Comparison of axial, coronal, and primary 3D review in MDCT colonography for the detection of small polyps: a phantom...

The purpose of this phantom study is to compare the influence of the reading technique (axial images alone in comparison to 3D endoluminal, coronal, and combined 2D/3D review methods) on the sensitivity and inter-reader variability with MDCT colonography for the detection of small colonic polyps.

An anthropomorphic pig colon phantom with 75 randomly distributed simulated small polyps of 2-8mm size, was distended with air and scanned in a water phantom using multidetector-row CT with 4mm x 1mm collimation. Three radiologists rated the presence of polyps on a five-point scale. Performance with axial sections alone was compared to the performance with coronal sections, virtual endoscopy (VE), and a combined 2D/3D approach. We calculated sensitivities for polyp detection and used ROC analysis for data evaluation.

There was no significant difference between the mean area under the curve (A(z)) for axial images and VE (A(z)=0.934 versus 0.932), whereas coronal images were significantly inferior (A(z)=0.876) to both. The combined 2D/3D approach yielded the best results, with an A(z) of 0.99. Differences in sensitivity between individual readers were significant in axial images (sensitivity, 75-93%, p=0.001) and coronal images (sensitivity, 69-80%, p=0.028), but became non-significant with VE (83-88%, p=0.144) and the combined 2D/3D approach (95-97%, p=0.288).

Evaluation of axial sections alone leads to significant differences in detection rates between individual observers. A combined 2D/3D evaluation improves sensitivities for polyp detection and reduces inter-individual differences to an insignificant level.