Is phase contrast 2D or 3D?
The most commonly used applications today for phase-contrast imaging are: 1) in 2D mode to create a quick vascular scout image prior to performing a non-PC MRA technique; 2) in cine mode to quantify blood flows and velocities within the heart and great vessels; 3) in cine mode for qualitative or quantitative CSF flow …
What is phase contrast MR angiography?
Phase contrast angiography relies on dephasing the moving spins submitted to a bipolar gradient. For a bipolar gradient of a given intensity and time, the moving spins will dephase in proportion to their velocity. Similar to spatial encoding in the phase direction, the possible phase values range from – π to + π.
What is MRI VENC?
VENC stands for velocity encoding, a parameter that must be specified before performing a phase-contrast (PC) MRI or MRA study. VENC, measured in cm/sec, should be chosen to encompass the highest velocities likely to be encountered within the vessel of interest.
What is a phase object?
Depicted ideally, phase objects are samples that change the phase but not the amplitude of a light wave. In contrast, amplitude objects only affect the amplitude but not the phase of light. Flat and unstained cells almost reach the characteristics of a phase object for visible light.
What is the safest MRI contrast agent?
Over the last three decades, gadolinium contrast injections have successfully been used in hundreds of millions of patients. It’s safe, not radioactive and is different (and better) than the contrast agents used for a CT scan. The U.S. Food and Drug Administration has approved Dotarem as safe for use in MRI scans.
What are the most common MRI contrast media and their use?
The most commonly used compounds for contrast enhancement are gadolinium-based. Such MRI contrast agents shorten the relaxation times of nuclei within body tissues following oral or intravenous administration.
What is MRI phase shift?
When the two waves are perfectly in phase with each other, their signals augment each other. When they are slightly out of phase with each other, the overall signal is diminished, and they are said to destructively interfere. When the phase shift between them reaches 180°, the two waves exactly cancel each other.
What are the reasons for performing a 2D vs 3D TOF MRA What is the difference between a phase contrast and a TOF sequence?
2D TOF is commonly used for imaging of long vascular segments running perpendicular to the plane of imaging (like the aorta or femoral arteries). The 3D mode is used for more compact anatomic regions with various flow directions (like the carotid bifurcation, circle of Willis, or renal arteries).
What is a bipolar gradient?
A bipolar gradient pulse is one in which the gradient is turned on in one direction for a period of time then turned on in the opposite direction for an equivalent amount of time. A positive bipolar gradient pulse has the positive lobe first and a negative bipolar gradient pulse has the negative lobe first.
What is velocity encoding in MRI?
Velocity-encoding (Venc) gradients are used to generate a phase shift in magnetic resonance phase contrast imaging proportional to the velocity of moving protons. This phenomenon can be used to depict and measure the velocity of spins and thus flow 1.
What is the advantage of phase contrast microscope?
One of the major advantages of phase contrast microscopy is that living cells can be examined in their natural state without previously being killed, fixed, and stained. As a result, the dynamics of ongoing biological processes can be observed and recorded in high contrast with sharp clarity of minute specimen detail.
What does phase contrast do?
Phase-contrast microscopy is a technique used for gaining contrast in a translucent specimen without staining the specimen. One major advantage is that phase-contrast microscopy can be used with high-resolution objectives, but it requires a specialized condenser and more expensive objectives.
What is the difference between phase and frequency MRI?
The frequency-encoding direction is along the x-axis in K-space (may or may not be that axis in the image, if it is rotated); this represents the time samples of the signal. The y-axis is the phase-encoding direction: each phase-encoding step yields a separate horizontal line.