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 'Gradient Echo Multi Slice' 
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Multiplanar Gradient Recalled Acquisition in the Steady StateInfoSheet: - Sequences - 
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(MPGR) Multiplanar gradient recalled acquisition in the steady state is a term for a fast gradient echo sequence with slice selective RF pulses.

See Gradient Recalled Echo Sequence and Gradient Echo Sequence.
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PRinciples of Echo Shifting using a Train of ObservationsInfoSheet: - Sequences - 
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(PRESTO) PRESTO is a 3 dimensional ultrafast gradient echo sequence that combines the whole brain coverage with T2* weighted imaging. PRESTO is useful for BOLD and perfusion imaging studies. In combination with parallel imaging techniques, PRESTO provides higher temporal resolution and more coverage compared to traditional multi slice imaging. In addition, the sensitivity to susceptibility artifacts and flow phenomena is reduced, compared with EPI techniques, enabling MRI scans throughout the brain including the skull base.

See also T2 Star.
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• View the DATABASE results for 'PRinciples of Echo Shifting using a Train of Observations' (2).Open this link in a new window

 
Further Reading:
  News & More:
Chest MRI Using Multivane-XD, a Novel T2-Weighted Free Breathing MR Sequence
Thursday, 11 July 2019   by www.sciencedirect.co    
T2-Weighted Liver MRI Using the MultiVane Technique at 3T: Comparison with Conventional T2-Weighted MRI
Friday, 16 October 2015   by www.ncbi.nlm.nih.gov    
MRI Resources 
Breast Implant - Fluorescence - Safety Training - Stent - MR Myelography - Libraries
 
Time of Flight AngiographyInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - MRA -
 
(TOF) The time of flight angiography is used for the imaging of vessels. Usually the sequence type is a gradient echo sequences with short TR, acquired with slices perpendicular to the direction of blood flow.
The source of diverse flow effects is the difference between the unsaturated and presaturated spins and creates a bright vascular image without the invasive use of contrast media. Flowing blood moves unsaturated spins from outside the slice into the imaging plane. These completely relaxed spins have full equilibrium magnetization and produce (when entering the imaging plane) a much higher signal than stationary spins if a gradient echo sequence is generated. This flow related enhancement is also referred to as entry slice phenomenon, or inflow enhancement.
Performing a presaturation slab on one side parallel to the slice can selectively destroy the MR signal from the in-flowing blood from this side of the slice. This allows the technique to be flow direction sensitive and to separate arteriograms or venograms. When the local magnetization of moving blood is selectively altered in a region, e.g. by selective excitation, it carries the altered magnetization with it when it moves, thus tagging the selected region for times on the order of the relaxation times.
For maximum flow signal, a complete new part of blood has to enter the slice every repetition (TR) period, which makes time of flight angiography sensitive to flow-velocity. The choice of TR and slice thickness should be appropriate to the expected flow-velocities because even small changes in slice thickness influences the performance of the TOF sequence. The use of sequential 2 dimensional Fourier transformation (2DFT) slices, 3DFT slabs, or multiple 3D slabs (chunks) are depending on the coverage required and the range of flow-velocities.
3D TOF MRA is routinely used for evaluating the Circle of Willis.

See also Magnetic Resonance Angiography and Contrast Enhanced Magnetic Resonance Angiography.
 
Images, Movies, Sliders:
 TOF-MRA Circle of Willis Inverted MIP  Open this link in a new window
    

 Circle of Willis, Time of Flight, MIP  Open this link in a new window
    
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Radiology-tip.comradCT Angiography,  Coronary Angiogram
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Medical-Ultrasound-Imaging.comColor Power Angio,  Doppler Ultrasound
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• View the DATABASE results for 'Time of Flight Angiography' (11).Open this link in a new window

 
Further Reading:
  Basics:
MR–ANGIOGRAPHY(.pdf)
  News & More:
Magnetic resonance angiography: current status and future directions
Wednesday, 9 March 2011   by www.jcmr-online.com    
MRI Resources 
Mobile MRI - Breast Implant - Quality Advice - Diffusion Weighted Imaging - Research Labs - Claustrophobia
 
Contrast Enhanced Gradient Echo SequenceInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
Contrast enhanced GRE sequences provide T2 contrast but have a relatively poor SNR. Repetitive RF pulses with small flip angles together with appropriate gradient profiles lead to the superposition of two resonance signals.
The first signal is due to the free induction decay FID observed after the first and all ensuing RF excitations.
The second is a resonance signal obtained as a result of a spin echo generated by the second and all addicted RF-pulses.
Hence it is absent after the first excitation, it is a result of the free induction decay of the second to last RF-excitation and has a TE, which is almost 2TR. For this echo to occur the gradients have to be completely symmetrical relative to the half time between two RF-pulses, a condition that makes it difficult to integrate this pulse sequence into a multiple slice imaging technique. The second signal not only contains echo contributions from free induction decay, but obviously weakened by T2-decay. Since the echo is generated by a RF-pulse, it is truly T2 rather than T2* weighted. Correspondingly it is also less sensitive to susceptibility changes and field inhomogeneities.
Companies use different acronyms to describe certain techniques.
Different terms (see also acronyms) for these gradient echo pulse sequences:
CE-FAST Contrast Enhanced Fourier Acquired Steady State,
CE-FFE Contrast Enhanced Fast Field Echo,
CE-GRE Contrast Enhanced Gradient-Echo,
DE-FGR Driven Equilibrium FGR,
FADE FASE Acquisition Double Echo,
PSIF Reverse Fast Imaging with Steady State Precession,
SSFP Steady State Free Precession,
T2 FFE Contrast Enhanced Fast Field Echo (T2 weighted).

In this context, 'contrast enhanced' refers to the pulse sequence, it does not mean enhancement with a contrast agent.
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• View the DATABASE results for 'Contrast Enhanced Gradient Echo Sequence' (4).Open this link in a new window

MRI Resources 
Shielding - Breast MRI - MR Myelography - Service and Support - MRA - Coils
 
Echo Spacing
 
Echo spacing is the distance in time between the echoes in multiple echo sequences like, e.g. echo planar imaging, fast spin echo. A short echo space produces compact sequence timing and less image artifacts. The shorter the rise time, the faster the gradients and therefore the echo spacing. Gradients with a shorter echo spacing will have a better resolution and more slices per TR.

See also Fast Spin Echo.
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• View the DATABASE results for 'Echo Spacing' (6).Open this link in a new window

 
Further Reading:
  Basics:
Fast Spin Echo(.pdf)
Tuesday, 24 January 2006   by www.81bones.net    
MRI Resources 
Liver Imaging - Abdominal Imaging - Directories - Research Labs - Process Analysis - Used and Refurbished MRI Equipment
 
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