Effect of Magnetic Resonance Imaging Field Strength on Delineation and Signal Intensity of Alar Ligaments in Healthy Volunteers

Abstract

A prospective study of healthy volunteers. To evaluate the influence of magnetic resonance imaging (MRI) field strength on the delineation and signal intensity of alar ligaments (AL) in healthy volunteers. The fact that AL physiologically show morphologic variabilities is well established. However, presence and etiology of high-signal intensities within the AL as well as the influence of the MRI field strength on the signal characteristics of AL are still not completely understood. METHODS.: Coronal and sagittal 2-mm proton-density weighted sequences were acquired in 50 healthy volunteers using different MRI field strengths (1 T, 1.5 T, 3 T). Delineation and signal characteristics of AL were evaluated by 2 neuroradiologists independently. Differences concerning delineation and signal intensity between the MRI scanners, inter rater reliability between the 2 readers, and intrarater reliability at different time points were calculated. Delineation of AL was significantly better both on 3 T and 1.5 T than on 1 T (P = 0.05) in sagittal as well as in coronal view. In coronal view delineation was significantly better on 3 T than on 1.5 T, whereas in sagittal view no significant difference was evident when comparing 1.5 T and 3 T. Concerning signal intensity of AL in sagittal view, there was no significant difference between the 3 different field strengths. Inter-rater and intrarater agreements were fair to moderate with respect to delineation as well as signal intensity of AL. 1.5 T and 3 T significantly improve the delineation of AL when compared with lower field strength (1 T), but signal intensity of the AL in healthy volunteers is not influenced by the field strength. Increased signal is present in asymptomatic subjects on both low- and high-field magnetic resonance systems. Accordingly, the pathologic relevance of increased signal intensity of the AL, regardless of field strength, may not be indicative of traumatic AL injury.