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"My probe is not the best, but does it really matter?"
A word from our CEO, Ashley Barker:
"This is going to be a bit of an essay but many customers have asked this question lately and I’m going to explain how faulty probes can affect your image and the mechanisms in play that can cause each effect.
Ultrasound transducers have an array of crystals bonded together to form an acoustic stack, these individual crystal (sometimes called elements) send and receive ultrasound pulses to form an image. Typical transducers have between 64 and 256 crystal forming the acoustic stack. In front of the acoustic stack is an acoustic lens that focuses the beam appropriate for the study type being performed. Over time, wear and tear, as well as accidental dropping , causes damage to the acoustic stack, the lens and the electrical connection that goes back to the machine. This can be a gradual degredation and as such, can go unnoticed.
Lens delamination results when the bonding between the acoustic lens and the acoustic stack is damaged allowing air into the void. Ultrasound does not travel through air, so you are left with dark regions which will drastically effect your image.
There are studies worldwide which show that as little as two consecutive non functioning crystals will affect the beam profile by introducing side lobes. Four faulty crystals can result in reduction of main beam intensity. Consequently, many of the quoted specifications from the manufacturer, including optimal depth of imaging, will no longer be valid. This non-functioning crystals can be as a result of crystal damage, wiring damage or air bubbles between the lens and array.
Although the Bmode image is affected by crystals not functioning, it is nowhere near as acutely effected as the Doppler functions , as the active aperture used in doppler studies can be as little as 8 elements, depending on your focal depth. Obviously you could have a very large percentage of dead elements within that aperture. Doppler signals received on a faulty probe can be completely incorrect and non diagnostic.
One way to evaluate the performance of an ultrasound probe is to evaluate the beam profile. Ideally we just want a narrow, focused main lobe, but in the real world small weaker side lobes are present on all transducers. With as little as 4 elements faulty within a transducer, the size of these side lobes can be massively increased, relative to the size of the main lobe and grating lobes (grating lobes are a type of side lobe directed back away from the forward direction of the beam at a large angle). All side lobes can dramatically decrease your signal to noise ratio (SNR). The combination of your ultrasound systems image processing algorithms, and your Sonographer’
Next, the image formed in an ultrasound system is a mathematical convolution based on the actual object and the impulse response of the system or spread point function. Dead elements within a transducer drastically alter this system response, having the effect of ‘smearing’
Testing a probe with a simple phantom is a form of subjective image quality analysis. This involves somebody who is familiar with ultrasound images, taking an assessment of the quality of the image on a phantom they are familiar with. This is likely to not detect many of the above discussed faults as again it uses B-Mode imaging which is the least effected modality when probe damage occurs. The human error is always a problem in this analysis. The only true way to certify a probe as acoustically functioning is to perform a full acoustic test. We are able to perform these tests in our Perth based repair laboratory.
If you have any doubts or concerns, take the time to let us assist you. We are committed to help maintain and where possible improve the quality of ultrasound imaging."
Ashley Barker, President and CEO of ProbeLogic
Probelogic PR Dept