Magnetic Resonance Imaging of Phosphocreatine and Determination of BOLD Kinetics in Lower Extremity Muscles using a Dual-Frequency Coil Array

Abstract

Magnetic resonance imaging (MRI) provides the unique ability to study metabolic and microvasculature functions in skeletal muscle using phosphorus and proton measurements. However, the low sensitivity of these techniques can make it difficult to capture dynamic muscle activity due to the temporal resolution required for kinetic measurements during and after exercise tasks. Here, we report the design of a dual-nuclei coil array that enables proton and phosphorus MRI of the human lower extremities with high spatial and temporal resolution. We developed an array with whole-volume coverage of the calf and a phosphorus signal-to-noise ratio of more than double that of a birdcage coil in the gastrocnemius muscles. This enabled the local assessment of phosphocreatine recovery kinetics following a plantar flexion exercise using an efficient sampling scheme with a 6 s temporal resolution. The integrated proton array demonstrated image quality approximately equal to that of a clinical state-of-the-art knee coil, which enabled fat quantification and dynamic blood oxygen level-dependent measurements that reflect microvasculature function. The developed array and time-efficient pulse sequences were combined to create a localized assessment of calf metabolism using phosphorus measurements and vasculature function using proton measurements, which could provide new insights into muscle function.

Water–fat separation in spiral magnetic resonance fingerprinting for high temporal resolution tissue relaxation time quantification in muscle

“…This multiparametric dynamic approach has the potential to help disentangle different physiological processes affecting T 2 , such as changes in pH and CO 2 levels. The dynamics measured with MRF are in agreement with previously published literature . After exercise, all volunteers showed an increase in both water T 1 and T 2 (Supporting Information Figure ).…”

Dynamic phosphocreatine imaging with unlocalized pH assessment of the human lower leg muscle following exercise at 3T

“…To recruit the soleus muscle, the subject would be required to perform plantar flexions with their knee partially flexed, as has been shown previously . Given the location of the soleus and the sensitivity profile of our coil array , we expect a ∼40% SNR drop in some voxels in the soleus compared with the gastrocnemius muscle. By introducing additional noise to our existing data, we estimated that data fitting would have coefficient of determination ( r 2 ) between 0.7 and 0.8, which, as expected, is lower than that reported for the gastrocnemius muscle (0.89 ± 0.05).…”

An eight‐channel sodium/proton coil for brain MRI at 3 T

“…Further, counter‐rotating currents were induced in the nested sodium array that reduced proton coil efficiency. Possible approaches to reduce counter‐rotating currents are to switch to an interleaved coil arrangement, where the proton array is offset with respect to the sodium array, or to install proton filters in the sodium array, which can be expected to reduce sodium performance by about 5% on each element …”

“…The inherent challenges of sodium MRI can therefore be addressed with high main magnetic fields, signal averaging and UTE pulse sequences, together with optimized radiofrequency (RF) coils. Recent publications have demonstrated that dual‐nuclei, multi‐channel phased array coils can achieve improved sodium sensitivity compared with birdcage volume coils and simultaneously enable standard proton MRI …”