High Signal Intensity on T1-Weighted MR Image Related to Vacuum Cleft in the Intervertebral Disk: Clinical and Phantom Study

Abstract

High signal intensity within the disk space on T1-weighted images is a unique and unusual feature of MR imaging. Calcification of the disk is known to be responsible for this phenomenon, and protein contained in fluid within the disk space is another cause (1, 2). Within this space, vacuum cleft-associated high signal intensity was revealed by T1-weighted imaging, a phenomenon which could not be explained by the mechanism mentioned above.It is well known that vacuum clefts in the disk space appear as signal voids on both T1 and T2-weighted im- 2 Purpose: To determine the possible mechanism by which an area of high signal intensity appears on T1-weighted MR images adjacent to a vacuum cleft in intervertebral disks. Materials and Methods:We analyzed a total of 14 disks in nine patients in whom a vacuum cleft with T1-signal hyperintensity was observed. Lesions were present from T11-12 to L5-S1 using a 1.5-T whole-body imager, sagittal spine-echo T1-weighted and gradient-echo images (flip angle, 20 and 60 ) were obtained. In order to identify the vacuum cleft, using plain radiographs in all patients and CT scans in two were also obtained. A 3% agar-gel block containing empty slits to form a magnetic susceptibility difference, a phantom was designed. The air spaces were 1.6 mm in thickness, 25 mm in width, and 20 to 25 mm in depth with 1.6-mm spacing.Results: In all patients, vacuum clefts were confirmed by plain radiographs and CT scans. At the level containing air, T1-weighted images (both spin-echo and gradientecho) showed a signal void resulting from the intervertebral disk vacuum cleft. A hyperintense band adjacent to the vacuum cleft was, however, observed. A gradient-echo image with a 60 flip angle showed a brighter signal intensity than one with a 20 angle. Our phantom study gave the same results. Conclusion:The magnetic susceptibility artifact may be responsible for the T1-signal hyperintensity observed adjacent to the vacuum cleft in intervertebral disks. In addition, in order to generate signal hyperintensity, the desiccating disk material must contain a certain amount of water molecules.