Contrast resolution in multidetector-row CT with 16 detector rows: phantom study

This study was performed for evaluation of high- and low-contrast resolution in multidetector-row CT (MDCT) with 16 detector rows. For evaluating high-contrast resolution, a phantom was scanned ten times at 100 mA s with 24 patterns of scan parameters under several X-ray beam widths, X-ray tube voltages, X-ray tube rotation times, and helical pitches. Three radiological technologists observed the images visually. For evaluating low-contrast resolution, a phantom was scanned ten times at 100 mA s with the 24 patterns of scan parameters, which were the same as for high-contrast resolution. The images were examined based on receiver operating characteristic (ROC) curves. The high-contrast resolution deteriorated in the off-center locations when helical pitches of 1.375:1 or 1.75:1 were used. High helical pitch (>0.9375:1) and low tube voltage had significant effects on the low-contrast resolution. However, a wide X-ray beam width and short X-ray tube rotation time had no definite influence. Therefore, a helical pitch of 0.5625:1 should be used when the contrast resolutions are really important, and a wide X-ray beam width and short X-ray tube rotation time can improve the temporal resolution without deterioration of contrast resolution.