Improved prediction of incident vertebral fractures using opportunistic QCT compared to DXA

Abstract

Objectives: To compare opportunistic quantitative CT (QCT) with dual energy X-ray absorptiometry (DXA) in their ability to predict incident vertebral fractures.

Methods: We included 84 patients aged 50 years and older, who had routine CT including the lumbar spine and DXA within a 12-month period (baseline) as well as follow-up imaging after at least 12 months or who sustained an incident vertebral fracture documented earlier. Patients with bone disorders aside from osteoporosis were excluded. Fracture status and trabecular bone mineral density (BMD) were retrospectively evaluated in baseline CT and fracture status was reassessed at follow-up. BMD_QCT was assessed by opportunistic QCT with asynchronous calibration of multiple MDCT scanners.

Results: Sixteen patients had incident vertebral fractures showing lower mean BMD_QCT than patients without fracture (p = 0.001). For the risk of incident vertebral fractures, the hazard ratio increased per SD in BMD_QCT (4.07; 95% CI, 1.98-8.38), as well as after adjusting for age, sex, and prevalent fractures (2.54; 95% CI, 1.09-5.90). For DXA, a statistically significant increase in relative hazard per SD decrease in T-score was only observed after age and sex adjustment (1.57; 95% CI, 1.04-2.38). The predictability of incident vertebral fractures was good by BMD_QCT (AUC = 0.76; 95% CI, 0.64-0.89) and non-significant by T-scores. Asynchronously calibrated CT scanners showed good long-term stability (linear drift ranging from - 0.55 to - 2.29 HU per year).

Conclusions: Opportunistic screening of mainly neurosurgical and oncologic patients in CT performed for indications other than densitometry allows for better risk assessment of imminent vertebral fractures than dedicated DXA.

Key points: • Opportunistic QCT predicts osteoporotic vertebral fractures better than DXA reference standard in mainly neurosurgical and oncologic patients. • More than every second patient (56%) with an incident vertebral fracture was misdiagnosed not having osteoporosis according to DXA. • Standard ACR QCT-cutoff values for osteoporosis (< 80 mg/cm ³ ) and osteopenia (≤ 120 mg/cm ³ ) can also be applied scanner independently in calibrated opportunistic QCT.

Keywords: Bone density; Multidetector computed tomography; Osteoporosis; Photon absorptiometry; Spinal fractures.

Fig. 1

Left: baseline CT of a 72-year-old female patient with osteopenia according to DXA (T = − 1.7) and osteoporosis according to opportunistic QCT (BMD = 70.5 mg/cm³). Right: in follow-up after 5.2 years, the patient had sustained an incident vertebral compression fracture of L2

Fig. 2

Routine CT scan of a 63-year-old female patient for follow-up purpose after metastatic gastric cancer and liver transplant with administration of oral and intravenous contrast medium in portal venous phase. For two MDCT scanners (Siemens Somatom Definition AS [in this example] and Sensation Cardiac 64), retrospective measurements of an in-plane calibration phantom present underneath patients during routine scans were used for asynchronous calibration and evaluation of long-term scanner stability

Fig. 3

Kaplan-Meier curves of time periods without an incident vertebral fracture stratified by opportunistic QCT into patients with normal (> 120 mg/cm³), osteopenic (80 ≤ BMD ≤ 120 mg/cm³), or osteoporotic BMD (< 80 mg/cm³)

Fig. 4

Kaplan-Meier curves of time periods without an incident vertebral fracture stratified by DXA into patients with normal bone mass (T > − 1), osteopenia (− 2.5 < T ≤ − 1), or osteoporosis (T ≤ − 2.5)

Fig. 5

Receiver-operating characteristics curves for predicting incident vertebral fractures by opportunistic QCT (BMD) and DXA (T-score)