The emerging role of photon-counting detector CT: primary experience on the integrated assessment of acute knee injuries.

Early accurate diagnosis of osseous and soft tissue injuries following acute knee trauma is crucial for guiding clinical management and preventing chronic instability. Radiography is the appropriate first imaging test applied to detect traumatic osseous injuries. CT is indicated based on clinical symptoms and radiographic concordance. In this acute phase, soft tissue injuries are often clinically overlooked due to swelling and restricted motion, which significantly limit comprehensive physical examination. Moreover, both x-ray and conventional CT imaging are insufficient for addressing this issue due to their limited soft tissue contrast resolution. If clinical suspicion of soft tissue injury persists, an MRI will be performed at a later stage. This may lead to undesirable delays in diagnosis and treatment, thereby potentially impacting patient outcomes. Photon-counting detector CT (PCD-CT) offers enhanced, integrated diagnostic possibilities. The use of spectral imaging data, including color-coded virtual non-calcium (VNCa) images, enables the detection of bone marrow edema (BME) and visualization of key stabilizing soft tissue structures, which may assist emergency department clinicians in determining initial treatment, follow-up, and the need for additional imaging. This technical note illustrates the integral use of ultra-high resolution spectral PCD-CT in a case of a knee injury following an alpine skiing accident. RELEVANCE STATEMENT: The integration of photon-counting detector computed tomography with spectral imaging in acute knee trauma enhances visualization of osseous and soft tissue structures, improving diagnostic accuracy. It may optimize early triage and guide initial treatment for soft tissue injuries. KEY POINTS: Photon-counting detector CT (PCD-CT) enables comprehensive fracture, edema, and soft tissue assessment. Case-based notable correlation between injuries suspected on color-coded spectral imaging and MRI. Photon-counting detector CT (PCD-CT) may enhance early clinical decision-making in knee trauma.