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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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News  (7)  Resources  (1)  Forum  (6)  
 
Multi Echo Imaging
 
Multi echo imaging sequences use a series of echoes acquired as a train following after a single excitation pulse. Multiple symmetrical or asymmetrical echoes can be acquired, typically T2 weighted. In spin echo imaging, each echo is formed by a 180° pulse, but also a FSE (TSE, RARE) or EPI sequence can be used. As a difference to a normal fast spin echo sequence, in multi echo imaging, separate images are produced from each echo of the train with different T2 weightings. The signal height reduces with transverse relaxation. This drop in signal can be used to calculate a pure T2 image.
See also Fast Spin Echo.
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Further Reading:
  Basics:
A very simple, robust and fast method for estimating and displaying average time constants of T2 decays from multiecho MRI images using color intensity projections
   by arxiv.org    
What MRI Sequences Produce the Highest Specific Absorption Rate (SAR), and Is There Something We Should Be Doing to Reduce the SAR During Standard Examinations?
Thursday, 16 April 2015   by www.ajronline.org    
  News & More:
Automatic Mapping Extraction from Multiecho T2-Star Weighted Magnetic Resonance Images for Improving Morphological Evaluations in Human Brain
Wednesday, 5 June 2013   by www.hindawi.com    
RARE
Monday, 3 December 2012   by www2.warwick.ac.uk    
MRI Resources 
MRI Physics - MRI Technician and Technologist Career - Collections - Intraoperative MRI - Supplies - Case Studies
 
Negative Oral Contrast AgentsForum -
related threadsInfoSheet: - Contrast Agents - 
Intro, Overview, 
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 - Contrast Agents -
 
Categories of negative oral contrast agents:
Gastrointestinal diamagnetic contrast agents
Gastrointestinal superparamagnetic contrast agents
Perfluorochemicals
Negative oral contrast media are usually based on superparamagnetic particles and act by inducing local field inhomogeneities, which results in shortening of both T1 and T2 relaxation times. Superparamagnetic contrast agents have predominant T2 weighted effects. Biphasic contrast media are agents that have different signal intensities on different sequences, depending on the concentration at which they are used.
Suitable materials for oral contrast agents should have little or no absorption by the stomach or intestines, complete excretion, no motion or susceptibility artifacts, affordability, and uniform marking of the gastrointestinal tract. Benefits of negative oral contrast agents are the reduction of ghosting artifacts caused by the lack of signal. Superparamagnetic iron oxides produce also in low concentrations a noticeable signal loss; but can generate susceptibility artifacts especially in gradient echo sequences. Perfluorochemicals do not dilute in the bowel because they are not miscible with water.
High cost, poor availability, and limited evaluations of side effects are possible disadvantages.
Negative oral contrast agents are used e.g., in MRCP, where the ingestion of 600-900 ml of SPIO cancels out the signal intensity of the lumen (in addition after the injection of a gadolinium-based contrast medium, the enhancement of the inflammatory tissues is clearer seen), and in MR abdominal imaging of Crohn's disease in combination with mannitol.


Contrast Guidance
Blueberry or pineapple juices are useable for examinations of the pancreas (MRCP, upper abdominal imaging) as cheep contrast agents, because of the content of magnetic substances (e.g. manganese). See also Ferristene, Ferumoxsil, Oral Magnetic Particles, Gastrointestinal Imaging.
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Further Reading:
  Basics:
Components of Oral Contrast Agent for Magnetic Resonance Imaging(.pdf)
   by www.ffcr.or.jp    
MRI Resources 
Claustrophobia - Universities - Pediatric and Fetal MRI - Coils - MRI Technician and Technologist Career - Sequences
 
Oxygen Mapping
 
The activation of the brain is mirrored in the local changes in metabolism and hemodynamics (brit. haemodynamics). By using heavily T2 weighted scans activated brain areas show an increase in signal intensity as oxyhaemoglobin (brit. oxyhaemoglobin) is diamagnetic and deoxyhemoglobin (brit. deoxyhaemoglobin) is paramagnetic. Oxygen mapping will benefit from high field strength.
See also Blood Oxygenation Level Dependent Contrast, Haemoglobin, Perfusion Imaging, Diamagnetism, Paramagnetism.
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Further Reading:
  News & More:
Potential and Limitations of Oxygen-17 MR Perfusion Measurements
Monday, 1 March 2004   by www.case.edu    
Gold Acupuncture Needle MRI Pain Discovery
Friday, 3 January 2014   by www.healthcmi.com    
Brain-imaging technique could offer invaluable prognostic data
Thursday, 16 February 2012   by www.theengineer.co.uk    
Searchterm 'T2 Weighted' was also found in the following services: 
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Sensitivity EncodingInfoSheet: - Sequences - 
Intro, 
Overview, 
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etc.
 
(SENSE™) A MRI technique for relevant scan time reduction. The spatial information related to the coils of a receiver array are utilized for reducing conventional Fourier encoding. In principle, SENSE can be applied to any imaging sequence and k-space trajectories. However, it is particularly feasible for Cartesian sampling schemes. In 2D Fourier imaging with common Cartesian sampling of k-space sensitivity encoding by means of a receiver array enables to reduce the number of Fourier encoding steps.
SENSE reconstruction without artifacts relies on accurate knowledge of the individual coil sensitivities. For sensitivity assessment, low-resolution, fully Fourier-encoded reference images are required, obtained with each array element and with a body coil.
The major negative point of parallel imaging techniques is that they diminish SNR in proportion to the numbers of reduction factors. R is the factor by which the number of k-space samples is reduced. In standard Fourier imaging reducing the sampling density results in the reduction of the FOV, causing aliasing. In fact, SENSE reconstruction in the Cartesian case is efficiently performed by first creating one such aliased image for each array element using discrete Fourier transformation (DFT).
The next step then is to create a full-FOV image from the set of intermediate images. To achieve this one must undo the signal superposition underlying the fold-over effect. That is, for each pixel in the reduced FOV the signal contributions from a number of positions in the full FOV need to be separated. These positions form a Cartesian grid corresponding to the size of the reduced FOV.
The advantages are especially true for contrast-enhanced MR imaging such as dynamic liver MRI (liver imaging) , 3 dimensional magnetic resonance angiography (3D MRA), and magnetic resonance cholangiopancreaticography (MRCP).
The excellent scan speed of SENSE allows for acquisition of two separate sets of hepatic MR images within the time regarded as the hepatic arterial-phase (double arterial-phase technique) as well as that of multidetector CT.
SENSE can also increase the time efficiency of spatial signal encoding in 3D MRA. With SENSE, even ultrafast (sub second) 4D MRA can be realized.
For MRCP acquisition, high-resolution 3D MRCP images can be constantly provided by SENSE. This is because SENSE resolves the presence of the severe motion artifacts due to longer acquisition time. Longer acquisition time, which results in diminishing image quality, is the greatest problem for 3D MRCP imaging.
In addition, SENSE reduces the train of gradient echoes in combination with a faster k-space traversal per unit time, thereby dramatically improving the image quality of single shot echo planar imaging (i.e. T2 weighted, diffusion weighted imaging).
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Further Reading:
  News & More:
Image Characteristics and Quality
   by www.sprawls.org    
MRI Resources 
Developers - Claustrophobia - - Mass Spectrometry - Jobs pool - Fluorescence
 
Spin Echo Multi SliceInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
(SEMS) This pulse sequence is composed of a 90° RF pulse followed by a 180° refocusing pulse. Both RF pulses are applied in the presence of a slice select gradient.
By choosing of different TR and TE, depending on the T1 and T2 values of the tissues, proton density, T1 weighted and T2 weighted images can be acquired.
The inversion recovery option enlarge the RF pulses with a 180° inverting pulse, applied a TI time before the beginning of the pulse sequence in order to manipulate image contrast.
See also Spin Echo Sequence.
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Further Reading:
  Basics:
Fast Spin Echo(.pdf)
Tuesday, 24 January 2006   by www.81bones.net    
MRI Resources 
Colonography - Universities - Shoulder MRI - PACS - MR Myelography - Crystallography
 
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