2. Flow & Phenomena 50.pptx

The use of an additional gradient to correct the effects of intra-voxel dephasing is a technique known as what? Pre saturation gradient Spoiling Gradient moment nulling Rewinder

Gradient moment nulling

What pulse imaging technique is employed in TOF MRA? Spin-echo. STIR. Gradient-echo. FLAIR.

Gradient-echo.

In time-of-flight (TOF) imaging, areas of signal void can be seen on the image due to the:I. Turbulent flowII. Vortex flowIII. Laminar flow I & II II& III I & III I

I & II

As slice thickness decreases, the effects of the time of flight phenomenon ____ Increase Decrease is not affcted

Increase

As the TR increases, the entry slice phenomenon: Increases Decreases It is not affected

Increases

Intra-voxel dephasing increases as the TE: Increases Decreases It is not affected A & C

Increases

When counter-current flow slice acquisition is applied, the entry slice phenomenon: Increases Decreases It is not affected

Increases

Flow Comp help reduce TOF Entry Slice Intra voxel dephasing Signal void

Intra voxel dephasing

Phase miss mapping is the result of which of the following: TOF phenomenon Entry slice phenomenon Intra-Voxel dephasing All of the above

Intra-Voxel dephasing

The flow phenomenon that is characterized by phase differences between flowing and stationary nuclei within a voxel is known as ____ Time of flight phenomenon Entry slice phenomenon Intra-voxel dephasing

Intra-voxel dephasing

Parabolic flow is also known as: Laminar flow Turbulent flow Spiral flow Vortex flow

Laminar flow

MRA stands for: Magnetic Resonance Arteriogram Magnetic Resonance Assessment Magnetic Resonance Angiography Magnetic Resonance Angioplasty

Magnetic Resonance Angiography

The use of the gradient moment nulling technique will directly have an effect on the: Minimum TR Maximum TR Minimum TE Maximum TE

Minimum TE

Blood flow that receives a 180-degree rephasing pulse but not a 90-degree excitation pulse produces what type of signal? Low signal No signal High signal

No signal

Blood flow that receives a 90-degree excitation pulse but not a 180-degree No signal High signal Low signal

No signal

TOF MRA is most sensitive to blood flow in what direction in relation to the slice? Perpendicular Parallel Oblique All directions

Perpendicular

Which of the following blood vessel will experience the highest flow velocity? Renal artery Hepatic artery Portal vein LT common carotid artery

Portal vein

The effects of time of flight and entry slice phenomena can be minimized by which method? Gradient moment nulling Pre-saturation RF pulse Respiratory compensation None of the above

Pre-saturation RF pulse

Compared to 3D TOF MRA: 2D TOF MRA is more effective in the areas of: High velocity flow Slow flow Where high resolution is required to visualize small vessels

Slow flow

Gradient moment nulling is most effective on which type of flow? Slow turbulent flow Slow laminar flow Fast vortex flow Fast laminar flow

Slow laminar flow

3D TOF is more often used in Small area of coverage Slow flow Large area of coverage Areas with large degrees of motion

Small area of coverage

Blood flow that slows to the point of immobility is known as what type of flow? Stagnant flow Vortex flow Laminar flow Turbulent flow

Stagnant flow

As slice TR increases, the effects of the time of flight phenomenon _____ Increase Stay the same Decrease

Stay the same

Signal void increases as: Velocity of flow decreases TE increases Slice thickness increases All answers are correct

TE increases

Flow void is directly related to: TOF phenomenon Entry slice phenomenon Intra-Voxel dephasing All of the above

TOF phenomenon

GRE pulse sequences will allow obtaining a bright signal from flowing protons. This is because: The rephasing gradient is slice selected The rephasing gradient is not slice selected The rephasing gradient is not used to rephase flowing protons

The rephasing gradient is not slice selected

The speed at which blood flows through an excited slice and only receives one RF pulse is known as what type of phenomenon? Time of flight phenomenon Entry slice phenomenon Intra-voxel rephrasing Intra-voxel dephasing

Time of flight phenomenon

What would be the best parameter selection to saturate the background signal from stationary protons in a TOF MRA technique? Use short TE Use IR pulse sequences Use very short TR Use incoherent GRE

Use very short TR

Flow that is characterized by slow down in areas where blood vessels divide or become thinner is known as: Laminar Spiral Vortex Turbulent

Vortex

The MRA technique most affected by slow flow is ______ MRA. 2D 3D 4D All are affected the same

3D

What will be the approximate blood velocity in a blood vessel containing 500 ml of blood in a 12 cm area? 20 cm/sec 40 cm/sec 55 cm/sec 75 cm/sec

40 cm/sec

Flow-related enhancement increases as: Velocity of flow decreases TE decreases Slice thickness increases All answers are correct

All answers are correct

Pre-saturation bands can be used to: Saturate signal from desired structures within the FOV Saturate signal from flowing protons coming into the FOV Saturate signal from desired structures outside the FOV All answers are correct

All answers are correct

The effects of the entry slice phenomenon depend upon which factor(s)? Repetition time Slice thickness Velocity of flow All answers are correct

All answers are correct

Which of the following is a disadvantage of TOF MRA? Parallel flow can be suppressed Slow flow can be suppressed Stationary tissue with short Ti relaxation times can produce signal All answers are correct

All answers are correct

Which of the following should be used in a TOF-MRA? Incoherent GRE Flow-Comp Counter Current Flow Slices perpendicular to Blood Vessels All answers are correct

All answers are correct

What blood vessel will show more effects of intra-voxel dephasing? Aorta Renal vein Splenic artery Iliac artery

Aorta

Blood vessels will have low or no signal intensity in spin echo pulse sequences due to protons: Are excited by the 90 pulse but not refocused by the 180 Are excited by the 90 pulse and refocused by the 180 Blood have a long T1 and T2 relaxation time

Are excited by the 90 pulse but not refocused by the 180

Several techniques can be used to enhance the signal coming from flowing Presaturation bands Balance GRE with gradient moment nulling application Double IR FSE

Balance GRE with gradient moment nulling application

What option will increase the entry slice the most? Long TR Co-current flow Thinner slices Counter-current flow

Counter-current flow

As echo time decreases, the effects of the time of flight phenomenon _____ Increase Decrease Is not affected

Decrease

As slice thickness increases, the effects of the time of flight phenomenon _____ Increase Stay the same Decrease

Decrease

When slice thickness is increased, the effects of the entry slice phenomenon ___ Increase Decrease It is not affected A & B

Decrease

Intra-voxel dephasing decreases as the TE : Increases Decreases It is not affected

Decreases

What is the main purpose of using presaturation bands in the TOF MRA technique? Increase signal intensity from blood vessels Eliminate undesired signal from flowing protons Increase signal from background tissues Reduce intravoxel dephasing

Eliminate undesired signal from flowing protons

The TE does not affect the TOF Phenomenon Entry Slice Phenomenon Intra Voxel Dephasing All answers are correct

Entry Slice Phenomenon

Which is a flow-related artifact? Breathing Peristalsis Entry slice Cardiac

Entry slice

The flow phenomenon characterized by the contrast differences between fresh flowing nuclei entering a slice and stationary tissue within that slice is known as what? Intra-Voxel rephrasing Time of flight phenomenon Intra-voxel dephasing Entry slice phenomenon

Entry slice phenomenon

Entry slice phenomenon is most prominent in what slices? First slices Middle slices Last slices Affects all the same

First slices

Which of the following is the formula that is used to calculate blood flow velocity? Flow volume + vessel area Vessel area Flow volume Flow volume / Vessel area

Flow volume / Vessel area

What set up would be the best to produce Bright Blood Images? GRE / Pre-Sat / Co-current flow SE / Counter-current flow / Flow-Comp GRE / Co-current flow / Flow-Comp GRE / Counter-current flow / Flow-Comp

GRE / Counter-current flow / Flow-Comp