Nuclear cardiology has a new heavyweight contender, a gamma camera with a table capacity of 440 pounds, a gantry bore of 27.5 inches, and digital detectors that make the most of tough situations.
"I have seen a lot of labs, and one of the issues is that, while cameras may do an excellent job of imaging, they have some limitations in terms of heavier or larger patients," said Dr. Gordon DePuey, a professor of radiology at Columbia University and director of nuclear medicine at St. Luke's Roosevelt Hospital Center in New York City. "GE has tried to address that issue with this instrument."
In tests on about 30 patients at St. Luke's, GE Healthcare's latest gamma camera, called Ventri, hammered vintage GE cameras on count rates and clinical results. In these preliminary tests, Ventri, which the company began selling in late January, was 30% to 40% more sensitive, according to DePuey.
"In four of (the 30 patients tested), we saw defects on Ventri that weren't as well defined or that were not seen using the older cameras," he said.
Ventri's superior performance stems directly from its digital detectors, which are essentially small versions of the Elite detectors built into GE's flagship, the general-purpose Infinia gamma camera. The ones on board Ventri measure 14.4 x 7.3 inches. But there is more behind its performance than detectors.
A table cutout, covered with fabric, minimizes attenuation. This cutout corresponds to the area of the chest where the heart is located. The table lowers to allow patients easier access and make positioning easier for technologists.
"You can eyeball the patient and see where you want them to sit, so that when they lie down, the heart falls into that cutout area," said Linda Thompson, chief nuclear medicine technologist at St. Luke's.
Thompson uses a mini-camera, similar to ones used as Web cams, to keep track of patients from her console. The optical camera is mounted on a wall looking from the feet of the patient down the gantry.
A one-piece armrest to reduce strain is another patient-friendly feature. Such innovations are important, not only for patient comfort, but for the quality of the exam.
"Patient motion is perhaps the biggest cause of artifacts in myocardial perfusion SPECT," DePuey said. "Making the patient comfortable and monitoring the patient position should improve image quality."
The New York City hospital, among the first to use the new gamma camera, is waiting on another innovation: a patient "holder" that will help overweight patients lie prone on the table. This position typically is difficult for obese patients to maintain, according to DePuey.
"If you have a big belly, and you try to lie on your stomach, you tend to roll over like Humpty Dumpty," he said.
Ironically, obese patients are precisely the ones who benefit most from prone imaging, which counters diaphragmatic attenuation.
"If you have a protuberant abdomen, your guts push up your left hemidiaphragm, which gets in the way of the inferior wall of the left ventricle. This causes attenuation artifacts, which can lead to false-positive studies," DePuey said. "A very careful examination of the study by an expert observer can get around that. But a way to help is to image the patient prone, because this pushes the diaphragm down and allows the heart to float up so it separates out from the diaphragm."
Ventri relies on a special software program for patients with dextrocardia, a condition characterized by the heart being on the right rather than the left side of the chest. This program guides the detectors, fixed at a 90 degrees angle, to sweep from the patient's left to right side.
More adaptations may be on the way. For example, the modular Ventri might be leveraged to serve as the nuclear component of a hybrid SPECT/CT dedicated to cardiology, according to the company. A slip-ring gantry with an x-ray tube and CT detector could be placed between the table and the ring on which the gamma detectors are mounted.
The first such configuration would likely be just for attenuation correction. But the design could be adapted to support a diagnostic multislice CT capable of performing coronary angiography.
Demand for such a product will have to be proven before GE, known as a conservative, market-driven company, can be expected to develop such a hybrid. The current design of Ventri, dedicated to cardiac SPECT, is likely to dominate for some time to come.
