Utility of the fast-field-echo resembling a computed tomography using restricted echo-spacing sequence in evaluating ossification of the posterior longitudinal ligament of the cervical spine

Background: Ossification of the posterior longitudinal ligament (OPLL) is a degenerative disease of the cervical spine. Due to the ectopic calcification of the posterior longitudinal ligament, the spinal cord or nerve roots may be compressed, producing neurological symptoms. Computed tomography (CT) is considered the "gold standard" for the diagnosis of OPLL; however, its ability to visualize soft-tissue lesions is limited. This study aimed to evaluate the utility of the magnetic resonance imaging (MRI) using the fast-field-echo resembling a computed tomography using restricted echo-spacing (FRACTURE) sequence in comparison to CT in the detection of OPLL of the cervical spine. Methods: OPLL was evaluated in 40 patients (mean age: 56.8±9.5 years, 18 women) using CT and MRI with the FRACTURE sequence. Two radiologists evaluated the following morphological parameters on both examinations: type of OPLL, distribution of OPLL, ossification thickness, canal-occupying ratio, K-line, dural calcification, and intervertebral vacuum phenomenon. Inter-observer and inter-modality agreement were analyzed. A Bland-Altman analysis was used for the quantitative data, and the Kappa coefficient was used for the categorical data. Results: The inter-observer agreement of FRACTURE-MRI images, and the inter-modality agreement between the FRACTURE-MRI images and CT images were calculated. Measurements of ossification thickness and canal-occupying ratio showed strong inter-observer agreement for the FRACTURE sequence, and strong inter-modality agreement between FRACTURE-MRI and CT. The inter-observer and inter-modality agreement was strong to perfect for the type of OPLL [0.864 (0.742-0.986) and 0.841 (0.697-0.984)], distribution of OPLL [0.785 (0.641-0.930) and 0.774 (0.645-0.903)], K-line [0.838 (0.662-1.000) and 0.893 (0.750-1.000)], dural calcification [0.806 (0.596-1.000) and 0.826 (0.638-1.000)], respectively. However, the consistency in detecting the intervertebral vacuum phenomenon was relatively poor, with values of 0.541 (0.186-0.896) and 0.483 (0.130-0.836), respectively. Conclusions: MRI with the FRACTURE sequence may be sufficient for assessing OPLL of the cervical spine. Under specific conditions, the FRACTURE sequence could serve as an alternative to conventional CT examination, reducing both the associated costs and radiation exposure.