Examination the most suitable requirements of CT scan. No. 3 head CT

The head is relatively small compared with the other parts of human body, but the brain is essentially covered with the cranial bone. On the head CT scan, particularly the region between pons and cerebellum, is the part showing the virtual volume effect due to the cranial bone, the sharp artifact due to the difference of X-ray absorption, and also sharply deteriorated images due to the pixel noise. We examined the minimum power and the window width (ww) for diagnostic accuracy of CT images. We determined the minimum standard possible to obtain images with high quality in the routine observation of the head CT scan using TOSHIBA X-vision/GX (the gas detection type). In the routine observation, we found it sufficient to adjust the power to 130 kV/150 mA for all area of the head. But in the pons region, which shows sharp artifacts, ww should be adjust to 150. In the hypothalamus, the noise-SD shows low as well as 5, and so it is good to adjust ww to 110. We recommend that in should be determined to find out a meeting point between the possible lowest power and the quality of images, not to follow after the excess high quality of images in the routine observation. (K.H.)