Abstract
ObjectiveOur purpose was to validate an early enhancement time point for accurately measuring the myocardial contrast partition coefficient (lambda) using dynamic-equilibrium magnetic resonance imaging.Materials and MethodsThe pre- and post-contrast longitudinal relaxation rates (reciprocal of T1) of the interventricular septum (R1m) and blood pool (R1b) were obtained from fifteen healthy volunteers and three diabetic patients with hypertension using two optimized T1 mapping sequences (modified Look-Locker inversion recovery) on a 3-Tesla magnetic resonance scanner. Reference lambda values were calculated as the slope of the regression line of R1m versus R1b at dynamic equilibrium (multi-point regression method). The simplified pre-/post-enhancement two-acquisition method (two-point method) was used to calculate lambda by relating the change in R1m and R1b using different protocols according to the acquisition stage of the post-enhancement data point. The agreement with the referential method was tested by calculating Pearson's correlation coefficient and the intra-class correlation coefficient.ResultsThe lambda values measured by the two-point method increased (from 0.479±0.041 to 0.534±0.043) over time from 6 to 45 minutes after contrast and exhibited good correlation with the reference at each time point (r≥0.875, p<0.05). The intra-class correlation coefficient on absolute agreement with the reference lambda was 0.946, 0.929 and 0.922 at the 6th, 7th and 8th minutes and dropped from 0.878 to 0.403 from the 9th minute on.ConclusionsThe time-efficient two-point method at 6–8 minutes after the Gd-DTPA bolus injection exhibited good agreement with the multi-point regression method and can be applied for accurate lambda measurement in normal myocardium.
Highlights
Many previous studies have shown that the myocardial extracellular volume fraction (ECV), known as the distribution volume fraction of contrast (Vd) or fibrosis index, is able to provide information valuable for characterizing myocardial fibrosis and correlates well with histology findings [1,2,3,4,5,6,7,8]
The lambda values measured by the two-point method increased over time from 6 to 45 minutes after contrast and exhibited good correlation with the reference at each time point (r$0.875, p,0.05)
The dynamic-equilibrium cardiovascular magnetic resonance (MR) imaging method has been widely used to calculate l and ECV [4,7,10,11,12,13] based on the longitudinal relaxation rates (R1 = 1/T1) of the myocardium (R1m = 1/T1m) and blood (R1b = 1/T1b) measured both before contrast injection and at plasma– tissue dynamic equilibrium of the contrast agent
Summary
Many previous studies have shown that the myocardial extracellular volume fraction (ECV), known as the distribution volume fraction of contrast (Vd) or fibrosis index, is able to provide information valuable for characterizing myocardial fibrosis and correlates well with histology findings [1,2,3,4,5,6,7,8]. The dynamic-equilibrium cardiovascular magnetic resonance (MR) imaging method has been widely used to calculate l and ECV [4,7,10,11,12,13] based on the longitudinal relaxation rates (R1 = 1/T1) of the myocardium (R1m = 1/T1m) and blood (R1b = 1/T1b) measured both before contrast injection and at plasma– tissue dynamic equilibrium of the contrast agent (the two-point method) This method is derived from a regression method requiring multiple measurements of R1m and R1b at dynamic equilibrium after the contrast is administered [2,14] and is more time-efficient in the clinical setting. The most efficient and reliable timing for the post-contrast R1 measurement remains uncertain
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