Srikant Kamesh Iyer 1 , Brianna Moon 2 , Eileen Hwuang 2 , Yuchi Han 3 , Michael Solomon 2 , Harold Litt 1 , 3 , Walter R. Witschey , 1
10 January 2019
Journal of Cardiovascular Magnetic Resonance
Parametric mapping, T1ρ, Compressed sensing, Multicoil reconstruction, Fast minimization, Endogenous contrast techniques
Endogenous contrast T1ρ cardiovascular magnetic resonance (CMR) can detect scar or infiltrative fibrosis in patients with ischemic or non-ischemic cardiomyopathy. Existing 2D T1ρ techniques have limited spatial coverage or require multiple breath-holds. The purpose of this project was to develop an accelerated, free-breathing 3D T1ρ mapping sequence with whole left ventricle coverage using a multicoil, compressed sensing (CS) reconstruction technique for rapid reconstruction of undersampled k-space data.
We developed a cardiac- and respiratory-gated, free-breathing 3D T1ρ sequence and acquired data using a variable-density k-space sampling pattern (A = 3). The effect of the transient magnetization trajectory, incomplete recovery of magnetization between T1ρ-preparations (heart rate dependence), and k-space sampling pattern on T1ρ relaxation time error and edge blurring was analyzed using Bloch simulations for normal and chronically infarcted myocardium. Sequence accuracy and repeatability was evaluated using MnCl 2 phantoms with different T1ρ relaxation times and compared to 2D measurements. We further assessed accuracy and repeatability in healthy subjects and compared these results to 2D breath-held measurements.
The error in T1ρ due to incomplete recovery of magnetization between T1ρ-preparations was T1ρ healthy = 6.1% and T1ρ infarct = 10.8% at 60 bpm and T1ρ healthy = 13.2% and T1ρ infarct = 19.6% at 90 bpm. At a heart rate of 60 bpm, error from the combined effects of readout-dependent magnetization transients, k-space undersampling and reordering was T1ρ healthy = 12.6% and T1ρ infarct = 5.8%. CS reconstructions had improved edge sharpness (blur metric = 0.15) compared to inverse Fourier transform reconstructions (blur metric = 0.48). There was strong agreement between the mean T1ρ estimated from the 2D and accelerated 3D data ( R 2 = 0.99; P < 0.05) acquired on the MnCl 2 phantoms. The mean R1ρ estimated from the accelerated 3D sequence was highly correlated with MnCl 2 concentration (R 2 = 0.99; P < 0.05). 3D T1ρ acquisitions were successful in all human subjects. There was no significant bias between undersampled 3D T1ρ and breath-held 2D T1ρ (mean bias = 0.87) and the measurements had good repeatability (COV 2D = 6.4% and COV 3D = 7.1%).
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