Abstract
T1 mapping is a promising quantitative tool for assessing diffuse cardiomyopathies. The purpose of this study is to quantify in vivo accuracy of the Modified Look-Locker Inversion Recovery (MOLLI) cardiac T1 mapping sequence against the spin echo gold standard, which has not been done previously. T1 accuracy of MOLLI was determined by comparing with the gold standard inversion recovery spin echo sequence in the calf muscle, and with a rapid inversion recovery fast spin echo sequence in the heart. T1 values were obtained with both conventional MOLLI fitting and MOLLI fitting with inversion efficiency correction. In the calf (n = 6), conventional MOLLI fitting produced inconsistent T1 values with error ranging from 8.0% at 90° to 17.3% at 30°. Modified MOLLI fitting with inversion efficiency correction improved error to under 7.4% at all flip angles. In the heart (n = 5), modified MOLLI fitting with inversion correction reduced T1 error to 5.5% from 14.0% by conventional MOLLI fitting. This study shows that conventional MOLLI fitting can lead to significant in vivo T1 errors when not accounting for the lower adiabatic inversion efficiency often experienced in vivo.
Highlights
Myocardial T1 mapping is a non-invasive MRI based tissue characterization technique that uses measurements of the T1 relaxation time in the heart for diagnosis and treatment
Our in vivo data showed that conventional Modified Look-Locker Inversion Recovery (MOLLI) (Eq.1) provided fairly inaccurate and inconsistent in vivo T1 values in muscle tissues when compared with the standard spin echo based methods
The correction for apparent T1 used in the conventional MOLLI fitting was originally derived for spoiled gradient echo (SPGR) Look-Locker imaging assuming 100% inversion efficiency and may not be adequate for describing a more complicated balanced steady-state free precession (bSSFP) signal evolution in MOLLI (Fig.1), especially at reduced inversion efficiency
Summary
Myocardial T1 mapping is a non-invasive MRI based tissue characterization technique that uses measurements of the T1 relaxation time in the heart for diagnosis and treatment. The MOLLI (Modified Look Locker Inversion Recovery) sequence [10] is a fast 2D inversion recovery (IR) balanced steady-state free precession (bSSFP) based T1 mapping method for cardiac imaging that is increasingly being used to probe differences between healthy and diseased states in the myocardium. While the accuracy of MOLLI has been studied extensively using computer simulations and water phantoms [10,11,12,13], a direct comparison of MOLLI with the gold standard IR spin echo (IR-SE) method has not yet been performed in vivo, where tissues may behave differently from water phantoms. This work aims to quantify MOLLI accuracy in vivo by comparing with the accurate but time-consuming gold standard IR-SE sequence in the calf muscle and with a rapid IR fast spin echo (IR-FSE) sequence in the heart of healthy volunteers. We quantified the effect of correcting for imperfect inversion efficiency [13,14,15] on the T1 accuracy of MOLLI
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