<b>Diagnostic Accuracy of Non-Contrast CT in Detection of Acute Ischemic Stroke Taking Diffusion-Weighted Magnetic Resonance Imaging as Gold Standard</b>

Background: Acute ischemic stroke requires rapid and accurate imaging diagnosis to guide time-sensitive treatment, particularly in emergency settings where non-contrast computed tomography is often the first-line modality. Although diffusion-weighted magnetic resonance imaging is considered the reference standard for early ischemic detection, its availability is limited in many resource-constrained environments. Objective: To determine the diagnostic accuracy of non-contrast CT in the detection of acute ischemic stroke using diffusion-weighted MRI as the gold standard. Methods: This prospective diagnostic accuracy study was conducted in the Department of Radiology, Combined Military Hospital, Kohat, from July 2024-Dec 2024. A total of 232 patients aged 40-80 years presenting with acute ischemic symptoms within 7 days of symptom onset underwent non-contrast CT followed by diffusion-weighted MRI within 24 hours. Imaging findings were compared using a 2 × 2 contingency table to calculate sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy. Results: Of 232 patients, 224 (96.6%) had acute ischemic stroke confirmed on diffusion-weighted MRI. Non-contrast CT showed 172 true-positive, 6 true-negative, 2 false-positive, and 52 false-negative findings, yielding a sensitivity of 76.8%, specificity of 75.0%, positive predictive value of 98.9%, negative predictive value of 10.3%, and diagnostic accuracy of 76.7%. In patients presenting within 4 hours, CT positivity was only 4.8% compared with 85.7% on MRI, whereas in those presenting after 4 hours, CT positivity increased to 90.5% versus 98.9% on MRI. Conclusion: Non-contrast CT remains a valuable initial imaging modality for suspected stroke because of its accessibility and high confirmatory value when positive, but it has limited sensitivity in the hyperacute phase and cannot reliably exclude acute ischemic stroke when negative. Diffusion-weighted MRI remains superior for early ischemic detection.