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Volumetric Imaging
 
Volumetric imaging is a 3D technique where all the MRI signals are collected from the entire tissue sample and imaged as a whole entity, therefore providing a high signal to noise ratio. The acquisition of isotropic voxels or thin slices with high spatial resolution allows to create multiplanar reconstructions in all planes; a compensation for the usually longer scan time. The acquisition time can be reduced by parallel imaging technique.
New T2 weighted variants of 3D sequences (FSE-XETA, T2-SPACE, VISTA) have been introduced that differ from conventional FSE sequences. An echo train containing up to 200 echoes obtained at a minimum echo spacing allows very fast acquisition. A flip angle modulation (flip angle sweep - FAS) during the FSE readout carries magnetization as long as possible to avoid blurring and provide optimal signal at the effective echo time. This type of imaging is well suited for brain and spine MRI procedures.
Newer T1 weighted variants include Liver Acquisition with Volume Acquisition (LAVA) and T1W High Resolution Isotropic Volume Examination (THRIVE), which have advantages for dynamic breath hold imaging in liver and abdominal examinations.

See also Volume Imaging, 3 Dimensional Imaging.
 
Images, Movies, Sliders:
 Brain MRI Sagittal T1 001  Open this link in a new window
    
 Circle of Willis, Time of Flight, MIP  Open this link in a new window
    
SlidersSliders Overview

 MRI of the Skull Base  Open this link in a new window
    
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• View the NEWS results for 'Volumetric Imaging' (1).Open this link in a new window.
 
Further Reading:
  Basics:
Cutting Edge Imaging of THE Spine
February 2007   by www.pubmedcentral.nih.gov    
3-D VOLUMETRIC IMAGING FOR STEREOTACTIC LESIONAL AND DEEP BRAIN STIMULATION SURGERY
MRI Resources 
Examinations - Movies - IR - Databases - Online Books - Knee MRI
 
Stimulated Echo
 
A form of a spin echo produced by three pulse RF sequences, consisting of two RF pulses following an initial exciting RF pulse. The stimulated echo appears at a time delay after the third pulse equal to the interval between the first two pulses. Although classically produced with 90° pulses, any RF pulses other than an ideal 180° can produce a stimulated echo. The intensity of the echo depends in part on the T1 relaxation time because the excitation is 'stored' as longitudinal magnetization between the second and third RF pulses. For example, use of stimulated echoes with spatially selective excitation with orthogonal magnetic field gradients permits volume-selective excitation for spectroscopic localization.
mri safety guidance
Image Guidance
Artifacts may appear as a series of fine lines. A narrow bandwidth causes a wide read window, which allows the stimulated echo to be incorporated into the image data. This can be supported by increasing the received bandwidth, which would narrow the read window, thus not incorporating the extraneous echo. Another help would be to change the first echo time, which may change the spacing of the stimulated echoes to outside that of the read window for the second echo.
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• View the DATABASE results for 'Stimulated Echo' (8).Open this link in a new window

 
Further Reading:
  Basics:
Magnetic resonance imaging
   by www.scholarpedia.org    
Clinical evaluation of a speed optimized T2 weighted fast spin echo sequence at 3.0 T using variable flip angle refocusing, half-Fourier acquisition and parallel imaging
Wednesday, 25 October 2006
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