Validation in the canine model of a new non-invasive method of measuring coronary blood flow reserve: Split dose thallium-201 rest/stress imaging

Diffusely impaired coronary blood flow reserve is difficult to measure non- invasively. We developed and tested a quantitative non-invasive method of m easuring coronary blood flow reserve using thallium-201 perfusion imaging. Ten anesthetized dogs were injected simultaneously at rest with thallium-20 1 and either Ru-103 or Sn-113 microspheres. SPECT images were obtained foll owed by varying doses of intravenous adenosine, and a second thallium-201 d ose was injected simultaneously with either Nb-95 or Sc-46 microspheres. SP ECT images were then repeated. The heart was removed, sectioned and counted , along with arterial blood samples. Blood flow was calculated at rest and stress. Peak resting counts in four regions in each of three SPECT slices w ere subtracted from stress values and stress/rest thallium-201 count ratios (coronary flow reserve (CFR)) were calculated and correlated with the corr esponding microsphere flow ratios. Overall correlation of the imaging and m icrosphere flow ratios was 0.77 (p = 0.0001). Regional correlation coeffici ents ranged from 0.65-0.86 (p = 0.0001). Coronary blood flow reserve ratios by the microsphere method ranged from 0.7 to 5.3, and by thallium-201 imag ing from 0.33-2.45. The non-invasively measured coronary blood flow reserve with thallium-201 imaging and adenosine stress correlates well with micros phere-measured coronary blood flow reserve over a wide range of coronary fl ows, and should be useful in clinical studies of CFR impairment.