Candidate image processing for real-time volumetric CT subtraction angiography.

Since a 256-slice CT can perform real time observation of the volumetric cine images at multiple angles, volumetric CT angiography can provide much useful clinical information. Conventional CT subtraction angiography is generated by subtracting the non-enhanced CT image (mask CT image) from each contrast-enhanced CT image. Since even conventional CT subtraction angiography takes a few minutes to compute the image, volumetric CT subtraction angiography images require computation of an enormous amount of volumetric cine data (image base CT subtraction angiography: ICTSA) which means an excessively long calculating time. To reduce calculating time, we developed the raw data base CT subtraction angiography (RCTSA) that subtracts raw data instead of the reconstructed four-dimensional image sets. Image quality of the two image processing methods was evaluated in phantom and animal studies. Evaluation items were image noise, CT number uniformity, and subtracting RCTSA from ICTSA. ICTSA calculates the number of volume data; however, RCTSA uses the number of CT rotations. Moreover, since RCTSA can also be started subtraction early in the process of data acquisition, it reduced the number of calculations considerably. As there is a longer CT acquisition time, RCTSA shortens the ratio of the calculating time compared to that of ICTSA. RCTSA is useful image processing to reduce CT subtraction angiography examination time instead of ICTSA.