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Spiral CT Offers Better Detection of Disease, More Accurate Staging

Spiral CT Offers Better Detection of Disease, More Accurate Staging

BALTIMORE-The advent of spiral CT offers advantages over regular CT scans, Elliot K. Fishman, MD, said at a conference sponsored by the Johns Hopkins School of Medicine, where he is professor of radiology and oncology.

With spiral CT, Dr. Fishman said, a scan can be completed in a single breathhold, minimizing inconsistencies. By keeping the x-ray turned on and moving the patient, the entire abdomen can be scanned in only 32 to 40 seconds. This faster throughput improves patient cooperation and compliance.

More important, spiral CT creates images with close interscan spacing. Data accumulate as volumes, not slices, so radiologists can sample data at any interval. "Compared to standard dynamic CT," he said, "spiral CT offers increasedsensitivity, more accurate staging, and an increased role in patient care."

Recent advances in spiral CT scanning have highlighted the liver (Figures ), he said. With CT, optimal lesion detection requires separate scans of both arterial and venous phases, to increase the chance of detecting both hyper- and hypovascular tumors. Now, a single spiral CT scan can do both at the same time.

Equipped with a Silicon Graphics work station, Dr. Fishman has used real-time 3D rendering to create vascular maps in less than 10 minutes. "Spiral CT costs only $500 to $600 per scan, compared to $3,000 to $4,000 for an angiogram," he said. "It provides the same information but is far less invasive."

While standard CT usually maps data at 8 mm intervals, spiral CT can go down to 4 mm without additional radiation dose or scan time. This has increased detection by 10% and accuracy by almost a third in both the liver and lung.

Once the lesion is found, Dr. Fishman said, the objective of scanning shifts to patient management. "You can create 3D imaging maps to assess resectability, plan surgery, or simulate surgery in advance."

Spiral CT is proving useful in other disease sites. Research from Japan into gastric carcinomas, for example, indicates that the technique can look at the depth of invasion of the gastric wall.

Spiral CT has also been used to help maximize cortical-medulla differentiation in kidney tumors. For pancreatic cancer, it has proved to be better than 95% accurate in detecting lesions, and 85% accurate for staging. "Overall," he said, "spiral CT offers a tremendous opportunity for surgical planning, monitoring, and rapid tumor volumetrics."

Spiral vs Standard CT

Standard CT scanning and spiral CT differ in the time it takes to acquire the data. With standard dynamic CT, an image is typically obtained in 1 to 2 seconds; this is followed by a 4- to 5-second period in which the table moves to the next positiona. Thus, approximately 8 to 12 scans can be obtained per minute, depending on the scanner used.

With spiral CT, the patient is placed in the scanner and moves at a constant speed through the scanning gantry. Instead of the x-ray tube coming on and off at select intervals, the x-ray tube stays on during the entire process, allowing data to be acquired in a continuous stream.

With spiral CT, the patient needs to hold his or her breath only one time, whereas with dynamic CT, 30 to 50 individual breath-holds may be needed per study, depending on the area scanned.

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