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.

28 results found
Article

LumiFlow

LumiFlow is a postprocessing technique for color or power Doppler ultrasound, which produces a relief-like visualization of the depicted vasculature.  Physics Lumiflow can be applied to both color and power Doppler imaging. It applies a shading with an artifical light source to create a three-...
Article

CT pelvis (protocol)

The CT pelvis protocol serves as an outline for the acquisition of a pelvic CT. As a separate examination, it might be performed as a non-contrast or contrast study or might be combined with a CT hip or rarely with a CT cystogram. A pelvic CT might be also conducted as a part of other scans such...
Article

Velocity encoding

Velocity encoding or Venc is referred to as an operator-controlled parameter for the determination of the maximum velocity within a velocity encoded phase contrast imaging study. Usage Velocity-encoding (Venc) gradients are used to generate a phase shift in magnetic resonance phase contrast im...
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Nyquist limit

The Nyquist limit represents the maximum Doppler shift frequency that can be correctly measured without resulting in aliasing in color or pulsed wave ultrasound.  Physics The Nyquist limit always equals Pulse Repetition Frequency (PRF)/2. The US machine can display the Nyquist limit either as ...
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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

Reynolds number

The Reynolds number (Re) is the primary parameter used to define the transition of fluid motion between laminar and turbulent flow patterns 1. The Reynolds number represents the ratio of inertia forces to viscous forces, and as such has no units (i.e. is a dimensionless quantity) 1.  Calculatio...
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End-diastolic velocity (Doppler ultrasound)

End-diastolic velocity (EDV) is an index measured in spectral Doppler ultrasound. On a Doppler waveform, the EDV corresponds to the point marked at the end of the cardiac cycle (just prior to the systolic peak) 1. In some equipment, the timing of cardiac cycle events may be automatically marked ...
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

Intima-media thickness

Intima-media thickness (IMT) is an indirect sonographic assessment of the degree of atheromatous vascular disease of end organs. The thickness of the media and the intima of the vessels changes following many conditions and it can be easily and reliably assessed with ultrasound on B mode in the ...
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

Electrical interference artifact (ultrasound)

Electrical interference artifact is an ultrasound artifact usually caused by the ultrasound machine being too close to the unshielded electrical equipment. The disturbance appears as arc-like moving bands in the ultrasound image.  While the presence of electrical equipment  (e.g unshielded vent...
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

Pulsatility index (ultrasound)

The pulsatility index (PI) (also known as the Gosling 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 resistive index (RI), it is typically used to assess the resistance in a ...
Article

Indocyanine green lymphangiography

Indocyanine green (ICG) lymphangiography is an emerging imaging technique used to visualize lymphatic vessels and map their course as they drain to sentinel lymph nodes.  History Indocyanine green is a fluorescent dye discovered by researchers at Kodak working on near-infrared photography in 1...
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

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

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. Measurement The ratio is determined on ultrasound using ...
Article

Doppler waveforms

Doppler waveforms refer to the morphology of pulsatile blood flow velocity tracings on spectral Doppler ultrasound. Waveforms differ by the vascular bed (peripheral, cerebrovascular, and visceral circulations) and the presence of disease. Radiographic features Ultrasound Doppler Most authori...
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

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

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. Synchronisation 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

Phase contrast imaging

Phase contrast imaging is an MRI technique that can be used to visualize moving fluid. Basic principle Spins that are moving in the same direction as a magnetic field gradient develop a phase shift that is proportional to the velocity of the spins. This is the basis of phase-contrast angiograp...
Article

Pulsatile portal venous flow

A pulsatile portal venous flow pattern is an abnormal form of portal venous flow and 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 pul...
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

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 than s...
Article

Scintigraphy performed with Tc-99m labeled RBCs

Tc-99m labeled RBCs - with radiolabelling technique in vivo or in vitro of red cells 3 - is one of the technetium radiopharmaceuticals used in the non-invasive assessment of gastrointestinal (GI) bleeding 2, characterized by high sensitivity (93%) and specificity (95%) 4. It is capable, in fact,...
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

Abnormal ductus venosus waveforms

Abnormal ductus venosus waveforms can arise in a number of conditions ranging from aneuploidy to vascular malformations and fetal tumors. "A wave" reversal can be seen in 5% of euploid fetuses 9. Pathology Abnormal waveforms in fetal ductus venosus flow assessment can occur in a number of situ...

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