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MED 107- MEDICAL PHYSICS II > 97. MRI: RADIO FREQUENCY COILS > Flashcards

97. MRI: RADIO FREQUENCY COILS Flashcards

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1
Q
  1. What are Radio Frequency coils?
A
  • they are coils that consist of loops of wire
  • they transmit the Radio Frequency Pulses
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2
Q
  1. What happens when a current passes through a Radio Frequency Coil?
A
  • a magnetic field is produced
  • this is at a 90° angle to the direction of the External
    Magnetic Field (B₀)
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3
Q
  1. What effects the MR signal directly?
A
  • the configuration of the Radio Frequency Transmitter
  • the configuration of the Receiver Probes
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4
Q
  1. List the types of coils that are currently used in MR Imaging?
A
  1. Transmit Coils
  2. Receiver Coils
  3. Surface Coils
  4. Phased Array Coils
  5. Volume Coils
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5
Q
  1. What are Transmit Coils?
A
  • these are the coils that transmit the Radio frequency
    pulses
  • they transmit energy
  • this is transmitted at the resonant frequency of
    Hydrogen
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6
Q
  1. What can be said about the energy that is transmitted from the Transmit Coils?
A
  • it is in the form of a short, intense burst of Radio
    Frequency
  • this is known as the Radio Frequency Pulse
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7
Q
  1. Why is the energy transmitted at the Resonant frequency of Hydrogen in Transmit Coils?
A
  • the aim is to flip the Net Magnetisation Vector to the
    Transverse Plane
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8
Q
  1. What are the main coils that are used to transmit Radio Frequency pulses in most systems?
A
  1. A BODY COIL
    - this is located within the bore of the magnet
  2. A HEAD COIL
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9
Q
  1. What are Receiver Coils?
A
  • these are coils that are placed in the Transverse Plane
  • they generate a voltage within them
  • they also detect the Radio Frequency Pulses
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10
Q
  1. How do Receiver Coils generate a voltage within them?
A
  • this happens when a moving magnetic field cuts across
    the loops of wire
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11
Q
  1. What does this voltage become?
A
  • this voltage becomes the MR signal
  • this is what forms the image
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12
Q
  1. What is a necessary step that needs to happen in order for an MR signal to be induced?
A
  • the Transverse Magnetisation must occur
  • this is when the Net Magnetisation Vector is placed in
    the Transverse Plane
  • this must happen in a perpendicular direction to the
    Receiver Coils
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13
Q
  1. Label this diagram?
A
  1. Transmit Coils
  2. Receiver Coils
  3. Receiver Coils
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14
Q
  1. What are Surface Coils?
A
  • these are coils that are placed in contact with the
    surface that we want to image
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15
Q
  1. What is the purpose of Surface Coils?
A
  • they improve the Signal to Noise ratio (SNR)
  • this happens when the imaging structures are placed
    near the surface of the patient
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16
Q
  1. What is the relationship between the Signal to Noise Ratio (SNR) and the distance of the surface coil from the patient?
A
  • they are inversely proportional

THE SHORTER THE DISTANCE BETWEEN THE COIL AND THE PATIENT:
- the greater the Signal to Noise Ratio will be

17
Q
  1. Why is the Signal to Noise ratio greater when the Surface Coil is closer to the patient being examined?
A
  • the coil is closer to the signal-emitting anatomy
  • the only noise that is received is that in the immediate
    area of the coil
  • there is no other external noise
18
Q
  1. What are two characteristics of the shape of the Surface Coil?
A
  1. small
  2. specifically shaped
    (they can be circular or square)
19
Q
  1. Why are the Surface Coils specifically shaped?
A
  • this allows them to be easily placed near the anatomy
    that we want to image
  • this is done with there being very little pain or
    discomfort to the patient
20
Q
  1. What are the advantage of using Surface Coils?
A
  1. THE SIGNAL TO NOISE RATIO IS ENHANCED
  2. THE SPATIAL RESOLUTION OF SMALL STRUCTURES
    CAN BE ACHIEVED
21
Q
  1. What happens when we use Local Coils?
A
  • the Body Coil is used to Transmit the Radio
    Frequency Pulse
  • the Local Coil is used to receive the MR Signal
22
Q
  1. What body parts do we use the Surface Coils to image?
A
  1. Shoulder
  2. Elbow
  3. Wrist
  4. Hand
  5. Eye Ball
  6. Local Anatomy
    (Prostate)

MED 107- MEDICAL PHYSICS II (108 decks)

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