[Evaluation of the variable-speed injection method for three-dimensional CT angiography of the trunk]

In three-dimensional CT angiography (3DCTA) studies, the CT values within blood vessels ideally should be uniform because the reproducibility and detectability of the morphological characteristics of blood vessels change depending on the threshold value selected. The time-density curve (TDC) therefore should be maintained at a certain level. However, conventional contrast medium injectors have a fixed injection speed, and the injection speed must therefore be changed in a stepwise manner. This means that it is not possible to maintain the TDC precisely. However, recent advances in the performance capabilities of contrast medium injectors allow the injection speed to be changed continuously with a user-selectable injection-speed ratio, permitting studies to be performed using the so-called "variable-speed injection method". We have conducted studies using this new method to determine the optimal injection speed ratio that permits the TDC to be maintained at the desired level. Our results showed that an injection-speed ratio of 0.5 permits the TDC to be maintained at the optimal level, improving the reproducibility and detectability of blood vessel morphology in 3DCTA studies. In addition, when contrast medium injection was terminated at a time point > or =50% of the preset contrast medium injection time, the mean CT value was not adversely affected (i.e., was not significantly reduced), making it possible to reduce the amount of contrast medium administered to the patient.