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Part1and 2 Mri Registry Review
- 1. Basic Image Formation Part I Magnets Amanda Golsch BSc RT(R)(MR)
- 16. PART II The RF System Gradient Coils Transmit and Receive Bandwidth
Hinweis der Redaktion
- Each substance should be evaluated for magnetic susceptibility. Magnetic susceptibility is a substances ability to become magnetized.
- Paramagnetic substances have a low and positive (+ 1) magnetic susceptibility.
- This concept is very important for registry purposes. A current (negatively charged electrons) that flows through a long straight wire creates a magnetic field about the wire.
- Vertical magnets are great for patients who are claustrophobic due to their open design.
- In order to produce a static field direct current is needed. Increasing the amount of current (or turns of wire) increases the field strength as well as heating of the wire.
- The further away the transmit coil the more RF you need, so you increase the SAR. Lower SAR levels are achieved with the use of transmit/receive coils. The body coil has a uniform transmission, and a higher RF.
- Transmit bandwidth sends the RF pulse to a prescribed location and the frequency ranges are narrowed or expanded to determine slice thickness. Example to determine absolute receiver bandwidth. If 256 frequency samples are collected during an 8 millisecond sampling period, the absolute receiver bandwidth is 32 kHz.