In Vivo Human Eye Magnetic Resonance Imaging at 7.0 Tesla in Volunteers and Patients: Preliminary data

Abstract

Purpose: In vivo imaging of the spatial arrangement of ocular substructures and intraocular pathologies is an emerging MRI application, which requires high spatial resolution over a small field of view and is challenging due to signal intensity constraints and involuntary eye movements. For these reasons this work examines the feasibility of human eye imaging at 7.0 T using an in-house developed six channel transmit/receive radiofrequency (RF) coil tailored for the human eye and orbital anatomy.

Methods: A symmetric coil design was used to cover each eye with three planar transceiver loop elements. MRI was conducted on a 7.0 T scanner (Magnetom, Siemens Healthcare, Germany). Electromagnetic field including specific absorption rate simulations were performed to study the performance of the RF coil. Simulations were validated in phantom studies. Eye imaging at 7.0 T was performed on healthy subjects and patients with choroidal melanomas using T1- and T2-weighted imaging techniques. In selected cases ex vivo imaging of the enucleated eyes was conducted on 7.0 T and 9.4 T scanners (ClinScan, Bruker, Germany).

Results: The light weight RF coil was conformed to a broad range of head geometries. Phantom experiments using T1- and T2-weighted imaging techniques tailored for eye imaging revealed RF-induced heating of less than 0.3 K for a total scan time of 50 min. In vivo imaging with scanning times less than 3 min demonstrated a rather uniform signal intensity for sagittal, coronal, and transverse views. In patients with intraocular pathologies the tumor and its relationship to the surrounding structures e.g. retinal detachment could be clearly visualized. Intratumoral inhomogenities could be indentified and compared with histopathology.

Conclusions: This study demonstrates that human eye MRI at 7.0 T is feasible in clinically acceptable scan times in patients. Our preliminary results indicate that the use of proposed coil array yields a signal-to-noise ratio which affords a spatial resolution, which is elusive if not prohibitive at lower magnetic fields. The results reported here facilitate the depiction of anatomical details of the eye and orbit including subtle details. Improvements in image quality can be achieved by tailoring pulse sequences established for eye imaging at 1.5 T/3.0 T for the 7.0 T environment.

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)