PET vs. SPECT Technology

The future success of PET may be grounded in its inherently better image resolution. In cardiac scanning, it has generally been reported that PET offers a resolution of 5 to 7 mm, compared with a cardiac SPECT resolution of 12 to 15 mm.  Better performance has allowed data to emerge suggesting that as many as one in 10 scans interpreted as normal on SPECT would have been abnormal if done on PET due to the presence of unseen microvascular, triple-vessel disease. PET’s superior diagnostic capability is achieved partly through advances in hardware, particularly quantification, which leverages numerical precision to identify global perfusion defects in the heart that otherwise might be hidden from qualitative SPECT scans.

PET may have an ace in the hole in its ability to quantify results. Quantification is now being built into PET/CTs sold into mainstream medical practices. SPECT scanners lack the resolution of PET/CTs and SPECT vendors have yet to commercialize systems capable of quantification.

A big difference between the two technologies is the half-life of the isotope that each radiopharmaceutical tracer uses. SPECT tracers have a relatively long half-life (technetium-99m has a half-life of six hours), whereas rubidium-82 is only 75 seconds. This short half-life is a limitation of the current front-line
cardiac PET radiotracer, which does not leave much room for error when imaging and presents the inability to do exercise stress testing. 

New iterative reconstruction (IR) software such as UltaSPECT is improving SPECT image quality by boosting the signal-to-noise ratio. Just as in CT scans, IR can also help reduce dose by enhancing lower-quality scans.