Abstract: An introduction to 2D X-ray radiography and 3D computed tomography (CT) which are used in clinics and hospitals worldwide is given. The development, principles and primary applications of modern medical image equipment such as digital subtraction angiography, computed radiography, digital radiography, spiral CT, positron emission tomography/CT, and phase-contrast imaging are also described. Image post-processing is a very important part of modern medical imaging equipment. Combined with medical a priori knowledge, modern CT scanners have even more powerful capabilities in computer-aided diagnosis.