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
Multipath artifact
A multipath artifact is an ultrasound beam artifact in which the primary beam reflects off anatomy at an angle, resulting in a portion of the beam returning to the transducer, whilst another portion takes a longer duration as it reflects a second structure. This phenomenon results in a propagati...
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
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
Sievert (SI unit)
The sievert (symbol Sv) is the SI unit of dose equivalent and is dimensionally-equivalent to one joule per kilogram. The sievert represents the stochastic effects of ionizing radiation as adjusted by a tissue weighting factor to account for differing responses of different human tissues to ioniz...
Article
Fourier transformation
The Fourier transform is a mathematical formula that converts a signal in time (or spatial) domain t to one in the frequency domain ω.
A frequency domain signal F(ω) is obtained by modulating the time domain signal f(t) to a special sinusoidal wave e-jωt across all time (from negative infinity ...
Article
Cross-excitation artifact (MRI)
Cross-excitation artifact is a type of MRI artifact and refers to the loss of signal within a slice due to pre-excitation from RF pulse meant for an adjacent slice.
The frequency profile of the RF pulse is imperfect; this means that during slice selection there is some degree of excitation of t...
Article
Radicals
Radicals (formerly called free radicals) are uncharged atoms or molecules in which an electron orbit has a single unpaired electron.
Terminology
Historically the International Union of Pure and Applied Chemistry (IUPAC) also used the term radical for any joined up group of atoms forming a side...
Article
Octreotide scintigraphy
Octreotide scintigraphy uses 111In-labeled octreotide, which is a somatostatin analog; it is also known as Octreoscan, a brand name for 111In-labeled pentetreotide. Pentetreotide is a DTPA-conjugated form of octreotide, originally manufactured by Mallinckrodt Nuclear Medicine LLC, which now form...
Article
Photocathode
A photocathode is a negatively charged electrode in a light detection device such as the input screen in an image intensifier (II) that is coated with a photosensitive compound. When this is struck by light photons, the absorbed energy causes electron emission due to the photoelectric (PE) effec...
Article
CT stair-step artifact
The CT stair-step artifact is found in straight structures which are oriented obliquely with respect to movement of the table and appear around the edges of sagittal and coronal reformatted images when wide collimations and non-overlapping reconstruction intervals are used.
It is also seen in c...
Article
Color flash artifact
The color flash artifact is a commonly encountered artifact on color Doppler ultrasound, representing spurious flow signal arising due to tissue/transducer motion.
Physics
The flash artifact is caused by movement of reflective tissues (e.g. due to respiration), or the transducer, which genera...
Article
Fiber assignment by continuous tracking algorithm (FACT)
Fiber assignment by continuous tracking (FACT) algorithms are a commonly used deterministic post-processing algorithm for magnetic resonance tractography studies.
In these algorithms, axonal fiber bundles are reconstructed - voxel by voxel - following the direction of the main eigenvector. The ...
Article
Paul Lauterbur
Paul C Lauterbur (1929-2007) is remembered as one of the co-developers of MRI, for which he was co-awarded the Nobel Prize for Medicine or Physiology in 2003, with Peter Mansfield.
Early life
Paul Christian Lauterbur was born on 6 May 1929 in Sidney, Ohio.
In 1951 he graduated with a bachelor...
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
High-resolution CT
High-resolution CT (HRCT) is a scanning protocol in which thin sections (usually 0.625 to 1.25 mm) are acquired and reconstructed using a sharp algorithm (e.g. bone algorithm).
It has been classically used for:
interstitial lung disease imaging: HRCT chest
temporal bone imaging
Article
Flip angle
The flip angle is an MRI phenomenon by which the axis of the hydrogen proton shifts from its longitudinal plane (static magnetic field B0) Z axis to its transverse plane XY axis by excitation with the help of radiofrequency (RF) pulses. A RF pulse is sent in at the precise Larmor frequency in re...
Article
Film dosimeter
Film dosimeters are used to measure radiation exposure to workers to monitor radiation safety and ensuring that they receive doses below the appropriate limit.
Film badges are the cheapest and most common monitoring device. They consist of a small case with a piece of film situated between fil...
Article
SeHCAT
SeHCAT™ (23-seleno-25-homo-tauro-cholic acid or tauroselcholic acid) is a radiopharmaceutical used in the investigation of bile salt malabsorption, which is a cause of chronic diarrhea.
Characteristics
physical half-life: 118 days
Uses, dosage and timings
A capsule containing SeHCAT is inge...
Article
Magnetic field homogeneity
One of the key concepts in assessing the quality of a magnet is that of magnetic field homogeneity, as it will relate to image quality and the presence of artifacts.Field homogeneity refers to the uniformity of the main magnetic field when no patient is present, measured in parts per million (pp...
Article
Repetition time
The repetition time (TR) is the time from the application of an excitation pulse to the application of the next pulse. It determines how much longitudinal magnetization recovers between each pulse. It is measured in milliseconds.
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