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58-1031: MRA may refer to: Medicine and science [ edit ] Magnetic resonance angiography Mineralocorticoid receptor antagonist Monoamine releasing agent Multiresolution analysis Organisations [ edit ] Madison-Ridgeland Academy Maharashtra Rationalist Association , an organisation in India Marketing Research Association Mauritius Revenue Authority Metal Roofing Alliance Metropolitan Redevelopment Authority of Western Australia Microcredit Regulatory Authority Monland Restoration Army Moral Re-Armament Motorcycle Roadracing Association Mountain Rescue Association Mugi Rekso Abadi ,

116-410: A pulse , which can be felt in different areas of the body, such as the radial pulse . Arterioles have the greatest collective influence on both local blood flow and on overall blood pressure. They are the primary "adjustable nozzles" in the blood system, across which the greatest pressure drop occurs. The combination of heart output ( cardiac output ) and systemic vascular resistance , which refers to

174-428: A 3D volume in the body. To display this 3D dataset on a 2D device such as a computer monitor, some rendering method has to be used. The most common method is maximum intensity projection (MIP), where the computer simulates rays through the volume and selects the highest value for display on the screen. The resulting images resemble conventional catheter angiography images. If several such projections are combined into

232-453: A cine loop or QuickTime VR object, the depth impression is improved, and the observer can get a good perception of 3D structure. An alternative to MIP is direct volume rendering where the MR signal is translated to properties like brightness, opacity and color and then used in an optical model. MRA has been successful in studying many arteries in the body, including cerebral and other vessels in

290-523: A constant velocity, v x {\displaystyle v_{x}} , along the direction of the applied bipolar gradient: The accrued phase is proportional to both v x {\displaystyle v_{x}} and the 1st moment of the bipolar gradient, Δ m 1 {\displaystyle \Delta m_{1}} , thus providing a means to estimate v x {\displaystyle v_{x}} . γ {\displaystyle \gamma }

348-411: A diameter less than that of red blood cells ; a red blood cell is typically 7 micrometers outside diameter, capillaries typically 5 micrometers inside diameter. The red blood cells must distort in order to pass through the capillaries. These small diameters of the capillaries provide a relatively large surface area for the exchange of gasses and nutrients. Systemic arterial pressures are generated by

406-715: A different phase since it moves constantly through the gradient, thus also giving its speed of the flow. Since phase-contrast can only acquire flow in one direction at a time, 3 separate image acquisitions in all three directions must be computed to give the complete image of flow. Despite the slowness of this method, the strength of the technique is that in addition to imaging flowing blood, quantitative measurements of blood flow can be obtained. Whereas most of techniques in MRA rely on contrast agents or flow into blood to generate contrast (Contrast Enhanced techniques), there are also non-contrast enhanced flow-independent methods. These methods, as

464-1082: A media company in Indonesia Myanmar Restaurant Association Royal Museum of the Armed Forces and Military History (abbreviated MRA in French), a museum in Belgium Other [ edit ] Mail retrieval agent Market reduction approach Member's Representational Allowance in the United States House of Representatives Men's Rights Activist (or men's rights activism) Minimum reception altitude Mutant registration acts (comics) Mutual recognition agreement Northern Mariana Islands , US territory, ITU country code See also [ edit ] All pages with titles beginning with MRA All pages with titles containing MRA Topics referred to by

522-473: A non-contrast enhanced mask image. This approach has been shown to improve diagnostic quality, because it prevents motion subtraction artifacts as well as an increase of image background noise, both direct results of the image subtraction. An important condition for this approach is to have excellent body fat suppression over large image areas, which is possible by using mDIXON acquisition methods. Traditional MRA suppresses signals originating from body fat during

580-425: A subtraction mask to extract the vascular tree in the succeeding images. Allows the operator to divide arterial and venous phases of a blood-groove with visualisation of its dynamics. Much less time has been spent researching this method so far in comparison with other methods of MRA. BOLD venography or susceptibility weighted imaging (SWI): This method exploits the susceptibility differences between tissues and uses

638-466: A thin slice. Time-of-flight (TOF) or inflow angiography, uses a short echo time and flow compensation to make flowing blood much brighter than stationary tissue. As flowing blood enters the area being imaged it has seen a limited number of excitation pulses so it is not saturated, this gives it a much higher signal than the saturated stationary tissue. As this method is dependent on flowing blood, areas with slow flow (such as large aneurysms) or flow that

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696-428: A variety of different magnetized proton spins to lose phase coherence (intra-voxel dephasing phenomenon), resulting in a loss of signal. This phenomenon may result in the overestimation of arterial stenosis. Other artifacts observed in MRA include: Occasionally, MRA directly produces (thick) slices that contain the entire vessel of interest. More commonly, however, the acquisition results in a stack of slices representing

754-415: Is a major challenge in flow dependent MRA. It causes the differences between the blood signal and the static tissue signal to be small. This either applies to PC-MRA where the phase difference between blood and static tissue is reduced compared to faster flow and to TOF-MRA where the transverse blood magnetization and thus the blood signal are reduced. Contrast agents may be used to increase blood signal – this

812-405: Is achieved by subtracting the systolic data, where the arteries appear dark, from the diastolic data set, where the arteries appear bright. Requires the use of electrocardiographic gating. Trade names for this technique include Fresh Blood Imaging (Toshiba), TRANCE (Philips), native SPACE (Siemens) and DeltaFlow (GE). 4D dynamic MR angiography (4D-MRA): The first images, before enhancement, serve as

870-411: Is commonly used in traumatic brain injuries (TBI) and for high resolution brain venographies. Similar procedures to flow effect based MRA can be used to image veins. For instance, Magnetic resonance venography (MRV) is achieved by exciting a plane inferiorly while signal is gathered in the plane immediately superior to the excitation plane, and thus imaging the venous blood which has recently moved from

928-424: Is composed of collagen fibers and elastic tissue —with the largest arteries containing vasa vasorum , small blood vessels that supply the walls of large blood vessels. Most of the layers have a clear boundary between them, however the tunica externa has a boundary that is ill-defined. Normally its boundary is considered when it meets or touches the connective tissue. Inside this layer is the tunica media , which

986-463: Is currently the most common method of performing MRA. The contrast medium is injected into a vein, and images are acquired both pre-contrast and during the first pass of the agent through the arteries. By subtraction of these two acquisitions in post-processing, an image is obtained which in principle only shows blood vessels, and not the surrounding tissue. Provided that the timing is correct, this may result in images of very high quality. An alternative

1044-470: Is different from Wikidata All article disambiguation pages All disambiguation pages Magnetic resonance angiography A variety of techniques can be used to generate the pictures of blood vessels, both arteries and veins , based on flow effects or on contrast (inherent or pharmacologically generated). The most frequently applied MRA methods involve the use intravenous contrast agents , particularly those containing gadolinium to shorten

1102-696: Is especially important for very small vessels and vessels with very small flow velocities that normally show accordingly weak signal. Unfortunately, the use of gadolinium-based contrast media can be dangerous if patients suffer from poor renal function. To avoid these complications as well as eliminate the costs of contrast media, non-enhanced methods have been researched recently. Flow-independent NEMRA methods are not based on flow, but exploit differences in T 1 , T 2 and chemical shift to distinguish blood from static tissue. Gated subtraction fast spin-echo: An imaging technique that subtracts two fast spin echo sequences acquired at systole and diastole. Arteriography

1160-457: Is in plane of the image may not be well visualized. This is most commonly used in the head and neck and gives detailed high-resolution images. It is also the most common technique used for routine angiographic evaluation of the intracranial circulation in patients with ischemic stroke. Phase-contrast (PC-MRA) can be used to encode the velocity of moving blood in the magnetic resonance signal's phase . The most common method used to encode velocity

1218-458: Is made up of smooth muscle cells, elastic tissue (also called connective tissue proper ) and collagen fibres. The innermost layer, which is in direct contact with the flow of blood, is the tunica intima . The elastic tissue allows the artery to bend and fit through places in the body. This layer is mainly made up of endothelial cells (and a supporting layer of elastin rich collagen in elastic arteries). The hollow internal cavity in which

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1276-461: Is needed to be injected into the patient. The greatest drawbacks of the method are its comparatively high cost and its somewhat limited spatial resolution . The length of time the scans take can also be an issue, with CT being far quicker. It is also ruled out in patients for whom MRI exams may be unsafe (such as having a pacemaker or metal in the eyes or certain surgical clips). MRA procedures for visualizing cranial circulation are no different from

1334-413: Is null: The bipolar gradient can be applied along any axis or combination of axes depending on the direction along which flow is to be measured (e.g. x). Δ Φ {\displaystyle \Delta \Phi } , the phase accrued during the application of the gradient, is 0 for stationary spins: their phase is unaffected by the application of the bipolar gradient. For spins moving with

1392-438: Is primarily influenced by activity of the sympathetic vasomotor nerves innervating the arterioles. Enhanced sympathetic activation prompts vasoconstriction, reducing the lumen diameter. A reduced lumen diameter consequently elevates the blood pressure within the arterioles. Conversely, decreased sympathetic activity within the vasomotor nerves causes vasodilation of the vessels thereby decreasing blood pressure. The aorta

1450-607: Is the Larmor frequency of the imaged spins. To measure Δ Φ {\displaystyle \Delta \Phi } , of the MRI signal is manipulated by bipolar gradients (varying magnetic fields) that are preset to a maximum expected flow velocity. An image acquisition that is reverse of the bipolar gradient is then acquired and the difference of the two images is calculated. Static tissues such as muscle or bone will subtract out, however moving tissues such as blood will acquire

1508-468: Is the application of a bipolar gradient between the excitation pulse and the readout. A bipolar gradient is formed by two symmetric lobes of equal area. It is created by turning on the magnetic field gradient for some time, and then switching the magnetic field gradient to the opposite direction for the same amount of time. By definition, the total area (0th moment) of a bipolar gradient, G bip {\displaystyle G_{\text{bip}}} ,

1566-476: Is the effect when an artery is cut due to the higher arterial pressures. Blood is spurted out at a rapid, intermittent rate, that coincides with the heartbeat. The amount of blood loss can be copious, can occur very rapidly, and be life-threatening. Over time, factors such as elevated arterial blood sugar (particularly as seen in diabetes mellitus ), lipoprotein , cholesterol , high blood pressure , stress and smoking , are all implicated in damaging both

1624-411: Is the non-invasive character of the examination (no catheters have to be introduced in the body). Another advantage, compared to CT angiography and catheter angiography, is that the patient is not exposed to any ionizing radiation . Also, contrast media used for MRI tend to be less toxic than those used for CT angiography and catheter angiography, with fewer people having any risk of allergy. Also far less

1682-443: Is the root systemic artery (i.e., main artery). In humans, it receives blood directly from the left ventricle of the heart via the aortic valve . As the aorta branches and these arteries branch, in turn, they become successively smaller in diameter, down to the arterioles . The arterioles supply capillaries , which in turn empty into venules . The first branches off of the aorta are the coronary arteries , which supply blood to

1740-605: Is to use a contrast agent that does not, as most agents, leave the vascular system within a few minutes, but remains in the circulation up to an hour (a " blood-pool agent "). Since longer time is available for image acquisition, higher resolution imaging is possible. A problem, however, is the fact that both arteries and veins are enhanced at the same time if higher resolution images are required. Subtractionless contrast-enhanced magnetic resonance angiography: recent developments in MRA technology have made it possible to create high quality contrast-enhanced MRA images without subtraction of

1798-465: Is unique because the blood in it is not "oxygenated", as it has not yet passed through the lungs. The other unique artery is the umbilical artery , which carries deoxygenated blood from a fetus to its mother. Arteries have a blood pressure higher than other parts of the circulatory system. The pressure in arteries varies during the cardiac cycle . It is highest when the heart contracts and lowest when heart relaxes . The variation in pressure produces

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1856-450: The T 1 of blood to about 250 ms, shorter than the T 1 of all other tissues (except fat). Short-TR sequences produce bright images of the blood. However, many other techniques for performing MRA exist, and can be classified into two general groups: 'flow-dependent' methods and 'flow-independent' methods. One group of methods for MRA is based on blood flow. Those methods are referred to as flow dependent MRA. They take advantage of

1914-431: The arterioles , and then to the capillaries , where nutrients and gasses are exchanged. After traveling from the aorta , blood travels through peripheral arteries into smaller arteries called arterioles , and eventually to capillaries . Arterioles help in regulating blood pressure by the variable contraction of the smooth muscle of their walls, and deliver blood to the capillaries . This smooth muscle contraction

1972-413: The capillary vessels that join arteries and veins, and there was no notion of circulation. Diogenes of Apollonia developed the theory of pneuma , originally meaning just air but soon identified with the soul itself, and thought to co-exist with the blood in the blood vessels. The arteries were thought to be responsible for the transport of air to the tissues and to be connected to the trachea . This

2030-563: The endothelium and walls of the arteries, resulting in atherosclerosis . Atherosclerosis is a disease marked by the hardening of arteries. This is caused by an atheroma or plaque in the artery wall and is a build-up of cell debris, that contain lipids , (cholesterol and fatty acids ), calcium and a variable amount of fibrous connective tissue . Accidental intra-arterial injection either iatrogenically or through recreational drug use can cause symptoms such as intense pain, paresthesia and necrosis . It usually causes permanent damage to

2088-414: The heart to the lungs . Large arteries (such as the aorta) are composed of many different types of cells, namely endothelial, smooth muscle, fibroblast, and immune cells. As with veins, the arterial wall consists of three layers called tunics, namely the tunica intima , tunica media , and tunica externa , from innermost to outermost. The externa , alternatively known as the tunica adventitia ,

2146-476: The systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in the pulmonary circulation that carry blood to the lungs for oxygenation, and the umbilical arteries in the fetal circulation that carry deoxygenated blood to the placenta . It consists of a multi-layered artery wall wrapped into a tube-shaped channel. Arteries contrast with veins , which carry deoxygenated blood back towards

2204-644: The 3D data can not only be used to create cross sectional images, but also projections can be calculated from the data. Three-dimensional data acquisition might also be helpful when dealing with complex vessel geometries where blood is flowing in all spatial directions (unfortunately, this case also requires three different flow encodings, one in each spatial direction). Both PC-MRA and TOF-MRA have advantages and disadvantages. PC-MRA has fewer difficulties with slow flow than TOF-MRA and also allows quantitative measurements of flow. PC-MRA shows low sensitivity when imaging pulsating and non-uniform flow. In general, slow blood flow

2262-403: The acquisition of the images two different approaches exist. In general, 2D and 3D images can be acquired. If 3D data is acquired, cross sections at arbitrary view angles can be calculated. Three-dimensional data can also be generated by combining 2D data from different slices, but this approach results in lower quality images at view angles different from the original data acquisition. Furthermore,

2320-488: The actual image acquisition, which is a method that is sensitive to small deviations in the magnetic and electromagnetic fields and as a result may show insufficient fat suppression in some areas. mDIXON methods can distinguish and accurately separate image signals created by fat or water. By using the 'water images' for MRA scans, virtually no body fat is seen so that no subtraction masks are needed for high quality MR venograms. Non-enhanced magnetic resonance angiography: Since

2378-450: The blood flows is called the lumen . Arterial formation begins and ends when endothelial cells begin to express arterial specific genes, such as ephrin B2 . Arteries form part of the circulatory system . They carry blood that is oxygenated after it has been pumped from the heart . Coronary arteries also aid the heart in pumping blood by sending oxygenated blood to the heart, allowing

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2436-411: The collective resistance of all of the body's arterioles , are the principal determinants of arterial blood pressure at any given moment. Arteries have the highest pressure and have narrow lumen diameter. Systemic arteries are the arteries (including the peripheral arteries ), of the systemic circulation , which is the part of the cardiovascular system that carries oxygenated blood away from

2494-465: The excited plane. Differences in tissue signals, can also be used for MRA. This method is based on the different signal properties of blood compared to other tissues in the body, independent of MR flow effects. This is most successfully done with balanced pulse sequences such as TrueFISP or bTFE. BOLD can also be used in stroke imaging in order to assess the viability of tissue survival. MRA techniques in general are sensitive to turbulent flow, which causes

2552-480: The fact that the blood within vessels is flowing to distinguish the vessels from other static tissue. That way, images of the vasculature can be produced. Flow dependent MRA can be divided into different categories: There is phase-contrast MRA (PC-MRA) which utilizes phase differences to distinguish blood from static tissue and time-of-flight MRA (TOF MRA) which exploits that moving spins of the blood experience fewer excitation pulses than static tissue, e.g. when imaging

2610-401: The forceful contractions of the heart's left ventricle . High blood pressure is a factor in causing arterial damage. Healthy resting arterial pressures are relatively low, mean systemic pressures typically being under 100  mmHg (1.9  psi ; 13  kPa ) above surrounding atmospheric pressure (about 760 mmHg, 14.7 psi, 101 kPa at sea level). To withstand and adapt to

2668-465: The head and neck, the aorta and its major branches in the thorax and abdomen, the renal arteries, and the arteries in the lower limbs. For the coronary arteries, however, MRA has been less successful than CT angiography or invasive catheter angiography. Most often, the underlying disease is atherosclerosis , but medical conditions like aneurysms or abnormal vascular anatomy can also be diagnosed. An advantage of MRA compared to invasive catheter angiography

2726-494: The heart muscle itself. These are followed by the branches of the aortic arch, namely the brachiocephalic artery , the left common carotid , and the left subclavian arteries. The capillaries are the smallest of the blood vessels and are part of the microcirculation . The microvessels have a width of a single cell in diameter to aid in the fast and easy diffusion of gasses, sugars and nutrients to surrounding tissues. Capillaries have no smooth muscle surrounding them and have

2784-482: The heart, to the body , and returns deoxygenated blood back to the heart. Systemic arteries can be subdivided into two types—muscular and elastic—according to the relative compositions of elastic and muscle tissue in their tunica media as well as their size and the makeup of the internal and external elastic lamina. The larger arteries (>10  mm diameter) are generally elastic and the smaller ones (0.1–10 mm) tend to be muscular. Systemic arteries deliver blood to

2842-454: The heart; or in the pulmonary and fetal circulations carry oxygenated blood to the lungs and fetus respectively. The anatomy of arteries can be separated into gross anatomy , at the macroscopic level , and microanatomy , which must be studied with a microscope . The arterial system of the human body is divided into systemic arteries , carrying blood from the heart to the whole body, and pulmonary arteries , carrying deoxygenated blood from

2900-475: The injection of contrast agents may be dangerous for patients with poor kidney function, others techniques have been developed, which do not require any injection. These methods are based on the differences of T 1 , T 2 and chemical shift of the different tissues of the voxel. A notable non-enhanced method for flow-independent angiography is balanced steady-state free precession (bSSFP) imaging which naturally produces high signal from arteries and veins. For

2958-472: The limb; often amputation is necessary. Among the Ancient Greeks before Hippocrates , all blood vessels were called Φλέβες, phlebes . The word arteria then referred to the windpipe . Herophilos was the first to describe anatomical differences between the two types of blood vessel. While Empedocles believed that the blood moved to and fro through the blood vessels, there was no concept of

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3016-427: The muscles to function. Arteries carry oxygenated blood away from the heart to the tissues, except for pulmonary arteries , which carry blood to the lungs for oxygenation (usually veins carry deoxygenated blood to the heart but the pulmonary veins carry oxygenated blood as well). There are two types of unique arteries. The pulmonary artery carries blood from the heart to the lungs , where it receives oxygen. It

3074-650: The name suggests, do not rely on flow, but are instead based on the differences of T 1 , T 2 and chemical shift of the different tissues of the voxel. One of the main advantages of this kind of techniques is that we may image the regions of slow flow often found in patients with vascular diseases more easily. Moreover, non-contrast enhanced methods do not require the administration of additional contrast agent, which have been recently linked to nephrogenic systemic fibrosis in patients with chronic kidney disease and kidney failure . Contrast-enhanced magnetic resonance angiography uses injection of MRI contrast agents and

3132-465: The phase image to detect these differences. The magnitude and phase data are combined (digitally, by an image-processing program) to produce an enhanced contrast magnitude image which is exquisitely sensitive to venous blood, hemorrhage and iron storage. The imaging of venous blood with SWI is a blood-oxygen-level dependent (BOLD) technique which is why it was (and is sometimes still) referred to as BOLD venography. Due to its sensitivity to venous blood SWI

3190-399: The positioning for a normal MRI brain. Immobilization within the head coil will be required. MRA is usually a part of the total MRI brain examination and adds approximately 10 minutes to the normal MRI protocol. Artery An artery (from Greek ἀρτηρία (artēríā) ) is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in

3248-438: The pressures within, arteries are surrounded by varying thicknesses of smooth muscle which have extensive elastic and inelastic connective tissues . The pulse pressure, being the difference between systolic and diastolic pressure, is determined primarily by the amount of blood ejected by each heart beat, stroke volume , versus the volume and elasticity of the major arteries. A blood squirt , also known as an arterial gush,

3306-403: The same term [REDACTED] This disambiguation page lists articles associated with the title MRA . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=MRA&oldid=1159795000 " Category : Disambiguation pages Hidden categories: Short description

3364-413: Was as a result of finding the arteries of cadavers devoid of blood. In medieval times, it was supposed that arteries carried a fluid, called "spiritual blood" or "vital spirits", considered to be different from the contents of the veins . This theory went back to Galen . In the late medieval period, the trachea , and ligaments were also called "arteries". William Harvey described and popularized

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