A clinical comparison of rigid and inflatable endorectal-coil probes for MRI and 3D MR spectroscopic imaging (MRSI) of the prostate

Abstract

Purpose: To compare the data quality and ease of use of four endorectal-coil probe setups for prostate MRI.

Materials and methods: Four endorectal-coil probe setups were compared: 1) air-inflated probe; 2) perfluorocarbon (PFC)-inflated probe; 3) rigid, smaller prototype coil; and 4) rigid, smaller coil designed for biopsying the prostate. Signal-to-noise ratio (SNR), positioning, shimming, MRI motion artifact, and MR spectroscopic imaging (MRSI) spectral quality were assessed.

Results: Rigid coils provided approximately 2.5-fold higher SNR than inflatable coils near the peripheral zone midline. The biopsy probe sensitivity decreased dramatically by the apex. The rigid probes, as compared to the inflatable probes, took longer to place (10 +/- 2 vs. 7 +/- 2 minutes, P < 0.0002), tended to be placed too superiorly, required repositioning more often (73% vs. 20%, P < 0.003), and had higher motion artifacts (P < 0.001). Shimming time was least for the PFC-inflated probe (2 +/- 0.5 minutes, P < 0.05). The air-inflated probe produced larger linewidths (P < 0.01) and tended to have longer shim times (7 +/- 4 minutes) and poorer spectral quality.

Conclusion: The inflatable coil is a good clinical choice due to ease of use, good coverage, and low motion artifacts. PFC-inflation is recommended as it provided higher quality data than air-inflation. The rigid, smaller probes have higher SNR and produce less tissue distortion and may be preferred for certain applications.

Figure 1

Axial images of the prostate taken with the different probes. a: Air-inflated probe. b: Biopsy-rigid probe. c: Nonbiopsy-rigid probe.

Figure 2

Anterior/posterior SNR into the prostate, at the midline, relative to the maximum with the inflatable coil. Locations of the coils and the peripheral zone (PZ) and central gland relative to the rectal wall are shown. Locations of the coils are marked with ovals. [Color figure can be viewed in the online issue, which is available at http://www.interscience.wiley.com.]

Figure 3

R/L SNR across the prostate, at the peripheral zone, relative to the maximum with the inflatable coil. Typical size of the peripheral zone is shown.

Figure 4

S/I SNR along the prostate, at the peripheral zone, relative to the maximum with the inflatable coil. Typical size and position of the prostate is indicated. The biopsy coil loses SNR at the apex.

Figure 5

Positioning error common for rigid probes. Sagittal images after original probe placement (left) and after the probe was repositioned (right). The location of the coils is indicated by the ovals. [Color figure can be viewed in the online issue, which is available at http://www.interscience.wiley.com.]

Figure 6

Example MR images and MR spectra for the air-inflated endorectal probe. T2-weighted image with MRSI grid (left), an array of spectra from the grid shown in the image (middle), and a spectrum from the outlined voxel in the array (right).

Figure 7

Example MR images and MR spectra for the nonbiopsy-rigid endorectal probe. T2-weighted image with MRSI grid (left), an array of spectra from the grid shown in the image (middle), and a spectrum from the outlined voxel in the array (right).

Figure 8

Example MR images and MR spectra for the PFC-inflated endorectal probe. T2-weighted image with MRSI grid (left), an array of spectra from the grid shown in the image (middle), and a spectrum from the outlined voxel in the array (right).

Figure 9

MRI motion artifact scores for the different probe setups. The boxes show the 25th–75th percentiles and the whiskers indicate the extreme cases. The horizontal lines indicate the means.

Figure 10

MR spectral quality scores for the different probe setups. The boxes show the 25th–75th percentile range and the whiskers indicate the extreme cases. The horizontal lines indicate the means.