To obtain optimal clinical results, it is critical for the user to understand the relationship between probe performance and the resultant clinical data. This is the first in a series of articles that will focus on the mechanisms and effects of transducer damage.
The acoustic stack is the heart of your transducer (see picture above). It comprises of
- backing layer
- piezoelectric elements (elements make up the array)
- matching layer
- acoustic lens
Backing Layer - this reduces the ring-down time of each element, a critical factor in ensuring optimal axial resolution and low noise.
Piezoelectric Elements (making up the acoustic array) - this is a block of ceramic that is cut into columns of elements. (eg 64, 128, 256). The elements are individually fired by the ultrasound machine to generate an ultrasound pulse that is propagated into the body, and in turn, receives the returned echos converting them back to electrical signals, to be processed by the ultrasound machine.
Matching Layer - this matches the acoustic impedance of the array with the lens and body tissue. Accurate matching increases the efficiency of both sound transmission and reception.
Acoustic Lens - this provides electrical isolation of the patient and some "Out of Plane" acoustic focus.
The matching layer, lens and backing layer can detach (delaminate) from the array and create substantial echo dropout in the image. This is commonly mistaken for array failure and the probe is scrapped when it could have been repaired.
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The next article in this series will give the clinical user a fundamental understanding of how different types of transducers are excited by the ultrasound machine and what terms like "acoustic line density" mean to you. |
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