武藤 晃一

We improve the waveform of the Radiofrequency (RF) pulse for the purpose of reducing the Specific Absorption Rate (SAR) of MRI equipments. Two RF waveforms are examined: the standard ±2π sinc function muldplied by a double exponendal function (sincDE), and the sincDE multiplied by a correctional function (sincDEF). We simulate the RF excitations of magnetization resulting from our RF pulses by solving the Bloch equation numerically, and evaluate the slice characteristics and the phase diagram of the magnetization. The results for our RF pulses are comparable to those for the standard ±2π sinc function. The areas (integrations with respect to time) of sincDE and sincDEF are 65.8% and 87.0% that of the standard ±2π sinc function, respectively. Both rectangle ratios of the frequency characteristics of sincDE and sincDEF are 115.5% that of the standard ±2π sinc function, which can be considered to be comparable to that of the standard ±2π sinc function. It is thought that the reductions of the areas of RF pulses decrease SAR.

Abnormal interventricular septal wall motion has been observed in various heart diseases. To assess the regional contractility of interventricular septum precisely, DANTE tagging cine MRI of septal slices parallel to the vertical long axis of left ventricle were acquired in 6normal volunteers and in 12 patients with a variety of heart diseases. DANTE tags were generated at end diastole with a 8 mm grid with about 60 intersection points on septal slice. Quadrangle area as a basic unit was calculated at end systole (S_ES) and end diastole (S_ES). Percent area contraction (PAC) was derived from the following formula: PAC= [(S_ES-S_ES)/S_ED]×100%. In addition, a quantitative map of the PAC was made to estimate regional contractility easily by visual inspection. The PAC was 29.4±1.3% in normal volunteers and the map of the PAC showed a homogeneous pattern. In patient with anteroseptal myocardial infarction reduced PAC units were localized at anterior site of interventricular septum, and in patients with inferior myocardial infarction, decreased PAC units were observed in inferoposterior site of interventricular septum. In a patient with dilated cardiomyopathy, the map demonstrated a diffused focal distribution of decreased PAC units. In conclusion, the PAC derived from DANTE-tagging cine MRI is a very useful index to evaluate regional contractility of interventricular septum, and the map of PAC can reflect regional abnormal contractility in accordance with clinical settings.

In this study, we investigated quantitative evaluation of aortic calcification employing thoracic images scanned by helical CT.<BR>To measure a volume of aortic calcification in a series of thoracic images, we developed a software on Apple Macintosh personal computer that extract calcification semiautomatically. The measurement process of calcification in this program consists of the following steps: (1)manual designation of an approximate center point in the aorta area on the first image, (2)semiautomatical extraction of aortic ROI by successive radial edge detection, (3) measurement of the sum of calcification pixels in the ROI and of the sum of scored calcification values that was weighted by the factors alloted to the CT numbers of the calcification pixels, and (4)calculation of the total sum of the number of the calcification pixels and the total sum of scored calcification values by applying(1)-(3) repeatedly to whole slice images of a patient.<BR>We proccessed 10 series of thoracic helical CT images containing aortic calcification at an interval of 2 years.<BR>In consequence, our evaluation method could quantitate the temporal change of amounts of aortic calcification.

To accurately evaluate regional septal wall motion using the mechanical strain analyzing method on the interventricular septal section, DANTE-tagging cine MRI was performed in 4 normal volunteers,3 patients with anteroseptal myocardial infarction and 1 patient with dilated cardiomyopathy. Although the %shortening and %strain curves showed complex patterns, the megn %contraction (changes of ROI area) was 72.7±2.8%, and the %contraction curve of any ROI was smooth in normal subjects. In patients with heart diseases, the %contraction was generally lower than that of normal volunteers, and expansion was shown in some patients. The patterns of %shortening and %strain curves were also complicated.&lt;BR&gt;In conclusion, the DANTE-tagging method is useful for accurate evaluation of regional wall motion in detail.

We set up a server and client system with CTN server (Mallinkrodt Institute of Radiology) and personal computer (PC) client to evaluate medical image database from practical point of view. We prepared 189 CT images of a single study. The images had been stored in ACR-NEMA Ver.2 format. We transformed the image data to DICOM3 format using a batch program. The maximum number of images in a series was limited to a hundred in CTN software. On the PC client, the images were displayed in an unexpected order. The reason of the problem was that the DIC-OM3 has not a query and retrieve service for an acquisition number. It is necessary to set up a supplemental data-base system to retrieve proper images from the image server.

近年、密結合型マルチプロセッサワークステーションにより並列処理を行い、高速に画像生成することが盛んに行われている。また、一方で多数の高性能ワークステーションがネットワークを介して接続されている環境は一般化しつつある。このような、疎結合環境においても分散処理により、高速に画像が生成されることを示した。通常、分散処理を行うには、あらかじめ決られた大きさの部分処理を適当な方法で分散するが、使用するホストの台数や処理能力、負荷状況により、最も効率的な部分処理の大きさ(粒度)は変化する。そこで、本研究では、複数台のワークステーションで頭部画像を生成する場合を例にとり、計算に参加するホストの台数に対する、最も効率の良い粒度を実験的に求めた。