Transcript Document

“How we do…..
CMR of the Coronaries Arteries”
Gavin Bainbridge, Sven Plein, John Greenwood
CMR Clinical Research Group
Leeds General Infirmary, UK
www.cmr.leeds.ac.uk
This presentation is for members of SCMR as an educational guide
– it represents the views and practices of the authors, and not necessarily those of SCMR
Choice of Technique
1. “Whole Heart Technique” - a 3D volume of the heart is
acquired from transverse slices at isotropic spatial
resolution. Data can be reformatted off-line in any desired
plane using post-processing software.
2. “Targeted Technique” - left & right coronary arteries are
imaged separately using a smaller 3D volume specifically
adapted for each coronary artery.
Choice of Technique
1. Breath-holding - it is possible to acquire a 3D data set in a
long breath-hold, especially when using multi-channel coil
arrays and parallel imaging. However the achievable
spatial resolution and SNR are limited.
2. Navigator-gated free breathing technique - this method has
the benefit of allowing much longer acquisitions with
subsequently better SNR and resolution. We prefer this
method in the vast majority of our patients and will focus
on it in the subsequent slides.
Initial Preparation
• Plan a “4 Chamber cine”
– Refer to “How I do” a CMR
Volume study by James
Moon.
• Increase the number of cardiac
phases to 50 to assist with
coronary artery motion
tracking.
– Tip- use a parallel imaging
technique to reduce breathhold duration.
Low Resolution 3D Coronary Survey
• Position “navigator” on the dome
of the right hemi-diaphragm,
approximately 2/3 into the liver
• Coverage should include the
inferior border of the heart up to
the pulmonary artery bifurcation
• Set ‘longest trigger delay’ for
optimal diastolic imaging
• Check for “navigator efficiency”
If poor:
– practise breathing patterns
with patient
– Reposition the navigator to
avoid vascular structures or fat
planes below the diaphragm
Coronary artery rest periods
• Whilst the coronary survey is acquiring, scroll through the
phases of the 4Ch cine and note the time points in the
cardiac cycle when each coronary artery is stationary.
• NB: this is different for LCA and RCA
• Note the stationary over-lap range for the left and right
coronary arteries
Coronary artery rest periods
Left
Coronary
Early
Diastole
550ms
Right
Coronary
500ms
Late
Diastole
1100ms
900ms
Over-lap
Range
Up to ~
900ms
From ~
550ms
• The optimal timing range for imaging the left and right
coronary arteries in this example is between 550 - 900ms.
• If the overlap between left and right coronary arteries is
small (<50ms), a timing range suited to the more important
artery is selected.
• Note - the left artery is usually more difficult to see and
therefore timings chosen should favour imaging of the left
coronary artery.
Planning a 3D Whole Heart acquisition
• Adjust number of slices to cover left ventricular apex to pulmonary
artery bifurcation by checking coverage on the 3D Coronary Survey
images.
• Select a “trigger delay” that corresponds to, or slightly after, the start
point of the optimal timing range
• Adjust the “shot” or “acquisition” duration to fit in the optimal
timing range (best results are obtained below 100ms).
• Reduce the rectangular field of view (RFOV) to reduce scan time.
3D Coronary dataset is manually
reformatted to delineate course of
individual coronary arteries
The targeted technique: Left Coronary
Artery using ‘3-Point Plan Scan’
• Point #1
– Origin of ‘left main stem’
• Point #2
– Mid-distal portion of ‘left anterior
descending artery’
• Point #3
– Mid-distal portion of ‘circumflex’
Targeted Left Coronary Artery
The targeted technique: Right Coronary
Artery using ‘3-Point Plan Scan’
• Point #1
– Origin of RCA
• Point #2
– Mid portion of RCA
• Point #3
– Distal portion of RCA
Targeted Right Coronary Artery
Common Problems
1. No rest period between systole/diastole is seen
Solution = repeat high temporal resolution scan at
the correct cardiac frequency and reassess for rest
periods. Hint:
• timings are more accurate when performed just before
the actual coronary artery acquisition.
• Consider cine scan during free-breathing if heart rate
changes during breath-hold.
• correct input of the heart rate (for the 4Ch cine) ensures
that the full cardiac cycle is captured to allow accurate
identification of the rest periods.
Common Problems
2. Still no rest period seen.
Solution 1. = check for early rest period during
systole and scan with a tight window (<50ms).
• It is sometimes possible and necessary to scan
during systole if there is a short natural rest period.
• A short acquisition duration is necessary to avoid
blurring
Common Problems
3. Still no rest period seen in systole or diastole.
Solution 2. = select longest trigger delay and scan
with a tight window (<50ms )
• In some cases there are no natural coronary artery ‘rest
periods’ in the cardiac cycle. Scanning at the longest
trigger delay and a short acquisition duration is a
compromise that may be useful in some cases.
Common Problems
4. Heart rate is 90 bpm or above
Solution = scan with the tightest scan window
possible
• This will minimise blurring of the coronary arteries
and due to the high heart rate, the scan will be
completed in a faster time.
Coronary Imaging Tips
• Remember:
– Coronary blurring occurs with the slightest
movement
– Keep scan times to a sensible limit
– Higher spatial resolution equals longer scan
times.
– Longer scan times can lead to more patient
movement