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Cardiac Gating
 
This method synchronize the heartbeat with the beginning of the TR, whereat the r wave is used as the trigger. Cardiac gating times the acquisition of MR data to physiological motion in order to minimize motion artifacts. ECG gating techniques are useful whenever data acquisition is too slow to occur during a short fraction of the cardiac cycle.
Image blurring due to cardiac-induced motion occurs for imaging times of above approximately 50 ms in systole, while for imaging during diastole the critical time is of the order of 200-300 ms. The acquisition of an entire image in this time is only possible with using ultrafast MR imaging techniques. If a series of images using cardiac gating or real-time echo planar imaging EPI are acquired over the entire cardiac cycle, pixel-wise velocity and vascular flow can be obtained.
In simple cardiac gating, a single image line is acquired in each cardiac cycle. Lines for multiple images can then be acquired successively in consecutive gate intervals. By using the standard multiple slice imaging and a spin echo pulse sequence, a number of slices at different anatomical levels is obtained. The repetition time (TR) during a ECG-gated acquisition equals the RR interval, and the RR interval defines the minimum possible repetition time (TR). If longer TRs are required, multiple integers of the RR interval can be selected. When using a gradient echo pulse sequence, multiple phases of a single anatomical level or multiple slices at different anatomical levels can be acquired over the cardiac cycle.
Also called cardiac triggering.

 
Images, Movies, Sliders:
 Cardiac Infarct Short Axis Cine Overview  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 Infarct 4 Chamber Cine  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 
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• Related Searches:
    • Synchronization, Cardiac
    • Cerebro Spinal Fluid Pulsation Artifact
    • Cardiac MRI
    • Cardiac Synchronization
    • Synchronization, Prospective
 
Further Reading:
  Basics:
Cardiac MRI - Technical Aspects Primer
Wednesday, 7 August 2002
Electrocardiogram in an MRI Environment: Clinical Needs, Practical Considerations, Safety Implications, Technical Solutions and Future Directions
Wednesday, 25 January 2012   by cdn.intechopen.com    
Motion-compensation of Cardiac Perfusion MRI using a Statistical Texture Ensemble(.pdf)
June 2003   by www.imm.dtu.dk    
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Cine SequenceInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
Cine sequences used in cardiovascular MRI are collection of images (usually at the same spatial location) covering of one full period of cardiac cycle or over several periods in order to obtain complete coverage.
The pulse sequence used, is either a standard gradient echo pulse sequence, a segmented data acquisition, a gradient echo EPI sequence or a gradient echo with balanced gradient waveform. In cardiac gating studies it is possible to assign consecutive lines either to different images, yielding a multiphase sequence with as many images as lines, or the lines are grouped together into segments and assigned to the same image. The overall time to acquire such a segment has to be small compared to the RR-interval of the cardiac cycle, i. e. 50 ms, and hence contains typically 8 to 16 image lines.
This strategy is called segmented data acquisition, and has the advantage of reducing overall imaging time for cardiac images so that they can be acquired within a breath hold, but obviously decreasing the temporal resolution of each individual image. This method shows dynamic processes, such as the ejection of blood out of the heart into the aorta, by means of fast imaging and displaying the resulting images in a sequential-loop, the impression of a real-time movie is generated. Ejection fractions and stroke volumes calculated from these cine MRI images in different cardiac axes have been shown to be more accurate than any other imaging modality.
See also Cardiac Gating.

 
Images, Movies, Sliders:
 Angulation of Cardiac Planes Cine Images of Septal Infarct  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 Cardiac Infarct Short Axis Cine Overview  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 Infarct 4 Chamber Cine  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 
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Further Reading:
  News & More:
Study Shows Cardiac MRI Use Reduces Adverse Events for Patients with Acute Chest Pain
Monday, 10 June 2013   by www.healthcanal.com    
Study identifies new way to predict prognosis for heart failure patients
Tuesday, 10 December 2013   by medicalxpress.com    
MRI Resources 
Image Quality - Databases - Mass Spectrometry - Cardiovascular Imaging - Safety Training - Brain MRI
 
AIRIS II™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.hitachimed.com/products/airis_2.asp

From Hitachi Medical Systems America Inc.;
the AIRIS II, an entry in the diagnostic category of open MR systems, was designed by Hitachi Medical Systems America Inc. (Twinsburg, OH, USA) and Hitachi Medical Corp. (Tokyo) and is manufactured by the Tokyo branch. A 0.3 T field-strength magnet and phased array coils deliver high image quality without the need for a tunnel-type high-field system, thereby significantly improving patient comfort not only for claustrophobic patients.


Device Information and Specification
CLINICAL APPLICATION Whole body
CONFIGURATION Vertical Field, Open MRI
SURFACE COILS QD Head, MA Head and Neck, QD C-Spine, MA or QD Shoulder, MA CTL Spine, QD Knee, Neck, QD TMJ, QD Breast, QD Flex Body (4 sizes), Small and Large Extrem., QD Wrist, MA Foot and Ankle (WIP), PVA (WIP)
SPECTROSCOPY No
SYNCHRONIZATION Cardiac gating, ECG/peripheral, respiratory gating (2 modes)
PULSE SEQUENCES SE, GE, GR, IR, FIR, STIR, FSE, ss-FSE, FLAIR, EPI -DWI, SE-EPI, ms - EPI, SSP, MTC, SARGE, RSSG, TRSG, MRCP, Angiography: CE, 2D/3D TOF
IMAGING MODES Single, multislice, volume study
TR SE: 30 - 10,000msec GE: 20 - 10,000msec IR: 50 - 16,700msec FSE: 200 - 16,7000msec
TE SE : 10 - 250msec IR: 10 -250msec GE: 5 - 50 msec FSE: 15 - 2,000
SINGLE/MULTI SLICE 0.05 sec/image (256 x 256)
FOV 5cm to 42 cm continuous
SLICE THICKNESS 2D: 2 - 100 mm; 3D: 0.5 - 5 mm
DISPLAY MATRIX 1280 x 1024
MEASURING MATRIX 512 x 512
PIXEL INTENSITY Level Range: -2,000 to +4,000
SPATIAL RESOLUTION Sub millimeter
MAGNET TYPE Self-shielded, permanent
BORE DIAMETER
or W x H
110 x 43 cm
MAGNET WEIGHT 15,700 kg
H*W*D 79 x 111 x 73 cm
POWER REQUIREMENTS 208/220/240 V, single phase
COOLING SYSTEM TYPE Air-cooled
CRYOGEN USE
FIELD STRENGTH 0.3 T
STRENGTH 15 mT/m
5 GAUSS FRINGE FIELD 2.0 m lateral, 2.5 m vert./long
SHIMMING Auto shimming, 3-axis/patient, and volume shim

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Altaire™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.hitachimed.com/products/altaire.asp

From Hitachi Medical Systems America, Inc.;
the AIRIS made its debut in 1995. Hitachi followed up with the AIRIS II system, which has proven equally successfully. 'All told, Hitachi has installed more than 1,000 MRI systems in the U.S., holding more than 17 percent of the total U.S. MRI installed base, and more than half of the installed base of open MR systems,' says Antonio Garcia, Frost and Sullivan industry research analyst. Now Altaire employs a blend of innovative Hitachi features called VOSI™ technology, optimizing each sub-system’s performance in concert with the other sub-systems, to give the seamless mix of high-field performance and the patient comfort, especially for claustrophobic patients, of open MR systems.


Device Information and Specification
CLINICAL APPLICATION Whole body
CONFIGURATION Vertical Field, Open MRI
SURFACE COILS DualQuad T/R Body Coil, MA Head, MA C-Spine, MA Shoulder, MA Wrist, MA CTL Spine, MA Knee, MA TMJ, MA Flex Body (3 sizes), Neck, small and large Extremity, PVA (WIP), Breast (WIP), Neurovascular (WIP), Cardiac (WIP) and MA Foot//Ankle (WIP)
SPECTROSCOPY No
SYNCHRONIZATION Cardiac gating, ECG/peripheral, respiratory gating (2 modes)
PULSE SEQUENCES SE, GE, GR, IR, FIR, STIR, ss-FSE, FSE, DE-FSE/FIR, FLAIR, ss/ms-EPI, ss/ms EPI- DWI, SSP, MTC, SE/GE-EPI, MRCP, SARGE, RSSG, TRSG, BASG, Angiography: CE, PC, 2D/3D TOF
IMAGING MODES Single, multislice, volume study
TR SE: 30 - 10,000msec GE: 3.6 - 10,000msec IR: 50 - 16,700msec FSE: 200 - 16,7000msec
TE SE : 8 - 250msec IR: 5.2 -7,680msec GE: 1.8 - 2,000 msec FSE: 5.2 - 7,680
SINGLE/MULTI SLICE 0.05 sec/image (256 x 256)
FOV 5cm to 45 cm continuous
SLICE THICKNESS 2D: 2 - 100 mm; 3D: 0.5 - 5 mm
DISPLAY MATRIX 1280 x 1024
MEASURING MATRIX 512 x 512
PIXEL INTENSITY Level Range: -2,000 to +4,000
SPATIAL RESOLUTION Sub millimeter
MAGNET TYPE Self-shielded, superconducting
BORE DIAMETER
or W x H
115 x 47 cm
MAGNET WEIGHT 41,700 kg
H*W*D 256 x 348 x 236 cm
POWER REQUIREMENTS 208 V +/- 10%, 3 phase
COOLING SYSTEM TYPE Water-cooled
CRYOGEN USE Refill 1/year
FIELD STRENGTH 0.7 T
STRENGTH 22 mT/m
5 GAUSS FRINGE FIELD 3.1 m lateral, 3.6 m vertical
SHIMMING Auto shimming, 3-axis/patient and active shimming

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Further Reading:
  News & More:
Altaire High-Field Open MRI(.pdf)
2001
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Arrhythmia Rejection
 
With this method irregular RR intervals in cardiac gating during cardiovascular imaging are rejected and then repeated to improve the image quality, whereby the cardiac frequency is used as a basis of the normal heart rate.
The RR interval window determines the percentage variation of the heart rate. Variations of the acquired data outside the window are rejected and not used in the image reconstruction. Also one interval after the arrhytmic beat will be rejected.
Arrhythmia rejection may be inappropriate for patients with certain pathologies, because if the RR interval is constant long, short, long, - all intervals would be rejected. Also a disadvantage is the time consume, but in some cases this function is mandatory, e.g. for diverse retrospective triggered sequences.

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Further Reading:
  Basics:
A Guide To Cardiac Imaging
   by www.simplyphysics.com    
  News & More:
Irregular heartbeat may lead to silent strokes
Wednesday, 5 November 2014   by www.techtimes.com    
MRI Resources 
Education - Shoulder MRI - Brain MRI - Manufacturers - Implant and Prosthesis - Coils
 
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