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 'T2 Weighted' 
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Result : Searchterm 'T2 Weighted' found in 2 terms [] and 44 definitions []
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Gradient Echo SequenceForum -
related threadsInfoSheet: - Sequences - 
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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.
 
Images, Movies, Sliders:
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 Circle of Willis, Time of Flight, MIP  Open this link in a new window
    
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• Related Searches:
    • Black Boundary Artifact
    • Steady State Free Precession
    • MRI History
    • Contrast Enhanced MRI
    • Ultrafast Gradient Echo Sequence
 
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 
Stent - Supplies - Education - Safety Training - Stimulator pool - MRI Technician and Technologist Schools
 
Half Fourier Acquisition Single Shot Turbo Spin EchoInfoSheet: - Sequences - 
Intro, 
Overview, 
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etc.MRI Resource Directory:
 - Sequences -
 
(HASTE) A pulse sequence with data acquisition after an initial preparation pulse for contrast enhancement with the use of a very long echo train (Single shot TSE), whereat each echo is individually phase encoded. This technique is a heavily T2 weighted, high speed sequence with partial Fourier technique, a great sensitivity for fluid detection and a fast acquisition time of about 1 sec per slice. This advantage makes it possible for using breath-hold with excellent motionless MRI, e.g. used for liver and lung imaging.

See also Segmented HASTE.
 
Images, Movies, Sliders:
 Anatomic Imaging of the Lungs  Open this link in a new window
      

Courtesy of  Robert R. Edelman
 Fetus (Brain) and Dermoid in Mother  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 
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• View the DATABASE results for 'Half Fourier Acquisition Single Shot Turbo Spin Echo' (5).Open this link in a new window

 
Further Reading:
  News & More:
EVALUATION OF HUMAN STROKE BY MR IMAGING
2000
The cerebello-pontine angle, ACNR • VOLUME 2 NUMBER 3, Page 16
2002
MRI Resources 
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Hepatobiliary Contrast AgentsInfoSheet: - Contrast Agents - 
Intro, Overview, 
Characteristics, 
Types of, 
etc.MRI Resource Directory:
 - Contrast Agents -
 
The characteristics of a hepatobiliary contrast agent are specific liver uptake and excretion via the biliary system. The paramagnetic substance (e.g. manganese, gadolinium) is taken up by normal hepatocytes. Diseased liver tissue did not include hepatocytes or their function is disturbed. Therefore, the signal of healthy liver tissue increases on T1 weighted sequences, but not in the liver lesions.
Another type of liver imaging contrast agent is superparamagnetic iron oxide. These particles accumulate in the reticuloendothelial system (RES) of the liver, and darken the healthy liver tissue in T2 weighted images. RES cells (including Kupffer cells) are existing in healthy liver tissue, in altered tissue with reduced RES activity or without RES cells the contrast agent concentration is also low or not existing, which improves the liver to lesion contrast.
Benefits of hepatobiliary contrast agents:
•
Liver lesions (e.g., tumor, metastases, haemangioma etc.) are better detectable and to characterize.
•
These contrast agents are useful to analyze and evaluate the liver function (in cases of diffuse liver diseases e.g., cirrhosis).
•
Imaging of the gallbladder and biliary system is improved.

Differences of a hepatobiliary contrast agent compared with a targeted contrast agent for Kupffer cells:
•
The higher number of hepatocytes than Kupffer cells improves the uptake effectiveness of the contrast agent.
•
Hepatobiliary contrast agents enable a better opacification of the biliary ducts and the gallbladder caused by the biliary excretion.
•
Hepatobiliary contrast media are fast excreted agents. RES targeted contrast agents remain longer in the body, a fact that can increase possible side effects.

See also Superparamagnetic Contrast Agents, Hepatobiliary Chelates, Liver Imaging, Endoremâ„¢, Primovistâ„¢, and Classifications, Characteristics, etc.

See also the related poll result: 'The development of contrast agents in MRI is'
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• View the DATABASE results for 'Hepatobiliary Contrast Agents' (11).Open this link in a new window

 
Further Reading:
  Basics:
Contrast MRI Best at Finding Liver Trouble - But Timing Matters
Sunday, 6 March 2011   by www.searchmedica.com    
  News & More:
Iron overload: accuracy of in-phase and out-of-phase MRI as a quick method to evaluate liver iron load in haematological malignancies and chronic liver disease
Friday, 1 June 2012   by www.ncbi.nlm.nih.gov    
EMA's final opinion confirms restrictions on use of linear gadolinium agents in body scans
Friday, 21 July 2017   by www.ema.europa.eu    
MAGNETIC RESONANCE IMAGING OF FOCAL LIVER LESIONS(.pdf)
2002
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Inversion Recovery SequenceForum -
related threadsInfoSheet: - Sequences - 
Intro, 
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etc.
 
Inversion Recovery Sequence Timing Diagram (IR) The inversion recovery pulse sequence produces signals, which represent the longitudinal magnetization existing after the application of a 180° radio frequency pulse that rotates the magnetization Mz into the negative plane. After an inversion time (TI - time between the starting 180° pulse and the following 90° pulse), a further 90° RF pulse tilts some or all of the z-magnetization into the xy-plane, where the signal is usually rephased with a 180° pulse as in the spin echo sequence. During the initial time period, various tissues relax with their intrinsic T1 relaxation time.
In the pulse sequence timing diagram, the basic inversion recovery sequence is illustrated. The 180° inversion pulse is attached prior to the 90° excitation pulse of a spin echo acquisition. See also the Pulse Sequence Timing Diagram. There you will find a description of the components.
The inversion recovery sequence has the advantage, that it can provide very strong contrast between tissues having different T1 relaxation times or to suppress tissues like fluid or fat. But the disadvantage is, that the additional inversion radio frequency RF pulse makes this sequence less time efficient than the other pulse sequences.

Contrast values:
PD weighted: TE: 10-20 ms, TR: 2000 ms, TI: 1800 ms
T1 weighted: TE: 10-20 ms, TR: 2000 ms, TI: 400-800 ms
T2 weighted: TE: 70 ms, TR: 2000 ms, TI: 400-800 ms

See also Inversion Recovery, Short T1 Inversion Recovery, Fluid Attenuation Inversion Recovery, and Acronyms for 'Inversion Recovery Sequence' from different manufacturers.
 
Images, Movies, Sliders:
 Brain MRI Inversion Recovery  Open this link in a new window
    
 Knee MRI Sagittal STIR 002  Open this link in a new window
 Brain MRI Coronal FLAIR 001  Open this link in a new window
    
 
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• View the DATABASE results for 'Inversion Recovery Sequence' (8).Open this link in a new window

 
Further Reading:
  Basics:
The equation for a repeated inversion recovery sequence
Contrast mechanisms in magnetic resonance imaging
2004   by www.iop.org    
  News & More:
FLAIR Vascular Hyperintensity: An Important MRI Marker in Patients with Transient Ischemic Attack
Thursday, 14 July 2022   by www.dovepress.com    
MRI Resources 
Databases - Open Directory Project - Cardiovascular Imaging - Portals - Online Books - DICOM
 
Knee MRI
 
Knee MRI, with its high soft tissue contrast is one of the main imaging tools to depict knee joint pathology. MRI allows accurate imaging of intra-articular structures such as ligaments, cartilage, menisci, bone marrow, synovium, and adjacent soft tissue.
Knee exams require a dedicated extremity coil, providing a homogenous imaging volume and high SNR to ensure best signal coverage. A complete knee MR examination includes for example sagittal and coronal T1 weighted, and proton density weighted pulse sequences +/- fat saturation, or STIR sequences. For high spatial resolution, maximal 4 mm thick slices with at least an in plane resolution of 0.75 mm and small gap are recommended. To depict the anterior cruciate ligament clearly, the sagittal plane has to be rotated 10 - 20° externally (parallel to the medial border of the femoral condyle). Retropatellar cartilage can bee seen for example in axial T2 weighted gradient echo sequences with Fatsat. However, the choice of the pulse sequences is depended of the diagnostic question, the used scanner, and preference of the operator.
Diagnostic quality in knee imaging is possible with field strengths ranging from 0.2 to 3T. With low field strengths more signal averages must be measured, resulting in increased scan times to provide equivalent quality as high field strengths.
More diagnostic information of meniscal tears and chondral defects can be obtained by direct magnetic resonance arthrography, which is done by introducing a dilute solution of gadolinium in saline (1:1000) into the joint capsule. The knee is then scanned in all three planes using T1W sequences with fat suppression. For indirect arthrography, the contrast is given i.v. and similar scans are started 20 min. after injection and exercise of the knee.
Frequent indications of MRI scans in musculoskeletal knee diseases are:
e.g., meniscal degeneration and tears, ligament injuries, osteochondral fractures, osteochondritis dissecans, avascular bone necrosis and rheumatoid arthritis.

See also Imaging of the Extremities and STIR.
 
Images, Movies, Sliders:
 Sagittal Knee MRI Images T1 Weighted  Open this link in a new window
      

 Anatomic MRI of the Knee 2  Open this link in a new window
    
SlidersSliders Overview

 Knee MRI Coronal Pd Spir 001  Open this link in a new window
 Sagittal Knee MRI Images STIR  Open this link in a new window
      

 Axial Knee MRI Images T2 Weighted  Open this link in a new window
 Anatomic MRI of the Knee 1  Open this link in a new window
    
SlidersSliders Overview

 
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• View the DATABASE results for 'Knee MRI' (4).Open this link in a new window


• View the NEWS results for 'Knee MRI' (4).Open this link in a new window.
 
Further Reading:
  Basics:
Musculoskeletal MRI at 3.0 T: Relaxation Times and Image Contrast
Sunday, 1 August 2004   by www.ajronline.org    
Knee, Anterior Cruciate Ligament Injuries (MRI)
Tuesday, 28 March 2006   by www.emedicine.com    
  News & More:
NSAIDs May Worsen Arthritis Inflammation
Monday, 21 November 2022   by www.itnonline.com    
A Knee MRI in Half the Time? It's Possible
Thursday, 8 April 2021   by www.diagnosticimaging.com    
Seniors, patients, astronauts will all benefit from new USask research on bone health
Saturday, 27 February 2021   by www.yorktonthisweek.com    
3D mapping algorithm reads knee MRIs for new arthritis treatments
Thursday, 11 June 2020   by www.healthimaging.com    
MRI T2 Mapping of the Knee Providing Synthetic Morphologic Images: Comparison to Conventional Turbo Spin-Echo MRI
Tuesday, 1 October 2019   by pubs.rsna.org    
Researcher uses MRI to measure joint's geometry and role in severe knee injury
Tuesday, 23 September 2014   by medicalxpress.com    
Abnormalities on MRI predict knee replacement
Monday, 9 March 2015   by medicalxpress.com    
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