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.

371 results found
Article

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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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...
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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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Dual-energy mammography

Dual-energy digital mammography is a complementary breast imaging modality. The technique consists of high-energy and low-energy digital mammograms after administration of iodinated contrast agent. Breast is exposed to low- and high-energy X-ray beams during a single breast compression in MLO ...
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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 polarisation

Dynamic nuclear polarisation (DNP) is a phenomenon by which polarisation is transferred from a polarising 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 co...
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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 180o RF pulses following the 90°/180° in a spin echo sequence. This is accomplished by rapidly reversing the readout or frequency- ...
Article

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

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...
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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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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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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 magnetisation 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 is a component of the image intensifier in fluoroscopic systems which converts the energy from x-rays into light photons. It is composed of a fluorescent material such as caesium iodide activated with sodium (CsI:Na) and coats the entrance surface of the image intensifier. ...
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

Entry slice phenomenon

Entry slice phenomenon occurs when unsaturated spins in blood first enter into a slice or slices. It is characterised 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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Equivalent dose

Equivalent dose (symbol HT) is a measure of the radiation dose to tissue where an attempt has been made to allow for the different relative biological effects of different types of ionising radiation. In quantitative terms, equivalent dose is less fundamental than absorbed dose, but it is more b...
Article

Ernst angle

The Ernst angle is the flip angle that maximises signal in T1-weighted sequences that have a short repetition time (TR). When the TR is very short, the best flip angle to maximise signal can be quite small. Choosing the Ernst angle in this setting can increase signal by several fold. However, i...
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Exposure

The term exposure refers to the concentration, in air, of radiation at a specific point and is the ionization produced in a specific volume of air: E = Q / m where E is exposure, Q is the quantity of charge on the ions and m is the unit mass of air. Exposure describes the ability of X-rays to i...
Article

Fat suppressed imaging

Fat suppression is commonly used in magnetic resonance (MR) imaging to suppress the signal from adipose tissue or detect adipose tissue 1. It can be applied to both T1 and T2 weighted sequences.  Due to short relaxation times, fat has a high signal on magnetic resonance images (MRI). This high ...
Article

Fat-water swapping artifact

Fat-water swapping artifact is seen in a significant proportion of fat/water suppressed sequences using the Dixon method. The artefact follows a computational error in areas of field inhomogeneity resulting in incorrectly determining whether a voxel contains water or fat. The images have geogra...
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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 ...
Article

Fetal dosimetry

NB - Please consult original article(s) and discuss with you local radiology department/radiation physicist before making any clinical decision. Although exposure to the gravid uterus is to be avoided when ever possible, and only deliberately performed after careful weighing up of the pros and ...
Article

Filament circuit

The tungsten cathode needs to be heated for thermionic emission to take place. Thus a 10 V potential difference and a 3-6 amperes of filament current is supplied, which forms the filament circuit.  This should not be confused with tube current which determines the flow of electrons from cathode...
Article

Filtered back projection

Filtered back projection is an analytic reconstruction algorithm designed to overcome the limitations of conventional back-projection; it applies a convolution filter to remove blurring. It was, up until recently the primary method in crossectional image reconstruction.  It utilises simultaneou...
Article

Filters

Filters are metal sheets placed in the x-ray beam between the window and the patient that are used to attenuate the low-energy (soft) x-ray photons from the spectrum. Filtering is the removal of these low energy x-rays from the beam spectrum which would otherwise not contribute to image quality ...
Article

Fixing solution

Fixing solution is used in the darkroom to fix (i.e. remove unexposed silver) the developed and rinsed x-ray film in conventional radiography. Components fixing agent: sodium/ammonium thiosulfate, dissolves unexposed silver hardner: potassium alum, to harden the gelatin emulsion in film acid...
Article

Flat panel detectors

Flat panel detectors (FPD) are used in direct digital radiography (DDR) for conversion of X-rays to light (indirect conversion) or charge (direct conversion) which is read out using thin film transistors (TFT array). Types They are of two types: indirect conversion FPDs outermost layer is sc...
Article

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...
Article

Flow void

Flow voids refer to a signal loss occurring with blood and other fluids, like CSF or urine, moving at sufficient velocity relative to the MRI apparatus. It is a combination of time-of-flight and spin-phase effects usually seen in spin echo techniques (such as T1 and T2-weighted images) 2. Physi...
Article

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...
Article

Flying focus tomosynthesis

Flying focus is a technology of image acquisition in digital breast tomosynthesis characterized by a continuous sweep during shooting. Sharpness in digital systems is determined by the modulation transfer function (MTF), which determine contrast transfer as a function of spatial frequency. Sin...
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Focal spot

Focal spot is the area of the anode surface which receives the beam of electrons from the cathode. Basic concept Size and shape of the focal spot is determined by the size and shape of the electron beam when it strikes the anode 1. Size and shape of the electron beam is determined by: dimens...
Article

Fourier transform

Fourier transform is a mathematical operation which converts a time domain signal into a frequency domain signal. Discussion Fourier transform is integral to all modern imaging, and is particularly important in MRI. The signal received at the detector (receiver coils in MRI, piezoelectric disc...
Article

Fourier transformation

The Fourier transform is a mathematical formula that converts a signal in time (or spatial) domain t to one in the frequency domain ω. A frequency domain signal F(ω) is obtained by modulating the time domain signal f(t) to a special sinusoidal wave e-jωt across all time (from negative infinity ...
Article

Free induction decay

Free induction decay (FID) refers a short-lived sinusoidal electromagnetic signal which appears immediately following the 90° pulse. It is induced in the receiver coil by the rotating component of the magnetization vector in the x-y plane which crosses the coil loops perpendicularly. It does not...
Article

Functional MRI

Functional magnetic resonance imaging (fMRI) is a technique used to obtain functional information by visualising cortical activity. fMRI detects subtle alteration in blood flow in response to stimuli or actions. It is used in two broad ways: clinical practice typically in pre-surgical patients...
Article

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...
Article

Gallium 67 scintigraphy

Gallium 67 is a photon-emitting radiotracer which is used in the form of various salts like citrate and nitrate. Once administered, imaging may consist of planar (2 dimensional) , SPECT, and SPECT/CT acquisitions. Once injected it binds to plasma proteins (especially transferrin), and has a pred...
Article

Gamma-aminobutyric acid (GABA) peak

Gamma-aminobutyric acid (GABA) is the principle inhibitory neurotransmitter in the central nervous system 1 and as such, is one of the compounds examined in MR spectroscopy.  It is present in the human brain at a concentration of about 1 mM, a whole order of magnitude lower than some of the more...
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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...
Article

Gauss (unit)

The gauss (symbol: G or Gs) is a legacy CGS unit of magnetic flux density, which was superseded by the tesla. One gauss is defined as one maxwell per cm2 (Mx/cm2), which equates to 10-4 tesla, and is therefore a small unit. This is one of the reasons for its stubborn persistence in some scientif...
Article

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

Glutamine-Glutamate peak

Glutamate-Glutamine (Glx) peak is one of the regions assessed on MR spectroscopy, and resonates between 2.2 and 2.4 ppm chemical shift. It overlaps with the GABA peak and cannot be routinely separated from each other.
Article

Godfrey Hounsfield

Sir Godfrey N Hounsfield (1919-2004) pioneered the CT scanner making him one of the greats in the history of radiology. For his work, he received the Nobel Prize in Physiology or Medicine in 1979. This was remarkable because he had had no previous experience of working in the medical field but w...
Article

Gradient coils

Gradient coils are used to produce deliberate variations in the main magnetic field (B0). There are three sets of gradient coils, one for each direction. The variation in the magnetic field permits localization of image slices as well as phase encoding and frequency encoding. The set of gradient...
Article

Gradient echo sequences

Gradient echo sequences (GRE) are an alternative technique to spin echo sequences, differing from it in two principal points: utilization of gradient fields to generate transverse magnetisation flip angles of less than 90° Compared to the spin echo and inversion recovery sequences, gradient e...
Article

Gray (SI unit)

The gray (symbol Gy) is the SI unit of absorbed dose and is defined as the absorption of one joule of energy, in the form of ionising radiation, per kilogram of matter, i.e. one gray = 1 J/kg 2. Terminology One gray is a large unit and is usually used with a prefix, e.g. milligray (mGy), micro...
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Grid cut off

Grid cutoff is an unwanted absorption of x-rays via an x-ray grid, observed when a grid is employed incorrectly, most often seen with parallel grids. The term cutoff stems from the phenomenon in which the primary x-ray beam is 'cut off' by grid lines, leading to an overall decrease in optical de...
Article

Grids

Grids are placed between the patient and the x-ray film to reduce the scattered radiation (produced mainly by the Compton effect) and thus improve image contrast. They are made of parallel strips of lead with an interspace having an aluminium or organic spacer. The strips can be oriented either...
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Gyromagnetic ratio

The gyromagnetic ratio, often denoted by the symbol γ (gamma) is the ratio of the magnetic momentum in a particle to its angular momentum. The SI unit is the radian per second per tesla (rad⋅s−1⋅T−1).  The gyromagnetic ratio of the proton is 2.675 221 900(18) x 108 s-1⋅T-1. Since a proton wil...
Article

Half-life time

Physical half-life time (Tp) The time interval required for an amount of certain radioactive nuclei to decay to its half of original value. Biological half-life time (Tb)  The time interval required for the body to eliminate 50% of any substance by normal routes of elimination: metabolic turn...
Article

Half-value layer

Half-value layer (HVL) is the width of a material required to reduce the air kerma of an x-ray or gamma-ray to half its original value. This applies to narrow beam geometry only as broad-beam geometry will experience a large degree of scatter, which will underestimate the degree of attenuation. ...
Article

Harmonic imaging

Harmonic imaging is a technique in ultrasonography that provides images of better quality as compared with conventional ultrasound technique. Physics Harmonic imaging exploits non-linear propagation of ultrasound through the body tissues. The high-pressure portion of the wave travels faster th...
Article

Helical CT image acquisition

Helical ("spiral") CT image acquisition was a major advance on the earlier stepwise ("stop and shoot") method. With helical CT, the patient is moved through a rotating x-ray beam and detector set. From the perspective of the patient, the x-ray beam from the CT traces a helical path. The helical...
Article

Henry (SI unit)

The henry (symbol: H) is the SI derived unit of electrical inductance.  Terminology As per all other eponymous SI units when the unit is written out in full it is not capitalised, but when shortened to its symbol it is capitalised. History and etymology The henry is named in honour of Joseph...
Article

Herringbone artifact

Herringbone artifact, also called as crisscross artifact or corduroy artifact, is an MRI artifact, it appears as a fabric of herring bone. The artefact is scattered all over the image in a single slice or multiple slices. Causes electromagnetic spikes by gradient coils fluctuating power suppl...
Article

High-intensity focused ultrasound

High-intensity focused ultrasound (HIFU) is a promising non-invasive thermal ablation technique. Unlike diagnostic ultrasound, HIFU focuses the ultrasound waves precisely upon a target. In a similar way to how light can be focused to a burning point by a magnifying glass, ultrasound passes thro...
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High resolution CT

High resolution CT is a scanning protocol in which thin sections (usually 0.625 to 1.25 mm) are acquired and reconstructed using a sharp algorithm (e.g. bone algorithm). It has been used for: lung imaging temporal bone imaging Lung imaging Two techniques have been used: spaced axial (non-h...
Article

High voltage generator

X-ray units require a high voltage generator to achieve the necessary power required of an x-ray tube. AC power will supply x-ray units with sinusoidal currents, resulting in 'peaks and troughs', limiting an x-ray tube to produce x-rays only half of the 1/60th of s second cycle.  A single-phase...
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Historical aspects of ultrasound in medicine

The first written document dealing with the use of waves in spatial orientation dates back to 1794, when Lazaro Spallanzani (“Opus coli di fisica”), analyzed the basic mechanisms of spatial orientation of the bats, proposing other mechanisms of spatial orientation than the visual – ophthalmic sy...
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Hormesis

Hormesis is a controversial concept in toxicology. The proposed concept is that very tiny amounts of a toxin may potentially have beneficial biological effects, rather than deleterious effects. In the context of radiology it refers to a proposed modification to the linear no-threshold theory to...
Article

Hounsfield unit

The Hounsfield unit (HU) is a quantity commonly used in computed tomography (CT) scanning to express CT numbers in a standardised and convenient form. Hounsfield units, created by and named after Sir Godfrey Hounsfield, are obtained from a linear transformation of the measured attenuation coeffi...
Article

Hunter's angle

Hunter's angle (HA) is a term coined from a neurosurgeon, Hunter Sheldon, at Huntington Medical Research Institutes. He placed his comb on the spectrum at approximately a 45° angle and connected several of the peaks. If the angle and peaks roughly corresponded to the 45° angle, the curve was con...
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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...
Article

Image intensifier

Image intensifiers are utilised to convert low energy radiation into visible light images. Frequently the detector portion of an x-ray c-arm use in operating theatres, the image intensifier has a low scatter input portion comprised of low absorption substances such as titanium or aluminium 1,2. ...
Article

Image plate artifact

Image plate artifact is caused by backscatter radiation. Backscatter radiation is transmitted through the back of the cassette to the cassette hinge where the lead coating gets weakened or cracked.  To reduce backscatter, the radiographer should collimate where possible.
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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...
Article

Indium-111 OncoScint

Indium-111 OncoScint is a radiopharmaceutical used in SPECT imaging. It is a labelled monoclonal antibody that is directed against TAG-72, which is a tumour-associated antigen associated with ~95% of colorectal carcinomas and 100% of ovarian carcinomas 1,2. Background hepatic uptake limits sensi...
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...
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In-phase and out-of-phase sequences

In-phase (IP) and out-of-phase (OOP) sequences correspond to paired MRI gradient echo (GRE) sequences obtained with the same repetition time (TR) but with two different echo time (TE) values.  Applications The main application of the IP-OOP sequences is to identify pathological (microsopic) fa...
Article

Intensifying screen

Intensifying screens are used in the x-ray cassette to intensify the effect of the x-ray photon by producing a larger number of light photons. It decreases the mAs required to produce a particular density and hence decreases the patient dose significantly. In cassettes, which use double emulsion...
Article

Intensity modulated radiation therapy (IMRT)

Intensity Modulated Radiation Therapy (IMRT) represents the radiotherapeutic modality where the intensity of the radiation delivered, could be modulated during the treatment to focus on the tumour tissue and spare the adjacent anatomical structures/tissue(s). Therefore the increased dose of radi...
Article

International System of Units

The International System of Units, or the SI units (shortened from the French Système international d'unités) is the globally-adopted system of units of measurement. It is the modern iteration of the metric system. It superseded all prior systems including CGS and MKS, although in certain fields...
Article

Intravascular (blood pool) MRI contrast agents

Intravascular MRI contrast agents normally remain confined to the intravascular space, compared to Gd-DTPA which distributes throughout the extracellular fluid space. This is a result of intravascular agents having a molecular weight of approximately 70,000 and above, compared to a molecular wei...
Article

Intravenous MRI contrast agents

Intravenous MRI contrast agents include chelates of paramagnetic ions, both ionic and nonionic. The particulates, sequestered in the liver, spleen, and lymph nodes, the intravascular agents, confined to the blood pool, and tumour specific agents are discusses separately (see bottom).  NOTE: Thi...
Article

Inverse Fourier transformation

The inverse Fourier transform is a mathematical formula that converts a signal in the frequency domain ω to one in the time (or spatial) domain t. A time domain signal f(t) is obtained by demodulating a frequency domain signal F(ω) using a special sinusoidal wave ejωt across all time (from nega...
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...
Article

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...
Article

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...
Article

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.
Article

Ionising radiation

Ionising radiation is the term given to forms of radiation that are energetic enough to displace orbiting electrons from the atoms they interact with, thus forming ions.  Forms of ionising radiation Indirect X-rays and gamma radiation are the commonest forms of ionising radiation. Occasionall...
Article

Kilovoltage peak

Kilovoltage peak (kVp) is the peak voltage applied to the x-ray tube. It determines the highest energy of x-ray photon. It is responsible for the acceleration of electrons from the cathode to the anode. It also determines tube current in space charge region.  Increase in kVp shifts the x-ray sp...
Article

K space

K space is an abstract concept and refers to a data matrix containing the raw MRI data. This data is subjected to mathematical function or formula called a transform to generate the final image. A discrete Fourier or fast Fourier transform 1-3 is generally used though other transforms such as th...
Article

K-trans (MR perfusion)

K trans is a measure of capillary permeability obtained using dynamic contrast-enhanced (DCE) MR perfusion. It is calculated by measuring the accumulation of gadolinium-based contrast agent in the extravascular-extracellular space.  Increased permeability of vessels in the brain is seen in a va...
Article

Lactate peak

Lactate is one of the more important compounds assessed on MR spectroscopy, and resonates at 1.3 ppm chemical shift, with a characteristic double peak at long TEs. It is however superimposed on the lipid band, and using an intermediate TE (e.g. 144ms) will invert only lactate allowing it to be d...
Article

LaPlace's law

LaPlace's law is useful in thinking about dilated tubular structures, such as the bowel or vessels (e.g. aortic aneurysms). The relationship between wall tension and radius shows why more dilated regions of a tube develop more wall stress and therefore are at higher risk for perforation: wall t...
Article

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 5...
Article

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 ...
Article

Linear attenuation coefficient

Linear attenuation coefficent (µ) is a constant that describes the the fraction of attenuated incident photons in a monoenergetic beam per unit thickness of a material. Its complement is the transmitted portion of the beam. It is expressed numerically in units of cm-1. Calculating µ The intens...
Article

Line focus principle

Line focus principle explains the relationship between the anode surface and the effective focal spot size. Basic concept The focal spot is the area of the target upon which the electron beam impinges. The energy of the electrons in the electron beam is mostly converted into heat (approximatel...
Article

Lipids peak

Lipids are a collection of related compounds examined in MR spectroscopy. They resonates at 1.3 ppm chemical shift, and are markers of severe tissue damage with liberation of membrane lipids, as is seen in cerebral infarction or cerebral abscesses. It is also encountered in cerebral metastases a...
Article

Loopogram

A loopogram is a fluoroscopic study of an ileal conduit, which is a type of urinary diversion. Terminology This procedure is also known is an ileal conduitogram, ileal loopography or ileostoureterography.  Procedure It is a retrograde study in which contrast is injected via the anterior abdo...

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