Edinburgh Napier University

  Introduction
High frequency ultrasound scanning (HFUS), at a frequency of 20MHz, allows real-time two-dimensional imaging of internal structures in a non-invasive manner and can identify areas of oedema underlying the skin. To date, no studies exploring the repeatability of HFUS in pressure ulcer examination have been published. The aim of the study was to investigate the inter- and intra-rater repeatability of HFUS.

Methods
This study was conducted with a convenience sample of 24 healthy able-bodied adults (21 females, 3 males; 32.08 ± 12.25 years; BMI 24.94 ± 5.57) with intact skin on their heels and seating interface (‘at risk’ sites of pressure ulcer development). Written informed consent was obtained prior to commencement of data collection. Three points on both heels (lateral, posterior and medial aspects) and seating interface (coccyx, and left and right ischial tuberosities) were marked by researcher one and scanned by two researchers on two consecutive days. Researchers were blinded to each other’s scanning. HFUS images were qualitatively analysed by two researchers blinded to each other to determine if images were ‘normal’ or ‘abnormal’. In an attempt to quantitatively analyse the images, a novel method of pixel intensity summation was applied to the images. Statistical analysis was conducted using SPSS Version 11.5.

Results
Qualitative visual analysis showed very good agreement (0.88 kappa statistic) between both researchers and 83% of the images were classified as normal. Intraclass correlation coefficients (ICCs) conducted on pixel intensity summation results showed generally low inter- and intra-rater repeatability (25% moderate or high ICCs; ICC ≥ 0.6).

Conclusions
Differences in images taken by different researchers on separate occasions may be due to probe placement or orientation or tissue characteristic variations from day to day. Although quantitative ICCs showed low inter- and intra-rater repeatability, qualitative visual analysis showed better agreement. In practice, clinicians aim to determine if the images are ‘normal’ or ‘abnormal’, thus qualitative visual analysis appears to be the gold standard in HFUS interpretation. Quantitative methods of analysing HFUS images, in relation to pressure ulcer prevention, require further exploration.