Three-dimensional photonic scanning (3D-PS) captures body surface topography, from which extensive body shape and anthropometrics can be extracted using computer algorithms.
This technique projects light (typically infrared) on to the body surface, and cameras record the distortion of these light patterns to generate a point cloud. Computer algorithms then reconstruct the 3D body surface topography (see Figure 1), allowing automatic landmarks to be located through customised software. From these landmarks, a variety of girths, diameters and volumes can be derived using further algorithms.
The protocol for conducting three-dimensional photonic scan involves the following stages:
Figure 1 Image processing involves the application of computer algorithms to clean (a) the point cloud to reconstruct (b) the skin surface. The software then automatically identifies (c) body landmarks, allowing (d) application of an e-tape measure,
generating digital information on distances, girths and curvature.
Adpated from: .
Three dimensional photonic scanning is a feasible alternative to traditional anthropometry. It is much quicker, precise and provides additional relevant information (e.g. shape and size variability). It has the potential to contribute in a number of ways to research and to clinical practice.
The success of several large national sizing surveys in the UK and US demonstrate the capacity of the technique to be applied to large numbers of individuals across the entire adult age range, and across the spectrum of ethnic variability.
The ease of use, high acceptability and low time requirement per participant makes 3D-PS ideal for large-scale anthropometric surveys, potentially including obesity screening. Furthermore, the visualisation provided by this technique is likely to aid/maintain patient motivation and hence compliance, a key issue in obesity management given the tendency for individuals to regain weight previously lost.
TBK has been used primarily as a marker for body cell mass (BCM), total body protein and can also be used to estimate FFM. In general, the accuracy of the whole body measurement of TBK is 1–5% for adults, decreasing slightly for the preterm infant. This method was originally applied for predicting total body fat in the 1960s. Although the TBK-fat method is no longer in use, studies support the continued use of TBK for total body protein, body cell mass and skeletal muscle in both adults and children.
The method does not assess body composition values per se, but it provides an array of measurements that capture body size and shape.
The system used determines the density of the point cloud and the software used for the generation of estimates as they are typically integrated. Data processing and analysis is conducted by proprietary software. Initial data processing cleans the point cloud by rejecting inconsistent data points arising from artifacts in the scanning area. Software incorporates automatic landmark identification, whereby algorithms automatically extract key anatomical locations. These are then used to guide an ‘e-tape measure’, which provides a large number of girths, depths and diameters.
Using the different dimensions extracted from the scanner, principal component analysis (PCA) can be used to investigate the variation of body shape in the data set. Where the data does not assume a normal distribution, independent component analysis can identify more distinct (or independent) modes of variation in body shape.
Key characteristics of three-dimensional photonic scanning are summarised in Table 1.
Table 1 Characteristics of three dimensional photonic scanning.
|Number of participants||Large|
|Researcher burden of data collection||Low|
|Researcher burden of coding and data analysis||Low|
|Risk of reactivity bias||No|
|Risk of recall bias||No|
|Risk of social desirability bias||No|
|Risk of observer bias||Yes|
|Suitability for field use||Not suitable|
|Participant literacy required||No|
Considerations relating to the use of 3D-PS for anthropometry in specific populations are described in Table 2.
Table 2 Anthropometry by 3D-PS in different populations.
|Pregnancy||Suitable in principle. However, it requires validation.|
|Infancy and lactation||May not be suitable as the protocol requires the participant to stay still for 1- 24 seconds (depending on the instrument used).|
|Toddlers and young children||3D-PS is acceptable in children aged 5 years and above, though with current hardware/software, and body movement artefacts, approximately one third of scans may be unsuccessful because of movement.|
|Older Adults||Suitable as long as participant is able to stand still e.g. may not be applicable in Alzheimer patients or in individuals with neurological disorders that can produce tremor.|
Refer to section: practical considerations for objective anthropometry
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