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 " Second " in a series of articles that will focus on the mechanisms and effects of transducer damage.
The Ultrasound system excites the piezoelectric elements (crystals) in the array with a short duration electrical pulse. To create a single acoustic beam, a typical active aperture of 32 to 64 elements is pulsed simultaneously. With Linear and Curved array transducers, this process is sequentially repeated across the array until all the acoustic lines are created to form an image. Line density is normally measured in terms of lines per degree in sector images, or lines per millimeter in linear images. In general terms, the higher the line density, the finer the picture.
With a Phased array probe, the entire array of elements is used to create each acoustic line, and through the use of electronic delay lines, the beam is steered and focused to create the sector display format.
Although various manufacturers' use different techniques to fire the transducer elements, they all operate under the same physical, mechanical and electrical constraints.
For an ultrasound system to acquire and display the data accurately, it is important that all the elements used to form the acoustic line are operating correctly.
In the B-mode image of either the Linear or Curved array probes, element dropout can be seen as a dark line running down the picture, most noticable in the near field. Although this may have minimal effect on the B-mode image, the effect on the doppler display or colour flow image can be dramatic.
With the Phased array probes, as all elements fire simultaneously to form the B-mode image, it is almost impossible to see the effect of "elements down" on the imaging. In fact, we have seen up to 30 elements down and no real effect on the B-mode image. However, again, the effect on the Doppler or Colour flow image is dramatic. With as little as 5 non-firing elements the doppler sensitivity can be halved.
It then follows that the condition of the probe is of the utmost importance to ensure the data is accurately captured and displayed on your ultrasound system. If you have any doubt as to how your probe is performing, we offer a full acoustic testing service for most makes and models of ultrasound probes.
 |
Next article includes a study of fully functioning probes and comparision probes with non-firing elements.
|
|
