Articles
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31 results found
Article
MR vessel wall imaging
MR vessel wall imaging (VW-MRI) refers to MRI techniques used to evaluate for disease within the walls of arteries, beyond the luminal abnormalities depicted on angiographic imaging. This can be used anywhere in the body but is particularly important intracranially in distinguishing between vari...
Article
Spontaneous echocardiographic contrast (SEC)
Spontaneous echocardiographic contrast (SEC), also known as “echocardiographic smoke” is an echogenic swirling pattern of blood flow created by enhanced ultrasonic back-scatter from clumping of the cellular components of blood in instances of stagnating or low-velocity (low-flow states) 1. It di...
Article
Contrast-enhanced MR angiography
Contrast-enhanced MR angiography (MRA) is a technique involving 3D spoiled gradient-echo (GE) sequences, with the 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 gra...
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
Doppler angle correction
Doppler angle correction refers to an imaging post-processing method used to adjust for the effects of insonation angle on the Doppler shift.
Measurement of flow velocity with Doppler imaging is dependent on the angle between the ultrasound beam and the target (insonation angle), with the maxim...
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...
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 signal hyperintensity of spins entering into an imaging slice. As a result of being unsaturated, these spins give more sig...
Article
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 3. The US machine can display the Nyquist limit either a...
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
Non contrast enhanced MR angiography
Non-contrast-enhanced MR angiography is a type of MR angiography that does not use gadolinium contrast to image the blood vessels, unlike the contrast enhanced MR angiography.
Techniques
The earliest method that is used to image the blood vessels is by exploiting the inflow effect of the blood...
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
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
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
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
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
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
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
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...
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
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...
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