[Expansion of sensitivity area for magnetic resonance imaging of the hand using parallel-array coil].

It is difficult for Rheumatoid Arthritis (RA) patients to remain in a strenuous position for a long time during examinations. The field of view (FOV): 250 mm is needed for hand examinations from the wrist to the finger. Two channel phased array coils are effective to use when examinations of the 'off center' are taken for the upper and lower extremities. The area of the array coils' sensitivity can be expanded by shifting both coil elements 40-60% in the opposite direction of the element's diameter. This method is given credibility due to the increased signal-to-noise ratio (SNR) in the peripheral regions (shifted directions), but loses value in the central area, as indicated by the decrease in SNR. This was confirmed in the image of the hand using visual assessment including the fat suppression technique. It was verified that the sensitivity area was expanded using Scheffe's method of paired comparison (Ura's modified method). An application at the other regions of the body can be expected to be used in the case of using parallel positioned coils during clinical situation.

[Examination of measurement and its method of compensation of the sensitivity distribution using phased array coil for body scan].

The influence on the quality of images by measurement of a sensitivity distribution and the use of a sensitivity compensation filter was considered using an opposite-type phased array coil and volume-type phased array coil. With the opposite-type phased array coil, the relation between coil interval and filter was investigated for the IIC filter, SCIC filter (GE), and the Normalize filter (SIEMENS). The SCIC filter and Normalize filter showed distance dependability over the coil interval of SNR and uniformity was observed, and the existence of an optimal coil interval was suggested. Moreover, with the IIC filter, distance dependability over a coil interval was small, and the decrease in contrast with use was remarkable. On the other hand, with the volume-type phased array coil, the overlap of an array element was investigated to determine the influence it had on sensitivity distribution. Although the value stabilized in the arrangement center of an array element, and its near, was shown when volume-type phased array coil was used, SNR and uniformity decreased as it separated from the center. This showed that overlap of an array element does not have an adverse influence on image quality when the already optimized arrangement is used.

[Examination of sensitivity distribution characteristics depending on the position of the array coil].

The opposite-type array coil is useful because it is easy to attach in magnetic resonance imaging (MRI) examinations away from the center area. It is not well understood that sensitivity characteristics change when coil elements shift. We studied the effect when both coil elements (17×14 cm) shifted to the opposite side; we examined a hand including the wrist. The signal-to-noise ratio (SNR) of the axial image by the subtraction map declined 2.6%/cm. The profile of the sagittal and coronal view by the SNR map shows that the greater the distance between the center of the upper and lower coil elements, the lower the SNR is on the center of the examination area and the higher the SNR is on the edge of the examination area. In removing 10 cm from each of the coil elements, the profile became wide and linear. In the case of removing more than 7.5 cm, the wide area of uniformity was shown in the center of the images of sensitivity distribution. Uniformity by the segment method increased more than 10 cm. Use of the opposite-type array coil when shifting both coil elements to the opposite side may extend the examination area.