Cardiac Ultrasound Windows–Transducer and Breathing Techniques for Maximizing Image Resolution
©Walter Rasmussen, R.D.C.S.
Using the Transducer:
The ribcage and lungs can be great obstacles to viewing the heart however, the skilled sonographer has learned to use subtle, minute changes in position, pressure, or angulation of the transducer combined with patient positioning and breath control to overcome the challenges of obtaining good images.
To illustrate the use of a transducer, close one eye and hold a hand up close to the open one, spreading the fingers as far apart as possible. Fix the gaze upon an object just on the other side of the hand and then move the position of the open eye to simulate how a transducer position and angle can be changed in order to illuminate anatomical structures directly under the ribs.
As shown in the following illustrations, this is not simply a matter of placing the transducer between a rib space. As the probe is slid in to position, the specific area of interest can be spotlighted, even if it is directly beneath a rib.
Gently digging-in to the intercostal spaces with the edge of the transducer or applying horizontal force and opposing it with the thumb in order to stretch the skin can in some situations, provide just a boost to the image quality needed.
Stabilize the transducer with the side/base of the hand or with the ring and middle fingers in contact with the skin surface.
Every patient is different and therefore presents challenges that only experience can provide answers for, but the suggestions outlined in this guide can make a huge difference in the acquisition of high quality images for novice sonographers.
Developing confidence while searching with the transducer:
Looking for a better probe position can be one of the most difficult challenges for the novice sonographer because in doing so, the current image is lost and may not be easily found again. A skilled sonographer looks for alternative transducer positions as a matter of routine and creates a mental map of which probe positions looked the best and where they are located so that returning to each one is easier.
It is often the case that upon finding a view, portions of it are not well visualized from one single combination of probe position, pressure, and angulation. For example, in the parasternal long axis view (PLAX) as shown above on the top photo the body of the left ventricle, with the mitral valve, are seen clearly, but the aortic root and valve look distorted or significantly less visible. This is often due to a rib that is blocking some of the ultrasound from reaching the base of the heart. If a sub-optimal portion of the view cannot be resolved without sacrificing the clarity of the rest of the image, split the view-up by recording a clip in one position and then moving the transducer so that a separate clip shows the previously poorly imaged area at its best.
Because bone totally blocks ultrasound and can cause shadowing of portions of an image, the probe needs to be moved to a position that allows the beam to be swept through the area of interest with minimal shadowing. Rib shadow becomes less of a factor as chest wall thickness increases.
Working with the Patient’s breath:
One of the key techniques for improving the ultrasound image is to have the patient inhale or exhale so that the heart moves from behind a rib or lung tissue. This technique should be explored with every patient because with it, a dramatic improvement in the image can be made. Try having the patient inhale or exhale and observe if the image improves. The position of the transducer may need to be moved to follow the heart as it moves with the lungs. When the image improves, the patient may need to be instructed to repeat that specific point in the respiratory cycle over and over, while the sonographer records as many clips as needed to complete the study, making the process tedious, but the result is a higher quality study.