In vivo 39K MR imaging of human muscle and brain

To implement potassium 39 ((39)K) magnetic resonance (MR) imaging with a 7-T MR imaging system and to evaluate its feasibility for in vivo imaging of human muscle and brain.

Three healthy volunteers were examined with approval of the ethical review board of Heidelberg University. Written informed consent was obtained from all volunteers. Because the available 7-T MR imaging system did not support (39)K, a frequency conversion scheme was developed and connected to the imaging unit. The standard X-nucleus frequency of lithium 7 (115 MHz) was converted to the frequency of (39)K at 7 T (14 MHz). Relaxation times of healthy thigh muscle and brain tissue were estimated by using multiple-echo and inversion-recovery sequences. Data analysis was conducted with a nonlinear least squares curve fitting tool. In vivo (39)K MR imaging of healthy human thigh muscle and brain was performed.

With use of the custom-built frequency conversion scheme, (39)K MR imaging is feasible with a commercially available 7-T MR imaging system. Nominal spatial resolutions of 8 × 8 × 16 mm(3) and 9.5 × 9.5 × 9.5 mm(3) were achieved for human thigh muscle and brain, respectively. Acquisition time was 30 minutes for both muscle and brain tissue. The measured potassium concentration (uncorrected for fat fraction) of thigh muscle tissue (112-124 mmol/L) lies within the expected range.

In vivo (39)K MR imaging in humans can be performed in clinically feasible measurement times (approximately 30 minutes) with voxel sizes of approximately 1 mL.