Evaluation of Gd-DOTA as a marker for myocardial blood flow using 68Ga-DOTA and 15O-water positron emission tomography

Gadolinium-DOTA and similar MRI contrast agents are suggested as markers for myocardial blood flow (MBF). Contrary to MRI, the PET signal is directly proportional to radioactivity concentration and hence a PET analogue of Gd-DOTA could be used to assess the kinetics of DOTA-based agents without the challenges of measuring Gd concentrations with MRI. The aim of the present work was to assess the suitability of Gd-DOTA as a marker of MBF by comparing 68 Ga-DOTA as a PET analogue of Gd-DOTA to the gold standard for non-invasive measurement of MBF, 15 O-water PET. 24 patients underwent dynamic 15 O-water-PET during rest and pharmacological stress followed by 68 Ga-DOTA-PET and Gd-DOTA dynamic contrast enhanced MRI on an integrated PET/MR scanner. 68 Ga-DOTA-PET was analysed using single-tissue and two-tissue irrreversible compartment models. The DCE MRI perfusion data was analysed using a single-tissue reversible compartment model. K 1 of 68 Ga-DOTA was compared with 15 O-water. Permeability-surface area product for 68 Ga-DOTA was estimated using the Renkin-Crone equation. Kinetics of 68 Ga-DOTA were well-described by a single-tissue compartment model. The permeability surface area product of 68 Ga-DOTA was 0.70+0.15×MBF (mL/cm 3 /min), corresponding to an extraction of around 30% at typical hyperemic MBF values. Average whole myocardium 68 Ga-DOTA K 1 values ranged between 0.35 and 1.36 mL/cm 3 /min compared to 0.68 and 4.55 mL/cm 3 /min for 15 O-water. 68 Ga-DOTA and Gd-DOTA K 1 values showed no significant differences. The correlation between 68 Ga-DOTA MBF and 15 O-water MBF was moderate (r 2 =0.66). Extraction of DOTA is low and depends on flow resulting in a high variability and uncertainty of hyperemic MBF values.