Before you start performing echocardiography, there are some basic ultrasound principles you need to understand. If you are already familiar with the principles of ultrasound and sonographic image generation, you can skip ahead to the next section: Echocardiography principles.
Principles of ultrasound
Ultrasound waves are essentially sound waves, much like the waves that transmit the sounds that we hear every day. The difference is that frequency of ultrasound waves are above the upper limit of the range which can be detected by the human ear: 20,000 Hz, and therefore we cannot hear them. In practice, ultrasound waves used by modern echocardiographic machines have much higher frequencies.
Ultrasound machines (echocardiography machines being among them) have a probe which contains a set of crystals known as piezoelectric crystals, which when stimulated by an electric current are capable of generating ultrasound waves. They can also work the other way around, meaning that they can receive ultrasound waves and convert them back to an electric current, which is then transmitted back to the ultrasound machine. Therefore the probe can generate ultrasound waves which travel through the body being studied, bounce off the organs and tissues inside, and get reflected back to the probe which receives and converts them to an electrical current and sends it back to the machine. The machine then uses this data to reconstruct an image depicting all of the objects that lie in the path of the ultrasound waves, pretty much the same way your brain reconstructs an image based on the light rays that are reflected into your eyes and converted to nerve impulses sent to the brain.
Early when ultrasound technology was still in development, only one crystal was used to generate one thin beam or line of ultrasound which was reflected back, and the resulting image was only what lay along that line. Later on, this was improved so that the crystal was made to rotate, sending beams of ultrasound waves in many directions to form a sector, which is why the ultrasound or echocardiography “window” is in the shape of a sector in case you were wondering. The objects closest to the probe lie in the apex of the sector. Current technological advances permit the placement of thousands of crystals in a probe, each firing simultaneously in a different direction, eliminating the need for rotation.
As mentioned above, ultrasound waves are reflected by different objects or substances by varying extents depending on the substance’s density, and this is the basis on which ultrasound is able to discern between various tissues and organ borders. You don’t need to worry about this because the machine takes care of it for you and only delivers you the final result in the form of a nice clean image. The reason why this matters to you though, is that very dense tissues such as bone completely reflect ultrasound waves and do not let them pass through, precluding their ability to see what lies beyond. In other terms: you won’t see anything if the probe is lying on a rib for example. This fact is particularly bothersome in echocardiography, where ribs are always in your way, so you’ll have to learn to work around them.
The next section will give you an idea about Echocardiography and the basic views of the heart: Echocardiography principles.