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Dose Reduction Does Not Affect Detection of Bone Marrow Lesions with Dual-energy CT Virtual Noncalcium Technique

Posted Nov 30, 2012 Updated Apr 10, 2023
By Gregor Pache MD , Stefan Bulla MD , Tobias Baumann MD , Jörg Bayer MD , Kilian Reising MD , Peter Strohm MD , Mathias Langer MD , Philipp Blanke MD
8 min read

Rationale and Objectives

The aim of this study was to evaluate if a dose-reduced, dose-neutral dual-energy computed tomographic (CT) virtual noncalcium technique can equally detect posttraumatic bone marrow lesions (BMLs) of the knee.

Materials and Methods

Fifty patients underwent DE CT imaging with either a standard dose (group A) or a dose equal to that of a single-energy CT scan (group B) (28% dose reduction) and magnetic resonance imaging for knee trauma workup. Calcium was virtually subtracted from the images. Two radiologists rated the presence of abnormal soft tissue–like attenuation in the bone marrow in a total of 12 femoral and tibial regions and performed Hounsfield unit measurements thereafter. Receiver-operating characteristic curve analysis was used for four-point rating scores and Hounsfield unit measurements. Fractures were classified.

Results

Magnetic resonance imaging depicted 170 BMLs (35 femoral, 135 tibial). Mean age, number of fractures, attenuation values and number of regions with BMLs were not significantly different between the groups. Visual rating revealed overall areas under the curves of 0.983 and 0.979 for observers 1 and 2, respectively. Visual judgment was superior to attenuation measurements for femoral regions regardless of the dose applied. Analysis of variance of all CT values revealed a significant influence for the presence of edema ( P < .001) but no differences for the radiation dose used ( P = .424). Interobserver agreement was excellent (κ = 0.944).

Conclusions

Dose reduction does not affect the detectability of posttraumatic BMLs with a dual-energy CT virtual noncalcium technique, thereby providing potential additional information compared with single-energy CT imaging without additional radiation dose.

The introduction of dual-source spiral computed tomographic (CT) scanners has revived dual-energy (DE) CT imaging, thereby providing new applications such as the virtual unenhanced scanning, in which iodine can be virtually removed from a contrast-enhanced CT examination . This technique was recently adopted to virtually subtract calcium from cancellous bone to allow bone marrow assessment . This “virtual noncalcium” (VNCa) technique was proven in a feasibility study to detect posttraumatic bone bruises of the knee with computed tomography, an imaging diagnosis associated solely with magnetic resonance (MR) imaging (MRI) thus far . However, additional information was obtained by raising the radiation dose to approximately 28% that used for a single-energy CT knee scan . The routine application of this technique is problematic because of this drawback. However, if this examination were feasible at a dose equal to that of single-energy CT imaging without losing diagnostic image quality, the additional knowledge about the presence and the distribution pattern of bone marrow lesions might facilitate further patient management .

Thus, it was our aim to investigate the diagnostic performance regarding the detectability of posttraumatic bone marrow lesions of the knee with a dose-reduced, dose-neutral application compared with the established DE CT VNCa protocol, with MRI as the standard of reference.

Materials and methods

Study Population

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CT Protocol

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Image Reconstruction

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DE Postprocessing

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MRI Protocol

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Image Analysis

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Statistical Analysis

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Results

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Table 1

Patient Characteristics

Variable Group A (Standard Dose) (n = 25) Group B (Reduced Dose) (n = 25)P Men/women 16/9 14/11 .773 Mean age (y) 38.3 ± 14.9 39.1 ± 13.5 .620 Age range (y) 18–67 18–74 – Mean time between CT imaging and MRI (d) 1.72 ± 2.41 1.92 ± 2.45 .792 Number of fractures 15 16 – Injury mechanism Traffic accident 14 12 Fall from height 11 13 Type of tibial plateau fracture (AO class) A 0 1 B 10 11 C 3 2 Femoral condyle fracture 1 2 – Proximal tibia shaft fracture 1 0 – Mean attenuation value (HU) −78.74 −81.2 .37 Number of regions with MRI-proven bone marrow lesion 86 84 .615 Number of patients without BME 3 2 –

BME, bone marrow edema; CT, computed tomographic; HU, Hounsfield units; MRI, magnetic resonance imaging.

Data are expressed as mean ± standard deviation or as numbers.

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Figure 1, A 54-year-old woman (a–c) and a 43-year-old woman (d–f) with posttraumatic bone bruises in the lateral tibial plateau after traffic accidents. In both standard-dose (a,b) and dose-reduced (d,e) transverse dual-energy computed tomographic grayscale (a,d) and color-coded virtual noncalcium images (b,e) , bone bruises are clearly visible, consistent with magnetic resonance findings (c,f) . In both patients, computed tomography revealed small fracture lines directly adjacent to the tibial plateau (not shown) caused by circumscribed depression fractures (AO class B1).

Table 2

Rank Correlation Coefficients of Edema Scores Derived from Dual-energy Computed Tomography and Magnetic Resonance Imaging

Overall (95% CI) Group A (95% CI) Group B (95% CI) Intergroup P Value Reader 1 0.968 (0.963–0.973) 0.972 (0.965–0.977) 0.964 (0.956–0.972) .120 Reader 2 0.965 (0.959–0.970) 0.969 (0.961–0.975) 0.962 (0.952–0.969) .207 Interreader P value 0.431 0.529 0.737

CI, confidence interval.

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Table 3

Areas under the Curves for Visual Judgment for Observers 1 and 2 and for Computed Tomographic Numbers

ROC Analysis Reader Group A (95% CI) Group B (95% CI) Group A + Group B (95% CI) Overall Femur Tibia Four-point scale 1 0.985 (0.964–0.995) 0.981 (0.958–0.993) 0.983 (0.969–0.992) 0.970 (0.944–0.986) 0.983 (0.962–0.995) Four-point scale 2 0.978 (0.955–0.992) 0.980 (0.956–0.992) 0.979 (0.964–0.989) 0.940 (0.907–0.964) 0.987 (0.966–0.996) Attenuation (HU) 0.895 (0.855–0.928) 0.943 (0.910–0.966) 0.918 (0.893–0.938) 0.864 (0.820–0.901) 0.966 (0.939–0.983)

CI, confidence interval; HU, Hounsfield units; ROC, receiver-operating characteristic.

Figure 2, Transverse dose-reduced dual-energy computed tomographic bone window (a) , grayscale (b) , and color-coded (d) virtual noncalcium images and T2-weighted magnetic resonance image (c) of posttraumatic bone bruises in the lateral femoral condyle of a 27-year-old woman. The subtle edema in the posterior region was visually detected (rated 2 by both observers), although Hounsfield unit values did not indicate edema (−57 Hounsfield units).

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Figure 3, Box plots of mean attenuation measurements (Hounsfield units [HU]) in the femur and tibia for normal and pathologic marrow regardless of the dose used. Boxes indicate first to third quartiles, and bold lines indicate medians.

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Figure 4, A 42-year-old man with a traumatic knee contusion. Transverse (a) and coronal (c) source dual-energy computed tomography bone window revealing a small bone island in the posteromedial femoral condyle ( arrow in c) . On the T2-weighted magnetic resonance image (d) , a bone bruise can be ruled out, whereas incomplete masking of the lesion on grayscale (not shown) and color-coded (b) virtual noncalcium images made one of the observers report a bone marrow lesion (rated as less pronounced attenuation change, score 2), while the other observer judged this region as equivocal (score 1).

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Discussion

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Conclusions

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Academic Radiology, Volume 19, Issue 12
Journals General Radiology
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