Peter Wassenaar MS, Presenter: Nothing to Disclose

Titus Lanz PhD, Abstract Co-Author: Employee, RAPID MR International, LLC

Kathryn Richdale OD, MS, Abstract Co-Author: Nothing to Disclose

John Christoforidis MD, Abstract Co-Author: Nothing to Disclose

Petra Schmalbrock PhD, Abstract Co-Author: Nothing to Disclose

Michael Vinzenz Knopp MD, PhD, Abstract Co-Author: Nothing to Disclose

Regina Maria Koch MD, Abstract Co-Author: Nothing to Disclose

Steffen Sammet MD, PhD, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

Imaging of the eye/orbit at 7T is feasible, and considered safe with the setup described above. High spatial resolutions and increased signal give way to superior image quality.

Ultrahigh field MRI will be beneficial to advance MRI of the eye by overcoming current spatial resolution limits, e.g. for characterizing melanoma, assessment of optic nerve vascular disease, macular degeneration, or for ocular biometry of the ciliary body or lens. Safe, dedicated eye coils and pulse sequence optimization are needed.

A dedicated 4cm, receive only RF surface coil was developed (Rapid MR International, LLC) and used with a head volume transmit coil at 7T (Philips Achieva). A combination of active decoupling to turn off the receive coil during transmit and passive protection with a fuse in case of malfunction were implemented as safety features. Safety assessments included temperature measurements in phantoms, fresh enucleated and in situ pig and dog eye. Nonmagnetic temperature probes (Luxtron) were inserted in the vitreous humor, behind the globe, and on the cornea. Testing was conducted using Turbo Spin Echo sequences at the highest RF power levels the scanner can deliver given hardware and software limits set by the manufacturer. Initial contrast optimization studies were carried out in healthy volunteer and in situ pig eyes and included T1-weighted 3D Inversion Recovery prepared Turbo Field Echo (IR-TFE) sequences with a range of TI and shot intervals TS (TI=700-3750ms, TS=2000-6000ms, TR=4-10ms, TE=3-6ms, turbo-factor 128-256).

No temperature increase was observed within the accuracy range of the probe (0.2°C) during 20 min scans at the highest RF power levels (>3.2W/kg). The depth penetration of the coil was about 30mm, i.e. ¾ of its diameter. Excellent depiction of the eye anatomy is achieved, with clear visualization of the lens and ciliary body and chorio-retina. Motion artifacts were minimized by mentally focusing on a near vision target. Best SNR and CNR was achieved with TS/TI=5000/3750ms allowing for a reconstructed voxel size of 0.1x0.1x0.5mm3 in 5:20min scan time in vivo.

Wassenaar, P, Lanz, T, Richdale, K, Christoforidis, J, Schmalbrock, P, Knopp, M, Koch, R, Sammet, S, et al, , Development and Safety Assessment of a Dedicated Eye Coil for 7T MRI.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6016639.html