Impact of the Choice of Native T₁ in Pixelwise Myocardial Blood Flow Quantification

Background: Quantification of myocardial blood flow (MBF) from dynamic contrast-enhanced (DCE) MRI can be performed using a signal intensity model that incorporates T₁ values of blood and myocardium.

Purpose: To assess the impact of T₁ values on pixelwise MBF quantification, specifically to evaluate the influence of 1) study population-averaged vs. subject-specific, 2) diastolic vs. systolic, and 3) regional vs. global myocardial T₁ values.

Study type: Prospective.

Subjects: Fifteen patients with chronic coronary heart disease.

Field strength/sequence: 3T; modified Look-Locker inversion recovery for T₁ mapping and saturation recovery gradient echo for DCE imaging, both acquired in a mid-ventricular short-axis slice in systole and diastole.

Assessment: MBF was estimated using Fermi modeling and signal intensity nonlinearity correction with different T₁ values: study population-averaged blood and myocardial, subject-specific systolic and diastolic, and segmental T₁ values. Myocardial segments with perfusion deficits were identified visually from DCE series.

Statistical tests: The relationships between MBF parameters derived by different methods were analyzed by Bland-Altman analysis; corresponding mean values were compared by t-test.

Results: Using subject-specific diastolic T₁ values, global diastolic MBF was 0.61 ± 0.13 mL/(min·g). It did not differ from global MBF derived from the study population-averaged T₁ (P = 0.88), but the standard deviation of differences was large (0.07 mL/(min·g), 11% of mean MBF). Global diastolic and systolic MBF did not differ (P = 0.12), whereas global diastolic MBF using systolic (0.62 ± 0.13 mL/(min·g)) and diastolic T₁ values differed (P < 0.05). If regional instead of global T₁ values were used, segmental MBF was lower in segments with perfusion deficits (bias = -0.03 mL/(min·g), -7% of mean MBF, P < 0.05) but higher in segments without perfusion deficits (bias = 0.01 mL/(min·g), 1% of mean MBF, P < 0.05).

Data conclusion: Whereas cardiac phase-specific T₁ values have a minor impact on MBF estimates, subject-specific and myocardial segment-specific T₁ values substantially affect MBF quantification.

Level of evidence: 3 TECHNICAL EFFICACY STAGE: 3.