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Result : Searchterm 'Homogeneity' found in 4 terms [] and 44 definitions []
| previous 16 - 20 (of 48) nextResult Pages : [1] [2 3 4 5 6 7 8 9 10] | | | | Searchterm 'Homogeneity' was also found in the following services: | | | | |
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REASON
Combination of problems
Image Guidance
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(FAT SAT) A specialized technique that selectively saturates fat protons prior to acquiring data as in standard sequences, so that they produce a negligible signal. The presaturation pulse is applied prior to each slice selection. This technique requires a very homogeneous magnetic field and very precise frequency calibration.
Fat saturation does not work well on inhomogeneous volumes of tissue due to a change in the precessional frequencies as the difference in volume affects the magnetic field homogeneity. The addition of a water bag simulates a more homogeneous volume of tissue, thus improving the fat saturation. Since the protons in the water bag are in motion due to recent motion of the bag, phase ghosts can be visualized.
Fat saturation can also be difficult in a region of metallic prosthesis. This is caused by an alteration in the local magnetic field resulting in a change to the precessional frequencies, rendering the chemical saturation pulses ineffective.
See also Fat Suppression, and Dixon. | | | | | | • View the DATABASE results for 'Fat Saturation' (9).
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Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization: a net magnetic moment in the absence of an external magnetic field. More recently: a material is ferromagnetic, only if all of its magnetic ions add a positive contribution to the net magnetization (for differentiation to ferrimagnetic and antiferromagnetic materials). If some of the magnetic ions subtract from the net magnetization (if they are partially anti-aligned), then the material is ferrimagnetic. If the ions anti-align completely so as to have zero net magnetization, despite the magnetic ordering, then it is an antiferromagnet. All of these alignment effects only occur at temperatures below a certain critical temperature, called the Curie temperature (for ferromagnets and ferrimagnets) or the Néel temperature (for antiferromagnets). Typical ferromagnetic materials are iron, cobalt, and nickel.
In MRI ferromagnetic objects, even very small ones, as implants or incorporations distort the homogeneity of the main magnetic field and cause susceptibility artifacts. | | | | • View the DATABASE results for 'Ferromagnetism' (7).
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| | | | • View the DATABASE results for 'Gradient Echo' (121).
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| | | Searchterm 'Homogeneity' was also found in the following services: | | | | |
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| | | | • View the DATABASE results for 'Image Quality' (42).
| | | • View the NEWS results for 'Image Quality' (4).
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