A 16‐element phased‐array head coil

Abstract

Volume-array coils offer increased signal-to-noise ratio (SNR) over standard volume coils near the array elements while preserving the SNR at the center of the volume. As the number of array elements is increased, the SNR advantage as well as the complexity of actually constructing the array increases also. In this study, a 16-channel receive-only array for imaging of the brain is demonstrated and compared to a circularly polarized (CP) head coil of similar shape and diameter. The array was formed from a 2 x 8 grid of square elements placed on a cylindrical form. Mutual coupling was minimized by a combination of overlapping element placement and current-reducing matching networks. Simultaneous data acquisition from the 16 individual elements was performed using a four-channel receiver system with each channel time domain multiplexed by a factor of 4. Theoretical and experimental comparisons between the array and a standard CP head coil show that the array offers an increase in SNR of nearly a factor of 3 near its surface while maintaining a comparable SNR to that of the CP head coil in the center of the region of interest.

Rapid Volumetric MRI Using Parallel Imaging With Order-of-Magnitude Accelerations and a 32-Element RF Coil Array

“…Note that the net SNR is always highest for the largest number of elements, despite the fact that the smaller individual coils of the multielement arrays have markedly reduced individual SNR at the selected depth. This result is consistent with the predictions of superposition principles, which suggest that the loss of depth sensitivity by small individual elements will be compensated by an associated increase in the number of elements, provided that noise from individual coil circuits is kept under control (15)(16)(17)(18). As an illustration of the superposition argument, imagine that a single rectangular coil is divided into two coils each with half the total area.…”

4T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

“…Depending upon the specific application the size, geometry and number of receiver coils to yield an "optimum result" whether it be homogeneity, localized SNR or acceleration for parallel imaging will vary, and has been extensively discussed in the literature (1,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) and remains an active area of research. In our case the number of elements in the array was limited by the number of receivers on our system (n=4).…”

“…SNR in these "gap areas" can be further increased by adding more coil elements to the array and providing more complete coverage. Sensitivity near the center of the brain was near optimal since it has been demonstrated previously that a phased array with full coverage of a head provided similar sensitivity as an optimized quadrature volume coil (10,28). Since the 1 H portion of the volume coil can also be used for reception at the proton frequency, anatomical images from the entire brain can also be acquired in the same setting without the need for patient repositioning or changes in hardware configuration.…”

Evaluation of Image Quality of a 32-Channel versus a 12-Channel Head Coil at 1.5T for MR Imaging of the Brain

“…[8][9][10][11] While PI is the most common use of multichannel coils, the additional data acquired by the coil elements can be processed by standard techniques to maximize spatial resolution and SNR. 1,2,[12][13][14] Recent studies with site-specific multichannel receiver coils and more conservative acceleration of scanning times have reported improvements in diagnostic quality in nondynamic organs, such as the breast and musculoskeletal system. [15][16][17] Consequently, there is evidence that a multichannel coil and standard processing techniques can confer some of the advantages to image quality that are characteristic of increasing field strengths.…”