RF transmission in MRI

[jobinshere@gmail.com]

Hi i have some Doubt in the RF Transmission in MRI Scanner.
1.Mainly the [b]theory behind the impedance matching importance in RF transmission,how it is happening while RF Transmission.

2.And is this RF is like a oscillating current to the body coil of the scanner to create RF.

3.Once the RF is emitted,if iam using a 3.0T scanner the larmour frequency will be 127.74MHz,will the RF will be pulsed only in one frequency which is 127.74 to create the resonance and to get image.

4.And if the gradient slope is applied in isocentre, frequncy will be 127.74MHz and i have acquired the signal,and what will be done if i wanted to acquire the image from nearby area which having spin difference 128.00MHZ will the table will move to isocentre to acquire the image or the RF frequency from the RF amp will change to 128 MHZ to resonate that area.

Thanks in advance
Jobins

[aelster]

In an MR scanner, a range of frequencies is transmitted by each RF-pulse, not just the single center (Larmor) frequency. This is known as the RF-bandwidth (different from the receiver bandwidth). The RF-bandwidth depends on the type of pulse used. Spatially selective pulses (such as sinc-like ones) typically excite a relatively narrow range of frequencies (RF bandwidth ≈ 2 kHz). Nonselective pulses (so-called hard or rectangular pulses) excite a much larger range (RF bandwidth ≈ 250 kHz).

So, depending on how far away the body section to be imaged is from magnet isocenter and the type of RF excitation desired, the table (patient) may or may not need to be moved.

[jamesgherrera]

Radio frequency (RF) is any of the electromagnetic wave frequencies that lie in the range extending from around 3 kHz to 300 GHz, which include those frequencies used for communications or radar signals. RF usually refers to electrical rather than mechanical oscillations. However, mechanical RF systems do exist. Although radio frequency is a rate of oscillation, the term "radio frequency" or its abbreviation "RF" are used as a synonym for radio – i.e., to describe the use of wireless communication, as opposed to communication via electric wires.

[BeulahSpray]

This is known as the RF-bandwidth (different from the receiver bandwidth). The RF-bandwidth depends on the type of pulse used. Spatially selective pulses (such as sinc-like ones) typically excite a relatively narrow range of frequencies (RF bandwidth ≈ 2 kHz). Nonselective pulses (so-called hard or rectangular pulses) excite a much larger range (RF bandwidth ≈ 250 kHz).