Is There a Need for Dedicated PET Imaging Devices?
PET devices have earned dedicated followings in multipurpose imaging in oncology, cardiology and neurology. While PET/CT largely dominates oncology, the demand for PET imaging for specific diseases is increasing, as does the need for low-cost, smaller dedicated scanners in cardiology and neurology.
Among the factors driving demand for dedicated PET in cardiology are the currently limited supply of Tc-99m, the superior diagnostic power of PET over SPECT, the non-feasibility of cardiac PET/CT in cardiology offices, the long-standing uncertainty surrounding cardiac SPECT reimbursement and growing public awareness and concern of radiation dose. New dedicated cameras require smaller doses of tracers and low risk of toxicity, at superior image quality.
“Initially, whole-body SPECT devices were used for cardiac imaging,” recalls Jamshid Maddahi, MD, professor of molecular and medical pharmacology, David Geffen School of Medicine at University of California, Los Angeles (UCLA). “However, as the volume of cardiac SPECT grew, smaller dedicated cardiac SPECT devices were developed.” He sees the same trend beginning to develop in PET.
Current PET devices for cardiac imaging are about five times more expensive than SPECT devices. A dedicated cardiac PET device would clearly narrow that gap in the future, coupled with some clinical advantages. Yet, experts agree that PET/CT is holding its diagnostic edge, namely in CT angiography and other key exams.
In neurology, PET fits the bill nicely in dementia imaging. While referrals are relatively low in most centers compared to the number of oncology patients, existing scanners can already accommodate all neuro referrals, says David S.W. Djang, MD, a nuclear medicine physician at Seattle Nuclear Medicine in Seattle, Wash. However, with the present interest in amyloid imaging, diagnostic applications are on the horizon and this would enhance the interest of scanner manufacturers in neurology, says Adriaan A. Lammertsma, PhD, professor at the department of nuclear medicine & PET Research VU University Medical Centre, Amsterdam, The Netherlands. However, the development of hybrid MR/PET systems may offer new clinical applications in neurology that surpass the utility of a dedicated brain PET system.
Breast imaging is one area where dedicated PET has emerged, with one device currently on the market (Naviscan’s Positron Emission Mammography scanner). A dedicated camera usually costs 10 to 20 percent the cost of a full-size PET camera, says William W. Moses, PhD, senior staff scientist at Lawrence Berkeley National Laboratory in Berkeley, Calif. Performance is much higher as well. The camera is more dose efficient, while the spatial resolution and image quality are significantly better, he adds.
Another limitation of cardiac PET is the expenditure on PET tracers. At present, N-13 ammonia needs an on-site cyclotron with an expensive initial investment (exceeding $1 million) and subsequent operating cost, while the other PET tracer Rubidium-82, requires a generator that costs about $40,000 a month for the lab, shares Maddahi. An 18F-labeled PET perfusion tracer (18F fluorpiridaz), developed by Lantheus Medical Imaging, is currently undergoing clinical trials. Maddahi is the lead principal investigator of the trials and phase 3 studies will begin within the next few months.
Maddahi envisions that a commercial system could be ready for market in two to three years. The combined availability of the new 18F-labeled PET tracer and dedicated cardiac PET device could answer the call to make cardiac PET imaging more practical and economically feasible in the coming years.
Among the factors driving demand for dedicated PET in cardiology are the currently limited supply of Tc-99m, the superior diagnostic power of PET over SPECT, the non-feasibility of cardiac PET/CT in cardiology offices, the long-standing uncertainty surrounding cardiac SPECT reimbursement and growing public awareness and concern of radiation dose. New dedicated cameras require smaller doses of tracers and low risk of toxicity, at superior image quality.
“Initially, whole-body SPECT devices were used for cardiac imaging,” recalls Jamshid Maddahi, MD, professor of molecular and medical pharmacology, David Geffen School of Medicine at University of California, Los Angeles (UCLA). “However, as the volume of cardiac SPECT grew, smaller dedicated cardiac SPECT devices were developed.” He sees the same trend beginning to develop in PET.
Current PET devices for cardiac imaging are about five times more expensive than SPECT devices. A dedicated cardiac PET device would clearly narrow that gap in the future, coupled with some clinical advantages. Yet, experts agree that PET/CT is holding its diagnostic edge, namely in CT angiography and other key exams.
In neurology, PET fits the bill nicely in dementia imaging. While referrals are relatively low in most centers compared to the number of oncology patients, existing scanners can already accommodate all neuro referrals, says David S.W. Djang, MD, a nuclear medicine physician at Seattle Nuclear Medicine in Seattle, Wash. However, with the present interest in amyloid imaging, diagnostic applications are on the horizon and this would enhance the interest of scanner manufacturers in neurology, says Adriaan A. Lammertsma, PhD, professor at the department of nuclear medicine & PET Research VU University Medical Centre, Amsterdam, The Netherlands. However, the development of hybrid MR/PET systems may offer new clinical applications in neurology that surpass the utility of a dedicated brain PET system.
Breast imaging is one area where dedicated PET has emerged, with one device currently on the market (Naviscan’s Positron Emission Mammography scanner). A dedicated camera usually costs 10 to 20 percent the cost of a full-size PET camera, says William W. Moses, PhD, senior staff scientist at Lawrence Berkeley National Laboratory in Berkeley, Calif. Performance is much higher as well. The camera is more dose efficient, while the spatial resolution and image quality are significantly better, he adds.
Making dedicated PET devices
Dedicated PET devices are not a new idea, but a concept coming back in vogue. In the 1980s, a large percentage of the PET cameras built were dedicated neuro cameras. The design concept for the cardiac dedicated PET is similar to the design concept for a dedicated device for neurology, shares Maddahi. “Dedicated [non-CT] PET devices use rod sources, rather than CT, to produce transmission maps for attenuation correction. These devices dominated the market before PET/CT devices became popular due to increasing use of PET in oncology.” The disadvantage of dedicated whole-body PET (non-CT) systems for cardiac imaging was their large size, says Maddahi.Another limitation of cardiac PET is the expenditure on PET tracers. At present, N-13 ammonia needs an on-site cyclotron with an expensive initial investment (exceeding $1 million) and subsequent operating cost, while the other PET tracer Rubidium-82, requires a generator that costs about $40,000 a month for the lab, shares Maddahi. An 18F-labeled PET perfusion tracer (18F fluorpiridaz), developed by Lantheus Medical Imaging, is currently undergoing clinical trials. Maddahi is the lead principal investigator of the trials and phase 3 studies will begin within the next few months.
Maddahi envisions that a commercial system could be ready for market in two to three years. The combined availability of the new 18F-labeled PET tracer and dedicated cardiac PET device could answer the call to make cardiac PET imaging more practical and economically feasible in the coming years.