Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

359 results found
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Mach bands

Mach bands or the Mach effect refers to an optical phenomenon from edge enhancement due to lateral inhibition of the retina 2. This is an inbuilt edge enhancement mechanism of the retina, where the edges of darker objects next to lighter objects will appear lighter and vice versa; creating a fal...
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Voxel

Voxel is a contraction of the words 'volume' and 'element' and was coined as a 3-D equivalent of a pixel. It is an individual point in space on a 3-dimensional, regular matrix. The location of each voxel is encoded by its relative relationship to other voxels. A tensor is a voxel that contains ...
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MR angiography

MR angiography (MRA) is an alternative to conventional angiography and CT angiography, eliminating the need for iodinated contrast media and ionising radiation. It has evolved into several techniques with different advantages and applications: contrast enhanced MR angiography non-contrast enha...
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MRI pulse sequence abbreviations

This article contains a list of commonly and less commonly used MRI pulse sequence abbreviations and their meaning. If available, an explanation is included in a separate article. spin echo sequences (SE) T1: T1 weighted IR: inversion recovery T2 : T2 weighted RARE: rapid acquisition with r...
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Fluid attenuation inversion recovery

Fluid attenuation inversion recovery (FLAIR) is a special inversion recovery sequence with a long inversion time (TI) which results in removing signal from the cerebrospinal fluid (CSF) from the resulting images.1  To null the signal from fluid, the inversion time (TI) of the FLAIR pulse sequen...
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Motion artifact

Motion artifact is a patient-based artifact that occurs with voluntary or involuntary patient movement during image acquisition. Misregistration artifacts, which appear as blurring, streaking, or shading, are caused by patient movement during a CT scan.  Blurring also occurs with patient moveme...
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CT artifacts

CT artifacts are common and can occur for various reasons. Knowledge of these artifacts is important because they can mimic pathology (e.g. partial volume artefact) or can degrade image quality to non-diagnostic levels.  CT artifacts can be classified according to the underlying cause of the ar...
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Iodinated contrast media

Iodinated contrast media are contrast agents frequently used via intravenous administration in computed tomography, although they are also used in fluoroscopy, angiography and venography, and even occasionally, plain radiography. Although the intravenous route is common, they are also administer...
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Partial volume averaging (CT artifact)

Partial volume artifact occurs when tissues of widely different absorption are encompassed on the same CT voxel producing a beam attenuation proportional to the average value of these tissues.  The last generation of CT scanners and its reduction in the volume of a voxel has substantially reduc...
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Ring artifact

Ring artifacts are a CT phenomenon that occur due to miscalibration or failure of one or more detector elements in a CT scanner. They occur close to the isocentre of the scan and are usually visible on multiple slices at the same location. They are a common problem in cranial CT. The remedy is ...
Article

X-ray production

X-rays are produced due to sudden deceleration of fast moving electrons when they collide and interact with the target anode. In this process of deceleration, more than 99% of the electron energy is converted into heat and less than 1% of energy is converted into X-rays. Definitions Cathode T...
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Chemical shift artifact

Chemical shift artifact or misregistration is a type of MRI artifact. It is a common finding on some MRI sequences, and used in MRS. Chemical shift is due to the differences between resonance frequencies of fat and water. It occurs in the frequency encode direction where a shift in the detected...
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Diamagnetism

Diamagnetism is the property of materials that have no intrinsic atomic magnetic moment, but when placed in a magnetic field weakly repel the field, resulting in a small negative magnetic susceptibility. Materials like water, copper, nitrogen, barium sulfate, and most tissues are diamagnetic. T...
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Gastrointestinal MRI contrast agents

Gastrointestinal MRI contrast agents are varied and can be either positive or negative agents. Acceptance of the use of MRI in abdominal imaging has been limited in part by difficulty in distinguishing bowel from intra-abdominal masses and normal organs. The use of enteric contrast agents can ai...
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Iodine

Iodine (chemical symbol, I) is a chemical element with the atomic number 53. It is a shiny purplish solid in the halogen group. Its name is derived from ιωδησ, Greek for violet-coloured.
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Elastography

Elastography is a newer technique that exploits the fact that a pathological process alters the elastic properties of the involved tissue. This change in elasticity is detected and imaged using elastography. Radiographic technique Sono-elastography  strain elastography (also known as static o...
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Biological effects of ultrasound

The biological effects of ultrasound refer to the potential adverse effects the imaging modality has on human tissue. These are primarily via two main mechanisms: thermal and mechanical. Despite this, ultrasound has a remarkable record for patient safety with no significant adverse bioeffects re...
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Milliamperage-seconds (mAs)

Milliamperage-seconds more commonly known as mAs is a measure of radiation produced (milliamperage) over a set amount of time (seconds) via an x-ray tube. It directly influences the radiographic density, when all other factors are constant. An increase in current (mA) results in a higher produc...
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Reflection

Reflection of a sound wave occurs when the wave passes between two tissues of different acoustic speeds and a fraction of the wave 'bounces' back. This forms one of the major principles of ultrasound imaging as the ultrasound probe detects these reflected waves to form the desired image. Angle ...
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Computed tomographic (CT) colonography

Computed tomographic (CT) colonography, also called CTC, virtual colonoscopy (VC) or CT pneumocolon, is a powerful minimally invasive technique for colorectal cancer screening. Indications screening test for colorectal carcinoma colon evaluation after incomplete or unsuccessful conventional c...
Article

Hyperintense on T1-weighted images (mnemonic)

Mnemonics for bright or hyperintense T1-weighted lesions include: My Best Friend is Pretty Cool 3 Fs and 4 Ms Mnemonic My Best Friend is Pretty Cool: M: melanin B: blood (i.e. methaemoglobin in subacute haemorrhage) F: fat and slow flow P: protein; paramagnetic substances (e.g. manganese...
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Aliasing artifact (CT)

Aliasing artifact, otherwise known as undersampling, in CT refers to an error in the accuracy proponent of analogue to digital converter (ADC) during image digitisation.  Image digitisation has three distinct steps: scanning, sampling, and quantization.  When sampling, the brightness of each p...
Article

Phase-encoded motion artifact

Phase-encoded motion artifact is one of many MRI artifacts occurring as a result of tissue/fluid moving during the scan. It manifests as ghosting in the direction of phase-encoding, usually in the direction of the short axis of the image (i.e left to right on axial or coronal brains, and anterio...
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Gibbs and truncation artifacts

Gibbs artifact is a type of MRI artifact. It refers to a series of lines in the MR image parallel to abrupt and intense changes in the object at this location, such as the CSF-spinal cord and the skull-brain interface  The MR image is reconstructed from k-space which is a finite sampling of the...
Article

Comet-tail artifact

The comet-tail artifact is a grey-scale ultrasound finding seen when small calcific / crystalline / highly reflective objects are interrogated and is believed to be a special form of reverberation artifact. It is similar to the colour comet-tail artifact and is seen in similar situations, altho...
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Moiré fringes

Moiré fringes are an interference pattern most commonly seen when acquiring gradient echo images using the body coil. Because of lack of perfect homogeneity of the main magnetic field from one side of the body to the other, aliasing of one side of the body to the other results in superimpositio...
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MRI artifacts

MRI artifacts are numerous and give an insight into the physics behind each sequence. Some artifacts affect the quality of the MRI exam while others do not affect the diagnostic quality but may be confused with pathology. When encountering an unfamiliar artifact, it is useful to systematically ...
Article

Aliasing in MRI

Aliasing in MRI, also known as wrap-around, is a frequently encountered MRI artifact that occurs when the field of view (FOV) is smaller than the body part being imaged. The part of the body that lies beyond the edge of the FOV is projected onto the other side of the image. This can be correcte...
Article

Dual energy CT

Dual energy CT utilises two separate energy sets to examine the differing attenuation properties of matter, having a significant advantage over traditional single energy CT. Independent attenuation values at two energy sets can create virtual non-contrast images from contrast enhanced imaging as...
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Magnets

Magnets used for MRI are of three types: permanent, resistive and superconductive. Permanent MRI magnets use permanently magnetized iron like a large bar magnet that has been twisted into a C-shape where the two poles are close together and parallel. In the space between the poles the magnetic ...
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Quenching

Quenching refers to rapid expulsion of the liquid cryogen used to maintain the MR magnet in a superconducting state. Discussion Modern MRI scanners contain superconducting magnets which have very low energy consumption, made possible by maintaining internal subzero temperatures by way of a 'cr...
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Photoelectric effect

Photoelectric effect, or photoelectric absorption (PEA) is a form of interaction of X-ray or gamma photon with the matter. A low energy photon interacts with the electron in the atom and removes it from its shell. The probability of this effect is maximum when the energy of the incident photon...
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Transient elastography

Transient elastography most often refers to a type of elastography which relies on a mechanical pulse generated by an external probe. The principle is similar to shear wave elastography, in that the elastic modulus is generated from shear wave velocity, but the application of the pulse from an ...
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Shear wave elastography

Shear wave elastography is a developing variation of ultrasound imaging. The concept is similar to strain elastography, but instead of using transducer pressure to compare a shift in an ultrasound A-line (thereby measuring changes in strain), a higher intensity pulse is transmitted to produce s...
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Eddy currents

In accordance with Faraday's Law of Induction, rapidly changing gradient magnetic fields can induce stray currents, known as eddy currents, in the surrounding conducting materials. Eddy currents are unwanted as they generate their own magnetic fields, which oppose the original magnetic field vi...
Article

Diffusion kurtosis imaging

Diffusion kurtosis imaging (DKI) is an advanced neuroimaging modality which is an extension of diffusion tensor imaging by estimating the kurtosis (skewed distribution) of water diffusion based on a probability distribution function. It provides a high order diffusion of water distribution and a...
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Diffusion weighted imaging

Diffusion weighted imaging (DWI) is a form of MR imaging based upon measuring the random Brownian motion of water molecules within a voxel of tissue. The relationship between histology and diffusion is complex; however, in general, highly cellular tissues or those with cellular swelling exhibit ...
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T2 shine through

T2 shine-through refers to high signal on DWI images that is not due to restricted diffusion, but rather to high T2 signal which 'shines through' to the DWI image. T2 shine through occurs because of long T2 decay time in some normal tissue. This is most often seen with subacute infarctions due ...
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Mammography

Mammography is a dedicated radiographic technique for imaging the breast. Types of mammography In general terms, there are two types of mammography: screening and diagnostic. Mammography differs significantly in many respects from the rest of diagnostic imaging. Screening mammography  In ge...
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Thyroid scan (Tc-99m)

Tc-99m [pertechnetate] thyroid scan is a functional nuclear medicine study used to assess the thyroid gland. patient preparation fast for 4 hours prior to exam radiopharmaceutical Tc-99m pertechnetate dose and route of administration 3-5 mCi IV time of imaging 20 minutes after Tc-99m per...
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X-ray artifacts

Artifacts can present in a variety of ways including abnormal shadow noted on a radiograph or degraded image quality and have been produced by artificial means from hardware failure, operator error and software (post-processing) artifacts.  There are common and distinct artifacts for film, comp...
Article

Computed tomography

Computed tomography (CT) scanning, also known as computerised axial tomography (CAT) scanning, is a diagnostic imaging procedure that uses X-rays to build cross-sectional images ("slices") of the body. Cross-sections are reconstructed from measurements of attenuation coefficients of X-ray beams ...
Article

CT cholangiography

CT cholangiography is a technique of imaging the biliary tree with the usage of hepatobiliary excreted contrast. It is useful in delineating biliary anatomy, identifying a bile leak or looking for retained gallstones within the biliary system. Indications Second-line test (after ultrasound) wh...
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Diffusion tensor imaging

Diffusion tensor imaging is an extension of diffusion weighted imaging (DWI) that allows data profiling based upon white matter tract orientation. DWI is based on the measurement of Brownian motion of water molecules. This motion is restricted by membranous boundaries. In white matter, diffusio...
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Physics curriculum

The physics curriculum is one of our curriculum articles and aims to be a collection of articles that represent core physics knowledge, including all modalities including x-ray, CT, MRI, ultrasound, nuclear medicine and mammography.  We've just started working on this, so only MRI is present at...
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Magnetisation transfer

Magnetisation transfer (MT) imaging is an MRI technique that can be used to exploit contrast between tissues where 1H protons are present in three states1: bound to macromolecules in free water as water in the hydration layer between the macromolecules and the free water To assess MT, an off...
Article

Electron-positron annihilation

Electron-positron annihilation is the process in which a positron (from B+ decay) collides with an electron resulting in their annihilation. Being of opposite charges and same mass they act as a collision of subatomic particle and anti-particle. According to the law of conservation of energy, t...
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Bone scan

Bone scans are a nuclear medicine (scintigraphic) study that makes use of Technetium 99m (commonly Tc99m-methylene diphosphonate (MDP)) as the active agent. The study has three phases which follow intravenous injection of the tracer. Sometimes a fourth (delayed/delayed) phase is performed.  Cl...
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CT scanner (evolution)

CT scanners were first introduced in 1971 with a single detector for brain study under the leadership of Godfrey Hounsfield, an electrical engineer at EMI (Electric and Musical Industries Ltd). Thereafter, it has undergone several changes with an increase in the number of detectors and decrease ...
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Contrast-induced nephropathy

Contrast-induced nephropathy (CIN) is the third most common cause of all hospital-acquired acute renal failure and accounts for ~10% of all cases. There is still an ongoing debate regarding its occurrence after intravenous contrast medium administration because most of the cases occur after intr...
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Superparamagnetism

Superparamagnetic materials consist of individual domains of elements that have ferromagnetic properties in bulk. Their magnetic susceptibility is between that of ferromagnetic and paramagnetic materials.  The figure illustrates the effect of a superparamagnetic material (grey circle) on the ma...
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Paramagnetism

Paramagnetic materials include oxygen and ions of various metals like Fe (iron), Mg (magnesium), and Gd (gadolinium). These ions have unpaired electrons, resulting in a positive magnetic susceptibility. The magnitude of this susceptibility is less than 0.1% of that of ferromagnetic materials. T...
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Ferromagnetism

Ferromagnetic materials generally contain iron, nickel, or cobalt. These materials include magnets, and various objects that might be found in a patient, such as aneurysm clips, parts of pacemakers, shrapnel, etc.  These materials have a large positive magnetic susceptibility, i.e. when placed ...
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Magnetism

Magnetism is a property of matter that is a result of the orbiting electrons in atoms. The orbiting electrons cause the atoms to have a magnetic moment associated with an intrinsic angular momentum called spin.  Magnetic field strengths are measured in tesla (T), a derived SI unit. The equivale...
Article

Repetition time

The repetition time (TR) is the time from the application of an excitation pulse to the application of the next pulse. It determines how much longitudinal magnetization recovers between each pulse. It is measured in milliseconds.
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Flip angle

The flip angle is an MRI phenomenon by which the axis of the hydrogen proton shifts from its longitudinal plane (static magnetic field B0) Z axis to its transverse plane XY axis by excitation with the help of radiofrequency (RF) pulses. A RF pulse is sent in at the precise Larmor frequency in re...
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Echo time

The echo time (TE) refers to the time between the application of the radiofrequency excitation pulse and the peak of the signal induced in the coil. It is measured in milliseconds. The amount of T2 relaxation is controlled by the TE.
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MRI physics

The basic process The way MR images are generated is complicated and is much harder to understand than plain radiography, CT and ultrasound. It has strong underpinnings in physics which must be understood before any real sense of 'how it works' is gained.  What follows is a very abbreviated, '...
Article

Resonance and radiofrequency

Protons in a magnetic field have a microscopic magnetisation and act like tiny toy tops that wobble as they spin.The rate of the wobbling or precession is the resonance or Larmor frequency. In the magnetic field of an MRI scanner at room temperature, there is approximately the same number of pro...
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Reverberation artifact

Reverberation artifact occurs when an ultrasound beam encounters two strong parallel reflectors. When the ultrasound beam reflects back and forth between the reflectors ("revereberates"), the ultrasound transducer interprets the sound waves returning from the reverbration as deeper structures s...
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Gadolinium

Gadolinium (Gd) is a metallic element (atomic number 64) that can be chelated into paramagnetic agents that are injected intravenously during MR imaging. The gadolinium ion is useful as an MRI agent because it has seven unpaired electrons, which is the greatest number of unpaired electron spins...
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Radiofrequency coils

Radiofrequency coils (RF coils) are the "antennae" of the MRI system, broadcasting the RF signal to the patient and/or receiving the return signal. RF coils can be receive-only, in which case the body coil is used as a transmitter; or transmit and receive (transceiver). Surface coils are the si...
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Phased array

A phased array ultrasound transducer is typically 2-3 cm long, consisting of 64-128 elements. It is a smaller assembly than a sequential array and can be either linear or curvilinear. A sector field of view is produced by all elements firing to create a single waveform. Small delays in element ...
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Convex array

Convex (sequential) arrays, also known as curvilinear or curved linear arrays, are similar to linear arrays but with piezoelectric elements arranged along a curved transducer head. Ultrasound beams are emitted at 90 degrees to the transducer head. This arrangement results in a trapezoidal field ...
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Linear array

Ultrasound transducers that produce images via linear array typically contain 256-512 elements, making them the largest assembly. Each element produces a scan line that makes up the ultrasound image. Multiple adjacent elements combine to produce an ultrasound beam that is emitted at 90 degrees ...
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Ultrasound transducer

An ultrasound transducer converts electrical energy into mechanical (sound) energy and back again, based on the piezoelectric effect. It is the hand-held part of the ultrasound machine that is responsible for the production and detection of ultrasound waves. It consists of five main components:...
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Inversion recovery sequences

Inversion recovery pulse sequences are a type of MRI sequence used to selectively null the signal for certain tissues (e.g. fat or fluid). Inversion recovery can also generate heavily T1-weighted images and was originally developed for this purpose. Physics Basically, an inversion recovery (I...
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Ring down artifact

Ring down artifact is a special type of resonance artifact. Its appearance is similar to the ladder-like reverberation of comet-tail artifact, but it is produced by a completely different mechanism. The artifact is only associated with gas bubbles, and occurs when an ultrasound pulse encounters...
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Photon

A photon is, in simple terms, an elementary particle. It has a zero mass (rest mass) and travels at the speed of light. It is defined as stable with no electric charge and exhibits both wavelike and particle-like properties. For the sake of this article, a photon refers to an uncharged particle ...
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RadLex

RadLex is a lexicon of radiological information that has been produced by the RSNA.  It is an ontological system whose principle aim is to develop a useful vocabulary for radiologists.  In the words of the RSNA "As images, imaging reports, and medical records move online, radiologists need a u...
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Godfrey Hounsfield

Sir Godfrey Hounsfield (b. 28 Aug 1919, d. 12 Aug 2004) pioneered the CT scanner making him one of the greats in the history of radiology. For his work, he received the Nobel Prize in Stockholm in 1979. This was remarkable because Godfrey had no previous experience of working in the medical fiel...
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As low as reasonably achievable (ALARA)

As low as reasonably achievable (ALARA) is a principle of radioprotection stating that whenever ionizing radiation has to be applied to humans, animals or materials exposure should be as low as reasonably achievable. It is fundamental to the principles of radiation protection.
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Cardiac MRI

Cardiac MRI consists of using MRI to study heart anatomy and pathology. Advantages Main advantages of cardiac MRI in comparison with other techniques are: a better definition of soft tissues use of different types of sequences improves diagnostic accuracy avoid ionising radiation neverthel...
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Portosystemic shunt ratio

The portosystemic shunt ratio is a measure performed using ultrasound to quantify the abnormal flow of portal venous blood that is shunted away from the hepatic sinusoidal circulation in the context of a congenital portosystemic shunt 1. Ultrasound The ratio is determined using the following e...
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Dose limits

Dose limits are recommended by the International Commission on Radiological Protection (ICRP), they are in place to ensure that the individuals are not exposed to an unnecessarily high amount of ionising radiation. Dose limits are a fundamental component of radiation protection, and breaching th...
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Lead apron

Lead aprons are one of the key parts of personal radiation protection equipment along with lead gloves, lead glasses, and thyroid shields. In medical imaging, there are two main types 1: 0.25 mm lead equivalence weighs 1-5 kg ("lightweight apron") attenuates 75% of the x-ray beam at 50 kVp ...
Article

Background radiation

Background radiation refers to exposure to ionising radiation in day-to-day life, excluding occupational exposures. Ionising radiation occurs naturally in the environment 1,2: radioactive gas (e.g. radon, thoron): 0.2-2.2 mSv/year external terrestrial (e.g. building materials): 0.3-1 mSv/year ...
Article

Entrance skin dose

The entrance skin dose is the measure of the radiation dose that is absorbed (mGy) by the skin as it reaches the patient. Entrance skin dose is a directly measurable quantity, often, measured using thermoluminescent dosimeters (TLD) 1. Entrance skin dose is often a benchmark measurement used to ...
Article

Inverse square law

The inverse square law describes the principle of dose reduction as the distance from the source increases. This assumes a point source. If radiation spreads over a spherical area, as the radius increases, the area over which the dose is distributed increases according to A=4πr^2 where A is the...
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Radiation damage (biomolecular)

Biomolecular radiation damage can result when biological tissues are exposed to ionising radiation from direct exposure or via Compton scattering. Ionisation is known to lead to the production of free radicals; free radicals are uncharged molecules that possess an unpaired valence electron. Con...
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Radiation protection

Radiation protection is based on the three fundamental principles of justification of exposure, keeping doses as low as reasonably achievable (optimisation) and the application of dose limits. The International Commission on Radiological Protection (ICRP) is responsible for the development of th...
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Background radiation equivalent time

Subjecting a patient to radiation exposure is a measured, justified means aiding patient care. Each medical imaging examination utilises ionising radiation adheres to the fundamental principles of radiation protection. The general public's understanding of ionising radiation is limited 1; this ...
Article

Signal to noise ratio

Signal to noise ratio (SNR) is a generic term which, in radiology, is a measure of true signal (e.g. reflecting actual anatomy) to noise (e.g. random quantum mottle). A lower signal to noise ratio generally results in a grainy appearance to images.  Each modality has its own source(s) of noise ...
Article

SeHCAT

SeHCAT (23-seleno-25-homo-tauro-cholic acid) is a radiopharmaceutical used in the investigation of bile salt malabsorption, which is a cause of chronic diarrhoea.  Characteristics physical half-life: 118 days Uses, dosage and timings A capsule containing SeHCAT is ingested with water. The pa...
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Side lobe artifact

Side lobe artifacts occur where side lobes reflect sound from strong reflector that is outside of the central beam, and where the echoes are displayed as if they originated from within the central beam. Ultrasound transducer crystals expand and contract to produce primary ultrasound beams in th...
Article

Vicarious contrast material excretion

Vicarious contrast material excretion (VCME) defines excretion of water-soluble contrast material in a way other than via normal renal secretion.  The most common vicarious excretion of water-soluble contrast material is via the liver, resulting in increased bile density seen in the gallbladder...
Article

T2 relaxation

T2 relaxation refers to the progressive dephasing of spinning dipoles following the 90° pulse as seen in a spin-echo sequence due to tissue-particular characteristics, primarily those that affect the rate of movement of protons, most of which are found in water molecules. This is alternatively k...
Article

Focussed Assessment with Sonography for Trauma (FAST) scan

Focussed Assessment with Sonography for Trauma (FAST) scan is a point-of-care ultrasound examination performed at the time of presentation of a trauma patient.  It is invariably performed by a clinician, who should be formally trained, and is considered as an 'extension' of the trauma clinical ...
Article

Digital radiography

Digital radiography is based on the use of discrete values in comparison to conventional radiography which uses analogue/continuous values. It removes the requirement of dark room procedures. Types computed radiography (CR) uses photostimulable phosphor plates (PSP) in cassettes direct digit...
Article

Indium-111 oxine labelled white blood cell scan

Indium-111 oxine labelled white blood cell scan is a nuclear medicine test which attempts to localise infection and/or inflammation by injecting the patient's previously extracted and radioactively labelled white blood cells.  Procedure The patient's blood is withdrawn and white blood cells ex...
Article

CT enterography

Computed tomographic (CT) enterography is a non-invasive technique for diagnosis of small bowel disorders. Advantages  evaluates the entire thickness of the bowel wall offers information about the surrounding mesentery, the mesenteric vasculature and the perienteric fat useful in the assessm...
Article

Susceptibility weighted imaging

Susceptibility weighted imaging (SWI) is an MRI sequence which is particularly sensitive to compounds which distort the local magnetic field and as such make it useful in detecting blood products, calcium, etc. Physics SWI is a 3D high-spatial resolution fully velocity corrected gradient echo ...
Article

Image reconstruction (CT)

Image reconstruction in computed tomography is a rapidly evolving industry, the race to produce an efficient yet accurate image reconstruction method while keeping scan dose to a minimum has defined improvements in CT over the past decade. The mathematical problem that CT image reconstruction i...

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