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Questions and Answers
T1-weighted images are primarily used for demonstrating pathology.
T1-weighted images are primarily used for demonstrating pathology.
False
In a dual spin-echo sequence, three 180-degree pulses are sent after each 90-degree pulse.
In a dual spin-echo sequence, three 180-degree pulses are sent after each 90-degree pulse.
False
The turbo factor refers to the number of 90-degree pulses sent in a fast spin-echo sequence.
The turbo factor refers to the number of 90-degree pulses sent in a fast spin-echo sequence.
False
T2-weighted images are advantageous for demonstrating anatomy due to their bright appearance.
T2-weighted images are advantageous for demonstrating anatomy due to their bright appearance.
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Single-shot fast spin-echo sequence captures all necessary echoes to form an image in one TR.
Single-shot fast spin-echo sequence captures all necessary echoes to form an image in one TR.
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The effective TE is filled at the point when the center of K-Space is reached in fast spin-echo sequences.
The effective TE is filled at the point when the center of K-Space is reached in fast spin-echo sequences.
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A long turbo factor results in a shorter effective TE.
A long turbo factor results in a shorter effective TE.
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FAST (Turbo) spin-echo sequences can capture multiple echoes per TR.
FAST (Turbo) spin-echo sequences can capture multiple echoes per TR.
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A pulse sequence is solely a simple diagram of RF pulses without any events.
A pulse sequence is solely a simple diagram of RF pulses without any events.
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Inversion recovery is typically applied to spin-echo sequences.
Inversion recovery is typically applied to spin-echo sequences.
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The 90-degree RF pulse flips net magnetization vector into the longitudinal axis.
The 90-degree RF pulse flips net magnetization vector into the longitudinal axis.
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The time between two 90-degree pulses in a Spin Echo sequence is known as TE.
The time between two 90-degree pulses in a Spin Echo sequence is known as TE.
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Spin Echo sequences are the foundation for understanding all other imaging sequences.
Spin Echo sequences are the foundation for understanding all other imaging sequences.
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Free induction decay (FID) is a strong signal sufficient for image formation.
Free induction decay (FID) is a strong signal sufficient for image formation.
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An IR sequence uses a flip angle of 90 degrees before the usual spin-echo or gradient echo sequence.
An IR sequence uses a flip angle of 90 degrees before the usual spin-echo or gradient echo sequence.
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The gradient echo sequences are classified under the same category as spin-echo sequences.
The gradient echo sequences are classified under the same category as spin-echo sequences.
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SS sequences have very short TR and TE times, allowing for rapid acquisition suitable for breath-hold.
SS sequences have very short TR and TE times, allowing for rapid acquisition suitable for breath-hold.
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The transverse magnetization precesses at the Larmor frequency to create the FID signal.
The transverse magnetization precesses at the Larmor frequency to create the FID signal.
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Gradient Echo sequences are known for increasing T2 weighting in imaging.
Gradient Echo sequences are known for increasing T2 weighting in imaging.
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Protons in fat recover more slowly than protons in water during the Inversion Recovery sequence.
Protons in fat recover more slowly than protons in water during the Inversion Recovery sequence.
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During SSFP, high signal intensity is observed in tissues with short T2 values.
During SSFP, high signal intensity is observed in tissues with short T2 values.
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The main purpose of the inverting 180-degree pulse in an IR sequence is to saturate all tissues.
The main purpose of the inverting 180-degree pulse in an IR sequence is to saturate all tissues.
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Incoherent Gradient Echo sequences employ frequency encoding gradient rephasing to enhance image contrast.
Incoherent Gradient Echo sequences employ frequency encoding gradient rephasing to enhance image contrast.
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The time between the inversion 180-degree pulse and the 90-degree pulse affects the T1 contrast in IR images.
The time between the inversion 180-degree pulse and the 90-degree pulse affects the T1 contrast in IR images.
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B-Diffusion Weighted Imaging (DWI) mainly helps in identifying salvageable and non-salvageable tissue after a brain stroke.
B-Diffusion Weighted Imaging (DWI) mainly helps in identifying salvageable and non-salvageable tissue after a brain stroke.
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Magnetization Transfer (MT) contrast is used to enhance the visibility of stationary nuclei.
Magnetization Transfer (MT) contrast is used to enhance the visibility of stationary nuclei.
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Functional MRI (fMRI) captures images of the brain only at rest and does not respond to stimuli.
Functional MRI (fMRI) captures images of the brain only at rest and does not respond to stimuli.
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Phase Contrast MRA (PC-MRA) utilizes coherent GRE sequences and is noted for having shorter scan times compared to other techniques.
Phase Contrast MRA (PC-MRA) utilizes coherent GRE sequences and is noted for having shorter scan times compared to other techniques.
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Time of Flight MRA (TOF-MRA) uses TR and flip angle combinations to enhance the signal from flowing nuclei.
Time of Flight MRA (TOF-MRA) uses TR and flip angle combinations to enhance the signal from flowing nuclei.
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A-STIR sequence uses a TI value around 300-400 ms to suppress fat signals.
A-STIR sequence uses a TI value around 300-400 ms to suppress fat signals.
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The Inversion Recovery (IR) sequence allows for the suppression of specific tissues by timing the TI value correctly.
The Inversion Recovery (IR) sequence allows for the suppression of specific tissues by timing the TI value correctly.
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FLAIR is used to enhance the signal from fluids in imaging.
FLAIR is used to enhance the signal from fluids in imaging.
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Single shot EPI (SS-EPI) fills all lines of K-Space in multiple TRs.
Single shot EPI (SS-EPI) fills all lines of K-Space in multiple TRs.
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GE-EPI is recognized as being slower than SE-EPI.
GE-EPI is recognized as being slower than SE-EPI.
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The TI value used in B-FLAIR sequences is approximately 1000 ms.
The TI value used in B-FLAIR sequences is approximately 1000 ms.
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Perfusion Weighted Imaging (PWI) relies on GRE or EPI sequences with contrast enhancement.
Perfusion Weighted Imaging (PWI) relies on GRE or EPI sequences with contrast enhancement.
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Inversion Recovery sequences are classified based on the longitudinal magnetization they measure.
Inversion Recovery sequences are classified based on the longitudinal magnetization they measure.
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In a Gradient Echo (GRE) sequence, a 180-degree pulse is used for rephasing.
In a Gradient Echo (GRE) sequence, a 180-degree pulse is used for rephasing.
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The flip angle in GRE sequences is typically greater than 90 degrees.
The flip angle in GRE sequences is typically greater than 90 degrees.
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SINGLE-SHOT FAST SPIN-ECHO sequences fill all of K-Space in a single excitation.
SINGLE-SHOT FAST SPIN-ECHO sequences fill all of K-Space in a single excitation.
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T2 relaxation in a GRE sequence is referred to as T2* (T2 star).
T2 relaxation in a GRE sequence is referred to as T2* (T2 star).
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Spoiled GRE sequences destroy the residual transverse magnetization after each TR.
Spoiled GRE sequences destroy the residual transverse magnetization after each TR.
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In a Steady State (SS) or Coherent GRE sequence, the TR is longer than both T1 and T2 times of the tissues.
In a Steady State (SS) or Coherent GRE sequence, the TR is longer than both T1 and T2 times of the tissues.
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Half-Fourier transformation is used to fill the remaining half of K-Space in a GRE sequence.
Half-Fourier transformation is used to fill the remaining half of K-Space in a GRE sequence.
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Transverse relaxation in SE sequences experiences true transverse relaxation due to the use of a 180-degree pulse.
Transverse relaxation in SE sequences experiences true transverse relaxation due to the use of a 180-degree pulse.
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Study Notes
Pulse Sequences and Image Contrast
- The presentation is about pulse sequences and their impact on image contrast in medical imaging, specifically Magnetic Resonance Imaging (MRI).
- The speaker, Dr. Hayder Jasim Taher, PhD of Medical Imaging, is from The Islamic University.
- The presentation outlines pulse sequences, including classifications, modifications of Spin Echo (SE) sequences, and Gradient Echo (GRE) sequences.
- It also discusses Echo Planar Imaging (EPI).
What is a Pulse Sequence?
- A pulse sequence is a series of parameters (RF pulses and gradients) used to manipulate the magnetization of the tissues in an MRI examination.
- The sequence determines the signal that is later used to form a MR image.
- Involves manipulating a patient's longitudinal magnetization using RF pulses and gradients in specific timing patterns.
- This interplay directly affects the image quality.
- K-space is filled by acquired signals.
Classification of Pulse Sequences
- Pulse sequences are broadly categorized into spin echo and gradient echo sequences.
- Others include inversion recovery and echo-planar imaging (EPI).
- Spin-echo sequence (SE).
- Gradient Echo sequence (GRE).
- Inversion Recovery sequences (IR).
- Echo Planar Imaging (EPL)
Spin Echo (SE) Sequence
- Consists of 90-degree and 180-degree RF pulses.
- The 90-degree pulse flips the net magnetization vector in the transverse plane.
- A subsequent 180-degree pulse rephases the dephasing magnetization, resulting in a stronger echo signal.
- TR (Time to Repeat) is the time between successive 90-degree pulses.
- TE (Time to Echo) is the time between the 90-degree pulse and the acquisition of the echo signal.
Modifications of SE Sequences
- A-DUAL SPIN-ECHO sequence: Uses two 180-degree pulses after each 90-degree pulse to acquire two separate echoes per TR. This modified SE sequence achieves proton density and T2 weighted images.
- B-FAST (TURBO) SPIN-ECHO sequence: Sends multiple 180-degree pulses after a 90-degree pulse, increasing the speed of filling K-space. A turbo factor determines the number of 180-degree pulses, influencing the scan time and weighting.
- C-SINGLE-SHOT FAST SPIN-ECHO sequence: Accomplishes full K-space filling with just one 90-degree pulse, allowing faster image acquisition. Half of the K-space is calculated mathematically.
Gradient Echo (GRE) Sequences
- Avoids 180-degree pulses, employing gradients for rephasing magnetization.
- Has a smaller flip angle, typically less than 90 degrees.
- Faster scan times.
- Two types of GRE sequences:- Spoiled or incoherent and steady-state or coherent.
Inversion Recovery (IR) Sequence
- Includes a 180-degree pulse before the usual spin-echo sequence to saturate some tissues, enhancing contrast between different tissues.
- This helps in showing more contrast of different tissues.
- Different tissues recover at different speeds, providing tissue-specific contrast in the final images.
- This sequence is used with specific modifications like STIR (Short Inversion Recovery)
Echo Planar Imaging (EPI)
- Enables faster image acquisition by filling multiple K-space lines in a single TR.
- Different variations such as spin-echo EPI (SE-EPI), gradient-echo EPI (GE-EPI), and single-shot EPI (SS-EPI).
Some Examples of Pulse Sequences in EPI
- Perfusion Weighted Imaging (PWI): Used to study the uptake of contrast by brain, liver and other tissues.
- Diffusion Weighted Imaging(DWI): Used to evaluate the diffusion of water molecules to locate abnormal tissue or damaged tissue.
- Functional MRI (fMRI): Used to show brain activity during different stimuli.
- Magnetization Transfer (MT) Contrast: Used to increase contrast of vessels and other diseases in the body.
Summary of Presentation
- The presentation covered various types of pulse sequences, which each have a unique benefit and are crucial in medical imaging for better understanding and diagnosis of medical cases.
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Description
This quiz covers the fundamentals of pulse sequences in Magnetic Resonance Imaging (MRI) and their effects on image contrast. Participants will explore various classifications and modifications of Spin Echo and Gradient Echo sequences, as well as Echo Planar Imaging. Test your understanding of how these sequences influence MRI image quality.
