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Result : Searchterm 'Orthogonal' found in 1 term [] and 14 definitions []
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Rotating Frame Zeugmatography
 
Technique of MR imaging that uses a gradient of the RF excitation field (to give a corresponding variation of the flip angle along the gradient as a means of encoding the spatial location of spins in the direction of the RF field gradient) in conjunction with a static magnetic field gradient (to give spatial encoding in an orthogonal direction). It can be considered to be a form of Fourier transformation imaging.
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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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Slice Select Gradient
 
(Gs)The slice select gradient is a magnetic field gradient applied to select the slice position in the direction of this gradient (x-direction). For orthogonal slices, the magnetic field gradient is applied perpendicular to the desired slice plane. Oblique and double-oblique slices are exited by simultaneously applying 2 or 3 gradient fields.
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Further Reading:
  Basics:
Factors influencing flip angle mapping in MRI: RF pulse shape, slice-select gradients, off-resonance excitation, and B0 inhomogeneities.
Tuesday, 1 August 2006   by www.ncbi.nlm.nih.gov    
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Stimulated Echo
 
A form of a spin echo produced by three pulse RF sequences, consisting of two RF pulses following an initial exciting RF pulse. The stimulated echo appears at a time delay after the third pulse equal to the interval between the first two pulses. Although classically produced with 90° pulses, any RF pulses other than an ideal 180° can produce a stimulated echo. The intensity of the echo depends in part on the T1 relaxation time because the excitation is 'stored' as longitudinal magnetization between the second and third RF pulses. For example, use of stimulated echoes with spatially selective excitation with orthogonal magnetic field gradients permits volume-selective excitation for spectroscopic localization.
mri safety guidance
Image Guidance
Artifacts may appear as a series of fine lines. A narrow bandwidth causes a wide read window, which allows the stimulated echo to be incorporated into the image data. This can be supported by increasing the received bandwidth, which would narrow the read window, thus not incorporating the extraneous echo. Another help would be to change the first echo time, which may change the spacing of the stimulated echoes to outside that of the read window for the second echo.
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Further Reading:
  Basics:
Magnetic resonance imaging
   by www.scholarpedia.org    
Clinical evaluation of a speed optimized T2 weighted fast spin echo sequence at 3.0 T using variable flip angle refocusing, half-Fourier acquisition and parallel imaging
Wednesday, 25 October 2006
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Volume Selective Excitation
 
The selective excitation of spins in only a limited region of space. This can be particularly useful for spectroscopy as well as imaging. Spatial localization of the signal source may be achieved through spatially selective excitation and the resulting signal may be analyzed directly for the spectrum corresponding to the excited region. It is usually achieved with selective excitation.
Typically, a single dimension of localization can be achieved with one selective RF excitation pulse (and a magnetic field gradient along a desired direction), while a localized volume (3D) can be excited with a stimulated echo produced with three selective RF pulses whose selective magnetic field gradients are mutually orthogonal, having a common intersection in the desired region. Similar 'crossed plane' excitation can be used with selective 180° refocusing pulses and conventional spin echoes.
A degree of spatial localization of excitation can alternatively be achieved with depth pulses, e.g. when using surface coils for excitation as well as signal detection. An indirect application of selective excitation for volume-selected spectroscopy is to use appropriate combinations of signals acquired after selective inversion of different regions, in order to subtract away the signal from undesired regions.
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