Search

To determine the limits of agreement of hepatic fat fraction and R2* relaxation rate quantified with accelerated magnetic resonance (MR) imaging reconstructed with combined compressed sensing and parallel imaging compared with conventional fully sampled acquisitions.Eleven subjects with type 2 diabetes and a healthy control subject were recruited with the approval of the Newcastle and North Tyneside 2 ethics committee and written consent. Undersampled data at ratios of 2.6×, 2.9×, 3.8×, and 4.8× were prospectively acquired in addition to fully sampled data by using five gradient echoes per repetition time at 3.0 T. Fat fraction maps were calculated by using combined compressed sensing and parallel imaging (CS-PI) reconstruction and Bland-Altman analysis performed to assess bias and 95% limits of agreement. Inter- and intrarater analysis was performed for quantitative fat fraction and R2* relaxation rate, and image quality was assessed with a four-point scale by two independent observers.The fat fractions from the accelerated acquisitions had 95% limits of agreement of 1.2%, 1.2%, 1.1%, and 1.5%, respectively, with no bias. When compared with the intra- and interrater 95% limits of agreement (0.7% and 0.8%), acceleration of up to 3.8× did not greatly degrade the fat fraction measurements. No or minimal artifact was detected at 2.6× and 2.9× accelerations, moderate artifact was detected at 3.8× acceleration, and substantial artifact was detected at 4.8× acceleration.Prospective undersampling and CS-PI reconstruction of liver fat fractions can be used to accelerate liver fat fraction measurements. The fat fractions and image quality produced were acceptable up to a factor of 3.8×, thereby shortening the required breath-hold duration from 17.7 seconds to 4.7 seconds.

Purpose To investigate the effect of R2* modeling in conventional and accelerated measurements of skeletal muscle fat fraction in control subjects and patients with muscular dystrophy. Materials and Methods Eight patients with Becker muscular dystrophy and eight matched control subjects were recruited with approval from the Newcastle and North Tyneside 2 Research Ethics Committee and with written consent. Chemical-shift images with six widely spaced echo times (in 3.5-msec increments) were acquired to correlate R2* and muscle fat fraction. The effect of incorporating or neglecting R2* modeling on fat fraction magnitude and variance was evaluated in a typical three-echo protocol (with 0.78-msec increments). Accelerated acquisitions with this protocol with 3.65×, 4.94×, and 6.42× undersampling were reconstructed by using combined compressed sensing and parallel imaging and fat fraction maps produced with R2* modeling. Results Muscle R2* at 3.0 T (33-125 sec(-1)) depended on the morphology of fat replacement, the highest values occurring with the greatest interdigitation of fat. The inclusion of R2* modeling removed bias, which was greatest at low fat fraction, but did not increase variance. The 95% limits of agreement of the accelerated acquisitions were tight and not degraded by R2* modeling (1.65%, 1.95%, and 2.22% for 3.65×, 4.94×, and 6.42× acceleration, respectively). Conclusion Incorporating R2* modeling prevents systematic errors in muscle fat fraction by up to 3.5% without loss of precision and should be incorporated into all muscular dystrophy studies. Fat fraction measurements can be accelerated fivefold by using combined compressed sensing and parallel imaging, modeling for R2* without loss of fidelity.

A prospective study approved by the local ethics committee was performed to establish the normal range and reproducibility of myocardial T1 values as assessed with single-breath-hold T1 mapping with high spatial resolution. With a 1.5-T magnetic resonance (MR) imaging system, baseline and contrast material-enhanced modified Look-Locker inversion recovery, or MOLLI, imaging was performed in 15 healthy volunteers who had given written informed consent. Image quality scores and myocardial T1 values were derived for standard short-axis segments and sections. Results were compared with those from a second MR imaging study performed on the same day (baseline only) and those from a third study performed on a different day (baseline and contrast enhanced; eight volunteers). Intra- and interobserver agreement were determined. Myocardial T1 maps were obtained rapidly in a reproducible fashion. A normal range for baseline and postcontrast myocardial T1 was established (baseline mean T1 in short-axis sections, 980 msec +/- 53 [standard deviation]; 95% confidence interval: 964, 997; number of sections, 43). This technique could enable direct quantification of changes in tissue characteristics in ischemic and inflammatory myocardial diseases.