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
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
Gauss (unit)
The gauss (symbol: G or Gs) is a legacy CGS unit of magnetic flux density, which was superseded by the tesla (T). One gauss is defined as one maxwell per cm2 (Mx/cm2), which equates to 10-4 tesla, and is therefore a small unit. This is one of the reasons for its stubborn persistence in some scie...
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
Dose limits
Dose limits are recommended by the International Commission on Radiological Protection (ICRP). They are in place to ensure that individuals are not exposed to an unnecessarily high amount of ionizing radiation. Dose limits are a fundamental component of radiation protection, and breaching these ...
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
Thermoluminescent dosimeter
Thermoluminescent dosimeter (TLD) is a passive radiation detection device that is used for personal dose monitoring or to measure patient dose.
Parts
plastic holder
nickel-coated aluminum card with TLD discs
the discs are made of a thermoluminescent material, commonly calcium sulphate doped...
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
Radiofrequency transmitter
The radiofrequency (RF) transmitter is the generator of the radiofrequency current which is delivered to the transmitting coil. This creates a signal which is used to excite protons in the imaging field. Radiofrequency coils can be both transmitters and receivers of the radiofrequency signal or ...
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
Peter Mansfield
Sir Peter Mansfield (1933-2017) was an English physicist best known for his research into, and development of MRI, for which he was awarded the Nobel Prize in Physiology or Medicine in 2003 1.
Early life
Peter Mansfield was born on the 9 October, 1933 in Lambeth, London. His father, Sidney wor...
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.
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...
Article
Axial plane for imaging of the brain
A consistent axial plane for imaging of the brain needs to be chosen to allow for reproducible image acquisition and comparison. Unlike the sagittal plane, which is intrinsically defined by our inherent left-right plane of symmetry, axial and coronal planes need to be agreed upon and over the ye...
Article
Dexel
Dexels, a portmanteau of detector elements, analogous to pixels, refers to the individual radiation-sensitive elements of the detector component of a scanner, e.g. computed tomography. It is important to appreciate that there is not necessarily a one-to-one correspondence between dexels and the ...
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