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Demand for premium nuclear medicine cameras should increase assophisticated techniques such as dual-isotope and monoclonal antibodyimaging proliferate. Realizing the potential of these techniques,however, requires corresponding improvements in camera
Demand for premium nuclear medicine cameras should increase assophisticated techniques such as dual-isotope and monoclonal antibodyimaging proliferate. Realizing the potential of these techniques,however, requires corresponding improvements in camera performance,according to Gary W. Enos, vice president of Twinsburg, OH-basedSummit Nuclear.
Summit Nuclear, a wholly owned subsidiary of Summit World Tradeof Hudson, OH, distributes Hitachi-manufactured nuclear medicinesystems in the U.S. Summit World Trade is also a minority jointventure partner with Hitachi in Hitachi Medical Systems America,which sells Hitachi MRI and ultrasound equipment in this market.
Summit Nuclear and Hitachi work closely on product developmentissues, Enos said. In addition to collaborating with Hitachi onnuclear camera development, Summit designed the Vision nuclearmedicine workstation based on IBM's RS/6000 platform. This computersystem is sold by Hitachi in Japan and other overseas markets(SCAN 7/3/91).
The firms obtained Food and Drug Administration market clearancelast fall for a radically designed digital nuclear medicine systemin both single-head and dual-head configurations (SCAN 10/7/92).Summit had installed 23 dual-head Vision T22 and 20 single-head1024 RZ digital nuclear medicine cameras in the U.S. as of lastmonth, Enos told SCAN.
The RZ camera uses a single 50 x 36-cm detector, while theT22 sports two of the largest rectangular detectors availableon the market, each with 56 x 40-cm dimensions. Both cameras useindividual 10-bit analog-to-digital converters on each photomultipliertube. These converters digitize the nuclear event signals priorto coordinate determination, corrections and other signal processingfunctions, he said.
Most nuclear cameras use a single 8-bit analog-to-digital converterto digitize the signals after PM tube summing. Digitizing thenuclear event signals earlier in the camera process, however,boosts speed and enhances energy and contrast resolution, Enossaid. Digitizing the signal at each PM tube requires multipleconverters: 55 on the RZ and 168 on the T22 (84 on each detector).
Rather than using the traditional analog Anger technique ofsumming and windowing nuclear events, Hitachi's digital camerasuse maximum entropy technology to validate nuclear events at thePM tube, he said.
This technique saves processing time and reduces count loss.A lower count loss provides more counts incident to the crystalfor use in processing and producing the image, Enos said.
Each pixel on a 1024 x 1024-pixel detector grid has its ownx,y location, he said. As nuclear events are received at thatpixel, the camera immediately measures the z energy level. Validevents are decoded and processed. The camera stops analyzing eventswith unacceptable z levels, remaining open for reception of anothervalid event.
"The grid is being looked at always for the maximum energyloci," Enos said. "The locus is known for its energyeven as we begin to determine what its pixel location is. If ithas inappropriate energy, we don't spend the time to go and findthe x,y coordinate."
Since digital signal processing of the nuclear event structurestarts at the PM tube level, technological advances resultingin improved contrast and energy resolution are easily incorporatedin the systems through software upgrades, he said.
INTEREST IN SIMULTANEOUS, DUAL-ENERGY imaging was high at theJune Society of Nuclear Medicine meeting in Toronto, Enos said.However, presenters cautioned that special correction routineswere needed to counter a high level of distortion and energy spill-down.
There might have been fewer caveats regarding dual-energy imagingif researchers had used all-digital systems, Enos said. Digitizingat the PM tube provides a better signal from each tube with knownperformance characteristics over multiple energy levels. Thisimproves both energy resolution and separation of energies.
"Our cameras can simultaneously acquire and have pureregistration of multiple (energy) files," he said.
Summit initiated a dual-energy research effort following theSNM meeting in conjunction with digital Vision users, first withphantoms and then clinical trials of both the RZ and T22 cameras,Enos said. The vendor expects to present a white paper on dual-isotopeimaging to the nuclear medicine community over the next 30 days.The paper will outline both the prerequisites and benefits ofdual-energy work found by Summit users.
While Summit hopes to show advantages of its camera technologyin this clinical arena, it will also be looking for additionalcorrections that can be made to the technology to fine-tune thedigital systems for dual-isotope imaging, he said.
One of the most promising areas for dual-isotope imaging isin cardiac imaging. Several Summit users are injecting thalliumat rest, then stressing the patient and injecting sestamibi. After20 minutes, both the rest and stress studies can be collectedat the same time, Enos said.
Other Vision T22 and RZ users have had success using Cytogen'sOncoScint indium-111 labeled monoclonal antibody cancer agentsimultaneously with technetium or other nuclear agents, he said.Dual-energy imaging can help locate the OncoScint-targeted tumorby superimposing a known structure imaged with the second isotope.
Good energy resolution and a special medium-energy collimatoralso make the digital systems effective in imaging with OncoScintalone, providing a less diffuse image of the tumor and betterboundary definition, Enos said. Eight T22 users--a quarter ofthe installed base--currently use OncoScint on a routine or near-routinebasis.
Prospects for nuclear medicine remain relatively bright despitethe general downturn in medical equipment sales, both becauseof increased interest in biologic disease processes and the relativelylow cost of the technology, he said.
The Vision digital technology adds about $35,000 to the priceof a nondigital single-head Hitachi/Summit camera, Enos said.Even with premium SPECT cameras reaching about $600,000, however,there is a substantial price differential over MRI and other hospitalcapital acquisitions.
Nuclear cameras also have a relatively long life of eight to12 years, he said. When hospitals do replace their planar cameras,they look first to ECT systems, with a preference for multi-headunits.