Dual-energy CT in sacral fragility fractures: defining a cut-off Hounsfield unit value for the presence of traumatic bone marrow edema in patients with osteoporosis

Abstract

Background: Demographic change entails an increasing incidence of fragility fractures. Dual-energy CT (DECT) with virtual non-calcium (VNCa) reconstructions has been introduced as a promising diagnostic method for evaluating bone microarchitecture and marrow simultaneously. This study aims to define the most accurate cut-off value in Hounsfield units (HU) for discriminating the presence and absence of bone marrow edema (BME) in sacral fragility fractures.

Methods: Forty-six patients (40 women, 6 men; 79.7 ± 9.2 years) with suspected fragility fractures of the sacrum underwent both DECT (90 kVp / 150 kVp with tin prefiltration) and MRI. Nine regions-of-interest were placed in each sacrum on DECT-VNCa images. The resulting 414 HU measurements were stratified into "edema" (n = 80) and "no edema" groups (n = 334) based on reference BME detection in T2-weighted MRI sequences. Area under the receiver operating characteristic curve was calculated to determine the desired cut-off value and an associated conspicuity range for edema detection.

Results: The mean density within the "edema" group of measurements (+ 3.1 ± 8.3 HU) was substantially higher compared to the "no edema" group (-51.7 ± 21.8 HU; p < 0.010). Analysis in DECT-VNCa images suggested a cut-off value of -12.9 HU that enabled sensitivity and specificity of 100% for BME detection compared to MRI. A range of HU values between -14.0 and + 20.0 is considered indicative of BME in the sacrum.

Conclusions: Quantitative analysis of DECT-VNCa with a cut-off of -12.9 HU allows for excellent diagnostic accuracy in the assessment of sacral fragility fractures with associated BME. A diagnostic "one-stop-shop" approach without additional MRI is feasible.

Keywords: Bone bruise; Bone marrow edema; Dual-energy computed tomography; Fragility fracture; Virtual non-calcium imaging.

Conflict of interest statement

JPG serves as a research consultant for Siemens Healthcare GmbH and receives speaker honoraria outside of the presented work. The other authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.

© 2022. The Author(s).

Figures

Fig. 1

Virtual non-calcium (VNCa) image of the sacrum (coronal view). The red circles represent the nine locations where Hounsfield units (HU) were measured within regions of interest

Fig. 2

a Axial CT image that fails to demonstrate a discrete fracture line in the sacrum. b Color-coded coronal DECT reconstruction image with region-of-interest measurement in the right inferior region of the sacrum. Blue represents lower HU values of approximately -50 HU, whereas yellow/light green indicates higher HU values around + 10 HU. c Coronal T2-weighted STIR sequence demonstrates edema in the same locations

Fig. 3

Dotplots showing the distribution of Hounsfield unit (HU) measurements using dual-energy CT. The red dotted line indicates the calculated cut-off value of -12.9 Hounsfield units (HU), which allowed for the most accurate discrimination between the presence or absence of bone marrow edema (left). Employing the cut-off value to calculate classification functions of diagnostic accuracy results in the highest possible sensitivity and specificity (right)

Fig. 4

Box-and-whisker plot showing the distribution of Hounsfield unit (HU) measurements at the fourth or fifth lumbar vertebra in patients with osteoporosis (“fracture and osteoporosis”), patients without osteoporosis but with osteoporotic fractures (“fracture and suspected osteoporosis”) and patients without osteoporosis and without osteoporotic fractures (“no fracture”)

Fig. 5

a Coronal VNCa reformatting of dual-energy CT suggested the absence of edema at the upper measurement sites (-47.1 HU and -57.7 HU), whereas the presence of edema was indicated for the lower measurement sites (+ 7.3 HU and + 7.4 HU). b Corresponding sagittal T2( STIR image (at 1.5 Tesla) of the same patient with marked edema in the lower sacrum (red circle). In contrast, no edema was ascertained in the upper sacrum (white arrow). c Axial T2 STIR image (at 1.5 Tesla) confirmed the presence of edema in both sides of the lower sacrum (red circle)