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 edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

15 results found
Article

Blooming artifact (ultrasound)

Blooming or color bleed artifact occurs when the color signal indicating blood flow extends beyond its true boundaries, spreading into adjacent regions with no actual flow. This artifact mainly affects the portion of the image distal to the vessel and the transducers. It is somewhat similar to ...
Article

Cardiac MRI

Cardiac MRI consists of using MRI to study heart anatomy, physiology, and pathology. Advantages In comparison to other techniques, cardiac MRI offers: improved soft tissue definition protocol can be tailored to likely differential diagnoses a large number of sequences are available dynamic...
Article

Contrast enhanced MR angiography

Contrast enhanced MR angiography (MRA) is a technique involving 3D spoiled gradient-echo (GE) sequences, with administration of gadolinium-based contrast agents (GBCA). It can be used to assess vascular structures of almost any part of the body. Its key features are: T1 weighted spoiled gradien...
Article

Diastolic pseudogating

Diastolic pseudogating appears as periodic bright and dark signal in arteries such as the aorta as one progresses through a series of images. Synchronization of the cardiac cycle and the pulse sequence results in high signal in the artery during diastole when blood is relatively stationary and l...
Article

Doppler angle

Doppler angle corrects for the usual clinical situation when an ultrasound beam is not parallel to the Doppler signal. For instance, if one wants to evaluate an artery, the best angle for evaluation would be at zero degrees (parallel to the vessel). The strongest signal and best waveforms would...
Article

Doppler waveforms

Doppler waveforms are often misinterpreted and/or overlooked. They can provide great deal of information if carefully understood. Radiographic features Ultrasound Doppler When interrogating flow with spectral Doppler, the three basic arterial waveforms are 1,2: triphasic forward flow in sy...
Article

Maximum intensity projection

Maximum Intensity Projection (MIP) consists of projecting the voxel with the highest attenuation value on every view throughout the volume onto a 2D image 1. Such an algorithm is rather simple: for each XY coordinate, only the pixel with the highest Hounsfield number along the Z-axis is represe...
Article

Phase contrast imaging

Phase contrast imaging is an MRI technique that can be used to visualize moving fluid. It is typically used for MR venography as a non-IV-contrast requiring technique.  Spins that are moving in the same direction as a magnetic field gradient develop a phase shift that is proportional to the vel...
Article

Portosystemic shunt ratio

The portosystemic shunt ratio is a measure performed using ultrasound to quantify the abnormal flow of portal venous blood that is shunted away from the hepatic sinusoidal circulation in the context of a congenital portosystemic shunt 1. Ultrasound The ratio is determined using the following e...
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

Pulsatile portal venous flow

A pulsatile portal venous flow pattern can result from both physiological and pathological causes. In well subjects mild pulsatility, or in rare situations, even marked pulsatility has been described, particularly in thin subjects, with a venous pulsatility index of >0.5 with an inverse correla...
Article

Pulsatility index (ultrasound)

The pulsatility index is a calculated flow parameter in ultrasound, derived from the maximum, minimum, and mean Doppler frequency shifts during a defined cardiac cycle. Along with the resistivity index (RI), it is typically used to assess the resistance in a vascular system. Terminology Pulsat...
Article

Spectral Doppler (ultrasound)

Utilizing automated Fourier analysis to convert returning sound waves into a series of individual frequencies, spectral Doppler refers to ultrasound modalities which yield graphical representations of flow velocity over time.  Terminology The frequency of the sound waves returned to an ultraso...
Article

Tc-99m labeled RBC

Tc-99m labeled RBC is one of the technetium radiopharmaceuticals used in the assessment of GI bleeding. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life:  normal distribution: heart, vessels, spleen miscellaneous facts: threshold for detection is 0.0...
Article

Time of flight angiography

Time of flight angiography (TOF) is an MRI technique to visualize flow within vessels, without the need to administer contrast. It is based on the phenomenon of flow-related enhancement of spins entering into an imaging slice. As a result of being unsaturated, these spins give more signal that s...

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