The Effect of Reconstruction Algorithm on Conspicuity of Polyps in CT Colonography

Effect of visualization display colour on polyp conspicuity at virtual colonoscopy

AIM

To investigate the effect of different colour three-dimensional (3D) displays on polyp detection at virtual colonoscopy (VC).

METHODS

Five VC trained observers were shown "brief flashes" (lasting 0.2s) of 125 3D endoluminal image snap-shots, repeated for each of six display colours (750 images total). One hundred images contained a single polyp (diameter range 5-42 mm) and 25 contained no polyp ("normal"). Images were reviewed in random order over five reading sessions, readers recording either normality or presence and location of a polyp. Multilevel logistic regression was used to examine any influence of colour on polyp detection stratified according to polyp size (medium 5-9 mm/large >or=10mm). The kappa statistic was used to assess effect of colour on observer agreement.

RESULTS

Individual reader polyp detection rates ranged between 75-94%. Compared to the default pink "soft tissue" display, the odds of polyp detection were 0.65 (CI 0.41,1.01) for green, 0.82 (0.53,1.30) for blue, 1 (0.63,1.59) for red, 1.12 (0.7,1.79) for monochrome, and 1.15 for yellow (0.72,1.84). Overall, there was no significant difference between the displays (p=0.11). Including normal cases, there was no overall difference in correct case classification between the six colours (p=0.44). The odds of detecting large versus medium polyps was significantly greater for 3/5 observers; odds ratio (OR) 2.84-10.1, although unaffected by display colour (p=0.3).

CONCLUSION

The background colour display generally has a minimal effect on polyp detection at VC, although green should be avoided.

Pitfalls in Multi–Detector Row CT Colonography: A Systematic Approach

Thin-section multi-detector row computed tomographic (CT) colonography is a powerful tool for the detection and classification of colonic lesions. However, each step in the process of a CT colonographic examination carries the potential for misdiagnosis. Suboptimal patient preparation, CT scanning protocol deficiencies, and perception and interpretation errors can lead to false-positive and false-negative findings, adversely affecting the diagnostic performance of CT colonography. These problems and pitfalls can be overcome with a variety of useful techniques and observations. A relatively clean, dry, and well-distended colon can be achieved with careful patient preparation, thereby avoiding the problem of residual stool and fluid. Knowledge of the morphologic and attenuation characteristics of common colonic lesions and artifacts can help identify bulbous haustral folds, impacted diverticula, an inverted appendiceal stump, or mobile polyps, any of which may pose problems for the radiologist. A combined two-dimensional and three-dimensional imaging approach is recommended for each colonic finding. A thorough knowledge of the various pitfalls and pseudolesions that may be encountered at CT colonography, along with use of dedicated problem-solving techniques, will help the radiologist differentiate between definite colonic lesions and pseudolesions.

CT colonography: effect of colonic distension on polyp measurement accuracy and agreement-in vitro study

RATIONAL AND OBJECTIVES

To investigate the effect of colonic distension on polyp measurement accuracy and reader agreement.

MATERIALS AND METHODS

Institutional review board permission was obtained. A sealed colectomy specimen from a patient with familial adenomatous polyposis was scanned using a four-detector-row computed tomography (CT) after half and full air distension. A histopathologist measured the maximum dimension of all polyps in the opened specimen. Digital photographs and line drawings were used to individually match polyps visible in the CT datasets. Two observers (radiologist, technician) independently estimated the maximum polyp diameter using both two-dimensional (2D) and three-dimensional (3D) surface rendering. Full-distension measurements were repeated 1 week later. Accuracy was analyzed using paired t-test. Observer agreement was assessed using Bland Altman limits of agreement.

RESULTS

Twenty-three polyps (4-15 mm) were identified. 2D measurements were significantly smaller than histologic size at both half distension (radiologist first): mean difference [md] -1.1 mm, md -1.7 mm, and full distension md -1.1 mm, md 1.4 mm (all P < .001). 3D measurements were not significantly different from true size other than after half distension for the technician (md -0.7 mm, P = .01). 95% Bland Altman limits for interobserver agreement were narrower after full distension, and better using 2D (half-distension span of agreement approximately 4.7 mm and 6 mm for 2D and 3D, respectively). 2D intraobserver span of agreement between half and full distension was approximately 3.8 mm and 3.2 mm for the radiologist and technician, respectively, compared with 6.2 mm and 5.5 mm using 3D.

CONCLUSION

3D polyp measurement is more accurate than 2D. However, in the presence of suboptimal distension, inter- and intraobserver agreement is superior using 2D.

Polyp detection with CT colonography: primary 3D endoluminal analysis versus primary 2D transverse analysis with computer-assisted reader software

PURPOSE

To retrospectively compare primary three-dimensional (3D) endoluminal analysis with primary two-dimensional (2D) transverse analysis supplemented by computer-assisted reader (CAR) software for computed tomographic (CT) polyp detection and reader reporting times.

MATERIALS AND METHODS

Ethical permission and patient consent were obtained from all donor institutions for use of CT colonography data sets. Twenty CT colonography data sets from 14 men (median age, 61 years; age range, 52-78 years) with 48 endoscopically proved polyps were selected. Polyp coordinates were documented in consensus by three unblinded radiologists to create a reference standard. Two radiologists read the data sets, which were randomized between primary 3D endoluminal views with 2D problem solving and 2D views supplemented by CAR software. Reading times and diagnostic confidence were documented. The CAR software highlighted possible polyps by superimposing circles on the 2D transverse images. Data sets were reread after 1 month by using the opposing analysis method. Detection rates were compared by using the McNemar test. Reporting times and diagnostic confidence were compared by using the paired t test and Mann-Whitney U test, respectively.

RESULTS

Mean sensitivity values for polyps measuring 1-5, 6-9, and 10 mm or larger were 14%, 53%, and 83%, respectively, for 2D CAR analysis and 16%, 53%, and 67%, respectively, for primary 3D analysis. Overall sensitivity values were 41% for 2D CAR analysis and 39% for primary 3D analysis (P=.77). Reader 1 detected more polyps than reader 2, particularly when using the 3D fly-through method (P=.002). Mean reading times were significantly longer with the 3D method (P=.001). Mean false-positive findings were 1.5 for 2D analysis and 5.5 for 3D analysis. Reader confidence was not significantly different between analysis methods (P=.42).

CONCLUSION

Two-dimensional CAR analysis is quicker and at least matches the sensitivity of primary 3D endoluminal analysis, with fewer false-positive findings.