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.
717 results found
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
Beam width artifact
Ultrasound beam width artifact occurs when a reflective object located beyond the widened ultrasound beam, after the focal zone, creates false detectable echoes that are displayed as overlapping the structure of interest.
Features
To understand this artifact, it is important to remember that t...
Article
Electron
The electron is a subatomic particle that has negligible mass (9.109 x 10-31 kg) and is negatively charged (-1.6 x 10-19 Coulombs). 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 pos...
Article
Digital radiography
Digital radiography is based on capturing and storing the radiograph using discrete (digital) values 1 as opposed to conventional film radiography, which uses analog (continuous) values. It removes the requirement of dark room procedures.
Terminology
The term digital radiography is often used ...
Article
Cassette
Cassettes are rigid holders used in conventional and computed radiography (CR) for the screen film system and imaging plate respectively.
The back side of the cassette has rubber or felt for adequate contact between the screen film system or with the imaging plate. The front of the cassette is...
Article
Fluoroscopy
Fluoroscopy is an imaging modality that allows real-time x-ray viewing of a patient with high temporal resolution. It is based on an x-ray image intensifier coupled to a still/video camera. In recent years flat panel detectors (like those used in direct digital radiography) have been replacing t...
Article
Doppler shift
Doppler shift or Doppler effect is defined as the change in frequency of sound wave due to a reflector moving towards or away from an object, which in the case of ultrasound is the transducer.
Terminology
When sound of a given frequency is discharged and subsequently reflected from a source th...
Article
Biomolecular radiation damage
Biomolecular radiation damage may result from exposure of biological tissues to ionizing radiation from direct exposure, or via Compton scattering.
Mechanism of tissue radiation damage
Direct effect
occurs when energy is directly deposited to the biological macromolecule (e.g. DNA, RNA, prote...
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 movemen...
Article
MR tagging
Cardiac MR tagging or myocardial tagging refers to an MRI-based acquisition method designed for the analysis of myocardial deformation.
Technique
The method exploits tissue magnetization as a tissue property. A local magnetic saturation grid of dark-lined tissue markers known as tags are induc...
Article
Bremsstrahlung radiation
X-rays are produced by high-energy electrons bombarding a target, especially targets with a high proton number (Z). When bombarding electrons penetrate the target, some electrons travel close to the nucleus due to the attraction of its positive charge and are subsequently influenced by its elect...
Article
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...
Article
Whole-body diffusion-weighted MRI
Whole-body diffusion-weighted MRI (WB-MRI) is an advanced imaging technique that combines anatomical and functional MRI sequences to provide a comprehensive assessment of the whole-body in a single examination.
WB-MRI uses the properties of diffusion-weighted imaging for oncological disease sta...
Article
Iterative reconstruction (CT)
Iterative reconstruction refers to an image reconstruction algorithm used in CT that begins with an image assumption and compares it to real-time measured values while making constant adjustments until the two are in agreement.
Computer technology limited early scanners in their ability to perf...
Article
Gradient coils
Gradient coils are used to produce deliberate variations in the main magnetic field (B0). There are three sets of gradient coils, one for each direction. The variation in the magnetic field permits localization of image slices as well as phase encoding and frequency encoding. The set of gradient...
Article
Sequential CT image acquisition
Sequential CT scanning, also referred to as "scan-move-scan" or "step and shoot", was the conventional method of image acquisition in computed tomography before the advent of helical CT.
Terminology
In sequential scanning, the patient is moved forward along the longitudinal axis of the CT sca...
Article
Virtual grid
Virtual grid software is a relatively new innovation utilizing no physical grid at all. Instead, the original purpose of a grid is replicated by an algorithm 1 based on fundamental mathematics (i.e. Laplace transformation, wavelet transformation and Gaussian decomposition) which iteratively reco...
Article
Spin (physics)
Spin, an intrinsic quantum property associated with elementary particles, challenges classical intuition by presenting an angular momentum quantized in half-integer (fermions) or integer values (bosons) 1,2.
The quantum nature of spin does not imply a physical rotation of particles. Instead, sp...
Article
Electron binding energy
The electron binding energy is the minimum energy that is required to remove an electron from an atom, as the negatively charged electrons are held in place by the electrostatic pull of the positively charged nucleus. The electron binding energy is measured in electronvolts (eV), where 1 eV = 1....
Article
Decibel
The decibel (dB) is a unit that measures the relative difference between two sound intensities. The relationship is logarithmic:
dB = 10 log (I2 / I1)
dB = relative intensity of the sounds
I1 = intensity of sound 1
I2 = intensity of sound 2
Informally, decibel is a unit of "loudness", which...
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