ADAC battles triple-head vendors over cardiac turf

ADAC Laboratories reported last month that sales of its new GenesysVertex variable-angle dual-detector camera are boosting the company'sfinancial results. Vertex spearheaded strong growth in ADAC'sthird-quarter revenues, leading the company to claim that dual-headcameras will take a big bite out of triple-head sales.

Triple-head vendors are quick to dispute ADAC's contention,however, and several have a few tricks up their sleeve to defendtriple-head's competitive position.

Milpitas, CA-based ADAC reported third-quarter revenues of$39.7 million (end-June), an increase of 28% over last year'sfigure of $31.1 million. Net income was $4.5 million, comparedto net income of $3.5 million in the same period a year ago, a29% increase.

ADAC has installed Vertex at two beta sites and reported thatit plans to ship 15 Vertex units this quarter. The performanceof the beta-site units demonstrates that adjustable dual-headtechnology lives up to expectations, according to the company.Vertex cut scanning time from 25 minutes per scan to 8.5 minutesat its beta site at St. Clair Memorial Hospital in Pittsburgh.

"For the first time, you're seeing proof that (adjustabledual-head) works," said David L. Lowe, president and COO."The fact that it offers a significant throughput advantageis validated."

Vertex doubles throughput for bone scans, which constitute38% of all nuclear medicine studies, according to ADAC. Vertexis also 33% faster than triple-head cameras for cardiac studies,and that spells trouble for the triple-head segment, Lowe said.

"According to our estimates, 90% of all triple-head camerasprocured were financially justified based on their ability todo cardiac single-photon emission computed tomography," Lowesaid. "Vertex improves cardiac SPECT beyond that of a triple-head,plus it provides the flexibility of doing total body with thesame throughput capabilities of a dual-head camera. We expectthat the introduction of Vertex will cannibalize a great numberof triple-head sales."

Not surprisingly, that position is disputed by vendors of triple-headcameras.

The time advantage for dual-head cardiac studies is minimaland applies only to a limited number of procedures, accordingto James L. Besett, general manager for Picker International'snuclear medicine division. The image quality of triple-head camerasis also higher than that of an adjustable dual-head cameras becauseof the triple-head's smaller field-of-view, Besett said.

"An (adjustable dual-head camera) cannot make up for thefact that its basic spatial resolution is not nearly as good asa triple-head," Besett said. "There's quite a differencein image quality."

PICKER AND OTHER VENDORS are taking advantage of the triple-headcamera's third detector to solve a long-time medical imaging dilemma:the attenuating effect of human anatomy on diagnostic images.

In cardiac SPECT, attenuation artifacts from the anterior wallof the heart and other anatomical structures interfere with signalsfrom the posterior wall of the heart. Such artifacts can resembleperfusion defects, according to Besett.

One technique to compensate for posterior wall artifacts issimultaneous transmission-emission attenuation correction. Thetechnique is intended to improve image quality by correcting signalattenuation caused as gamma rays pass through the body from theback wall of the heart. Both Picker and Siemens are developingattenuation-correction techniques.

The method involves the use of two sources of radioactivityduring a scan: the injected radiopharmaceutical and a line sourceof radioactivity mounted in a ring opposite one of the triple-head'sdetectors. As the camera makes its sweep around the patient, thethree detectors acquire emissions from the radioisotope injectedinto the patient. At the same time, the detector opposite theline source acquires gamma rays transmitted from the source.

Data from the line-source transmissions are used to measurethe attenuation patterns of the body near the heart. The dataenable physicians to reconstruct the amount of attenuation causedby anatomy during cardiac SPECT.

"What this does in the final image is eliminate the posterior-wallartifact of cardiac imaging," Besett said. "That isone of the last obstacles (in cardiac SPECT) to overcome."

Triple-head cameras are well suited for attenuation correctionbecause the technique can be performed simultaneously with thecardiac scan. Single-head and dual-head cameras are capable ofattenuation correction, but must perform a second scan of thepatient to acquire data for the attenuation map. Such a proceduretakes twice as long and can be less accurate if the patient movesduring the procedure.

Triple-head cameras will require some modification to performsimultaneous emission and transmission attenuation correction.In addition to mounting a line-source holder on the camera's gantry,the technique will require the use of special collimators. Picker'sapproach uses cardiac fan-beam collimators, while Siemens employsa recently developed cone-shaped collimator.

Picker plans to display its version of the technique, calledsimultaneous emission/transmission processing (STEP), at thisyear's Radiological Society of North America meeting in November.A Siemens product based on the method is six to 12 months away,according to Eric Woronowicz, group product manager for Siemens'nuclear medicine division.

Attenuation correction SPECT should help nuclear medicine resistinroads other modalities are making into cardiac imaging, Woronowiczsaid.

"Nuclear medicine is under the gun from other modalitiesto produce better images," Woronowicz said. "If we don't,then we'll be in trouble. We'll lose heart business from echocardiographyand MRI. We have to produce better images, and everybody realizesthat."