High‐field MRSI of the prostate using a transmit/receive endorectal coil and gradient modulated adiabatic localization

Abstract

Purpose: To demonstrate in vivo magnetic resonance spectroscopic imaging (MRSI) of the human prostate at 4.0T using a transmit/receive endorectal coil and a pulse sequence designed specifically for this application. Materials and Methods:A solid, reusable endorectal probe was designed for both radiofrequency transmission and reception. Finite difference time domain (FDTD) simulations were performed to characterize the coil's electric field distribution, and temperature measurements were performed in a beef tissue phantom to determine the coil's safe operating limit. The localization by selective adiabatic refocusing (LASER) pulse sequence was implemented using six gradient modulated offset independent adiabatic (GOIA) pulses for very sharp, B 1 -insensitive voxel localization.Results: Based on the simulations and temperature measurements, the coil's safe operating limit was conservatively estimated to be 1.0W for 15 minutes. The transition width of the GOIA pulse selection profiles was only 6% of the bandwidth, compared with 22% for a specific absorption rate (SAR)-matched conventional adiabatic pulse. Using the coil and pulse sequence described here, MRSI data were successfully acquired from a patient with biopsyproven prostate cancer, with a nominal voxel size of 0.34 cc in a scan time of 15 minutes. Conclusion:This work demonstrates the safe and effective use of a transmit/receive endorectal coil for in vivo MRSI of the prostate.

Improving SNR and B1 transmit field for an endorectal coil in 7 T MRI and MRS of prostate cancer

“…Consequently, this results in low bandwidths in combination with conventional RF pulses and high SAR values when using broadband adiabatic pulses at 7 T. Conversely, when using local RF coils for transmitting B 1 at high duty cycles, RF power deposition can remain low and adiabatic sequences can be applied within safety guidelines (10 W/kg local SAR averaged over 10 g of tissue (10)). In fact, adiabatic RF pulses have already been explored for MRSI in the prostate (7, 24) as well as for other regions in the body (15, 25, 26) showing insensitivity to B 1 nonuniformities and excellent sharp slice profiles compared to nonadiabatic sequences.…”

Single‐shot single‐voxel lactate measurements using FOCI‐LASER and a multiple‐quantum filter

“…They should largely eliminate the chemical shift displacement problem. A similar strategy has been reported for single‐voxel localization , MRSI , and MEGA editing in brain, and for MRSI in prostate . An MQF module was then inserted in the centre of this sequence to selectively detect lactate signals while suppressing signals from the 1.3 ppm resonance of lipids.…”

Spectroscopic imaging with improved gradient modulated constant adiabaticity pulses on high-field clinical scanners

“…An effective method to reduce RF amplitude is to apply VERSE (Variable Rate Selective Excitation) method [10,11]. VERSE uses gradient modulation to decrease peak RF amplitude, and adiabatic pulses with very large BW (20 kHz) and short duration (3.5 ms) have been designed [12,13] for localized MRS. FOCI (Frequency Offset Corrected Inversion) pulse appears to have been used more in human studies [12,14,15] compared to GOIA (Gradient Offset Independent Adiabaticity) pulses [13,16]. However these demonstrations have been performed mainly on research scanners and despite their benefits, these pulses are not widespread for MRSI on clinical systems.…”