Question

In an MRI scan, a higher magnetic field requires higher frequency radio waves to resonate with the nuclear type whose density and location are being imaged. What effect does going to a larger magnetic field have on the most efficient antenna to broadcast those radio waves? Does it favor a smaller or larger antenna?

a) Larger magnetic fields favor smaller antennas.

b) Larger magnetic fields favor larger antennas.

c) Magnetic field size does not affect antenna efficiency.

d) Larger magnetic fields favor antennas of any size.

Answer 1

Larger magnetic fields in MRI require higher frequency radio waves, and because antenna size is inversely proportional to frequency, a larger magnetic field favors a smaller antenna.

Step-by-step explanation:

When considering the effect of a larger magnetic field on the efficiency of the antenna used in Magnetic Resonance Imaging (MRI), it is important to understand the resonance phenomenon of the nuclei. In an MRI, to resonate with a specific nuclear type, such as protons within the body, higher frequency radio waves are necessary as the strength of the magnetic field increases. These radio waves are broadcast, absorbed, and reemitted during the MRI process. The size of the antenna is inversely proportional to the frequency of the radio waves; thus, a higher frequency required by a stronger magnetic field will favor a smaller antenna.

As the magnetic field increases, so does the frequency of the radio waves needed to cause the resonance of protons. In terms of radio wave frequency and antenna size, the relationship is given by the principle that the resonant frequency of an antenna is directly related to its size—smaller antennas are used for higher frequencies, and larger antennas are used for lower frequencies. Therefore, the correct answer to the question is that larger magnetic fields favor smaller antennas (a). This is due to the higher frequency radio waves required to match the proton resonance conditions within the larger magnetic field.