Cardiovascular Applications of Hyperpolarized MRI

Many applications of MRI are limited by an inherently low sensitivity. Previous attempts to overcome this insensitivity have focused on the use of MRI systems with stronger magnetic fields. However, the gains that can be achieved in this way are relatively small and increasing the magnetic field invariably leads to greater technical challenges. More recently, the development of a range of techniques, which can be gathered under the umbrella term of “hyperpolarization,” has offered potential solutions to the low sensitivity. Hyperpolarization techniques have been demonstrated to temporarily increase the signal available in an MRI experiment by as much as 100,000-fold. This article outlines the main hyperpolarization techniques that have been proposed and explains how they can increase MRI signals. With particular emphasis on the emerging technique of dynamic nuclear polarization, the existing preclinical cardiovascular applications are reviewed and the potential for clinical translation is discussed

In vivo magnetic resonance spectroscopy: basic methodology and clinical applications

The clinical use of in vivo magnetic resonance spectroscopy (MRS) has been limited for a long time, mainly due to its low sensitivity. However, with the advent of clinical MR systems with higher magnetic field strengths such as 3 Tesla, the development of better coils, and the design of optimized radio-frequency pulses, sensitivity has been considerably improved. Therefore, in vivo MRS has become a technique that is routinely used more and more in the clinic. In this review, the basic methodology of in vivo MRS is described—mainly focused on 1H MRS of the brain—with attention to hardware requirements, patient safety, acquisition methods, data post-processing, and quantification. Furthermore, examples of clinical applications of in vivo brain MRS in two interesting fields are described. First, together with a description of the major resonances present in brain MR spectra, several examples are presented of deviations from the normal spectral pattern associated with inborn errors of metabolism. Second, through examples of MR spectra of brain tumors, it is shown that MRS can play an important role in oncology

Creating a clinical platform for carbon‐13 studies using the sodium‐23 and proton resonances

Purpose Calibration of hyperpolarized 13C‐MRI is limited by the low signal from endogenous carbon‐containing molecules and consequently requires 13C‐enriched external phantoms. This study investigated the feasibility of using either 23Na‐MRI or 1H‐MRI to calibrate the 13C excitation. Methods Commercial 13C‐coils were used to estimate the transmit gain and center frequency for 13C and 23Na resonances. Simulations of the transmit B1 profile of a Helmholtz loop were performed. Noise correlation was measured for both nuclei. A retrospective analysis of human data assessing the use of the 1H resonance to predict [1‐13C]pyruvate center frequency was also performed. In vivo experiments were undertaken in the lower limbs of 6 pigs following injection of hyperpolarized 13C‐pyruvate. Results The difference in center frequencies and transmit gain between tissue 23Na and [1‐13C]pyruvate was reproducible, with a mean scale factor of 1.05179 ± 0.00001 and 10.4 ± 0.2 dB, respectively. Utilizing the 1H water peak, it was possible to retrospectively predict the 13C‐pyruvate center frequency with a standard deviation of only 11 Hz sufficient for spectral–spatial excitation‐based studies. Conclusion We demonstrate the feasibility of using the 23Na and 1H resonances to calibrate the 13C transmit B1 using commercially available 13C‐coils. The method provides a simple approach for in vivo calibration and could improve clinical workflow.</p