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 GRAPPA          GeneRalized Autocalibrating Partially Parallel Acquisition 
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Generalized Autocalibrating Partially Parallel AcquisitionInfoSheet: - Sequences - 
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(GRAPPA) GRAPPA is a parallel imaging technique to speed up MRI pulse sequences. The Fourier plane of the image is reconstructed from the frequency signals of each coil (reconstruction in the frequency domain).
Parallel imaging techniques like GRAPPA, auto-SMASH and VD-AUTO-SMASH are second and third generation algorithms using k-space undersampling. A model from a part of the center of k-space is acquired, to find the coefficients of the signals from each coil element, and to reconstruct the missing intermediary lines. The acquisition of these additional lines is a form of self-calibration, which lengthens the overall short scan time. The acquisition of these k-space lines provides mapping of the whole field as well as data for the image contrast.
Algorithms of the GRAPPA type work better than the SENSE type in heterogeneous body parts like thoracic or abdominal imaging, or in pulse sequences like echo planar imaging. This is caused by differences between the sensitivity map and the pulse sequence (e.g. artifacts) or an unreliable sensitivity map.
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Parallel Imaging TechniqueForum -
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In parallel MR imaging, a reduced data set in the phase encoding direction(s) of k-space is acquired to shorten acquisition time, combining the signal of several coil arrays. The spatial information related to the phased array coil elements is utilized for reducing the amount of conventional Fourier encoding.
First, low-resolution, fully Fourier-encoded reference images are required for sensitivity assessment. Parallel imaging reconstruction in the Cartesian case is efficiently performed by creating one aliased image for each array element using discrete Fourier transformation. The next step then is to create an full FOV image from the set of intermediate images. Parallel reconstruction techniques can be used to improve the image quality with increased signal to noise ratio, spatial resolution, reduced artifacts, and the temporal resolution in dynamic MRI scans.
Parallel imaging algorithms can be divided into 2 main groups:
Image reconstruction produced by each coil (reconstruction in the image domain, after Fourier transform): SENSE (Sensitivity Encoding), PILS (Partially Parallel Imaging with Localized Sensitivity), ASSET.
Reconstruction of the Fourier plane of images from the frequency signals of each coil (reconstruction in the frequency domain, before Fourier transform): GRAPPA.
Additional techniques include SMASH, SPEEDER™, IPAT (Integrated Parallel Acquisition Techniques - derived of GRAPPA a k-space based technique) and mSENSE (an image based enhanced version of SENSE).
 
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Further Reading:
  Basics:
Parallel MRI Using Multiple Receiver Coils
   by www-math.mit.edu    
Coil Arrays for Parallel MRI: Introduction and Overview.
   by www.mr.ethz.ch    
  News & More:
Cardiac MRI Becoming More Widely Available Thanks to AI and Reduced Exam Times
Wednesday, 19 February 2020   by www.dicardiology.com    
The Effects of Breathing Motion on DCE-MRI Images: Phantom Studies Simulating Respiratory Motion to Compare CAIPIRINHA-VIBE, Radial-VIBE, and Conventional VIBE
Tuesday, 7 February 2017   by www.kjronline.org    
Implementation of Dual-Source RF Excitation in 3 T MR-Scanners Allows for Nearly Identical ADC Values Compared to 1.5 T MR Scanners in the Abdomen
Wednesday, 29 February 2012   by www.plosone.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
MRI Resources 
Distributors - Portals - MRI Technician and Technologist Career - Online Books - - Supplies
 
Biograph mMR
 
www.healthcare.siemens.com/magnetic-resonance-imaging/mr-pet-scanner/biograph-mmr FDA cleared and CE Mark 2011.
The Biograph mMR has a fully-integrated design for simultaneous PET/MRI imaging. The dedicated hardware includes solid-state, avalanche photodiode PET detector and adapted, PET-compatible MR coils.
The possibility of truly simultaneous operation allows the acquisition of several magnetic resonance imaging (MRI) sequences during the positron emission tomography (PET) scan, without increasing the examination time.
See also Hybrid Imaging.
Device Information and Specification
CLINICAL APPLICATION
Whole Body
CONFIGURATION
Simultaneous PET/MRI
3 Tesla
Full range of MRI coils
CHANNELS
up to 32
PET ACQUISITION MODES
3D
MRI ACQUISITION MODES
2D/3D, spectroscopy;; iPAT, GRAPPA (k-space), noncontrast angiography, radial motion compensation
PET EFFECTIVE AXIAL FOV
26 cm (typical overlap 23%)
MRI FOV
A-P 45, R-L 50, H-F 50 cm
PET RING DIAMETER
65.6 cm
PATIENT SCAN RANGE
199 cm
HORIZONTAL SPEED
200 mmsec
TABLE CAPACITY
200 kg
PET DETECTOR
Solid state, 4032 avalanche photo diodes
DETECTOR SCINTILLATION MATERIAL
LSO, 28672 crystals
CRYSTAL SIZE
4 x 4 x 20 mm
MAGNET WEIGHT
9000 kg
DIMENSION H*W*D (gantry included)
335 x 230 x 242 cm (finshed covers)
5-GAUSS FRINGE FIELD
2.6 m / 4.6 m
CRYOGEN USE
Zero boil off rate, approx. 10 years
COOLING SYSTEM
PET system: water; MRI system: water
up to 200 T/m/s
MAX. AMPLITUDE
45 mT/m
Aautomatic, patient specific shim; active shim 3 linear and 5 non-linear channels (seond order)
POWER REQUIREMENTS
380 / 400 / 420 / 440 / 460 / 480 V, 3-phase + ground; Total system 110kW
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Further Reading:
  Basics:
Performance Measurements of the Siemens mMR Integrated Whole-Body PET/MR Scanner
Friday, 11 November 2011   by jnm.snmjournals.org    
Global Trends in Hybrid Imaging
Monday, 1 November 2010   by pubs.rsna.org    
  News & More:
Positron Emission Tomographic Imaging in Stroke
Monday, 28 December 2015   by www.ncbi.nlm.nih.gov    
A world's first in imaging – integrated whole-body molecular MR system available for clinical use testing
Thursday, 18 November 2010   by www.siemens.com    
FDA Clears New System to Perform Simultaneous PET, MRI Scans
Friday, 10 June 2011   by www.prnewswire.com    
Frost & Sullivan Award Underlines Siemens Healthcare's Contribution to New Product Innovation in the North American Medical Imaging Market
Wednesday, 13 July 2011   by multivu.prnewswire.com    
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MAGNETOM 7T
 
www.healthcare.siemens.com/magnetic-resonance-imaging/7t-mri-scanner/magnetom-7t From Siemens Medical Systems;
The MAGNETOM 7T is designed as an open research platform. 7T MRI provides anatomical detail at the submillimiter scale, enhanced contrast mechanisms, outstanding spectroscopy performance, ultra-high resolution functional imaging (fMRI), multinuclear whole-body MRI and functional information.
This ultra high field (UHF) MRI device is a research system and not cleared, approved or licensed in any jurisdiction for patient examinations.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Compact
7 Tesla
High-performance, ultra high field coils available. Integration and support for coil developments.
CHANNELS (min. / max. configuration)
32, optional 8 channels TX array
Chemical shift imaging, single voxel spectroscopy, multinuclear imaging optional
IMAGING TECHNIQUES
iPAT, mSENSE and GRAPPA (image, k-space), noncontrast angiography, plaque imaging, radial motion compensation
FOV
40 x 40 x 30 cm³ less than 8% nonlinearity
BORE DIAMETER
or W x H
60 cm
TABLE CAPACITY
200 kg
MAGNET WEIGHT (gantry included)
35017 kg
DIMENSION H*W*D (gantry included)
320 x 240 x 317,5 cm
5-GAUSS FRINGE FIELD
7.9 m / 5.6 m
CRYOGEN USE
Zero boil off rate
COOLING SYSTEM
Water
up to 200 T/m/s
MAX. AMPLITUDE
up to 70 mT/m
Up to 3rd order shim coils, user configurable B0 shim ? B0 maps and ROI definition
POWER REQUIREMENTS
2000 Volts, 650A
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Further Reading:
  Basics:
MAGNETOM 7T Product Brochure
   by www.healthcare.siemens.com    
  News & More:
Ultra-high-field MRI may allow earlier diagnosis of Parkinson's disease
Wednesday, 5 March 2014   by www.sciencedaily.com    
Feasibility of Using Ultra-High Field (7 T) MRI for Clinical Surgical Targeting
Thursday, 17 May 2012   by www.plosone.org    
Ultrahigh-Field MRI May Detect Additional Pathology in EAE
Sunday, 20 October 2013   by www.msdiscovery.org    
MRI Resources 
Crystallography - Pediatric and Fetal MRI - MRI Accidents - Diffusion Weighted Imaging - Databases - Services and Supplies
 
MAGNETOM Aera
 
www.healthcare.siemens.com/magnetic-resonance-imaging/0-35-to-1-5t-mri-scanner/magnetom-aera/ From Siemens Medical Systems;
Received FDA clearance in 2010.
The MAGNETOM Aera is a patient friendly, comfortable 1.5 Tesla MRI system with advanced radio frequency chain.
The system is equipped with the Tim 4G and Dot system (Total imaging matrix + Day optimizing throughput), to enhance both productivity and image quality.
Tim 4G technology provides improved SNR. The standard system configuration of 48 radio frequency channels and 204 coil elements creates an imaging matrix that allows maximum use of coil elements at full field of view. Dot provides improved image consistency through new features like auto align, auto FoV and automatic bolus detection.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Open bore
Head, spine, torso/ body coil, neurovascular, cardiac, neck, shoulder, knee, wrist, foot//ankle and multi-purpose flex coils. Peripheral vascular, breast, shoulder. Up to 60% more SNR with Tim 4G.
CHANNELS (min. / max. configuration)
48, 64
IMAGING TECHNIQUES
iPAT, mSENSE and GRAPPA (image, k-space), noncontrast angiography, plaque imaging, radial motion compensation, Dixon, improved workflow with Dot, Caipirinha - single digit breath-holds for 3-D body imaging.
MINIMUM TR
3-D GRE: 0.95 (256 matrix)
MINIMUM TE
3-D GRE: 0.22 (256 matrix), Ultra-short TE
FOV
0.5 - 50
BORE DIAMETER
or W x H
At isocenter: L-R 70 cm, A-P (with table) 55 cm
TABLE CAPACITY
250 kg
MAGNET WEIGHT (gantry included)
3121 kg
DIMENSION H*W*D (gantry included)
145 x 231 x 219 cm
5-GAUSS FRINGE FIELD
2.5 m / 4.0 m
CRYOGEN USE
Zero boil off rate, approx. 10 years
COOLING SYSTEM
Water
up to 200 T/m/s
MAX. AMPLITUDE
33 or 45 mT/m
3 linear with 20 coils, 5 nonlinear 2nd-order
POWER REQUIREMENTS
380 / 400 / 420 / 440 / 460 / 480 V, 3-phase + ground; 85 kVA
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