Free‐breathing multitasking multi‐echo MRI for whole‐liver water‐specific T₁, proton density fat fraction, and quantification

Abstract

PurposeTo develop a 3D multitasking multi‐echo (MT‐ME) technique for the comprehensive characterization of liver tissues with 5‐min free‐breathing acquisition; whole‐liver coverage; a spatial resolution of 1.5 × 1.5 × 6 mm3; and simultaneous quantification of T1, water‐specific T1 (T1w), proton density fat fraction (PDFF), and .MethodsSix‐echo bipolar spoiled gradient echo readouts following inversion recovery preparation was performed to generate T1, water/fat, and contrast. MR multitasking was used to reconstruct the MT‐ME images with 3 spatial dimensions: 1 T1 recovery dimension, 1 multi‐echo dimension, and 1 respiratory dimension. A basis function–based approach was developed for T1w quantification, followed by the estimation of and T1‐corrected PDFF. The intrasession repeatability and agreement against references of MT‐ME measurements were tested on a phantom and 15 clinically healthy subjects. In addition, 4 patients with confirmed liver diseases were recruited, and the agreement between MT‐ME measurements and references was assessed.ResultsMT‐ME produced high‐quality, coregistered T1, T1w, PDFF, and maps with good intrasession repeatability and substantial agreement with references on phantom and human studies. The intra‐class coefficients of T1, T1w, PDFF, and from the repeat MT‐ME measurements on clinically healthy subjects were 0.989, 0.990, 0.999, and 0.988, respectively. The intra‐class coefficients of T1, PDFF, and between the MT‐ME and reference measurements were 0.924, 0.987, and 0.975 in healthy subjects and 0.980, 0.999, and 0.998 in patients. The T1w was independent to PDFF (R = −0.029, P = .904).ConclusionThe proposed MT‐ME technique quantifies T1, T1w, PDFF, and simultaneously and is clinically promising for the comprehensive characterization of liver tissue properties.

Golden‐Angle Radial MRI: Basics, Advances, and Applications

“…In addition, stack-of-stars golden-angle radial sampling has also been demonstrated for imaging nonmoving organs in neuroimaging, 51,92 and it is also good for quantitative MRI, such as MR parameter mapping. 48,51,93,94 Stack-of-stars golden-angle radial sampling is often compared against 3D golden-angle Cartesian sampling, in which the phase-encoding steps in the ky-kz plane can be segmented into different interleaves rotated by the golden angle. [95][96][97] The main advantage of the 3D golden-angle Cartesian trajectory is that all k-space data are sampled directly on a Cartesian grid, so that the time-consuming NUFFT is not needed for image reconstruction.…”

“…In particular, the flexibility to provide varying temporal resolution with golden‐angle radial sampling can be exploited to reconstruct the same DCE‐MRI dataset for simultaneous qualitative assessment (with low temporal resolution) and quantitative perfusion analysis (with high temporal resolution). In addition, stack‐of‐stars golden‐angle radial sampling has also been demonstrated for imaging nonmoving organs in neuroimaging, 51,92 and it is also good for quantitative MRI, such as MR parameter mapping 48,51,93,94 …”

Free‐breathing, non‐ECG, simultaneous myocardial T1, T2, T2*, and fat‐fraction mapping with motion‐resolved cardiovascular MR multitasking

“…However, this framework has yet to include T 2 * and fat fraction (FF) mapping in the heart. Multi‐echo extensions of Multitasking for T 1 , T 2 , and T 2 * mapping in the brain 30 and T 1 , R 2 *, and FF mapping in the liver 31 have been described. However, adding multiple echoes after every excitation pulse comes at the price of prolonged scan time and reduced temporal resolution, limiting the direct translation of these multi‐echo extensions to cardiac imaging.…”

Accelerating multi‐echo chemical shift encoded water–fat MRI using model‐guided deep learning

“…Furthermore, the acquisition time for free-breathing multi-parametric imaging can be as long as 5 min. 16 Therefore, accelerated water-fat imaging is an active area of research in the MRI community. 17,18 However, the aliasing artifacts induced by the undersampled data present a major challenge.…”

“…In addition, many patients, including children 14 and adults, 15 are unable to sustain prolonged breath‐holds in abdominal imaging. Furthermore, the acquisition time for free‐breathing multi‐parametric imaging can be as long as 5 min 16 . Therefore, accelerated water–fat imaging is an active area of research in the MRI community 17,18 .…”