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36 Cards in this Set
- Front
- Back
Whether gradient field adds or subtracts from the main magnetic field depends on
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the direction of the current passing through gradient coils.
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the direction of the current passing through gradient coils is called -?-
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the polarity of the gradient.
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What are magnetic field gradients generated by?
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coils of wire situated within the bore of the magnet.
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sequences that use a gradient to reduce magnetic homogeneity effects, as opposed to a 180° RF pulse used in spin echo sequences are called ?
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Gradient echo pulse sequences
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FSE is ?
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Fast spin echo
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what is an Echo Train
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FSE employs a train of 180° rephasing pulses, each one producing a spin echo.
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What is a much faster version of conventional spin echo?
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Fast spin echo (FSE)
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Which sequences are considered the considered the "gold standard" in that the contrast they produce is understood and is predictable. ?
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Spin echo sequences
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Spin echo sequences produce Which type of images?
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They produce T1, T2 and PD weighted images of good quality and may be used in any part of the body for any indication.
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What are the 5 Advantages of Spin Echo sequencing?
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-1Good image quality
-2 Very versatile - 3True T2 weighting -4 Available on all systems -5Gold standard for image contrast and weighting |
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What is/are the Disadvantages of spin echo sequencing?
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- Long scan times
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A dual echo means what?
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A dual echo sequence consists of two 180° pulses applied to produce two spin echoes
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a sequence that provides two images per slice location; one that is proton density weighted and one that is T2 weighted is ?
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A dual echo sequence consists of two 180° pulses applied to produce two spin echoes
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The first echo of a dual echo sequence = ? TE and a -?- TR and results in what type of images?
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1.Short TE (TE1)
2. Long TR 3. Results in a set of Proton Density weighted images. |
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The second echo of a dual echo sequence has a 1._____TE (TE2) and a 2. ______TR and results in a 3.____ weighted set of images.
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1. long TE (TE2)
2. long TE (TE2) 3. T2 weighted |
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Timing parameters in spin echo
TR = |
time between each 90 degree excitation pulse
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Timing parameters in spin echo
TE = |
time between 90 degree excitation pulse and the peak of the spin echo.
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Timing parameters in spin echo
TE = + = |
TE = TAU + TAU = 2TAU
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After the application of the 90° RF pulse, spins
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lose precessional coherence.
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After the application of the 90° RF pulse, spins lose precessional coherence and what is created?
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FID is created.
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After the application of the 90° RF pulse, spins lose precessional coherence
FID is created then _________occurs, |
T2* decay occurs
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After the application of the 90° RF pulse, spins lose precessional coherence
FID is created T2* decay occurs and then - ? - |
A 180° RF pulse flips the dephased nuclei through 180°.
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After the application of the 90° RF pulse, spins lose precessional coherence
FID is created T2* decay occurs A 180° RF pulse flips the dephased nuclei through 180°. WHAT IS THIS PROCESS CALLED ? |
This is called RE-PHASING.
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When does a spin echo occur?
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Whenever a 180° RF rephasing pulse is applied, a spin echo results
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Rephasing the NMV does what?
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Rephasing the NMV ;Eliminates the effect of the magnetic field inhomogeneities, (T2* Decay).
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This regenerated signal is called 1.__ ____ and, because an RF pulse has been used to generate it, it is specifically called a 2.___ ____ .
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1. an echo
2. spin echo. |
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In a spin echo pulse sequence there is a 1.__ ______ _____ followed by a 2.____ _____ _____ followed by 3. __ ____ .
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1. 90° excitation pulse
2. 180° rephasing pulse 3. an echo. |
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The spin echo pulse sequence is AKA what?
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Conventional spin echo pulse sequences
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Conventional spin echo pulse sequences are used to produce what types of images?
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T1
T2 or Proton Density weighted images. |
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One of the most basic pulse sequences used in MRI.
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Conventional spin echo pulse sequences aka The spin echo pulse sequence
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Spins are rephased in two ways:
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• by using a 180° RF pulse
• by using a gradient. |
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The main purposes of pulse sequences are:
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to rephase spins and remove inhomogeneity effects and therefore produce a signal or echo that contains information on the decay characteristics of tissue;
• to enable manipulation of the TE and TR to produce different types of contrast. |
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T2* decay = The rate of dephasing due to inhomogeneities.
Magnetic field inhomogeneities cause the NMV to dephase before intrinsic magnetic fields of the nuclei can produce dephasing, i.e. T2* happens before T2 ------- SO ------- T2* is faster than T2 decay since it is a combination of two effects: 1._____ _____ ____ 2. _________ _____ ______ ______ ________ . |
1. T2 decay itself
2. Dephasing due to magnetic field inhomogenities. |
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TR controls
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the amount of T1 contrast
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TE controls
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the amount of T2 contrast
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TR controls the amount of T1 contrast
TE controls the amount of T2 contrast PD - TR controls the amount of T1 contrast TE controls the amount of T2 contrast PD - CONTROLS ? |
between T1 & T2
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