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.

34 results found
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2-hydroxyglutarate

2-hydroxyglutarate is a metabolite that accumulates in the brains of patients with IDH-1 mutated (IDH-1 positive) brain tumours, particularly diffuse low-grade gliomas. Although not in widespread clinical use, it is likely that 2-hydroxyglutarate, which resonates at 2.25 ppm, will be able to be ...
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Alanine peak

Alanine is one of the compounds examined in MR spectroscopy. It resonates at 1.48 ppm chemical shift. It is elevated in meningiomas.
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Arterial spin labelling (ASL) 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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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...
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Cerebral blood flow (CBF)

Cerebral blood flow (CBF) is one of the parameters generated by perfusion techniques (CT perfusion and MR perfusion). CBF is defined as the volume of blood passing through a given amount of brain tissue per unit of time, most commonly milliliters of blood per minute per 100g of brain tissue 1. ...
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Cerebral blood volume (CBV)

Cerebral blood volume (CBV) (often relative CBV: see below) is one of the parameters generated by perfusion techniques (CT perfusion and MR perfusion). CBV is defined as the volume of blood in a given amount of brain tissue, most commonly milliliters of blood per 100 g of brain tissue 1. CBV ca...
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Choline peak

Choline is a precursor of acetylcholine (ACH), a component of cell membranes which is commonly examined in MR spectroscopy. It resonates at 3.2 ppm chemical shift. It is a marker of cellular membrane turnover and therefore elevated in neoplasms, demyelination and gliosis. In the setting of glio...
Article

Congenital cholesteatoma

Congenital cholesteatomas are identical to epidermoid cysts, differing only in name and location.  Pathology They are intraosseous inclusions of ectoderm, and are therefore comprised of keratin debris and cholesterol. Characteristically, they are located at the petrous apex. In contrast middle...
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...
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 setting on imaging we are...
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...
Article

Diffusion weighted MRI in acute stroke

Diffusion weighted imaging (DWI) is a commonly performed MRI sequence for evaluation of acute ischaemic 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 app...
Article

Diffusion-tensor MRI imaging and fiber tractography

Diffusion-tensor imaging (DTI) is an MRI technique that uses anisotropic diffusion to estimate the axonal (white matter) organisation of the brain. Fiber tractography (FT) is a 3D reconstruction technique to access neural tracts using data collected by DTI. Within cerebral white matter, water m...
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Double inversion recovery sequence

Double inversion recovery (DIR) is a MRI pulse sequence which suppresses signal from the CSF as well as from the white matter and hence enhances any inflammatory lesion. To obtain such sequence in 3T MRI scanner, two inversion times are required. TI1 which is used for suppression of CSF and usu...
Article

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...
Article

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...
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

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...
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

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...
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

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

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

Mean transit time (MTT)

Mean transit time (MTT) corresponds to the average time, in seconds, that red blood cells spend within a determinate volume of capillary circulation. It is assessed as part of the CT perfusion protocol, which is basically used in the context of ischaemic stroke diagnosis and management, and MR p...
Article

MR perfusion weighted imaging

Perfusion weighted imaging is a term used to denote a variety of MRI techniques able to give insights into the perfusion of tissues by blood.  There are three techniques in wide use to derive one or more perfusion values:  ​techniques ​dynamic susceptibility contrast (DSC) MR perfusion dynam...
Article

MR spectroscopy

MR spectroscopy (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 has low NAA, high Choline". This is perhaps a little harsh, however it is fair to...
Article

Myo-inositol peak

Myo-inositol is one of the compounds images with MR spectroscopy (MRS) at both 1.5T and 3T and is seen to resonate at 3.5 ppm chemical shift (right of the choline peak).  Myo-inositol is a precursor of both phosphatidylinositol (the major inositol-containing phospholipid) and of phosphatidylino...
Article

N-acetylaspartate (NAA) peak

N-acetylaspartate (NAA) is one of the more important compounds assessed on MR spectroscopy, and resonates at 2.0 ppm chemical shift.  NAA is the acetylated form of the amino acid, aspartate, which is found in high concentrations in neurons and is a marker of neuronal viability. It is therefore ...
Article

Negative enhancement integral

The negative enhancement integral in MR perfusion is used to calculate the relative cerebral blood volume (rCBV).  It represents the area described by the baseline and the signal loss due to passage of contrast bolus in tissue. 
Article

Relaxometry

Relaxometry is measurement of relaxation times from MR images. T1, T2 and T2* can be estimated using the appropriate pulse sequence and parameters. T2 relaxometry has found useful in quantitating signal changes on T2-weighted images as in evaluating mesial temporal sclerosis. Details T2 rela...
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

T2 shine through

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

T2 washout

T2 washout is a phenomenon encountered on diffusion weighted imaging (DWI) which results in DWI images (e.g. B = 1000) appearing normal despite abnormal ADC maps.  For the phenomenon to occur a particular combination of ADC and T2 signal intensity is required.  increased T2 signal facilitated...
Article

Thallium 201 chloride

Thallium 201 Chloride is a radiopharmaceutical used in cardiac imaging. Characteristics photon energy: 80 keV physical half life: 55 hours biological half life rest: 3 minutes exercise: 30 seconds normal distribution: myocardium, skeletal muscle, GI tract, liver, kidneys excretion: renal...

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