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.
716 results found
Article
Photomultiplier tube (Gamma camera)
The photomultiplier tube array of a Gamma camera detects the visible light produced by the scintillator and converts it to a measurable electronic signal 1.
A series of photomultiplier tubes are mounted behind the scintillation crystal 1. Each photomultiplier tube is composed of a tightly seal...
Article
Scintillator (gamma camera)
The scintillator is the component of a gamma camera which receives the gamma rays emitted from a radionuclide in a nuclear medicine scan and converts it to visible light photons. It is located just behind the collimator device.
A scintillator crystal may have properties of phosphorescence, wher...
Article
Collimator (Gamma camera)
The collimator of a Gamma camera used in nuclear medicine differs in structure and function to the beam collimators used in general radiography.
They typically consist of a lead disc drilled with tens of thousands of closely packed holes, separated from each other by septa.
Each hole only acce...
Article
Photoluminescence
Photoluminescence is a property of a material to absorb, store and convert photons to light. Photoluminescent materials have important applications in radiology.
Types
Fluorescence is the instantaneous emission of light following photon absorption. It typically occurs within 10-8 seconds.
Exa...
Article
Transformer
A transformer is a passive electrical device used to transfer electrical energy from one circuit to another, via the phenomenon of electromagnetic induction.
It is fundamental in the modulation of voltage and current in the x-ray generator.
Components
primary coil
a set of insulated wires at...
Article
Tube shielding
Tube shielding refers to the use of a material within the X-ray tube housing to limit leakage of scattered radiation, to protect both patients and staff from unnecessary exposure.
Lead (Pb) is an ideal material for this purpose due to its high atomic density (Z = 82). Due to these properties, i...
Article
Focusing cup
A focusing cup is a negatively charged, shallow depression on the surface of the cathode of an x-ray tube, which concentrates the electron beam towards the focal spot of the anode. It is typically composed of nickel.
The negative charge of the focusing cup helps to accelerate the electrons towa...
Article
Continuous X-ray spectrum
The continuous X-ray spectrum refers the range of photon energies produced in an X-ray tube due to the properties of Bremsstrahlung radiation.
The energy of X-ray photons can take a value from zero to the maximum kinetic energy of the incident electrons.
Both the continuous X-ray spectrum and ...
Article
Mass attenuation coefficient
The mass attenuation coefficient (also known as the mass absorption coefficient) is a constant describing the fraction of photons removed from a monochromatic x-ray beam by a homogeneous absorber per unit mass.
It is equivalent to the linear attenuation coefficient divided by the density of the...
Article
Pixel shift (reregistration)
Pixel shift or reregistration is a post-processing technique used to improve misregistration artifact in digital subtraction angiography, where two images to be subtracted are spatially realigned with respect to one another, by shifting pixels vertically, horizontally or obliquely.
Pixel shift...
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
Mean glandular dose
The mean glandular dose (MGD) is an estimate of the average absorbed dose to the glandular tissues of a breast during mammography. It is measured in Gray (Gy).
The most commonly accepted method of calculating the mean glandular dose is described by Dance et al (2000):
...
Article
Cardiac strain imaging
Strain imaging is a cardiac imaging technique that detects ventricular deformation patterns and functional abnormalities before they become obvious as regional wall motion abnormalities on conventional cine imaging or echo. It has become more popular lately due to several technological improveme...
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 (...
Article
Cardiac tissue characterization
Cardiac tissue characterization is a term for an approach in cardiac imaging used for the evaluation of the myocardial tissue in respect to its inherent properties as opposed to cardiac function e.g. in cine or strain imaging.
In cardiac magnetic resonance imaging tissue characterization typica...
Article
Late gadolinium enhancement
Late gadolinium enhancement is a technique used in cardiac MRI for cardiac tissue characterization, in particular, the assessment of myocardial scar formation and regional myocardial fibrosis 1-5.
Terminology
Late gadolinium enhancement is also known under the terms ‘late enhancement’ or ‘dela...
Article
T2* mapping - myocardium
T2* mapping is a magnetic resonance imaging technique used to calculate the T2* time of tissue and display them voxel-vice on a parametric map. It is used for myocardial tissue characterization 1-4 and has been investigated for other tissues 5,6.
Clinical applications
T2* relaxation time has b...
Article
Emerging medical imaging technologies
This article is a summary of emerging medical imaging technologies in development or in the early phase of clinical adoption. The methods are listed by modality.
Radiography
dark-field radiography
x-ray phase-contrast imaging
CT
dark-field CT
deep-learning reconstruction
photon counting ...
Article
Photon-counting computed tomography
Photon-counting computed tomography (PCCT) is a new technology in CT that could represent the next major technological milestone in the field. Briefly, photon-counting CT uses energy-resolving detectors, thereby enabling scanning at multiple energies.
Technique
Physical principles
Current cli...
Article
Color-write priority
Color-write priority is an adjustable setting of color Doppler duplex ultrasound and determines whether a particular pixel on the image displays color or grayscale B-mode information at the moment.
Color-write priority is rarely changed directly during routine ultrasound imaging, even though it...
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