Myocardial perfusion imaging (MPI) with SPECT has long been an important tool in the assessment of heart conditions, but it has disadvantages such as a lack of specificity and relatively high radiation dose. The rise of PET/CT has created the prospect that more accurate MPI scans could be performed at a lower dose.
A group from the Heart Institute at Intermountain Medical Center, led by cardiologist Dr. Kent Meredith, compared MPI scans performed with a SPECT camera in 2012 to those conducted with a PET/CT system in 2013. There were 197 patients in the SPECT group and 200 patients in the PET/CT group.
The researchers found that PET/CT had 100% sensitivity for detecting myocardial ischemia, compared with 94.6% for SPECT. But it was in specificity where PET/CT really outstripped SPECT, at 88% versus only 30.3% for SPECT.
PET/CT's accuracy was also much higher, with a positive predictive value of 98.3%, compared with 72.9% for SPECT. PET/CT's negative predictive value was 100%, compared with 74.1% for SPECT.
SPECT MPI also delivered false-positive results 6% of the time, while there were no false positives with PET/CT MPI. That translates into fewer follow-up procedures, the researchers noted.
Finally, PET/CT's radiation dose is a fraction of what is delivered during SPECT. SPECT typically uses low-energy radiopharmaceuticals that require longer exam times to acquire enough signal to create an image, according to the researchers. Also, the long half-life of SPECT tracers means they can remain in the patient's system for up to two days, producing an average radiation dose of around 30 mSv.
PET/CT radiotracers, on the other hand, typically have half-lives of two minutes, and their higher energy levels mean that images can be produced more quickly, with a radiation dose of around 2 mSv.
In further research, the group plans to analyze PET/CT's effects on cost reduction and the downstream procedures required for working up patients.
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