Sci-PM Thurs - 03: 3-D angiography: Effect of the maximum intensity projection on the measurement of artery diameters

Abstract

Our goal was to determine the impact of the maximum intensity projection (MIP) algorithm on quantitative analysis used for diagnosis and treatment planning of extracranial arterial disease. We performed 3-D computed rotational angiography (CRA) on 26 consecutive symptomatic patients to verify an internal carotid artery (ICA) stenosis originally found using duplex ultrasound. These volumes of data were visualized using two different post-processing projection techniques: MIP and digitally reconstructed radiographic (DRR) projection. A DRR is a radiographic image simulating a conventional digitally subtracted angiogram (DSA), but it is derived computationally from the same CRA dataset as the MIP. By visualizing a single volume with two different projection techniques, the post-processing effect of the MIP algorithm is isolated. Vessel measurements were made, according to the NASCET guidelines, and percentage stenosis grades were calculated. The NASCET-type stenosis grades tended to be underestimated on average by 2.4% with the MIP algorithm, although this was not statistically significant (P=0.09). Moreover, the vessel measurements from the MIPs were consistently 0.17 mm larger than those from DRRs (P<0.0001). Thus, when applied to high-contrast, high-resolution CRA images, the MIP algorithm slightly increased the apparent dimensions of the arteries. This difference is not clinically relevant, due to the fact that it is only a fraction of the 0.38 mm voxel spacing. Moreover, the MIP dimensions could actually represent the truth, and that it is the sharp decrease near the edge of the intensity profile of the radiographic images that causes an underestimation of the absolute dimensions.