Abstract
Stress and rest T1-mapping may assess for myocardial ischemia and extracellular volume (ECV). However, the stress T1 response is method-dependent, and underestimation may lead to misdiagnosis. Further, ECV quantification may be affected by time, as well as the number and dosage of gadolinium (Gd) contrast administered. We compared two commonly available T1-mapping approaches in their stress T1 response and ECV measurement stability. Healthy subjects (n = 10, 50% female, 35 ± 8 years) underwent regadenoson stress CMR (1.5 T) on two separate days. Prototype ShMOLLI 5(1)1(1)1 sequence was used to acquire consecutive mid-ventricular T1-maps at rest, stress and post-Gd contrast to track the T1 time evolution. For comparison, standard MOLLI sequences were used: MOLLI 5(3)3 Low (256 matrix) & High (192 matrix) Heart Rate (HR) to acquire rest and stress T1-maps, and MOLLI 4(1)3(1)2 Low & High HR for post-contrast T1-maps. Stress and rest myocardial blood flow (MBF) maps were acquired after IV Gd contrast (0.05 mmol/kg each). Stress T1 reactivity (delta T1) was defined as the relative percentage increase in native T1 between rest and stress. Myocardial T1 values for delta T1 (dT1) and ECV were calculated. Residuals from the identified time dependencies were used to assess intra-method variability. ShMOLLI achieved a greater stress T1 response compared to MOLLI Low and High HR (peak dT1 = 6.4 ± 1.7% vs. 4.8 ± 1.3% vs. 3.8 ± 1.0%, respectively; both p < 0.0001). ShMOLLI dT1 correlated strongly with stress MBF (r = 0.77, p < 0.001), compared to MOLLI Low HR (r = 0.65, p < 0.01) and MOLLI High HR (r = 0.43, p = 0.07). ShMOLLI ECV was more stable to gadolinium dose with less time drift (0.006–0.04% per minute) than MOLLI variants. Overall, ShMOLLI demonstrated less intra-individual variability than MOLLI variants for stress T1 and ECV quantification. Power calculations indicate up to a fourfold (stress T1) and 7.5-fold (ECV) advantage in sample-size reduction using ShMOLLI. Our results indicate that ShMOLLI correlates strongly with increased MBF during regadenoson stress and achieves a significantly higher stress T1 response, greater effect size, and greater ECV measurement stability compared with the MOLLI variants tested.
Highlights
Abbreviations ANOVA Analysis of variance BMI Body mass index balanced steady-state free precession (bSSFP) Balanced steady-state free precession coronary artery disease (CAD) Coronary artery disease cardiovascular magnetic resonance (CMR) Cardiovascular magnetic resonance extracellular volume (ECV) Extracellular volume Gd Gadolinium HLA Horizontal long axis
One participant was excluded after CMR detection of a large, incidental myocardial infarction on Late gadolinium enhancement (LGE) imaging, leaving a total of ten healthy participants (50% female; mean age 35 ± 8 years) included in the study
We demonstrate that: (1) the regadenoson effect can be measured by stress T1-mapping, paving the way to clinical applications similar to those demonstrated previously with adenosine[10,13,35,36]; (2) ShMOLLI stress T1-mapping correlates strongly with myocardial blood flow (MBF) and achieves a greater overall stress T1 response compared to the modified Look-Locker inversion recovery (MOLLI) variants tested; and (3) ShMOLLI ECV can be robustly estimated at lower Gd doses and a wide range of times, and quickly achieves a post-Gd steady-state equilibrium with greater measurement stability over time and less variability compared with MOLLI variants
Summary
Abbreviations ANOVA Analysis of variance BMI Body mass index bSSFP Balanced steady-state free precession CAD Coronary artery disease CMR Cardiovascular magnetic resonance ECV Extracellular volume Gd Gadolinium HLA Horizontal long axis. Sequence selection is an important consideration for stress T1-mapping applications as clinical patients with cardiopulmonary disease may not tolerate such long breath-holds during stress. ShMOLLI uses a 9 heart-beat breath-hold for acquisition, is largely heart-rate independent due to its in-built conditional reconstruction algorithm, and is potentially a ‘one-stop-shop’ T1-mapping sequence for native, stress and post-contrast T1-mapping[19,21]. Underestimation of stress T1 reactivity due to method-dependent heart-rate sensitivity, along with related impacts on measuring post-contrast T1 and ECV after vasodilator stress, has potentially important clinical implications. The current study sought to determine the relationship between the two most widely available short breath-hold T1-mapping methods in normal physiology and has two main aims: 1) to directly compare the relationship between ShMOLLI and MOLLI in terms of their stress T1 response, variability, and effect size; and 2) compare their response with regards to ECV measurement stability over time
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