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
Creatine peak
Creatine is one of the compounds examined in MR spectroscopy. It resonates at 3.0 ppm chemical shift (with a second usually smaller peak at 3.95 ppm 2).
It is found in metabolically active tissues (brain, muscle, heart), where it is important in the storage and transfer of energy. It tends to b...
Article
Receiver operating characteristic curve
The receiver operating characteristic (ROC) curve is a statistical relationship used frequently in radiology, particularly with regards to limits of detection and screening.
The curves on the graph demonstrate the inherent trade-off between sensitivity and specificity:
y-axis: sensitivity
x-a...
Article
Sensitivity
Sensitivity is one of the 4 basic diagnostic test metrics in addition to specificity, positive predictive value and negative predictive value. Sensitivity is a measure of how good a diagnostic test is at detecting disease when it is present and is calculated by dividing the number of true positi...
Article
Specificity
Specificity is one of the 4 basic diagnostic test metrics in addition to sensitivity, positive predictive value and negative predictive value. Specificity is a measure of how good a diagnostic test is at identifying people who are healthy and is calculated by dividing the number of true negative...
Article
Sensitivity and specificity
Sensitivity and specificity are fundamental characteristics of diagnostic imaging tests.
The two characteristics derive from a 2x2 box of basic, mutually exclusive outcomes from a diagnostic test:
true positive (TP): an imaging test is positive and the patient has the disease/condition
false ...
Article
Image compression
Image compression is a technique applied to digital images to decrease the amount of space required to store an image and increase the speed with which the image can be retrieved or transmitted.
Compression may be lossless or lossy:
lossless compression retains all original data, for example P...
Article
Grids
Grids are placed between the patient and the x-ray film to reduce the scattered radiation reaching the detector (produced mainly by the Compton effect) and thus improve image contrast.
They are made of parallel strips of high attenuating material such as lead with an interspace filled with low ...
Article
Positron emission tomography
Positron emission tomography (PET) is a modern non-invasive imaging technique for quantification of radioactivity in vivo. It involves the intravenous injection of a positron-emitting radiopharmaceutical, waiting to allow for systemic distribution, and then scanning for detection and quantificat...
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 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 uniform and ...
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
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
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
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.
Unable to process the form. Check for errors and try again.