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| Spin Echo sequences acquire imaging with ___blood (also use Spatial Pre saturation) |
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| Gradient Echo sequences render images with __Blood (also use Gradient moment nulling) |
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| Black blood imaging is possible with Spin Echo when a 90° excitation pulse followed by a 180° rephasing pulse is used with slice selective pulses (so flowing blood usually receives only 1 pulse and therefore returns no signal) |
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Term
| Since inversion Recovery sequences are also acquired with 90°/180° RF pulses, they can also provide images with Black blood (these can be long in scan time so typically FSE-IR is used) |
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| A technique known as Double IR Prep applies a non-slice selective 180° pulse followed by a slice selective 180° pulse and a TI equivalent to the null point of flowing spins in blood entering the slice enables saturation of this flow by the 90° excitation pulse |
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Definition
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| Triple IR prep is the same as double but with an additional slice selective inverting pulse applied during the TI null point of Fat. This third 180° RF pulse must be timed so that the null point of Fat & Flowing nuclei coincide. |
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Term
Several techniques can be used to enhance signal from flowing blood including:
-Gradient echo pulse sequence
-Gradient moment Nulling
-Contrast enhancement |
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Term
Several techniques can be used to enhance signal from flowing blood including:
-Gradient echo pulse sequence
-Gradient moment Nulling
-Contrast enhancement |
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Definition
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Term
MRA - Magnetic Resonance Angiography uses variations of gradient echo acquisitions to yield high signal within flowing vessels.
Vascular contrast is maximized by either 1. enhancing the signal from flowing nuclei, or 2. suppressing signal from stationary nuclei |
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Definition
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Term
| When stationary spins are suppressed, the appearance of vasculature is enhanced by the increased signal from unsaturated spins , which flow into the image volume and receive RF excitation for the first time (sometimes known as ____but more accurately termed ___) |
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Definition
| Inflow effect ; Enrty-slice phenomenon |
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Term
There are Four MRA techniques that utilize different phenomena to increase the signal from flowing spins and can be used to evaluate the cardiovascular system.
Name them |
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Definition
1. Sigital Subtraction MRA (DS-MRA)
2. Time of Flight MRA (TOF-MRA)
3. Phase Contrast MRA (PC-MRA)
4. Contrast Enhancement MRA (CE-MRA) |
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Term
There are Four MRA techniques that utilize different phenomena to increase the signal from flowing spins and can be used to evaluate the cardiovascular system.
Name them |
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Definition
1. Sigital Subtraction MRA (DS-MRA)
2. Time of Flight MRA (TOF-MRA)
3. Phase Contrast MRA (PC-MRA)
4. Contrast Enhancement MRA (CE-MRA) |
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Term
Digital Subtraction MRA:
Also known as Fresh blood imaging
allows visualization over a wider FOV
Involves the acquisition of two T2 weighted data sets #1 during systolic flow and #2 during diastolic flow. The two data sets are then subtracted so to isolate either the arterial or venous flow. This technique is reliant on MOTION and not a true depiction of anatomy |
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Definition
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Term
TOF-MRA:
Relies on Flow-related enhancement, the flip angle and TR are selected so that stationary spins are saturated, while the inflow effect from fully magnetized flowing fresh spins produce high vascular signal |
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Definition
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Term
2D vs 3D TOF-MRA:
2D
•a flip angle of 45-60° with a TR of 40-50 ms
2D TOF is optimal in areas of Slower-velocity flow |
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Definition
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2D vs 3D TOF-MRA:
3D
•offer higher SNR and are NOT sutable for imaging venous flow |
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Definition
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Term
| What hybrid technique provides the high resolution of 3D inflow technique coupled with the wider coverage of 2D inflow MRA? |
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Definition
| MOTSA (Multiple Overlapping Thin Section Angiography) |
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Term
| in MOTSA the area of intrest is covered by a number of small 3D slabs each one overlapping its neighbor. The overlap is required to prevent an artefact known as ____ |
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Definition
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Term
| Another remedy for unwanted background signal is an option known as Magnetization Transfer Contrast (MTC. Off resonance RF pulses are applied during the imaging sequences to surpress the signals from macromolucules (like those found in gray and white matter) allowing better visualization of bright vasculature. |
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Definition
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Term
TOF-MRA
Parameters
TR - 45 ms
TE - Minimum
Flip Angle - 60° |
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Definition
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Term
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Definition
Adv:
-Reasonable imaging times
-Sensativity to slow flow
-Reduced sensitivity to inta-voxel dephasing
Disadv:
-Sensitive to T1 effects (hemorrhagic lesions may mimic vessels)
-Saturation of in-plane flow |
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Term
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Definition
Adv:
-Large area of coverage
-Sensative to slow flow
Disadv:
-Lower resolution than 3D
-Saturation of in-plane flow
-Sensitive to patient motion
-Vessels may appear jagged-edged on the reformatted images due to non-isotropic voxels |
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Definition
Adv:
-High resolution for small vessels
-more tolerant of patient motion
-high SNR
-vessels less jagged on reformatted images
Disadv:
-Saturation of in-plane flow
-Small area of coverage |
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Term
| To overcome susceptibility artefacts present on MRA, ___TEs and ____voxel volumes should be used |
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Definition
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Term
| Poor background suppression can be corrected by either using TEs that acquire data when fat and water are out of phase OR by using Magnetization Transfer Technique |
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Definition
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Term
| Suppression of in-plane vascular signal (especially 3D) can be overcome by the utilazation of Ramped RF pulses. Ramped RF pulses set ____across a 3D acquisition so that it increases acros the volume of the slab. |
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Definition
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Term
| Pulsation artefact can be reduced by timing the acquisition to the Cardiac Cycle a Technique known as ___. |
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Definition
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Term
| MIP (Maximum Intensity Projection) results in a reformatted image that appears to be projected onto a 2D surface. There is no depth cueing |
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Definition
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| SSD (Shaded Surface Display) improves 3D perception of the data by using a formula from the world of 3D computer graphics known as Phong's Formula |
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Definition
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Term
| _____ includes pulses with two lobes that are equal in strength: one negative gradient pulse and one positive gradient pulse. They allow for distinction between stationary tissues and spins within flowing blood |
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Definition
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Term
VENC (Velocity Encoding)
Unit used is cm/s and should be selected to produce signal from blood flowing at that velocity.
Slow flow = 10 cm/s (Venous)
Medium = 50 cm/s (Combo)
Fast = 80 cm/s (Arterial) |
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Definition
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Term
VENC (Velocity Encoding)
Purpose is to cause a greater phase shift in moving spins than in stationary spins (Used with bipolar gradients)
Stationary spins with be restored to their original position after both lobes have been applied where as moving spins will have changed their position. |
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Definition
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VENC
In fast-flowing blood, spins travel rapidly along the gradient, so the gradient needs to be _____ |
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Definition
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| Since flow can occur is multiple directions, Bipolar Gradients are applied in all three dimension, These are known as ____. |
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| One of the benefits of PC-MRA is the ability to evaluate multidirectional flow, unlike TOF-MRA which can only visualize flow perpendicular to the slice plane |
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Definition
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Term
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Definition
Adv:
-Sensitivity to a variety of vascular velocities
-Reduced intra-voxel dephasing
-Increased background suppression
-Magnitude & Phase images (can eval flow direction similar to US Dopplar)
Disadv:
-Long imaging times in 3D
-Sensitive to turbulence |
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Term
| TOF-MRA & PC-MRA are standard for imaging the Head, but for the Neck, body, & Peripheral vascular structures____ is the go to choice |
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Definition
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Term
| The recommended dosage for Gadolinium is ____ |
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Definition
0.1 mmol/kg or body weight
This is approx 0.1ml/lb |
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Term
Imaging planes for Cardiac are different due to the oblique nature of the heart. These view used to demonstrate the chambers of the heart in profile are called
Long Axis 2 chamber view (Sag to the <3)
Long Axis 4 chamber viw (Cor to the <3)
Short Axis (Axial to the <3) |
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Definition
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Term
There are 2 mothods of Cardiac gating that can be used
•EKG
•Peripheral |
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Definition
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Term
EKG review
P wave represents - Artial Systole
QRS complex represents Ventricular Systole
T wave represents Ventricular Diastole |
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Definition
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Term
| When cardiac EKG gatig is used, the RF pulse is initiated by the ___ wave. The peak of the ___ wave is used to trigger each pulse sequence |
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Definition
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Term
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Definition
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Term
| Since cardiac gating uses each R wave to trigger the pulse sequence, the TR depends entirely on the time interval between each R wave. This is called the ____ and is controlled by the patients heart rate |
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Definition
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Term
Cardiac Imaging:
Obtaining T2 weighting (& PD) can be troublesome, but most systems use a method where every 2nd or 3rd R wave can be used as a trigger. |
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Definition
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