Fundamental Elements for Successful Performance of CT Colonography (Virtual Colonoscopy)

There are many factors affecting the successful performance of CT colonography (CTC). Adequate colonic cleansing and distention, the optimal CT technique and interpretation with using the newest CTC software by a trained reader will help ensure high accuracy for lesion detection. Fecal and fluid tagging may improve the diagnostic accuracy and allow for reduced bowel preparation. Automated carbon dioxide insufflation is more efficient and may be safer for colonic distention as compared to manual room air insufflation. CT scanning should use thin collimation of ≤3 mm with a reconstruction interval of ≤1.5 mm and a low radiation dose. There is not any one correct method for the interpretation of CTC; therefore, readers should be well-versed with both the primary 3D and 2D reviews. Polyps detected at CTC should be measured accurately and reported following the "polyp size-based" patient management system. The time-intensive nature of CTC and the limited resources for training radiologists appear to be the major barriers for implementing CTC in Korea

Primary uncleansed 2D versus primary electronically cleansed 3D in limited bowel preparation CT-colonography. Is there a difference for novices and experienced readers?

The purpose of this study was to compare a primary uncleansed 2D and a primary electronically cleansed 3D reading strategy in CTC in limited prepped patients. Seventy-two patients received a low-fibre diet with oral iodine before CT-colonography. Six novices and two experienced observers reviewed both cleansed and uncleansed examinations in randomized order. Mean per-polyp sensitivity was compared between the methods by using generalized estimating equations. Mean per-patient sensitivity, and specificity were compared using the McNemar test. Results were stratified for experience (experienced observers versus novice observers). Mean per-polyp sensitivity for polyps 6 mm or larger was significantly higher for novices using cleansed 3D (65%; 95%CI 57–73%) compared with uncleansed 2D (51%; 95%CI 44–59%). For experienced observers there was no significant difference. Mean per-patient sensitivity for polyps 6 mm or larger was significantly higher for novices as well: respectively 75% (95%CI 70–80%) versus 64% (95%CI 59–70%). For experienced observers there was no statistically significant difference. Specificity for both novices and experienced observers was not significantly different. For novices primary electronically cleansed 3D is better for polyp detection than primary uncleansed 2D

CT colonography: optimisation, diagnostic performance and patient acceptability of reduced-laxative regimens using barium-based faecal tagging

To establish the optimum barium-based reduced-laxative tagging regimen prior to CT colonography (CTC). Ninety-five subjects underwent reduced-laxative (13 g senna/18 g magnesium citrate) CTC prior to same-day colonoscopy and were randomised to one of four tagging regimens using 20 ml 40%w/v barium sulphate: regimen A: four doses, B: three doses, C: three doses plus 220 ml 2.1% barium sulphate, or D: three doses plus 15 ml diatriazoate megluamine. Patient experience was assessed immediately after CTC and 1 week later. Two radiologists graded residual stool (1: none/scattered to 4: >50% circumference) and tagging efficacy for stool (1: untagged to 5: 100% tagged) and fluid (1: untagged, 2: layered, 3: tagged), noting the HU of tagged fluid. Preparation was good (76–94% segments graded 1), although best for regimen D (P = 0.02). Across all regimens, stool tagging quality was high (mean 3.7–4.5) and not significantly different among regimens. The HU of layered tagged fluid was higher for regimens C/D than A/B (P = 0.002). Detection of cancer (n = 2), polyps ≥6 mm (n = 21), and ≤5 mm (n = 72) was 100, 81 and 32% respectively, with only four false positives ≥6 mm. Reduced preparation was tolerated better than full endoscopic preparation by 61%. Reduced-laxative CTC with three doses of 20 ml 40% barium sulphate is as effective as more complex regimens, retaining adequate diagnostic accuracy

물질 혼합비율과 구조적 특징의 통합 재구성 모델을 이용한 전자적 장세척 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 8. 신영길.대장 컴퓨터 단층 촬영 영상에서 조영 처리된 잔여물을 제거하기 위해 전자적 장세척 방법이 이용된다. 본 논문에서는 전자적 장세척 방법에서 결함의 주요 원인이 되는 부분 용적 효과와 가성 상승 효과를 동시에 해결하기 위해 물질 혼합비율과 구조적 특징의 통합 재구성 모델을 이용한 전자적 장청소 기법을 제안한다. 먼저 대장 컴퓨터 단층 촬영 영상에서 공기, 조영 처리된 잔여물, 공기와 조영 처리된 잔여물 사이의 경계 (공기-잔여물 경계), 대장외부의 연조직과 조영 처리된 잔여물 사이의 경계 (연조직-잔여물 경계), 그리고 공기, 연조직, 조영 처리된 잔여물이 만나는 경계 (공기-연조직-잔여물 경계) 영역을 포함한 결장 요소를 분할한다. 분할된 공기와 공기-잔여물 경계 영역에 대해서는 각 복셀의 밀도값을 동일하게 공기의 대표 밀도값으로 대체함으로써 잔여물을 제거한다. 반면에 분할된 연조직-잔여물 경계와 공기-연조직-잔여물 경계 영역에 대해서는 물질 혼합비율과 구조적 특징을 계산한다. 물질 혼합비율은 두 물질간 혹은 세 물질간 전이 모델을 이용하여 예측하고 구조적 특징은 헤시안 행렬의 아이겐 분석에 기반하여 계산한다. 계산된 물질 혼합비율과 구조적 특징을 이용하여 연조직-잔여물 경계와 공기-연조직-잔여물 경계 영역에 속하는 각 복셀의 밀도값이 재구성된다. 물질 혼합비율과 구조적 특징의 통합 재구성 모델은 각 복셀 내의 연조직의 부분 용적을 유지시키는 동시에 조영 처리된 잔여물의 가성 상승 효과로 인해 약화된 잔여물에 잠긴 대장 주름 및 용종이 보존될 수 있도록 한다. 따라서 제안된 전자적 장세척 방법에서는 부분 용적 효과로 인한 연조직-잔여물 경계의 계단무늬 결함과 가성 상승 효과로 인한 잔여물에 잠긴 대장 주름 및 용종의 지나친 세척 결함을 피할 수 있다. 또한 본 논문에서는 기존 세 물질간 전이 모델의 연산 복잡도를 줄이기 위해 단순 세 물질간 전이 모델을 제안한다. 단순 세 물질간 전이 모델에서는 두 물질간 전이 모델을 반복 적용시킴으로써 얻어진 세 쌍의 (공기-연조직, 공기-잔여물, 연조직-잔여물) 두 물질간 혼합비율을 구하고 이를 삼각형을 이용한 무게중심좌표 상에서의 보간방법을 이용해 하나의 세 물질간 혼합비율로 변환한다. 열개의 임상 데이터를 이용하여 제안한 전자적 장세척 방법의 성능을 평가하였다. 방사선 전문의에 의한 장세척 품질 평가에서 제안 방법이 물질 혼합비율을 이용한 기존 방법에 비해 더 높은 점수의 장세척 결과를 보였으며, 특히 잔여물에 잠긴 대장 주름 및 용종이 더 잘 보존되는 것을 확인하였다. 이러한 결과는 잔여물에 잠긴 대장 주름 영역을 수동 분할하여 제안 방법과 기존 방법에 의한 장세척 결과 영상에서 해당 영역의 평균 밀도값과 주름 보존 비율을 비교한 결과에서도 마찬가지로 입증되었다. 또한 기존의 두 물질간 전이 모델로는 잘 해결되지 않았던 공기-연조직-잔여물 경계 영역에서의 산등성이 형태의 결함에 대해서도 제안 방법에서는 단순 세 물질간 전이 모델을 이용하여 공기-연조직-잔여물 경계 영역에서의 결함을 제거하고 전체 대장의 표면이 깨끗하게 재구성되는 것을 확인하였다.Electronic cleansing (EC) is the process of virtually cleansing the colon by removal of the tagged materials (TMs) in computed tomographic colonography (CTC) images and generating electronically cleansed images. We propose an EC method using a novel reconstruction model. To mitigate partial volume (PV) and pseudo-enhancement (PEH) effects simultaneously, material fractions and structural responses are integrated into a single reconstruction model. In our approach, colonic components including air, TM, interface layer between air and TM (air-TM interface) and interface layer between soft-tissue (ST) and TM (ST-TM interface), and T-junction (i.e., locations where air-TM interface with the colon wall) are first segmented. For each voxel in the segmented TM and air-TM interface, CT density value is replaced with the pure material density of air and thus the unexpected ST-like layers at the air-TM interface (caused by PV effect) are simply removed. On the other hand, for each voxel in the segmented ST-TM interface and T-junction, the two- and three-material fractions at the voxel are derived using a two- and three-material transition models, respectively. For each voxel in the segmented ST-TM interface and T-junction, the structural response is also calculated by rut- and cup-enhancement functions based on the eigenvalue signatures of the Hessian matrix. Then, CT density value of each voxel in ST-TM interface and T-junction is reconstructed based on both the material fractions and structural responses to conserve the PV contributions of ST in the voxel and preserve the folds and polyps submerged in TMs. Therefore, in our ST-preserving reconstruction model, the material fractions remove the aliasing artifacts at the ST-TM interface (caused by PV effect) effectively while the structural responses avoid the erroneous cleansing of the submerged folds and polyps (caused by PEH effect). To reduce the computational complexity of solving the orthogonal projection problem in the three-material model, we currently propose a new projection method for the three-material model that provides a very quick estimate of the three-material fractions without the use of code-book, which is pre-generated by uniformly sampling the model representation in material fraction space and used to find the best match with the observed measurements. In our new projection method for the three-material model, three pairs of two-material fractions are calculated by using the two-material model and then simply combined into a single triple of three-material fractions based on the barycentric interpolation in material fraction space. Experimental results using clinical datasets demonstrated that the proposed EC method showed higher cleansing quality and better preservation of submerged folds and polyps than the previous method. In addition, by using the new projection method for the three-material model, the proposed EC method clearly reconstructed the whole colon surface without the T-junction artifacts, which are observed as distracting ridges along the line where the air-TM interface touches the colon surface when the two-material model does not cope with the three-material fractions at T-junctions.Docto

Using computed tomography colonography in patients at high risk of colorectal cancer - a prospective study in a university hospital in South America

OBJECTIVES: The purpose of our study was to report the results of the implementation of computed tomography colonography in a university hospital setting serving a Brazilian population at high risk of colorectal cancer. METHODS: After creating a computed tomography colonography service in our institution, 85 patients at high risk of colorectal cancer underwent computed tomography colonography followed by a same-day optical colonoscopy from September 2010 to May 2012. The overall accuracy of computed tomography colonography in the detection of lesions ≥6 mm was compared to that of optical colonoscopy (direct comparison). All colonic segments were evaluated using quality imaging (amount of liquid and solid residual feces and luminal distension). To assess patient acceptance and preference, a questionnaire was completed before and after the computed tomography colonography and optical colonoscopy. Fisher's exact test was used to measure the correlations between colonic distension, discomfort during the exam, exam preference and interpretation confidence. RESULTS: Thirteen carcinomas and twenty-two lesions ≥6 mm were characterized. The sensitivity, specificity and accuracy of computed tomography colonography were 100%, 98.2% and 98.6%, respectively. Computed tomography colonography was the preferred method of investigation for 85% of patients. The preparation was reported to cause only mild discomfort for 97.6% of patients. According to the questionnaires, there was no significant relationship between colonic distension and discomfort (p>;0.05). Most patients (89%) achieved excellent bowel preparation. There was a statistically significant correlation between the confidence perceived in reading the computed tomography colonography and the quality of the preparation in each colonic segment (p≤0.001). The average effective radiation dose per exam was 7.8 mSv. CONCLUSION: It was possible to institute an efficient computed tomography colonography service at a university hospital that primarily assists patients from the public health system, with high accuracy, good acceptance and effective radiation doses. Our results seem to be comparable to other centers of excellence and fall within acceptable published guidelines, showing that a successful computed tomography colonography program can be reproduced in a South American population screened in a university hospital

CT colonography with limited bowel preparation for the detection of colorectal neoplasia in an FOBT positive screening population

Item does not contain fulltextPURPOSE: Aim was to evaluate the accuracy of computed tomography colonography (CTC) for detection of colorectal neoplasia in a Fecal Occult Blood Test (FOBT) positive screening population. METHODS: In three different institutions, consecutive FOBT positives underwent CTC after laxative free iodine tagging bowel preparation followed by colonoscopy with segmental unblinding. Each CTC was read by two experienced observers. For CTC and for colonoscopy the per-polyp sensitivity and per-patient sensitivity and specificity were calculated for detection of carcinomas, advanced adenomas, and adenomas. RESULTS: In total 22 of 302 included FOBT positive participants had a carcinoma (7%) and 137 had an adenoma or carcinoma >/=10 mm (45%). CTC sensitivity for carcinoma was 95% with one rectal carcinoma as false negative finding. CTC sensitivity for advanced adenomas was 92% (95% CI: 88-96) vs. 96% (95% CI: 93-99) for colonoscopy (P = 0.26). For adenomas and carcinomas >/=10 mm the CTC per-polyp sensitivity was 93% (95% CI: 89-97) vs. 97% (95% CI: 94-99) for colonoscopy (P = 0.17). The per-patient sensitivity for the detection of adenomas and carcinomas >/=10 mm was 95% (95% CI: 91-99) for CTC vs. 99% (95% CI: 98-100) for colonoscopy (P = 0.07), while the per-patient specificity was 90% (95% CI: 86-95) and 96% (95% CI: 94-99), respectively (P < 0.001). CONCLUSION: CTC with limited bowel preparation performed in an FOBT positive screening population has high diagnostic accuracy for the detection of adenomas and carcinomas and a sensitivity similar to that of colonoscopy for relevant lesions.1 december 201