Q/A: Rb-82 PET gaining importance in cardiac imaging
Bracco’s CardioGen-82 (Rubidium Rb-82 generator) is the only generator-based PET myocardial perfusion agent approved by the FDA. Health Imaging News discuss the pros and cons of Rb-82 PET in cardiac imaging Gary V. Heller, MD, PhD, director of nuclear cardiology at Hartford Hospital in Conn., and Sharmila Dorbala, MBBS, associate director of nuclear cardiology at Brigham and Women's Hospital at Harvard Medical School in Boston.
What percentage of cardiac imaging is being delayed by the isotope shortage?
Dorbala: Around 10 percent of the imaging is being delayed by isotope shortage.
Heller: We have days in which we can’t get any technetium and days in which we get a limited amount of technetium and both of those occur about four times a month (around 15 percent).
What are the benefits of using Rb-82 PET imaging over technetium?
Dorbala: 1. Availability round the clock (no need to order a dose). 2. Quick imaging protocols (seven minutes per scan). 3. Excellent image quality even in obese individuals. 4. Reduced occupational radiation exposure to staff. 5. Ability to image peak stress left ventricular function.
Heller: 1. Higher image quality and efficiency. 2. It takes two-four hours to do SPECT studies while it takes 20-30 minutes to perform a PET study. 3. Higher diagnostic accuracy.
What are the drawbacks of using Rb-82 PET?
Dorbala: 1. High cost of the generator is the primary concern. 2. We may have limited imaging on patients that are extremely obese or greater than 400 lbs (especially at the end of generator life). 3. We do not have the option of reimaging patients as with Tc-99m radiotracers.
Heller: 1. The tracer is supplied on a monthly basis and a volume of three patients a day is required to make it economically feasible. 2. One cannot perform exercises or form a stress and right now it’s limited to pharmacological stress.
Why is there a delay in switching from cardiac SPECT to PET?
Dorbala: Firstly, the hardware is not widely available as with SPECT and it is more expensive. The inability to use PET with exercise is also a factor limiting the adoption rates. In most institutions, majority of the patients exercise on a treadmill, and half or less are unable exercise and need pharmacological stress. Whereas with SPECT scanner, we could perform either of those stresses, with PET, we are limited to pharmacological. The next main consideration is the fixed monthly cost of the generator.
Heller: If physicians had a choice with all things being equal between PET and SPECT, they would always choose PET because of higher diagnostic accuracy. But because of its instrumentation, expensive camera technology– ($500,000 to $3 million dollars), you can’t set it up in your office and give it a try. There are some companies doing mobile PET and that is becoming very important.
Will Rb-82 PET imaging gain importance in future? If so, what will be the driving force behind the adoption?
Dorbala: Rb-82 PET imaging will gain importance in the future and the likely driving force will be the widespread availability of PET hardware (for oncology applications) combined with the increasing frequency of obese patients, and shortages of SPECT radiotracers. Also, currently there are no other widely available PET perfusion radiotracers (except for sites with cyclotron which can use N-13 ammonia).
Heller: Ease of use and higher diagnostic accuracy are the two driving forces for Rb-82 PET. Next is the technetium shortage and finally is the decline in reimbursement for SPECT which is not happening with PET. This is an important time for PET imaging; the image quality has always been recognised as superior to SPECT and the instrumentation is now becoming available. In the next few years many people will turn to PET because of better instrumentation, better accessibility, better access to radiotracers and new developments coming along with time.