Quantitative multi-dimensional assessment of cardiovascular system (qMACS): Technical development (RF_SA_459)

Imaging assessment of the cardiac and aortic structure and function is a key component for diagnosis, risk stratification, and procedural planning in patients with cardiovascular diseases. MR is a versatile imaging modality and holds great potential for comprehensive cardioaortic imaging. We recently introduced an MR Multitasking¹ based 3D multi-dimensional assessment of cardiovascular system (MACS) technique to provide cardiac phase-resolved, multi-contrast imaging of the whole heart and thoracic aorta in a single scan without the need for ECG triggering or respiratory navigation^2,3. However, MACS lacks T1 and T2 mapping and is thus limited in assessing complex vascular and myocardial pathologies. In this work, a quantitative MACS (qMACS) technique was developed to produce T1, T2 maps and co-registered bright blood, dark blood, gray blood anatomical and cine images in a single 10-minute ECG-less, free-breathing scan.

Methods: The qMACS technique resolves respiratory and cardiac motion and provides a wide range of contrast weightings, multi-contrast cine images, and T1 and T2 maps by repeating a magnetization-prepared (inversion-recovery [IR], T2 prepared IR, and T2 preparation) spoiled gradient echo readout series with tiny-golden-angle stack-of-stars k-space sampling and adopting the MR Multitasking imaging framework (Fig. 1). A dictionary based matching method is used for T1 and T2 mapping⁴. The performance of the technique was assessed through phantom studies and in-vivo studies of 12 healthy volunteers and 3 patients.

Results: Fig. 2A shows images of the ventricular chambers (coronal view and short axis view [SAX]) and thoracic aorta (candy-cane view) at the mid-diastolic end-expiration phase in a representative healthy subject. A comparison of the proposed 3D qMACS multi-contrast cine images with breath-hold 2D cine images from a healthy subject is shown in Fig. 2B. Phantom results shown in Fig. 3A demonstrated good quality of qMACS maps. Substantial correlation (R = 0.98/0.99 for T1/T2) and agreement (ICC = 0.99/1.0 for T1/T2) were found between qMACS and reference measurements (Fig. 3B). Fig. 3C shows a comparison between reference and qMACS maps of 3 subjects in different views. Septal T1 values using the proposed approach (1271 ± 42 ms) were higher than those from a 2D MOLLI sequence (1203 ± 28 ms), which is known to underestimate T1, while T2 values from the proposed approach (37 ± 2 ms) were in good agreement with those from a 2D T2-prep GRE sequence (41 ± 2ms). Moreover, end-diastolic volume, end-systolic volume, and ejection fraction measurements from qMACS were in good agreement with those from 2D cine imaging (Fig. 2CD).

Conclusion: This work demonstrates the technical feasibility of multi-contrast qualitative and quantitative imaging of the cardioaortic system with a 10- minute ECG-less, free-breathing scan. Clinical validation in patients with diverse cardiovascular diseases is warranted.