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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. image weighting T1 T2 T2*: T2 star PD: proton density DWI: diffusion-weighted imaging and ADC: apparent diff...

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 darker and vice versa, creating a fals...

Turbo inversion recovery magnitude

Turbo inversion recovery magnitude (TIRM) is an inversion recovery MRI pulse sequence that displays the magnitude of a turbo/fast spin echo, without regard for the phase/polarity of the longitudinal magnetization. This method of image reconstruction is the dominant form of inversion recovery use...

Steady-state free precession MRI

Steady-state free precession MRI (SSFP) is a type of gradient echo MRI pulse sequence in which a steady, residual transverse magnetization (Mxy) is maintained between successive cycles. The sequence is noted for its superiority in dynamic/cine assessment of cardiac function. Discussion To unde...

T2 weighted image

T2 weighted image (T2WI) is one of the basic pulse sequences on MRI. The sequence weighting highlights differences on the T2 relaxation time of tissues. Summary repetition time (TR): long echo time (TE): long flip angle: less important than with T1 weighting fat: intermediate-bright fluid:...

Spatial resolution

Spatial resolution refers to the ability of an imaging modality to differentiate two adjacent structures as being distinct from one another. Other related terms include definition or visibility of detail. Spatial resolution is expressed in line pairs per mm (lp mm). The absence of spatial reso...

MRI

MRI (an abbreviation of magnetic resonance imaging) is an imaging modality that uses non-ionizing radiation to create useful diagnostic images. In simple terms, an MRI scanner consists of a large, powerful magnet in which the patient lies. A radio wave antenna is used to send signals to the bod...

B0

The B0 in MRI refers to the main static magnetic field and is measured in teslas (T). The majority of MRI systems in clinical use are 1.5 T, with increasing numbers of 3 T systems being installed. Since 2017, 7 T clinical scanners have been available, see ultrahigh field MRI. Altering the field...

T1 weighted image

T1 weighted image (also referred to as T1WI or the "spin-lattice" relaxation time) is one of the basic pulse sequences in MRI and demonstrates differences in the T1 relaxation times of tissues. A T1WI relies upon the longitudinal relaxation of a tissue's net magnetization vector (NMV). Basicall...

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...

Valence shell

The valence shell of an atom is the outermost shell of the electron cloud. It plays a large part in determining the chemical, thermal, optical and electrical properties of the element. This occurs because it often not full and movement of electrons may occur between it and a) electrons from o...

Structure of the atom

The structure of the atom is key to the majority of the techniques used in radiology, and a general understanding of atomic structure is worthwhile. An atom is the smallest constituent of a chemical element that still maintains the chemical properties of that element. The following is a simplif...

Kerma

Kerma is a measure of energy transferred from radiation to matter and is an acronym for kinetic energy released to matter. It is related to, but not the same as absorbed dose. Kerma is measured by the SI unit, the gray (joules per kilogram). Kerma measures the amount of energy that is transferr...

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...

Stochastic effects

Stochastic effects occur by chance and can be compared to deterministic effects which result in a direct effect. Cancer induction and radiation induced hereditary effects are the two main examples of stochastic effects. Models Cancer induction as a result of exposure to radiation is thought by...

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 ionizing radiation. In quantitative terms, equivalent dose is less fundamental than absorbed dose, but it is more b...

Absorbed dose

Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation. It is equal to the energy deposited per unit mass of a medium, and so has the unit joules (J) per kilogram (kg), with the adopted name of gray (Gy) where 1 Gy = 1 J.kg-1. The absorbed dose is not a good indica...

Tube arcing

Tube arcing occurs when there is a short-circuit within the tube, typically from the cathode to the tube envelope. The result is a temporary loss of x-ray output and a localized artifact. A number of causes of tube arcing are recognized 1: insulator surface flashover insulator breakdown va...

Ring artifact

Ring artifacts are a CT phenomenon that occurs due to the miscalibration or failure of one or more detector elements in a CT scanner. Less often, it can be caused by insufficient radiation dose or contrast material contamination of the detector cover 2. They occur close to the isocenter of the s...

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...

Nephrogenic systemic fibrosis

Nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy, occurs almost exclusively in patients with renal impairment and is associated with administration of gadolinium-based contrast agents (GBCAs) used in MRI. The American College of Radiology (ACR) has divided ga...

Mammography

Mammography is a dedicated radiographic technique for imaging the breast, and the resultant images are known as mammograms. Types of mammography In general terms, there are two types of mammography: screening and diagnostic. Mammography differs significantly in many respects from the rest of ...

Magic angle effect (MRI artifact)

The magic angle is an MRI artifact which occurs on sequences with a short TE (less than 32ms; T1 weighted sequences, proton density weighted 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 hype...

MR spectroscopy

The technique of magnetic resonance spectroscopy (usually shortened to MR spectroscopy or MRS) allows tissue to be interrogated for the presence and concentration of various metabolites. Grossman and Yousem said "If you need this to help you, go back to page 1; everything except Canavan (disease...

Fetal dosimetry

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

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 magnetic resonance spectroscopy (MRS). This artifact occurs in the frequency-encoding direction and is due to spatial misregistration of fat and water molecules. Chemi...

BOLD imaging

Blood oxygenation level dependent (BOLD) imaging is the standard technique used to generate images in functional MRI (fMRI) studies, and relies on regional differences in cerebral blood flow to delineate regional activity. Blood flow in the brain is highly locally controlled in response to oxy...

1.5 T vs 3.0 T

Comparing 1.5 T vs 3.0 T (1.5 tesla vs 3.0 tesla) MRI systems identifies several differences; a 3 T system has increased signal-to-noise ratio (SNR) increased spatial resolution increased temporal resolution increased specific absorption rate (SAR) increased acoustic noise Terminology It...

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