Presentation on theme: "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."— Presentation transcript:
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 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.
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
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