Measuring myocardial blood flow with ⁸²rubidium using Gjedde-Patlak-Rutland graphical analysis

Myocardial blood flow (MBF) is measured with ⁸²Rb using non-linear, least-squares computerised modelling. The study aim was to explore the feasibility of Gjedde-Patlak-Rutland (GPR) graphical analysis as a simpler method for measuring MBF.

Patients had myocardial perfusion imaging using adenosine (n = 45) or regadenoson (n = 33) for stressing. Blood ⁸²Rb clearance into myocytes (K₁) was measured from Cedar-Sinai QPET software using the modified Crone-Renkin equation of Lortie et al. (K₁ = [1-0.77 × e^-B/MBF] × MBF) to convert K₁ to MBF (ml/min/100 ml), where B (63 ml/min/100 ml) is myocardial permeability-surface area product. Using aorta or left ventricular cavity (LV) to measure arterial blood ⁸²Rb concentration, blood ⁸²Rb clearance into myocardium (Z) was measured from GPR analysis based on data acquired between 1 and 3 min post-injection. As units of K₁ and Z are, respectively, ml/min/ml intracellular space and ml/min/ml total tissue including extracellular space, myocardial extracellular fluid volume (ECV) is 1 - [Z/K₁]. Using Z/K₁ (see Results) to modify its index, the Lortie equation was changed to Z = (1-0.77 × [Formula: see text]e^-B_Z^/MBF_Z)*MBF_Z, following which MBF_Z was calculated from Z. In GPR analysis, spillover of activity from LV to myocardium conveniently 'drops out' in the intercept of the plot.

Both agents increased myocardial blood flow almost equally. ECV was ~ 35 ml/100 ml at rest, increasing to ~ 40 ml/100 ml after stress. Z/K₁, averaged between stress, rest, stressing agents and arterial ROI, was 0.62, so B_Z was taken as 39 (i.e. 0.62 × 63) ml/min/100 ml. Based on LV, MBF_Z (y) correlated with MBF (x): y = 0.43x + 22 ml/min/100 ml; r = 0.84; n = 156). Their respective stress/rest ratios showed a moderate correlation (r = 0.64; n = 78).

GPR analysis offers promise as a valid and analytically simpler technique for measuring myocardial blood flow, which, as with any clearance measured from GPR analysis, has units of ml/min/ml total tissue volume, and merits development as a polar map display.