Accelerated multi‐snapshot free‐breathing mapping based on the dual refocusing echo acquisition mode technique (DREAM): An alternative to measure RF nonuniformity for cardiac MRI

Abstract

Background: Field inhomogeneities in MRI caused by interactions between the radiofrequency field and the patient anatomy can lead to artifacts and contrast variations, consequently degrading the overall image quality and thereby compromising diagnostic value of the images. Purpose: To develop an efficient free-breathing and motion-robust B + 1 mapping method that allows for the investigation of spatial homogeneity of the transmitted radiofrequency field in the myocardium at 3.0T. Three joint approaches are used to adapt the dual refocusing echo acquisition mode (DREAM) sequence for cardiac applications: (1) electrocardiograph triggering; (2) a multi-snapshot undersampling scheme, which relies on the Golden Ratio, to accelerate the acquisition; and (3) motion-compensation based on low-resolution images acquired in each snapshot. Study type: Prospective. Phantom/subjects: Eurospin II T05 system, torso phantom, and five healthy volunteers. Field strength/sequence: 3.0T/DREAM. Assessment: The proposed method was compared with the Bloch-Siegert shift (BSS) method and validated against the standard DREAM sequence. Cardiac B + 1 maps were obtained in free-breathing and breath-hold as a proof of concept of the in vivo performance of the proposed method. Statistical tests: Mean and standard deviation (SD) values were analyzed for six standard regions of interest within the myocardium. Repeatability was assessed in terms of SD and coefficient of variation. Results: Phantom results indicated low deviation from the BSS method (mean difference = 3%). Equivalent B + 1 distributions for free-breathing and breath-hold in vivo experiments demonstrated the motion robustness of this method with good repeatability (SD < 0.05). The amount of B + 1 variations was found to be 26% over the myocardium within a short axis slice. Data conclusion: The feasibility of a cardiac B + 1 mapping method with high spatial resolution in a reduced scan time per trigger was demonstrated. The free-breathing characteristic could be beneficial to determine shim components for multichannel systems, currently limited to two for a single breath-hold.

3D Free‐breathing multichannel absolute Mapping in the human body at 7T

“…Furthermore, the method has also been used to show respiration‐induced changes in the human body at 3T 38 . However, the DREAM mapping technique is very sensitive to flow‐induced artifacts, 39 which has also been confirmed by our own experiments, and it has a limited dynamic FA range 9 . Less flow/motion sensitivity has been observed by AFI.…”

Free‐breathing 3D cardiac T1mapping with transmit B1correction at 3T

“…Notice the similarity in estimated T 1 values for each tissue type (e.g., myocardium, liver, muscle) even with significant variations in estimated across different regions (Figure 9A). The 3D maps of the heart (Figure 9B) show larger values in lateral/anterior regions than septal/inferior regions, which is consistent with literature 39 . Group analysis of maps acquired from all subjects is shown in Figure 10.…”

“…These observations were consistent throughout simulation, phantom, and in vivo results. The estimated B + 1 values of the myocardium show spatial variations that are consistent with those reported in literature 39 (i.e., the B + 1 values in the lateral/anterior regions were 10%-30% larger than the septal/inferior regions). However, the B + 1 distributions within the blood pool should be carefully interpreted, as flow effects were not considered in joint T 1 and FA estimation.…”

“…The 3D B + 1 maps of the heart (Figure 9B) show larger B + 1 values in lateral/anterior regions than septal/inferior regions, which is consistent with literature. 39 Group analysis of B + 1 maps acquired from all subjects is shown in Figure 10. B + 1 variation ranged from 21%-32% and 11%-15% across the septal-lateral and inferior-anterior regions of the myocardium in the left ventricle, respectively.…”

Cartesian dictionary‐based native T1and T2mapping of the myocardium

“…The Multimapping B 1 maps were validated in three healthy subjects in which B 1 mapping was performed using the single-shot dual refocusing echo mode (DREAM) technique, 35,36 in addition to the Multimapping technique. Details of the B 1 mapping validation experiments are provided in Supporting Information Section 3.…”