X-ray Imaging in Preclinical Studies of Bone, Pulmonary and Soft Tissues

Discovered by Wilhelm Roentgen in 1895, X-ray technology is the oldest and most commonly used form of medical imaging and remains an important tool for the diagnosis of many disorders. X-rays are generated when a beam of electrons is accelerated by high voltage and hits a metal probe. The kinetic energy released is transformed into quanta of emitted X-ray radiation. X-rays are absorbed by the material through which they pass (interact through Compton effect, Raleigh scattering and photoelectric effect) and are affected by density of the sample. For example, bone absorption typically contrasts clearly in X-ray and is frequently shown (as with traditional film X-ray) as white areas surrounded by darker areas of tissue (Figure 1). In the body, X-ray absorption is different for bone, muscle and fat. X-ray with contrast agents also finds utility in a large number of medical applications, including angiography. X-rays are recorded on X-ray sensitive material. Traditionally, images were obtained on photographic film, however, modern systems capture X-rays on electronic detectors and image information can be stored as a digital file for convenient use and recall. Despite development of newer technologies such as computed tomography (CT), ultrasound imaging, nuclear imaging and magnetic resonance imaging (MRI), X-ray imaging remains popular for many applications owing to the relatively fast, high-resolution imaging performance at relatively low cost. Radiography can be of 2 types: a single acquisition planar (or projection) radiography or dynamically acquired fluoroscopy. Planar radiography, is often applied in investigating bone health (measurement of bone density, bone fractures, etc), chest radiography (pneumonia, lung cancer), mammography (screening for breast cancer), identifying ulcers or detecting certain types of colon cancer in abdomen, intestines, liver and bladder. Radiographic fluoroscopy produces real-time images of internal body structure and is used to detect a number of diseases associated with the stomach and intestine, genitals and urinary tract1,2. X-ray Imaging in Preclinical Studies of Bone, Pulmonary and Soft Tissues