[Anatomy and pathology of the retrobulbar space in MRI using a high-resolution surface coil]

Because of its high soft tissue resolution and its lack of radiation hazard, MRI is considered a valuable method in the diagnosis of orbital disease. Insufficient spatial resolution was considered the main drawback of orbital MRI. Another problem was the chemical shift artifact caused by shifting of the signal of fat and water. To optimize image quality, a high-resolution coil with a small diameter was constructed. Twenty patients with intraorbital changes were examined with MRI. We used a special surface coil with a diameter of 4 cm. For optimal image quality we modified the bandwidth and other parameters of the sequences. For comparison additional measurements were performed in 13 patients with the standard surface coil (diameter 11 cm) and/or the head coil. The best results were obtained with a middle bandwidth (78 Hz); the chemical shift was reduced significantly. Little motion artifacts are visible in every examination caused by involuntary eye movements, which led to evaluation limitations in 3 cases. Compared to the examination with normal coils, the detection of details was much better. In 3 cases small changes were only found with the high-resolution orbital coil. With the high-resolution surface coil it is possible to examine the orbit. It is like looking through a magnifying glass. Using an optimized bandwidth, both the signal-to-noise and the chemical shift are acceptable. The new orbital coil is especially useful for the detection of small orbital lesions.