Clinical Comparison Between a Currently Available Single-Loop and an Investigational Dual-Channel Endorectal Receive Coil for Prostate Magnetic Resonance Imaging: A Feasibility Study at 1.5 and 3 T

Developments in proton MR spectroscopic imaging of prostate cancer

In this paper, we review the developments of 1H-MR spectroscopic imaging (MRSI) methods designed to investigate prostate cancer, covering key aspects such as specific hardware, dedicated pulse sequences for data acquisition and data processing and quantification techniques. Emphasis is given to recent advancements in MRSI methodologies, as well as future developments, which can lead to overcome difficulties associated with commonly employed MRSI approaches applied in clinical routine. This includes the replacement of standard PRESS sequences for volume selection, which we identified as inadequate for clinical applications, by sLASER sequences and implementation of 1H MRSI without water signal suppression. These may enable a new evaluation of the complementary role and significance of MRSI in prostate cancer management.

A multitransmit external body array combined with a 1 H and 31 P endorectal coil to enable a multiparametric and multimetabolic MRI examination of the prostate at 7T

Purpose

In vivo¹H and ³¹P 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 ¹H and ³¹P spectroscopic imaging of the prostate using a ³¹P and ¹H endorectal radiofrequency coil (ERC) in combination with a multitransmit body array at 7 Tesla (T).

Methods

An ERC with a ³¹P transceiver loop coil and ¹H receive (Rx) asymmetric microstrip (³¹P/¹H ERC) was designed, constructed and tested in combination with an external 8‐channel ¹H 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 ¹H 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 ¹H and ³¹P spectroscopic imaging.

Results

Electromagnetic field simulations of the ³¹P loop coil showed no differences in the E‐ and B‐fields of the ³¹P/¹H ERC compared with a previously safety validated ERC without ¹H microstrip. The hotspot of the specific absorption rate (SAR) at the feed point of the ³¹P/¹H ERC loop coil was 9.42 W/kg when transmitting on ³¹P at 1 W. Additional in vivo measurements showed a maximum temperature increase at the SAR hotspot of 0.7°C over 6 min on ³¹P at 1.9 W transmit (Tx) power, indicating safe maximum power levels. When transmitting with the external ¹H body array at 40W for 2:30 min, the temperature increase around the ERC was < 0.3°C. Up to 3.5 cm into the prostate the ¹H microstrip of the ERC provided higher SNR than the 8CH. The total coil combination allowed acquisition of an mpMRI protocol and the assessment of ³¹P and ¹H metabolites of the prostate in all test subjects.

Conclusion

We developed a setup with a ³¹P transceiver and ¹H 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 ¹H and ³¹P MRSI at 7T in patients with prostate cancer within one MR examination.