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Dual Energy CT Virtual Non-Calcium Technique detects
Post-Traumatic Bone Bruise of the Knee
SOMATOM Definition Dual Energy Scanning
Authors:
Gregor Pache, MD; Stefan Bulla, MD; Philipp Blanke MD and Mathias Langer Prof., MD
Department of Radiology, University of Freiburg, Germany
History
A 49-year old male patient, with sustained high-energy knee trauma due to a skiing accident, was referred to our department. As the radiography result was equivocal a CT scan of the knee was performed to rule out a fracture.
Diagnosis
CT revealed a small circumscribed fracture in the posteromedial tibia plateau (Fig.2). Additionally a Dual Energy CT (DECT) virtual non-calcium image (VNCa) (Fig.1b) was calculated (r value = 1.43) revealing bone marrow edema in the posteromedial and posterolateral tibia plateau. Although the edema appeared subtle on the gray-scale VNCa image the color-coded VNCa made the bone bruises obvious (Fig.1d). In light of these findings subsequently performed corresponding T2-weighted MR image confirmed both bone bruises (Fig.1c). Sagittal T2-weighted image revealed a complete anterior cruciate ligament tear (Fig.3).
Comments
The DECT virtual non-calcium technique subtracts calcium from cancellous bone, making post-traumatic bone bruises of the knee potentially detectable with CT. It is well known that the bone bruise pattern can predict associated soft tissue injuries. Typically, as seen in our case, bone bruises of the posterolateral tibial plateau are associated with anterior cruciate ligament tears. Although DECT will not replace MRI in the evaluation of knee trauma, DECT might be helpful to guide further diagnostic work-up. DECT might also constitute an option for those patients who have contraindications to MR imaging or for whom MR imaging is not available. Most importantly, as compared with the 8.71 mGy required for a single-energy CT scan, it was possible to obtain this extra information without additional radiation dose.
Fig.1a: Axial Dual Energy CT bone window shows intact osseous structures at this height of the tibial plateau.
Fig.1b:Gray-scale virtual non-calcium (VNCa) image reveals bilateral bone marrow edema (arrows).
Fig.1c: Corresponding T2-weighted MR image of post-traumatic bone bruises in the posteromedial and posterolateral tibia plateau (arrows).
Fig.1d: Colour-coded virtual non-calcium image makes the bone bruises more obvious (arrows).
Fig.2: Coronal Dual Energy CT bone window revealing a small fracture in the posteromedial tibia plateau (arrow).
Fig.3: Sagittal T2-weighted MR image rerevealing a complete tear of the anterior cruciate ligament (arrow).
Examination Protocol
| Scanner | SOMATOM Definition |
| Scan area | Knee |
| Scan length | 139 mm |
| Scan direction | Cranio-Caudal |
| Scan time | 34 s |
| Tube voltage (A/B) | 140/80 kV |
| Tube current (A/B) | 43/183 mAS |
| Dose modulation | none |
| CTDIvol | 8.69 mGy |
| DLP | 131 |
| Rotation time | 1 s |
| Pitch | 0.7 |
| Slice collimation | 20x0.6 mm |
| Slice width | 2 mm |
| Spatial Resolution | 0.33 mm |
| Reconstructed increment | 1.0 |
| Reconstruction kernel | D30 |
The information presented in this case study is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any health care practitioner reading
this information is reminded that they must use their
own learning, training and expertise in dealing with
their individual patients. This material does not substitute for that duty and is not intended by Siemens Medical Systems to be used for any purpose in that regard.
The drugs and doses mentioned herein are consistent with the approval labeling for uses and/or indications of the drug. The treating physician bears the sole responsibility for the diagnosis and treatment of patients, including drugs and doses prescribed in connection with such use. The Operating Instructions must always be strictly followed when operating the CT System. The source for the technical data is the corresponding data sheets. Results may vary.
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