Using MRI to quantify skeletal muscle pathology in Duchenne muscular dystrophy: A systematic mapping review

There is a great demand for accurate non-invasive measures to better define the natural history of disease progression or treatment outcome in Duchenne muscular dystrophy (DMD) and to facilitate the inclusion of a large range of participants in DMD clinical trials. This review aims to investigate which MRI sequences and analysis methods have been used and to identify future needs. Medline, Embase, Scopus, Web of Science, Inspec, and Compendex databases were searched up to 2 November 2019, using keywords “magnetic resonance imaging” and “Duchenne muscular dystrophy.” The review showed the trend of using T1w and T2w MRI images for semi-qualitative inspection of structural alterations of DMD muscle using a diversity of grading scales, with increasing use of T2map, Dixon, and MR spectroscopy (MRS). High-field (>3T) MRI dominated the studies with animal models. The quantitative MRI techniques have allowed a more precise estimation of local or generalized disease severity. Longitudinal studies assessing the effect of an intervention have also become more prominent, in both clinical and animal model subjects. Quality assessment of the included longitudinal studies was performed using the Newcastle-Ottawa Quality Assessment Scale adapted to comprise bias in selection, comparability, exposure, and outcome. Additional large clinical trials are needed to consolidate research using MRI as a biomarker in DMD and to validate findings against established gold standards. This future work should use a multiparametric and quantitative MRI acquisition protocol, assess the repeatability of measurements, and correlate findings to histologic parameters

7Li 2D CSI of human brain on a clinical scanner.

Lithum salts have been widely used in the treatment of mood disorders, but the mechanism of action is still not clear. In this work, a methodology for two-dimensional Lithium-7 imaging on clinical systems is presented. The data were acquired using a phosphorus volume head coil that was re-tuned for the Lithium-7 frequency. A spectroscopic sequence was used to acquire the free induction decay (FID) after volume excitaion using a hard pulse. The results obtained on the head of patients undergoing lithium treatment(n=7, 0.6mEq/1 average serum level) demonstrate that images of adequate signal to noise ratio (100:1) can be obtained in acceptable imaging times(55 min) using the proposed methodology. The distribution of 7Li appears uniform in the brains of the patients studied

Molecular imaging with endogenous substances

Dynamic nuclear polarization has enabled hyperpolarization of nuclei such as (13)C and (15)N in endogenous substances. The resulting high nuclear polarization makes it possible to perform subsecond (13)C MRI. By using the dynamic nuclear polarization hyperpolarization technique, 10% polarization was obtained in an aqueous solution of 100 mM (13)C-labeled urea, ready for injection. The in vivo T(1) relaxation time of (13)C in the urea solution was determined to 20 ± 2 s. Due to the long relaxation time, it is possible to use the hyperpolarized substance for medical imaging. A series of high-resolution (≈1-mm) magnetic resonance images were acquired, each with a scan time of 240 ms, 0-5 s after an i.v. injection of the hyperpolarized aqueous [(13)C]urea solution in a rat. The results show that it is possible to perform (13)C angiography with a signal-to-noise ratio of ≈275 in ≈0.25 s. Perfusion studies with endogenous substances may allow higher spatial and/or temporal resolution than is possible with current proton imaging techniques