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36 Cards in this Set
- Front
- Back
- 3rd side (hint)
TR INCREASED |
Benefits: INCREASED SNR & INCREASED # of Slices Limitation: INCREASED Scan time & DECREASED T1 Weighting
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TR DECREASED |
Benefits: DECREASED SCAN TIME & INCREASED T1 Weighting Limitations: DECREASED SNR & DECREASED # of Slices TE |
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TE INCREASED |
Benefits: INCREASED T2 Weighting Limitation: DECEADED SNR |
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TE DECREASED |
Benefits: INCREASED SNR LIMITATION: DECREASED T2 Weighting |
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NEX INCREASED |
Benefits: INCREASED SNR & more signal averaging Limitation: direct proportional increase in Scan time |
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NEX DECREASED |
Benefits: Direct proportional decease in Scan time Limitation: decreased SNR & less signal averaging |
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Slice thickness increased |
Benefits: increased SNR & Increased coverage of anatomy Limitation: Decreased spatial resolution & more partial voluming |
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Slice thickness decreased |
Benefits: increased Spatial resolution & reduced partial volume averaging Limitation: decreased SNR & decreased coverage of anatomy |
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FOV Increased |
Benefit: Increased SNR & Increased coverage of anatomy Limitation: Decreased spatial resolution & decreased likelihood of aliasing |
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FOV Decreased |
Benefit: increased spatial resolution & increased likelihood of aliasing Limitation: Decreased SNR & decreased coverage of anatomy |
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Matrix increased |
Benefit: increased spatial resolution Limitation: increased scan time and decreased SNR if pixel is small |
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Matrix decreased |
Benefit: decreased scan time and increased SNR if pixel is large Limitation: decreased spatial resolution |
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Receive bandwidth increased |
Benefit: decrease in chemical shift and decrease in minimum TE Limitation: decreased SNR |
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Receive bandwith decreased |
Benefit: Increased SNR Limitation: Increase in chemical shift and increase in minimum TE |
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Launch coil |
Benefit: increased area of received signal Limitation: lower SNR, sensitive to artifacts, aliasing with small FOV |
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Small coil |
Benefit: Increased SNR, less sensitive to artifacts, less prone to aliasing with a small FOV LIMITATION: Decreased area of received signal |
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An RF pulse of what flip angle will maximize the component of the net magnetization projected into the transverse plane |
90 degree |
The net magnetization is initially aligned with the main magnetic field before any RF energy is transmitted to the protons however, the magnetization can be measured in order to create MR images only when it is present in the transverse plane. Therefore, RF energy must be applied in order to deflect the net magnetization away from its alignment with the main magnetic field and projected into the transverse plane which is perpendicular to the axis of the main magnetic field ( RF flip angle ) |
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T1 Relaxation refers to ________ relaxation |
Longitudinal |
T1time describes the ease with which protons dissipate the RF energy they absorbed during the transmission of an RF pulse . Immediately after an RF pulse is delivered to the protons, the longitudinal net magnetization is deflected into the transverse plane. The longitudinal net magnetization gradually recovers according to the T1 time of that population of protons. This process of recovery is called longitudinal relaxation. |
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Which of the following statements is false? A) T1 relaxation refers to the longitudinal recovery of magnetization while T2 relaxation refers to the transverse decay of magnetization B) T1 and T2 relaxation occurs simultaneously C) echoes collected in the transverse plane demonstrate only T2 relaxation differences. D) T2 relaxation occurs much more quickly than T1 relaxation |
C) Echoes collected in the transverse plane demonstrate only T2 relaxation differences |
Depending upon specific imaging parameters used in a given MR measurement, echoes collected in the transverse plane can contain information concerning tissue contrast according to the tissues inherent proton densities, T1 relaxation times and T2 relaxation times. T2 relaxation describes the time course of spin spin interactions which calls decay of transverse magnetization. T1 relaxation describes the Tom course of spin lattice interactions which caused the recovery of longitudinal magnetization. T1 relaxation and T2 relaxation or independent processes but they occur simultaneously. However, in the vast majority of tissues, the T2 time is shorter than the T1time |
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If the professional frequency of the protons net magnetization is approximately 21 MHz a ____ tesla magnetic field is being experienced by the patients protons |
0.5 |
In order to disturb protons, RF pulses are transmitted at the processional frequency of protons which is calculated by the Laramore equation: (proton processional frequency) =(magnetic field strength) x (proton gyromagnetic ratio). Assuming a gyromagnetic ratio of 42.6 MHz/Tesla for protons, the resulting field strength can be calculated. |
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What is the definition of T1 relaxation? |
The time it takes the net longitudinal magnetization of protons to grow to 63% of its final amplitude |
The T1 relaxation time describes the Tom course of the recovery of the longitudinal magnetization aligned with the main magnetic field. T one is defined as the amount of time required for the longitudinal magnetization to recover 63% of its full magnitude |
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The edema associated with pathology in the brain has much longer T2 relaxation time than surrounding normal brain tissue. On a T2 weighted image what does this result in? |
A high signal intensity in the area of edema |
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The edema associated with pathology in the brain has much longer T2 relaxation time than surrounding normal brain tissue. On a T2 weighted image what does this result in? |
A high signal intensity in the area of edema |
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Which of the following dephasing mechanisms affects the size of the resulting spin echo? |
Spin – spin interactions |
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After a 90° RF pulse, if three 180° RF pulses are applied to generate three echoes, which of the following is responsible for the third echo being smaller than the first echo? |
Spin – spin interactions |
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The MR Echo is NOT: A) detected as magnetic changes that induce a voltage into an RF coil B) collected when the magnetization in the transverse plane has been rephased C) A tiny signal containing contrast information necessary for tissue differentiation D) collected only one time for a given image |
D) collected only one time for a given image |
The tiny echo signal is generated by all of the protons within the excited slice and therefore contains contrast information about all of the tissues within that slice. It is detected when the transverse magnetization rephases and induces a voltage in a RF coil. The number of echoes collected is equal to the size of the acquisition matrix along the phase encoding direction |
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What is the time from the initial RF excitation pulse to the echo called? |
TE / Echo Time |
The T1 is the time between the initial 180° RF pulse and the 90° excitation pulse in an inversion recovery sequence. The TE is the time between the RF excitation pulse and the center of the echo. The TR is the time between successive RF excitation pulses |
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The proton’s _________ contributes to its magnetic properties. 1) spinning motion 2) positive charge 3) mass |
1 & 2 Spinning motion and positive charge |
A proton behaves like a charged, spinning particle which exhibits magnetic properties. It behaves like a tiny dipole, or bar magnet. An objects mass contributes to it inherent gravitational properties, but it has no effect on the objects magnetic properties. For example, a proton contains much more mass than an electron, although they both have opposite but equal charge. Likewise, a proton and neutron contain equal mass although the neutron contains no charge and demonstrates no magnetic properties |
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True or False More protons align with the main magnetic field then against the main magnetic field |
True |
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On a T2 weighted image CSF appears bright because it has a _______________ relaxation time |
Long T2 |
CSF behaves like a water-based fluid because it has relatively long T1 and T2 times compared to other substances within the body. Because CSF has a long T1 time, a long TR must be used in a T2 weighted image in order to eliminate T1 weighted contrast effects. Because CSF has a long T2, spin spin interactions occur less frequently which allows more protons to contribute to the CSF signal compared to most other substances in the brain |
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The processional frequency of the net magnetization of protons in a magnetic field is determined by which of the following? |
The Gyromagnetic ratio and the field strength |
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The RF pulse should be transmitted at a frequency of approximately _______ MHz in order to disturb protons experiencing a 4 tesla field. |
170 |
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Z axis |
Superior to Inferior Top to bottom Axial |
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X axis |
Left to right Sagittal |
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Y axis |
Anterior to posterior Coronal |
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Which of the following is NOT a requirement for magnetic resonance imaging? A) atomic nuclei with odd number of protons B) A strong magnetic field C) ionizing radiation D) RF energy |
C) Ionizing radiation |
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