Physics: Mri (Cardiac Mri)

Front 1

How is cardiac imaging synchronized

Back 1

The methods used to synchronize with cardiac motion essentially rely on the electrocardiogram (ECG)

Front 2

What are the 2 methods by which the ECG is messed up

Back 2

Induced currents

The magneto-hydrodynamic effect

Front 3

What does the magneto-hydodynamic effect do

Back 3

the motion of the blood (electric conductor) in the magnetic field produces an electric current which adds on to the cardiac conduction signal. This effect appears on the trace as an increase in the T wave

Front 4

What are some causes of current induced ECG changes

Back 4

Currents induced by gradient variation, RF pulses and breathing, which alter the ECG trace.

Front 5

What is the result of a poor ECG signal when trying to gate a study

Back 5

ECG signal degradation will result in a lack of synchronization, lack of diagnostic value of the ECG monitoring trace. Indeed it is vital to have an R wave that clearly stands out from the rest of the trace to be machine-detectable.

Front 6

What r 2 types of cardiac gating

Back 6

prospective gating
retropective gating

Front 7

What is prospective cardiac gating

Back 7

R wave serves to trigger MRI acquisitions, which will then all occur at the same moment in the cardiac cycle: this is prospective gating

Front 8

In Cardiac MR what is the length of the TR determined by

Back 8

The TR is a multiple of the length of the cardiac cycle (1 or 2 cardiac cycles).

Front 9

How long is the TR

Back 9

a cardiac cycle

Front 10

What is AR

Back 10

Not sure what AR stands for but its the time not being recorded

Front 11

What is TD in this image

Back 11

trigger delay

Front 12

What is the TR equivalent to if it is 1 cardiac cycle

Back 12

the RR interval

Front 13

What is the benefit of cardiac imaging

Back 13

Cardiac synchronization limits the artifacts linked to the motion of the heart and blood flow

Front 14

What is the advantage of retrospective gating

Back 14

The advantage of retrospective gating is the possibility of imaging the entire cardiac cycle, whereas in prospective gating, there is a lapse of time at the end of the diastole

Front 15

What is flash artifact

Back 15

the first image has a stronger signal, (flash artifact) because longitudinal magnetization has had an added interval in which to recuperate. Partial saturation and the balancing of longitudinal magnetization only occur in the subsequent images

Front 16

How is flash artifact prevented

Back 16

This drawback can be overcome by continuing to apply radiofrequency pulses and gradients during the lapse of free time at the end of the diastole, without recording a signal, to keep longitudinal magnetization in equilibrium

Front 17

Does retrospective imaging get flash artifact

Back 17

no, retrospective gating is not subject to flash artifacts as there is no lapse of free time in the cardiac cycle.

Front 18

What is retrospective gating in cardiac imaging

Back 18

Or MRI acquisition is continuous, with a simultaneous ECG recording to reorganize the data during image reconstruction: this is retrospective gating.

Front 19

What occurs with each R wave in retrospective gating

Back 19

With each R wave, the phase encoding gradient changes.

Front 20

What is the advantage of retrospective cardiac gating

Back 20

The advantage of retrospective gating is the possibility of imaging the entire cardiac cycle, whereas in prospective gating, there is a lapse of time at the end of the diastole.

Front 21

What happens with each RR interval in retrospective gating

Back 21

With each R wave, the phase encoding gradient changes

Front 22

What does that mean that the phase encoding gradient changes

Back 22

Front 23

What are the MR sequences of choice for cardiac imaging

Back 23

Fast MRI sequences will be the technique of choice in cardiac exploration (ultrafast spin echo, fast gradient echo)

Front 24

What are other options which may accelerate cardiac imaging

Back 24

Single-shot sequences

Front 25

What is another name for dark blood imaging

Back 25

“dark blood” contrast (PRESTO dark-blood / black-blood)

Front 26

What is the main function of dark blood imaging

Back 26

In morphological cardiac MRI, the main priority is to clearly delineate the heart chambers and vascular lumen

Front 27

What is dark blood imaging a variation of

Back 27

This imaging is based on spin echo sequences, in their fast and ultrafast variants, with prospective gating and diastole acquisition

Front 28

What is the cause of dark blood contrast

Back 28

contrast results from the outflow effect of the moving spins in the blood, and suppression of the blood signal prior to acquisition

Front 29

How fast is the spin echo sequences, combined with the multiplane technique

Back 29

can be carried out in breath-hold (5 to 15 seconds depending on the machine).

Front 30

How many heartbeats to a slice in ultrafast sequence

Back 30

Ultrafast spin echo sequences can acquire a slice in a single R-R interval (a heartbeat).