Absolute blood contrast concentration and blood signal saturation on myocardial perfusion MRI: Estimation from CT data

Purpose: To determine the optimal contrast injection rate and absolute blood gadolinium concentration for optimal first-pass imaging. Materials and Methods: The concentration of contrast medium in left ventricle (LV) was estimated from dynamic computed tomography (CT) by administering iodinated contrast medium of volume (0.2 mL/kg) equivalent to 0.1 mmol/kg of gadolinium injection in 50 subjects. A blood sample study was performed to determine the relationship between blood signal and gadolinium concentration on per-fusion MRI. Results: The mean peak gadolinium concentration in LV increased as the injection rate increased from 1 mL/sec (3.7 ± 1.2 mM), to 4 mL/sec (6.9 ± 2.7 mM) (P < 0.01). However, no significant improvement was found with an increase in the injection rate from 4 mL/sec to 5 mL/sec (6.8 ± 1.5 mM, P = 0.86). In a blood sample study the linear relationship between blood signal and gadolinium concentration was maintained in the range of ≤0.67 mM (r = 0.992), which corresponds to a peak blood concentration following a 0.01 mmol/kg gadolinium injection. Conclusion: The optimal contrast injection rate for myocardial perfusion magnetic resonance imaging (MRI) appears to be 4 mL/sec. Saturation of arterial input signal is inevitable if the dose of gadolinium contrast medium exceeds 0.01 mmol/kg. These findings are essential for accurate quantification of myocardial blood flow from perfusion MRI.