Differentiation of osteolytic metastases and Schmorl's nodes in cancer patients using dual-energy CT: advantage of spectral CT imaging.

PURPOSE: To assess the reliability of dual-energy CT (DECT) spectral imaging for the differentiation of bone metastases (BMs) from Schmorl's nodes (SNs) in the vertebrae of cancer patients.

MATERIALS AND METHODS: In this retrospective study, 102 cancer patients who underwent DECT (GE spectral CT Discovery CT750 HD scanner) had 110 low density vertebral lesions. Each lesion was characterized as a BM or SN, based on the typical MRI or SPECT/PET-CT findings as well as size and number change in the 6 months follow-up. The means of 140 kVp polychromatic CT values, 40-140 keV monochromatic CT values, slopes (k) of the spectral curves, bone(water) and water(bone) densities of BMs and SNs were measured and compared with independent-samples t-test. The difference values of the two lesions and their respective normal bone tissue were calculated (normal density-lesion density) and compared using independent-samples t-test. ROC curves were used to compare the diagnostic efficacies of these measures in the identification of SNs and BMs.

RESULTS: 110 lesions consisting of 69 BMs and 41 SNs were identified. The spectral curve patterns and slopes for BMs and SNs were different (p<0.05). The water(bone) density of BMs (1009.02 ± 59.25mg/cm(3)) was higher than that of SNs (892.00 ± 83.65 mg/cm(3)) (p<0.01) while the bone(water) density (43.57 ± 50.87 mg/cm(3)) was lower than that of SNs (174.60 ±94.61 mg/cm(3)) (p<0.01). The 40 keV CT value, k, bone(water) density and water(bone) density had a higher diagnostic efficacy for differentiating the two lesions than polychromatic CT value (p<0.05).

CONCLUSIONS: Dual-energy CT imaging is accurate enough for identification of osteolytic metastases and Schmorl's nodes.