MRI Pulse Sequences Overview
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Questions and Answers

What is the primary purpose of the 180-degree RF pulse in the Spin Echo (SE) pulse sequence?

  • To bring protons back into phase (correct)
  • To excite the net longitudinal magnetization
  • To increase the rate of dephasing
  • To induce a free induction decay signal

Which of the following is NOT a category of pulse sequences in MRI?

  • Echo planar imaging
  • Spin-echo
  • Phase contrast (correct)
  • Gradient echo

In Spin Echo (SE) sequences, what does the term 'TR' stand for?

  • Time to Reception
  • Time to Repeat (correct)
  • Time to Rephase
  • Time to Reveal

Which sequence relies on filling K-space for the acquisition of signals?

<p>All of the above (D)</p> Signup and view all the answers

What is the result of the 90-degree RF pulse in the Spin Echo pulse sequence?

<p>It flips the net magnetization vector into the transverse plane. (A)</p> Signup and view all the answers

In the context of pulse sequences, which statement is true regarding Echo Planar Imaging (EPI)?

<p>EPI allows rapid imaging with less time per slice. (B)</p> Signup and view all the answers

What occurs during the T2 decay in the Spin Echo sequence after applying the 180-degree pulse?

<p>Protons are rephased, leading to a stronger echo. (D)</p> Signup and view all the answers

Which aspect does the phase encoding gradient influence during a Spin Echo sequence?

<p>The localization of the received signal (D)</p> Signup and view all the answers

What type of images are particularly useful for demonstrating anatomy in MRI?

<p>T1-weighted images (B)</p> Signup and view all the answers

Which modification of the Spin Echo sequence involves sending two 180-degree pulses after each 90-degree pulse?

<p>Dual Spin-Echo Sequence (A)</p> Signup and view all the answers

What is the turbo factor in Fast Spin Echo sequences?

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

What effect does a short turbo factor have on the effective TE in Fast Spin Echo sequences?

<p>Decreases effective TE and increases T1 weighting (C)</p> Signup and view all the answers

In T2-weighted images, how do diseased tissues typically appear?

<p>Bright (C)</p> Signup and view all the answers

What differentiates the Fast Spin Echo from conventional Spin Echo sequences?

<p>It fills multiple lines of K-Space per TR (B)</p> Signup and view all the answers

What is the primary benefit of using multiple echoes in Fast Spin Echo sequences?

<p>Increased scanning speed (A)</p> Signup and view all the answers

What is the primary purpose of the first 180-degree pulse in a Dual Spin-Echo sequence?

<p>To create proton density weighted image (C)</p> Signup and view all the answers

What is the primary advantage of using a single-shot fast spin-echo sequence?

<p>It captures all echoes needed for an image in a single TR. (B)</p> Signup and view all the answers

How does the gradient echo (GRE) sequence differ fundamentally from the spin-echo (SE) sequence?

<p>GRE uses gradients for rephasing instead of a 180-degree pulse. (B)</p> Signup and view all the answers

What is T2* relaxation in the context of GRE sequences?

<p>It includes both irreversible dephasing and field inhomogeneity effects. (D)</p> Signup and view all the answers

What effect does a smaller flip angle have in GRE sequences?

<p>It allows for earlier recovery of longitudinal magnetization. (D)</p> Signup and view all the answers

What happens to the residual transverse magnetization (TM) in spoiled GRE sequences?

<p>It is destroyed by RF pulses or gradients. (C)</p> Signup and view all the answers

How does the absence of a 180-degree pulse affect T2 relaxation in GRE sequences?

<p>It causes incomplete transverse relaxation and less accurate imaging. (A)</p> Signup and view all the answers

Which of the following statements is true regarding fast turbo factor in imaging?

<p>It enhances effective T2 and reduces overall scan time. (C)</p> Signup and view all the answers

What is a common feature of fast spin-echo sequences?

<p>They mathematically reconstruct half of K-Space data. (A)</p> Signup and view all the answers

What characterizes steady-state or coherent GRE sequences?

<p>They maintain both longitudinal and transverse magnetization. (A)</p> Signup and view all the answers

Which of the following is true about Incoherent (Spoiled) Gradient Echo pulse sequences?

<p>They spoil the residual transverse magnetization to minimize its effect on image contrast. (B)</p> Signup and view all the answers

What is the role of the 180-degree pulse in Inversion Recovery (IR) sequences?

<p>It flips longitudinal magnetization to negative Z-axis and saturates tissues. (D)</p> Signup and view all the answers

What determines the contrast in Inversion Recovery (IR) sequences?

<p>The time interval between inversion and excitation pulses (TI). (B)</p> Signup and view all the answers

Which GR sequence is best suited for studying rapid physiologic processes?

<p>Steady State Free Precession (SSFP) (B)</p> Signup and view all the answers

Which of the following best describes the effect of flip angles between 30° and 45° in steady-state GRE sequences?

<p>They favor the establishment of steady state. (C)</p> Signup and view all the answers

Why does tissue with long T2 values appear with high signal intensity in steady-state GRE sequences?

<p>They maintain coherence, allowing better signal collection. (C)</p> Signup and view all the answers

What is a key feature of steady-state coherent GRE sequences in comparison to other sequences?

<p>They have very short TR and TE, allowing quick acquisition. (B)</p> Signup and view all the answers

What is the purpose of applying a 180-degree pulse in Inversion Recovery?

<p>To completely saturate fat and water. (A)</p> Signup and view all the answers

How does the time inversion (TI) affect tissue suppression in Inversion Recovery sequences?

<p>The TI should correspond to the time it takes a tissue to recover to the transverse plane. (B)</p> Signup and view all the answers

Which of the following is a primary characteristic of the A-STIR pulse sequence?

<p>It is employed to null the fat signal. (B)</p> Signup and view all the answers

What TI value is typically used in the B-FLAIR sequence?

<p>2000 ms (C)</p> Signup and view all the answers

What is the primary advantage of 4-Echo Planar Imaging (EPI) in MRI?

<p>Reduced scanning time by filling multiple lines of K-Space in a single TR. (C)</p> Signup and view all the answers

What technique utilizes a TI value of 0.69 times the T1 relaxation time?

<p>Standard Inversion Recovery (IR) (B)</p> Signup and view all the answers

What occurs at the halfway stage of the recovery phase after 180-degree inversion pulse?

<p>Magnetization is at zero, leading to no LM available for transverse plane flipping. (B)</p> Signup and view all the answers

Which statement about Inversion Recovery imaging is correct?

<p>It increases contrast between different types of tissue based on their T1 relaxation. (A)</p> Signup and view all the answers

What is the primary characteristic of spin echo echo planar imaging (SE-EPI)?

<p>It is generated by multiple 180° pulses. (B)</p> Signup and view all the answers

What is the main advantage of GE-EPI over SE-EPI?

<p>Faster acquisition speeds. (B)</p> Signup and view all the answers

Which imaging technique is primarily used to assess restricted diffusion in tissues?

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

What is the primary purpose of the Magnetization Transfer (MT) Contrast technique?

<p>To suppress background tissue. (D)</p> Signup and view all the answers

Which technique uses Time of Flight (TOF) for blood vessel visualization?

<p>Magnetic Resonance Angiography (MRA) (B)</p> Signup and view all the answers

What is a distinctive feature of Phase Contrast MRA compared to Time of Flight MRA?

<p>It provides excellent background suppression. (B)</p> Signup and view all the answers

What type of imaging does Functional MRI (fMRI) primarily assess?

<p>Dynamic brain activity during stimulus. (B)</p> Signup and view all the answers

In what scenario is Perfusion Weighted Imaging (PWI) most utilized?

<p>To assess blood supply to lesions. (C)</p> Signup and view all the answers

Flashcards

Pulse Sequence

A time-dependent series of RF pulses and gradients used to create an MRI image.

Spin Echo (SE)

An MRI pulse sequence using 90-degree and 180-degree RF pulses to create a strong signal (spin echo).

Free Induction Decay (FID)

A weak signal produced by precessing transverse magnetization before rephasing.

TR (Time to Repeat)

Time between successive 90-degree RF pulses in a pulse sequence.

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TE (Time to Echo)

Time between the 90-degree RF pulse and the reception of the echo signal.

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Gradient Echo (GRE)

MRI pulse sequence relying on gradients to create image without a 180-degree pulse.

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Slice Selection Gradient

Gradient used to select a specific slice of tissue for imaging.

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Phase Encoding Gradient

Gradient varying in strength to encode the different phases of spins in a slice.

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Spin Echo (SE) Sequence

A fundamental MRI pulse sequence used in many exams. It creates images using 90-degree and 180-degree radiofrequency (RF) pulses. T1-weighted images show anatomy well, while T2-weighted images show disease better.

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Dual Spin-Echo Sequence

A modified Spin Echo sequence that uses two 180-degree pulses after a 90-degree pulse, generating two echoes per repetition time (TR).

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Fast (Turbo) Spin-Echo Sequence

A modified Spin Echo sequence acquiring multiple echoes per repetition time (TR) using multiple 180-degree pulses. This gives quicker scans.

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Turbo Factor

The number of 180-degree pulses in a fast Spin Echo sequence. It is also known as echo train length.

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Repetition Time (TR)

The time interval between successive 90-degree RF pulses in an MRI sequence.

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Echo Time (TE)

The time interval between the 90-degree RF pulse and the detection of an echo.

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Effective TE

The echo time where the center of the k-space is filled in a fast spin echo sequence; often where the echo signal is strongest.

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K-space

A 2D representation of the spatial data needed to reconstruct an MRI image.

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Steady-State GRE Sequence

A gradient echo sequence where the TR is shorter than tissue T1 and T2, resulting in simultaneous longitudinal and transverse magnetization. Uses short TR and TE for rapid imaging of physiological processes.

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Incoherent GRE Sequence

A gradient echo sequence that spoils residual transverse magnetization, minimizing its effect on image contrast. This sequence increases T1 contrast.

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Inversion Recovery (IR) Sequence

An MRI sequence starting with a 180-degree pulse to invert longitudinal magnetization (LM). Recovery of LM depends on T1 values. This is a way to increase T1 contrast. Time from 180 to 90-degree pulse is TI.

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180-degree Pulse

An RF pulse that inverts the longitudinal magnetization (LM) from positive to negative.

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Time to Invert (TI)

The time between the inverting 180-degree pulse and the 90-degree excitation pulse in an inversion recovery (IR) sequence. It determines the contrast.

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Longitudinal Magnetization (LM)

The magnetization component along the z-axis of the tissue. 90 and 180 degree pulses affect these components.

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Transverse Magnetization (TM)

The magnetization component perpendicular to the Z-axis. Part of the steady-state image.

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T1 values

Characteristic time constant for longitudinal magnetization recovery in a tissue. (Different in different tissues).

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Inversion Recovery (IR) Sequence

An MRI pulse sequence using an 180-degree pulse to invert tissue magnetization, followed by a 90-degree pulse to create an image. This allows for selective suppression of certain tissues.

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Tissue Suppression (IR)

Techniques in Inversion Recovery (IR) Sequences that use different timing delays (TI) to reduce or eliminate signal from specific tissues, like fat or cerebrospinal fluid (CSF).

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STIR (Short Inversion Recovery)

A type of Inversion Recovery sequence used to suppress fat signals in MRI images.

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FLAIR (Fluid Attenuated Inversion Recovery)

A type of Inversion Recovery sequence used to suppress cerebrospinal fluid (CSF) signals, enhancing other tissues.

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TI (Inversion Time)

The time interval between the 180-degree inversion pulse and 90-degree excitation pulse in Inversion Recovery (IR) sequences.

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180-degree pulse

an RF pulse that inverts the longitudinal magnetization of tissues

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90-degree pulse

Excitation pulse in MRI that flips magnetization into the transverse plane

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Echo Planar Imaging (EPI)

A type of MRI technique that acquires MRI images quickly

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Spin Echo EPI (SE-EPI)

Echo planar imaging using multiple 180-degree pulses to generate spin echoes.

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Gradient Echo EPI (GE-EPI)

Echo planar imaging using gradients for rephasing.

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Perfusion Weighted Imaging (PWI)

Dynamic MRI using GRE or EPI sequences with contrast to study contrast uptake by lesions.

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Diffusion Weighted Imaging (DWI)

MRI using GRE or EPI to show restricted diffusion (e.g., in infarcted tissue).

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Functional MRI (fMRI)

Dynamic MRI comparing brain images during stimulation and rest to show activity.

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Magnetization Transfer (MT) Contrast

Technique to suppress background tissue, highlighting vessels and certain diseases.

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Magnetic Resonance Angiography (MRA)

Technique to image blood vessels by highlighting flowing blood.

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Time of Flight MRA (TOF-MRA)

MRA technique using GRE sequences to highlight moving blood (arteries and veins).

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Fast Spin-Echo

A type of MRI sequence that acquires multiple echoes within a single repetition time (TR), increasing image acquisition speed.

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Turbo Factor

The number of 180° pulses in a fast spin-echo sequence; determines the number of echoes acquired per TR.

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Effective TE

The echo time corresponding to the center of the k-space data, often the strongest signal in a fast spin-echo sequence.

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Single-Shot Fast Spin-Echo

A fast spin-echo sequence where all echoes are acquired in a single TR, reducing scan time by acquiring half of k-space and calculating the other half mathematically.

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Gradient Echo (GRE)

A type of MRI sequence that uses gradients instead of 180° pulses for signal rephasing, enabling faster scans.

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T2* Relaxation

The relaxation process in GRE sequences, affected by magnetic field inhomogeneities, offering contrasting properties when compared to normal T2 relaxation.

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Spoiled GRE

A GRE sequence where residual transverse magnetization (TM) is eliminated each repetition time (TR), preventing it from affecting the next repetition.

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K-space

A two-dimensional representation of the spatial frequency data needed to reconstruct an MRI image from various spatial frequencies.

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Study Notes

Pulse Sequences and Image Contrast

  • Pulse sequences are a series of parameters that create MRI images
  • Pulse sequences involve RF pulses and gradients to form a MR image
  • A pulse sequence is diagram of interplay of:
    • Patient's net longitudinal magnetization
    • Transmission of RF pulses (90, 180 degrees or any angle)
    • Activation of X, Y, and Z gradients
    • K-Space filling with acquired signals or 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)
    • Types of GRE sequences
      • Steady-State (or Coherent)
      • Incoherent (Spoiled)
  • Inversion Recovery (IR) sequence
    • Types of IR sequences
      • STIR (Short Inversion Recovery)
      • FLAIR (Fluid-Attenuated Inversion Recovery)
  • Echo Planar Imaging (EPI)
    • Examples of EPI sequences
      • Perfusion Weighted Imaging (PWI)
      • Diffusion Weighted Imaging (DWI)
      • Functional MRI (fMRI)
      • Magnetization Transfer (MT) Contrast
      • Magnetic Resonance Angiography (MRA)
        • Time of Flight (TOF)
        • Phase Contrast (PC)

Spin Echo (SE)

  • SE sequences consist of 90° and 180° RF pulses
  • 90° pulse flips magnetization vector to transverse plane
  • Free induction decay (FID) is a weak initial signal
  • 180° pulse causes protons to re-phase
  • Repetition Time (TR): Time between 90° pulses
  • Echo Time (TE): Time between 90° pulse and echo reception

Modifications of SE Sequences

  • Dual Spin Echo: Two 180° pulses per TR
  • Fast/Turbo Spin Echo: Multiple 180° pulses per TR, faster scan times

Fast (Turbo) Spin Echo

  • Multiple 180° pulses are sent after each 90° pulse
  • Fills K-Space quickly, increasing scanning speed
  • Turbo factor: Number of 180° pulses
  • Effective TE (time to echo) increases with turbo factor
  • T1 weighting decreases and T2 weighting increases with a longer TE

Single-Shot Fast Spin Echo

  • All echoes are acquired in a single TR
  • Acquires half of K-space in a single excitation
  • Significantly reduces scan time

Gradient Echo (GRE)

  • GRE sequences use gradients for signal rephasing (no 180° pulse)
  • Flip angle is typically smaller than 90° (e.g., 30°, 45°)
  • Shorter TR reduces scan time
  • "T2*" relaxation is associated with magnetic field inhomogeneity

Types of GRE Sequences

  • Steady-State/Coherent GRE: Residual TM is refocused
  • Incoherent/Spoiled GRE: Residual TM is destroyed, increased T1 weighting

Inversion Recovery (IR)

  • IR sequence begins with a 180° inversion pulse
  • LM (longitudinal magnetization) is inverted (negative) and then recovers
  • Recovered LM differs for different tissues based on T1 values
  • Inversion Time (TI): Time between inversion pulse and 90° excitation
  • TI is used to change contrast and potentially suppress specific tissues

Types of IR Sequences

  • STIR (Short Inversion Recovery): Suppresses fat signal
  • FLAIR (Fluid-Attenuated Inversion Recovery): Suppresses CSF signal

Echo Planar Imaging (EPI)

  • EPI fills multiple K-space lines in a single TR
  • Reduced scanning time
  • Can be Spin Echo (SE-EPI) or Gradient Echo (GE-EPI)

Examples of EPI Sequences

  • PWI (Perfusion-Weighted Imaging): Measures contrast agent uptake in dynamic fashion
  • DWI (Diffusion-Weighted Imaging): Demonstrates restricted diffusion of water (e.g., in brain infarcts)
  • fMRI (Functional MRI): Captures brain activity during various conditions by measuring changes in blood flow (with stimuli)
  • MRA (Magnetic Resonance Angiography): Captures blood vessels, especially TOF and PC
  • Demonstrates arterial and venous flow and background suppression

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Pulse Sequences and Image Contrast (MRI) PDF

Description

Explore the fascinating world of MRI pulse sequences through this quiz. Learn about the different types of pulse sequences, including Spin Echo, Gradient Echo, and Inversion Recovery, and how they contribute to image contrast in MRI. Test your knowledge on the parameters involved in creating MR images and the classification of various sequences.

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