Hyperpolarized MRI - An Update and Future Perspectives.

In recent years, hyperpolarized 13C magnetic resonance spectroscopic (MRS) imaging has emerged as a complementary metabolic imaging approach. Hyperpolarization via dissolution dynamic nuclear polarization is a technique that enhances the MR signal of 13C-enriched molecules by a factor of > 104, enabling detection downstream metabolites in a variety of intracellular metabolic pathways. The aim of the present review is to provide the reader with an update on hyperpolarized 13C MRS imaging and to assess the future clinical potential of the technology. Several carbon-based probes have been used in hyperpolarized studies. However, the first and most widely used 13C-probe in clinical studies is [1-13C]pyruvate. In this probe, the enrichment of 13C is performed at the first carbon position as the only modification. Hyperpolarized [1-13C]pyruvate MRS imaging can detect intracellular production of [1-13C]lactate and 13C-bicarbonate non-invasively and in real time without the use of ionizing radiation. Thus, by probing the balance between oxidative and glycolytic metabolism, hyperpolarized [1-13C]pyruvate MRS imaging can image the Warburg effect in malignant tumors and detect the hallmarks of ischemia or viability in the myocardium. An increasing number of clinical studies have demonstrated that clinical hyperpolarized 13C MRS imaging is not only possible, but also it provides metabolic information that was previously inaccessible by non-invasive techniques. Although the technology is still in its infancy and several technical improvements are warranted, it is of paramount importance that nuclear medicine physicians gain knowledge of the possibilities and pitfalls of the technique. Hyperpolarized 13C MRS imaging may become an integrated feature in combined metabolic imaging of the future.

Isokinetic strength and degeneration of lower extremity muscles in patients with myotonic dystrophy; an MRI study.

Our aim was to determine isokinetic strength and degeneration of lower extremity muscles in patients with Myotonic Dystrophy (DM1). In 19 patients with DM1 and 19 matched controls, strength measured by isokinetic dynamometry was expressed as percentage of expected strength (ePct), adjusted for age, height, weight and gender. MRI of the hip, thigh and calf muscles were obtained. Fat fraction (FF), mean contractile cross-sectional area (cCSA) and specific strength (Nm/cm2) were calculated. Patients' ankle plantar flexors, knee flexors and extensors had higher FF (Δ: 0.08 - 0.42) and lower cCSA (Δ: 3.2 -17.1 cm2) compared to controls (p ≤ 0.005). EPct (Δ: 19.5 - 41.6%) and specific strength (Δ: 0.27 - 0.96 Nm/cm2) were lower in the majority of patients muscle groups (p˂0.05). Close correlations were found for patients when relating ePct to; FF for plantar flexors (R2=0.742, p<0.001) and knee extensors (R2=0.732, p<0.001), cCSA for plantar flexors (R2=0.696, p<0.001) and knee extensors (R2=0.633, p<0.001), and specific strength for dorsal flexors (ρ=0.855, p = 0.008). In conclusion, patients had weaker lower extremity muscles with higher FF, lower cCSA and specific strength compared to controls. Muscle degeneration determined by quantitative MRI strongly correlated to strength supporting its feasibility to quantify muscle dysfunction in DM1.

Diffusion tensor imaging MR Neurography detects polyneuropathy in type 2 diabetes.

AIM: To evaluate if diffusion-tensor-imaging MR-Neurography (DTI-MRN) can detect lesions of peripheral nerves due to polyneuropathy in patients with type 2 diabetes. METHODS: Ten patients with type 2 diabetes with polyneuropathy (DPN), 10 patients with type 2 diabetes without polyneuropathy (nDPN) as well as 20 healthy controls (HC) were included. DTI-MRN covered proximal (sciatic nerve) and distal regions (tibial nerve) of the lower extremity. Fractional-anisotropy (FA) and diffusivity (mean (MD), axial (AD) and radial (RD)) were calculated and compared to neuropathy severity. Conventional T2-relaxation-time and proton-spin-density data were obtained from a multi-echo SE sequence. Furthermore, we evaluated sensitivity and specificity of DTI-MRN from receiver operating characteristics (ROC). RESULTS: The proximal and distal FA was lowest in patients with DPN compared with nDPN and HC (p < 0.01). Likewise, proximal and distal RD was highest in patients with DPN (p < 0.01). MD and AD were also significantly different though less pronounced. ROC curve analyses of DTI separated nDPN and DPN with area-under-the-curve values ranging from 0.65 to 0.98. T2-relaxation-time and proton-spin-density could not differentiate between nDPN and DPN. CONCLUSION: DTI-MRN accurately detects DPN by lower nerve FA and higher RD. These alterations are likely to reflect both proximal and distal nerve fiber pathology in patients with type 2 diabetes.