CT scan with IV contrast is the imaging study with the highest sensitivity for acute appendicitis in adults. It reliably shows an enlarged appendix, wall thickening, and periappendiceal fat stranding, as well as related signs like an appendicolith or abscess, making it most likely to detect true cases. It also helps identify other causes of right lower quadrant pain, reducing missed diagnoses and unnecessary surgery. Ultrasound can be helpful but is operator-dependent and less sensitive in adults, especially in those who are obese or have gas-filled bowels. Plain abdominal X-ray is largely unhelpful for diagnosing appendicitis. MRI is very accurate and avoids radiation, but it’s less available in emergency settings and takes longer, so CT with contrast remains the preferred, most sensitive option in adults.