Dynamic Fractional Myocardial Blood Volume Mapping Using Ferumoxytol-enhanced CMR Multitasking with Subspace Dose Harmonization
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Published on: May 24, 2021
Thomas A Coudert1, Arutyun Pogosyan1, Zhengyang Ming1
1Division of Cardiology, David Geffen School of Medicine at UCLA and VA Greater Los Angeles Healthcare System, Los Angeles, California, USA; Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, California, USA; Department of Bioengineering, University of California, Los Angeles, California, USA; Physics and Biology in Medicine Graduate Program, University of California, Los Angeles, California, USA.
Background:
Fractional myocardial blood volume (fMBV) represents the vascular compartment within myocardial tissue and may reflect changes in microvascular status and health. Conventionally derived from multi-dose Modified Look-Locker Inversion (MOLLI) recovery T1 mapping with ferumoxytol, MOLLI-based fMBV requires repeated breath-holds, inter-dose image registration, and static end-diastolic estimates. CMR Multitasking enables free-breathing, non-electrocardiogram (ECG)-gated imaging and offers a subspace that captures shared motion and contrast dynamics. This subspace representation can be exploited to harmonize multi-dose acquisitions directly in parameter space, enabling motion-resolved dynamic fMBV mapping while reducing reliance on post-hoc image-space registration.
Methods:
Thirteen healthy volunteers (11 females, 28.2±10.0 years) and twelve ischemic heart disease (IHD) patients (1 female, 67.2±7.1 years) underwent multi-dose ferumoxytol imaging at 3.0T using both breath-held ECG-triggered 5(3)3(3)3 MOLLI and free-running 2-dimensional Multitasking T1 mapping sequences. MOLLI-Multitasking agreement was assessed in healthy volunteers; patient data were used for exploratory dynamic fMBV analysis. Multitasking data were harmonized across respiratory- and cardiac-motion subspace dimensions for cross-dose alignment. Pixel-wise fMBV was estimated using a two-compartment water exchange model. fMBV agreement with MOLLI was assessed using Bland-Altman analysis. Dynamic fMBV changes were also evaluated from the Multitasking data. In IHD patients, fMBV kinetic metrics (upslope and diastolic-to-systolic distribution) for cycle-dependent variation in dynamic fMBV were computed to assess systolic compression and diastolic recoil. Cardiac positron emission tomography (PET) derived perfusion and CMR-derived strain and late gadolinium enhancement served as references.
Results:
In healthy volunteers, Multitasking produced motion-resolved fMBV maps with strong MOLLI agreement (bias -0.11%, p=0.84). Subspace harmonization reduced cross-dose variability and aligned cardiac phases. Healthy subjects showed significant diastolic-to-systolic variation (10.55±2.12% vs. 7.73±2.76%, p=0.0004). In IHD patients, ischemic segments exhibited elevated diastolic fMBV with significant systolic compression (16.36±3.44% vs. 10.01±2.24%, p=0.013), remote myocardium showed similar phasic variation (11.16±0.68% vs. 7.98±0.57%, p<0.0001). At the same time, scar demonstrated reduced fMBV with attenuated modulation (7.74±1.95% vs. 5.59±1.97%, p=0.099). Abnormal dynamic fMBV regions corresponded to PET defects and impaired circumferential strain.
Conclusion:
Ferumoxytol-enhanced Multitasking with subspace harmonization enables free-breathing, cardiac-resolved dynamic fMBV mapping, overcoming practical limitations of MOLLI-derived fMBV. This approach enables non-invasive assessment of dynamic myocardial blood volume across the cardiac cycle, with potential utility for characterizing microvascular function in ischemic heart disease.
