Multidetector Computed Tomography: Types of spiral computed tomography technology in which multiple slices of data are acquired simultaneously improving the resolution over single slice acquisition technology.Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.Tomography, Spiral Computed: Computed tomography where there is continuous X-ray exposure to the patient while being transported in a spiral or helical pattern through the beam of irradiation. This provides improved three-dimensional contrast and spatial resolution compared to conventional computed tomography, where data is obtained and computed from individual sequential exposures.Tomography: Imaging methods that result in sharp images of objects located on a chosen plane and blurred images located above or below the plane.Radiographic Image Interpretation, Computer-Assisted: Computer systems or networks designed to provide radiographic interpretive information.Positron-Emission Tomography: An imaging technique using compounds labelled with short-lived positron-emitting radionuclides (such as carbon-11, nitrogen-13, oxygen-15 and fluorine-18) to measure cell metabolism. It has been useful in study of soft tissues such as CANCER; CARDIOVASCULAR SYSTEM; and brain. SINGLE-PHOTON EMISSION-COMPUTED TOMOGRAPHY is closely related to positron emission tomography, but uses isotopes with longer half-lives and resolution is lower.Tomography, Optical Coherence: An imaging method using LASERS that is used for mapping subsurface structure. When a reflective site in the sample is at the same optical path length (coherence) as the reference mirror, the detector observes interference fringes.Imaging, Three-Dimensional: The process of generating three-dimensional images by electronic, photographic, or other methods. For example, three-dimensional images can be generated by assembling multiple tomographic images with the aid of a computer, while photographic 3-D images (HOLOGRAPHY) can be made by exposing film to the interference pattern created when two laser light sources shine on an object.Triiodobenzoic Acids: Triiodo-substituted derivatives of BENZOIC ACID.Tomography Scanners, X-Ray Computed: X-ray image-detecting devices that make a focused image of body structures lying in a predetermined plane from which more complex images are computed.Radiographic Image Enhancement: Improvement in the quality of an x-ray image by use of an intensifying screen, tube, or filter and by optimum exposure techniques. Digital processing methods are often employed.Cone-Beam Computed Tomography: Computed tomography modalities which use a cone or pyramid-shaped beam of radiation.Tomography, Emission-Computed: Tomography using radioactive emissions from injected RADIONUCLIDES and computer ALGORITHMS to reconstruct an image.Iopamidol: A non-ionic, water-soluble contrast agent which is used in myelography, arthrography, nephroangiography, arteriography, and other radiological procedures.Contrast Media: Substances used to allow enhanced visualization of tissues.Sensitivity and Specificity: Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. (From Last, Dictionary of Epidemiology, 2d ed)Coronary Angiography: Radiography of the vascular system of the heart muscle after injection of a contrast medium.Radiation Dosage: The amount of radiation energy that is deposited in a unit mass of material, such as tissues of plants or animal. In RADIOTHERAPY, radiation dosage is expressed in gray units (Gy). In RADIOLOGIC HEALTH, the dosage is expressed by the product of absorbed dose (Gy) and quality factor (a function of linear energy transfer), and is called radiation dose equivalent in sievert units (Sv).Tomography, Emission-Computed, Single-Photon: A method of computed tomography that uses radionuclides which emit a single photon of a given energy. The camera is rotated 180 or 360 degrees around the patient to capture images at multiple positions along the arc. The computer is then used to reconstruct the transaxial, sagittal, and coronal images from the 3-dimensional distribution of radionuclides in the organ. The advantages of SPECT are that it can be used to observe biochemical and physiological processes as well as size and volume of the organ. The disadvantage is that, unlike positron-emission tomography where the positron-electron annihilation results in the emission of 2 photons at 180 degrees from each other, SPECT requires physical collimation to line up the photons, which results in the loss of many available photons and hence degrades the image.Cardiac-Gated Imaging Techniques: Timing the acquisition of imaging data to specific points in the cardiac cycle to minimize image blurring and other motion artifacts.Reproducibility of Results: The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.Bronchography: Radiography of the bronchial tree after injection of a contrast medium.Tomography, Optical: Projection of near-IR light (INFRARED RAYS), in the 700-1000 nm region, across an object in parallel beams to an array of sensitive photodetectors. This is repeated at various angles and a mathematical reconstruction provides three dimensional MEDICAL IMAGING of tissues. Based on the relative transparency of tissues to this spectra, it has been used to monitor local oxygenation, brain and joints.Angiography: Radiography of blood vessels after injection of a contrast medium.Calcinosis: Pathologic deposition of calcium salts in tissues.Predictive Value of Tests: In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.Image Processing, Computer-Assisted: A technique of inputting two-dimensional images into a computer and then enhancing or analyzing the imagery into a form that is more useful to the human observer.Iohexol: An effective non-ionic, water-soluble contrast agent which is used in myelography, arthrography, nephroangiography, arteriography, and other radiographic procedures. Its low systemic toxicity is the combined result of low chemotoxicity and low osmolality.Electron Microscope Tomography: A tomographic technique for obtaining 3-dimensional images with transmission electron microscopy.Radiography, Abdominal: Radiographic visualization of the body between the thorax and the pelvis, i.e., within the peritoneal cavity.Coronary Artery Disease: Pathological processes of CORONARY ARTERIES that may derive from a congenital abnormality, atherosclerotic, or non-atherosclerotic cause.Observer Variation: The failure by the observer to measure or identify a phenomenon accurately, which results in an error. Sources for this may be due to the observer's missing an abnormality, or to faulty technique resulting in incorrect test measurement, or to misinterpretation of the data. Two varieties are inter-observer variation (the amount observers vary from one another when reporting on the same material) and intra-observer variation (the amount one observer varies between observations when reporting more than once on the same material).Incidental Findings: Unanticipated information discovered in the course of testing or medical care. Used in discussions of information that may have social or psychological consequences, such as when it is learned that a child's biological father is someone other than the putative father, or that a person tested for one disease or disorder has, or is at risk for, something else.Coronary Stenosis: Narrowing or constriction of a coronary artery.Vascular Malformations: A spectrum of congenital, inherited, or acquired abnormalities in BLOOD VESSELS that can adversely affect the normal blood flow in ARTERIES or VEINS. Most are congenital defects such as abnormal communications between blood vessels (fistula), shunting of arterial blood directly into veins bypassing the CAPILLARIES (arteriovenous malformations), formation of large dilated blood blood-filled vessels (cavernous angioma), and swollen capillaries (capillary telangiectases). In rare cases, vascular malformations can result from trauma or diseases.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Tomography, X-Ray: Tomography using x-ray transmission.Artifacts: Any visible result of a procedure which is caused by the procedure itself and not by the entity being analyzed. Common examples include histological structures introduced by tissue processing, radiographic images of structures that are not naturally present in living tissue, and products of chemical reactions that occur during analysis.Phantoms, Imaging: Devices or objects in various imaging techniques used to visualize or enhance visualization by simulating conditions encountered in the procedure. Phantoms are used very often in procedures employing or measuring x-irradiation or radioactive material to evaluate performance. Phantoms often have properties similar to human tissue. Water demonstrates absorbing properties similar to normal tissue, hence water-filled phantoms are used to map radiation levels. Phantoms are used also as teaching aids to simulate real conditions with x-ray or ultrasonic machines. (From Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990)Phlebography: Radiographic visualization or recording of a vein after the injection of contrast medium.Fluorodeoxyglucose F18: The compound is given by intravenous injection to do POSITRON-EMISSION TOMOGRAPHY for the assessment of cerebral and myocardial glucose metabolism in various physiological or pathological states including stroke and myocardial ischemia. It is also employed for the detection of malignant tumors including those of the brain, liver, and thyroid gland. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1162)Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Temporal Bone: Either of a pair of compound bones forming the lateral (left and right) surfaces and base of the skull which contains the organs of hearing. It is a large bone formed by the fusion of parts: the squamous (the flattened anterior-superior part), the tympanic (the curved anterior-inferior part), the mastoid (the irregular posterior portion), and the petrous (the part at the base of the skull).Plaque, Atherosclerotic: Lesions formed within the walls of ARTERIES.Azygos Vein: A vein which arises from the right ascending lumbar vein or the vena cava, enters the thorax through the aortic orifice in the diaphragm, and terminates in the superior vena cava.Preoperative Care: Care given during the period prior to undergoing surgery when psychological and physical preparations are made according to the special needs of the individual patient. This period spans the time between admission to the hospital to the time the surgery begins. (From Dictionary of Health Services Management, 2d ed)Severity of Illness Index: Levels within a diagnostic group which are established by various measurement criteria applied to the seriousness of a patient's disorder.Cholangiopancreatography, Magnetic Resonance: Non-invasive diagnostic technique for visualizing the PANCREATIC DUCTS and BILE DUCTS without the use of injected CONTRAST MEDIA or x-ray. MRI scans provide excellent sensitivity for duct dilatation, biliary stricture, and intraductal abnormalities.Feasibility Studies: Studies to determine the advantages or disadvantages, practicability, or capability of accomplishing a projected plan, study, or project.Coronary Vessel Anomalies: Malformations of CORONARY VESSELS, either arteries or veins. Included are anomalous origins of coronary arteries; ARTERIOVENOUS FISTULA; CORONARY ANEURYSM; MYOCARDIAL BRIDGING; and others.Radiography, Thoracic: X-ray visualization of the chest and organs of the thoracic cavity. It is not restricted to visualization of the lungs.Image Enhancement: Improvement of the quality of a picture by various techniques, including computer processing, digital filtering, echocardiographic techniques, light and ultrastructural MICROSCOPY, fluorescence spectrometry and microscopy, scintigraphy, and in vitro image processing at the molecular level.Coronary Vessels: The veins and arteries of the HEART.Body Burden: The total amount of a chemical, metal or radioactive substance present at any time after absorption in the body of man or animal.Cerebral Angiography: Radiography of the vascular system of the brain after injection of a contrast medium.Urography: Radiography of any part of the urinary tract.Diagnostic Imaging: Any visual display of structural or functional patterns of organs or tissues for diagnostic evaluation. It includes measuring physiologic and metabolic responses to physical and chemical stimuli, as well as ultramicroscopy.Algorithms: A procedure consisting of a sequence of algebraic formulas and/or logical steps to calculate or determine a given task.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Aortic Valve: The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle.Aortography: Radiographic visualization of the aorta and its branches by injection of contrast media, using percutaneous puncture or catheterization procedures.Radiation ProtectionBronchial Arteries: Left bronchial arteries arise from the thoracic aorta, the right from the first aortic intercostal or the upper left bronchial artery; they supply the bronchi and the lower trachea.Intestinal Volvulus: A twisting in the intestine (INTESTINES) that can cause INTESTINAL OBSTRUCTION.Pulmonary Veins: The veins that return the oxygenated blood from the lungs to the left atrium of the heart.Mercury Radioisotopes: Unstable isotopes of mercury that decay or disintegrate emitting radiation. Hg atoms with atomic weights 185-195, 197, 203, 205, and 206 are radioactive mercury isotopes.Extravasation of Diagnostic and Therapeutic Materials: The escape of diagnostic or therapeutic material from the vessel into which it is introduced into the surrounding tissue or body cavity.Petrous Bone: The dense rock-like part of temporal bone that contains the INNER EAR. Petrous bone is located at the base of the skull. Sometimes it is combined with the MASTOID PROCESS and called petromastoid part of temporal bone.Perfusion Imaging: The creation and display of functional images showing where the blood flow reaches by following the distribution of tracers injected into the blood stream.Electrocardiography: Recording of the moment-to-moment electromotive forces of the HEART as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a CATHODE RAY TUBE DISPLAY.Double-Balloon Enteroscopy: Endoscopy of the small intestines accomplished while advancing the endoscope into the intestines from the stomach by alternating the inflation of two balloons, one on an innertube of the endoscope and the other on an overtube.Spondylolysis: Deficient development or degeneration of a portion of the VERTEBRA, usually in the pars interarticularis (the bone bridge between the superior and inferior facet joints of the LUMBAR VERTEBRAE) leading to SPONDYLOLISTHESIS.Solitary Pulmonary Nodule: A single lung lesion that is characterized by a small round mass of tissue, usually less than 1 cm in diameter, and can be detected by chest radiography. A solitary pulmonary nodule can be associated with neoplasm, tuberculosis, cyst, or other anomalies in the lung, the CHEST WALL, or the PLEURA.Vascular Calcification: Deposition of calcium into the blood vessel structures. Excessive calcification of the vessels are associated with ATHEROSCLEROTIC PLAQUES formation particularly after MYOCARDIAL INFARCTION (see MONCKEBERG MEDIAL CALCIFIC SCLEROSIS) and chronic kidney diseases which in turn increase VASCULAR STIFFNESS.Radiometry: The measurement of radiation by photography, as in x-ray film and film badge, by Geiger-Mueller tube, and by SCINTILLATION COUNTING.Pericardium: A conical fibro-serous sac surrounding the HEART and the roots of the great vessels (AORTA; VENAE CAVAE; PULMONARY ARTERY). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers.Renal Veins: Short thick veins which return blood from the kidneys to the vena cava.Wounds, Nonpenetrating: Injuries caused by impact with a blunt object where there is no penetration of the skin.Scimitar Syndrome: An anomalous pulmonary venous return in which the right PULMONARY VEIN is not connected to the LEFT ATRIUM but to the INFERIOR VENA CAVA. Scimitar syndrome is named for the crescent- or Turkish sword-like shadow in the chest radiography and is often associated with hypoplasia of the right lung and right pulmonary artery, and dextroposition of the heart.Aortic Valve Stenosis: A pathological constriction that can occur above (supravalvular stenosis), below (subvalvular stenosis), or at the AORTIC VALVE. It is characterized by restricted outflow from the LEFT VENTRICLE into the AORTA.Neoplasms, Connective and Soft Tissue: Neoplasms developing from some structure of the connective and subcutaneous tissue. The concept does not refer to neoplasms located in connective or soft tissue.Pulmonary Embolism: Blocking of the PULMONARY ARTERY or one of its branches by an EMBOLUS.Follow-Up Studies: Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.Equipment Design: Methods of creating machines and devices.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Heart Valve Prosthesis: A device that substitutes for a heart valve. It may be composed of biological material (BIOPROSTHESIS) and/or synthetic material.Myocardial Perfusion Imaging: The creation and display of functional images showing where the blood is flowing into the MYOCARDIUM by following over time the distribution of tracers injected into the blood stream.Chest Pain: Pressure, burning, or numbness in the chest.X-Ray Microtomography: X-RAY COMPUTERIZED TOMOGRAPHY with resolution in the micrometer range.Ultrasonography, Interventional: The use of ultrasound to guide minimally invasive surgical procedures such as needle ASPIRATION BIOPSY; DRAINAGE; etc. Its widest application is intravascular ultrasound imaging but it is useful also in urology and intra-abdominal conditions.Focal InfectionSwine, Miniature: Genetically developed small pigs for use in biomedical research. There are several strains - Yucatan miniature, Sinclair miniature, and Minnesota miniature.Rare Diseases: A large group of diseases which are characterized by a low prevalence in the population. They frequently are associated with problems in diagnosis and treatment.Intra-Abdominal Fat: Fatty tissue inside the ABDOMINAL CAVITY, including visceral fat and retroperitoneal fat. It is the most metabolically active fat in the body and easily accessible for LIPOLYSIS. Increased visceral fat is associated with metabolic complications of OBESITY.Multimodal Imaging: The use of combination of imaging techniques or platforms (e.g., MRI SCAN and PET SCAN) encompassing aspects of anatomical, functional, or molecular imaging methods.Fluorine Radioisotopes: Unstable isotopes of fluorine that decay or disintegrate emitting radiation. F atoms with atomic weights 17, 18, and 20-22 are radioactive fluorine isotopes.Chi-Square Distribution: A distribution in which a variable is distributed like the sum of the squares of any given independent random variable, each of which has a normal distribution with mean of zero and variance of one. The chi-square test is a statistical test based on comparison of a test statistic to a chi-square distribution. The oldest of these tests are used to detect whether two or more population distributions differ from one another.Radiography, Interventional: Diagnostic and therapeutic procedures that are invasive or surgical in nature, and require the expertise of a specially trained radiologist. In general, they are more invasive than diagnostic imaging but less invasive than major surgery. They often involve catheterization, fluoroscopy, or computed tomography. Some examples include percutaneous transhepatic cholangiography, percutaneous transthoracic biopsy, balloon angioplasty, and arterial embolization.Magnetic Resonance Angiography: Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in CEREBRAL ANGIOGRAPHY as well as for studies of other vascular structures.Equipment Failure Analysis: The evaluation of incidents involving the loss of function of a device. These evaluations are used for a variety of purposes such as to determine the failure rates, the causes of failures, costs of failures, and the reliability and maintainability of devices.Earthquakes: Sudden slips on a fault, and the resulting ground shaking and radiated seismic energy caused by the slips, or by volcanic or magmatic activity, or other sudden stress changes in the earth. Faults are fractures along which the blocks of EARTH crust on either side have moved relative to one another parallel to the fracture.Risk Factors: An aspect of personal behavior or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with a health-related condition considered important to prevent.Models, Anatomic: Three-dimensional representation to show anatomic structures. Models may be used in place of intact animals or organisms for teaching, practice, and study.Heart Valve Prosthesis Implantation: Surgical insertion of synthetic material to repair injured or diseased heart valves.Subtraction Technique: Combination or superimposition of two images for demonstrating differences between them (e.g., radiograph with contrast vs. one without, radionuclide images using different radionuclides, radiograph vs. radionuclide image) and in the preparation of audiovisual materials (e.g., offsetting identical images, coloring of vessels in angiograms).Risk Assessment: The qualitative or quantitative estimation of the likelihood of adverse effects that may result from exposure to specified health hazards or from the absence of beneficial influences. (Last, Dictionary of Epidemiology, 1988)Stents: Devices that provide support for tubular structures that are being anastomosed or for body cavities during skin grafting.Ultrasonography: The visualization of deep structures of the body by recording the reflections or echoes of ultrasonic pulses directed into the tissues. Use of ultrasound for imaging or diagnostic purposes employs frequencies ranging from 1.6 to 10 megahertz.ROC Curve: A graphic means for assessing the ability of a screening test to discriminate between healthy and diseased persons; may also be used in other studies, e.g., distinguishing stimuli responses as to a faint stimuli or nonstimuli.Colon, Transverse: The segment of LARGE INTESTINE between ASCENDING COLON and DESCENDING COLON. It passes from the RIGHT COLIC FLEXURE across the ABDOMEN, then turns sharply at the left colonic flexure into the descending colon.Arthrography: Roentgenography of a joint, usually after injection of either positive or negative contrast medium.Renal Artery: A branch of the abdominal aorta which supplies the kidneys, adrenal glands and ureters.Hepatic Artery: A branch of the celiac artery that distributes to the stomach, pancreas, duodenum, liver, gallbladder, and greater omentum.Echocardiography: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.Cardiac Catheterization: Procedures in which placement of CARDIAC CATHETERS is performed for therapeutic or diagnostic procedures.Cadaver: A dead body, usually a human body.Aortic Valve Insufficiency: Pathological condition characterized by the backflow of blood from the ASCENDING AORTA back into the LEFT VENTRICLE, leading to regurgitation. It is caused by diseases of the AORTIC VALVE or its surrounding tissue (aortic root).Aorta, Abdominal: The aorta from the DIAPHRAGM to the bifurcation into the right and left common iliac arteries.Neck: The part of a human or animal body connecting the HEAD to the rest of the body.Angiography, Digital Subtraction: A method of delineating blood vessels by subtracting a tissue background image from an image of tissue plus intravascular contrast material that attenuates the X-ray photons. The background image is determined from a digitized image taken a few moments before injection of the contrast material. The resulting angiogram is a high-contrast image of the vessel. This subtraction technique allows extraction of a high-intensity signal from the superimposed background information. The image is thus the result of the differential absorption of X-rays by different tissues.Prosthesis Design: The plan and delineation of prostheses in general or a specific prosthesis.Arteriovenous Fistula: An abnormal direct communication between an artery and a vein without passing through the CAPILLARIES. An A-V fistula usually leads to the formation of a dilated sac-like connection, arteriovenous aneurysm. The locations and size of the shunts determine the degree of effects on the cardiovascular functions such as BLOOD PRESSURE and HEART RATE.Prognosis: A prediction of the probable outcome of a disease based on a individual's condition and the usual course of the disease as seen in similar situations.Four-Dimensional Computed Tomography: Three-dimensional computed tomographic imaging with the added dimension of time, to follow motion during imaging.Swine: Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).Heart Atria: The chambers of the heart, to which the BLOOD returns from the circulation.Bronchoscopy: Endoscopic examination, therapy or surgery of the bronchi.Technetium Tc 99m Sestamibi: A technetium imaging agent used to reveal blood-starved cardiac tissue during a heart attack.Acute Disease: Disease having a short and relatively severe course.Statistics, Nonparametric: A class of statistical methods applicable to a large set of probability distributions used to test for correlation, location, independence, etc. In most nonparametric statistical tests, the original scores or observations are replaced by another variable containing less information. An important class of nonparametric tests employs the ordinal properties of the data. Another class of tests uses information about whether an observation is above or below some fixed value such as the median, and a third class is based on the frequency of the occurrence of runs in the data. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed, p1284; Corsini, Concise Encyclopedia of Psychology, 1987, p764-5)Portal Vein: A short thick vein formed by union of the superior mesenteric vein and the splenic vein.Aneurysm, False: Not an aneurysm but a well-defined collection of blood and CONNECTIVE TISSUE outside the wall of a blood vessel or the heart. It is the containment of a ruptured blood vessel or heart, such as sealing a rupture of the left ventricle. False aneurysm is formed by organized THROMBUS and HEMATOMA in surrounding tissue.Catheter Ablation: Removal of tissue with electrical current delivered via electrodes positioned at the distal end of a catheter. Energy sources are commonly direct current (DC-shock) or alternating current at radiofrequencies (usually 750 kHz). The technique is used most often to ablate the AV junction and/or accessory pathways in order to interrupt AV conduction and produce AV block in the treatment of various tachyarrhythmias.Renal Artery Obstruction: Narrowing or occlusion of the RENAL ARTERY or arteries. It is due usually to ATHEROSCLEROSIS; FIBROMUSCULAR DYSPLASIA; THROMBOSIS; EMBOLISM, or external pressure. The reduced renal perfusion can lead to renovascular hypertension (HYPERTENSION, RENOVASCULAR).Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Cerebral Infarction: The formation of an area of NECROSIS in the CEREBRUM caused by an insufficiency of arterial or venous blood flow. Infarcts of the cerebrum are generally classified by hemisphere (i.e., left vs. right), lobe (e.g., frontal lobe infarction), arterial distribution (e.g., INFARCTION, ANTERIOR CEREBRAL ARTERY), and etiology (e.g., embolic infarction).Liver Neoplasms: Tumors or cancer of the LIVER.Reference Standards: A basis of value established for the measure of quantity, weight, extent or quality, e.g. weight standards, standard solutions, methods, techniques, and procedures used in diagnosis and therapy.Tuberculosis, Lymph Node: Infection of the lymph nodes by tuberculosis. Tuberculous infection of the cervical lymph nodes is scrofula.Carotid Artery Diseases: Pathological conditions involving the CAROTID ARTERIES, including the common, internal, and external carotid arteries. ATHEROSCLEROSIS and TRAUMA are relatively frequent causes of carotid artery pathology.Pulmonary Artery: The short wide vessel arising from the conus arteriosus of the right ventricle and conveying unaerated blood to the lungs.Constriction, Pathologic: The condition of an anatomical structure's being constricted beyond normal dimensions.Reference Values: The range or frequency distribution of a measurement in a population (of organisms, organs or things) that has not been selected for the presence of disease or abnormality.Single-Blind Method: A method in which either the observer(s) or the subject(s) is kept ignorant of the group to which the subjects are assigned.Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.Graft Occlusion, Vascular: Obstruction of flow in biological or prosthetic vascular grafts.Macula Lutea: An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. (From Cline et al., Dictionary of Visual Science, 4th ed)Magnetic Resonance Imaging, Cine: A type of imaging technique used primarily in the field of cardiology. By coordinating the fast gradient-echo MRI sequence with retrospective ECG-gating, numerous short time frames evenly spaced in the cardiac cycle are produced. These images are laced together in a cinematic display so that wall motion of the ventricles, valve motion, and blood flow patterns in the heart and great vessels can be visualized.Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Heart Valve Diseases: Pathological conditions involving any of the various HEART VALVES and the associated structures (PAPILLARY MUSCLES and CHORDAE TENDINEAE).Myocardial Infarction: NECROSIS of the MYOCARDIUM caused by an obstruction of the blood supply to the heart (CORONARY CIRCULATION).Stroke Volume: The amount of BLOOD pumped out of the HEART per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Coronary Disease: An imbalance between myocardial functional requirements and the capacity of the CORONARY VESSELS to supply sufficient blood flow. It is a form of MYOCARDIAL ISCHEMIA (insufficient blood supply to the heart muscle) caused by a decreased capacity of the coronary vessels.Neoplasm Staging: Methods which attempt to express in replicable terms the extent of the neoplasm in the patient.Linear Models: Statistical models in which the value of a parameter for a given value of a factor is assumed to be equal to a + bx, where a and b are constants. The models predict a linear regression.Image Interpretation, Computer-Assisted: Methods developed to aid in the interpretation of ultrasound, radiographic images, etc., for diagnosis of disease.Lumbar Vertebrae: VERTEBRAE in the region of the lower BACK below the THORACIC VERTEBRAE and above the SACRAL VERTEBRAE.Oxygen Radioisotopes: Unstable isotopes of oxygen that decay or disintegrate emitting radiation. O atoms with atomic weights 13, 14, 15, 19, and 20 are radioactive oxygen isotopes.Heart: The hollow, muscular organ that maintains the circulation of the blood.Carotid Stenosis: Narrowing or stricture of any part of the CAROTID ARTERIES, most often due to atherosclerotic plaque formation. Ulcerations may form in atherosclerotic plaques and induce THROMBUS formation. Platelet or cholesterol emboli may arise from stenotic carotid lesions and induce a TRANSIENT ISCHEMIC ATTACK; CEREBROVASCULAR ACCIDENT; or temporary blindness (AMAUROSIS FUGAX). (From Adams et al., Principles of Neurology, 6th ed, pp 822-3)Diagnostic Techniques, Ophthalmological: Methods and procedures for the diagnosis of diseases of the eye or of vision disorders.Carbon Radioisotopes: Unstable isotopes of carbon that decay or disintegrate emitting radiation. C atoms with atomic weights 10, 11, and 14-16 are radioactive carbon isotopes.Lung: Either of the pair of organs occupying the cavity of the thorax that effect the aeration of the blood.Echocardiography, Transesophageal: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues using a transducer placed in the esophagus.Pancreatic Neoplasms: Tumors or cancer of the PANCREAS. Depending on the types of ISLET CELLS present in the tumors, various hormones can be secreted: GLUCAGON from PANCREATIC ALPHA CELLS; INSULIN from PANCREATIC BETA CELLS; and SOMATOSTATIN from the SOMATOSTATIN-SECRETING CELLS. Most are malignant except the insulin-producing tumors (INSULINOMA).