The book explores in detail the crucial contribution of magnetic resonance imaging (MRI) of the sacroiliac joints to the understanding and diagnosis of ankylosing spondylitis (SpA). By focusing on this specific imaging technique, we highlight its prominent role in the early detection of the disease, well before the onset of obvious radiological manifestations.The book examines how MRI of the sacroiliac joints offers precise visibility of the inflammatory and structural alterations characteristic of SpA, enabling finer assessment of lesions and early intervention. By exploring the advances and clinical applications of this imaging modality, the book offers a comprehensive perspective on its usefulness in the monitoring, diagnosis and management of ankylosing spondylitis.