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
MRI sequences (overview)
An MRI sequence is a number of radiofrequency pulses and gradients that result in a set of images with a particular appearance. This article presents a simplified approach to recognizing common MRI sequences, but does not concern itself with the particulars of each sequence.
For a more complete...
Article
Dixon method
The Dixon method, also known as the Dixon technique, is an MRI sequence based on chemical shift imaging and designed to achieve uniform fat suppression. It has been gaining popularity as it has some advantages over other fat suppression techniques, namely:
suppression of fat signal is more unif...
Article
Direct digital radiography
Direct digital radiography (abbreviated as DR, DDR, or DX) is a type of digital radiography in which the digital registration of the image takes place directly at the detector with no intermediate processing step such as cassette readout in computed radiography (CR).
Terminology
Direct digital...
Article
Vicarious contrast media excretion
Vicarious contrast media excretion (VCME) refers to the excretion of intravascularly-administered water-soluble iodinated contrast media in a way other than via normal renal excretion. More rarely it may occur following oral contrast medium administration 6.
Epidemiology
The most common vicari...
Article
Radiology information system
A radiology information system, also referred to as RIS, is software for patient management in radiology, complementary to PACS. While systems vary and are usually customized for institutions, most systems provide some of the following functions:
patient scheduling and list management
predefin...
Article
Flash mode (CEUS)
Flash mode is a technique specific to CEUS-capable ultrasound devices, and in brief is a short ultrasound pulse with a very high mechanical index, resulting in almost complete destruction of the contrast agent microbubbles in the imaging plane.
Physics
The microbubbles utilized as contrast ag...
Article
Diffusion-weighted imaging in acute ischemic stroke
Diffusion-weighted imaging (DWI) is a commonly performed MRI sequence for the evaluation of acute ischemic stroke and is very sensitive in the detection of small and early infarcts. Conventional MRI sequences (T1WI, T2WI) may not demonstrate an infarct for 6 hours, and small infarcts may be hard...
Article
Electronvolt (unit)
An electronvolt (eV) is defined as the energy required to accelerate a single electron at rest through an electron potential difference of one volt in a vacuum 3. This is different from the electrical potential difference applied to the X-ray tube in terms of kiloVolts (kV) 3. However, the kV ap...
Article
Mean transit time (MTT)
Mean transit time (MTT) corresponds to the average time, in seconds, that red blood cells spend within a determinate volume of capillary circulation. It is assessed as part of the CT perfusion protocol and MR perfusion.
Mean transit time is calculated by dividing cerebral blood volume (CBV) by ...
Article
MRI in patients with pacemaker systems
MRI in patients with cardiac implantable electronic devices (CIED) has increasingly become a requirement in radiological departments 1-8. Especially in the setting of patients with MR conditional pacemaker systems, where all the manufacturer's instructions are followed and a standardized institu...
Article
T2 shine through
T2 shine-through refers to high signal on DWI images that is not due to restricted diffusion, but rather to high T2 signal which 'shines through' to the DWI image. T2 shine through occurs because of long T2 decay time in some normal tissue.
This is most often seen with subacute infarctions due ...
Article
C-arm
C-arm is a term employed to refer to image intensifiers used in a variety of settings, including interventional suites and operating theaters. The machine is similar to the letter ''C'' in its appearance with the x-ray tube on one end and the image intensifier on another.
Article
Acoustic impedance
Acoustic impedance (Z) is a physical property of tissue. It describes how much resistance an ultrasound beam encounters as it passes through a tissue.
Acoustic impedance depends on:
the physical density of the tissue (d, in kg/m3)
the velocity of the soundwave transmitted through the tissue m...
Article
Contrast enhancement
Contrast enhancement is a ubiquitous term in radiology and can be used in three ways.
Firstly, it may refer to any method of exaggerating the visible difference between adjacent structures on imaging by administering contrast media/agents. This includes differentiating between normal structure...
Article
Power Doppler
Power Doppler is a technique that uses the amplitude of Doppler signal to detect moving matter. Power Doppler:
is independent of velocity and direction of flow, so there is no possibility of signal aliasing
is independent of angle, allowing detection of smaller velocities than color Doppler, f...
Article
Peak systolic velocity (Doppler ultrasound)
Peak systolic velocity (PSV) is an index measured in spectral Doppler ultrasound. On a Doppler waveform, the peak systolic velocity corresponds to each tall “peak” in the spectrum window 1.
Explanation
When traveling with their greatest velocity in a vessel (i.e. during systole), red blood cel...
Article
Kerma
Kerma is a measure of energy transferred from radiation to matter and is an acronym for kinetic energy released to matter. It is related to, but not the same as absorbed dose. Kerma is measured by the SI unit, the gray (joules per kilogram) 1,3.
Kerma measures the amount of energy that is trans...
Article
Speckle artifact
Speckle artifact may be encountered in ultrasound. It is caused by the scattering of waves from the surface of small structures within a certain tissue. The artifact produces a textured appearance.
Because speckle can make it harder to distinguish soft tissue differences, modern ultrasound mac...
Article
Thallium-201 scintigraphy
Thallium-201 (Tl-201) is a radiopharmaceutical used for scintigraphy, primarily of the myocardium. The element thallium is treated by the body as an analog of potassium; it is produced in a cyclotron by bombarding thallium-203 with protons.
Characteristics
thallium is a monovalent cation
usua...
Article
Gadolinium contrast agents
Gadolinium-based contrast media (GBCM), gadolinium-based contrast agents (GBCAs), or simply gadolinium contrast agents, are molecular complexes containing the rare earth metal gadolinium, chelated to a carrier ligand. They are a type of paramagnetic contrast agent, which are the primary class of...
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