Magnetic Resonance Imaging (MRI)

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Questions and Answers

What type of coils are used for generating a varying magnetic field along the z axis?

Circular coils

Rectangular coils

Saddle coils

Helmholtz pairs (correct)

What is the primary function of gradient coils in an MRI system?

To receive RF signals

To generate static magnetic fields

To maintain patient comfort

To produce secondary magnetic fields (correct)

Which coil creates a varying magnetic field from top to bottom?

Y coil (correct)

X coil

Helmholtz coil

Z coil

How do RF coils contribute to image formation in MRI?

They transmit and receive signals Signup and view all the answers

What happens to protons during the RF pulse excitation phase?

They jump to higher energy states Signup and view all the answers

What causes the net magnetization vector to turn toward the transverse plane?

Protons processing in phase Signup and view all the answers

How fast do protons rotate around their axis, according to the information provided?

63,000,000 rotations per second Signup and view all the answers

What is the initial state of protons before the RF pulse is applied?

In equilibrium with the magnetic field Signup and view all the answers

What is the primary use of Magnetic Resonance Imaging (MRI)?

To visualize detailed internal structures Signup and view all the answers

Which of the following is NOT an advantage of MRI?

Inexpensive Signup and view all the answers

What component of the MRI system is essential for creating the magnetic field?

Superconducting magnet Signup and view all the answers

Which disadvantage of MRI relates specifically to patient safety?

Danger to patients with metallic implants Signup and view all the answers

What is the purpose of the gradient coils in an MRI system?

To produce variations in the main magnetic field Signup and view all the answers

How are protons aligned during the MRI process?

Within a strong magnetic field Signup and view all the answers

What effect can patient movement have during MRI scanning?

It may cause blurry images. Signup and view all the answers

What is a significant temperature requirement for the superconducting magnet in an MRI system?

Liquid helium temperature Signup and view all the answers

Study Notes

Magnetic Resonance Imaging (MRI)

MRI is a medical imaging technique used in radiology to visualize detailed internal structures
It uses the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body

Indications for MRI

MRI visualizes detailed internal structures
NMR is used to image atomic nuclei

Concept of MRI image

The MRI image is a display of radio frequency signal intensities emitted by magnetized tissue during imaging
Tissue becomes magnetized because it contains protons (magnetic nuclei of hydrogen atoms)
When placed in a strong magnetic field, some protons align with the field, producing the magnetization of the tissue

Advantages of MRI

No ionizing radiation, no short/long-term effects
Variable thickness, any plane
Better contrast resolution and tissue discrimination
Various sequences to characterize abnormal tissue
Many details without intravenous (IV) contrast

Disadvantages of MRI

Very expensive
Dangerous for patients with metallic devices within the body
Difficult for claustrophobic patients (fear of enclosed spaces)
Movement during scanning may cause blurry images
RF transmitters can cause severe burns if mishandled
Not easily available

Components of the MRI System

Magnet:
- A key element, integrated into the system
- Includes RF and gradient systems
- Superconducting magnet: heart and most expensive part of the MRI scanner
- The magnetic field requirement in modern MRI scanners is limited to 3T
- The main magnet is superconducting, cooled to LHe temperature(liquid Helium) and mounted in an efficient cryostat
- Has a horizontal bore to accommodate the patient
Gradient coils:
- Used to produce deliberate variations in the main magnetic field
- Usually three sets, one for each direction
- The variation in the magnetic field permits localization of image slices, also phase encoding and frequency encoding.
- The gradient coils for the z-axis are Helmholtz pairs, and the x and y axes have paired saddle coils -Generate secondary magnetic fields within the primary magnetic field
- Arranged opposing one another for +ve and -ve pulses.
- Cause variation in magnetic field, allowing spatial variation along the main field direction
- Responsible along with RF pulses for slice and voxel formation
- An extra magnetic field added to the main magnetic field
- X coil creates a varying magnetic field from left to right
- Y coil creates a varying magnetic field from top to bottom
- Z coil creates a varying magnetic field from head to toe
RF coils:
- Act as antennas; transmitting and receiving RF signals.
- Loops of wire (circular or rectangular).
- Located inside the gradient coils
- Produce the field that rotates spins by an angle dependent on the pulse sequence
- Detect the signal emitted by spins inside the body
- Coils start RF pulses (excitation- protons jump to higher energy levels by absorbing radiation)
- Coils stop RF pulses (relaxation - protons return to original state emitting radiation)
Other components:
- Power supplies
- Computer systems
- Documentation systems
- Cooling systems (for the superconducting magnet)
- Receives RF signal then performs conversion from analog to digital. A digital signal representing the body part is stored temporarily in image space or case space, during data acquisition. Digital signal then sent to image processor where mathematical formula known as Fourier transformation is applied to display MRI scan on a monitor.

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Description

This quiz covers the fundamentals of MRI, including its techniques, indications, advantages, and disadvantages. Explore how MRI uses nuclear magnetic resonance to produce detailed images of internal structures without ionizing radiation. Test your knowledge on the principles and applications of this vital medical imaging technique.