Effect of Thin Overlapping Reconstruction on the Attenuation of Small (≤ 3 cm) Renal Cysts in the Nephrographic Phase of MDCT: a Phantom Study

To evaluate the effect of thin overlapping reconstruction on the attenuation of small (≤ 3 cm) renal cysts in the nephrographic phase of multidetector CT (MDCT). We scanned a phantom kidney containing spheres of various sizes (10, 20, and 30 mm) using both 4- and 16-channel MDCT scanners, and reconstructed images with various slice thickness (T, mm) and intervals (I, mm). The attenuation increase (AI) was measured for each sphere in 240-HU diluted solution of contrast material and compared with the attenuation in 35-HU solution. On the 4-channel MDCT, thin overlapping reconstruction (T/I 3/1, compared with 5/5) lowered the AI as much as 17 HU in the 10 mm-sphere and 6 HU in the 20 mm-sphere (p < 0.05). Thin slicing alone was also effective; however overlapping alone was not. On the 16-channel MDCT, AI in the 10 mm-sphere was significantly lower than on the 4-channel MDCT with T/I = 5/5 (p < 0.05), however thinner slicing or overlapping did not affect the attenuation significantly in all of the spheres. The effect of thin overlapping reconstruction on minimizing falsely elevated attenuation in the nephrographic phase was significant only in cysts 20 mm on the 4-channel MDCT