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.

636 results found
Article

Compression paddle

A compression paddle is a device found in mammographic units which is used to compress the breast. It consists of a flat radiolucent plate positioned parallel to the support table, and attached to either a mechanical or pneumatic assembly. It is controlled by the operator by a foot pedal. Full...
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Compton effect

Compton effect or Compton scatter is one of principle forms of photon interaction. It is the main cause of scattered radiation in a material. It occurs due to the interaction of the photon (x-ray or gamma) with free electrons (unattached to atoms) or loosely bound valence shell (outer shell) ele...
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Computed radiography

Computed radiography (CR) is the use of photostimulable phosphor as an image receptor. The image receptor is held in a similar casing (cassette) to that of the traditional film screen. Computed radiography harnesses the absorption of radiation, trapping electrons at energy levels via the process...
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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...
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Computed tomography texture analysis

Computed tomography texture analysis (or CTTA) is a method to obtain new useful biomarkers that provide objective and quantitative assessment of tumor heterogeneity by analyzing the differences and patterns within the pixel values of an image. CTs can be worked with as a matrix of numbers, corre...
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Computer vision syndrome

Computer vision syndrome is a condition that affects primarily workers who use computers (including tablets and other devices with computer screens) many hours a day with symptoms that can include blurred vision, eye strain, and headache. Epidemiology Computer vision syndrome is a growing phen...
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Cone beam CT

Cone beam CT (CBCT) is a variant type of computed tomography (CT), and is used particularly in dental and extremity imaging but has recently found new application in dedicated breast imaging 4,5. It differs from conventional CT in that it uses a cone-shaped x-ray beam and two dimensional detecto...
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Cone beam effect

Cone beam effect artifacts are seen in multidetector row CT (cone beam CT) acquisitions 1. Modern CT scanners use more detector arrays to increase the number of sections acquired per rotation. This causes the x-ray beams to become cone-shaped as opposed to fan-shaped 2. As a result instead of co...
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Continuous X-ray spectrum

The continuous X-ray spectrum refers the range of photon energies produced in an X-ray tube due to the properties of Bremsstrahlung radiation. The energy of X-ray photons can take a value from zero to the maximum kinetic energy of the incident electrons. Both the continuous X-ray spectrum and ...
Article

Contrast-enhanced mammography

There are 2 types of contrast-enhanced mammography examination – temporal subtraction and dual-energy.  Initial work in the early 2000s used temporal subtraction, but artefacts due to patient movement during prolonged compression limited its diagnostic usefulness. Travieso et al produced a usef...
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Contrast enhanced MR angiography

Contrast-enhanced MR angiography (MRA) is a technique involving 3D spoiled gradient-echo (GE) sequences, with administration of gadolinium-based contrast agents (GBCA). It can be used to assess vascular structures of almost any part of the body. Its key features are: T1 weighted spoiled gradien...
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Contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) involves the administration of intravenous contrast agents consisting of microbubbles/nanobubbles of gas. Ultrasound contrast agents First generation First-generation ultrasound contrast agents contained microbubbles of air that were dissolved in blood when...
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Contrast-enhanced voiding urosonography

Contrast-enhanced voiding urosonography (occasionally abbreviated as ce-VUS) is a relatively novel contrast-enhanced ultrasonographic technique utilizing microbubbles to detect vesicoureteral reflux.  Indications Suspected or confirmed vesicoureteral reflux is currently the primary indication ...
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Contrast enhancement

Contrast enhancement is a ubiquitous term in radiology and can be used in three ways.  Firstly, it may refer to any method of exaggerating the visible difference between adjacent structures on imaging by administering contrast media/agents. This includes differentiating between normal structure...
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Contrast improvement factor

The contrast improvement factor of an anti-scatter grid is the ratio of contrast obtained with the use of the grid to the contrast without the use of the grid. Hence, the contrast improvement factor reflects the increased image quality obtained from grid use. Most grids will have a contrast im...
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Contrast medium

Contrast media are a group of chemical agents developed to aid in the characterization of pathology by improving the contrast resolution of an imaging modality. Specific contrast media have been developed for every structural imaging modality, and every conceivable route of administration. Bari...
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Contrast resolution

Contrast resolution in radiology refers to the ability of any imaging modality to distinguish between differences in image intensity. The inherent contrast resolution of a digital image is given by the number of possible pixel values, and is defined as the number of bits per pixel value.  Imagi...
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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 with a curved transducer head. Ultrasound beams are emitted at 90 degrees to the transducer head. This arrangement results in a trapezoidal f...
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Coronary MR angiography

Coronary MR angiography (coronary MRA) is a developing approach to imaging the coronary arteries. Advantages of coronary MRA include avoidance of the intravenous iodinated contrast and ionizing radiation used in coronary CT angiography and conventional angiography. A disadvantage of coronary M...
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Coulomb per kilogram

The SI unit for exposure to ionizing radiation is coulomb per kilogram (Ckg-1) and curiously unlikely other SI radiation units, a specific name has not been adopted for this unit. This unit officially replaced the old unit, the roentgen in 1975, with an official transition period lasting at leas...
Article

Creatine peak

Creatine is one of the compounds examined in MR spectroscopy. It resonates at 3.0 ppm chemical shift and is found in metabolically active tissues (brain, muscle, heart) where it is important in storage and transfer of energy. It tends to be maintained at a relatively constant level, and is predo...
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Cross-excitation artifact (MRI)

Cross-excitation artifact is a type of MRI artifact and refers to the loss of signal within a slice due to pre-excitation from RF pulse meant for an adjacent slice. The frequency profile of the RF pulse is imperfect; this means that during slice selection there is some degree of excitation of t...
Article

CSF flow studies

CSF flow studies are performed using a variety of MRI techniques and are able to qualitatively assess and quantify pulsatile CSF flow. The most common technique used is time-resolved 2D phase contrast MRI with velocity encoding.  Note, when referring to CSF flow in the context of imaging we are...
Article

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 artifact) or can degrade image quality to non-diagnostic levels.  CT artifacts can be classified according to the underlying cause of the ar...
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...
Article

CT dose

CT dose is measured and reported via a variety of methods, put simply, it can be divided into three primary categories: exposure, absorbed dose, and effective dose.  It is important to note that to accurately determine a patients dose from a CT scan one must know the patient size and the radiat...
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CT dose index

CT dose index (CTDI) (measured in mGy) is a standardized measure of radiation dose output of a CT scanner which allows the user to compare radiation output of different CT scanners. In the past CTDI100 (measured over a 100 mm long ionization chamber) and CTDIw (weighted average of dose across a ...
Article

CT enteric contrast medium

Enteric contrast media can be given to patients before their CT to improve its diagnostic accuracy. Historically, a combination of oral and intravenous contrast media were always given prior to a CT abdomen. Contemporaneously, improved CT scanners mean that oral contrast agents are no longer rou...
Article

CT enteroclysis

Computed tomographic (CT) enteroclysis refers to a hybrid technique that combines the methods of fluoroscopic intubation-infusion small bowel examinations with that of abdominal CT. Indications CT enteroclysis is complementary to capsule endoscopy in the elective investigation of small-bowel d...
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CT fluoroscopy

Computed tomography (CT) fluoroscopy combines the conventional advantages of both CT and fluoroscopy and has an important role in image-guided interventions where real-time imaging is required. Historically, fluoroscopy was the main image guidance tool for interventional radiology procedures. T...
Article

CT liver volumetry (liver transplantation protocol)

CT liver volumetry is an essential imaging study in preoperative assessment for living donor liver transplantation. NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on CT hardware and software, radiologists' and referrers' pre...
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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 Sir Godfrey Hounsfield, an electrical engineer at EMI (Electric and Musical Industries Ltd). Thereafter, it has undergone multiple improvements with an increase in the number of detectors and...
Article

CT stair-step artifact

The CT stair-step artifact is found in straight structures which are oriented obliquely with respect to movement of the table and appear around the edges of sagittal and coronal reformatted images when wide collimations and non-overlapping reconstruction intervals are used. It is also seen in c...
Article

Curie (unit)

The curie (symbol Ci) was the unit for radioactive decay in the cgs system. One curie was defined as the radioactivity of one gram of pure radium-226; this is equivalent to 3.7 x 1010 decays per second. It was officially replaced by the becquerel in 1975.  Terminology One curie was too large t...
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Cybersecurity

Cybersecurity is the protection of digital data, software and hardware from risks including attacks or other problems related to their integrity and/or data confidentiality. Cybersecurity may utilize many different types of tools and protocols including encryption, firewalls and other infrastruc...
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Dalton (unit)

The dalton (symbol: Da), also known as an atomic mass unit, is a unit of mass that is equal to one twelfth of the mass of a free carbon-12 atom at rest. Its value is approximately equal to 1.660 x 10−27 kg. The molar mass of an entity, when measured in daltons, is approximately equal to the sum ...
Article

David E Kuhl

David E Kuhl (1929-2017) was a pioneering nuclear physician, who played a key role in the development of positron emission tomography (PET), and more generally nuclear medicine. Early life David Edmund Kuhl was born on 27 October 1929 in St Louis, Missouri. He went to Temple University in Phil...
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Decibel

The decibel (dB) is a unit that measures the relative difference between two sound intensities. The relationship is logarithmic: dB = 10 log (I2 / I1) dB = relative intensity of the sounds I1 = intensity of sound 1 I2 = intensity of sound 2 Informally, we use decibel as a unit of "loudness,...
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Dependence of magnetization (proton density, field strength and temperature)

The dependence of magnetism is based on proton density (PD), field strength and temperature. There is a frictional interchange of energy between the protons and the lattice (spin-lattice interaction), such that a balanced exchange occurs between the two energy states and the thermal equilibrium ...
Article

Detective quantum efficiency

Detective quantum efficiency (DQE) is one of the fundamental physical variables related to image quality in radiography and refers to the efficiency of a detector in converting incident x-ray energy into an image signal.  The words "quantum efficiency" have a precise meaning, because the DQE me...
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Deterministic effects

Deterministic effects describe a cause and effect relationship between ionizing radiation and certain side-effects. They are also known as non-stochastic effects to contrast them with chance-like stochastic effects (e.g. cancer induction). These effects depend on dose, dose rate, dose fractiona...
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Dexel

Dexels, a portmanteau of detector elements, analogous to pixels, refers to the individual radiation-sensitive elements of the detector component of a scanner, e.g. computed tomography. It is important to appreciate that there is not necessarily a one-to-one correspondence between dexels and the ...
Article

dGEMRIC (delayed gadolinium-enhanced MRI of cartilage)

dGEMRIC, or delayed gadolinium-enhanced MRI of cartilage is a technique that can be used quantitatively to assess glycosaminoglycan content of cartilage or qualitatively to asses the overall structures of cartilage. When the technique is adapted and applied to menisci it is called dGEMRIM. At a...
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Diagnostic reference level

A diagnostic reference level is a specified radiation dose for a given imaging study that is not expected to be exceeded. If a radiation dose does exceed the diagnostic reference level for a particular study, this should prompt an investigation into radiographic technique or equipment performan...
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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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Diastolic pseudogating

Diastolic pseudogating appears as periodic bright and dark signal in arteries such as the aorta as one progresses through a series of images. Synchronization of the cardiac cycle and the pulse sequence results in high signal in the artery during diastole when blood is relatively stationary and l...
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Dielectric effect artifact

Dielectric effect artifact is an MRI artifact encountered most often on body MRI with 3 T units. Artifact At 3 T, the radiofrequency (RF) wavelength measures 234 cm in air, and the speed and wavelength of the RF field is shortened to ~26 cm within the body as a result of dielectric effects. Ho...
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 tensor imaging and fiber tractography

Diffusion tensor imaging (DTI) is an MRI technique that uses anisotropic diffusion to estimate the axonal (white matter) organization of the brain. Fiber tractography (FT) is a 3D reconstruction technique to assess neural tracts using data collected by diffusion tensor imaging. Diffusion-weigh...
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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. In general simplified terms, highly cellular tissues or those with cellular swelling exhibit lower diffusion coefficients. Diffusion is particular...
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Diffusion weighted MRI in acute stroke

Diffusion weighted imaging (DWI) is a commonly performed MRI sequence for evaluation of acute ischemic stroke, and is sensitive in the detection of small and early infarcts. Conventional MRI sequences (T1WI, T2WI) may not demonstrate an infarct for 6 hours, and small infarcts may be hard to appr...
Article

Digital radiography

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

Direct digital radiography (DDR) refers to direct digital registration of the image at the detector with no intermediate processing step required to obtain the digital signals as in computed radiography (CR). There are two primary methods of conversion, either indirect or direct: Indirect conv...
Article

Disintegrations per second

Disintegrations per second (dps), also known as decays per second, represents the number of atoms of a radioactive isotope that decay per second. One becquerel is equivalent to one disintegration per second.  Counts per second (cps) is the number of disintegrations per second, as measured by a ...
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Distance measurement

Ultrasound machines perform distance measurement to synthesize images from returning echoes. To generate images for an ultrasound scan, machines need to determine the distance of reflective interfaces from the transducer. Simply, the formula used is: distance = (speed x time)/2 Where: distanc...
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Dixon method

The Dixon method is an MRI sequence based on chemical shift and designed to achieve uniform fat suppression. It has been gaining popularity as it has some advantages over other fat suppression techniques, namely:  suppression of fat signal is more uniform and less affected by artifacts than man...
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Doppler angle

Doppler angle corrects for the usual clinical situation when an ultrasound beam is not parallel to the Doppler signal. For instance, if one wants to evaluate an artery, the best angle for evaluation would be at zero degrees (parallel to the vessel). The strongest signal and best waveforms would...
Article

Doppler shift

Doppler shift or Doppler effect is defined as the change in frequency of sound wave due to a reflector moving towards or away from an object, which in the case of ultrasound is the transducer. Terminology When sound of a given frequency is discharged and subsequently reflected from a source th...
Article

Doppler waveforms

Doppler waveforms refer to the morphology of pulsatile blood flow velocity tracings on spectral Doppler ultrasound. Waveforms differ by the vascular bed (peripheral, cerebrovascular, and visceral circulations) and the presence of disease. Radiographic features Ultrasound Doppler Most authori...
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Dose area product

The dose area product (DAP) or kerma area product (KAP) is a method of radiation dose monitoring used in radiographic and fluoroscopic studies. It provides an indication of the radiation dose received by a patient. It is calculated as the product of dose and beam area (Gy.cm2), and is measured ...
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Dose length product

Dose length product (DLP) measured in mGy*cm is a measure of CT tube radiation output/exposure. It is related to volume CT dose index (CTDIvol), but CTDIvol represents the dose through a slice of an appropriate phantom. DLP accounts for the length of radiation output along the z-axis (the long a...
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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 individuals are not exposed to an unnecessarily high amount of ionizing radiation. Dose limits are a fundamental component of radiation protection, and breaching these ...
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Dosimeters

Dosimeters are a form of radiation monitoring devices. They are used regularly for a number of key roles including both patient and personal dosimetry, environmental monitoring, spectroscopy, radiopharmaceutical and equipment checking Function  Energy enters the dosimeter which converts this e...
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Double inversion recovery sequence

Double inversion recovery (DIR) is an inversion recovery MRI pulse sequence that uses two different inversion pulses. The technique can be used to suppress signal from two different tissues or to suppress signal that moved between the two pulses. In the first instance, used in neuroimaging, two...
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Double oblique multiplanar reconstruction

Double oblique is a type of multiplanar reconstruction used in cardiac cross-sectional imaging. It is useful for an accurate assessment of the ascending aorta and aortic annulus, and is particularly useful for pre- and post-procedure evaluation of a transcatheter aortic valve replacement (TAVR)....
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Doubling dose

The doubling dose refers to the radiation dose required to double the number of spontaneous genetic mutations in a given population of cells. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) have traditionally estimated the doubling dose in humans at 1.0 Gy. ...
Article

D-SPECT

D-SPECT represents the next step in the evolution of SPECT technology and is based on a unique acquisition geometry. It has nine arrays of cadmium zinc telluride (CZT) detectors, each of which rotates around its central axis with programmable angular rotation 1. The detectors are very compact al...
Article

Dual energy CT

Dual energy CT, also known as spectral CT, is a computed tomography technique that uses two separate x-ray photon energy spectra, allowing the interrogation of materials that have different attenuation properties at different energies. Whereas conventional single energy CT produces a single imag...
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Dynamic contrast enhanced (DCE) MR perfusion

Dynamic contrast-enhanced (DCE) MR perfusion, sometimes also referred to as permeability MRI, is one of the main MRI perfusion techniques which calculates perfusion parameters by evaluating T1 shortening induced by a gadolinium-based contrast bolus passing through tissue. The most commonly calcu...
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Dynamic nuclear polarization

Dynamic nuclear polarization (DNP) is a phenomenon by which polarization is transferred from a polarizing agent to a biological tracer, enhancing the nuclear energy difference and thereby increasing the signal-to-noise ratio (SNR) dramatically.
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Dynamic susceptibility contrast (DSC) MR perfusion

Dynamic susceptibility contrast (DSC) MR perfusion is one of the most frequently used techniques for MRI perfusion, and relies on the susceptibility induced signal loss on T2*-weighted sequences which results from a bolus of gadolinium-based contrast passing through a capillary bed. The most com...
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Echo planar imaging

Echo planar imaging is performed using a pulse sequence in which multiple echoes of different phase steps are acquired using rephasing gradients instead of repeated 180 degree radiofrequency pulses following the 90°/180° in a spin echo sequence. This is accomplished by rapidly reversing the read...
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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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Eddy currents

Eddy currents (also known as Foucault currents) are the result of rapidly changing gradient magnetic fields that in turn induce stray currents in the surrounding conducting materials. They form in accordance to Faraday's Law of Induction. Eddy currents are unwanted as they generate their own ma...
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Effect of gradient strength and bandwidth on slice thickness

Slice thickness is dependent on gradient strength and bandwidth, to attain a slice thickness, a range of frequencies must be transmitted to produce resonance across the whole slice. This range of frequencies is the transmitter RF (radiofrequency) bandwidth (tBW). Slice thickness is determined by...
Article

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  Sono-elastography is the term used when ult...
Article

Elbow protocol (MRI)

The MRI elbow protocol encompasses a set of different MRI sequences for the routine assessment of the elbow joint.  Note: This article aims to frame a general concept of an MRI protocol for the assessment of the elbow joint. Protocol specifics will vary depending on MRI scanner type, specific h...
Article

Electrical interference artifact (ultrasound)

Electrical interference artifact is an ultrasound artifact usually caused by the ultrasound machine being too close to the unshielded electrical equipment. The disturbance appears as arc-like moving bands in the ultrasound image.  While the presence of electrical equipment  (e.g unshielded vent...
Article

Electromagnetic induction

Electromagnetic induction is the induction of electric current via changing magnetic fields. Magnetic fields are generated by moving charges (equivalent to electrical current). Ampere’s law or Fleming’s right-hand rule determines the magnitude and direction (i.e. clockwise or anti-clockwise) of ...
Article

Electromagnetic radiation

Electromagnetic radiation refers to the waves or quanta of the electromagnetic field as they propagate through space. The speed of electromagnetic waves is invariant in a vacuum, being ~ 3x108 m/s and represented by the symbol, c, otherwise known as the speed of light. The types of electromagnet...
Article

Electron

The electron is a subatomic particle that has negligible mass and is negatively charged. The properties of x-rays and their interaction with matter concern the orbiting electrons within the atom. In classical physics the electrons orbit the central positively charged nucleus in shells, the oute...
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Electron binding energy

The electron binding energy is the minimum energy that is required to remove an electron from an atom, as the negatively charged electrons are held in place by the electrostatic pull of the positively charged nucleus. The electron binding energy is measured in electron volt (eV), where 1 eV = 1....
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Electron capture

Electron capture is the radioactive decay process by which an atom's inner orbital electron is absorbed within the nucleus followed by conversion of a proton to a neutron and emission of a neutrino (ve) 1. Accompanying this decay method is the emission of Bremsstrahlung, characteristic x-ray emi...
Article

Electron paramagnetic resonance imaging

Electron paramagnetic resonance imaging (EPR) and spectroscopy and is a preclinical imaging modality with potential to be translated into a clinical imaging technique in the future. In brief, EPR allows detection and quantification of free radical molecules with unpaired electrons, thus allowing...
Article

Electron-positron annihilation

Electron-positron annihilation is the process in which a positron collides with an electron resulting in the annihilation of both particles.  Electrons (or β- particles) and positrons (or β+ particles) are of equal mass but opposite charge. Positrons are the antimatter equivalent of an electron,...
Article

Electronvolt (unit)

An electronvolt (eV) is defined as the energy required to accelerate a single electron at rest through an electron potential difference of 1 volt in a vacuum. 1 eV ≈ 1.603 x 10-19 J Electronvolts are a more mathematically convenient method to describe the miniscule quantity of energy associate...
Article

Elevational resolution (ultrasound)

Elevational (azimuthal) resolution represents the extent to which an ultrasound system is able to resolve objects within an axis perpendicular to the plane formed by the axial and lateral dimensions. As one component of overall spatial resolution, the elevational axis represents the height or “t...
Article

Emerging methods in medical imaging

This article is a summary of emerging imaging technologies currently in development or in the early phase of clinical adoption. The methods are listed by modality.  Radiography phase-contrast imaging CT deep-learning reconstruction photon counting CT virtual non-contrast imaging Ultrasoun...
Article

End-diastolic velocity (Doppler ultrasound)

End-diastolic velocity (EDV) is an index measured in spectral Doppler ultrasound. On a Doppler waveform, the EDV corresponds to the point marked at the end of the cardiac cycle (just prior to the systolic peak) 1. In some equipment, the timing of cardiac cycle events may be automatically marked ...
Article

Energy difference between spin up and spin down states

The energy difference between spin up and spin down states of hydrogen are important in understanding net magnetization vector of tissue for magnetic resonance imaging. Each hydrogen atom is formed by one proton and one orbiting electron. Because the atomic number is 1, it has a spin quantum nu...
Article

Entrance phosphor

The entrance phosphor (or input phosphor) is a component of the image intensifier in fluoroscopic systems that converts the energy from x-rays into light photons. It is composed of a fluorescent material such as cesium iodide activated with sodium (CsI:Na) and coats the entrance surface of the i...
Article

Entrance skin dose

The entrance skin dose (or entrance surface dose), abbreviated as ESD, 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 ski...
Article

Entry slice phenomenon

Entry slice phenomenon occurs when unsaturated spins in blood first enter into a slice or slices. It is characterized by the bright signal in a blood vessel (artery or vein) at the first slice that the vessel enters. Usually, the signal is seen on more than one slice, fading with distance. This ...

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