Effect of Thin Overlapping Reconstruction on the Attenuation of Small Renal Cysts in the Nephrographic Phase of MDCT: a Phantom Study

Objective: To evaluate the effect of thin overlapping reconstruction on the attenuation of small $({\leq}3cm)$ renal cysts in the nephrographic phase of multidetector CT (MDCT). Materials and Methods: 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. Results: 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 20mm-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. Conclusion: The effect of thin overlapping reconstruction on minimizing falsely elevated attenuation in the nephrographic phase was significant only in cysts ${\leq}20$ mm on the 4-channel MDCT.