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MRI Resources 
Quality Advice - Crystallography - Research Labs - Image Quality - Breast MRI - Colonography
 
Signa Infinity 1.0Tâ„¢InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.gehealthcare.com/usen/mr/index.html From GE Healthcare;
the Signa Infinity Magnetic Resonance system is a short bore, high performance, whole-body imaging system operating at 1.0 Tesla. The system can image in any orthogonal or oblique plane (including single and double axis oblique), using a wide variety of pulse sequences.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Short bore
Head and body coil standard; all other coils optional; open architecture makes system compatible with a wide selection of coils
SYNCHRONIZATION
ECG/peripheral, respiratory gating
PULSE SEQUENCES
Standard: SE, IR, 2D/3D GRE and SPGR, Angiography;; 2D/3D TOF, 2D/3D Phase Contrast;; 2D/3D FSE, 2D/3D FGRE and FSPGR, SSFP, FLAIR, optional: EPI, 2D/3D Fiesta, FGRET, Spiral
IMAGING MODES
Localizer, single slice, multislice, volume, fast, POMP, multi slab, cine
TR
4.4 msec to 12000 msec in increments of 1 msec
TE
1.0 to 2000 msec; increments of 1 msec
SINGLE/MULTI SLICE
Simultaneous scan and reconstruction;; up to 100 images/second with Reflex 100
1 cm to 48 cm continuous
2D 0.7 mm to 20 mm; 3D 0.1 mm to 5 mm
1280 x 1024
MEASURING MATRIX
128x512 steps 32 phase encode
PIXEL INTENSITY
256 gray levels
0.08 mm; 0.02 mm optional
MAGNET WEIGHT
3613 kg
H*W*D
172 x 208 x 216 cm
POWER REQUIREMENTS
480 or 380/415 V
COOLING SYSTEM TYPE
Closed-loop water-cooled gradient
Less than 0.03 L/hr liquid helium
STRENGTH
SmartSpeed 23 mT/m, HiSpeed Plus 33 mT/m
5-GAUSS FRINGE FIELD
4.0 m x 2.8 m axial x radial
Active
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MRI Resources 
Directories - Spectroscopy - Safety Products - Nerve Stimulator - Movies - NMR
 
Signa Infinity 1.5Tâ„¢ TwinSpeed with ExciteInfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.gehealthcare.com/usen/mr/s_excite15/index.html From GE Healthcare;
three dedicated MRI systems - a neuro imager, a cardiovascular system, and a whole body scanner - all in one system.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Short bore
Head and body coil standard; all other coils optional; open architecture makes system compatible with a wide selection of coils
Optional 2D/3D brain and prostate
SYNCHRONIZATION
ECG/peripheral, respiratory gating
PULSE SEQUENCES
Standard: SE, IR, 2D/3D GRE and SPGR, Angiography: 2D/3D TOF, 2D/3D Phase Contrast;; 2D/3D FSE, 2D/3D FGRE and FSPGR, SSFP, FLAIR, EPI, optional: 2D/3D Fiesta, FGRET, Spiral, Tensor
IMAGING MODES
Localizer, single slice, multislice, volume, fast, POMP, multi slab, cine
TR
1.2 to 12000 msec in increments of 1 msec
TE
0.4 to 2000 msec in increments of 1 msec
SINGLE/MULTI SLICE
Simultaneous scan and reconstruction;; up to 200 or 400 images per second
1 cm to 48 cm continuous
2D 0.7 mm to 20 mm; 3D 0.1 mm to 5 mm
1280 x 1024
MEASURING MATRIX
128x512 steps 32 phase encode
PIXEL INTENSITY
256 gray levels
60 cm
MAGNET WEIGHT
3863 kg
H*W*D
172 x 208 x 216 cm
POWER REQUIREMENTS
480 or 380/415
COOLING SYSTEM TYPE
Closed-loop water-cooled gradient
Less than 0.03 L/hr liquid He
STRENGTH
Zoom 40 mT/m, whole body 23 mT/m
5-GAUSS FRINGE FIELD
4.0 m x 2.8 m axial x radial
Active
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• View the DATABASE results for 'Signa Infinity 1.5T™ TwinSpeed with Excite' (2).Open this link in a new window

 
Further Reading:
  News & More:
Twin Gradient Technology - Potential Advantages For Diffusion Weighted MRI(.pdf)
   by www.paulrharvey.co.uk    
MRI Resources 
MRI Accidents - Absorption and Emission - Pathology - Process Analysis - Liver Imaging - Collections
 
Pulse Sequence Timing DiagramInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
Spin Echo Timing Diagram The schematic figures of a pulse sequence timing diagram illustrate the steps of basic hardware activity that are incorporated into a pulse sequence. Time during sequence execution is indicated along the horizontal axes. Each line belongs to a different hardware component. One line is needed for the radio frequency transmitter and also one for each gradient (Gs = slice selection gradient x, Gf = phase encoding gradient y, Gf = frequency encoding gradient z, also called readout gradient).
In picture 1, a timing diagram for a 2D pulse sequence is shown.
Slice selection and signal detection are repeated in duration, relative timing and amplitude, each time the sequence is repeated. A single phase encoding component is present each time the sequence is executed.
Additional lines are added for ADC (Analog to Digital Converter) and sampling. A gradient pulse is shown as a deviation above or below the horizontal line. Simultaneous component activities such as the RF pulse and slice selection gradient are indicated as a non-zero deviation from both lines at the same horizontal position. Simple deviations from zero show constant amplitude gradient pulse. Gradient amplitudes that change during the measurement, e.g. phase encoding are represented as hatched regions.

Spin Echo Timing Diagram The second picture shows a timing diagram for a 3D pulse sequence.
Volume excitation and signal detection are repeated in duration, relative timing and amplitude, each time the sequence is repeated. Two phase encoding components are present, one in the phase encoding direction and the other in slice selection direction (irrespectively incremented in amplitude) in each time the sequence is executed. A description of the comparison of hardware activity between different pulse sequences.
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• View the DATABASE results for 'Pulse Sequence Timing Diagram' (7).Open this link in a new window

MRI Resources 
Hospitals - Spine MRI - Education - Open Directory Project - Blood Flow Imaging - Intraoperative MRI
 
Gradient Echo SequenceForum -
related threadsInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
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
    
SlidersSliders Overview

 
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• View the DATABASE results for 'Gradient Echo Sequence' (70).Open this link in a new window

 
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 
Breast MRI - Shoulder MRI - Movies - Cardiovascular Imaging - MRI Centers - Pediatric and Fetal MRI
 
BandwidthForum -
related threads
 
(BW) Bandwidth is a measure of frequency range, the range between the highest and lowest frequency allowed in the signal. For analog signals, which can be mathematically viewed as a function of time, bandwidth is the width, measured in Hertz of a frequency range in which the signal's Fourier transform is nonzero.
•
The receiver (or acquisition) bandwidth (rBW) is the range of frequencies accepted by the receiver to sample the MR signal. The receiver bandwidth is changeable (see also acronyms for 'bandwidth' from different manufacturers) and has a direct relationship to the signal to noise ratio (SNR) (SNR = 1/squareroot (rBW). The bandwidth depends on the readout (or frequency encoding) gradient strength and the data sampling rate (or dwell time).
Bandwidth is defined by BW = Sampling Rate/Number of Samples.
A smaller bandwidth improves SNR, but can cause spatial distortions, also increases the chemical shift. A larger bandwidth reduces SNR (more noise from the outskirts of the spectrum), but allows faster imaging.
•
The transmit bandwidth refers to the RF excitation pulse required for slice selection in a pulse sequence. The slice thickness is proportional to the bandwidth of the RF pulse (and inversely proportional to the applied gradient strength). Lowering the pulse bandwidth can reduce the slice thickness.
mri safety guidance
Image Guidance
A higher bandwidth is used for the reduction of chemical shift artifacts (lower bandwidth - more chemical shift - longer dwell time - but better signal to noise ratio). Narrow receive bandwidths accentuate this water fat shift by assigning a smaller number of frequencies across the MRI image. This effect is much more significant on higher field strengths. At 1.5 T, fat and water precess 220 Hz apart, which results in a higher shift than in Low Field MRI.
Lower bandwidth (measured in Hz) = higher water fat shift (measured in pixel shift).

See also Aliasing, Aliasing Artifact, Frequency Encoding, and Chemical Shift Artifact.
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• View the DATABASE results for 'Bandwidth' (19).Open this link in a new window

 
Further Reading:
  Basics:
Bandwidth
   by en.wikipedia.org    
  News & More:
Automated Quality Assurance for Magnetic Resonance Image with Extensions to Diffusion Tensor Imaging(.pdf)
   by scholar.lib.vt.edu    
A Real-Time Navigator Approach to Compensating for Motion Artifacts in Coronary Magnetic Resonance Angiography
   by www.cs.nyu.edu    
MRI Resources 
Raman Spectroscopy - MR Guided Interventions - Libraries - Absorption and Emission - Hospitals - MRI Training Courses
 
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