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 'Spatial Frequency' 
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Result : Searchterm 'Spatial Frequency' found in 1 term [] and 5 definitions [], (+ 18 Boolean[] results
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MRI Resources 
Mobile MRI Rental - Fluorescence - Image Quality - General - Research Labs - MRI Reimbursement
 
Twister Gradient
 
A gradient pulse designed to dephase low spatial frequency components in an image. The simplest such design is to choose the gradient strength so that a linear phase change of -p to p is generated across the image.
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MRI Resources 
Blood Flow Imaging - Breast MRI - Libraries - Devices - Patient Information - Shielding
 
Signa Ovation™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.gehealthcare.com/usen/mr/ovation/index.html From GE Healthcare;
the Signa Ovation™ is a patient-friendly open MRI scanner designed not only to handle a typical patient mix, but to accommodate larger patients, patients who are claustrophobic, and others who have difficulty tolerating the close quarters of conventional MR machines.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Integrated transmit and receive body coil; head coil, 4 channel neurovascular array, 8 channel CTL array, 2 channel shoulder array, 3 channel large extremity array, 3 channel small extremity array, 4 channel foot array, 3 channel wrist array
SYNCHRONIZATION
Standard cardiac gating, ECG/peripheral, respiratory gating
PULSE SEQUENCES
Standard: SE, IR, 2D/3D GRE and SPGR, 2D/3D TOF, 2D/3D FSE, 2D/3D FGRE and FSPGR, SSFP, FLAIR, EPI, optional: 2D/3D Fiesta, true chem sat, fat/water separation, single shot diffusion EPI, line scan diffusion
IMAGING MODES
Localizer, single slice, multislice, volume, fast, POMP, multi slab, cine, slice and frequency zip, extended dynamic range, tailored RF
TR
1.3 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;; 80 images/second reconstruction
3cm to 40 cm continuous
2D: 1.4mm - 20mm 3D: 0.2mm - 20mm
1280 x 1024
MEASURING MATRIX
128x512 steps 32 phase//freq.
PIXEL INTENSITY
256 gray levels
0.08 mm; 0.02 mm optional
MAGNET TYPE
Permanent
175 x 85 x 447 cm
MAGNET WEIGHT
19200 kg
H*W*D
530 x 175 x 250 cm
POWER REQUIREMENTS
200 - 480, 3-phase
GRADIENT COOLING
None
MAX. GRADIENT AMPLITUDE
19 mT/m
5-GAUSS FRINGE FIELD
2.5 m/2.5 m
Computerized passive shimming during magnet setup, autoshim per series with automatic table motion to magnet isocenter for each prescription
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• View the DATABASE results for 'Signa Ovation™' (2).Open this link in a new window

MRI Resources 
Process Analysis - Spine MRI - Liver Imaging - Services and Supplies - Health - Safety Products
 
Echo Planar ImagingInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
Echo Planar Imaging Timing Diagram (EPI) Echo planar imaging is one of the early magnetic resonance imaging sequences (also known as Intascan), used in applications like diffusion, perfusion, and functional magnetic resonance imaging. Other sequences acquire one k-space line at each phase encoding step. When the echo planar imaging acquisition strategy is used, the complete image is formed from a single data sample (all k-space lines are measured in one repetition time) of a gradient echo or spin echo sequence (see single shot technique) with an acquisition time of about 20 to 100 ms. The pulse sequence timing diagram illustrates an echo planar imaging sequence from spin echo type with eight echo train pulses. (See also Pulse Sequence Timing Diagram, for a description of the components.)
In case of a gradient echo based EPI sequence the initial part is very similar to a standard gradient echo sequence. By periodically fast reversing the readout or frequency encoding gradient, a train of echoes is generated.
EPI requires higher performance from the MRI scanner like much larger gradient amplitudes. The scan time is dependent on the spatial resolution required, the strength of the applied gradient fields and the time the machine needs to ramp the gradients.
In EPI, there is water fat shift in the phase encoding direction due to phase accumulations. To minimize water fat shift (WFS) in the phase direction fat suppression and a wide bandwidth (BW) are selected. On a typical EPI sequence, there is virtually no time at all for the flat top of the gradient waveform. The problem is solved by "ramp sampling" through most of the rise and fall time to improve image resolution.
The benefits of the fast imaging time are not without cost. EPI is relatively demanding on the scanner hardware, in particular on gradient strengths, gradient switching times, and receiver bandwidth. In addition, EPI is extremely sensitive to image artifacts and distortions.
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• View the DATABASE results for 'Echo Planar Imaging' (19).Open this link in a new window


• View the NEWS results for 'Echo Planar Imaging' (1).Open this link in a new window.
 
Further Reading:
  Basics:
New Imaging Method Makes Brain Scans 7 Times Faster
Sunday, 9 January 2011   by www.dailytech.com    
MRI Resources 
Universities - MRI Technician and Technologist Jobs - Liver Imaging - IR - Calculation - Developers
 
Signa Profile™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.gehealthcare.com/usen/mr/profilei/index.html From GE Healthcare;
the New Signa Profile/i is a patient friendly open MRI system that virtually eliminates patient anxiety and claustrophobia, without compromising diagnostic utility.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Integrated transmit body coil, body flex sizes: M, L, XL, quadrature, head coil quadrature, 4 channel neurovascular array, 8 channel CTL array, quad. c-spine, 2 channel shoulder array, extremity coil, 3 channel wrist array, 4 channel breast array, 6, 9, 11 inch general purpose loop coils
SYNCHRONIZATION
Standard cardiac gating, 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 FRFSE, FGRE and FSPGR, SSFP, FLAIR, EPI, optional: 2D/3D Fiesta, fat/water separation, T1 FLAIR
IMAGING MODES
Localizer, single slice, multislice, volume, fast, POMP, multi slab, cine, slice and frequency zip, extended dynamic range, tailored RF
TR
6 to 12000 msec in increments of 1 msec
TE
1.3 to 2000 msec in increments of 1 msec
SINGLE/MULTI SLICE
Simultaneous scan and reconstruction;; 80 images/second reconstruction
3cm to 40 cm continuous
2D: 2.7mm - 20mm 3D: 0.2mm - 5mm
1280 x 1024
MEASURING MATRIX
128x512 steps 32 phase//freq.
PIXEL INTENSITY
256 gray levels
0.08 mm; 0.02 mm optional
MAGNET TYPE
Permanent
120 x 44 cm
MAGNET WEIGHT
10,000 kg w/gradient enclosure
H*W*D
147 x 214 x 193 cm
POWER REQUIREMENTS
200 - 480, 3-phase
COOLING SYSTEM TYPE
None required
STRENGTH
15 mT/m
5-GAUSS FRINGE FIELD
1.7 m/1.7 m
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• View the DATABASE results for 'Signa Profile™' (2).Open this link in a new window

MRI Resources 
RIS - Abdominal Imaging - DICOM - Implant and Prosthesis pool - Blood Flow Imaging - Musculoskeletal and Joint MRI
 
Chemical Shift ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Please note that there are different common names for this artifact.
Artifact Information
NAME
Chemical shift, black boundary, spatial misregistration, relief
DESCRIPTION
Black or bright band
During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.
mri safety guidance
Image Guidance
For artifact reduction helps a smaller water fat shift (higher bandwidth), a higher matrix, an in phase TE or a spin echo technique. Since the misregistration offset is present in the read out axis the patient may be rescanned with this axis parallel to the fat-water interface. Steeper gradient may be employed to reduce the chemical shift offset in mm. Another strategy is to employ specialized pulse sequences such as fat saturation or inversion recovery imaging. Fat suppression techniques eliminate chemical shift artifacts caused by the lack of fat signal.

See also Black Boundary Artifact and Magnetic Resonance Spectroscopy.
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• View the DATABASE results for 'Chemical Shift Artifact' (7).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
  News & More:
What is chemical shift artefact? Why does it occur? How many Hz at 1.5 T?
   by www.revisemri.com    
Abdominal MRI at 3.0 T: The Basics Revisited
Wednesday, 20 July 2005   by www.ajronline.org    
MRI Resources 
Devices - Raman Spectroscopy - Breast Implant - MRI Technician and Technologist Jobs - Quality Advice - Bioinformatics
 
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