In vivo facial soft tissue thicknesses of adult Australians

Abstract

Facial soft tissue thicknesses (FSTT) set important quantitative guides in craniofacial identification, but so far Australian FSTTs have only been published for supine cadavers. This study aimed to use B-mode ultrasound to measure FSTTs in living Australians (N=63 participants; n=52 [x¯=21 years, s=2 years]; and n=11 [x¯=54years, s=13years]) using 14 craniometric landmarks with participants in both upright and supine positions. The multiple pre-existing Australian cadaver investigations (n=7 reporting FSTT means and 6 of these reporting raw datasets) enabled living and cadaveric samples drawn from the same parent population to be compared. By using a non-invasive and safe imaging method (no ionising radiation) repeated measurements could be taken in the in vivo participants to gauge measurement reliability (and compare to pre-existing reliability for cadaver measurements): mean r-TEM=12%; max r-TEM=25%. In terms of changes between upright and supine positions (as measured by B-mode ultrasound) only 2 of 14 measured landmarks had FSTT changes in excess of 1mm. Comparisons of the in vivo ultrasound data to pre-existing needle puncture studies demonstrated that mean B-mode ultrasound measurements were very similar to cadaver values. Contrary to popular thought, but in keeping with the findings of prior meta-analyses, cadaver FSTT data are good proxies to living subjects, at least as measured by ultrasound. To increase sample sizes and triangulate upon ground truth FSTT values, weighted grand means combining all Australian samples were calculated (n range=280-385) and compared to the multi-group 2018 adult T-Tables (max. n=10,333).

Facial soft tissue thickness (FSTT) estimation models—And the strength of correlations between craniometric dimensions and FSTTs

“…For each FSTT measurement, a large amount of ultrasonic gel was applied to the transducer to serve as a readily deformable standoff platform for the transducer device [2,19], such that the skin surface could be easily differentiated on the ultrasound image and with minimal unwanted soft tissue compression. When a clear view of both the bone and the uncompressed soft tissue was obtained, a still-frame DICOM image was acquired on the MindRay 1 DP-50 machine.…”

B‐mode Ultrasound Measurement of Facial Soft Tissue Thickness for Craniofacial Identification: A Standardized Approach

“…In the medical arena, B‐mode popularity has essentially made their A‐mode counterparts obsolete (but note here that these are still used for flaw detection applications in engineering). This preference is already manifested in the FSTT literature, where in the last 10 years, FSTT studies using ultrasound exclusively employ B‐mode imaging .…”

“…Some research teams use gel standoff platforms in the form of acoustic coupling gel , while others use commercially available, more dense and less deformable substrates . Some investigators use seated, but otherwise fully upright subject posture , yet others use reclined seated postures , some use supine posture , and some use prone postures . Some investigators implement popularly used craniometric and capulometric landmarks , while other investigative teams use heavily customized landmarks that are rarely employed by other practitioners .…”

“…A highly deformable hypo‐allergenic and water‐based acoustic gel (as used in diagnostic ultrasound, albeit in much larger quantities here) should be used to stand the transducer off the tissue surface interface to mitigate the risk of tissue compression while simultaneously maintaining the echo connectivity to the skin, that is, it should be used as a readily deformable standoff gel platform . Acoustic gel platforms should be used above stiffer commercially available standoff gel‐pads since the latter are designed for general imaging of tissues that are much less compressible and/or delicate than facial soft tissues.…”

“…When undertaking FSTT measurement, the ultrasound transducer should wherever possible be orientated so that the beam is perpendicular to the tissue interfaces of interest . This can be achieved either with the transducer held in the vertical or horizontal plane depending on what provides the best profile read of the anatomy on‐screen and does not interfere with adjacent facial anatomy or participant comfort.…”