Phantom testing of the sensitivity and precision of a sub-epidermal moisture scanner

Cohen L P and Gefen A

Objectives

To experimentally detect water content changes in order to assess the sensitivity and precision of the SEM Scanner in human phantoms of the heel and skull and face.

To determine if there was a statistically significant difference between SEM readings associated with water content at test site vs another adjacent site.

Materials & Methods

  • Laboratory study
  • 3 Dimensional (3D) printed phantoms of the skeleton of the heel, skull and face developed (Figure 1)
  • To replicate soft tissue – 07.cm baby diapers were cut and attached to the phantoms- the thickness represents the thickness of the human heel or face
  • The diaper samples were attached to the posterior calcaneal aspect (the most common site for a heel pressure ulcer (PU) and the left lateral aspect to act as the reference site
  • A similar process was followed for the face and skull – samples were sited at the anterior aspect of the maxilla bone a common site for CPAP related PU’s, again a reference site was also used
  • Reference site was repeatedly loaded with 1ml of water; Test site was repeatedly loaded with increasingly variable water content (2-4ml at 1ml intervals) to simulate development of localised oedema
  • SEM Scanner was then used to determine the delta between test and reference locations at each stage i.e. after each 1ml of water had been loaded.

Figure 1

Results

  • “For both phantoms the SEM Scanner was shown to be sensitive enough to detect the variation in water content”
  • Increasing volume of water demonstrated a corresponding consistent trend of increasing deltas
  • Locally increased water content at the body sites resulted in elevated SEM delta readings – confirms the SEM Scanner is able to detect fluid changes that are as small as 1ml
  • For the heel phantom reference difference in water contents by 2 and 3ml resulted in a statistically significant increase in SEM readings by 100% and 167% with respect to the 1ml difference (Table 1)

Table 1

Conclusions

  • Establishes the validity and sensitivity of the SEM Scanner under well controlled laboratory conditions
  • In both phantom configurations the locally increased water contents resulted in consistent statistically significant elevated device readings