“How we do….. CMR of the Coronaries Arteries”

Gavin Bainbridge, Sven Plein, John GreenwoodCMR Clinical Research GroupLeeds 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 breath-hold 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

• 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.

Up to ~

900ms

900ms1100msLate

Diastole

From ~ 550ms

500ms550msEarly Diastole

Over-lap Range

Right

Coronary

Left Coronary

Up to ~

900ms

900ms1100msLate

Diastole

From ~ 550ms

500ms550msEarly Diastole

Over-lap Range

Right

Coronary

Left Coronary

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 seenSolution = 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 aboveSolution = 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