AIM: To evaluate the value of postprocessing techniquesof CT colonography,including multiplanar reformation (MPR),virtual colonoscopy (VC),shaded surface display (SSD) andRaysum,in detection of colorectal carcinomas.METHODS: Sixty-four patients with colorectal carcinomaunderwent volume scanning with spiral CT.MPR,VC,SSDand Raysum images were obtained by using four kinds ofpostprocessing techniques in workstation.The results werecomparatively analyzed according to circumferential extent,lesion length and pathology pattern of colorectal carcinomas.All diagnoses were proved pathologically and surgically.RESULTS: The accuracy of circumferential extent ofcolorectal carcinoma determined by MPR,VC,SSD andRaysum was 100.0%,82.8%,79.7% and 79.7%,respectively.There was a significant statistical differencebetween MPR and VC.The consistent rate of lesion lengthwas 89.1%,76.6%,95.3% and 100.0%,respectively.There was a statistical difference between VC and SSD.The accuracy of discriminating pathology pattern was 81.3%,92.2%,71.9% and 71.9%,respectively.There was a statisticaldifference between VC and SSD.MPR could determineaccurately the circumference of colorectal carcinoma,Raysumcould determine the length of lesion more precisely thanSSD,VC was helpful in discriminating pathology patterns.CONCLUSION: MPR,VC,SSD and Raysum have advantageand disadvantage in detection of colorectal carcinoma,useof these methods in combination can disclose the lesionmore accurately. AIM: To evaluate the value of postprocessing techniques of CT colonography, including multiplanar reformation (MPR), virtual colonoscopy (VC), shaded surface display (SSD) and Raysum, in detection of colorectal carcinomas. METHODS: Sixty-four patients with colorectal carcinoma underwent volume scanning with spiral CT. MPR, VC, SSD and Raysum images were obtained by using four kinds of postprocessing techniques in workstation. The results werecomparativelycted according to circumferential extent, lesion length and pathology pattern of colorectal carcinomas. All-ill diagnostics were proved pathologically and surgically.RESULTS: The accuracy of circumferential extent of colorectal carcinoma determined by MPR, VC, SSD and Raysum was 100.0%, 82.8%, 79.7% and 79.7% respectively. There was a significant statistical difference between MPR and VC.The consistent rate of lesion lengthwas 89.1%, 76.6 %, 95.3% and 100.0% respectively. There was a statistical difference between VC and SSD. The accuracy of discriminating patholog y pattern was 81.3%, 92.2%, 71.9% and 71.9% respectively. There was a statistical difference between VC and SSD. MPR could determineaccurately the circumference of colorectal carcinoma, Raysum could determine the length of lesion more than than SDX, VC was helpful in discriminating pathology patterns. CONCLUSION: MPR, VC, SSD and Raysum have advantage and disadvantage in detection of colorectal carcinoma, use of these methods in combination can disclose the lesionmore accurately.