7 Tesla MR imaging of the human eye in vivo

Abstract

Purpose: To develop a protocol which optimizes contrast, resolution and scan time for three-dimensional (3D) imaging of the human eye in vivo using a 7 Tesla (T) scanner and custom radio frequency (RF) coil. Materials and Methods:Initial testing was conducted to reduce motion and susceptibility artifacts. Three-dimensional FFE and IR-TFE images were obtained with variable flip angles and TI times. T 1 measurements were made and numerical simulations were performed to determine the ideal contrast of certain ocular structures. Studies were performed to optimize resolution and signalto-noise ratio (SNR) with scan times from 20 s to 5 min.Results: Motion and susceptibility artifacts were reduced through careful subject preparation. T 1 values of the ocular structures are in line with previous work at 1.5T. A voxel size of 0.15 Â 0.25 Â 1.0 mm 3 was obtained with a scan time of approximately 35 s for both 3D FFE and IR-TFE sequences. Multiple images were registered in 3D to produce final SNRs over 40. Conclusion:Optimization of pulse sequences and avoidance of susceptibility and motion artifacts led to high quality images with spatial resolution and SNR exceeding prior work. Ocular imaging at 7T with a dedicated coil improves the ability to make measurements of the fine structures of the eye.

Quantification of Age-Related and per Diopter Accommodative Changes of the Lens and Ciliary Muscle in the Emmetropic Human Eye

“…Details of the experimental setup have been reported previously. 33,34 Briefly, the subject was positioned on the MRI bed in a foam head cushion to limit movement. To decrease motion artifacts from blinks, the imaged (right) eye was taped closed, and the left eye was used to fixate targets.…”

High resolution MR eye protocol optimization: Comparison between 3D-CISS, 3D-PSIF and 3D-VIBE sequences

“…3.5 min) was developed. The scan sequences yield a voxel volume of 0.004 mm 3 and an ineplane resolution 0.08 mm 2 significantly better as compared with other studies using 1.5T systems [5,14,28,30,32,33] and comparable even with higher field systems (3e7T) [6,12,22,29].…”

“…The imaging of ocular normal anatomy and pathology, requires high-quality images with excellent tissue contrast and anatomic detail. Several studies have explored which sets of imaging parameters may optimize contrast between various parts of ocular tissues and relative compartments [1,2,29]. In the present study, a comprehensive MRI protocol providing excellent spatial resolution 0.08 Â 0.08 Â 0.60 mm 3 within a rapid scanning time (approx.…”

“…As a result, different weighting techniques, such as T1, T2, and diffusion weighting, can reveal details of the eye's structures [1,2,5,23e30]. Particularly, T1-weighted (T1w) images can provide better anatomical detail but the strong orbital fat signal can over-saturate smaller adjacent structures [5,6,29,31]. T2-weighting can improve visualization of the inner surface of the globe, because of the bright vitreous signal, but is vulnerable to motion artifacts, H 0 artifacts and has lower SNR [22,31,32].…”

Impact of Magnetic Field Strength and Receiver Coil in Ocular MRI: A Phantom and Patient Study

“…The excellent image quality of MR-microscopy at a field strength of 7.1 Tesla was introduced in ex-vivo examinations of human eyes as well as in in-vivo examinations on animals [27]. To date there have been in vivo examinations of the eye at 7 Tesla [28,29]. Because, however, only a small number of clinical 7 Tesla fullbody MRI system are currently in operation, ocular imaging must be performed at lower field strength at most centers.…”