MR imaging of the optic nerve and chiasm at 7 Tesla improves lesion detection for Neuro-Ophthalmic conditions compared to conventional clinical field strength

Abstract

Purpose : Growth of a pituitary adenoma impinges on the optic chiasm causing visual field (VF) defects to varying degrees. Surgical removal of the tumor often restores most of the visual function. However, the VF defects occasionally reoccur years after successful treatment. MRI is currently an important tool for diagnosis and therapy planning. Conventional clinical scanners operate at a field strength of 3 Tesla (T). However, scanning patients at the ultra-high field strength of 7T has the potential to acquire higher resolution images than at 3T. In this study, we evaluate the additional value of 7T MRI in the diagnosis and treatment of pituitary macro-adenomas.

Methods : Nine controls and seven patients were scanned on a commercial Philips whole body 7T MR system. 3D T1-weighted gradient-echo with isotropic resolution (0.7mm³); and 2D T2-weighted spin echo (0.45x0.45x1.0mm³) were acquired. For comparison, standard clinical protocol was run on a 3T Philips system.

Results : The 7T scan protocol gave reproducible image quality for each of the patients scanned, with image quality superior to 3T. In three patients the 7T MRI revealed important clinical information that was not visible at 3T. In two patients, a small lesion was noted in the optic nerve (ON) at 7T (Figure 1) which was not visible in the 3T images. The location of the lesions corresponded to the VF defects. This was an important confirmation for the ophthalmologists to tailor treatment strategy. In a second patient, the thinner (1mm vs 3mm) slices that could be acquired at 7T due to its superior signal-to-noise showed tumor contact with the chiasm (Figure 2) whilst at 3T this was not visible. This was key for the neurosurgeon to plan the best intervention.

Conclusions : This study shows that 7Tesla MRI provides direct clinical opportunities for the treatment of patients with pituitary tumors and other neuro-ophthalmic conditions.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

VF defect recurrence 4 years post treatment. Hyperintense lesions in ON clearly visible and not visible on 3T. Location of lesions corresponds with VF defect

 

T1 (top) T2 (lower) pre-op MRI showing large pituitary macro-adenoma. 7T image shows contact between tumor and chiasm, this is not apparent on 3T