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Questions and Answers
A pulse sequence involves a complex interplay of various parameters including RF pulses and gradients to form an MR image.
A pulse sequence involves a complex interplay of various parameters including RF pulses and gradients to form an MR image.
True
Inversion recovery sequences are primarily applied to gradient echo sequences in practice.
Inversion recovery sequences are primarily applied to gradient echo sequences in practice.
False
Spin Echo (SE) pulse sequence consists of 90-degree and 270-degree RF pulses.
Spin Echo (SE) pulse sequence consists of 90-degree and 270-degree RF pulses.
False
The time between two 90-degree pulses is known as TE (Time to Echo).
The time between two 90-degree pulses is known as TE (Time to Echo).
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Gradient Echo sequences and Spin Echo sequences are the two main classifications of pulse sequences.
Gradient Echo sequences and Spin Echo sequences are the two main classifications of pulse sequences.
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Spin Echo sequences are crucial for understanding other imaging sequences.
Spin Echo sequences are crucial for understanding other imaging sequences.
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Phase encoding gradient is activated only during the reception of the signal in a pulse sequence.
Phase encoding gradient is activated only during the reception of the signal in a pulse sequence.
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The signal induced in the receiver coil after the 180-degree pulse is known as free induction decay (FID).
The signal induced in the receiver coil after the 180-degree pulse is known as free induction decay (FID).
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T2-weighted images are particularly poor at demonstrating pathology due to their inability to show diseased tissues effectively.
T2-weighted images are particularly poor at demonstrating pathology due to their inability to show diseased tissues effectively.
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In a conventional SE sequence, only one echo is obtained per TR.
In a conventional SE sequence, only one echo is obtained per TR.
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The Turbo factor refers to the number of 90-degree pulses sent after each 180-degree pulse.
The Turbo factor refers to the number of 90-degree pulses sent after each 180-degree pulse.
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The SINGLE-SHOT FAST SPIN-ECHO sequence acquires all echoes needed to form an image in multiple TRs.
The SINGLE-SHOT FAST SPIN-ECHO sequence acquires all echoes needed to form an image in multiple TRs.
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After a 180-degree pulse in a DUAL SPIN-ECHO sequence, the first TE is short, producing proton density weighted images.
After a 180-degree pulse in a DUAL SPIN-ECHO sequence, the first TE is short, producing proton density weighted images.
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The amplitude of the signal generated in a FAST (TURBO) SPIN-ECHO sequence remains constant regardless of the increasing TE.
The amplitude of the signal generated in a FAST (TURBO) SPIN-ECHO sequence remains constant regardless of the increasing TE.
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Turbo spin-echo sequences increase scan time when using a short turbo factor.
Turbo spin-echo sequences increase scan time when using a short turbo factor.
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Multiple echoes are obtained in a fast SE sequence due to sending multiple 90-degree pulses after a single 180-degree pulse.
Multiple echoes are obtained in a fast SE sequence due to sending multiple 90-degree pulses after a single 180-degree pulse.
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In GRE sequences, a 180-degree pulse is utilized for rephasing the transverse magnetization.
In GRE sequences, a 180-degree pulse is utilized for rephasing the transverse magnetization.
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The scanning time in GRE sequences can be reduced due to the smaller flip angle, which is usually less than 90 degrees.
The scanning time in GRE sequences can be reduced due to the smaller flip angle, which is usually less than 90 degrees.
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T2 relaxation in GRE sequences is referred to as T2* (T2 star) due to the effects of magnetic field inhomogeneity.
T2 relaxation in GRE sequences is referred to as T2* (T2 star) due to the effects of magnetic field inhomogeneity.
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Coherent GRE sequences destroy the residual transverse magnetization after each TR to avoid interference.
Coherent GRE sequences destroy the residual transverse magnetization after each TR to avoid interference.
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Half of the K-Space is acquired in a single excitation in the SINGLE-SHOT FAST SPIN-ECHO sequence.
Half of the K-Space is acquired in a single excitation in the SINGLE-SHOT FAST SPIN-ECHO sequence.
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SE sequences utilize a gradient-based approach for rephasing transverse magnetization.
SE sequences utilize a gradient-based approach for rephasing transverse magnetization.
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The GRADIENT ECHO sequence is characterized by a longer TR compared to SE sequences.
The GRADIENT ECHO sequence is characterized by a longer TR compared to SE sequences.
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In spoiled GRE sequences, the residual transverse magnetization is preserved to enhance signals.
In spoiled GRE sequences, the residual transverse magnetization is preserved to enhance signals.
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Flip angles of 30° to 45° with TR of 20 to 50 ms favor the steady state.
Flip angles of 30° to 45° with TR of 20 to 50 ms favor the steady state.
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Steady state sequences generally have long TR and TE values.
Steady state sequences generally have long TR and TE values.
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Inversion Recovery sequences are primarily used to enhance T2 weighting in images.
Inversion Recovery sequences are primarily used to enhance T2 weighting in images.
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Prior to the 90-degree pulse in Inversion Recovery, a 180-degree pulse is applied to saturate the tissues.
Prior to the 90-degree pulse in Inversion Recovery, a 180-degree pulse is applied to saturate the tissues.
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Protons in water recover faster than protons in fat according to their T1 values.
Protons in water recover faster than protons in fat according to their T1 values.
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The B-Incoherent Gradient Echo pulse sequence uses frequency encoding gradient rephasing.
The B-Incoherent Gradient Echo pulse sequence uses frequency encoding gradient rephasing.
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SS sequences can be used to study rapid physiologic processes due to their slow acquisition speeds.
SS sequences can be used to study rapid physiologic processes due to their slow acquisition speeds.
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The residual transverse magnetization effects on image contrast are minimized in Incoherent Gradient Echo sequences.
The residual transverse magnetization effects on image contrast are minimized in Incoherent Gradient Echo sequences.
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B-DIFFUSION WEIGHTED IMAGING (DWI) uses either GRE or FPI sequences to demonstrate areas with restricted diffusion.
B-DIFFUSION WEIGHTED IMAGING (DWI) uses either GRE or FPI sequences to demonstrate areas with restricted diffusion.
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DWI is primarily useful in the brain to identify salvageable and non-salvageable tissue after a stroke.
DWI is primarily useful in the brain to identify salvageable and non-salvageable tissue after a stroke.
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The technique of Magnetization Transfer (MT) contrast increases the visibility of stationary nuclei and decreases the visibility of flowing nuclei.
The technique of Magnetization Transfer (MT) contrast increases the visibility of stationary nuclei and decreases the visibility of flowing nuclei.
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Time of Flight MRA (TOF-MRA) typically uses incoherent GRE pulse sequences combined with TR and flip angle adjustments.
Time of Flight MRA (TOF-MRA) typically uses incoherent GRE pulse sequences combined with TR and flip angle adjustments.
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Phase Contrast MRA (PC-MRA) provides excellent background suppression but has longer scan times compared to other techniques.
Phase Contrast MRA (PC-MRA) provides excellent background suppression but has longer scan times compared to other techniques.
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The A-STIR sequence is designed to suppress the signal from fat tissue using a TI value of around 100-200 ms.
The A-STIR sequence is designed to suppress the signal from fat tissue using a TI value of around 100-200 ms.
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The B-FLAIR sequence typically uses a TI value of around 100-200 ms to suppress fluid signals.
The B-FLAIR sequence typically uses a TI value of around 100-200 ms to suppress fluid signals.
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Inversion Recovery (IR) sequences utilize a 90-degree pulse after a 180-degree inversion pulse.
Inversion Recovery (IR) sequences utilize a 90-degree pulse after a 180-degree inversion pulse.
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4-Echo Planar Imaging (EPI) fills all lines of K-Space in multiple TRs to form an image.
4-Echo Planar Imaging (EPI) fills all lines of K-Space in multiple TRs to form an image.
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GE-EPI sequences are slower than SE-EPI sequences.
GE-EPI sequences are slower than SE-EPI sequences.
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Spin echo echo planar imaging (SE-EPI) uses multiple 90° pulses instead of 180° pulses.
Spin echo echo planar imaging (SE-EPI) uses multiple 90° pulses instead of 180° pulses.
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In IR sequences, if the timing corresponds with the recovery of a specific tissue, no signal will be detected from that tissue.
In IR sequences, if the timing corresponds with the recovery of a specific tissue, no signal will be detected from that tissue.
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Perfusion Weighted Imaging (PWI) utilizes GRE sequences solely for dynamic MR imaging of brain lesions.
Perfusion Weighted Imaging (PWI) utilizes GRE sequences solely for dynamic MR imaging of brain lesions.
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Study Notes
Pulse Sequences and Image Contrast
- The presentation discusses pulse sequences used in medical imaging, specifically Magnetic Resonance Imaging (MRI).
- A pulse sequence is a series of parameters and events using radiofrequency (RF) pulses and magnetic field gradients to create an MRI image.
- The pulse sequence charts the interplay of patient longitudinal magnetization, RF pulse transmission (degrees), spatial localization gradients (X, Y, Z), signal acquisition (echoes), and filling of K-Space with acquired signals.
Outline of Presentation
- The presentation outlines the following 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, Incoherent)
- Inversion Recovery (IR)
- Types of IR sequences (STIR, FLAIR)
- Echo Planar Imaging (EPI)
- Specific 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-MRA), Phase Contrast (PC-MRA)).
What is a Pulse Sequence?
- A pulse sequence is a time-ordered interplay of events involving RF pulses (e.g., 90°, 180°) and gradients to create an MR image.
- It details the patient's net longitudinal magnetization.
- It describes RF pulse transmissions (90°, 180°, etc., or any degree).
- It explains the activation of X, Y, and Z gradient fields for spatial localization.
- It clarifies signal (echo) acquisition and K-Space filling with acquired data.
Spin Echo (SE)
- The SE sequence uses 90° and 180° radiofrequency pulses.
- The 90° pulse tilts the net magnetization vector from the z-axis to the transverse (XY) plane.
- A weak signal (free induction decay – FID) is induced.
- The 180° pulse rephases the dephasing magnetization, resulting in a stronger signal (spin echo).
- TR (Time to Repeat) is the time between successive 90° pulses.
- TE (Time to Echo) is the time between the 90° pulse and the echo signal.
Modifications of SE Sequences
- Dual Spin-Echo: Uses two 180° pulses per 90° pulses, producing two echoes per TR (Time to Repeat). This sequence yields both proton density and T2-weighted images.
- Fast (Turbo) Spin-Echo: Sends multiple 180° pulses after a 90° pulse, generating multiple echoes in a single TR. This greatly speeds up image acquisition. Retains T1 and T2 information.
- Single-Shot Fast Spin-Echo: Acquires multiple echoes in a single TR, further reducing scan time and obtaining almost half the K-space information in one excitation.
Gradient Echo (GRE)
- GRE sequences lack 180° pulses.
- Rephasing of magnetization is achieved by reversing gradients in the frequency encoding direction.
- Flip angles are generally smaller than those in SE sequences (often less than 90°).
- GRE sequences are faster due to reduced TR values.
- Two types: Steady-state (coherent) and Incoherent (spoiled).
Inversion Recovery (IR)
- IR sequences include an initial 180° pulse before a conventional spin-echo sequence.
- This inverts the longitudinal magnetization, eventually recovering to a positive value, allowing for better contrast.
- The time between the 180° pulse and the subsequent 90° excitation pulse (TI) is critical in determining tissue contrast.
- Two main types used in MRI: STIR and FLAIR.
Echo Planar Imaging (EPI)
- EPI acquires multiple K-space lines in a single TR, drastically reducing scan time.
- Two variations: spin-echo (SE-EPI); and gradient-echo (GE-EPI).
- EPI is used in dynamic imaging, diffusion weighting, perfusion imaging, and functional magnetic resonance imaging (fMRI).
Additional Techniques
- Perfusion Weighted Imaging (PWI): Dynamic imaging using contrast medium to study blood flow and tissue uptake.
- Diffusion Weighted Imaging (DWI): Evaluating restricted water diffusion, enhancing contrast to detect areas of injury or ischemia. Common for stroke detection.
- Functional MRI (fMRI): Measures brain activity through changes in blood flow and oxygenation. Useful in mapping brain functions.
- Magnetization Transfer (MT) Contrast: Suppressing background tissue to enhance the visibility of vessels and certain diseases.
- Magnetic Resonance Angiography (MRA): Acquiring images of blood vessels with high contrast.
- Time-of-Flight (TOF-MRA) and Phase Contrast (PC-MRA): Highlighting moving blood in vessels and blood flow. These techniques are used in vascular evaluation.
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Description
This quiz explores the intricacies of MRI pulse sequences, including Inversion Recovery and Spin Echo sequences. Test your knowledge on key concepts such as RF pulses, echo times, and the distinctions between gradient echo and spin echo sequences. Perfect for students and professionals in the field of medical imaging.
