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 continuously improved upon by countless contributing members. Our dedicated editors oversee each edit for accuracy and style. Find out more about articles.
More than 200 results
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. The concentration of these two brain metabolites increases in hepatic and hypo...
Article
Ripple
Ripple, or voltage ripple, refers to the fluctuation in voltage output of some X-ray generators. It is given a percentage value, and calculated as 100 x (Vmax - Vmin )/Vmax (%).
Single-phase and two-phase generators have 100% ripple. Three-phase generators have ripple values between 5 and 15%. ...
Article
Reynolds number
The Reynolds number (Re) is the primary parameter used to define the transition of fluid motion between laminar and turbulent flow patterns 1. The Reynolds number represents the ratio of inertia forces to viscous forces, and as such has no units (i.e. is a dimensionless quantity) 1.
Calculatio...
Article
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 100 g of brain tissue 1.
...
Article
Panoramic ultrasound
Panoramic ultrasound is an ultrasound technique which stitches multiple B-mode images together to create a single composite image with an increased field of view (FOV) 1.
Clinical Applications
It is useful in the evaluation of masses/objects of interest which are larger than the typical FOV 1....
Article
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...
Article
Thermionic emission
Thermionic emission is the emission of electrons from a heated metal (cathode). This principle was first used in the Coolidge tube and then later in the modern day x-ray tubes. Before the discovery of the principle, gas tubes were used for x-ray production.
The cathode has its filament circuit ...
Article
MRI pulse sequences
An MRI pulse sequence is a programmed set of changing magnetic gradients. Each sequence will have a number of parameters, and multiple sequences grouped together into an MRI protocol.
Parameters
A pulse sequence is generally defined by multiple parameters, including:
time to echo (TE)
time ...
Article
Magnetomotive ultrasound
Magnetomotive ultrasound (MMUS) is an emerging medical imaging modality, which utilizes the discrete tissue vibration caused by superparamagnetic iron oxide (SPIO) nanoparticles under an external magnetic field.
Physics
If an external time-varying magnetic field is applied (e.g. using an elec...
Article
MR liver iron quantification
MR liver iron quantification is a non-invasive means of measuring liver iron concentration, a key indicator in the management of patients with hemochromatosis (primary or secondary).
Advantages
Apart from being non-invasive, sampling occurs in a large cross-section of the liver, as opposed to ...
Article
Rutherford (unit)
The rutherford (symbol Rd) is an obsolete unit of radioactivity which was superseded by the introduction of the becquerel in 1975. One rutherford was equivalent to 1,000,000 nuclear disintegrations per second, or alternatively one becquerel equated to one microrutherford (μRd).
Terminology
As...
Article
Spiral pulse sequences
Spiral scanning on MRI is unlike spiral scanning on CT where the x-ray tube is continuously rotating and data is continuously being acquired. On MRI the word "spiral" refers to the pattern of sampling k-space. On conventional imaging sequences including spin echo and gradient echo and on fast im...
Article
Radiologist
What is a radiologist?
A radiologist is a specialist doctor who uses medical imaging such as x-ray, MRI, CT, ultrasound and angiography, to diagnose and treat human disease or injury. Radiologists undergo lengthy training and assessment in order to be accredited by relevant governing boards and...
Article
Magnetism
Magnetism is a property of matter that is a result of the orbiting electrons in atoms. The orbiting electrons cause the atoms to have a magnetic moment associated with an intrinsic angular momentum called spin.
Magnetic field strengths are measured in tesla (T), a derived SI unit. The equivale...
Article
Flow void
Flow voids is a term used when describing MRI studies and refers to signal loss occurring within moving fluids (usually blood but also frequently seen in CSF or urine) when the fluid is moving at a sufficient velocity relative to the MRI apparatus. Some MRI sequences are more susceptible to flow...
Article
Scattering (ultrasound)
Scattering occurs when a sound wave strikes a structure with a different acoustic impedance to the surrounding tissue and which is smaller than the wavelength of the incident sound wave. Such structures are known as “diffuse reflectors,” with examples being red blood cells and non-smooth surface...
Article
Herringbone artifact
Herringbone artifact, also known as spike artifact, crisscross artifact, or corduroy artifact, is an MRI artifact related to one or few aberrant data point(s) in k-space. In image space, the regularly spaced stripes resemble the appearance of a fabric with a herringbone pattern. The artifact cov...
Article
Samarium-153
Samarium-153 (Sm-153) is a radioisotope used in metabolic radiotherapy for the treatment of pain from bone metastases. It is produced in nuclear reactors, by neutron irradiation of samarium-152 (Sm-152 Sm2O3).
Samarium-153 decays by emitting both beta minus particles and gamma photons with a ch...
Article
Thermal index
The thermal index (TI) is intended as a measure of an ultrasound beam's thermal bioeffects, as absorption of sound waves may cause heating in tissue. It is often displayed on ultrasound screens (along with the mechanical index).
The thermal index depends on:
a measure of time-averaged acoustic...
Article
CLEAR
CLEAR, an abbreviation of constant level appearance, is an MR technique to achieve homogeneity correction by using coil sensitivity maps acquired in a reference scan. CLEAR is a term utilized by Philips and is comparable to PURE in Siemens MR scanners.
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