Masters of Manipulation

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Radiologists and vendors race to grasp and improve the tools of advanced visualization as imaging modalities churn out ever more information

Radiology stands on the cusp of the golden age of advanced visualization, with the two most commonly used high-tech modalities, CT and MRI, increasingly reliant on 3D reconstructions and 4D analysis for examination interpretation. As advanced visualization for CT and MRI comes of age—bolstered by augmented processing power and ever-increasing transmission speeds—how can radiologists optimize the tools at their disposal for the most rapid and accurate diagnoses?

Jeffrey C. Hellinger, MD, director of cardiovascular imaging and director of the 3D Medical Imaging Laboratory at The Children’s Hospital of Philadelphia, advocates an all-inclusive approach. When interpreting cardiac CT angiography (CTA) exams, Hellinger uses a combination of all tools. “The tools have strengths and weaknesses, advantages and disadvantages,” he says. “I interact freely among volume rendering, maximum-intensity projection (MIP), multiplanar reconstruction (MPR), and curved planar reconstruction.”

Gary Wendt, MD, associate professor of neuroradiology at the University of Wisconsin–Madison, finds that the limitations of advanced visualization for MR angiography (MRA) are more infrastructure based. “One of the biggest problems in advanced visualization, in general, is the lack of universal accessibility,” he says. “The Web-based products are getting better, but they still have their flaws.”

Each subspecialty uses a different toolset, but they all have one common goal: making interpretation as efficient as possible. As MRI resolution improves and 64-slice CT scanners gradually replace older 16-slice units, that goal is both closer and more remote than ever before.

Multislice CT

The evolution of CT scanners from 16 to 64 slices or more has meant an order-of-magnitude explosion in the number of images that compose a single study. While this exponential increase takes its toll on networks and IT infrastructure, it also opens new doors, allowing more detailed visualization of the heart than has ever been possible.

“As the technology continues to advance, it’s more important than ever that trainees (from residents to fellows to attending radiologists from academic settings and private practice) learn to use a workstation,” Hellinger says. “You’re not going to view each dataset with each tool, but on the fly, in real time, it’s important to know instinctively whether something will be better with volume rendering, MIP, MPR, or curved planar reconstruction. All the tools have to be used in collaboration.”

C. Dan Johnson, MD, chair of the department of radiology at the Mayo Clinic, Scottsdale, Ariz, specializes in CT colonography. He emphasizes the importance of learning the ins and outs of each tool. “They all have their advantages and disadvantages,” he says, “and they can all be useful in complete analysis of the colon.”

Johnson recommends striking a balance between 2D and 3D visualization, stressing that both have roles to play in comprehensive interpretation. “With 2D images, you have to put the image together in your mind, so sometimes it takes a little problem solving to determine if there’s a polyp,” he notes, “but the 3D data make discrimination of stool or residual barium from polyps more difficult. The very best interpretation includes a primary 2D review of the axial images, as well as the 3D review.”

Hellinger’s most common cardiovascular CTA applications include pediatric and adult congenital heart disease and congenital and acquired pediatric vascular disease. He uses volume rendering and MIP for angiographic analysis and MPR as the principal tool for diagnosis. Johnson focuses on polyp detection and finds simulated 3D flythrough and virtual dissection to be the most valuable tools in his arsenal. Both Hellinger and Johnson stress, however, that these tools must be used according to their strengths and weaknesses for the best, most efficient interpretation.

“I always tell people to be flexible and apply every tool when appropriate,” Hellinger says. “If you’re not, then there’s no advantage of 3D imaging beyond the source images. We can do everything imaginable to make treatment planning efficient, but it’s really up to the end user. Radiologists have to know the principles of 3D imaging. If they approach it in an educated way, then everything’s in place for efficient interpretation and patient