View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by RERO DOC Digital Library Leitthema Rechtsmedizin 2007 · 17:7–12 M.J. Thali1 · S. Ross1 · L. Oesterhelweg1 · S. Grabherr1 · U. Buck1 · S. Naether1 · DOI 10.1007/s00194-006-0419-6 C. Jackowski1 · S.A. Bolliger1 · P. Vock2 · A. Christe2 · R. Dirnhofer1 Online publiziert: 30. Dezember 2006 1 Center of Forensic Imaging, Institute of Forensic Medicine, University, Bern © Springer Medizin Verlag 2006 2 Institute of Diagnostic Radiology, University Hospital, Bern Virtopsy Working on the future of forensic medicine In recent times, few fields have witnessed 3D Photogrammetry-based This allows for a more detailed surface such impressive progress as imaging optical scanning documentation compared to 3D recon- methods and radiology: digital data ac- structions based on high resolution CT quisition and post-processing of images The standard for the documentation of in- data. have revolutionized the practice of imag- juries in forensic medicine is still photog- The color information is acquired us- ing and radiology and have determined a raphy with exact measurements. Howev- ing the Tritop software that combines dig- growing interest in this field on the part er, the photographic process reduces a 3D ital photography of the surface from many of other medical professions. The applica- wound to a 2D level in the same way as different angles into 3D color information tion of imaging methods for non-invasive classical x-ray documentation. of the object that can be correctly matched documentation and analysis of relevant Using the TRITOP/ATOS III (GOM, on the digital 3D surface model using cod- forensic findings in living and deceased Braunschweig, Germany) system the col- ed and uncoded markers placed on the persons has lagged behind the enormous ored 3D surface can be documented via object. Using this technology, documenta- technical development of imaging meth- detection of the distortion of light beams, tion ranging from fine detailed structures ods. There are only a few textbooks deal- projected onto the region of interest (skin lesions or fine object structure) to ing with forensic imaging and radiology (. Fig. 1) and the system can then recal- overview documentation (whole body or and most concentrate on classical pho- culate the 3D surface that caused the dis- objects such as an entire motor vehicle) is tography and roentgenographic meth- tortion. This system is usually used when possible. By documenting an injury pat- ods and hardly cover the newer three-di- high precision is required as it has an ac- tern and an instrument suspected of caus- mensional (3D) imaging techniques. Fo- curacy of measurement below 20 μm. ing the injury (. Fig. 2), a digital 3D geo- rensic 3D imaging and radiology, includ- ing all techniques and their many uses for forensic purposes, is now a rapidly grow- ing sub-discipline of forensic medicine. Virtopsy became the scientific umbrel- la, including technical tools which can be used to document forensically relevant findings in 3D. Fig. 1 7 3D surface The most important tools for daily scanner ATOS III and 6- row multislice CT scan- routine use are: ner, used by the Vir- F 3D photogrammetry-based topsy group in Bern. optical surface scanning Notice the wave pat- F Computed tomography tern, projected onto and magnetic resonance the corpse by a projec- tor unit and captured imaging by two CCD cameras F Postmortem biopsy mounted beside the F Postmortem angiography projector Rechtsmedizin 1 · 2007 | 7 Leitthema metric match analysis of the previously ac- quired data is possible, even when the in- jury of a living person is already healed or the dead body is buried. Computed tomography and magnetic resonance imaging Computed tomography (CT) was intro- duced in the early seventies by Houn- sfield and Cormack, for which they won the Nobel Prize in 1979. CT was also called computed axial tomography and Fig. 2 9 Surface scan of the sole of a shoe the examinations were thus named CAT used to cause an injury scans. CT uses the same technique as ra- diography uses to produce X-rays. How- ever, to obtain transverse (axial) images of body sections, the tube rotates around the longitudinal (z) axis of the body, trans- mitting radiation from many angular po- sitions through the body. X-rays are at- tenuated according to the radiographic density of tissues; these attenuated X-rays reach the detector system beyond the pa- Fig. 3 9 Reconstruction tient, contributing to the attenuation pro- in volume rendering file of one specific tube angle. The many technique (VRT) of a profiles measured during one rotation are whole body MSCT with used by the computer to calculate a den- different voxel opacities for skin, muscle and bo- sity map of the scanned slice with discrete ne. Multiple fractures of absolute density values of all image ele- the upper and lower ex- ments (pixels). Radiodensity is expressed tremities, open book in Hounsfield units (HU) whereby the ra- fracture of the pelvis diodensity of distilled water at standard pressure and temperature (STP) is de- fined as zero HU and air at STP is defined as −1000 HU. The above standards were chosen as they are universally available references and suited to the key applica- tion for which computed axial tomogra- phy was developed: imaging the internal anatomy of humans. Common tissues ha- ve defined radiodensities such as fat (-120 HU), muscle (+40 HU) or bone (+1000 HU). Metal objects can reach very high densities of far more than +1000 HU and will then cause streak artifacts. The first CT scanner was specifically engi- neered to image the brain and the total scan time was then approximately 25 min. Fig. 4 8 Cranial MRI of an accident victim using T1 (a) and T2 (b) weighted imaging. Extensive subdu- These CT scanners, now referred to as ral hematoma on the right with shifting of the midline structures and compression of the right lateral conventional CT scanners, acquired a set ventricle of discrete cross-sections by moving the patient step-by-step through the scanner. A major advance in CT technology oc- curred with the development and imple- mentation of helical or spiral CT in 1989. 8 | Rechtsmedizin 1 · 2007 Zusammenfassung · Abstract In a helical CT scanner the X-ray source Rechtsmedizin 2006 · 17:7–12 DOI 10.1007/s00194-006-0419-6 and the detector array are mounted on a © Springer Medizin Verlag 2006 permanently rotating gantry while the M.J. Thali · S. Ross · L. Oesterhelweg · S. Grabherr · U. Buck · S. Naether · C. Jackowski · patient is moved axially through the scan- S.A. Bolliger · P. Vock · A. Christe · R. Dirnhofer ner at a uniform speed. This technique al- Virtopsy. Zukunftsträchtige Forschung in der Rechtsmedizin lows the acquisition of a complete seam- less volume data set of a body region. This Zusammenfassung data set consists of volume elements „Computed-tomography-Verfahren“ sind storbenen Personen eingesetzt werden. Es called voxels (a portmanteau of the words während der letzen 10 Jahre weiterentwickelt handelt sich um ein minimal-invasives Ver- volumetric and pixel).The most recent worden und haben verschiedene Anwendun- fahren, mit dem forensisch relevante Bilder gen im rechtsmedizinischen Fachgebiet ge- erfasst werden können, die auch im Geri- advance in CT technology has been mul- funden. Die neueste Entwicklung besteht in chtssaal vorgeführt werden können. Die ra- tidetector row helical CT. Current mul- der „multislice computed tomography“, kom- sche Weiterentwicklung der Imaging-Techn- tislice scanners are able to acquire up to biniert mit „photogrammetry-based sur- nik könnte in der Zukunft eine Alternative zur 64 slices in 1 tube rotation. In combina- face optical scanning“ und „Image-rendering- konventionellen Obduktionen darstellen. tion with faster rotation times, a modern Techniken“. Diese Kombination kann für die 3-dimensionale Darstellung von Verletzungs- Schlüsselwörter 64-slice scanner is up to 192 times faster mustern zum Vergleich mit infrage kommen- 3D-bildgebene Verfahren · Leichnam · Verlet- than a single-slice spiral CT from the ear- den Tatwaffen sowie zum Screening nach pa- zungsmuster · Minimal-invasives Verfahren · ly 1990s. As a result, CT data can be ob- thologischen Befunden in lebenden oder ver- „Multislice computed tomography“ tained much faster, with thinner slice col- limation and with better contrast utiliza- tion than with single-slice helical CT. Virtopsy. Working on the future of forensic medicine With the development of multislice CT Abstract (MSCT) and current imaging worksta- Computed tomography techniques have ogy provides a minimally invasive procedure tions, the examiner is no longer restricted been developed over the last 10 years and for capturing forensically relevant images to the axial slice view. Isotropic (cuboid) have found various applications in the fo- which can be produced in the courtroom. The voxels are an ideal prerequisite for image rensic field. The most recent development is rapid developments in imaging techniques post-processing using multipla nar refor- multislice computed tomography combined could provide an alternative to conventional with photogrammetry-based surface optical autopsy procedures in the future. mation to obtain images in sagittal, coro- scanning and image rendering techniques. nal or oblique planes or even de tailed 3D This combination of techniques can be used Keywords presentation methods (. Fig. 3). to produce 3-dimensional images of injury 3D imaging techniques · Corpse · Injury pat- MSCT offers many advantages over patterns for comparison with suspect weap- tern · Minimally invasive technique · Mul- single-slice CT and is clearly the future of ons and also to screen for pathological condi- tislice computed tomography tions in the living or deceased. This technol- helical CT imaging. The newest CT gen- eration has a dual radiation source, which makes it possible to visualize and exam- ine tissues with different X-ray attenua- tion profiles during one scan.