Magnetic Resonance Imaging (MRI) Overview
37 Questions
2 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What effect does a short TE have in MRI imaging?

  • Enhances fluid differentiation
  • Minimizes T1 effects
  • Increases signal to noise ratio
  • Minimizes T2 effects (correct)

    • Which MRI imaging technique can improve the signal to noise ratio?

  • Increasing TE
  • Using gradient-echo instead of spin-echo
  • Volume acquisition (correct)
  • Decreasing the field of view (FOV)

    • Which hazard is related to static magnetic fields in MRI?

  • Projectiles and torque issues (correct)
  • Contrast-induced nephropathy
  • Heating during procedures
  • Claustrophobia

    • What type of magnetic field gradient can cause Peripheral Nervous Stimulation (PNS)?

    <p>Time-varying magnetic field gradients</p> Signup and view all the answers

    What is a potential hazard associated with contrast agents used in MRI?

    <p>Anaphylaxis</p> Signup and view all the answers

    What causes the magnetic field in hydrogen nuclei?

    <p>Their net spin</p> Signup and view all the answers

    Why is hydrogen used predominantly in MRI imaging?

    <p>It is the most abundant in human tissue</p> Signup and view all the answers

    What is the term used to describe the excess of lower energy spin-up nuclei?

    <p>Net Magnetisation Vector</p> Signup and view all the answers

    Which of the following statements about spin-up and spin-down nuclei is correct?

    <p>There is a small excess of spin-up nuclei</p> Signup and view all the answers

    How does the precessional frequency relate to the magnetic field strength?

    <p>It increases as field strength increases</p> Signup and view all the answers

    At a magnetic field strength of 1.5 T, how many more spin-up nuclei are present per million?

    <p>4.5 per million</p> Signup and view all the answers

    What is the alignment of nuclei in the presence of a strong magnetic field?

    <p>Some align parallel and some antiparallel</p> Signup and view all the answers

    Which of the following elements is NOT used actively in MRI?

    <p>Boron</p> Signup and view all the answers

    What occurs to the transverse magnetisation when RF is turned off?

    <p>Transverse magnetisation decreases</p> Signup and view all the answers

    Which of the following pulse sequences uses two RF pulses?

    <p>Spin-Echo</p> Signup and view all the answers

    What is the purpose of a short TR in T1 weighted imaging?

    <p>To minimize T2 effects</p> Signup and view all the answers

    Which type of image weighting is used to demonstrate differences in proton density?

    <p>Proton Density weighting</p> Signup and view all the answers

    T2 weighted images are most useful for demonstrating which of the following?

    <p>Common pathologies</p> Signup and view all the answers

    Which factor influences the signal intensity in MRI images due to tissue recovery time?

    <p>Time to echo (TE)</p> Signup and view all the answers

    What characterizes T2 decay compared to T1 recovery?

    <p>T1 and T2 occur simultaneously</p> Signup and view all the answers

    Which of the following best describes the signal intensity in MRI images?

    <p>High signal may not indicate tissue health</p> Signup and view all the answers

    What term describes the circular pathway of nuclei around the direction of the main magnetic field in MRI?

    <p>Precessional pathway</p> Signup and view all the answers

    What does the precessional frequency depend on?

    <p>Strength of the magnetic field</p> Signup and view all the answers

    What occurs when RF pulse is applied at the Larmor frequency?

    <p>Flip of the net magnetization vector to 90 degrees</p> Signup and view all the answers

    Which process describes the return of magnetic moments to alignment with the magnetic field?

    <p>Longitudinal relaxation (T1 recovery)</p> Signup and view all the answers

    What is the primary effect of resonance in MRI?

    <p>It increases transverse magnetization</p> Signup and view all the answers

    What happens to transverse magnetization when RF is turned off?

    <p>It decreases as nuclei lose coherence</p> Signup and view all the answers

    What characterizes T2 decay in MRI?

    <p>Nuclei transitioning from being in phase to out of phase</p> Signup and view all the answers

    What is a result of nuclei being excited into the transverse plane?

    <p>Nuclei lose longitudinal magnetization</p> Signup and view all the answers

    What is the primary function of the superconducting magnet in an MRI scanner?

    <p>To generate fields of 0.5T or higher</p> Signup and view all the answers

    Why are gradient coils essential in an MRI scanner?

    <p>They orientate the slice in three dimensions</p> Signup and view all the answers

    What is the purpose of the radiofrequency (RF) coils in an MRI system?

    <p>To transmit an RF pulse and to receive signals from hydrogen nuclei</p> Signup and view all the answers

    How does the gradient coil contribute to the auditory experience during an MRI scan?

    <p>By causing loud noises due to magnetic field variations</p> Signup and view all the answers

    What additional element is required for a superconducting magnet to function properly?

    <p>Cryogenic cooling with liquid helium</p> Signup and view all the answers

    What role does the MRI table play during an examination?

    <p>To position the patient for the MRI scan</p> Signup and view all the answers

    What is a characteristic feature of superconducting magnets used in MRI machines?

    <p>They are always active and generate strong magnetic fields</p> Signup and view all the answers

    Which of the following best describes the noise experienced during MRI scans?

    <p>Caused by the gradient coils varying the magnetic field</p> Signup and view all the answers

    Study Notes

    Magnetic Resonance Imaging (MRI)

    • MRI uses principles of electromagnetism to create images of the body's internal structures.
    • Atomic nuclei possess a positive charge and some have a net spin which causes magnetic fields.
    • The magnetic fields within magnetically resonant nuclei align in a strong magnetic field.
    • MRI predominantly uses hydrogen nuclei due to their abundance in human tissue and strong magnetic moment.

    MRI Active Nuclei

    • Hydrogen 1
    • Carbon 13
    • Nitrogen 15
    • Oxygen 17
    • Fluorine 19
    • Sodium 23
    • Phosphorus 31

    MRI Machine Structure

    • Magnet: Used for generating strong magnetic fields (0.5T or higher). Uses superconducting alloys for minimized resistance (cooled to 10K). Requires liquid helium cryogenic cooling.
    • Gradient Coils: Three sets, one for each direction/plane. Varying the magnetic field generates slices and orientations. Responsible for the loud noises during scanning.
    • Radiofrequency (RF) Coils: Transmit RF pulses to excite hydrogen nuclei. Receive signals from excited nuclei following the RF pulse.
    • Table: Positions patients precisely within the MRI machine.

    Principles of MRI

    • Hydrogen nuclei are randomly oriented without a strong magnetic field.
    • In the presence of a strong magnetic field, hydrogen nuclei align. some parallel, some antiparallel.
    • Spin-up and spin-down refer to the two possible alignments. Spin-down state requires more energy due to opposing the magnetic direction.
    • There's a small excess of lower energy spin-up nuclei which creates Net Magnetization Vector (NMV).
    • Nuclei precess, meaning they rotate, around the magnetic field line.
    • Precessional frequency is the rate at which magnetic moments rotate. It depends on the strength of the magnetic field.
    • The Larmor equation (ω = γΒ₀) describes the precessional frequency. γ is gyromagnetic ratio and is a constant; Β₀ is magnetic field strength.

    Principles of MRI - Precession

    • Nuclei precess around the magnetic field line.
    • Measured by precessional frequency (Hz) which is determined by magnetic field strength.

    Principles of MRI - Resonance

    • Resonance is when an external force causes another system to vibrate with greater amplitude.
    • The precessional (Larmor) frequency is the resonant frequency for hydrogen nuclei.

    Principles of MRI - Longitudinal Relaxation (T1 Recovery)

    • Longitudinal relaxation refers to the return of magnetic moments to alignment with the magnetic field from an excess of spin-up.
    • Recovery rate depends on tissue type and is termed T1 recovery.

    Principles of MRI - Transverse Relaxation (T2 Decay)

    • Transverse relaxation refers to the loss of signal produced by hydrogen atoms when precessing nuclei go from being in-phase to being out-of-phase.
    • Rate of decay depends on tissue type and is termed T2 decay.

    What Happens when RF is Turned Off?

    • T1 recovery and T2 decay occur simultaneously.
    • Transverse magnetization decreases.
    • Longitudinal magnetization increases (recovery).

    Image Contrast

    • MRI images show signal intensity (bright/dark).
    • Different tissues have different T1 and T2 relaxation times, which influence their signal intensity.
    • Fat and water produce a high signal, but relax at different rates.
    • Measuring different time periods (TE and TR) impacts signal intensity.

    MRI Imaging Technique

    • Pulse sequences control RF pulses and gradients to determine image weighting. Most basic pulse sequences are Spin-Echo and Gradient Echo.
    • Spin-echo sequences use 2 RF pulses (90° and 180°).
    • TE (Time to echo) and TR (Time to Repetition) control signal strength.
    • T1-weighted: Short TE, short TR; highlights fat.
    • T2-weighted: Long TE, long TR; highlights water.
    • Proton Density: Short TE, long TR; provides overall density information.

    MRI Imaging Parameters

    • Parameters like Time to echo (TE) and time to repetition (TR) are dependent on the timing procedure and greatly affect image appearance.
    • A table demonstrates the parameters for each image type (T1, T2, and PD).

    MRI Signal-to-Noise Ratio

    • Ratio between signal amplitude and background noise.
    • High-quality images require high signal-to-noise ratios.
    • Improving methods include using volume acquisitions rather than 2D, surface coils, spin-echo pulse sequences, increase in field of view (FOV), and adjusting TE or TR.

    Safety Considerations

    • Static magnetic fields: Hazards include projectiles, torque, and implant interference.
    • Time-varying magnetic field gradients: Hazards include peripheral nervous stimulation and acoustic noise.
    • Pulsed radiofrequency fields: Hazards include heating and heat stress.
    • Cryogens: A quench could cause the cryogens to become harmful.
    • Contrast agents: Hazards include nephrogenic systemic fibrosis (NSF), contrast-induced nephropathy (CIN), and potential anaphylaxis.
    • Pregnancy: Some risk factors present with contrast agents and heating, and further research is needed.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Description

    This quiz covers the fundamental principles of MRI, focusing on the electromagnetism used to create detailed images of the body's internal structures. It explores the active nuclei involved in MRI and the essential components of the MRI machine, such as magnets, gradient coils, and RF coils.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser