Atomic Structure and Motion Quiz
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Questions and Answers

What primarily determines the signal difference amongst tissues in a T2-weighted image?

  • Density of protons in the tissues
  • T1 relaxation times of the tissues
  • T2 relaxation times of the tissues (correct)
  • Magnetic field strength

    • Why is TR kept long in T2-weighted images?

  • To minimize proton density effects
  • To eliminate T1 effects (correct)
  • To strengthen the magnetic field
  • To enhance T1 effects

    • In a T2-weighted image, why does tissue B appear darker than tissue A at long TE?

  • Tissue B has a shorter T2, leading to loss of signal (correct)
  • Tissue B has a higher proton density
  • Tissue A reflects more light than tissue B
  • Tissue A has a shorter T2

    • What is the primary factor determining the contrast in a Proton Density (PD) image?

    <p>Density of protons in the tissue</p> Signup and view all the answers

    How does the TE affect the T2-weighting in an image?

    <p>Increases the signal difference at long TE</p> Signup and view all the answers

    What constitutes the majority of the mass of an atom?

    <p>Protons and neutrons</p> Signup and view all the answers

    What effect does the application of an external magnetic field have on protons in the human body?

    <p>Protons align with the direction of the external magnetic field.</p> Signup and view all the answers

    Which statement accurately describes precession in terms of protons?

    <p>Precession is the movement of the axis of rotation of a proton.</p> Signup and view all the answers

    What are the two main types of relaxation processes in MRI?

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

    What happens to protons when they are outside an external magnetic field?

    <p>They move randomly in any direction.</p> Signup and view all the answers

    Which element is the most abundant in the human body relevant to MRI?

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

    What are nucleons comprised of?

    <p>Protons and neutrons</p> Signup and view all the answers

    What physical property of protons contributes to the generation of a magnetic field?

    <p>Charge and spin</p> Signup and view all the answers

    What does the Larmor's equation express?

    <p>The relationship between precession frequency and external magnetic field strength.</p> Signup and view all the answers

    What is the result of the unbalanced forces of protons in the presence of an external magnetic field?

    <p>Formation of longitudinal magnetization along the Z-axis.</p> Signup and view all the answers

    What happens to the protons in an external magnetic field?

    <p>They align both parallel and antiparallel along the magnetic field.</p> Signup and view all the answers

    What characterizes transverse magnetization?

    <p>It is formed when the longitudinal magnetization tilts into the X-Y plane.</p> Signup and view all the answers

    What occurs after sending a radiofrequency (RF) pulse to the protons?

    <p>Some protons move to a higher energy level and cause tilting.</p> Signup and view all the answers

    Which axis is conventionally aligned with the external magnetic field?

    <p>Z-axis.</p> Signup and view all the answers

    Why can longitudinal magnetization not be measured directly?

    <p>It must first be transformed into transverse magnetization for measurement.</p> Signup and view all the answers

    What is the main effect of increasing the external magnetic field strength?

    <p>It increases the precession frequency.</p> Signup and view all the answers

    What is the primary role of the slice selection gradient in MR imaging?

    <p>To select which slice of tissue is being imaged</p> Signup and view all the answers

    What occurs immediately after the RF pulse is sent to the protons?

    <p>Transverse magnetization is formed</p> Signup and view all the answers

    Which gradient is activated during signal reception in MR imaging?

    <p>Frequency encoding gradient</p> Signup and view all the answers

    What process describes the recovery of longitudinal magnetization after RF excitation?

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

    What is the significance of T1 and T2 relaxation times in MR imaging?

    <p>They are key determinants of image contrast.</p> Signup and view all the answers

    What happens to longitudinal magnetization (LM) after the RF pulse is switched off?

    <p>It begins to recover along the Z-axis.</p> Signup and view all the answers

    Which factor is predominantly responsible for determining contrast in an MR image?

    <p>T1 and T2 relaxation times</p> Signup and view all the answers

    What is produced when the transverse magnetization vector precesses?

    <p>An MR signal</p> Signup and view all the answers

    What determines the image contrast in an Inversion Recovery sequence?

    <p>The time between 180-degree and 90-degree pulse (TI)</p> Signup and view all the answers

    What happens to tissues with short T1 in T1-weighted images?

    <p>They regain maximum longitudinal magnetization quickly.</p> Signup and view all the answers

    In a T1-weighted image, what effect does a short repetition time (TR) have on signal intensity?

    <p>It enhances the contrast between tissues with different T1 values.</p> Signup and view all the answers

    What maintains the strength of the MR signal immediately after RF pulse is turned off in T2-weighted images?

    <p>Dephasing of the magnetization.</p> Signup and view all the answers

    How can one make images T2-weighted?

    <p>By keeping the echo time (TE) longer.</p> Signup and view all the answers

    What characterizes T2-weighted images with tissues that have longer T2 values?

    <p>They retain their signal for a longer duration.</p> Signup and view all the answers

    What is the result of using a short echo time (TE) in T2-weighted imaging?

    <p>It results in a reduced contrast because both short and long T2 tissues appear bright.</p> Signup and view all the answers

    Study Notes

    Atomic Structure

    • Things are made up of atoms organized into molecules.
    • The most abundant atom in the human body is hydrogen.
    • Hydrogen is found in water and fat.
    • An atom has a central nucleus with electrons orbiting it.
    • The nucleus is made of protons and neutrons.
    • Protons have a positive charge.
    • Neutrons have no charge.
    • Electrons have a negative charge.

    Motion of Atoms

    • Spinning protons create a magnetic field.
    • Protons move randomly in the body.
    • When a magnetic field is applied, protons align and spin in the direction of the field.
    • The movement of the proton's rotation axis is called precession.
    • The number of precessions per second is called the precession frequency.
    • Precession frequency is directly proportional to the strength of the magnetic field.
    • This relationship is described by Larmor's equation: Wo = γ Bo

    Longitudinal Magnetization

    • Protons align parallel and antiparallel to the magnetic field.
    • The magnetic forces of protons cancel each other out, but there are more parallel protons.
    • This creates a magnetic vector along the Z-axis called longitudinal magnetization.

    Transverse Magnetization

    • A radiofrequency (RF) pulse causes protons to precess in phase with each other.
    • This tilts the magnetization into the transverse plane (X-Y).
    • This is called transverse magnetization.

    Localization of the Signal

    • Slice selection, phase encoding, and frequency encoding gradients are used to determine the source of a signal.
    • Slice Selection Gradient is turned on during the RF pulse.
    • Phase encoding is activated after the slice selection gradient.
    • Frequency encoding is applied during signal reception.

    Basic Steps of MR Imaging

    • Patient is placed in the magnet: Protons align and longitudinal magnetization is formed.
    • RF pulse is sent: Protons absorb energy and transverse magnetization is created.
    • MR signal is received: The precessing transverse magnetization generates a signal.
    • Image formation: The signal is converted into an image by a computer.

    T1, T2 Relaxations and Image Weighting

    • Relaxation is the process of protons returning to equilibrium after being disturbed by the RF pulse.
    • T1 and T2 relaxation times, along with proton density, determine image contrast.

    Longitudinal Relaxation (T1)

    • When the RF pulse is switched off, protons lose energy and align with the magnetic field, increasing longitudinal magnetization.
    • This is T1 relaxation.
    • The time it takes for longitudinal magnetization to recover is called T1 relaxation time.

    T1 Weighted Images

    • Tissues with short T1 recover their longitudinal magnetization quickly, producing a stronger signal.
    • Tissues with short T1 appear bright on T1-weighted images.

    Transverse Relaxation (T2)

    • When the RF pulse is switched off, the phase coherence of protons in the transverse plane decreases, causing a decrease in signal.
    • This is T2 relaxation.
    • The time it takes for transverse magnetization to decay is called T2 relaxation time.

    T2 Weighted Images

    • Tissues with a long T2 have a slower transverse magnetization decay, producing a stronger signal.
    • Tissues with long T2 appear bright on T2-weighted images.

    Proton Density (PD) Image

    • The number of protons in a tissue determines the signal intensity in a proton density (PD) image.
    • Long TR and short TE are used to minimize T1 and T2 effects, respectively, and highlight proton density.
    • Tissues with a higher proton density appear brighter on a PD image.

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    Principles of MRI PDF

    Description

    Test your knowledge on atomic structure and the motion of atoms. This quiz covers fundamental concepts such as protons, neutrons, electrons, and the effects of magnetic fields on atomic movement, including precession and Larmor's equation.

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