In vivo MR Diffusion Weighted Imaging at 7 Tesla - feasibility study in healthy subjects and patients with different ophthalmic disease

Abstract

Purpose: Diffusion-weighted imaging (DWI) of the eye and orbit is an emerging MRI application for ophthalmic research, preclinical imaging and diagnostic radiology. DWI probes and depicts self-diffusion of water in tissue on a microscopic scale and holds the promise to enhance diagnostic accuracy and provide further physiological information for different ophthalmic disease. The purpose of this study was to show the feasibility of in vivo DWI at 7 T with diffusion sensitized multi-shot RARE sequences.

Methods: In vivo MR imaging and DWI was performed at 7T in healthy subjects (n=5), patients with uveal melanoma and/or retinal detachment (n=5) and a patient with optic nerve glioma. A dedicated six element transmit and receive coil array was employed at 7.0 T and high resolution T1 weighted 3D FLASH imaging (TR=710.3ms, TE=3.6ms, spatial resolution = (0.3x0.3x1.0)mm³ and T2-weighted RARE imaging (TR=2940ms, TE=54ms, spatial resolution = (0.25x0.28x1.0)mm³ were conducted for anatomical imaging. For ADC mapping diffusion sensitized multi-shot RARE was used (7.0 T: TR=3000ms, TE=133ms, spatial resolution = (0.4x0.4x3.0)mm³). For diffusion sensitization b-values ranging from b=0 s/mm² to b=400 s/mm² were employed. To reduce eye movement during imaging the subjects followed an optoacoustic trigger protocol.

Results: The in vivo ADC map of patients with ocular mass clearly delineates hypointense tumor from the surrounding modest hypointense hemorrhage and the hyperintense vitreous body. These ADC differences induced an ample contrast between the subretinal hemorrhage and the tumor. ADC map of orbita in a patient with optic nerve glioma showed ample ADC contrast versus the subarachnoid space. The ADC map of the eye and optic nerve yielded a delineation of the tumor which is superior to the contrast in the T2 weighted images.

Conclusions: This work demonstrates the feasibility of in vivo MR microscopy and diffusion sensitized ms-RARE of the eye and optic nerve at 7.0T including T1w, T2w anatomical imaging along with DWI and ADC mapping. This study showed that ms-RARE based techniques offer immunity to B₀ inhomogeneities and hence are particularly suited for ophthalmic DWI. This is of clinical relevance since single-shot echo planar imaging is prone to magnetic susceptibility artifacts induced by the air filled nasal cavities and frontal sinuses surrounding the eye.