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 'Contrast Enhanced Gradient Echo Sequence' 
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Result : Searchterm 'Contrast Enhanced Gradient Echo Sequence' found in 1 term [] and 3 definitions [], (+ 15 Boolean[] results
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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.
 
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• Related Searches:
    • Contrast
    • MRI History
    • Ultrafast Gradient Echo Sequence
    • Abdominal Imaging
    • Steady State Free Precession
 
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 
Liver Imaging - Stent - Examinations - Anatomy - Diffusion Weighted Imaging - MRI Technician and Technologist Jobs
 
Lung ImagingMRI Resource Directory:
 - Lung Imaging -
 
Lung imaging is furthermore a challenge in MRI because of the predominance of air within the lungs and associated susceptibility issues as well as low signal to noise of the inflated lung parenchyma. Cardiac and respiratory triggered or breath hold sequences allow diagnostic imaging, however a comparable image quality with computed tomography is still difficult to achieve.
Assumptions for lung MRI:
•
Low signal to noise ratio of the inherently low lung proton density.
•
Cardiac and respiratory motion artifacts.
•
Magnetic susceptibility effects of large magnetic field gradients.
•
Very short transverse relaxation times and significant diffusion yielding short T2 (30-70 msec), short T2* (1-3 msec), and additional long T1 relaxation times (1300-1500 msec).
•
The extreme short T2 values are responsible for a fast signal decay during a single shot readout, resulting in blurring.

The current trends in MRI are the use of new imaging technologies and increasingly powerful magnetic fields. Among these technologies are parallel imaging techniques as well as ventilation agents like hyperpolarized helium for the use as an inert inhalational contrast agent to study lung ventilation properties. With hyperpolarized gases clear images of the lungs can be obtained without using a large magnetic field (see also back projection imaging). Single shot sequences (e.g. TSE or Half Fourier Acquisition Single Shot Turbo Spin Echo HASTE) used in lung MR imaging benefits from parallel imaging techniques due to reduced relaxation time effects during the echo train and therefore reduced image blurring as well as reduced motion artifacts.
In the future, more effective contrast agents may provide an alternative solution to the need for high field MRI. Dynamic contrast enhanced MRI perfusion has demonstrated a potential in the diagnosis of pulmonary embolism or to characterize lung cancer and mediastinal tumors. 3D contrast enhanced magnetic resonance angiography of the thoracic vessel.

See also the related poll result: 'MRI will have replaced 50% of x-ray exams by'
 
Images, Movies, Sliders:
 Anatomic Imaging of the Lungs  Open this link in a new window
      

Courtesy of  Robert R. Edelman
 Normal Lung Gd Perfusion MRI  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 MRI Thorax Basal Plane  Open this link in a new window
 
Radiology-tip.comradLung Scintigraphy
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• View the DATABASE results for 'Lung Imaging' (7).Open this link in a new window


• View the NEWS results for 'Lung Imaging' (3).Open this link in a new window.
 
Further Reading:
  Basics:
A safer approach for diagnostic medical imaging
Monday, 29 September 2014   by www.eurekalert.org    
Parallel Lung Imaging(.pdf)
  News & More:
Chest MRI a viable alternative to chest CT in COVID-19 pneumonia follow-up
Monday, 21 September 2020   by www.healthimaging.com    
CT Imaging Features of 2019 Novel Corona virus (2019-nCoV)
Tuesday, 4 February 2020   by pubs.rsna.org    
Polarean Imaging Phase III Trial Results Point to Potential Improvements in Lung Imaging
Wednesday, 29 January 2020   by www.diagnosticimaging.com    
Low Power MRI Helps Image Lungs, Brings Costs Down
Thursday, 10 October 2019   by www.medgadget.com    
Chest MRI Using Multivane-XD, a Novel T2-Weighted Free Breathing MR Sequence
Thursday, 11 July 2019   by www.sciencedirect.co    
Researchers Review Importance of Non-Invasive Imaging in Diagnosis and Management of PAH
Wednesday, 11 March 2015   by lungdiseasenews.com    
New MRI Approach Reveals Bronchiectasis' Key Features Within the Lung
Thursday, 13 November 2014   by lungdiseasenews.com    
MRI techniques improve pulmonary embolism detection
Monday, 19 March 2012   by medicalxpress.com    
  News & More:
Partnership with VIDA to streamline adoption of advanced MRI of the lungs
Monday, 11 September 2023   by www.itnonline.com    
MRI Resources 
Diffusion Weighted Imaging - Implant and Prosthesis - Examinations - Lung Imaging - Spectroscopy pool - MRI Technician and Technologist Schools
 
Contrast Enhanced Magnetic Resonance AngiographyInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - MRA -
 
(CE MRA) Contrast enhanced MR angiography is based on the T1 values of blood, the surrounding tissue, and paramagnetic contrast agent.
T1-shortening contrast agents reduces the T1 value of the blood (approximately to 50 msec, shorter than that of the surrounding tissues) and allow the visualization of blood vessels, as the images are no longer dependent primarily on the inflow effect of the blood. Contrast enhanced MRA is performed with a short TR to have low signal (due to the longer T1) from the stationary tissue, short scan time to facilitate breath hold imaging, short TE to minimize T2* effects and a bolus injection of a sufficient dose of a gadolinium chelate.
Images of the region of interest are performed with 3D spoiled gradient echo pulse sequences. The enhancement is maximized by timing the contrast agent injection such that the period of maximum arterial concentration corresponds to the k-space acquisition. Different techniques are used to ensure optimal contrast of the arteries e.g., bolus timing, automatic bolus detection, bolus tracking, care bolus. A high resolution with near isotropic voxels and minimal pulsatility and misregistration artifacts should be striven for. The postprocessing with the maximum intensity projection (MIP) enables different views of the 3D data set.
Unlike conventional MRA techniques based on velocity dependent inflow or phase shift techniques, contrast enhanced MRA exploits the gadolinium induced T1-shortening effects. CE MRA reduces or eliminates most of the artifacts of time of flight angiography or phase contrast angiography. Advantages are the possibility of in plane imaging of the blood vessels, which allows to examine large parts in a short time and high resolution scans in one breath hold. CE MRA has found a wide acceptance in the clinical routine, caused by the advantages:
•
3D MRA can be acquired in any plane, which means that greater vessel coverage can be obtained at high resolution with fewer slices (aorta, peripheral vessels);
•
the possibility to perform a time resolved examination (similarly to conventional angiography);
•
no use of ionizing radiation; paramagnetic agents have a beneficial safety.
 
Images, Movies, Sliders:
 CE-MRA of the Carotid Arteries  Open this link in a new window
    
SlidersSliders Overview

 CE MRA of the Aorta  Open this link in a new window
    
SlidersSliders Overview

 CE-MRA of the Carotid Arteries Colored MIP  Open this link in a new window
    
SlidersSliders Overview

 
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• View the DATABASE results for 'Contrast Enhanced Magnetic Resonance Angiography' (14).Open this link in a new window


• View the NEWS results for 'Contrast Enhanced Magnetic Resonance Angiography' (2).Open this link in a new window.
 
Further Reading:
  Basics:
Contrast-Enhanced MR Angiography(.pdf)
   by ric.uthscsa.edu    
CONTRAST ENHANCED MR ANGIOGRAPHY – PRINCIPLES, APPLICATIONS, TIPS AND PITFALLS(.pdf)
  News & More:
CONTRAST-ENHANCED MRA OF THE CAROTIDS(.pdf)
PERIPHERAL VASCULAR MAGNETIC RESONANCE ANGIOGRAPHY(.pdf)
CONTRAST ENHANCED MRI OF THE LIVER STATE-OF-THE-ART(.pdf)
MRI Resources 
Anatomy - Spine MRI - Research Labs - Libraries - MRI Technician and Technologist Schools - PACS
 
Contrast Enhanced MR VenographyInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - MRA -
 
(CEMRV) A 3D dynamic contrast enhanced magnetic resonance venogram with acquisition timing to account for the later arrival of the contrast agent in the venous system. The pulse sequence used, is an enhanced 3D fast gradient echo sequence, the same sequence that is used for MR angiography.

For Ultrasound Imaging (USI) see Venous Ultrasound at Medical-Ultrasound-Imaging.com.
 
Images, Movies, Sliders:
 CE-MRA of the Carotid Arteries Colored MIP  Open this link in a new window
    
SlidersSliders Overview

 PCA-MRA 3D Brain Venography Colored MIP  Open this link in a new window
    

 
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• View the DATABASE results for 'Contrast Enhanced MR Venography' (3).Open this link in a new window

MRI Resources 
Breast Implant - Lung Imaging - Databases - Supplies - MRI Technician and Technologist Jobs - General
 
Liver Acquisition with Volume AcquisitionInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(LAVA) The MRI technique LAVA is based on a 3 dimensional spoiled gradient echo pulse sequence. The optimized inversion pulse and a new fat suppression technique (called segmented special) provides enhanced image contrast and uniform fat suppression. Array spatial sensitivity encoding technique (ASSET) with partial data filling and shorter TR/TE enables to use short breath holds for dynamic liver imaging with multiple phases.
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• View the DATABASE results for 'Liver Acquisition with Volume Acquisition' (3).Open this link in a new window

 
Further Reading:
  Basics:
MR Field Notes
   by www.gehealthcare.com    
MRI Resources 
Portals - Safety pool - Colonography - Contrast Enhanced MRI - Intraoperative MRI - Online Books
 
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