Assessment of bone density using the 1.5 T or 3.0 T MRI-based vertebral bone quality score in older patients undergoing spine surgery: does field strength matter?

Abstract

Background context: Recently published studies have revealed a correlation between MRI-based vertebral bone quality (VBQ) score and bone mineral density (BMD) measured using dual X-ray absorptiometry (DXA) or quantitative computed tomography (QCT). However, no studies have determined if differences in field strength (1.5 vs 3.0 T) could affect the comparability of the VBQ score among different individuals.

Purpose: To compare the VBQ score obtained from 1.5 T and 3.0 T MRI (VBQ_1.5T vs VBQ_3.0T) in patients undergoing spine surgery and assess the predictive performance of VBQ for osteoporosis and osteoporotic vertebral fracture (VCF).

Design: A nested case‒control study based on an ongoing prospective cohort study of patients undergoing spine surgery.

Patient sample: All older patients (men aged >60 years and postmenopausal women) with available DXA, QCT and MR images within 1 month were included.

Outcome measures: VBQ score, DXA T-score, and QCT derived vBMD.

Methods: The osteoporotic classifications recommended by the World Health Organization and American College of Radiology were used to categorize the DXA T-score and QCT-derived BMD, respectively. For each patient, the VBQ score was calculated using T1-weighted MR images. Correlation analysis between VBQ and DXA/QCT was performed. Receiver operating characteristic (ROC) curve analysis, including determination of the area under the curve (AUC), was performed to assess the predictive performance of VBQ for osteoporosis.

Results: A total of 452 patients (98 men aged >60 years and 354 postmenopausal women) were included in the analysis. Across different BMD categories, the correlation coefficients between the VBQ score and BMD ranged from -0.211 to -0.511, and the VBQ_1.5T score and QCT BMD demonstrated the strongest correlation. The VBQ score was a significant classifier of osteoporosis detected by either DXA or QCT, with VBQ_1.5T showing the highest discriminative power for QCT-osteoporosis (AUC=0.744, 95% CI=0.685-0.803). In ROC analysis, the VBQ_1.5T threshold values ranged from 3.705 to 3.835 with a sensitivity between 48% and 55.6% and a specificity between 70.8% and 74.8%, while the VBQ_3.0T threshold values ranged from 2.59 to 2.605 with a sensitivity between 57.6% and 67.1% and a specificity between 67.8% and 69.7%.

Conclusions: VBQ_1.5T exhibited better discriminability between patients with and without osteoporosis than VBQ_3.0T. Considering the non-negligible difference in osteoporosis diagnosis threshold values between the VBQ_1.5T and VBQ_3.0T scores, it is essential to clearly distinguish the magnetic field strength when assessing the VBQ score.

Keywords: Bone mineral density; Field strength; Magnetic resonance imaging; Osteoporosis; Vertebral bone quality; Vertebral compression fracture.