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.

375 results found
Article

Photon starvation

Photon starvation is one source of streak artifact which may occurs in CT. It is seen in high attenuation areas, particularly behind metal implants. Because of high attenuation insufficient photons reach the detector surface resulting in characteristic artifact. During reconstruction process, th...
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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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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

Synthetic MRI

Synthetic MRI is a technique that generates contrast weighted images based on measurements of tissue properties from a single acquisition. Basic principles With synthetic MRI, different contrast weighted images can be obtained based on quantifications of a single multiple dynamic and multiple...
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Arterial spin labelling MR perfusion

Arterial spin labelling (ASL) MR perfusion is an MR perfusion technique which does not require intravenous administration of contrast (unlike DSC perfusion and DCE perfusion). Instead it exploits the ability of MRI to magnetically label arterial blood below the imaging slab. The parameter most c...
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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

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...
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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

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

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...
Article

Photostimulable phosphors

Photostimulable phosphors (PSP) are materials that store absorbed energy within excited electrons and release it in the form of light on exposure to laser energy. The process can be broken up as follows 1: an x or gamma photon interacts with the PSP and releases high energy secondary electrons...
Article

CT dose index

CT dose index (CTDI) 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 single slice) were...
Article

Signal-to-noise ratio

Signal-to-noise ratio (SNR) is a generic term which, in radiology, is a measure of true signal (i.e. 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

Metal artifact reduction sequence

A metal artifact reduction sequence (MARS) is intended to reduce the size and intensity of susceptibility artifacts resulting from magnetic field distortion. A variety of techniques are used for reducing metal artifacts at MRI, both for addressing artifacts due to the presence of metal in the i...
Article

Tube rating

Tube ratings are the defined input parameters (kVp, mA, exposure) that can be safely used during its operation without causing damage to the x-ray tube itself and unique to each individual x-ray tube model. When the electron beam strikes the target material in the anode only 1% of the kinetic e...
Article

Dose length product

Dose length product (DLP) is a measure of CT tube radiation output. It is related to 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 axis of the patient). DLP = (CTDIvol ) * (length of...
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

Developer solution

Developer solution is used in the darkroom for developing (i.e. converting latent image to visible image) x-ray films used in conventional (screen film) radiography. Components developer: hydroquinone (for high contrast) + metal/phenidone (for low contrast) the developer itself gets oxidised ...
Article

Intensifying screen

Intensifying screen is used in the 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 films, ...
Article

Anode

The anode is the component of the x-ray tube where x-rays are produced. It is a piece of metal, shaped in the form of a bevelled disk with the diameter between 55 and 100 mm, and thickness of 7 mm, connected to the positive side of the electrical circuit. The anode converts the energy of the ele...
Article

Air gap technique (plain radiography)

The utilisation of the air gap technique in general radiography is limited due to the need for equipment facilitation to create the air gap when it is not inherent in the standard technique. Horizontal-beam lateral hip There are many different methods of performing the horizontal beam lateral ...
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...
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...
Article

Beam collimators

Beam collimators are 'beam direction' devices used in the x-ray tube housing, along with an arrangement of mirrors and lights, in such a way that the light and x-ray fields match each other. They are made of lead shutters which completely absorb the photons, and thus reduce the patient dose as w...
Article

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...
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

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

Cathode

The cathode is part of an x-ray tube and serves to expel the electrons from the circuit and focus them in a beam on the focal spot of the anode. It is a controlled source of electrons for the generation of x-ray beams. The electrons are produced by heating the filament i.e. a coil of wire made f...
Article

Roentgen

The roentgen (or röntgen) was previously used as a unit to measure radiation exposure. It was defined as the quantity of x-rays that produces 2.580 × 10-4 coulombs of charge collected per unit mass (kilograms) of air at standard temperature and pressure (STP): 1 R = 0.000258 C/kg air. History a...
Article

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

Anode angle

The anode angle refers to the angle the target surface of the anode sits at in relation to the vertical.  Most x-ray tubes have an anode angle of 12-15 degrees but greater or lesser angles can also be used depending on the application. The degree of angulation of the anode effects the effective...
Article

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

Anode heel effect

Anode heel effect refers to the lower field intensity towards the anode in comparison to the cathode due to lower x-ray emissions from the target material at angles perpendicular to the electron beam. Basic concept The conversion of the electron beam into x-rays doesn’t simply occur at the sur...
Article

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...
Article

Magic angle effect (MRI artifact)

The magic angle is an MRI artifact which occurs on sequences with a short TE (less than 32ms; T1W sequences, PD sequences and gradient echo sequences).  It is confined to regions of tightly bound collagen at 54.74° from the main magnetic field (B0), and appears hyperintense, thus potentially be...
Article

Meglumine iotroxate (Biliscopin)

Meglumine iotroxate (BiliscopinTM) is an iodinated, intravenous contrast agent that is preferentially excreted into the biliary tree and is used in CT intravenous cholangiography. The typical dose is 100 mL Biliscopin (105 mg meglumine iotroxate/ml; 5.0 g iodine), which is administered via slow...
Article

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

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

Magnetic susceptibility artifact

Magnetic susceptibility artifacts (or just susceptibility artifact) refer to a variety of MRI artifacts that share distortions or local signal change due to local magnetic field inhomogeneities from a variety of compounds.  They are especially encountered while imaging near metallic orthopedic ...
Article

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...
Article

Radiation-induced carcinogenesis

Radiation-induced carcinogenesis is widely but not universally believed to occur at exposures from ionising radiation used in medical imaging. It is thought to be a stochastic effect of ionising radiation, with the linear no-threshold theory (LNT) proposing no "safe" level of radiation exposure,...
Article

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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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...
Article

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:...
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 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

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...
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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 ...
Article

Propagation speed

The propagation speed of sound waves through tissue is an important element of ultrasound scans. Ultrasound machines assume sound waves travel at a speed of 1540 m/sec through tissue 1. In reality, the speed of sound is affected by the density and elasticity of the medium through which it is tr...
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Stochastic effects

Stochastic effects occur by chance and can be compared to deterministic effects which result in a direct effect. Cancer induction as a result of exposure to radiation is thought by most to occur in a stochastic manner: there is no threshold point and risk increases in a linear-quadratic fashion...
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Deterministic effects

Deterministic effects describe a cause and effect relationship between radiation and certain side-effects. They are also called non-stochastic effects to contrast with chance-like stochastic effects (e.g. cancer induction). Deterministic effects have a threshold below which the effect does not ...
Article

Radiation-induced lung cancer

Radiation-induced lung cancers have been reported as a rare late complication of radiation therapy in both post-operative breast cancer and Hodgkin lymphoma patients. These occur 5-10 years (or later) after treatment 1-4. There appears to be increased risk of lung cancer in these patients if the...
Article

Radiation damage (skin injury)

Radiation-induced skin injuries can occur in both radiotherapy and fluoroscopic procedures such as interventional radiology.  Acute radiation doses above 2 Gy are known to result in erythema, permanent epilation will occur at 7 Gy and delayed skin necrosis transpires above doses of 12 Gy.  The...
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  strain elastography (also known as static o...
Article

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...
Article

Cardiac MRI

Cardiac MRI consists of using MRI to study heart anatomy, physiology and pathology. Advantages The main advantages of cardiac MRI in comparison with other techniques are: better definition of soft tissues use of different types of sequences improves diagnostic accuracy no ionising radiation...
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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

Non contrast enhanced MR angiography

Non contrast enhanced MR angiography is performed in several ways including: time of flight angiography phase contrast angiography three-dimensional (3D) electrocardiograph-triggered half-Fourier fast spin echo Generally, these techniques are time-consuming as compared with contrast enhanced...
Article

Phase contrast imaging

Phase contrast imaging is an MRI technique that can be used to visualise moving fluid. It is typically used for MR venography as a non-IV-contrast requiring technique.  Spins that are moving in the same direction as a magnetic field gradient develop a phase shift that is proportional to the vel...
Article

Radiopharmaceuticals

Radiopharmaceuticals are drugs that are bound to radioactive substances.  The pharmaceutically active portion determines the activity that will be measured and the radioactive portion emits radiation that can be measured by the scanner. A number of radiopharmaceuticals are used in human imaging...
Article

Octreotide scintigraphy

Octreotide scintigraphy uses 111In-labelled octreotide which is a somatostatin analog; it is also known as an OctreoscanTM, a brand name for 111In-labelled pentetreotide; pentetreotide is a DTPA-conjugated form of octreotide, originally manufactured by Mallinckrodt Nuclear Medicine LLC, which no...
Article

Absorption (ultrasound)

In ultrasound, absorption is the reduction in intensity of the sound waves as it passes through tissue. Most of the energy lost is in the form of heat.
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 ...
Article

Computed tomography texture analysis

Computed tomography texture analysis (or CTTA) is a new useful biomarker that provides an objective and quantitative assessment of tumour heterogeneity by analysing the differences in the pixel values of an image. Parameters assessed  Gray-level frequency distribution: pixel intensity histogra...
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

X-ray tube

An x-ray tube functions as a specific energy converter, receiving the electrical energy and converting it into two other forms of energy: x-radiation and heat. Heat is considered the undesirable product of this conversion process; therefore x-radiation is created by taking the energy from the el...
Article

Magnetic resonance neurography

Magnetic resonance neurography (MRN) is a relatively new non-invasive imaging technique for dedicated assessment of peripheral spinal nerves. It is used to assess peripheral nerve entrapments and impingements as well as localization and grading of nerve injuries and lesions. Dedicated high-res...
Article

Gallium 67 scintigraphy

Gallium 67 is a radiotracer which is used in the form of various salts like citrate and nitrate. Gamma camera imaging includes planar (2 dimensional) , SPECT and SPECT/CT scans. It has a predilection to sites of inflammation. It binds to inflammatory proteins and thus it pools up at the sites of...
Article

I-123 ioflupane

I123 ioflupane is a radiopharmaceutical for the diagnosis of Parkinson disease and its differential diagnoses. Characteristics iodine-123 is a cyclotron product physical half-life is 13.22 hours predominant energy of its gamma spectrum is 159 keV Ioflupane is the international nonproprietar...
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

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 ...
Article

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...
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

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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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

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...
Article

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

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...
Article

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...
Article

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

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

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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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 ...
Article

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...
Article

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...
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

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...
Article

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...
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...
Article

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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