Skin injury model classification based on shape vector analysis

Abstract

Background: Skin injuries can be crucial in judicial decision making. Forensic experts base their classification on subjective opinions. This study investigates whether known classes of simulated skin injuries are correctly classified statistically based on 3D surface models and derived numerical shape descriptors.Methods: Skin injury surface characteristics are simulated with plasticine. Six injury classes – abrasions, incised wounds, gunshot entry wounds, smooth and textured strangulation marks as well as patterned injuries - with 18 instances each are used for a k-fold cross validation with six partitions. Deformed plasticine models are captured with a 3D surface scanner. Mean curvature is estimated for each polygon surface vertex. Subsequently, distance distributions and derived aspect ratios, convex hulls, concentric spheres, hyperbolic points and Fourier transforms are used to generate 1284-dimensional shape vectors. Subsequent descriptor reduction maximizing SNR (signal-to-noise ratio) result in an average of 41 descriptors (varying across k-folds). With non-normal multivariate distribution of heteroskedastic data, requirements for LDA (linear discriminant analysis) are not met. Thus, shrinkage parameters of RDA (regularized discriminant analysis) are optimized yielding a best performance with λ = 0.99 and γ = 0.001.Results: Receiver Operating Characteristic of a descriptive RDA yields an ideal Area Under the Curve of 1.0for all six categories. Predictive RDA results in an average CRR (correct recognition rate) of 97,22% under a 6 partition k-fold. Adding uniform noise within the range of one standard deviation degrades the average CRR to 71,3%.Conclusions: Digitized 3D surface shape data can be used to automatically classify idealized shape models of simulated skin injuries. Deriving some well established descriptors such as histograms, saddle shape of hyperbolic points or convex hulls with subsequent reduction of dimensionality while maximizing SNR seem to work well for the data at hand, as predictive RDA results in CRR of 97,22%. Objective basis for discrimination of non-overlapping hypotheses or categories are a major issue in medicolegal skin injury analysis and that is where this method appears to be strong. Technical surface quality is important in that adding noise clearly degrades CRR.Trial registration: This study does not cover the results of a controlled health care intervention as only plasticine was used. Thus, there was no trial registration.

Virtopsy approach: Structured reporting versus free reporting for PMCT findings

“…Virtopsy R subsequently developed into a multi-tool documentation and analysis research project [17], combining 3D body surface imaging methods with merged CT/ and MRI-data and 3D shape analysis [34,35,36,37,38,39], the application of multidetector or multislice [40] CT and MRI found continued interest [41,42,43,44,45,46] also for problems specific to clinical forensic medicine [47,48], then for high-resolution micro-CT [49,50] and micro-MRI (MR microscopy) [51], magnetic resonance spectroscopy (time-of-death determinations) [52,53,54], image-guided percutaneous biopsy [55,56,57,58,59], postmortem angiography [60,61,62,63,64,65,66], post mortem identification [67,68], postmortem ventilation [69,70], and non-invasive tool and data display control such as the integration of a Kinect camera [71,72] or 3D printing and rapid prototyping [73]. Added value for the conventional autopsy results from improved planning and better diagnostics.…”

“…Added value for the conventional autopsy results from improved planning and better diagnostics. Some concise advantages are the identification and incorporation of bone bruises into accident reconstructions [45]), the identification of gas (relevant in diving related deaths [74,75,76]), the ability to identify pathology in decaying tissue (that can be difficult if not impossible to handle manually at dissection [77,78]), the ability to extract and use information related to (chemical) material composition [79,80], documentation of medical installations [81] and exploitation of digital data for reconstructive purposes [34,35,82,39]. Furthermore, advances in usage of reconstructive aspects of 3D CT reconstructions have lead to routine integration of forensic aspects into clinical forensic medicine (Fig.…”