ECHO : image optimisation

Images and text Genevieve Carbonatto

The most difficult and frustrating ultrasound examination in the Emergency department must be the ECHO exam. What can we do to optimise our images ? Here are some tips and tricks.

1. Positioning the patient

Some of our patients in the Emergency Department cannot be moved because of body habitus or illness, however most can be moved. Getting the patient to roll into the left lateral decubitus position with the left arm comfortably lifted so that the head lies on the arm will greatly improve image acquisition in most cases. This is because the lungs, through which it is impossible to insonate, will move away from the heart when the patient is rolled onto their left side and by lifting the left arm above the head, the space between the ribs will increase making it easier for the probe to fit between the ribs, improving contact of the face of the probe with the skin.

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2. Move the probe closer to a rib

Whilst ribs are the enemy of ultrasound (along with air), in ECHO they are potential friends. By moving your probe closer to a rib you will often improve your image. Why this is is not entirely clear. The face of the probe may be in better contact with the skin in this position.

3. Use the patient’s breathing

Use the respiration to aid imaging. Sometimes a small or a big breath in will move the heart into the rib space in which you have the probe and aid visualisation. Sometimes a breath out ( emptying the lungs of air) will move the lung off the heart and improve image optimisation.

4. Changing the gain

It is clear that if the image is too dark and the myocardium is not well visualised then increasing the gain will help. Sometimes there is too much “noise” and in fact decreasing the gain improves the image. Below the initial gain was too low and by increasing the gain, the myocardium is visualised.

Gain unadjusted                                                                                             Gain increased

5. Adjusting your depth

You want to adjust your depth so that you  get everything you want to see to take up as much of the screen as possible. Below in  the  first image of the PSAX the depth is not enough.  The pericardium posterior to the LV  is not entirely visible. In the second image the heart does not take up all of  the screen. There is too much depth. The third shows adequate depth.

Not enough depth – 11cm                                                                       Too much depth 15 cm ‘

Adequate depth – 13 cm

6. Adjusting your frequency

The sector or cardiac probe has a range of frequencies. If the patient is large, then decreasing the frequency may improve visualisation of the heart, while if the patient is slim then increasing the frequency will give you a better image. Adjust the frequency to get the best image possible.

7. Decreasing sector width

The sector width can be adjusted in cardiac ultrasound. While a full  sector width will give you an overall better image of the heart, by decreasing the sector width the frame rate will increase, improving temporal resolution. Why is that? Frame rate refers to how many times per second one complete sweep of the imaging sector is made. By decreasing the sector, there will be more sweeps per second. The machine will be able to update the image faster and therefore improve the temporal resolution. The image quality will therefore improve.

   

Full sector width                                                                       Narrow sector width – image quality is improved

The sector can also be tilted so that even if by decreasing the sector width you lose the overall image, the sector can still be tilted to the edges of the screen to improve visualisation of a specific area.

Tilted to the right  – the aortic root and LA visible         Tilted to the left – the LV cavity , RV and MV visible

Below I have chosen an example of a patient with a pericardial effusion. The ECHO was difficult. In the first clip the sector width is wide. The RA is not visible, and the RA wall especially is not visible. We want to see the wall because we want to know whether there is RA collapse in the setting of a pericardial effusion. Note that there is a lot of “noise” or unwanted echos in the near field. Decreasing the near gain was not helpful as the heart walls were not well visualised. Decreasing the sector width did however improve the image, enough to see RA collapse.

Full sector width

Narrow sector width

The images are still not great, but decreasing the sector width and improving the frame rate certainly improves the image.

 

8.  Changing your dynamic range.

Dynamic range refers to the range of echos that can be displayed on the ultrasound machine. The higher the dynamic range, the more grey differentiation can be seen. Increasing dynamic range will therefore improve visualisation of the heart if the myocardium is not well visualised. Increase your gain first to see how it affects the image – if you are getting too many unwanted echos or “noise” then decrease the gain a little and then increase the dynamic range. Below, I have an example of the opposite problem. I am finding it hard to properly see the heart because of the increased “noise” . Decreasing the gain does not produce the desired effect of removing all those echos, it simply makes the heart more difficult to visualise. The patient has a pericardial effusion (same patient as above) and I want to see the pericardial effusion well. By decreasing the dynamic range I get better white/black differentiation and the effusion is better visualised.

a .

b.

a. Dynamic range not adjusted  b. Dynamic range decreased – pericardial effusion and posterior wall of LV better visualised. LV cavity and descending aorta have fewer unwanted echos.

9.  Adjusting the focus.

Some machines have a fixed focal zone which is somewhere 2/3 down the screen. With others you can change the focal zone and if you are looking at a specific area this can be useful.

10. Be patient

If there is a characteristic that encapsulates the Emergency Physician or trainee in my view is how we deal with time pressure. We are used to working in a chaotic, high pressure environment with many different fires that need to be attended to at the same time. When you start doing ECHO, start with coming in 1 hour before your shift to be able to take your time to understand how moving the probe impacts on your images. Be patient and thoughtful. Try and get the perfect image. Do this 5 or 6 times. Once you get a sense of what you need to do then bring the ECHO to your emergency practice. Again, give yourself an achievable objective. Stay calm and stay focussed. Remember that some patients will always be difficult to scan whether they are scanned by you or by a cardiac sonographer. You will not always get every window or every view on every heart. The more you scan the better you will get at it.

Teaching point: ECHO is difficult. Image acquisition may be difficult. Improve your chances  by thinking through these  10 ways of  optimising your image .

1. Position the patient in the left lat position

2. Move closer to the rib with the probe

3. Use the patient’s breath

4. Adjust the gain ;  far gain/near gain/overall gain

5. Adjust the depth.

6. Adjust your frequency

7. Adjust the sector size

8. Adjust the dynamic range

9. Adjust the focus

10. Be patient, move the probe slowly using fine movements