3D postprocessing tools shed light on hidden polyps

February 11, 2006

In 2004, much of the talk swirling around CT colonography focused on whether 3D views were better than 2D for primary interpretation. In 2005, presentations at key meetings revolved around interpretation using 2D, 3D, and 360 degrees dissection. That last option was just one of several techniques illustrated during a case review session at the Sixth International Virtual Colonoscopy Symposium in Boston where physicians using six different vendor products highlighted the myriad ways that exist to interpret virtual colonoscopy scans.

In 2004, much of the talk swirling around CT colonography focused on whether 3D views were better than 2D for primary interpretation. In 2005, presentations at key meetings revolved around interpretation using 2D, 3D, and 360 degrees dissection. That last option was just one of several techniques illustrated during a case review session at the Sixth International Virtual Colonoscopy Symposium in Boston where physicians using six different vendor products highlighted the myriad ways that exist to interpret virtual colonoscopy scans.

The following is a list of physicians and the vendor products they demonstrated:

- Dr. Pamela Nugent, Uniformed Services, University of the Health Sciences, Bethesda, MD; Viatronix.

Nugent used the software to create a colon map and a colon center line. The center line helped navigate through the 3D view, which she used as her primary read, switching to 2D for problem solving. During the 3D fly-through, she used a window tool that, when passed over a suspicious lesion, showed the density of the lesion in colors ranging from white to red. This led to the determination of true polyps versus residual fluid and stool.

Nugent also demonstrated the use of bookmarks, marking polyps along the fly-through worthy of further investigation. A "paint" feature displayed already viewed areas of the 3D colon in green.

The product also features electronic cleansing, according to Janet Masini of Viatronix. It allows 3D volume rendering in real-time and supine and prone registration.

- Dr. Stuart Taylor, Department of Intestinal Imaging, St. Marks Hospital, UK, E-Z-EM; Vital Images.

Taylor demonstrated the integration of a commercially available CAD system (Medicsight) with a CT colonography workstation during his case review. He was able to change the CAD sensitivity to ignore smaller polyps and showed how CAD could be used as a second read.

One limitation of the CAD system was its performance in cases where patients underwent a reduced prep with fecal and fluid tagging. The protocol tended to produce too many false positives to be useful. Taylor showed one case where both he and the CAD system marked a suspicious lesion. He tried to confirm on 2D but remained unsure as to how to classify the lesion. On optical colonoscopy, the lesion turned out to be a piece of corn.

- Dr. Danielle Hock, Department of Radiology, Clinique Saint Joseph, Belgium; GE Healthcare.

Hock demonstrated GE's Advantage Workstation 4.2 with automatic dissection. The software provided a transparent 3D reconstruction of the colon. The tool then created a colon center line and dissected the 3D view. With this filet view, Hock was able to evaluate an open, flat version of the colon, which eliminated the need to perform forward and backward fly-throughs.

The viewing method is quick, Hock said, and allows her to perform more reads without feeling dizzy or getting headaches, as has occurred with 3D endoluminal views. She uses this dissected view as her primary read.

This 360 degrees dissection view of the colon, offered as part of the GE Advantage CT colonography software package, offers an alternative to the standard 2D or 3D approach.

- Dr. Patrik Rogalla, Department of Radiology, Charite Campus Mitte, Universitatsmedizin Berlin, Schumannst; Philips Medical Systems.

Rogalla demonstrated a combined 2D/3D approach. He illustrated use of a cube view which also eliminates the need for fly-throughs. The cube view combines endoluminal and dissection views. Rogalla also illustrated the use of digital subtraction, locating a partially covered polyp in a reconstruction based on a cleansed data set.

The Philips virtual colonoscopy application uses a perspective projection filet view as the primary interpretation view, although the user can switch to primary 2D or traditional endoluminal primary views, according to Tom Naypauer, product manager at Philips Medical Systems.

"The filet view allows the user to view all aspects of the endoluminal portions of the colon, on either side and between haustral folds," he said.

Additionally, a computer-assisted reader algorithm and electronic cleansing have been incorporated into the application. Both tools await FDA clearance.

- Dr. Todd Fibus, Emory University School of Medicine, Veterans Affairs Medical Center; TeraRecon.

Fibus conducted his primary read using 2D views, relying on a cube 3D view for problem solving. His case review showed the importance of supine and prone views, as polyps hidden on one view can be clearly seen on the other. Findings can be organized in a bookmark window along with thumbnail images. Fibus also emphasized the importance of using both 3D and 2D views by demonstrating a mostly flat polyp opposite a large ileocecal valve. While only vaguely seen on 2D, it was easily viewed on 3D.

CT colonography on the Aquarius workstation offers side by side analysis of prone and supine data sets; the ability to mark in the axial, coronal, sagittal, or 3D view; measurement/distance tools; stool subtraction/automatic cleansing; "cube view" for isolating pathology; and unfolded view for 360 degrees coverage of the colon, according to Steve Sandy, vice president of marketing at TeraRecon.

- Dr. Anno Graser, University of Munich-Grosshadern; Siemens.

Graser used the Siemens Leonardo colon package along with the CAD polyp-enhanced view (PEV) to review his case. PEV automatically suggests points of interest to the reader for review and evaluation. He shared an optical colonoscopy image e-mailed to him 13 hours before showing the successful resection of a polyp he had detected. Graser uses CAD as a second reader, and during the demonstration, it helped detect a large polyp and several small polyps hidden between colonic folds.

Siemens' syngo colon software package has a structured reporting template. It supports both 2D and 3D reading.-MT