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* [http://rad.usuhs.mil/medpix/index.html] - MedPix Medical Image Database - Free CME and CEU, Peer-reviewed teaching file
* [http://rad.usuhs.mil/medpix/index.html] - MedPix Medical Image Database - Free CME and CEU, Peer-reviewed teaching file
* [http://www.cirse.org Cardiovascular and Interventional Radiological Society of Europe]
* [http://www.cirse.org Cardiovascular and Interventional Radiological Society of Europe]
* [http://www.medicexchange.com Medicexchange] - Downloadable access to medical imaging software and related clinical research and developments.
* [http://www.auntminnie.com Aunt Minnie] - Radiology News and sounding board for practicing radiologists, residents and medical students
* [http://www.auntminnie.com Aunt Minnie] - Radiology News and sounding board for practicing radiologists, residents and medical students
* [http://www.radiologyinfo.org RadiologyInfo] - The radiology information resource for patients
* [http://www.radiologyinfo.org RadiologyInfo] - The radiology information resource for patients

Revision as of 14:34, 4 January 2007

This article focuses on radiology as a medical specialty. See also medical imaging and diagnostic imaging.
Image A: A normal chest X-ray. Image B: Q fever pneumonia.

Radiology is the specialty directing medical imaging technologies to diagnose and sometimes treat diseases. Originally it was the aspect 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. Today, following extensive training, radiologists also direct other imaging technologies (such as ultrasound, computed tomography (CT) and magnetic resonance imaging) to diagnose or treat disease. Interventional radiology is the performance of (usually minimally invasive) medical procedures with the guidance of imaging technologies. The acquisition of medical imaging is usually carried out by the radiographer or radiologic technologist. Nuclear medicine is the use of unsealed radiation sources within the body.

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

Subdivisions

Medical imaging

As a medical specialty, radiology can be classified into subfields.

Radiologist Training

USA

Diagnostic radiologists must complete four years of medical school plus five years of post-graduate training .The first postgraduate year is a preliminary internship in medicine, surgery or both, after which a four-year diagnostic radiology residency follows. 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 of residency (postgraduate year 3 or 4), and a second covering clinical diagnostic imaging knowledge which is usually taken at the beginning of the third or fourth year (PGY 4 or 5). 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 (PGY 5).

After completion of residency, radiologists may choose to either practice or enter into a fellowship program in a radiologic subspecialty (such as abdominal or thoracic imaging, MRI, musculoskeletal imaging, interventional radiology, neuroradiology, interventional neuroradiology, pediatric radiology, women's imaging, etc.). Fellowship training programs typically last between 1-2 years.

Radiology is currently considered a highly competitive field. Radiologists generally enjoy good compensation as well as a good balance between time required at work and time spent away from work. The field is rapidly expanding due to advances in computer technology which is closely linked to modern imaging.

The exams (radiography) are usually performed by radiologic technologists, (also known as diagnostic radiographers) who in the United States have a 2-year Associates Degree and the UK a 3 year Honours Degree.

Australia & New Zealand

Radiology training begins after completion of medical degree (6 years) and at least 2 years of hospital residency (internship and junior house medical officer (JHMO) ). It then comprises 5 years , one of which can be a fellowship.

Exams are in two parts:

  • Part 1, undertaken in first year comprises anatomy and physics pertaining to radiology.
  • Part 2, undertaken in fourth year comprises clinical / diagnositic radiology and pathology

Accreditation is via the Royal Australian and New Zealand College of Radiology (RANZCR)

Diagnostic radiology

Commonly used imaging modalities include plain radiography(X-rays), flouroscopy, mammography, 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.

Acquisition of radiological images

Patients have the following procedures to provide images for Radiological decisions to be made.

Projection 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. An X-Ray machine directs electromagnetic radiation upon a specified region in the body. This radiation tends to pass through less dense objects (skin, fat, muscle, and other tissues), but is absorbed or scattered by denser materials (bones, tumors, lungs affected by severe pneumonia). Radiation which has passed through a patient then strikes a cassette containing a screen of fluorescent phosphors and exposes x-ray film. Areas of film exposed to higher amounts of radiation will appear black or dark gray after development. The unexposed areas of film remain white. In Computed Radiography (CR), the x-ray photons are captured by phosphors within a cassette, which are then read-out by a scanning machine to give an electronic rendering of the image. In Digital Radiography (DR) the radiation strikes a plate of minute sensors yielding a digital image, which is then transmitted and stored by computer and viewed on a computer screen. In the U.S. all three modalities for obtaining images are currently in use, although the trend is away from film and toward digital imaging.

Fluoroscopy

Main article: Fluoroscopy

Fluoroscopy and angiography are special applications of X-ray imaging, in which 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 delineate anatomy and functioning of the blood vessels, the genitourinary system or the gastrointestinal tract.Two radiocontrasts are presently in use. Barium (as BaSO4) may be given orally or rectally for evaluation of the GI tract. Iodine,in multiple proprietary forms, may be given by oral, rectal, intraarterial or intravenous routes.. These radiocontrast agents strongly absorb or scatter X-ray radiation, and 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. Iodine contrast may also be concentrated in abnormal areas more or less than in normal tissues and make abnormalities(tumors,cysts,inflammation) more conspicuous. Additionally, in specific circumstances air can be used as a contrast agent for the gastrointestinal system and carbon dioxide can be used as a contrast agent in the venous system; in these cases, the contrast agent attenuates the X-ray radiation less than the surrounding tissues.

CT scanning

Spiral CT illustration

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 can allow 3D reconstructions of arteries and veins. Although radiographs provide higher spatial resolution, CT can detect more subtle variations in attenuation of X-rays. CT exposes the patient to more ionizing radiation than a radiograph. Spiral Multi-detector CT utilizes 8,16 or 64 detectors during continuous motion of the patient through the radiation beam to obtain much finer detail images in a shorter exam time. With computer manipulation these images can be reconstructed into 3D images of carotid, cerebral and coronary arteries. Faster scanning times in modern equipment has been associated with increased utilization.

Ultrasound

Main article: Medical ultrasonography

Medical ultrasonography uses ultrasound (high-frequency sound waves) to visualize soft tissue structures in the body in real time. No ionizing radiation is involved, but the quality of the images obtained using ultrasound is highly dependent on the skill of the person (ultrasonographer) 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.

Because ultrasound does not utilize ionizing radiation, unlike radiography, CT scans, and nuclear medicine imaging techniques, it is generally considered safer. For this reason, this modality plays a vital role in obstetrical imaging. Fetal development can be thoroughly evalauted allowing early diagnosis of fetal anomalies or confirmation of a normal gestation. Color-Flow Doppler Ultrasound measures the severity of peripheral vascular disease and is used by Cardiology for dynamic evaluation of the heart,heart valves and major vessels. Stenosis of the carotid arteries can presage cerebral infarcts (strokes). DVT in the legs can be found via ultrasound before it dislodges and travels to the lungs (pulmonary embolism),which can be fatal if left untreated. Ultrasound is useful for image-guided interventions like biopsies and drainages such as thoracentesis). It is also used in the treatment of kidney stones (renal lithiasis) via lithotripsy. Small portable ultrasound devices now replace peritoneal lavage in the triage of trauma victims by directly assessing for the presence of hemorrhage in the peritoneum and the integrity of the major viscera including the liver, spleen and kidneys. Extensive hemoperitoneum (bleeding inside the body cavity) or injury to the major organs may require emergent surgical exploration and repair.

MRI/NMR

Main article: Magnetic resonance imaging

File:Dicom mr.jpg
MR image of human knee

MRI uses strong magnetic fields to align spinning atomic nuclei (usually hydrogen protons) within body tissues, then uses a radio signal to disturb 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 become an essential tool in musculoskeltal radiology and neuroradiology. 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. Claustrophobia severe enough to terminate the MRI exam is reported in up to 5% of patients. Recent improvements in magnet design including stronger magnetic fields (3 Tesla),shortening exam times, wider, shorter magnet bores and more open magnet designs, have brought some relief for claustrophobic patients. MRI has great benefit in imaging the brain,spine, and musculoskeletal system. The modality can be contraindicated for patients with pacemakers, certain types of cerebral aneurysmal clips or metallic hardware due to the powerful magnetic fields and strong fluctuating radio signals the body is exposed to. Areas of potential advancement include functional imaging, 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 quasi-simultaneously so that the physiological information can be overlayed on co-registered with the anatomical structures to improve diagnostic accuracy.

PET scanning also falls under "nuclear medicine."

The applications of nuclear medicine can include bone scanning which traditionally has had a strong role in the work-up/staging of cancers. Myocardial perfusion imaging is a sensitive and specific screening exam for reversible myocardial ischemia, which when present requires angiographic confirmation and potentially life-saving balloon angioplasty, stenting or cardiac bypass grafting. Molecular Imaging is the new and exciting frontier in this field.

History of Radiology

Radiology began with Wilhelm Conrad Röntgen’s discovery of xrays in 1895.It was such a important advance in medicine that within ten years radiology was being used all over the Western world. In 1901, Roentgen received the first Nobel Prize in Physics. In 1905 the first English book on chest radiography was published. During World War I, Maria Skłodowska-Curie pushed for the use of mobile radiography units for the treatment of wounded soldiers. She personally provided the radon tubes for the French Army. In 1920 the Society of Radiographers was formed. In 1924 Gilbert Stead published his Elementary Physics for medical and radiology students, helping bring radiology to the level of a generally recognized medical specialty. In 1937 a patient with leukemia was treated at the University of California, Berkeley in the first therapeutic use of radioactivity for cancer. Also in 1937, Joseph Gilbert Hamilton started to use radioactive iodine as a diagnostic and therapeutic agent in the treatment of thyroid disease.

See also

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