This comprehensive compendium introduces a unique and novel approach to X-ray dose reduction by sparse repeat scanning. Based on sparse sampling in Radon space, the methods obviate the need for image reconstruction and reduce X-ray dose by up to 10 times of the normal dose without compromising the robustness and accuracy of the measurements. The methods consist of automatic rigid and deformable registration and changes detection in subsequent CT scans, and real-time needle tracking during interventional procedures.The technology is applicable to radiological follow-up of patients, to interventional radiology, and to related clinical procedures.This useful refence text benefits academics, researchers and practitioners in biomedical engineering, electronics, image reconstruction and related fields.