Magnetic Resonance Imaging (MRI) Techniques Quiz
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Questions and Answers

What is the primary purpose of diffusion weighted imaging (DWI)?

  • To suppress background tissue in MR images
  • To create dynamic images during brain stimuli
  • To differentiate between salvageable and non-salvageable tissue after a stroke (correct)
  • To provide detailed images of blood vessels

    • Which sequence is commonly used in magnetization transfer (MT) contrast?

  • Echo Planar Imaging (EPI)
  • Inversion Recovery
  • Gradient Echo (GRE) (correct)
  • Spin Echo

    • What distinguishes Time of Flight MRA (TOF-MRA) from Phase Contrast MRA (PC-MRA)?

  • TOF-MRA allows high signal from moving spins due to background saturation (correct)
  • TOF-MRA is faster but less effective at background suppression
  • TOF-MRA uses coherent GRE sequences while PC-MRA does not
  • PC-MRA shows arterial flow while TOF-MRA shows venous flow

    • What is the main advantage of using Magnetic Resonance Angiography (MRA)?

    <p>It shows blood vessels clearly with high signal from flowing nuclei</p> Signup and view all the answers

    Which imaging technique is primarily used to visualize areas with restricted diffusion?

    <p>Diffusion Weighted Imaging (DWI)</p> Signup and view all the answers

    What is the primary function of the 90-degree RF pulse in a Spin Echo pulse sequence?

    <p>To flip the net magnetization vector into the transverse plane</p> Signup and view all the answers

    Which of the following sequences is primarily used for Inversion Recovery?

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

    In a Spin Echo sequence, what role does the 180-degree pulse play?

    <p>It rephases protons to increase the signal strength</p> Signup and view all the answers

    What is the time between two 90-degree pulses in a Spin Echo sequence called?

    <p>TR (Time to Repeat)</p> Signup and view all the answers

    Which gradient is activated for localization during a Spin Echo pulse sequence?

    <p>Slice selection gradient</p> Signup and view all the answers

    What does the term 'free induction decay' (FID) refer to in the context of a Spin Echo sequence?

    <p>The initial weak signal induced in the receiver coil</p> Signup and view all the answers

    How do inversion recovery sequences differ from other pulse sequences?

    <p>They are specifically designed for spin-echo sequences</p> Signup and view all the answers

    What is the purpose of phase encoding in a Spin Echo sequence?

    <p>To contribute to signal localization and contrast</p> Signup and view all the answers

    What is the primary purpose of T2-weighted images in MRI?

    <p>To highlight diseased tissues effectively</p> Signup and view all the answers

    In a DUAL SPIN-ECHO Sequence, how many echoes are obtained per repetition time (TR)?

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

    What does the turbo factor refer to in the FAST (TURBO) SPIN-ECHO Sequence?

    <p>The number of 180-degree pulses sent after each 90-degree pulse</p> Signup and view all the answers

    What is an effect of a long turbo factor in FAST (TURBO) SPIN-ECHO Sequences?

    <p>Increased scan time with maximum signal amplitude</p> Signup and view all the answers

    What unique feature does the SINGLE-SHOT FAST SPIN-ECHO Sequence provide?

    <p>It captures all echoes required to form an image in one TR</p> Signup and view all the answers

    Which type of magnetic resonance sequence is characterized by the use of multiple 180-degree rephasing pulses?

    <p>FAST (TURBO) SPIN-ECHO</p> Signup and view all the answers

    How does the effective TE change with a short turbo factor in FAST (TURBO) SPIN-ECHO Sequences?

    <p>It decreases effectively</p> Signup and view all the answers

    Which of the following statements about T1-weighted images is correct?

    <p>T1-weighted images are effective for understanding anatomy and flow</p> Signup and view all the answers

    What is a primary characteristic of the Gradient Echo (GRE) sequence compared to the Spin Echo (SE) sequence?

    <p>It does not include a 180-degree pulse.</p> Signup and view all the answers

    How does the flip angle in a GRE sequence typically compare to that in an SE sequence?

    <p>It is smaller than 90 degrees.</p> Signup and view all the answers

    What occurs to transverse magnetization (TM) in spoiled or incoherent GRE sequences?

    <p>It is completely destroyed by an RF pulse or gradient.</p> Signup and view all the answers

    What does T2* relaxation in a GRE sequence account for?

    <p>Both true T2 relaxation and magnetic field inhomogeneity.</p> Signup and view all the answers

    In a steady state (SS) GRE sequence, what is the relationship between the TR and the T1 and T2 times of the tissues?

    <p>TR is shorter than both T1 and T2 times.</p> Signup and view all the answers

    What effect does the absence of a 180-degree pulse have on GRE sequences?

    <p>It causes dephasing due to magnetic field inhomogeneity.</p> Signup and view all the answers

    Which characteristic distinguishes coherent GRE sequences from incoherent GRE sequences?

    <p>They refocus residual transverse magnetization.</p> Signup and view all the answers

    What is the main benefit of acquiring all K-Space lines in a single excitation?

    <p>Reduces the overall scan time significantly.</p> Signup and view all the answers

    What happens to the magnetization at the halfway stage after a 180-degree inversion pulse?

    <p>Magnetization is at zero level.</p> Signup and view all the answers

    What is the typical TI value used for A-STIR sequences to suppress fat signals?

    <p>Around 100-200 ms.</p> Signup and view all the answers

    Which type of inversion recovery sequence primarily suppresses fluid signals?

    <p>B-FLAIR.</p> Signup and view all the answers

    In 4-Echo Planar Imaging (EPI), what is unique about the way K-Space is filled?

    <p>All lines of K-Space are filled in a single TR.</p> Signup and view all the answers

    What type of EPI uses multiple 180-degree pulses to generate echoes?

    <p>Spin Echo Echo Planar Imaging.</p> Signup and view all the answers

    Which imaging sequence is likely to be faster than SE-EPI?

    <p>Gradient Echo EPI.</p> Signup and view all the answers

    What is the primary use of Perfusion Weighted Imaging (PWI)?

    <p>Studying the uptake of contrast medium by lesions.</p> Signup and view all the answers

    What is the general time frame for the TI value in a B-FLAIR sequence?

    <p>Around 2000 ms.</p> Signup and view all the answers

    What is the typical range of flip angles used in steady-state free precession (SSFP) sequences?

    <p>30° to 45°</p> Signup and view all the answers

    How does the Inversion Recovery (IR) sequence primarily enhance T1 contrast in images?

    <p>By flipping tissues along the negative side of the Z-axis.</p> Signup and view all the answers

    What is one advantage of using steady-state sequences in MRI?

    <p>They can study rapid physiologic processes.</p> Signup and view all the answers

    What effect do spoiled (incoherent) gradient echo sequences have on image contrast?

    <p>They minimize the effect of residual transverse magnetization.</p> Signup and view all the answers

    During which phase do protons in fat recover compared to protons in water in the Inversion Recovery (IR) sequence?

    <p>Fat recovers faster than water.</p> Signup and view all the answers

    What is the purpose of the 90-degree excitatory pulse in an Inversion Recovery sequence?

    <p>To acquire signals based on longitudinal recovery.</p> Signup and view all the answers

    What is a characteristic of Gradient Echo (GRE) sequences compared to Spin Echo (SE) sequences?

    <p>GRE sequences typically provide higher T1 weighting.</p> Signup and view all the answers

    What technique is commonly used in SSFP sequences to improve T2 weighting?

    <p>Employing a gradient echo mechanism.</p> Signup and view all the answers

    Study Notes

    Pulse Sequences and Image Contrast

    • Pulse sequences are a series of parameters that lead to the creation of MR images.
    • They involve RF pulses and gradients.
    • They are a time chart of the interplay of:
      • Patient's net longitudinal magnetization.
      • Transmission of RF pulses (90°, 180°, etc.).
      • X, Y, and Z gradient activation for localization and signal (echo) acquisition.
      • K-Space filling with acquired signals/echoes.

    Outline of Presentation

    • What is a pulse sequence?
    • Classification of pulse sequences:
      • Spin Echo (SE)
      • Modifications of SE sequences:
        • Dual Spin-Echo
        • Fast (Turbo) Spin-Echo
        • Single-Shot Fast Spin-Echo
      • Gradient Echo (GRE)
      • Inversion Recovery (IR)
      • Echo Planar Imaging (EPI)

    Spin Echo (SE)

    • Consists of 90° and 180° RF pulses.
    • 90° pulse flips net magnetization into transverse plane.
    • Free induction decay (FID) is a weak signal.
    • 180° pulse rephases dephasing protons, increasing signal strength (spin echo).
    • TR (Time to Repeat): Time between 90° pulses.
    • TE (Time to Echo): Time between 90° pulse and echo reception.
    • Localization: Slice selection and phase encoding gradients used.

    Modifications of SE Sequences

    • Dual Spin-Echo: Two 180° pulses per TR (Time to Repeat), obtaining two echoes per TR.
      • PD (Proton Density) and T2 weighted images.
    • Fast (Turbo) Spin-Echo: Multiple 180° pulses after each 90° pulse. Fills K-Space faster.
      • Increases scan speed, but slightly increases T1 weighting.
    • Single-Shot Fast Spin-Echo: All echoes acquired in a single TR. K-Space filled more quickly, reducing scan time by half.
      • Uses half-Fourier transformation for the other half of the K-Space.

    Gradient Echo (GRE)

    • No 180° pulses. Rephasing by gradients, particularly frequency encoding reversal.
    • Smaller flip angle (typically less than 90°).
    • Faster scan times due to early longitudinal magnetization recovery.
    • T2* effects (magnetic field inhomogeneity) may be relevant.

    Inversion Recovery (IR)

    • 180° pulse inverts magnetization before the usual spin-echo sequence.
    • Tissues recover at different rates depending on their T1 values (time it takes to return to equilibrium).
    • Useful for suppressing fat or highlighting tissues that recover slowly.
      • STIR (Short Inversion Recovery) for fat suppression.
      • FLAIR (Fluid-Attenuated Inversion Recovery) for cerebrospinal fluid suppression.

    Echo Planar Imaging (EPI)

    • Reduces scanning time by filling multiple lines of K-Space in a single TR.
    • Single-Shot EPI (SS-EPI): Fills all K-Space lines in a single TR; extremely fast.
    • Spin Echo EPI (SE-EPI): Uses 180° pulses to generate echoes.
    • Gradient Echo EPI (GE-EPI): Employs gradients to rephase signals; faster than SE-EPI.

    Image Examples using EPI

    • Perfusion Weighted Imaging (PWI): Dynamic MR imaging, using contrast. Studies lesion uptake; used in brain, pancreas, liver, prostate.
    • Diffusion Weighted Imaging (DWI): Detects restricted diffusion of extracellular water, e.g. in infarcted tissue. Useful in brain stroke diagnosis.
    • Functional MRI (FMRI): Dynamic MR imaging, during stimulus or at rest; brain activation studies.
    • Magnetization Transfer (MT) Contrast: Suppresses background tissue and enhances vascular structures.
    • Magnetic Resonance Angiography (MRA): Images blood vessels with high signal from flowing blood; TOF (Time of Flight) or PC (Phase Contrast) MRA.

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    MRI Pulse Sequences PDF

    Description

    Test your knowledge on various Magnetic Resonance Imaging (MRI) techniques in this quiz. You will explore topics like diffusion weighted imaging, magnetization transfer contrast, time of flight MRA, and more. Ideal for students and professionals in radiology and medical imaging fields.

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