Keywords: Myocardium, Machine Learning/Artificial Intelligence, Motion Correction

Motivation: Cardiac T1 mapping is often limited by the need for breath-holding to prevent motion artifacts, which restricts its use in patients who cannot hold their breath.

Goal(s): To create a self-supervised deep learning method for motion-corrected, free-breathing cardiac T1 mapping without requiring large datasets or worrying about data variability.

Approach: We present a new self-supervised model that combines a signal relaxation model with anatomical constraints and employs the voxel-morph framework for motion correction. Our model's performance was assessed using a publicly available myocardial T1 mapping dataset.

Results: Our approach outperformed other state-of-the-art registration methods in terms of R2, DICE, and Hausdorff distance.

Impact: Our model offers the possibility of extending cardiac T1 mapping to patients who cannot perform breath-hold MRI procedures by ensuring robust motion correction for accurate T1 mapping, all without the necessity for large training datasets or worries about data anomalies.

Keywords: Myocardium, Low-Field MRI, Parametric mapping

Motivation: Myocardial T1 and T2 mapping has emerged as a useful clinical tool for the diagnosis of different heart disease. However, current mapping sequences were mostly developed with 2D breathhold acquisitions and validated at 1.5T or 3T. The investigation of myocardial mapping techniques on more affordable low-field MRI systems is scarce. 

Goal(s): To develop a highly-efficient free-breathing 3D whole-heart joint T1/T2 mapping sequence with isotropic-resolution at 0.55T.

Approach: The proposed sequence acquires 3 interleaved volumes for joint T1/T2 estimation and water/fat separation. 

Results: The proposed sequence shows good agreement with spin-echo reference in phantom and provides comparable results in-vivo with conventional 2D mapping sequences.

Impact: The proposed sequence enables comprehensive 3D joint T1/T2 mapping and water/fat anatomical evaluation of the whole-heart with 2mm isotropic-resolution at 0.55T during a fast free-breathing scan and thus shows promise for the detection of different cardiac diseases. 

Keywords: Myocardium, Heart, Bright- and black blood imaging, T1/T2 mapping

Motivation: Cardiovascular MR (CMR) provides comprehensive assessment of heart disease. However, conventional CMR examinations involve multiple sequential 2D acquisitions under breath-hold conditions.

Goal(s): To devise and develop a novel 3D free-breathing sequence for simultaneous assessment of cardiovascular anatomy via bright- and black-blood imaging and myocardial tissue quantification in a single scan. 

Approach: Implementation of an improved iNAV-based 5-heartbeat interleaved sequence (proACTION) with distinct IR and T2 preparation modules and non-rigid motion correction for robust and accurate myocardial tissue quantification. 

Results: proACTION provides accurate delineation of cardiac and vascular structures, while demonstrating good agreement with conventional mapping sequences in healthy subjects.

Impact: Comprehensive 3D whole-heart tissue characterization and clinically relevant anatomical information can be obtained in an efficient, free-breathing, and easier to use one-click-scan with the proposed proACTION approach.

Keywords: Myocardium, Transplantation

Motivation: To acquire T₁, T₂ and ECV maps in heart transplant recipients using a free-breathing technique that minimizes through-plane motion.

Goal(s): To characterize a free-breathing 2D joint T₁/T₂ cardiac MR fingerprinting technique named PARMA that includes a lung-liver navigator in the patient setting.

Approach: We compared the resulting maps to gold standard maps in a phantom and to clinical routine maps in 10 healthy volunteers and 9 heart transplant recipients.

Results: We found high accuracy in the phantom and high precision in the volunteers and heart transplant recipients.

Impact: This work demonstrates the feasibility of a free-breathing 2D joint T1/T2 MR fingerprinting in a heart transplant recipient population that cannot always perform long breath holds. The navigator allows a free breathing acquisition with limited through-plane motion.

Keywords: Myocardium, MR Fingerprinting, T1 mapping, T2 mapping, cardiovascular

Motivation: Current cardiac MRF sequences have been designed empirically, and thus do not exploit the full flexibility in sequence design of the MRF framework.

Goal(s): The goal of this project is to develop a sequence optimization method for cardiac MRF, which can be applied to shorten the breathhold and diastolic window.

Approach: An optimization method was implemented that simulates MRI signal generation, spiral undersampling, and pattern recognition during each iteration, using a pattern search algorithm to update multiple parameters.

Results: In simulations, phantoms, and healthy subjects, the shortened optimized scan yielded similar myocardial T₁ and T₂ values as a previously described cardiac MRF technique. 

Impact: This study proposes a sequence optimization method for cardiac MRF with many potential applications, including designing shortened scans to reduce breathhold requirements and limit motion artifacts.

Keywords: Myocardium, Cardiovascular

Motivation: Multi-parametric mapping is useful for comprehensive myocardial tissue characterization. However, 3D free-breathing cardiac multi-parametric mapping faces challenges.

Goal(s): Develop a 3D free-breathing cardiac multi-parametric mapping framework that is robust to confounders of motion, fat and field inhomogeneities and validate it for joint T1 and T1ρ mapping at 3T.

Approach: A subject-specific respiratory motion model was constructed to enable intra-bin 3D translational and inter-bin non-rigid motion correction. B1+ inhomogeneities were corrected with optimized dual-flip-angle strategy. A dual-echo Dixon readout was adopted for water-only mapping.

Results: The proposed technique achieved good agreement with conventional techniques in measuring T1 and T1ρ in phantoms and healthy subjects.

Impact: A novel framework was proposed for efficient 3D free-breathing multi-parametric mapping. The 3D simultaneous cardiac T1 and T1ρ mapping technique with scan time of ~ 5 minutes may serve as an efficient tool for diagnosing ischemic and non-ischemic cardiomyopathies.

Keywords: Myocardium, Relaxometry

Motivation: T_1ρ mapping is a promising non-contrast technique for the assessment of myocardial scar. Myocardial T_1ρ mapping techniques commonly acquire multiple images  in one breath hold to calculate a single-slice T_1ρ map. Recently, non-selective adiabatic pulses have been employed for spin-lock preparation (T_1ρ,adiab). FAST1ρ provides a two-fold acceleration for multi-slice myocardial T_1ρ,adiab mapping.

Goal(s): To assess the T_1ρ,adiab map quality of FAST1ρ compared to a single-slice 2D T_1ρ,adiab mapping sequence.

Approach: 10 healthy-volunteers were scanned with FAST1ρ and a single-slice sequence.

Results: FAST1ρ had no significant difference in intra-subject variability or subject-wise precision, to the single-slice sequence, and successfully visualized a myocardial scar.

Impact: FAST1ρ provides a two-fold acceleration for multi-slice myocardial T_1ρ,adiab mapping. It has no significant difference in intra-subject variability or subject-wise precision, compared to a single-slice sequence, and shows promise for characterization a myocardial scar.

Keywords: Myocardium, Cardiomyopathy

Motivation: LGE and ECV are standard cardiac MR (CMR) techniques for detecting focal and diffuse myocardial fibrosis, requiring gadolinium contrast agents. For patients with gadolinium contraindications, non-contrast CMR techniques are needed to detect myocardial fibrosis. 

Goal(s): To evaluate the performance of endogenous T1ρ dispersion imaging for myocardial fibrosis.

Approach: A recently proposed free-breathing T1ρ dispersion imaging technique was employed to image patients with non-ischemic cardiomyopathies. The endogenous parameters, T1ρ, myocardial fibrosis index (mFI), and native T1 were evaluated against LGE and ECV.

Results: T1ρ and mFI were elevated in the LGE region and mFI showed the best correlation with ECV among the tested parameters.

Impact: T1ρ dispersion imaging is a promising CMR technique for detecting myocardial fibrosis without exogenous contrast agents.

Keywords: Heart Failure, Heart, myocardial volume oxygenation consumption

Motivation: Whole-heart myocardial oxygen consumption (MVO₂) is the central factor that determines cardiac function and is a sign of heart diseases.

Goal(s): We proposed a high-resolution, free breathing, cardiac-phase resolved sequence to quantify MVO₂ in the beating hearts.

Approach: Healthy pigs were scanned at 3T. Coronary sinus images were acquired with a continuous, free-breathing, Radial T2Prep-IR sequence with flow compensation and water excitation and a 2D phase contrast sequence to quantify the MVO₂. Invasive ground truth was also measured to verify the accuracy of our estimation.

Results: The proposed method measured comparable SbO₂,OEF,MBF and MVO₂ values to the invasive ground truth.

Impact: The proposed free-breathing, motion-resolved cardiac MR Oximetry technique has the potential to non-invasively measure accurate myocardial oxygen consumption without using ionizing radiation and exogenous contrast agents.

Keywords: Myocardium, RF Pulse Design & Fields, T2ρ, adiabatic RF, rotating-frame relaxometry

Motivation: T_2ρ may provide complementary information between T_1ρ and T₂, but high sensitivity to field inhomogeneities has prevented its application in cardiac MRI.

Goal(s): We evaluated adiabatic T_2ρ preparations for human myocardium mapping at 3T.

Approach: To obtain T_2ρ preparations, adiabatic half-passage pulses were added before and after pairs of hyperbolic secant pulses. T_2ρ mapping was tested and compared  with adiabatic T_1ρ and T₂  maps in phantoms and 5 healthy subjects.

Results: T_2ρ maps yielded similar values to T₂, with improved repeatability and resilience to B₀ and B₁⁺ field inhomogeneities in phantom, and better precision and reproducibility in vivo, complementing T_1ρ.

Impact: Adiabatic T_2ρ preparations enable robust in vivo myocardial T_2ρ mapping at 3T, potentially enabling the use of an alternative rotating-frame relaxation contrast mechanism for cardiac tissue characterization at high field strengths.