X-rays are a type of electromagnetic wave with the ability to penetrate different objects. The atomic number and density of an object are the two main factors controlling the degree of photon absorption and penetration. This means that the photon penetration differs in different materials. A medium with a small atomic number and low density has lower absorption power. X-rays are used for the imaging of bones and some organs in medicine. These photons are utilized for therapeutic purposes as well.

To perform imaging, the patient is positioned between the X-ray source and the photon detector. The beam is radiated from the source towards the patient, passes through the body, and finally reaches the detector. Depending on the type of tissue in the beam path, a specific amount of radiation reaches the detector. Therefore, an attenuation map is created on the detector in form of different grayscale levels by tissues. For example, bones are made up of calcium which is relatively high in atomic number and has a high density and therefore a high absorption power. This causes bones to usually appear brighter and close to white in radiographic images. If a bone is fractured or has cracks, these imperfections appear as dark bands in the image due to the presence of empty space and air. These dark bands are seen vividly in the bright image of a bone. Lungs also appear dark in radiographic images due to the presence of air and cavities. But if there is an infection or tumor in the lung, they will appear as bright spots in their background as a result of their higher density.

Some applications of X-rays in medicine are as follows:

• Detection and diagnosis of:

• Fractures
• Infections
• Calcifications such as kidney stones
• Tumors
• Joint arthritis
• Osteoporosis
• Vascular stenosis
• Foreign bodies such as incidents of small objects swallowed by toddlers
• And …

Imaging applications of X-rays:

Plain radiography: Bone fractures, tumors and other abnormal masses, pneumonia, calcifications, foreign bodies, dental problems, etc. can be detected using plain radiographs. This method images all the tissue in the way on a 2D plane, therefore the possibility of a meticulous study of the inner structure of the object is hardly possible. Computed tomography was designed to overcome such issues.

Computer Tomography Scan (CT scan): The combination of plain radiography with computer processing enables the production of cross-section images of the body. These images can be combined to achieve a three-dimensional reconstruction of the object. CT images are higher in detail compared to plain radiographs and enable physicians to study the inner organs of the body from different angles.

Mammography: Mammography is the radiographic imaging of the breasts with the aim of early cancer diagnosis. Tumors usually appear as regular or irregular masses and are normally brighter than the background. Mammography can also detect small pieces of calcium called microcalcifications appearing as very bright spots on the image. Although microcalcifications are normally benign, they can indicate the presence of a certain type of cancer.

Fluoroscopy: In this technique, X-rays and a fluorescent screen are utilized to capture real-time radiographs of the movement of internal organs or diagnostic processes like contrast agent tracking after being injected or swallowed. Examples can be studying the movements of a beating heart or the movement of blood in vessels with the aid of contrast agents.

This technology is also used to guide a catheter during cardiac angioplasty as well as precise surgeries of implantation of different instruments inside the body.

Therapeutic applications of X-rays:

Radiotherapy in cancer treatment: X-rays and other types of high-energy photons can be used to eliminate tumors and cancerous cells by damaging their DNA. The radiation used in cancer treatment is much higher than the dose utilized in diagnostic imaging.