Machine Dependent Artifacts in Medical Imaging
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Questions and Answers

What is the advantage of using Fast Spin Echo sequences?

  • Reduced susceptibility artifacts
  • Improved spatial resolution
  • Increased signal-to-noise ratio
  • All of the above (correct)

    • What is the main limitation of Single-Shot Fast Spin Echo sequences?

  • Low signal-to-noise ratio (correct)
  • Increased SAR
  • Poor spatial resolution
  • Long acquisition times

    • What is the purpose of the initial 180° inverting pulse in Inversion Recovery sequences?

  • To flip the longitudinal magnetization into the +z-direction
  • To reduce T1 relaxation time
  • To flip the longitudinal magnetization into the −z-direction (correct)
  • To increase the signal-to-noise ratio

    • Why do FSE images often appear brighter in fatty tissues?

    <p>Due to reduced J-coupling effects in fat</p> Signup and view all the answers

    What is the advantage of using fat saturation techniques in FSE sequences?

    <p>To suppress fat signal</p> Signup and view all the answers

    What is the main disadvantage of using multiple 180° pulses in FSE sequences?

    <p>Increased SAR</p> Signup and view all the answers

    What is the advantage of using half-Fourier acquisition techniques in Single-Shot FSE sequences?

    <p>Rapid acquisitions with improved spatial resolution</p> Signup and view all the answers

    What can be used to decrease the SAR in FSE sequences?

    <p>Using less refocusing pulses rather than 180°</p> Signup and view all the answers

    What is the typical scan time for both PD and T2 weighting?

    <p>7 – 15 min</p> Signup and view all the answers

    What is one advantage of Spin Echo sequences?

    <p>Good image quality with high SNR</p> Signup and view all the answers

    What is the disadvantage of Spin Echo sequences in terms of tissue heating?

    <p>SAR is higher than in gradient-echo techniques</p> Signup and view all the answers

    What is the main difference between Fast Spin Echo and Turbo Spin Echo?

    <p>Number of 180° rephasing pulses</p> Signup and view all the answers

    What is the purpose of the 180° rephasing pulses in Fast Spin Echo?

    <p>To produce multiple SE in a given TR</p> Signup and view all the answers

    How does the echo train length (ETL) affect the scan time in Fast Spin Echo?

    <p>It decreases the scan time by the ETL</p> Signup and view all the answers

    What does the echo train length (ETL) represent?

    <p>Number of 180° rephasing pulses</p> Signup and view all the answers

    What is the advantage of Fast Spin Echo in terms of spatial resolution?

    <p>It has the same spatial resolution as Spin Echo</p> Signup and view all the answers

    What is the purpose of using a saturation band in Magnetic Resonance Imaging?

    <p>To reduce vascular motion and suppress moving structures</p> Signup and view all the answers

    What is the primary factor that affects the scan time in Conventional Spin Echo (SE) pulse sequences?

    <p>The repetition time (TR) and number of averages (NEX)</p> Signup and view all the answers

    Which of the following gating techniques can be used to compensate for cardiac motion?

    <p>ECG gating</p> Signup and view all the answers

    What is the benefit of swapping the phase direction of motion in Magnetic Resonance Imaging?

    <p>It places motion in a direction away from structures of interest</p> Signup and view all the answers

    How can the scan time in Conventional Spin Echo (SE) pulse sequences be reduced?

    <p>By reducing one or more of the TR, NEX, and number of phase encoding steps</p> Signup and view all the answers

    What is the primary advantage of using Conventional Spin Echo (SE) pulse sequences in Magnetic Resonance Imaging?

    <p>It provides high signal-to-noise ratio images</p> Signup and view all the answers

    Study Notes

    Machine Dependent Artifacts

    • Solutions to artifacts include gating, saturation bands, and swapping phase directions
    • Gating compensates for respiratory, heart, or vascular motion
    • Saturation bands can be used to reduce vascular motion and suppress structures in motion
    • Swapping phase directions can place motion away from structures of interest

    Pulse Sequences

    • Conventional Spin Echo (SE) pulse sequence
    • Scan time in conventional SE is a function of TR, NEX, and number of phase encoding steps
    • Very fast sequence allows for reduced scan time by filling multiple lines of k-space
    • Advantages of Fast Spin Echo (FSE) include improved spatial resolution and reduced susceptibility artifacts
    • Disadvantages of FSE include reduced detection of small areas of calcification or hemorrhage, inability to detect fat, and increased magnetization transfer effects

    Fast Spin Echo (FSE)

    • FSE uses a 90° flip angle followed by several 180° rephasing pulses to produce multiple SE in a given TR
    • Echo train length (ETL) or turbo factor determines the number of 180° rephasing pulses
    • Scan time decreases by ETL (turbo factor)

    Single-Shot FSE (SS-FSE)

    • SS-FSE acquires half of k-space in one shot with half-Fourier acquisition techniques
    • Advantages include very rapid acquisitions, suitable for multiple-slice breath-hold and real-time imaging
    • Disadvantages include reduced SNR due to half-k-space acquisition

    Inversion Recovery Sequence

    • Mechanism involves a 180° inverting pulse, followed by parameters for PD or T2 weighting
    • Parameters for PD weighting: Short TE (20 ms), long TR (2000 ms+), and typical scan time (7-15 min)
    • Parameters for T2 weighting: Long TE (80 ms+), long TR (2000 ms+), and typical scan time (7-15 min)

    Advantages and Disadvantages of SE and FSE

    • Advantages of SE: good image quality, high SNR, easy to understand image contrast, less artifact
    • Disadvantages of SE: long scan time, long TR, high SAR
    • Advantages of FSE: improved spatial resolution, reduced susceptibility artifacts
    • Disadvantages of FSE: reduced detection of small areas of calcification or hemorrhage, inability to detect fat, increased magnetization transfer effects

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    Description

    Learn about the techniques used to compensate for motion artifacts in medical imaging, including gating and saturation bands. Understand how to reduce respiratory, cardiac, and vascular motion.

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