The entry slice phenomenon arise in MRI when blood with unsaturated spins flows in the observed slice(s). These spins will emit a strong signal, because of their unsaturated status (flow related enhancement). The number of slices affected depends on the flowvelocity and the slice thickness; the direction of flow determines which slices are affected.
Time of FlightMRA is based on this entry slice phenomenon.
(PEAR) Each phase of the respiratory cycle coincides with the collection of phase encoded data. The low order phase encoded data, with is highly sensitive to motion, is collected towards the end of exhalation and beginning of inspiration. The high order data, which is less sensitive, is collected over the remaining part of each respiratory cycle.
The received radio frequency signal is too strong, parts of the signal get lost by converting from analog to digital, resulting in a washed out image.
Image Guidance
Auto-prescanning usually adjusts the amplification at the receiver in a way, that the received signal could be processed without any loss. Else the receiver gain must be corrected manually.
Radio frequency quadrature artifacts occur when the detector channels of the quadrature detector are disturbed.
A DC offset of one amplifier output can e.g., produce a bright point in the center of the field of view (see also central point artifact), or a higher gain of one detector channel can generate diagonally ghosting.
Image Guidance
Radio frequency quadrature artifacts are technical faults and must be eliminated by the service.
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