RF Surface Receive Array Coils: The Art of an LC Circuit

Abstract

The radiofrequency (RF) receive array coil is a complicated device with many inductors and capacitors and serves as one of the most critical magnetic resonance imaging (MRI) electronic devices. It directly determines the achievable level of signal-to-noise ratio (SNR). Simply put, however, the RF coil is nothing but an LC circuit. The receive array coil was first proposed more than 20 years ago, evolving from a simple arrangement with a few electronic channels to a complicated system of 128 channels, enabling highly sophisticated parallel imaging, at different field strengths. This article summarizes the basic concepts pertaining to RF receive coil arrays and their associated SNR and reviews the theories behind the major components of such arrays. This includes discussions of the intrinsic SNR of a receive coil, the matching circuits, low-noise preamplifiers, coupling/decoupling amongst coils, the coupling between receive and transmit coils, decoupling via preamplifiers, and baluns. An 8-channel receive array coil on a cylindrical former serves as a useful example for demonstrating various points in the review.

Size‐adaptable 13‐channel receive array for brain MRI in human neonates at 3 T

“…The frequency response ( S 21 ) of each complete channel was assessed with the network analyzer, while having the coil loaded with all three phantoms. A curve with the typical “dog‐ear” shape was obtained, as previously shown . The exciting magnetic field probe was placed approximately in front of the loop centers, at a constant distance guaranteed by a spacer attached to the probe.…”

Decoupling of a tight‐fit transceiver phased array for human brain imaging at 9.4T: Loop overlapping rediscovered

“…Additionally, when necessary, the nearest nonadjacent loops can be decoupled using transformers as previously described . Overlapping the loops allows for increasing their size without increasing the size of the array holder and, thus, providing greater penetration depth and tissue power deposition in comparison to gapped loops.…”

“…Therefore, we can conclude that the overlapping of loops provides good decoupling for a wide variety of human heads at 400 MHz without the necessity of readjusting the overlap. Additionally, when necessary, the nearest nonadjacent loops can be decoupled using transformers as previously described (11,31). Overlapping the loops allows for increasing their size without increasing the size of the array holder and, thus, providing greater penetration depth and tissue power deposition in comparison to gapped loops.…”

Eight‐channel decoupled array for cervical spinal cord imaging at 3T: six‐channel posterior and two‐channel anterior array coil

“…12 The similar sensitivity map between the conventional looploop pair and the proposed loop-butterfly pair suggests the comparable performance of the proposed design compared with the conventional design. The adjacent elements of the six-channel posterior array were geometrically decoupled and most nonadjacent elements were decoupled using the loop and butterfly elements.…”

“…8,9 The imaging field-of-view (FOV) can be enlarged by increasing the number of coil elements. 7,12 However, the preamp decoupling technique increases the complexities in array design because the low-input impedance preamplifiers are not ubiquitous. 7 One of the most difficult tasks in an array design is to eliminate the coupling between elements.…”