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
Color comet tail artifact
The color comet tail artifact is an ultrasonographic sign seen in a number of situations when color Doppler scanning is performed.
Typically the artifact, which resembles the grey scale comet tail artifact, is seen in a situation when a small highly reflective (usually calcific) object is inter...
Article
Compression paddle
A compression paddle is a device found in mammographic units which is used to compress the breast.
It consists of a flat radiolucent plate positioned parallel to the support table, and attached to either a mechanical or pneumatic assembly. It is controlled by the operator by a foot pedal.
Full...
Article
Zebra stripes
Zebra stripes, a.k.a. zebra artifacts, appear as alternating bright and dark bands in a MRI image. The term has been used to describe several different kind of artifacts causing some confusion.
Artifacts that have been described as a zebra artifact include the following:
moire fringes 1,2
spi...
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...
Article
Air gap technique
The air gap technique is a radiographic technique that improves image contrast resolution through reducing the amount of scattered radiation that reaches the image detector. In select situations, this technique can be used instead of an antiscatter grid as the primary scatter reduction method in...
Article
Convex array
Convex (sequential) arrays, also known as curvilinear or curved linear arrays, are similar to linear arrays but with piezoelectric elements arranged along with a curved transducer head. Ultrasound beams are emitted at 90 degrees to the transducer head. This arrangement results in a trapezoidal f...
Article
Nuclear magnetic resonance
Nuclear magnetic resonance (NMR) is a powerful technique which allows the study of the magnetic properties of an atom's nucleus 1. It involves placing nuclei within an external magnetic field enabling thus them to undergo precession 2. The 'resonance' part of the names implies the fact that a se...
Article
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...
Article
Spatial resolution (CT)
Spatial resolution in CT is the ability to distinguish between objects or structures that differ in density.
A high spatial resolution is important for one to discriminate between structures that are located within a small proximity to each other.
Factors affecting CT spatial resolution
fiel...
Article
Liver ultrasound
Liver ultrasound is a valuable diagnostic tool for assessing liver anatomy, size, and pathology. It is a non-invasive, painless, and relatively quick procedure that does not involve exposure to ionizing radiation.
Indications
Liver ultrasound is commonly utilized in the evaluation of various h...
Article
Cardiac ischemia protocol (MRI)
The cardiac MRI ischemia or stress protocol encompasses a set of different MRI sequences for the assessment of myocardial ischemia.
Note: This article aims to frame a general concept of a cardiac MRI protocol in the setting of vasodilator stress perfusion testing.
Protocol specifics will vary ...
Article
Dynamic nuclear polarization
Dynamic nuclear polarization (DNP) is a phenomenon by which polarization is transferred from a polarizing agent to a biological tracer, enhancing the nuclear energy difference and thereby increasing the signal-to-noise ratio (SNR) dramatically.
Article
Allan Macleod Cormack
Allan M Cormack (1924-1998) was a South African-American physicist who was instrumental in the development of CT 1,3.
Early life
Allan Macleod Cormack was born on 23 February 1924 in Johannesburg, South Africa. His parents - teacher Amelia MacLeod and engineer George Cormack - had both emigrat...
Article
Phased array
A phased array ultrasound transducer is typically 2-3 cm long, consisting of 64-128 elements. It is a smaller assembly than a sequential array and can be either linear or curvilinear.
A sector field of view is produced by all elements firing to create a single waveform. Small delays in element ...
Article
FABS position
The FABS position relates to MRI elbow examinations for improved visualization of the distal biceps brachii tendon insertion and is a mnemonic for elbow flexed, shoulder abducted and forearm supinated.
Article
Isomer
In nuclear physics, isomers are atomic species that are identical in nuclear composition, sharing the same mass and atomic numbers, but differ in their relative energy states, and will therefore differ in their manner of radioactive decay.
Examples of isomers include:
metastable technetium-99,...
Article
M-mode (ultrasound)
Often utilized for its excellent axial and temporal resolution of structures, M-mode (or motion mode) is a form of ultrasonography in which a single scan line is emitted, received, and displayed graphically. An M-mode recording is conventionally displayed with the abscissa representing time, and...
Article
Tc-99m sulfur colloid
Technetium-99m sulfur colloid is one of the technetium radiopharmaceuticals.
Characteristics
photon energy: 140 keV
physical half-life: 6 hours
biological half-life: 2 to 3 minutes
normal distribution:
liver: 85%
spleen: 10%
bone marrow: 5%
excretion: hepatic
target organ: liver, splee...
Article
FLAIR vascular hyperintensities
FLAIR vascular hyperintensities are hyperintensities encountered on FLAIR sequences within subarachnoid arteries related to impaired vascular hemodynamics 1,2. They are usually seen in the setting of acute ischemic stroke and represent slow retrograde flow through collaterals (and not thrombus) ...
Article
Missile effect - MRI safety
Missile effect (or projectile effect) denotes the attraction exerted by the static magnetic field of the MRI scanner on ferromagnetic objects accidentally introduced into the MRI-scanner room (i.e. oxygen bottles, scissors, chairs, etc). This effect involves the risk of impact with the patient (...
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