Magnetic Resonance - Technology Information Portal Welcome to MRI Technology
Info
  Sheets

Out-
      side
 



 
 'Coherent Gradient Echo' 
SEARCH FOR    
 
  2 3 5 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Result : Searchterm 'Coherent Gradient Echo' found in 3 terms [] and 3 definitions [], (+ 4 Boolean[] results
1 - 5 (of 10)     next
Result Pages : [1]  [2]
MRI Resources 
Liver Imaging - Jobs pool - MRI Technician and Technologist Career - Collections - Pathology - MRI Technician and Technologist Jobs
 
Coherent Gradient EchoInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
Coherent gradient echo sequences can measure the free induction decay (FID), generated just after each excitation pulse or the echo formed prior to the next pulse. Coherent gradient echo sequences are very sensitive to magnetic field inhomogeneity. An alternative to spoiling is to incorporate residual transverse magnetization directly into the longitudinal steady state. These GRE sequences use a refocusing gradient in the phase encoding direction during the end module to maximize remaining transverse (xy) magnetization at the time when the next excitation is due, while the other two gradients are, in any case, balanced.
When the next excitation pulse is sent into the system with an opposed phase, it tilts the magnetization in the -a direction. As a result the z-magnetization is again partly tilted into the xy-plane, while the remaining xy-magnetization is tilted partly into the z-direction.
A fully refocused sequence with a properly selected and uniform f would yield higher signal, especially for tissues with long T2 relaxation times (high water content) so it is used in angiographic, myelographic or arthrographic examinations and is used for T2* weighting. The repetition time for this sequence has to be short. With short TR, coherent GE is also useable for breath hold and 3D technique. If the repetition time is about 200 msec there's no difference between spoiled or unspoiled GE. T1 weighting is better with spoiled techniques.
The common types include GRASS, FISP, FAST, and FFE.
The T2* component decreases with long TR and short TE. The T1 time is controlled by flip angle. The common TR is less than 50 ms and the common TE less than 15 ms
Other types have stronger T2 dependence but lower SNR. They include SSFP, CE-FAST, PSIF, and CE-FFE-T2.
Examples of fully refocused FID sequences are TrueFISP, bFFE and bTFE.
spacer
 
• Share the entry 'Coherent Gradient Echo':  Facebook  Twitter  LinkedIn  
 
• Related Searches:
    • Dual Echo Sequence
    • Incoherent Gradient Echo (RF Spoiled)
    • Longitudinal Magnetization
    • Free Induction Decay
    • Transverse Magnetization
MRI Resources 
Case Studies - Spectroscopy - PACS - Software - Liver Imaging - MR Guided Interventions
 
Incoherent Gradient Echo (RF Spoiled)InfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
A gradient echo is generated by using a pair of bipolar gradient pulses. The gradient field is negatively pulsed, causing the spins of the xy-magnetization to dephase. A second gradient pulse is applied with the opposite polarity. During the pulsing, the spins that dephased begin to rephase and generate a gradient echo.
Spoiling can be accomplished by RF or a gradient. The incoherent RF spoiled type of a gradient echo sequence use a continuous shifting of the RF pulse to spoil the residual transverse magnetization. The phase of the RF excitation and receiver channel are varied pseudo randomly with each excitation cycle to prevent the xy magnetization from achieving steady state. T2* does not dominate image contrast, so T1 and PD weighting is practical. This method is effective and can be used to achieve a shorter TR, due to a lack of additional gradients. Spoiling eliminates the effect of the remaining xy-magnetization and leads to steady state longitudinal magnetization. These sequences can be used for breath hold, dynamic imaging and in cine and volume acquisitions.
spacer
MRI Resources 
Quality Advice - Process Analysis - Corporations - Knee MRI - Fluorescence - Liver Imaging
 
Incoherent Gradient Echo (Gradient Spoiled)InfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
The incoherent gradient echo (gradient spoiled) type of sequence uses a continuous shifting of the RF pulse to spoil the remaining transverse magnetization. The transverse magnetization is destroyed by a magnetic field gradient. This results in a T1 weighted image. Spoiling can be accomplished by RF or a gradient.
Gradient spoiling occurs after each echo by using strong gradients in the slice-select direction after the frequency encoding and before the next RF pulse. Because spins in different locations in the magnet thereby experience a variety of magnetic field strengths, they will precess at differing frequencies; as a consequence they will quickly become dephased. Magnetic field gradients are not very efficient at spoiling the transverse steady state. To be effective, the spins must be forced to precess far enough to become phased randomly with respect to the RF excitation pulse. In clinical MRI machines, the field gradients are set up in such a way that they increase and decrease relative to the center of the magnet; the magnetic field at the magnet 'isocenter' does not change.
The T1 weighting increases with the flip angle and the T2* weighting increases with echo time (TE). Typical repetition time (TR) are 30-500 ms and TE less than 15 ms.

See also Ernst Angle.
spacer
MRI Resources 
Image Quality - Contrast Agents - Safety Products - Pacemaker - Implant and Prosthesis - Case Studies
 
Contrast Enhanced Fast Field Echo with T2 Star WeightingMRI Resource Directory:
 - Sequences -
 
spacer
MRI Resources 
Universities - Chemistry - Open Directory Project - Calculation - Used and Refurbished MRI Equipment - MRI Accidents
 
SHORT Repetition Technique Based on Free Induction DecayInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
spacer

• View the DATABASE results for 'SHORT Repetition Technique Based on Free Induction Decay' (2).Open this link in a new window

MRI Resources 
Liver Imaging - Open Directory Project - Pregnancy - Shielding - Pediatric and Fetal MRI - MRI Training Courses
 
     1 - 5 (of 10)     next
Result Pages : [1]  [2]
 Random Page
 
Share This Page
FacebookTwitterLinkedIn

MR-TIP    
Community   
User
Pass
Forgot your UserID/Password ?    



Personalized protocols (age, gender, body habitus, etc.) lead to :
more automated planning 
improved patient comfort 
better diagnostics 
optimized image quality 
nothing 

Look
      Ups





MR-TIP.com uses cookies! By browsing MR-TIP.com, you agree to our use of cookies.

Magnetic Resonance - Technology Information Portal
Member of SoftWays' Medical Imaging Group - MR-TIP • Radiology-TIP • Medical-Ultrasound-Imaging • 
Copyright © 2003 - 2024 SoftWays. All rights reserved. [ 29 March 2024]
Terms of Use | Privacy Policy | Advertising
 [last update: 2024-02-26 03:41:00]