Carotid bifurcation: results of spliced hybrid subtraction angiography compared with standard temporal and hybrid images.

Hybrid subtraction angiography can provide a higher percentage of two-view examinations of the carotid bifurcation. Unfortunately, hybrid images are lower in signal-to-noise ratio (S/N) than temporal subtraction angiographic images and are often described as "noisy." The present study was designed to determine if the lower S/N of hybrid subtraction angiography could be restricted to the contralateral carotid bifurcation by "splicing" a small hybrid region of interest into a larger temporal image. Twenty-two selected images were examined on four image quality scales by seven readers. Similarity of reader scoring was characterized by cluster analysis and was good. Ipsilateral carotid arteries were preferred as temporal images, and contralateral carotid arteries were preferred as hybrid images. The splice image was preferred over both. The splice image retained the superiority of temporal subtraction angiography in the region of the ipsilateral carotid artery and incorporated the superiority of hybrid subtraction angiography in the region of the contralateral carotid artery. The splice image incorporated the best features of both image modalities.