Diagnostic and Prognostic Accuracy of Stress SPECT Myocardial Perfusion Imaging With Half the Usual Radiotracer Dose

SPECT MPI is well accepted as a reliable and cost-effective tool for diagnosis, risk stratification and management of patients with suspected or known coronary artery disease (CAD) (1;2). MPI represents approximately 40% of nuclear medicine patient studies and most of these use 99mTc-sestamibi or 99mTc-tetrofosmin(3). Rest/stress MPI using 99mTc-sestamibi and 99mTc-tetrofosmin uses more tracer doses than many other nuclear medicine tests and thus account for >50% of injected radiotracer activity(3). Thus, interruptions in the supply of 99Mo, the parent isotope of 99mTc, significantly affect stress MPI imaging and associated patient care.

Alternatives to 99mTc-sestamibi and 99mTc-tetrofosmin for perfusion imaging include 201Tl for SPECT imaging and 82Rb or 13NH3 for positron emission tomography (PET) imaging (4;5). MPI using 201Tl has similar diagnostic accuracy but image interpretation is more difficult due to greater scatter and attenuation. Moreover, the patient effective radiation dose for MPI using a standard injected dose of 3.5mCi of 201Tl is ~20 mSv. This radiation dose is twice that of 99mTc tracers which typically deliver an effective dose of ~10 mSv. PET imaging with 82Rb or 13NH3 is another alternative, but is much more expensive and not routinely available in Canada due to a very limited install base of PET scanners and associated cyclotrons. The number of SPECT cameras operational in Canada is more than 40 times the number of PET scanners.