Thoughts on Probe Testing and Analysis
It has been more than twenty years since the Acertara R&D team invented the probe tester known as FirstCall. At that time a seminal paper was published in the Journal of Diagnostic Medical Sonography1 that examined the effects of dead elements on image quality: since that time more than twenty published papers, countless poster presentations, and a doctoral thesis have been written on the subject. In 2019 the FDA released a new Ultrasound Guidance document that also mentioned the clinical importance of detecting dead elements. The literature has been clear that even minimal variations, e.g., as few as two consecutive dead elements in the middle of a 128-element array can have a potentially negative impact on the clinical efficacy of any given ultrasound examination. Probes are subject to normal degradation in performance via use and to degradation via a myriad of other avenues such as improper cleaning and storage, dropping, banging, electro-static discharge, etc. Further, the mechanical design of a given probe (i.e., form, fit and function) also plays a significant role in determining its susceptibility to damage during use. For example, tightly curved arrays(used in applications such as transvaginal and transrectal imaging) are very susceptible to damage at the apex of the curvature of the array.
How dead elements impact the B-mode imaging or Doppler performance of the ultrasound system is a function of both the number of contiguous dead elements and their position in the array. For example, one or two dead elements on the very edge of the array might not impact the image at all, while two dead elements in the center of the array may produce a shadow line artifact in the image
The following page illustrates a more systematic way of determining how many weak or dead elements you might be willing to accept in any given probe type and is a recommended tool to use when discussing the subject with clinicians. Although B-mode imaging is an essential mode of operation, Doppler is the mode most susceptible to performance degradation as a function of even a small number of dead and or weak elements as will be explained in next month’s article.
Until next month,
1 Phillips WH, Weigang B, Moore GW, et al. The Methods and Effects of Transducer Degradation on Image Quality and the Clinical Efficacy of Diagnostic Sonography. J. Diag. Med Sonography 2003; 19:3–13. doi: 10.1177/8756479302239545.
For example, if the full array has 128 elements, then the Green Zone might be 13 elements wide on either side of the array, as is the Yellow Zone. The number of elements that make up any given aperture varies as a function of type and manufacturer.