Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
-
To present and validate a new method that formalizes a direct link between k-space and wavelet domains to apply separate undersampling and reconstruction for high- and low-spatial-frequency k-space data. ⋯ The proposed method improves the reconstruction accuracy of high-spatial-frequency signal content and avoids incoherent artifacts in low-spatial-frequency regions. This new formulation also reduces the reconstruction time due to the smaller problem size.
-
Transverse relaxation (T2 ) mapping has many applications, including imaging of iron accumulation in grey matter. Using the typical multiecho spin-echo sequence with long echo trains, stimulated echo compensation can enable T2 fitting under conditions of variable radio frequency homogeneity arising from slice profile and in-plane radio frequency variation. Substantial reduction in the number of refocusing pulses could enable use at high magnetic fields where specific absorption rate is a major limitation, and enable multislice use with reduced incidental magnetization transfer at all field strengths. ⋯ All territories produce marginal results when using standard exponential fitting. Savings from reduced echoes can be used to substantially increase slice coverage. In multislice mode, the resulting incidental magnetization transfer decreased brain signal but had minimal effect on measured T2 values.
-
Arterial spin labeling has been developed and used for the quantitative and completely noninvasive assessment of myocardial perfusion in vivo. Here we propose a novel arterial spin labeling method called cine-ASL, which is based on an electrocardiogram-gated steady-pulsed labeling approach combined with simultaneous readout over the cardiac cycle using cine-fast low-angle shot. This method led to shorter acquisition times than the previously used Look-Locker flow-sensitive alternating inversion recovery gradient-echo technique while preserving spatial resolution and robustness with respect to cardiac motion. ⋯ In one animal, physiological stress was induced with higher anesthetic concentration to evaluate the response of both methods under vasodilation. Global myocardial perfusion increased from 5.6 to 16.0 mL g(-1) min(-1) with cine-ASL and from 6.3 to 18.7 mL g(-1) min(-1) with Look-Locker flow-sensitive alternating inversion recovery. Although this original scheme requires a separate T1 measurement to be fully quantitative, it improves arterial spin labeling sensitivity while maintaining compatibility with motion constraints in cardiac MRI in small rodents.
-
The aim of this study was to quantify changes in thoracic aortic wall shear stress (WSS) in asymptomatic patients with Marfan syndrome (MFS) compared with healthy controls. WSS in the thoracic aorta was quantified based on time-resolved 3D phase contrast MRI with three-directional velocity encoding (4D flow MRI, temporal resolution ∼44 ms, spatial resolution ∼2.5 mm) in 24 patients with confirmed MFS (age = 18 ± 12 years) and in 12 older healthy volunteers (age = 25 ± 3 years). Diameters of the thoracic aorta normalized to body surface area were similar for both groups. ⋯ WSS eccentricity was altered in most of the ascending aorta and proximal arch (P = 0.009-0.020). MFS patients demonstrated segmental differences in peak systolic WSS with a significantly higher WSS at the inner curvature in the proximal ascending aorta and at the anterior part in the more distal ascending aorta (P < 0.01). These findings indicate differences in WSS associated with MFS despite similar aortic dimensions compared to controls.
-
In whole-body MR/PET, the human attenuation correction can be based on the MR data. However, an MR-based field-of-view (FoV) is limited due to physical restrictions such as B0 inhomogeneities and gradient nonlinearities. Therefore, for large patients, the MR image and the attenuation map might be truncated and the attenuation correction might be biased. ⋯ In-plane distortions in a transaxially extended FoV of up to 600 mm were analyzed in phantom studies. In vivo measurements of the patient's arms lying outside the normal specified FoV were compared with and without the use of B0 homogenization using gradient enhancement. In summary, we designed a sequence that provides data for reducing the image distortions due to B0 inhomogeneities and gradient nonlinearities and used the data to extend the MR FoV.