Study shows superior sensitivity for 3D virtual colonography
Primary interpretation of diagnostic images is traditionally conducted in two-dimensional views. Although interpretative viewing in 2D planes has historically demonstrated excellent results, primary evaluation of CT colonography exams is best conducted in 3D view, according to a recent study published in the American Journal of Roentgenology.

“Disparate results from the existing large CT colonography (CTC) trials suggest that 2D polyp detection is less sensitive than 3D detection, but no direct evidence exists to support this claim,” the authors wrote.

Researchers from the department of radiology at the University of Wisconsin Medical School in Madison, Wis., and the department of radiology at the Uniformed Services University of Health Sciences in Bethesda, Md., conducted a retrospective blinded study of 730 consecutive patients with colonoscopy-proven CTC cases.

Ten radiologists interpreted the studies using a primary 2D approach, with 3D reserved for problem solving. In addition, primary 2D CTC performance was compared with the primary 3D CTC results from the original trial of 1,233 asymptomatic adults, according to the authors. The CTC interpretation was performed using V3D Colon software (Viatronix, Stony Brook, N.Y.).

The original trial was conducted by the United Stated Department of Defense (DoD) and consisted of 728 men and 505 women who underwent same-day CTC and optical colonoscopy over a 14-month period. The primary 2D cohort consisted of 730 consecutive CTC cases, representing the available Navy cohort from the DoD screening trial.

“Primary 3D CTC evaluation was significantly more sensitive for polyp detection than primary 2D evaluation for each of the four polyp categories considered (adenomas greater than or equal to 6mm and 10mm and all polyps greater than or equal to 6mm and 10mm),” the authors wrote.

A screening CT colonography (CTC) conducted in an asymptomatic average-risk 54-year-old man. Oblique orientation of 3D map shows location of 10-mm rectosigmoid polyp (red dot) that was identified at prospective primary 3D evaluation but was missed at retrospective primary 2D evaluation. Green line indicates automated centerline for endoluminal navigation. This large polyp was confirmed at same-day optical colonoscopy. Image and caption by permission of the American Roentgen Ray Society.  
The researchers noted that the differences in sensitivity for polyp detection were highly significant at the 6-mm size threshold using primary 3D for interpretation of the CTC exams. For all polyps ≥ 6 mm, which includes both adenomatous and nonadenomatous lesions, the sensitivity for the primary 3D approach was more than double that for primary 2D detection, 80.8 percent compared with 37.9 percent, respectively.

“Of the four large CTC trials to date evaluating cohorts with low prevalence of disease, the three (one single-center and two multicenter) trials restricted to a primary 2D approach for polyp detection fared rather poorly,” the authors noted. “In comparison, the DoD CTC screening trial used primary 3D polyp detection and showed that CTC sensitivity for clinically relevant polyps was comparable to optical colonoscopy.”

The scientists suggested that primary 3D polyp detection is more effective because the conspicuity of polyps among the folds is greatly enhanced compared with cross-sectional 2D images in which haustral folds and polyps have a similar appearance.

“In our experience, radiologists new to CTC interpretation generally begin as primary
2D reviewers because of their familiarity with this display from general CT evaluation but naturally gravitate toward 3D polyp detection over time,” the authors noted.

“From a logical standpoint, the more sensitive, but less specific, display—the 3D endoluminal view—is best for initial polyp detection, whereas the more specific but less sensitive display—cross-sectional 2D images—is needed for confirmation of suspected lesions,” the researchers advised.