DIAGNOSTICS SPINE Volume 37, Number 17, pp E1062–E1067 ©2012, Lippincott Williams & Wilkins E1062 www.spinejournal.com August 2012 Effect of Magnetic Resonance Imaging Field Strength on Delineation and Signal Intensity of Alar Ligaments in Healthy Volunteers Nina Lummel, MD ,* Veronika Schöpf, Dipl.Ing,† Harro Bitterling, MD,‡ Christian Zeif, MD ,* Andrea Kloetzer, MD,* Hartmut Brückmann, MD,* and Jennifer Linn, MD* Study Design. A prospective study of healthy volunteers. Objective. To evaluate the inﬂuence of magnetic resonance imaging (MRI) ﬁeld strength on the delineation and signal intensity of alar ligaments (AL) in healthy volunteers. Summary of Background Data. 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. Results. 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. Conclusion. 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 A lar ligaments (AL) connect the dens axis to the occipital condyles and play an important role in the movement and stability of the craniocervical junction. 1 ,2 Because of their suggested involvement in whiplash-associated disor- der after head or neck trauma, extensive in vivo and postmor- tem investigations have been performed on AL anatomy and signal characteristics on magnetic resonance imaging (MRI) since the 1990s. Imaging studies showed that the upper cervi- cal ligaments, including AL, can be adequately evaluated on MRI, 3 –7 especially using thin proton-density (PD)-weighted sequences. 8 Data consistently showed a high anatomic vari- ability of AL in the craniocaudal as well as in the anterodor- sal orientation, frequently with an asymmetric appearance. 4 ,7 ,8 Still not conclusively resolved is the presence and etiology of hyperintense signal alterations within AL. MRI-investigations using low-ﬁeld magnetic strength (0.2 T–0.5 T) 4 ,5 ,9 –11 as well as using higher-ﬁeld magnetic strength (1.5 T) 7 ,12 ,13 are incon- sistent on whether high-signal intensities in the AL account for anatomic variances or whether they should be interpreted as pathological ﬁndings indicative of AL trauma. As signal- to-noise ratio changes with the use of different magnetic ﬁeld strengths, an inﬂuence of the ﬁeld strength on the delineation and signal characteristics of AL is probable, however, it has not been systematically investigated to date. For this reason, we conducted this study to evaluate the inﬂuence of MRI ﬁeld strength on the delineation and signal intensity of AL in healthy volunteers. MATERIALS AND METHODS Subjects This study was approved by the regional ethics committee. Volunteers were recruited by a notice in our hospital entrance From the *Department of Neuroradiology, University of Munich, Munich, Germany; †MR Centre of Excellence, Medical University Vienna, Vienna, Austria; and ‡Sygehus Sønderjyll, Sønderborg, Danmark. Acknowledgment date: September 6, 2011. First revision: December 2, 2011. Second revision date: January 25, 2012. Third revision date: March 13, 2012. Acceptance date: March 16, 2012. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No beneﬁts in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Nina Lummel, MD, Department of Neuroradiology, University of Munich, Grosshadern, Marchioninistrasse 15, 81377 Munich, Germany; E-mail: nina.lummel@med. uni.muenchen.de 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. Key words: alar ligaments, delineation, signal characteristics, magnetic resonance imaging, ﬁeld strength, Tesla. Spine 2012;17:E1062–E1067 DOI: 10.1097/BRS.0b013e31825831ca Copyright © 2012 Lippincott Williams & Wilkins. 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