Picker adds momentum to digital SPECT conversion

Picker International took the plunge into digital scintillationcamera design with the introduction of sweeping changes to itsPrism SPECT camera series introduced at the RSNA meeting thismonth.

Digital components were featured on the Picker single-headPrism 1000XP, dual-head 2000XP and triple-head 3000XP. The PrismXP series is covered by existing Food and Drug Administration510(k) approvals, according to Norman Yager, Picker manager ofquality assurance and regulation. Sales commenced immediatelyafter the RSNA show.

The Prism XP series takes its cue from digital systems introducedin 1992 by Summit Nuclear and ISIS of Quebec. Like those systems,the Prism XP cameras feature analog-to-digital signal conversionfollowing the completion of photomultiplication at each of thedetector head's 49 photomultiplier tubes.

"Signals from each PMT are digitized," said JamesL. Besett, general manager of Picker's nuclear division. "Theentire output of the imaging electronics is digital."

Pulse-height analysis is performed digitally, but unlike theSummit and ISIS offerings, the Prism XP cameras still use theconventional approach developed by physicist Hal Anger to handledata summation and averaging tasks that go into image localization.

Picker makes few claims about image quality enhancements tobe gained from the new approach, beyond noting an expected three-foldincrease in count rates to 243,000 counts per second at the 20%window, according to Besett. The company also refers to generalimprovements in uniformity, linearity and energy correction.

The company's sales promotion for the XP series revolves aroundsystem size and complexity reductions, easy maintenance and performancefeatures that enable the introduction of simultaneous transmission-emissionprotocols for photon attenuation correction on the Prism 3000XP.

By eliminating one of every four components, Picker has madethe XP series far more compact than the old Prism product line.Acquisition circuit boards previously housed in a stand-alonecabinet are now located in a compartment attached to the sideof the scanner. The acquisition terminal was eliminated by transferringits functions to Picker's Odyssey workstation.

Going digital also introduced opportunities to convert to laptopcomputer service and remote diagnostics.

"We can now call up any of our cameras on a phone modemline with a simple laptop at the other end of the phone and inquireabout temperatures, potentiometer settings, and other performancemeasures. And we can effect a change over the phone because wehave more software control," Besett said.

Additional software control, especially in digitally definingenergy windows through which photon energy is analyzed, was theultimate goal for the designers of the Prism XP, Besett noted.That objective had to be met before Picker could introduce STEP,a photon attenuation correction technique aimed at increasingconsumer interest in Picker's triple-head Prism 3000XP.

During STEP, the scanner images two different photo peaks simultaneously:one from an external line source, such as gadolinium; the otherfrom an emission source, such as thallium-201, which is ingestedby the patient. By comparing the two waveforms, the system cancompensate for the effect of photon attenuation, which can distortthe results of cardiac studies.

Picker applied for FDA clearance to market STEP about a monthbefore the RSNA conference, according to David J. Archibald, nuclearmarketing manager. Archibald moved to Picker last month from Siemens'nuclear medicine division, where he had served as vice presidentand general manager until 1992.

Like Picker, ISIS stressed convenience over image quality intouting the capabilities of Isocam 2, its digital, dual-head workin progress. Peter deLuca, CEO of the Canadian company, citedfeatures such as autocontouring, automatic collimator changingand automatic quality assurance checks that were made possiblebecause of robotic components built into the gantry. The variable-anglesystem operates without the oscillating patient-bed requirementsfound on other 90/180´ variable dual-heads.

"These features add up to greater throughput and lessdowntime," said Frank J. Genova, general manager of Osiris,the U.S. subsidiary of ISIS.

The real advantage of the Isocam may lie in its 22.5 x 16.5-inchfield-of-view detectors. Daniel Gagnon, ISIS director of technology,digitized the signal at the point of each PMT to develop algorithmsthat consider more variables affecting the point of origin ofscintillation events than can be measured with conventional cameras.As a result, resolution improves because the system can pinpointthe source of radiation more accurately, Gagnon said.

The company claims resolutions of 2.5 mm full width, half maximum.That performance compares with resolutions of no better than 3.3FWHM for the best conventional Anger cameras, according to industrysources.

While this was the first time RSNA participants could see theIsocam 2, ISIS itself has had an industry presence since the unveilingof the single-head digital Isocam 1 as a works-in-progress atthe 1991 Society of Nuclear Medicine show. The FDA cleared thesystem for sale in February 1992. The first U.S.-based systemwill be installed this month, Genova said.

Iain Stark, a former president of the North American subsidiaryof Scottish gamma camera manufacturer Scintronix, recruited investorsto form ISIS after devising the company's digital approach tocamera design. He was joined by Terrence A. Mailloux, formerlythe executive general manager of health-care operations for HoechstCanada (SCAN 9/23/92). Mailloux left ISIS in February. Stark iscurrently employed part-time as chairman.

Major ISIS shareholders include Park Meditech, a Toronto-basedinvestment company, and Analogic, the Peabody, MA, imaging systemcomponents manufacturer. Analogic has in recent years turned toinvesting in imaging manufacturing concerns, such as Isis andB&K Medical, the diagnostic ultrasound company (SCAN 7/14/93).Park Meditech, which held 39% of ISIS as of March 1993, is movingtoward acquiring a majority interest, according to deLuca.

Summit Nuclear, the first company to introduce an all-digitalwhole-body gamma camera in the U.S., is looking to increase itslead in this emerging market segment. The Twinsburg, OH, company,which markets the Vision 1024RZ and Vision T-22 in the U.S. throughan agreement with Hitachi, has installed 50 systems since introducingthe Vision cameras at the 1992 RSNA conference.

The 1024RZ and T-22 are the most expensive systems in theirclasses. The T-22 costs about $50,000 more than competing nondigitaldual-head cameras, according to Gary Enos, vice-president. TheT-22 costs about $150,000 more than the single-head 1024RZ.

But high cost has not proved to be a significant liability,given the high resolution and wide field-of-view of these systems,Enos said.

"If customers can't justify spending $500,000 for theT-15, they often buy our single-head system, because they don'twant to give up on the software control and image resolution gainedthrough these systems," he said.

Summit featured the fourth revision level of its image processingsoftware at the RSNA conference. Four additional revisions areplanned for 1994. They include advancements in 511-keV imagingand multiple isotope imaging.