December 2, 2003
DFCI adds new combined PET/CT scanner to help physicians pinpoint cancers with extreme accuracy
A new "hybrid" whole-body scanner just entering service at Dana-Farber will enable patients to undergo two types of scans in the same machine, producing a combined image that enables physicians to pinpoint cancers with extreme accuracy.
The PET/CT machine, which went on line in early November after months of construction on floor L2 of the Dana Building, will also reduce the waiting list for patients needing scans in DFCI's existing, single-purpose PET machine.
Both CT (computed tomography) and the newer PET (positron emission tomography) have added valuable dimensions to cancer diagnosis, but each has limitations. A CT scan is a series of X-rays taken sequentially along the length of the body, producing images that resemble cross sections of organs and other structures. CT gives sharp views of anatomical features and differentiates between types of soft tissue, bone, and blood vessels. The technique reveals lesions, tumors, and metastases.
PET scans, meanwhile, focus more on how structures behave than on how they look. They detect the metabolic activity of tissues — how rapidly they are consuming the sugar that fuels biological growth. Cancerous tissue gulps sugar at a high rate, which shows up on PET scans as bright areas. PET can distinguish between dead scar tissue and active cancer, and detect cancers at a smaller, earlier stage than CT. However, PET lacks the power to clearly show those anatomical structures — particularly in the abdomen — that serve as landmarks for doctors in pinning down the tumor's location.
In a single test, the new hybrid machine produces a CT scan (left), a PET scan (center), and a fused image of both (right).
Brigham and Women's Hospital has installed an identical hybrid device, and this will enable oncology staff from BWH and DFCI to schedule patients more effectively because the two services are now united, explains Annick Van den Abbeele, MD, director of Nuclear Medicine at Dana-Farber. In October, she also assumed the responsibility for directing the Nuclear Medicine Oncology Program for the joint Dana-Farber-BWH program.
"We will now have access to three PET scanners: two PET/CT and a high-end dedicated PET scanner," Van Den Abbeele says. "The idea is to provide seamless, integrated services in nuclear medicine oncology so that patients can be seen on both sides of the street [DFCI and BWH] and have no difference in the quality of services."
Top to bottom, a CT scan, PET scan, and fused image from the same patient as shown above.
Fused images
Before the development of the hybrid PET/CT machines several years ago, patients would have a CT scan on one machine and a PET on another. Imaging experts would then compare the images, with the CT providing the physical landmarks for precisely locating the PET findings. However, even small body movements or changes in internal organs when switching between scans can reduce the tests' accuracy. "It is very difficult to duplicate a patient's position perfectly between two different systems," says Van den Abbeele.
With the combined machine, PET and CT scans are performed in one setting, one after the other, in an enlarged enclosure tube designed to reduce patient stress. When the resulting scans are superimposed and blended with computer software, they form a "fused image" that shows the bright cancerous areas in exact spatial relation to the patient's anatomy.
The two-in-one machine is also faster, producing a combined scan in 30-45 minutes compared with 70 minutes for the solo PET scanner, says Van den Abbeele. "This will allow us to scan more patients and easily access this important technology." The new equipment, manufactured by General Electric, cost more than $2 million.
According to Van den Abbeele and Rick Tetrault, administrative director of Nuclear Medicine, the machine demonstrated its advantages in the first few patients scanned. One had a history of lymphoma and was being studied for a mass in his chest wall, but the combination scans turned up something entirely unsuspected. "On the CT scan, there was a dark area that looked like fluid in the lungs," explains Van den Abbeele. "But when we examined the PET and the PET-CT fused images, we could see [because of brightness on the image] that it was a new tumor that had started to invade the space around the spinal cord [shown clearly in the CT scan]."
This finding prompted a significant change in the treatment approach for that patient, she says, "and it offered one example of how the combined anatomic and functional information provided by the PET/CT can make a major impact on the management of patients."
