The NMR phased array

TLDR

The NMR phased array, analogous to phased array radar and ultrasound, delivers the signal‑to‑noise ratio and resolution of a small surface coil across large fields‑of‑view without extending imaging time. The study presents methods for simultaneously acquiring and combining data from many closely positioned NMR receiving coils. By overlapping adjacent coils to eliminate mutual inductance, attaching low‑input‑impedance preamplifiers to suppress interference, and applying an algorithm that optimally combines the element data, the array can be used for all pulse sequences in imaging and spectroscopy. High‑resolution spin‑echo images of the thoracic and lumbar spine were obtained, and the phased array achieved 2‑ to 3‑fold higher SNR at 7 cm depth compared to a single large coil under identical parameters. © 1990 Academic Press, Inc.

Abstract

Abstract We describe methods for simultaneously acquiring and subsequently combining data from a multitude of closely positioned NMR receiving coils. The approach is conceptually similar to phased array radar and ultrasound and hence we call our techniques the “NMR phased array.” The NMR phased array offers the signal‐to‐noise ratio (SNR) and resolution of a small surface coil over fields‐of‐view (FOV) normally associated with body imaging with no increase in imaging time. The NMR phased array can be applied to both imaging and spectroscopy for all pulse sequences. The problematic interactions among nearby surface coils is eliminated (a) by overlapping adjacent coils to give zero mutual inductance, hence zero interaction, and (b) by attaching low input impedance preamplifiers to all coils, thus eliminating interference among next nearest and more distant neighbors. We derive an algorithm for combining the data from the phased array elements to yield an image with optimum SNR. Other techniques which are easier to implement at the cost of lower SNR are explored. Phased array imaging is demonstrated with high resolution (512 × 512, 48‐cm FOV, and 32‐cm FOV) spin‐echo images of the thoracic and lumbar spine. Data were acquired from four‐element linear spine arrays, the first made of 12‐cm square coils and the second made of 8‐cm square coils. When compared with images from a single 15 × 30‐cm rectangular coil and identical imaging parameters, the phased array yields a 2X and 3X higher SNR at the depth of the spine ( ∼ 7 cm). © 1990 Academic Press, Inc.