A quantitative analysis of spectral computed tomography characteristics of osseous metastases.

Introduction: Spectral detector computed tomography (SDCT) is a recent advancement that enables elemental material decomposition which could improve the detection of osseous metastases in the oncologic patient.

Methods: Sixteen patients who underwent oncologic staging SDCT as well as WBBS with Technetium-99 m hydroxydiphosphonate (Tc99m HDP) were included in this retrospective study. A total of 50 osseous metastases were identified and confirmed on bone scintigraphy. Quantitative ROI-based measurements of each lesion and a similar region of normal bone were performed, and the acquired spectral data were used for comparison. These parameters included effective atomic number (Z ), electron density (%EDW) and calcium suppression (HU). Receiver operating characteristic (ROC) analysis was performed.

Results: In comparison to normal bone, osseous metastases showed statistically significantly elevated values in effective atomic number, electron density and calcium suppression. ROC analysis demonstrated outstanding discrimination with area under the curve (AUC) values of 0.934 and 0.915 for effective atomic number and electron density, and excellent discrimination with an AUC value of 0.884 for calcium suppression. Threshold values of effective atomic number (Z ) >9.7, electron density >115% EDW and calcium suppression values >0 HU were demonstrated to be able to differentiate an osseous lesion from normal bone with a sensitivity of 82%, 82% and 84% and a specificity of 86%, 92% and 88% respectively.

Conclusion: Spectral analysis of osseous metastases demonstrated significantly elevated values in effective atomic number, electron density and calcium suppression as compared to normal bone which would be useful adjunct quantitative parameters in CT imaging to increase diagnostic confidence.