased by using weak ATF with the median value of PKA and Ka,r reduced by about 50%, but stent visibility was decreased compared to 15 pulses/s. Therefore, a combination of 7.5 pulses/s fluoroscopy and suitable ATF can bring dose reduction with avoiding trailing artifacts, but dose per pulse should be adjusted to maintain the stent visibility.

[Evaluation of time resolution in cardiac synchronized image reconstruction using multi-slice CT].

One of the newest CT application technologies is cardiac synchronized image reconstruction. In this technology, evaluation of time-resolution is very important. We developed a method of measuring time-resolution in cardiac synchronized reconstruction, and evaluated various scanning protocols. In our experiment, ECG-gated scanning was done by multi-slice CT (Aquilion16 Super Heart Edition, Toshiba Medical Systems Co., Ltd., Japan). The nominal slice thickness was 0.5 mm, and rotation time was 0.5 sec. Input heart rate was set at 40, 45, 50, 55, 60, 70, 75, 80, and 90 bpm, and helical pitch at 3.2, 4.0, and 4.8 (beam-pitch: 0.200, 0.250 and 0.300). We measured FWTM of the obtained sensitivity distribution and compared at each scanning protocol. Time resolution improved as helical pitch decreased and heart rate increased. However, phase-time resolution deteriorated as heart rate increased. The results of our experiment indicated that a segment center was determined by X-ray tube rotation time and heart rate, and the number of segments was determined by heart rate, helical pitch, and reconstruction position. Time resolution changed with X-ray tube rotation time, heart rate, helical pitch, and reconstruction position. In this report, we provide a reference for an optimal scanning protocol in cardiac synchronized image reconstruction.

[Report on the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America--balance between the time sensitivity profile and the slice sensitivity profile in multi-slice helical scanning].

PURPOSE: With multi-slice helical scanning, increasing helical pitch causes changes in the effective slice sensitivity profile and thus in a thickening of the effective slice thickness. However, the increase in helical pitch alters the time sensitivity profile, thereby decreasing the effective scan time. In this paper we report the results of our research concerning the setting of optimum conditions to resolve this issue. METHOD AND MATERIALS: The experiment was conducted with a moving phantom. The movement showed a variety of changes. RESULTS: When the subject was not in motion, increases in helical pitch resulted in deterioration in the image quality of the CT image. However, when the subject was in motion increases in helical pitch improved image quality. CONCLUSION: The general belief until now has been that helical pitch should be decreased in order to improve CT image quality. However, in the case of a moving subject, reduced helical pitch leads to deterioration in the time resolution and thus to a deterioration in the image quality. Through this study we have acquired an understanding of which helical pitch value is optimal in terms of the subject's rate of movement.