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Result : Searchterm 'MX' found in 1 term [] and 11 definitions []
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Mx
 
(MX) Dimension in the stationary (laboratory) frame of reference in the plane orthogonal (at right angles) to the direction of the static magnetic field (B0 or H0), z, and orthogonal to y, the other dimension in this plane. This is commonly defined to be in the direction of the frequency-encoding gradient.
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Signal Intensity
 
Signal intensity interpretation in MR imaging has a major problem.
Often there is no intuitive approach to signal behavior as signal intensity is a very complicated function of the contrast-determining tissue parameter, proton density, T1 and T2, and the machine parameters TR and TE. For this reason, the terms T1 weighted image, T2 weighted image and proton density weighted image were introduced into clinical MR imaging.
Air and bone produce low-intensity, weaker signals with darker images. Fat and marrow produce high-intensity signals with brighter images.
The signal intensity measured is related to the square of the xy-magnetization, which in a SE pulse sequence is given by
Mxy = Mxy0(1-exp(-TR/T1)) exp(-TE/T2) (1)
where Mxy0 = Mz0 is proportional to the proton or spin density, and corresponds to the z-magnetization present at zero time of the experiment when it is tilted into the xy-plane.

See also T2 Weighted Image and Ernst Angle.
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Further Reading:
  Basics:
Contrast mechanisms in magnetic resonance imaging
2004   by www.iop.org    
Image Characteristics and Quality
   by www.sprawls.org    
  News & More:
Specialized MRI sensor can detect light deep within tissues
Thursday, 22 December 2022
Study compares effect of food intake on manganese-based MRI contrast agent absorption
Saturday, 3 December 2022   by www.itnonline.com    
Kidney stone imaging with 3D ultra-short echo time (UTE) magnetic resonance imaging. A phantom study - Abstract
Wednesday, 11 March 2015   by www.urotoday.com    
MRI Resources 
Corporations - Mobile MRI - DICOM - Health - MRI Centers - MRI Technician and Technologist Schools
 
Spin Density
 
(N) The SI units is moles/m3.
Definition: The concentration of nuclei in tissue processing at the Larmor frequency in a given region; one of the principal determinants of the strength of the NMR signal from the region.
For water, there are about 1.1 x 105 moles of hydrogen per m3, or 0.11 moles of hydrogen/cm3.
The signal intensity measured is related to the square of the xy-magnetization, which in a SE pulse sequence is given by
Mxy = Mxy0(1-exp(-TR/T1)) exp(-TE/T2)
where Mxy0 = Mz0 is proportional to the proton or spin density, and corresponds to the z-magnetization present at zero time of the experiment when it is tilted into the xy-plane.
True spin density is not imaged directly, but must be calculated from signals received with different interpulse times. The spin density contrast can be generated by using a long TR and sampling the data immediately after the RF pulse (with a TE as short as possible).
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• View the NEWS results for 'Spin Density' (1).Open this link in a new window.
 
Further Reading:
  Basics:
Magnetic resonance imaging
   by www.scholarpedia.org    
How Many? A Dictionary of Units of Measurement © Russ Rowlett and the University of North Carolina at Chapel Hill
Wednesday, 21 March 2001   by www.unc.edu    
How does the proton get its spin?
Wednesday, 17 February 2010   by www.physorg.com    
Searchterm 'MX' was also found in the following services: 
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Partial Fourier Technique
 
The partial Fourier technique is a modification of the Fourier transformation imaging method used in MRI in which the symmetry of the raw data in k-space is used to reduce the data acquisition time by acquiring only a part of k-space data.
The symmetry in k-space is a basic property of Fourier transformation and is called Hermitian symmetry. Thus, for the case of a real valued function g, the data on one half of k-space can be used to generate the data on the other half.
Utilization of this symmetry to reduce the acquisition time depends on whether the MRI problem obeys the assumption made above, i.e. that the function being characterized is real.
The function imaged in MRI is the distribution of transverse magnetization Mxy, which is a vector quantity having a magnitude, and a direction in the transverse plane. A convenient mathematical notation is to use a complex number to denote a vector quantity such as the transverse magnetization, by assigning the x'-component of the magnetization to the real part of the number and the y'-component to the imaginary part. (Sometimes, this mathematical convenience is stretched somewhat, and the magnetization is described as having a real component and an imaginary component. Physically, the x' and y' components of Mxy are equally 'real' in the tangible sense.)
Thus, from the known symmetry properties for the Fourier transformation of a real valued function, if the transverse magnetization is entirely in the x'-component (i.e. the y'-component is zero), then an image can be formed from the data for only half of k-space (ignoring the effects of the imaging gradients, e.g. the readout- and phase encoding gradients).
The conditions under which Hermitian symmetry holds and the corrections that must be applied when the assumption is not strictly obeyed must be considered.
There are a variety of factors that can change the phase of the transverse magnetization:
Off resonance (e.g. chemical shift and magnetic field inhomogeneity cause local phase shifts in gradient echo pulse sequences. This is less of a problem in spin echo pulse sequences.
Flow and motion in the presence of gradients also cause phase shifts.
Effects of the radio frequency RF pulses can also cause phase shifts in the image, especially when different coils are used to transmit and receive.
Only, if one can assume that the phase shifts are slowly varying across the object (i.e. not completely independent in each pixel) significant benefits can still be obtained. To avoid problems due to slowly varying phase shifts in the object, more than one half of k-space must be covered. Thus, both sides of k-space are measured in a low spatial frequency range while at higher frequencies they are measured only on one side. The fully sampled low frequency portion is used to characterize (and correct for) the slowly varying phase shifts.
Several reconstruction algorithms are available to achieve this. The size of the fully sampled region is dependent on the spatial frequency content of the phase shifts. The partial Fourier method can be employed to reduce the number of phase encoding values used and therefore to reduce the scan time. This method is sometimes called half-NEX, 3/4-NEX imaging, etc. (NEX/NSA). The scan time reduction comes at the expense of signal to noise ratio (SNR).
Partial k-space coverage is also useable in the readout direction. To accomplish this, the dephasing gradient in the readout direction is reduced, and the duration of the readout gradient and the data acquisition window are shortened.
This is often used in gradient echo imaging to reduce the echo time (TE). The benefit is at the expense in SNR, although this may be partly offset by the reduced echo time. Partial Fourier imaging should not be used when phase information is eligible, as in phase contrast angiography.

See also acronyms for 'partial Fourier techniques' from different manufacturers.
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T1 WeightedInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
Every tissue in the human body has its own T1 and T2 value. This term is used to indicate an image where most of the contrast between tissues is due to differences in the T1 value.
This term may be misleading in that the potentially important effects of tissue density differences and the range of tissue T1 values are ignored.
If the machine parameters are chosen, so that TR less than T1 (typically under 500 ms) and TE less than T2 (typically under 30 ms), a power series expansion of the exponential functions and then neglecting second and higher order terms yields
Mxy = Mxy0 TR/T1
thus the expression becomes independent of T2 and yields the condition for T1 weighting. Therefore a T1 contrast is approached by imaging with a short TR, compared to the longest tissue T1 of interest and short TE, compared to tissue T2 (to reduce T2 contributions to image contrast). Due to the wide range of T1 and T2 and tissue density values that can be found in the body, an image that is T1 weighted for some tissues may not be so for others.
Lesions with short T1 are (bright in T1 weighted sequences):
fat (lipoma, dermoid)
sub-acute haemorrhage (metHb)
paramagnetic agent (Gd, pituitary)
protein-containing fluid (colloid cyst)
metastatic melanoma (melanotic).
 
Images, Movies, Sliders:
 MRI Orbita T1  Open this link in a new window
    
 MRI Liver In Phase  Open this link in a new window
    
 Sagittal Knee MRI Images T1 Weighted  Open this link in a new window
 MRI - Anatomic Imaging of the Ankle 2  Open this link in a new window
    
SlidersSliders Overview

 
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• View the DATABASE results for 'T1 Weighted' (56).Open this link in a new window

 
Further Reading:
  Basics:
A paired dataset of T1- and T2-weighted MRI at 3 Tesla and 7 Tesla
Thursday, 27 July 2023   by www.nature.com    
A practical guideline for T1 reconstruction from various flip angles in MRI
Saturday, 1 October 2016   by journals.sagepub.com    
Accurate T1 Quantification Using a Breath-hold Inversion Recovery TrueFISP Sequence
2003   by rsna2003.rsna.org    
  News & More:
T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI
Monday, 1 September 2008   by www.ncbi.nlm.nih.gov    
Possible New MRI Marker for Multiple Sclerosis Progression
Wednesday, 29 August 2007   by www.medpagetoday.com    
T1-weighted Phase Sensitive Inversion Recovery for Imaging Multiple Sclerosis Lesions in the Cervical Spinal Cord(.pdf)
   by www.healthcare.siemens.com    
MRI Resources 
MR Myelography - Breast MRI - Raman Spectroscopy - Musculoskeletal and Joint MRI - Examinations - MRI Centers
 
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