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RadiologistsImage:Chest x-ray.jpgRadiology traditionally was the branch of medicalscience dealing with the medical use of X-raysemitted by X-ray machinesor other such radiationdevices for the purpose of obtaining visual information as part of medical imaging. Radiologists now also use other imaging technologies (such as ultrasoundand magnetic resonance imaging) to diagnose or treat disease. Interventional radiologyis 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.
SubdivisionsAs a medical specialty, radiology can be classified into two subfields. Diagnostic radiologyis concerned with the use of various imaging modalities to aid in the diagnosisof disease. Radiation therapyuses radiationto 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. TrainingDiagnostic radiologists must complete four years of medical school(M.D.) or the alternative, osteopathic school(D.O.) plus a five year of post-graduate training (residency). The first year of residency is a preliminary year 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 physicsof medical imagingwhich is usually taken at the beginning of the second or third year, and a second covering clinical diagnostic imaging knowledge which 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. Many hospitals consider certification by the American Board of Radiology and by the American Osteopathic Board of Radiologyto be nearly equivalent. After completion of residency, radiologists may choose to either practice or enter into a fellowshipprogram in a radiologic subspecialty (such as abdominal CT, MRI, musculoskeletalimaging, interventional radiology, neuroradiology, pediatric radiology, etc.). Fellowship training programs typically last between one-to-two years. Radiology is currently considered a highly competitive field. Radiologists generally enjoy good compensationas 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. Diagnostic radiologyCommonly 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 radiographyMain article: Radiography Radiographs(or Roentgenographs, named after the discoverer of X-rays, Wilhelm Conrad Roentgen (1845-1923)) are often used for evaluation of bonystructures and soft tissues. Fluoroscopyand angiographyare special applications of X-rayimaging, 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 radiocontrastagent. 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 peristalsisin the digestive tract or blood flow in arteries and veins. CT scanningMain article: Computed tomography CTimaging 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. UltrasoundMain article: Medical ultrasonography Medical ultrasonographyuses 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 (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 there is no known harmful effect from ultrasound, unlike xrays and gamma rays, the modality plays a vital role in Obstetrics. Without harming the fetus, fetal development can be followed. Early intervention thus can bring about a successful birth. Color Flow Dopplerwell documents the severity of peripheral vascular disease. Stenosisof the carotid arteriescan herald cerebral infarctsor strokes. Intraluminal clotsin the venous systemsof the extremities may result in pulmonary embolism, which is often fatal if undiagnosed and untreated. Ultrasound is useful for image-guided interventionslike biopsies and drainages. It is also used in the treatment of kidney stones/renal lithiasisvia lithotripsy. The small and easy to use Sonositedevice replaces peritoneal lavagein the triage of traumavictims, by directly assessing the presence of hemorrhagein the peritoneumand the integrity of the major visceraincluding the liver, spleenand kidneys. Extensive hemoperitoneum or injury to the major organs may require emergent surgical exploration and repair. MRI/NMRMain article: Magnetic resonance imaging MRIuses strong magnetic fields to align spinning atomic nuclei(usually hydrogenprotons) within body tissues, then disturbs the axis of rotation of these nuclei and observes the radio frequencysignal 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 like 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 strong magnetic fields. Areas of potential advancement include functional imaging, cardiovascular MRI, as well as MR image guided therapy. Nuclear medicineMain article: Nuclear medicine th Nuclear medicineimaging 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 anatomicaldetail is limited in these studies, nuclear medicine is useful in displaying physiologicalfunction. As such, processes such as the growth of a tumorcan often be monitored, even when the tumor cannot be adequately visualized using any of the other modalities. The principal imaging device is the gamma camerawhich 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 physiologicalinformation can be overlayed on the anatomical structures to improve diagnostic accuracy. The applications of nuclear medicine can include bone scanningwhich traditionally has had a strong role in the work-up/staging of cancers. Myocardial perfusion imagingis a sensitive and specific screening examfor reversible myocardial ischemia, which when present requires angiographicconfirmation and potentially life-saving balloon angioplasty, stentingor cardiac bypass grafting. Molecular Imagingis the new and exciting frontier in this field. See also
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