The Efficacy Of HDCT In Detecting Polyps With CT Colonography:a Phantom Study

Part One The efficacy of adaptive statistical iterative reconstruction in detecting polyps with reduced dose CT colonography:a phantom studyObjective:To evaluate the efficacy of CT colonography (CTC) with adaptive statistical iterative reconstruction (ASIR) to detect phantom colonic polyps using a reduced radiation dose.Subjects and Methods:A series of twenty artificial polyps sized from1mm to10mm (ten sized smaller than5mm and ten sized over5mm) were established by ligation in an isolated segment of porcine colon. Volume data were acquired on High Definition CT scanner at different doses (10,20,30,40,50and100mAs at120KVp) using six different ASIR levels at0,10%,30%,50%,70%and100%. CT virtual endoscopy, multiplanar reformation and virtual dissection models were reconstructed. Two radiologists blinded to the polyps’location assessed every image setting. Average noise level, average signal to noise ratio (SNR)and average contrast to noise ratios (CNR) as well as detecting rates of the polyps were calculated and compared statistically among different acquisitions.Results:The phantom study revealed a tendency that SNR and CNR was increasing and the noise was decreasing with a higher percentage of ASIR at every dose level (P<0.05). The detecting rates of colonic polyps were increase significantly with a higher dose especially for those polyps less than5mm (P<0.05); however, the detecting rates had no significant increase with a higher ASIR level (P>0.05)Conclusion:Adaptive statistical iterative reconstruction could significantly reduce image noise and increase SNR and CNR in low dose CT colonography, it succeed in improving the detecting rates of artificial polyps over5mm but fail in those polyps smaller than5mm. Part Two The efficacy of spectral CT colonography in detecting small phantom polypsObjective:To evaluate the efficacy of CT colonography (CTC) with spectral imaging in detecting small phantom colonic polyps and find the best single spectral images.Subjects and Methods:Two segment of twenty artificial polyps sized from lmm to10mm (ten sized smaller than5mm and ten sized over5mm) were established by ligation in a segment of porcine colon. The phantom colon were inflated and immerged into0.1%iodine solution. Volume data were acquired on a64-multi detector germstone CT scanner single spectral images at45、60、75、90、105、120and135keV were reconstructed. CT virtual endoscopy (CTVE), multiplanar reformation (MPR) and virtual dissection (VD) models were reconstructed. Two radiologists blinded to the polyps location assessed every image setting. Contrast to noise ratios (CNR) as well as detecting rates of the polyps were calculated and compared statistically among different acquisitions.Results:The phantom study revealed that the detecting rates of colonic polyps were higher than conventional for those polyps less than5mm (P>0.05). The bset CNR is in75keV’s single spectral image.Conclusion:Spectral CT colonography efficiently, the best single spectral images is75keV.