Performance of external and internal coil configurations for prostate investigations at 7 T

Abstract

Three different coil configurations were evaluated through simulation and experimentally to determine safe operating limits and evaluate subject size-dependent performance for prostate imaging at 7 T. The coils included a transceiver endorectal coil (trERC), a 16-channel transceiver external surface array (trESA) and a trESA combined with a receive-only ERC (trESA1roERC). Although the transmit B 1 (B þ 1 ) homogeneity was far superior for the trESA, the maximum achievable B þ 1 is subject size dependent and limited by transmit chain losses and amplifier performance. For the trERC, limitations in transmit homogeneity greatly compromised image quality and limited coverage of the prostate. Despite these challenges, the high peak B þ 1 close to the trERC and subject sizeindependent performance provides potential advantages especially for spectroscopic localization where high-bandwidth radiofrequency pulses are required. On the receive side, the combined trESA1roERC provided the highest signal-tonoise ratio and improved homogeneity over the trERC resulting in better visualization of the prostate and surrounding anatomy. In addition, the parallel imaging performance of the trESA1roERC holds strong promise for diffusion-weighted imaging and dynamic contrast-enhanced MRI. Magn Reson Med 64:1625-1639,

Magnetic Resonance Imaging at Ultrahigh Fields

“…But feasibility of imaging in the human torso at 7 T, a more challenging goal due to the relative dimensions of the object versus the RF wavelength, was demonstrated in 2008 and 2009 [48]–[51], thus starting a new burgeoning activity in several laboratories.…”

“…Consequently, work carried out at 4 T and higher magnetic fields have been restricted predominantly to the head or the extremities [5] and breast [182] where the object size relative to the RF wavelength employed is manageable. In the torso, the exception was imaging the prostate but with a small endorectal coil positioned immediately adjacent to the tissue of interest [51], [182]. …”

Radiofrequency Fields and SAR for Transverse Electromagnetic (TEM) Surface Coils

“…The placement of the loop is intended to represent the placement of a surface coil within human anatomy, much like an endo-rectal RF coil used to image the prostate. 37 The FDTD solver can be used to visualize the magnetic fields of the loop with the sample. Along the plane of the coil, there is equal propagation of the B 1 + field (Figure 5b).…”

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

“…Most of the multichannel arrays that have been proposed for imaging the torso and/or large proportions of the body at 7 T are local transmit/receive (Tx/Rx) arrays that consist of various types of individual elements such as microstrip lines [18,[23][24][25], microstrip lines with meanders [26], loops [13,[27][28][29], or dipole antennas [30][31][32][33]. Some of these coils can be quite bulky and have thicknesses of more than 5 cm [26,30,31].…”