|ECR 2015 / C-0553|
|High resolution imaging of scaphoid fracture with Herbert screw treatment: comparative findings on a cadaveric wrist with digital tomosynthesis, CT, CT with iterative reconstruction and cone beam CT|
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Findings and procedure details
Experimental setup and imaging sessions
In this experimental study (Fig. 3), we performed image acquisition on a cadaveric forearm with four techniques: digital tomosynthesis (Definium 8000, GE Healthcare), high resolution CT, CT with iterative reconstruction (both Discovery 750HD, GE Healthcare) and cone beam CT with a supine scanner (Newtom 5G, QR, Verona).
Prior to the first imaging session, an orthopaedic surgeon induced a controlled transverse osteotomy of the scaphoid. A second imaging session was performed after reduction of the osteotomy with placement of a Herbert screw. Obtained images are qualitatively assessed for: detail, bony delineation, beam hardening and metallic artifacts.
Both radiography and tomosynthesis images clearly depict fracture of the scafoid (Fig. 4 left, white arrow). After placement of the Herbert screw, dark bands appear at the boundary of the metal in case of the tomosynthesis images (Fig. 4 right, black arrows). This artefact is caused by the reconstruction process.
The fracture of the scaphoid can also be readily visualised on high resolution CT with and without iterative reconstruction as well as on the cone beam examination (Fig. 5). When comparing the high resolution CT images with those reconstructed by means of iterative techniques, the cortical bone appears clearly sharper on the iteratively reconstructed images. This way the fracture of the scaphoid becomes much more obvious. The cortical bone delineation however becomes somewhat irregular, most clearly visible at the distal surface of the radius and the lateral surface of the capitate. This staircase artifact feature can best be seen on the magnification views of the scaphoid (black arrows). This reconstruction artefact also propagates in the radio-scaphoid and the scaphocapitate joint space respectively. Comparing these two convential CT studies with the cone beam study, the latter images show an even better resolution. The cortical bone aswell as the trabecular pattern are more delineable and the fracture of the scaphoid is equally discernible compared to the iteratively reconstructed CT images. In contrast to the CT images with iterative reconstruction, the distal surface of the radius appears much smoother on the magnification views of the scaphoid on the cone beam study.
When looking at the studies of the wrist taken after placement of the Herbert screw, it becomes obvious that the metal artefacts present on the high resolution CT can be greatly diminished by use of iterative recontruction algorithms (Fig. 6). However streak artefacts are still clearly recognizable on the CT images with iterative reconstruction, whereas they are virtually non-existent on the cone beam study.
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