Radiology

Chest X-ray

Radiology traditionally was the branch of medical science dealing with the medical use of X-rays emitted by X-ray machines or other such radiation devices for the purpose of obtaining visual information as part of medical imaging. Radiologists now also use other imaging technologies (such as ultrasound and magnetic resonance imaging) to diagnose or treat disease. Interventional radiology is the performance of (usually minimally invasive) medical procedures with the help of medical imaging.

Outside of the medical field, radiology also encompasses the examination of the inner structure of objects using X-rays or other penetrating radiation.

Subdivisions

As a medical specialty, radiology can be classified into two subfields. Diagnostic radiology is concerned with the use of various imaging modalities to aid in the diagnosis of disease.

Radiation therapy uses radiation to treat diseases such as cancer. While originally encompassed within radiology, therapeutic radiology — or, as it is now called, radiation oncology — is now a separate field.

Training

Diagnostic radiologists must complete four years of medical school (M.D. or D.O.) plus a five year residency. The first year of residency is either a transitional year where residents rotate through many different specialties or a prelim medicine or prelim surgery year, after which a four-year diagnostic radiology residency ensues. During residency, both oral and written national examinations must be passed for board certification in diagnostic radiology. There are two separate written examinations required for certification by the American Board of Radiology, one covering the physics of medical imaging which is usually taken at the beginning of the second or third year, the other exam tests diagnostic imaging knowledge and is usually taken at the beginning of the third or fourth year. Both written exams must be passed before being eligible to take the oral examination, which is typically taken at the end of the fourth year.

After completion of residency, radiologists may choose to either practice or enter into a fellowship program in a radiologic subspecialty (such as Abdominal CT, MRI, Musculoskeletal, Interventional Radiology, Neuroradiology, Pediatric Radiology, etc.). Fellowship training programs typically last between one-to-two years.

Radiology is currently considered one of the most highly competitive fields to gain admission to. Other highly competitive fields include Orthopedics, Anesthesiology and Dermatology.

Diagnostic radiology

Commonly used imaging modalities include plain radiography, computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and nuclear imaging techniques. These techniques are usually non-invasive. Each of these modalities has strengths and limitations which dictate its use in diagnosis.

Plain radiography

Main article: Radiography

Radiographs (or Roentgenographs, named after the discoverer of X-rays, Wilhelm Conrad Roentgen (1845-1923)) are often used for evaluation of bony structures and soft tissues. Fluoroscopy and angiography are special applications of X-ray imaging, where a fluorescent screen or image intensifier tube is connected to a closed-circuit television system, which allows real-time imaging of structures in motion or augmented with a radiocontrast agent. Radiocontrast agents are administered, often swallowed or injected into the body of the patient, to help delineate anatomy such as the blood vessels, the genitourinary system or the gastrointestinal tract. Specific radiocontrast agents are used for specific types of evaluations; for example, barium in a suspension is administered into the gastrointestinal tract and imaged with fluoroscopy or radiography. Radiocontrast agents, which strongly absorb X-ray radiation, in conjunction with the real-time imaging allows demonstration of dynamic processes, such as peristalsis in the digestive tract or blood flow in arteries and veins.

CT scanning

Main article: Computed tomography

CT imaging uses X-rays in conjunction with computing algorithms to image a variety of soft tissues in the body. CT is acquired in the axial plane, while coronal and sagittal images can be rendered by computer reconstruction. Radiocontrast agents are often used with CT for enhanced delineation of anatomy. Intravenous contrast allows 3D reconstructions of arteries and veins. Although radiographs provide higher resolution for bone X-rays, CT can generate much more detailed images of the soft tissues. CT exposes the patient to more ionizing radiation than a radiograph.

Ultrasound

Main article: Medical ultrasonography

Medical ultrasonography uses ultrasound (high-frequency sound waves) to vizualize soft tissue structures in the body in real time. No radiation is involved, but the quality of the images obtained using ultrasound is highly dependent on the skill of the person (ultrsonographer) performing the exam. The use of ultrasound in medical imaging has developed mostly within the last 30 years. The first ultrasound images were static and two dimensional (2D), but with modern-day ultrasonography 3D reconstructions can be observed in real-time; effectively becoming 4D.

MRI/NMR

Main article: Magnetic resonance imaging

MRI uses strong magnetic fields to align spinning atomic nuclei (usually hydrogen protons) within body tissues, then disturbs the axis of rotation of these nuclei and observes the radio frequency signal generated as the nuclei return to their baseline states. MRI scans give the best soft tissue contrast of all the imaging modalities. With advances in scanning speed and spatial resolution, and improvements in computer 3D algorithms and hardware, MRI has great potential for development in the next few years. One disadvantage is that the patient has to hold still for long periods of time in a noisy, cramped space while the imaging is performed. Recent improvements in magnet design have improved this, by developing wider, shorter magnet bores, and with more open magnet designs. MRI has great benefit in imaging the brain, spine, and musculoskeletal system. Other areas of potential advancement include functional imaging, and cardiovascular MRI, as well as MR image guided therapy.

Nuclear medicine

Main article: Nuclear medicine

Nuclear medicine imaging involves the administration into the patient of substances labelled with radioactive tracers which have affinity for particular tissues. The heart, lungs, thyroid, liver, gallbladder, and bones are commonly evaluated for particular conditions using these techniques. While anatomical detail is limited in these studies, nuclear medicine is useful in displaying physiological function. As such, processes such as the growth of a tumor can often be monitored, even when the tumor cannot be adequately visualized using any of the other modalities. The principal imaging device is the gamma camera which detects the radiation emitted by the tracer in the body and displays it as an image. Often the information is converted into a series of slices through the body. In the most modern devices Nuclear Medicine images can be fused with a CT scan taken at the same time so that the physiological information can be overlayed on the anatomical structures to improve diagnostic accuracy.

See also

• Radiobiology
• Radiography
• Radiosensitivity

External links

• Radiology Forums - online message boards for all radiology modalities. Share your knowledge and ideas.
• American College of Radiology - The premier national organization for radiologists
• The American Board of Radiology - The national organization responsible for Board Certification in Radiology, Radiation Oncology and Radiation Physics
• Radiology Society of North America - huge amount of information on radiology, including links to online journals Radiology and Radiographics
• American Roentgen Ray Society - much information on radiology, including online American Journal of Roentgenology
• Aunt Minnie - Radiology News and sounding board for practicing radiologists, residents and medical students
• RadiologyInfo - The radiology information resource for patients
• Society of Interventional Radiology Website

• Radiology Career Information
• Radiology - online radiology portal for students and professionals.
• A Digital Library of Radiology Education Resources
• A pediatric radiology digital library
• RadiologyWiki.org - A radiology specific wiki with a focus on education
• WikiRad - A radiology resident oriented wiki