Digirad refines solid-state technologyto develop Notebook Imager camera

Firm may license detectors to other vendors

The development of a solid-state digital gamma camera has finallymoved beyond the prototype stage. San Diego-based Digirad introduceda solid-state gamma camera at this week's Society of Nuclear Medicinemeeting that may prove whether the technology is clinically viable.

Digirad made its debut at last year's SNM conference in Minneapoliswith a solid-state detector head and hopes of carving out a successfulniche in a stagnant modality (SCAN 7/6/95). Solid-state camerashold the promise of higher energy resolution than Anger-stylecameras based on photomultiplier tubes, but issues about the highcost of solid-state technology have many vendors and cliniciansconcerned.

Since last year's meeting, Digirad has experienced severalbreakthroughs in its cadmium zinc telluride digital detector technologythat will enable it to offer a solid-state camera at a price hospitalscan afford, according to Karen Klause, president and CEO. Digiradhas improved the detector's room-temperature photo peak efficiency,resulting in a 600% increase in efficiency over solid-state effortsby other vendors, Klause said.

Digirad's detectors, called SpectrumPlus, have been incorporatedinto a gamma camera called Notebook Imager that was on displayin Digirad's SNM booth. Notebook Imager uses a single 8 x 8-inchSpectrumPlus detector head and is appropriate for all nuclearmedicine applications except whole-body bone scans, although itcan perform spot-view bone scans, Klause said. Digirad has contractedwith a third party for nuclear medicine software to process thedata acquired with the detector.

Because solid-state detectors do not require photomultipliertubes or large amounts of lead shielding to register photon events,the detectors are far lighter than conventional detectors. A SpectrumPlusdetector weighs a total of 25 pounds with collimator, and wouldweigh only 11 pounds without. This means that Notebook Imageris a highly mobile system that can be transported to emergencyrooms, according to Klause.

Solid state's big payoff, however, is in energy resolution,which translates into better image quality. A SpectrumPlus detector'sfull-width at half-maximum (the area around a radiopharmaceutical'senergy peak at which the detector collects photon emissions) isless than 5%, compared with 10% to 12% for sodium iodide cameras.This means that Digirad's cameras collect less unnecessary information.

"We can resolve the energy better," Klause said."That is why you get a better quality picture."

Digirad also believes that solid state confers advantages bydispensing with much of the imaging chain that sodium iodide camerasuse to convert analog scintillation events into digital signals.

"Because we've eliminated all the PMT tubes, when thephoton comes out of the patient and hits our cadmium zinc telluridecrystal, it is a direct (digital) conversion," Klause said."Regardless of what (other vendors) say, that they have digitaltechnology, they do not have a true digital camera. They havean analog-to-digital converter on their photomultiplier tubes,so when they deal with the data that goes to the computer, it'sdigital by that point. But they've converted it. Ours is digitalwhen it hits the crystal head."

Custom detectors. Digirad so far has restricted itself to asmall detector size because it has not yet fabricated the gantrythat would be required for a system with a large field-of-view.The company can manufacture detectors of varying sizes and shapesbecause the detector surface is not one large crystal but ratheris an array of 1 x 1-inch modules that contain the readout electronicsrequired for processing photon events. Notebook Imager, for example,has 64 such modules.

Because Notebook Imager does not have a gantry, the systemmust perform SPECT studies by rotating the patient around thedetector, rather than vice versa, as on most conventional cameras.Klause pointed out, however, that rotating upright chairs forSPECT studies are readily available on the market, and NotebookImager's software comes with SPECT processing protocols.

In the future, Digirad plans to develop large field-of-viewdetectors, either for gantries of its own design or those madeby other vendors. When it does, Klause believes that single-headSpectrumPlus cameras will be competitive with multihead sodiumiodide cameras due to solid state's greater efficiency.

"Our product is so much more efficient because of theenergy resolution, that with one head we can scan five times fasterthan with current technology," Klause said.

Digirad plans to market Notebook Imager directly at a pricerange around $250,000 and has filed a 510(k) application for theproduct. The company is not averse to signing OEM deals with othercompanies, however. It is in discussions with some vendors, severalof whom no doubt are looking for a competitive response in casethe solid-state research of GE Medical Systems develops into acommercial gamma camera in the near future (SCAN 7/6/95 and 2/15/95).

"We want to be able to bring this technology to marketas quickly as possible because the bottom line is that it saveshealthcare dollars," Klause said. "If there is an opportunity,through a partnership or relationship, that might allow us tobring the technology to market faster, we will consider it. "