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Result : Searchterm 'Fast Field Echo' found in 5 terms [] and 5 definitions [], (+ 15 Boolean[] results
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From ISOL Technology
'Ultra high field MR system, it's right close to you.
FORTE 3.0T is the new standard for the future ultra high field MR system.
If you are pushing the limits of your existing clinical MR scanner, the FORTE will surely take you to the next level of diagnostic imaging.
FORTE is the core leader of the medical technology in the 21st century. Proving effects of fMRI that cannot be measured with MRI less than 2.0T.'
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Short bore compact
128 x 128, 256 x 256, 512 x 512, 1024 x 1024
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From ISOL Technology
'RELAX is open type MRI system created by making up for the weakness of existing conventional MR systems and applying the strength and the application of the middle to high field MR without uncompromising the image quality.
RELAX offers you a premium mix of form, performance and functionality that are patient and user
friendly beyond comparison.
- New breed of MRI pursuing
- patients comfort'
Device Information and Specification CLINICAL APPLICATION Whole body lower than 2.4 m from the iso-center | | | | • View the DATABASE results for 'RELAX 0.35T™' (2).
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In simple ultra fast GRE imaging, TR and TE are so short, that tissues have a poor imaging signal and - more importantly - poor contrast except when contrast media enhanced ( contrast enhanced angiography). Therefore, the magnetization is 'prepared' during the preparation module, most frequently by an initial 180° inversion pulse.
In the pulse sequence timing diagram, the basic ultra fast gradient echo sequence is illustrated. The 180° inversion pulse is executed one time (to the left of the vertical line), the right side represents the data collection period and is often repeated depending on the acquisition parameters.
See also Pulse Sequence Timing Diagram, there you will find a description of the components.
Ultra fast GRE sequences have a short TR,TE, a low flip angle and TR is so short that image acquisition lasts less than 1 second and typically less than 500 ms. Common TR: 3-5 msec, TE: 2 msec, and the flip angle is about 5°.
Such sequences are often labeled with the prefix 'Turbo' like TurboFLASH, TurboFFE and TurboGRASS.
This allows one to center the subsequent ultra fast GRE data acquisition around the inversion time TI, where one of the tissues of interest has very little signal as its z-magnetization is passing through zero.
Unlike a standard inversion recovery (IR) sequence, all lines or a substantial segment of k-space image lines are acquired after a single inversion pulse, which can then together be considered as readout module. The readout module may use a variable flip angle approach, or the data acquisition may be divided into multiple segments (shots). The latter is useful particularly in cardiac imaging where acquiring all lines in a single segment may take too long relative to the cardiac cycle to provide adequate temporal resolution.
If multiple lines are acquired after a single pulse, the pulse sequence is a type of gradient echo echo planar imaging (EPI) pulse sequence. See also Magnetization Prepared Rapid Gradient Echo ( MPRAGE) and Turbo Field Echo ( TFE). | | | | • View the DATABASE results for 'Ultrafast Gradient Echo Sequence' (13).
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(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.
| | | | | | • View the DATABASE results for 'Gradient Echo Sequence' (70).
| | | | Further Reading: | | Basics:
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'Next generation MRI system 1.5T CHORUS developed by ISOL Technology is optimized for both clinical diagnostic imaging and for research development.
CHORUS offers the complete range of feature oriented advanced imaging techniques- for both clinical routine and research. The compact short bore magnet, the patient friendly design and the gradient technology make the innovation to new degree of perfection in magnetic resonance.'
Device Information and Specification
CLINICAL APPLICATION
Whole body
Spin Echo, Gradient Echo, Fast Spin Echo,
Inversion Recovery ( STIR, Fluid Attenuated Inversion Recovery), FLASH, FISP, PSIF, Turbo Flash ( MPRAGE ),TOF MR Angiography, Standard echo planar imaging package (SE-EPI, GE-EPI), Optional:
Advanced P.A. Imaging Package (up to 4 ch.), Advanced echo planar imaging package,
Single Shot and Diffusion Weighted EPI, IR/FLAIR EPI
STRENGTH
20 mT/m (Upto 27 mT/m)
| | | | • View the DATABASE results for 'CHORUS 1.5T™' (2).
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