Inductively Coupled RF Coil for Imaging a 40 µm-Thick Histology Sample in a Clinical MRI Scanner

Abstract

A histology coil is a U-shaped radio-frequency (RF) coil that is designed to provide a high signal-to-noise ratio (SNR) in magnetic resonance imaging (MRI) of microscopically thin samples. In this work, we demonstrate an inductively coupled histology coil that can be easily integrated with a human MRI scanner, providing a simple method to conduct novel, microscopic imaging experiments in a clinical scanner. All experiments were conducted in a 3T whole-body MRI scanner. The coil consisted of a U-shaped copper foil with tuning capacitors shunting the ends of the “U”. This design maximizes the B₁-field efficiency and the homogeneity in the coil’s cavity. For inductive coupling, the histology coil was connected to an untuned single-turn pick-up loop via a coaxial cable. A standard 3T receive-only surface coil, connected to the scanner’s standard receive circuitry, was then inductively coupled to the pick-up loop. Separately, the RF pulse transmitted from the MRI body coil inductively drove the histology coil. In gel phantom imaging, we confirmed a higher (threefold) SNR for the histology coil than for the scanner’s standard surface coil, as well as high B₁ homogeneity for the histology coil. Gradient echo images of a 40-µm-thick rat brain slice, at an in-plane resolution of 219 × 219 µm², could be obtained with SNR > 10 (in the cortex) in about 2 hours. Our work demonstrates the feasibility of imaging microscopically thin tissue slices in a clinical MRI scanner using an inductively coupled histology coil. The method can be applied to multi-modality and multi-orientation imaging of ex-vivo and engineered tissue samples.