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
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...
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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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Virtual reality
Virtual reality (VR) is an imaging technology that uses high-resolution computer-generated graphics and multi-sensor interaction technologies to provide an immersion into a virtual or artificial digital world.
Unlike augmented reality (AR) which overlays simulated objects into the real-world ba...
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
Radiation-induced lung cancer
Radiation-induced lung cancers are a potential long-term complication of radiotherapy to the chest.
Besides lung cancer, sarcomas (osteosarcomas are the most common arising from the irradiated bones, and malignant fibrous histiocytomas the most frequently arising from the soft tissues), breast...
Article
Dual-energy CT - clinical applications
Dual-energy CT or spectral CT is a computed tomography technique becoming increasingly common in clinical practice due to the rapid rise in computer technology and expanding literature exhibiting vast advantages over conventional single-energy CT.
This article is limited to its clinical applica...
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NIfTI (file format)
NIfTI is a type of file format for neuroimaging. Technically there are two NIfTI file format versions, the NIfTI-1 and NIfTI-2 file formats 1. The NIfTI-2 format is an update on NIfTI-1 that allows more data to be stored 1.
Clinical applications
NIfTI files are used very commonly in imaging in...
Article
Pixel
A pixel (or pel or picture element) may refer to either the smallest discrete element of the physical display or to the smallest element of an image 1,2. Voxel is its 3-dimensional equivalent, as employed in CT and other cross-sectional imaging modalities.
History and etymology
The history of ...
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 ...
Article
T1 values (1.5 T)
T1 values are a few hundred milliseconds (ms) for most tissues examined.
The following are approximate T1 values (ms) of several tissues for B0 = 1.5 T
fat = 260
liver = 500
muscle = 870
brain white matter = 780
brain grey matter = 920
CSF = 2500
Tissues that will have high signal on T1-...
Article
X-ray interaction with matter
X-rays in the diagnostic range interact with matter primarily via two major processes, which are fundamental in understanding how an image is formed in a radiographic exam. These processes are the:
photoelectric effect
Compton scatter
Article
K-trans (MR perfusion)
Ktrans is a measure of capillary permeability obtained using dynamic contrast-enhanced (DCE) MR perfusion. It is calculated by measuring the accumulation of gadolinium-based contrast agent in the extravascular-extracellular space.
Increased permeability of vessels in the brain is seen in a var...
Article
Entry slice phenomenon
Entry slice phenomenon occurs when unsaturated spins in blood first enter into a slice or slices. It is characterized by the bright signal in a blood vessel (artery or vein) at the first slice that the vessel enters. Usually, the signal is seen on more than one slice, fading with distance. This ...
Article
Pierre Curie
Pierre Curie (1859–1906) was a French physicist who was co-awarded the Nobel Prize for Physics in 1903, with his wife Marie Curie, and Henri Becquerel, for their pioneering work on radioactivity, which included the joint discovery with his wife of radium and polonium. He also discovered piezoele...
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Ring down artifact
Ring down artifact is a special type of resonance artifact. Its appearance is similar to the ladder-like reverberation of comet-tail artifact, but it is produced by a completely different mechanism.
The artifact is only associated with gas bubbles, and occurs when an ultrasound pulse encounters...
Article
Phase-encoded motion artifact
Phase-encoded motion artifact is one of many MRI artifacts occurring as a result of tissue/fluid moving during the scan. It manifests as ghosting in the direction of phase-encoding, usually in the direction of the short axis of the image (i.e left to right on axial or coronal brains, and anterio...
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
Helical CT image acquisition
Helical (a.k.a. spiral) CT image acquisition was a major advance on the earlier stepwise ("stop and shoot") method.
With helical CT, the patient is moved through a rotating x-ray beam and detector set. From the perspective of the patient, the x-ray beam from the CT traces a helical path. The he...
Article
Free induction decay
Free induction decay (FID) refers to a short-lived sinusoidal electromagnetic signal which appears immediately following the 90° pulse. It is induced in the receiver coil by the rotating component of the magnetization vector in the x-y plane which crosses the coil loops perpendicularly. It does ...
Article
RANZCR applied imaging technology examination
The RANZCR applied imaging technology (AIT) examination is one of two examinations comprising the RANZCR Phase 1 examinations, with the other examination being the anatomy examination.
These examinations can be sat together or independent of each other, however, trainees have a maximum of four ...
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