New CT Scanner Spots Knee Injuries That Standard Scans Miss

<p>Computed tomography (CT) is widely used for fracture detection and postsurgical evaluation. Recent advancements have opened new possibilities, particularly in spectral CT, which utilises the energy-dependant attenuation properties of tissues to enable tissue differentiation and enhance diagnostic capabilities. The two primary techniques employed in spectral CT are Dual-energy CT (DECT) and, more recently, photon-counting detector CT (PCD-CT). The overall aim of this thesis is to investigate the use of spectral CT for improved imaging of the injured knee.</p><p>In Study I, the diagnostic accuracy of DECT for detecting bone marrow lesions (BMLs) in patients with suspected anterior cruciate ligament (ACL) injury was assessed. BMLs, commonly observed on MRI as a result of bone contusions, provide insights into trauma mechanisms and associated injuries. In standard CT, the attenuation differences corresponding to these lesions are obscured by overlying bone. DECT overcomes this, generating virtual non-calcium (VNCa) images as colour overlays on the CT images. DECT knee images from 48 patients were evaluated for the presence and size of BMLs by two readers. Consensus MRI served as the reference standard. The diagnostic accuracy was moderate with 70.1 % (95% CI 63.3-76.2) and 69.1% (95% CI 61.7-75.9) overall sensitivity and specificity, moderate to substantial intrareader agreement and fair to moderate interreader agreement. Lesion volumes were comparable in the femur but underestimated in the tibia.</p><p>Study II evaluated the diagnostic accuracy of DECT and MRI for detecting ACL injuries. The ACL, being an important stabilising structure of the knee, is typically imaged using MRI. The diagnostic performance of DECT and MRI was evaluated, with arthroscopy serving as the reference standard. From the cohort in Study I, arthroscopy data was available for 21 patients who were included in the analysis. The combined sensitivity across all four readings for DECT was 76.3 % (95% CI 66.8-85.9), which was lower than that of MRI at 86.8% (95% CI 71.9-95.6). Both methods demonstrated high positive predictive values: 93.6% (95% CI 84.3-98.2) for DECT and 91.7% (95% CI 77.5-98.3) for MRI.</p><p>In Study III, a PCD-CT prototype was evaluated using a bovine knee specimen with an induced fracture and metallic osteosynthesis material. Virtual monoenergetic images (VMI) generated by the PCD-CT at 120 kV and 140 kV tube potentials were compared to conventional energy-integrating detector CT (EID-CT) images acquired with dual- and single-energy, both with and without iterative metal artefact reduction algorithm (iMAR). Four readers assessed image quality with respect to metal artefacts. PCD-CT 140 kV VMI at 150 keV received the highest scores and was significantly superior to single-energy Sn150 kV images with iMAR. While DECT iMAR images scored lower than PCD-CT images, the difference was not statistically significant. Image quality scores were also significantly lower for 120 kV tube potential and lower VMI values at 72 keV.</p><p>Study IV explored the metal artefact reduction capabilities of a commercially available PCD-CT in twelve patients with surgically treated tibial plateau fractures. PCD-CT 140 kV ultra-high resolution (UHR) scans were reconstructed as VMI at 70, 110 and 150 keV, using smooth and sharp kernels, with and without iMAR, as well as polychromatic images with an extra-sharp kernel. EID-CT Sn150 kV scans were reconstructed with smooth and sharp kernels, with and without iMAR. Five readers assessed the image quality. EID-CT iMAR images scored significantly higher for reducing metal artefact streaks, whereas bone-metal interface visualisation was comparable between PCD-CT high VMI and EID-CT with IMAR. PCD-CT with an extra sharp kernel was superior for bone visualisation.</p>