Digirad wins 510(k) clearance for solid-state digital gamma camera

Company now must prove system’s clinical utility

Is nuclear medicine in store for a new era in digital gamma camera design? Industry observers will find out shortly, as gamma camera developer Digirad of San Diego has received 510(k) clearance from the Food and Drug Administration for its Digirad 2020 TC Imager, a new portable gamma camera that uses solid-state digital detectors rather than sodium iodide scintillation crystals and photomultiplier tubes (PMTs).

Digirad's clearance came just days before the start of the Society of Nuclear Medicine meeting in San Antonio, and the firm's technology created a buzz at the conference. For the first time at an SNM show, Digirad displayed a completed prototype of the gamma camera (SCAN 5/28/97), and also showed clinical images from the system, including breast images acquired during studies using Du Pont Merck's Miraluma breast imaging agent (see story, page 1).

Digirad first appeared on the nuclear medicine scene in 1995, when it displayed a solid-state digital detector at the SNM meeting in Minneapolis (SCAN 7/6/95). The company's technology is based on cadmium zinc telluride (CZT) crystals, which, when combined with semiconductor electronics, are able to convert photons into digital signals without the use of PMTs or analog-to-digital converters. Although the technology must still be proven through clinical usage, solid-state detectors are believed to confer advantages in energy resolution, with a full-width half-maximum of less than 5%, compared with 10% to 12% for standard gamma cameras. This means that Digirad's camera collects less unnecessary information and rejects more radiation scatter. The detectors are far lighter than conventional PMT-based detector heads and should prove more reliable as well.

For its first commercial nuclear medicine product, Digirad decided to focus on a portable system. Thus, 2020 TC Imager (formerly known as Notebook Imager) is about the size of an ultrasound scanner, and has wheels attached for easy movement. The camera has one 8 x 8-inch SpectrumPlus detector head, located at the end of a movable arm rather than within a rotating gantry. The detector consists of 64 1 x 1-inch CZT modules, with each module performing the tasks usually conducted by a scintillation crystal, PMT, and analog-to-digital converter. While 2020 TC Imager's detector head is smaller than those on conventional gamma cameras, there is no technological limitation to the size of the detectors Digirad can build, according to Karen Klause, president and CEO.

Due to the relatively small size of the detector head, which results in a 20 x 20-cm field of view, 2020 TC Imager is more suited for organ-specific imaging than whole-body scans. Whole-body studies can be conducted, however, by acquiring data a section at a time, Klause said. Conducting SPECT studies with the system also requires some creativity. The camera has SPECT software on its workstation, and SPECT studies can be conducted by seating the patient in a rotating chair.

The FDA clearance puts Digirad in an enviable position. The company is the only vendor able to market a technology that could truly revolutionize nuclear medicine, and probably does not face any competition for at least the next several years. Digirad believes that it has advantages over other companies developing solid-state detectors, such as GE Medical Systems of Milwaukee and Bicron of Newbury, OH, due to an innovation it made last year that resulted in a 600% increase in the detector's room-temperature photo-peak efficiency compared with other solid-state detectors, Klause said.

Digirad's sales effort won't be a cakewalk, however. The technology is still quite new to clinicians, and will probably require extensive clinical study to be validated. Still, many nuclear medicine physicians are clamoring to get their hands on the system, and the company was encouraged by its booth traffic at the SNM meeting, Klause said.

Digirad plans to sell 2020 TC Imager directly in the U.S., with shipments beginning in the fourth quarter at a list price of around $250,000. The privately held company is in the midst of raising new equity funding with venture-capital firms and investment banks that will enable it to build its sales force and manufacturing capacity, Klause said.

In the future, Digirad is planning to develop new applications for its technology, which could include a gamma camera employing a full-sized gantry. The company would also like to extend its solid-state technology into other modalities, such as bone densitometry, x-ray, and nonmedical applications like industrial materials analysis x-ray and airport baggage detection, according to Klause.