Abstract
Dear Editor,
We read with great interest the article by Kohli et al., 1 titled “Streamlining the MRI-Derived Vertebral Bone Quality Score for Preoperative Osteoporosis and Osteopenia Screening”, published in *Global Spine Journal*. The authors should be commended for proposing a simplified MRI-derived vertebral bone quality score based on L1/L2 measurements (VBQ_L1/2), which may reduce measurement burden and improve the feasibility of opportunistic bone quality screening before lumbar spine surgery. Their finding that VBQ_L1/2 showed excellent agreement with the traditional VBQ_L1–4 method is promising. However, we wish to highlight a critical methodological concern: the clinical applicability of a shortened VBQ score depends not only on its agreement with the original method, but also on the transportability of its absolute cutoff values across MRI scanners, acquisition protocols, and patient populations. VBQ is derived from T1-weighted MRI signal intensity normalized to cerebrospinal fluid signal intensity. Although this normalization may reduce some variability, VBQ values are not inherently parameter-independent. Scanner field strength, echo time, repetition time, bandwidth, coil configuration, and post-processing methods may influence signal intensity and therefore the final VBQ value. A previous study by Liu et al. 2 demonstrated that VBQ values differed significantly between 1.5T and 3.0T MRI scanners under otherwise similar clinical conditions, and that even bandwidth changes within the same scanner affected VBQ measurement. These findings suggest that cutoff values derived from a single imaging environment may not be directly generalizable.
This issue is particularly relevant for VBQ_L1/2 because the proposed threshold was derived using receiver operating characteristic analysis and Youden index optimization in a single cohort. Although the reported sensitivity for detecting osteoporosis was high, the corresponding specificity was relatively low, which may increase false-positive referrals for DXA or quantitative CT and affect clinical workflow and resource use. In addition, patients with unsuitable MRI scans were excluded, and the prevalence of impaired bone quality in the analyzed cohort was high, both of which may influence predictive values and limit threshold generalizability. Therefore, before VBQ_L1/2 is adopted as a broadly applicable preoperative screening tool, further validation across MRI field strengths, acquisition parameters, institutions, and surgical populations is warranted. Future studies should clearly report key MRI parameters, assess cross-scanner reproducibility, develop calibration strategies when necessary, and evaluate clinically relevant screening consequences, including false-positive burden and downstream referral rates. We appreciate the valuable contribution of Kohli et al. Their simplified approach is attractive and clinically practical, but standardization and external validation remain essential before its cutoff values can be broadly generalized.
