Abstract
PURPOSE: In vivo (1) H and (31) P magnetic resonance spectroscopic imaging (MRSI) provide complementary information on the biology of prostate cancer. In this work we demonstrate the feasibility of performing multiparametric imaging (mpMRI) and (1) H and (31) P spectroscopic imaging of the prostate using a (31) P and (1) H endorectal radiofrequency coil (ERC) in combination with a multitransmit body array at 7 Tesla (T). METHODS: An ERC with a (31) P transceiver loop coil and (1) H receive (Rx) asymmetric microstrip ((31) P/(1) H ERC) was designed, constructed and tested in combination with an external 8-channel (1) H transceiver body array coil (8CH). Electromagnetic field simulations and measurements and in vivo temperature measurements of the ERC were performed for safety validation. In addition, the signal-to-noise (SNR) benefit of the (1) H microstrip with respect to the 8CH was evaluated. Finally, the feasibility of the setup was tested in one volunteer and three patients with prostate cancer by performing T2 -weighted and diffusion-weighted imaging in combination with (1) H and (31) P spectroscopic imaging. RESULTS: Electromagnetic field simulations of the (31) P loop coil showed no differences in the E- and B-fields of the (31) P/(1) H ERC compared with a previously safety validated ERC without (1) H microstrip. The hotspot of the specific absorption rate (SAR) at the feed point of the (31) P/(1) H ERC loop coil was 9.42 W/kg when transmitting on (31) P at 1 W. Additional in vivo measurements showed a maximum temperature increase at the SAR hotspot of 0.7 degrees C over 6 min on (31) P at 1.9 W transmit (Tx) power, indicating safe maximum power levels. When transmitting with the external (1) H body array at 40W for 2:30 min, the temperature increase around the ERC was < 0.3 degrees C. Up to 3.5 cm into the prostate the (1) H microstrip of the ERC provided higher SNR than the 8CH. The total coil combination allowed acquisition of an mpMRI protocol and the assessment of (31) P and (1) H metabolites of the prostate in all test subjects. CONCLUSION: We developed a setup with a (31) P transceiver and (1) H Rx endorectal coil in combination with an 8-channel transceiver external body array coil and demonstrated its safety and feasibility for obtaining multiparametric imaging and (1) H and (31) P MRSI at 7T in patients with prostate cancer within one MR examination.
