CT angiography has proved a reliable alternative to catheter angiography to evaluate living renal donors. The next step -- defining the best image reconstruction method -- has researchers busy.
Dr. Jeong Kon Kim and colleagues at the University of Ulsan's Asan Medican Center in Seoul, Korea, found that thin-slab visualization of CTA data sets is better than thick-slab reconstruction. They published their study in the August issue of the American Journal of Roentgenology.
The researchers evaluated 76 consecutive subjects undergoing nephrectomy. They examined the venous and arterial vasculature of donors' kidneys using four different reconstruction methods: sliding thin-slab visualization and thick-slab visualization, each with volume rendering and maximum intensity projection. The sliding thin-slab visualizations outperformed the thick-slab protocols.
Sensitivity for sliding thin-slab reconstruction to detect the supernumerary artery was 93% for both volume rendering and MIP, compared with 50% and 57% for thick-slab volume rendering and MIP, respectively. Specificity for the four visualization approaches was 98% for thin-slab volume rendering, 98% for thin-slab MIP, 95% for thick-slab volume rendering, and 98% for thick-slab MIP.
The same techniques applied to early branching artery detection showed a sensitivity of 83%, 100%, 50%, and 50% and a specificity of 99%, 100%, 99%, and 97%, respectively.
Two independent radiologists determined that their agreement with sliding thin-slab volume rendering and MIP was excellent for detecting supernumerary and early branching arteries (k = 0.820 to 0.859) and good for renal veins (k = 0.698 to 0.724).
Their level of agreement for thick-slab volume rendering and MIP was good for arteries (k = 0.706 to 0.791) and moderate for veins (k = 0.443 to 0.579). Their agreement between CTA and surgical findings was also better with the sliding thin-slab protocols.
Researchers injected 130 to 140 mL of contrast material at a rate of 3.5 to 4 mL/sec, while performing acquisition on a four-slice scanner with a 24 to 30-second delay after injection. Their imaging protocol included 1.24-mm slice thickness, 1.5 beam pitch, 7.5-mm table speed rotation, and 0.5-mm reconstruction intervals.
The study has limitations. CTA reconstruction was performed only on kidneys with very straightforward vascular anatomy. And even though the study considered two-week time intervals between imaging reviews, observers could have involuntarily memorized renal vasculatures.
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