Elscint uses slip rings to produce 3-D SPECT

Dynamic volumetric SPECT acquisition has been made possible throughthe application of slip-ring technology to nuclear medicine. Elscintintroduced Apex Helix, a continuously rotating dual-head camera,at the Society of Nuclear Medicine meeting in Cincinnati lastmonth.

Free of cables for the transmission of power and image data,slip-ring imaging systems do not have to wind and unwind in back-and-forthrotation. This allows for continuous and rapid image acquisition.Slip rings are used in medical imaging primarily with high-speedcomputed tomography scanners (SCAN 6/6/90).

Helix is the first nuclear medicine camera to use slip rings.The camera also marks the first time Elscint has applied sliprings to any imaging modality, said A. Robert Sohval, executivevice president and general manager of Elscint in the U.S.

Helix can perform four complete 360´ acquisitions in oneminute, compared to an acquisition time as long as 10 minutesfor one 360´ rotation on a conventional SPECT system, hesaid.

The system appears to offer substantial advances in nuclearmedicine diagnosis, although clinical testing of Apex Helix beganonly this month, in Israel. As with three-dimensional MRI andhelical CT, masses of image data may be resliced and processedto reveal additional information. Nuclear medicine physicianscan watch the 3-D image form as the exam proceeds, Sohval said.

The camera's dynamic and rapid acquisition could be beneficialwhen imaging with new, short-life isotopes, such as the technetiumcardiac agents from Du Pont (Cardiolite) and Squibb (Cardiotec),approved for market earlier this year.

"You can watch the uptake and dispersion of Cardiotecdynamically and actually quantify, for example, the washout time.This may provide additional diagnostic information that is inaccessiblewith other SPECT cameras," Sohval said.

The post-acquisition processing capabilities of 3-D SPECT couldalso improve imaging with the technetium heart agents. Since theseagents wash out quickly, it is often difficult to determine whento begin a study on conventional SPECT systems. Washout or uptakeof the agents could be missed if a study is begun too early ortoo late. Since Helix produces a series of images over time, thephysician can start the procedure at any point prior to uptakeand decide afterwards where to begin and end the data processing,he said.

DYNAMIC SPECT INTRODUCES the concept of temporal resolution tonuclear medicine, said Eitan Shaham, Elscint product manager fornuclear medicine.

"You can have SPECT information in short dynamic segmentsand keep track of changes along the time scale. This is impossiblewith cameras that cannot work as fast. This is the first systemthat can deliver true dynamic SPECT," he said.

Image quality can be controlled both as the exam takes placeand in postprocessing, Shaham said. Since the images are of 15-secondduration, it is possible to delete segments with motion artifactsor other distortions while maintaining most of the overall diagnosticinformation, he said.

The advantage of dynamic SPECT lies not so much in faster throughputas in improved diagnostic power. A whole-body 3-D SPECT exam mighttake 20 minutes, or about the time of a conventional planar whole-bodyprocedure. However, much more information is obtained in the 3-Dstudy, Shaham said.

Helix incorporates two types of slip rings. One, using brusheson a copper track, transmits power across the ring. The otheruses a patent-pending infrared optical transmission system forcommunication of the image data. About 80 megabytes of image dataare transmitted per second from the two jumbo, 54-cm-wide detectors,Sohval said.

Each detector has 95 photomultiplier tubes and a speciallydesigned, ultra-flared fanbeam collimator for use with small organslike the brain. The heads can swivel to face the same directionand image two seated patients simultaneously or perform a whole-bodystudy on a standing patient, Shaham said.

Helix should sell for about $500,000, which is in the rangeof most high-end multihead cameras. It is intended as a multipurposecamera for use in whole-body planar and SPECT work, as well asorgan-specific imaging. Elscint plans to install Helix later thisyear at Baptist Memorial Hospital of Memphis, its first U.S. clinicalsite, Sohval said.