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| Fig. 1: X-ray of a bird mummy from an Egyptian tomb, taken by Charles Thurstan Holland on 22 October 1896. [2] (Source: Wikimedia Commons) |
The rapid technological advances of imaging modalities in the last few decades have established clinical radiology as an essential player in the field of clinical medicine. [1] Yet while postmortem imaging has also been practiced since the days of the start of imaging, it wasn't until the founding of the Virtopsy Project in the late 1990s that many forensic departments worldwide began establishing relationships with clinical CT or MR suites with the aim of implementing routine imaging methods as supplements - or even replacements - of traditional autopsies. [2-4] Since then, forensic radiology has arisen in the field of forensic medicine as a new subspecialty that combines the fields of forensic pathology and radiology. [1,3]
Although the first radiographic image obtained was of a living hand, the rays were also soon used to look at nonliving tissue. [2] On October 23, 1896, Charles Thurstan Holland used these newly discovered rays to radiograph a bird mummy (Fig.1). [2] That same year, William Meadowcroft also included a radiographed hand of a mummified Egyptian princess in his The ABC of the X-rays (Fig 2). [5]
As radiology advanced, newer techniques were also progressively applied towards the forensic field. In the late 1970s, Wullenweber et al reported one of the earliest forensic applications of computed tomography (CT) to describe radiographic patterns of fatal cranial bullet wounds. [3,4] Following this report, the 1980s and 1990s saw a rise in publications, programs, and books dedicated to forensic imaging. [3,4] The most prominent of these, the Virtopsy Project, was founded at the Institute of Legal Medicine of the University of Berne in Switzerland. [3,4] Although it was not the first trial to use computed tomography (CT) or even magnetic resonance imaging (MRI) in a postmortem scanning, it was the very first to integrate a broad range of different techniques (CT, MRI, invasive biopsies, and 3D external scanning) while also examining a large number of cases in a systematic manner. [6]
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| Fig. 2: Radiograph of a mummified Egyptian princess hand obtained near the tombs of the Kings, Thebes, in 1892. [5] (Source: Wikimedia Commons) |
Forensic and clinical radiology differ significantly in several aspects. [3] In clinical radiology, specific pathologies must be ruled out or confirmed using a focused clinical protocol for a particular anatomical region, thus leading to a specific diagnosis. [3] Compared to this, forensic radiology is focused on detecting the cause of death and on generating insights into the deceased's mortal circumstances. [3] Because radiation safety is not an issue for the deceased, the imaging parameters used can be adjusted so that maximum image quality is obtained. [3,7] Compared to imaging in living patients, the radiologist also does not need to be concerned about movements, respiration artifacts, or adverse reactions to contrast media when imaging the deceased. [7] The lack of circulation, however, is often accompanied by typical postmortem sedimentation effects, which can obscure image reading or even mimick real pathologies. [3,7] Furthermore, while the methods of forensic imaging offer great ways of visualizing pathologies and complex anatomical relationships in nondestructive manners, dynamic contrast phases cannot be achieved postmortem, and the radiologist must therefore be accustomed to reading mostly unenhanced images. [7]
To properly evaluate postmortem images, it is important to remember that forensic radiology findings are heavily influenced by changes in the body after death. [7] Following the early stages of postmortem change in tissue structure, putrefaction brings along gas accumulation in many of the body's systems. [7] Whereas the distribution of gas caused by decomposition involves the entire body and has a dependency on corpse positioning, air embolisms only appear intravascularly. [7] Correct differentiation between air embolisms as vital reactions and gas accumulation due to decomposition is not an easy task for those who are not familiar with postmortem changes of the body, and the investigator must keep all these differences in mind when examining postmortem images. [7]
According to forensic guidelines, medical foreign material (such as tracheal tubes or vascular catheters) should not be removed prior to the scan for the purpose of documenting potential malpractice issues. [7] Based on the imaging routines of the Virtopsy Project, the deceased body will undergo conventional forensic autopsy combined with external inspection, postmortem computed tomography (pmCT), and eventually magnetic resonance imaging (MRI) of the whole body without contrast media. [7] In cases that will undergo postmortem computed tomography angiography (pmCTA), samples of peripheral blood and urine also have to be collected. [7]
Currently, a 16-row multidetector CT works sufficiently well for pmCT purposes (while a 4- or 6-row multidetector will also work, this comes with major concessions). [7] Data of the entire body should be acquired with a slice thickness of less than 3 mm in axial sections - with which sagittal and coronal reformations can then be calculated. [7] The mean duration of a whole- body pmCT scan depends strongly on the cooling capacity of the x-ray tube of the CT scanner, ranging from less than 1 minute (with a 64-slice CT) to almost 30 minutes (with an outdated 4-slice CT). [7] In a case where dense foreign material such as projectiles, metallic fragments, prostheses, osteosyntheses, or even dental fillings are present, an extended CT scale may be necessary for material differentiation. While the maximum width of the HU scale is 1,024 to +3,071 in clinical settings, an extended HU width that multiplies the standard-setting by a factor of 10 (-10,240 to +30,710) is favorable. [3]
A growing amount of evidence is supporting the use of forensic imaging as important supplements - or even replacements - to traditional autopsies. [4] While the subspecialty of forensic radiology remains largely undeveloped, clinical radiologists and forensic pathologists alike are aware of an increasing interest in the field. [1] Thus, with the aim of establishing a set of high-quality standards and guidelines, the International Society of Forensic Radiology and Imaging (ISFRI) was founded in 2013. [1,3] It is hoped that, in the future, such societies will act as a base for further international developments in forensic imaging. [3]
© Yuchen Liu. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] P. M. Flach, M. J. Thali, and R. Germerott, "Times Have Changed! Forensic Radiology - A New Challenge for Radiology and Forensic Pathology," Am. J. Roentgenol. 202, W325, (2014).
[2] A. M. K. Thomas, "Postmortem Imaging: Development and Historical Review," in Atlas of Postmortem Angiography, ed. by S. Grabherr, J. M. Grimm, and A. Heinemann (Springer, 2016).
[3] P. M. Flach et al., "Imaging in Forensic Radiology: an Illustrated Guide for Ppostmortem Computed Tomography Technique and Protocols," Forensic Sci. Med. Pathol. 10, 583 (2014).
[4] S. P. Stawicki et al., "Postmortem Use of Advanced Imaging Techniques: Is Autopsy Going Digital?," OPUS 12, 2, 17 (2008).
[5] W. H. Meadowcroft, The ABC of the X-rays, (Simpkin, Marshall, Hamilton, Kent and Co, 1896), p112.
[6] R. K. Badam et al., "Virtopsy: Touch-free autopsy," J Forensic Dent Sci. 9, 42 (2017).
[7] P. M. Flach et al., "Clinical and Forensic Radiology Are Not the Same," in Brogdon's Forensic Radiology 2nd Ed, ed. bu M. J. Thali, M. D. Viner and B. G. Brogdon (CRC Press, 2010).
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