Introduction: It is increasingly recognized that alternative methods of bone quality assessment, such as Hounsfield Units (HU) on computed tomography, may better predict biomechanical complications of instrumented fusion. The present study aims to address the influence of reconstruction plane and contrast administration on measured HU in patients undergoing lumbar spine imaging.
Methods: Patient with no prior history of spine surgery who underwent lumbar spine imaging were retrospectively identified. Three groups were generated: 1) patients without preexisting spine pathology who underwent high-resolution non-contrast lumbar computed tomography (CT) (n=150), 2) patients who underwent non-contrast and contrast-enhanced lumbar CT (n=100), and 3) patients who underwent non-contrast lumbar CT and lumbar CT myelograms (n=100).
Results: Mean age was 58.8±15.9 for group 1 (54.0% male), 65.5±15.9 for group 2 (61.4% male), and 65.2±14.2yr (53.5% male). Comparison of HU measures in group 1 showed significant differences across measurement modalities with the exception of axial versus coronal average measures (p=0.257), and coronal average versus sagittal average measures (p=0.010), and sagittal average vs mid-sagittal measures (p=0.726). There were significant differences in average axial HU for each vertebral body between contrast and noncontrast lumbar CT and between CT myelography and non-contrast CT. Linear regression analysis demonstrated extremely high correlation between measures for all methodologies (r² 0.850-0.986; all p< 0.001), and between contrast and non-contrast enhanced studies (r²=0.870; p< 0.001). Measurements on CT myelography were significantly correlated with those on non-contrast studies, though to a lesser degree (r²=0.745; p< 0.001).
Conclusion : HU measures on noncontrast CT appear similar across multiple different planes on CT, suggesting that a simpler methodology such as single-slice measurement on mid-sagittal reconstruction may allow for more rapid assessment of underlying bone quality. Consistent with prior work, contrast-enhanced CT sequences appear to reliably mirror underlying bone quality, though CT myelogram measures may vary in a more unpredictable way that precludes their use being used to interpret underlying bone quality.
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