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Result : Searchterm 'Out of Phase' found in 1 term [] and 17 definitions [], (+ 18 Boolean[] results
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Field Echo with Echo Time set for Water and Fat Signals in OppositionInfoSheet: - Sequences - 
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Gradient Echo SequenceForum -
related threadsInfoSheet: - Sequences - 
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Gradient Echo Sequence Timing Diagram (GRE - sequence) A gradient echo is generated by using a pair of bipolar gradient pulses. In the pulse sequence timing diagram, the basic gradient echo sequence is illustrated. There is no refocusing 180° pulse and the data are sampled during a gradient echo, which is achieved by dephasing the spins with a negatively pulsed gradient before they are rephased by an opposite gradient with opposite polarity to generate the echo.
See also the Pulse Sequence Timing Diagram. There you will find a description of the components.
The excitation pulse is termed the alpha pulse α. It tilts the magnetization by a flip angle α, which is typically between 0° and 90°. With a small flip angle there is a reduction in the value of transverse magnetization that will affect subsequent RF pulses. The flip angle can also be slowly increased during data acquisition (variable flip angle: tilt optimized nonsaturation excitation). The data are not acquired in a steady state, where z-magnetization recovery and destruction by ad-pulses are balanced. However, the z-magnetization is used up by tilting a little more of the remaining z-magnetization into the xy-plane for each acquired imaging line.
Gradient echo imaging is typically accomplished by examining the FID, whereas the read gradient is turned on for localization of the signal in the readout direction. T2* is the characteristic decay time constant associated with the FID. The contrast and signal generated by a gradient echo depend on the size of the longitudinal magnetization and the flip angle. When α = 90° the sequence is identical to the so-called partial saturation or saturation recovery pulse sequence. In standard GRE imaging, this basic pulse sequence is repeated as many times as image lines have to be acquired. Additional gradients or radio frequency pulses are introduced with the aim to spoil to refocus the xy-magnetization at the moment when the spin system is subject to the next α pulse.
As a result of the short repetition time, the z-magnetization cannot fully recover and after a few initial α pulses there is an equilibrium established between z-magnetization recovery and z-magnetization reduction due to the α pulses.
Gradient echoes have a lower SAR, are more sensitive to field inhomogeneities and have a reduced crosstalk, so that a small or no slice gap can be used. In or out of phase imaging depending on the selected TE (and field strength of the magnet) is possible. As the flip angle is decreased, T1 weighting can be maintained by reducing the TR. T2* weighting can be minimized by keeping the TE as short as possible, but pure T2 weighting is not possible. By using a reduced flip angle, some of the magnetization value remains longitudinal (less time needed to achieve full recovery) and for a certain T1 and TR, there exist one flip angle that will give the most signal, known as the "Ernst angle".
Contrast values:
PD weighted: Small flip angle (no T1), long TR (no T1) and short TE (no T2*)
T1 weighted: Large flip angle (70°), short TR (less than 50ms) and short TE
T2* weighted: Small flip angle, some longer TR (100 ms) and long TE (20 ms)

Classification of GRE sequences can be made into four categories:
See also Gradient Recalled Echo Sequence, Spoiled Gradient Echo Sequence, Refocused Gradient Echo Sequence, Ultrafast Gradient Echo Sequence.
 
Images, Movies, Sliders:
 MRI Liver In Phase  Open this link in a new window
    
 MRI Liver Out Of Phase  Open this link in a new window
    
 MVP Parasternal  Open this link in a new window
 Breast MRI Images T1 Pre - Post Contrast  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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Further Reading:
  Basics:
Enhanced Fast GRadient Echo 3-Dimensional (efgre3D) or THRIVE
   by www.mri.tju.edu    
  News & More:
MRI evaluation of fatty liver in day to day practice: Quantitative and qualitative methods
Wednesday, 3 September 2014   by www.sciencedirect.com    
T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI
Monday, 1 September 2008   by www.ncbi.nlm.nih.gov    
MRI Resources 
Cardiovascular Imaging - RIS - Shoulder MRI - MRI Centers - Chemistry - Pediatric and Fetal MRI
 
Imaginary Signal
 
Out of phase component of the signal from a quadrature detector.
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Further Reading:
  Basics:
Imaginary Number
   by mathworld.wolfram.com    
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In Phase Image
 
The term in phase refers to an image in which the signals from two spectral components (such as fat and water) add constructively in a voxel. T1 weighted in phase images are acquired by a gradient echo-based technique with a short TR, TE and a high flip angle greater than 60 degrees. To some degree, in phase sequences are more sensitive to detection of focal hepatic lesions than out of phase for evaluating reduced lesion-to-liver contrast, but the choice for a T1 gradient echo sequence is still based on field strength, advanced imaging techniques (breath hold imaging), and physician preference.
 
Images, Movies, Sliders:
 MRI Liver In Phase  Open this link in a new window
    
 
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Further Reading:
  News & More:
Direct Water and Fat Determination in Two-Point Dixon Imaging
April 2013   by scholarship.rice.edu    
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Ultrasound  (1) Open this link in a new window
Quadrature Detector
 
The quadrature detector is a part of the receiver that converts the high-frequency MRI signal to a lower frequency. This phase sensitive detector or demodulator detects the components of the signal in phase with a reference signal and 90° out of phase with the reference signal. The modulated signal contains i.e. the frequency range across the field of view encoded by the frequency encoding gradient. This may be performed by either analog or digital means.
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