Hepatic MR angiography: A multiobserver comparison of visualization methods

OBJECTIVE. MR angiography (MRA) is an established diagnostic method; howeve r. controversy remains over the best technique for display. In this study, we compared five methods of depicting hepatic MRA including a novel skeleto nization approach, using receiver operator characteristic (ROC) curves, int erobserver variability (kappa values), and speed of interpretation. SUBJECTS AND METHODS. Twenty-one patients scheduled for isolated liver perf usion therapy for metastatic disease underwent contrast-enhanced three-dime nsional MRA to determine vascular anatomy. Vascular anatomy was validated a t the time of surgery. We dis played the image data, using five techniques: maximum intensity projection, targeted maximum intensity projection, isoin tensity surface (isosurface), connected isointensity surface (connected iso surface), and ordered region growing skeleton (skeleton). Four observers, b linded to the surgical results, interpreted each technique in random order without patient identifiers. Areas under the ROC curves, kappa values of in terobserver variability, and time to interpret each display were compared. RESULTS. Skeletonized MRA had the highest area under the ROC curve (A(z), 0 .90 +/- 0.04) compared with the other techniques (p < 0.013), Kappa scores of agreement were also highest for skeletonized MRA (0.75 +/- 0.04) and had no overlap at the 95% confidence level compared with other techniques. Com pared with source images, all visualization methods were faster to interpre t, but the skeleton technique was more quickly (p = 0.04) interpreted than the other techniques. CONCLUSION. Skeletonized MRA with the skeleton connectivity algorithm is a semiautomated method of displaying complex arterial anatomy. Compared with other techniques, it is more accurate, more consistent among observers, and slightly faster to interpret. Skeletonization should be applicable to CT a ngiography and MRA.