PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) and EPI Diffusion-weighted MR Imaging at 3.0T: Pontine Magnetic Susceptibility Artifacts Depend on Pneumatization of the Sphenoid Sinus

Sohn, Chul Ho; Kim, In Soo

Abstract

PURPOSE
In the case of well pneumatized sphenoid sinus, magnetic susceptibility artifact can be visualized at the brainstem and especially at the pons on echo-planar imaging (EPI) diffusion-weighted imaging. Fast spin-echo periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) is a novel imaging method that can reduce these artifacts. In 3.0T MR, we first evaluate the degree of the relationship of pneumatization of the sphenoid sinus with the occurrence of magnetic susceptibility artifacts (MSA) on the echo planar imaging (EPI) diffusion-weighted imaging (DWI), and we evaluated using PROPELLER-DWI for cancellation of MSAs of the pons in the patients who had MSAs on the EPI-DWI.
MATERIALS AND METHODS
Sixty subjects (mean age: 58 years old and there were 30 men) who were classified according to the two types of sphenoid sinus underwent EPI-DWI. The two types of sphenoid sinus were classified by the degree of pneumatization on the sagittal T2-weighted image. The type-1 sphenoid sinus was 0% to less than 50% aeration of the bony sellar floor, and type-2 was 50% or more aeration of the boney sellar floor. Each of 10 subjects (n=20/60, mean age: 53) of the two types had PROPELLER and EPI-DWI performed simultaneously. We first evaluated the absence or presence of MSAs at the pons in the two types, and we compared EPI and PROPELLER-DWI in the subjects who underwent the two MR sequences simultaneously. We used 3.0T MR (Signa VHi, GE, MW, U.S.A.) with a standard head coil. All the MR images were interpreted by one neuroradiologiest.
RESULTS
For the type-1, two (6.7%) cases had MSAs and 28 (93.7%) cases did not have MSAs on the EPI-DWI. For the type-2, twenty-seven (90%) cases had MSAs and 3 (10%) cases did not have MSAs on the EPI-DWI. The degree of pneumatization of the sphenoid sinus was related with the occurrence of MSAs of the pons, according to the chi-square test (p=0.000). All twenty cases who had PROPELLER-DWI performed had no MASs at the pons regardless of the type of sphenoid sinus. But all ten cases of type-2 produced MASs on the EPI-DWIs
CONCLUSION
For EPI-DWI, a well aerated sphenoid sinus can induce MASs at the pons, and we should recognize this phenomenon to differentiate it from true infarcted lesion. PROPELLER DWI can be an optional tool to use for canceling this artifact.