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Result : Searchterm 'Fourier Transform' found in 8 terms [] and 38 definitions []
| previous 16 - 20 (of 46) nextResult Pages : [1 2] [3 4 5 6 7 8 9 10] | | | | Searchterm 'Fourier Transform' was also found in the following services: | | | | |
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(BW) Bandwidth is a measure of frequency range, the range between the highest and lowest frequency allowed in the signal. For analog signals, which can be mathematically viewed as a function of time, bandwidth is the width, measured in Hertz of a frequency range in which the signal's Fourier transform is nonzero.
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| | | | • View the DATABASE results for 'Chemical Shift' (29).
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Quick Overview Please note that there are different common names for this artifact.
DESCRIPTION
Black or bright band
During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.
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| | | | • View the DATABASE results for 'Chemical Shift Artifact' (7).
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The complex numbers extend the real numbers by including the imaginary unit i (satisfying i2 = - 1). The term 'complex' when used as an adjective means that the field of complex numbers is as the underlying number field considered. In MRI, complex data are used for example in the Fourier transforms. | | | | • View the DATABASE results for 'Complex Data' (3).
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Convolution is a mathematical way of combining two signals to form a third signal. It is the single most important technique in digital signal processing. This operation is mostly used together with Fourier transformations for MRI signal / image processing. | | | | • View the DATABASE results for 'Convolution' (2).
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