Communications of the ACM

The latest technology enables scanning of the body with multiple simultaneous energy levels. Multiple energy levels enable better tissue separation and, at the same time, give rise to new challenges related to visualization of this new type of data. Also, the radiation dose has been reduced approximately 70-fold over the past 10 years. A heart scan today results in less than one month worth of average background radiation.

The increased availability of CT scanners in modern hospitals and radiology clinics has provided an opportunity to scan the fragile mummies and learn about and reveal their interior content and structure without having to open or damage them. Not even the wrapping has to be touched. The first report on CT scanning of mummies was presented in 1979 by Harwood-Nash. 7 Scanning protocols for mummies require custom settings, as the body is completely dehydrated and regular CT protocols assume naturally hydrated tissues, as discussed by Conlogue. 5 Furthermore, standard protocols aim to minimize the radiation dose, and parameters (such as slice thickness) are set to the largest value that still yields sufficient image quality for clinical diagnosis. The scanning settings need a custom configuration to yield the best image quality. For mummies, the radiation dose is generally viewed as less of an issue, but some scholars have begun to raise concerns about DNA degradation. 6

The presence of metallic objects (such as amulets) can pose a challenge to CT scanning, as these objects potentially block X-ray radiation from reaching the sensor array, and the signal reconstruction suffers from artifacts. Such artifacts can now be reduced with state-of-the-art reconstruction algorithms but may also be reduced with modified scanning protocols and multi-energy CT. As museums around the world are increasingly digitizing their collections, a shift toward dedicated CT scanners (such as industrial and micro-CT scanners) is a possible development.

Rendering What Hides Inside

The data generated from a CT scan
after reconstruction is simply a stack
of tomographic images, where the pix-
Figure 3). This approach represents an
excellent case of a massively data par-
allel algorithm that fits modern GPU
architectures, with thousands of par-
allel processors, that execute threads
of ray casting programs. Each ray esti-
mates how simulated light is reflected
and attenuated as the ray propa-
gates from the user’s eye through the
volume,a and the final footprint of
a This follows the principle of reverse ray trac-
ing and allows for several optimizations of the
computation.

els within each image slice become samples, or voxels, in a 3D volume.

The rendering of images of the volumetric dataset on a computer screen is known as volume rendering, 13 or direct volume rendering (DVR), as the image is generated directly from the data without any intermediate ( polygonal) representation. The most common approach to DVR is raycasting, where the stack of images is traversed by simulated rays that collect the color contribution, g(s), from each sampled point as the rays traverse the stack (see

What would eventually become the Inside Explorer visualization table began in 2004, when the Research Group in Scientific Visualization at the Department of Science and Technology, Campus Norrköping, Linköping University, Sweden, began a collaboration with the Center for Medical Imaging and Visualization at Linköping University on a newly started project on virtual autopsies. The need to scan and visualize an entire cadaver before the forensic autopsy posed technical challenges. The most critical were how to deal with the large amounts of data and how to interactively view it when the available memory in a typical workstation was not enough to hold the data of an entire body. This challenge drove our thinking and development of fundamental data-handling components and rendering techniques to support full-body virtual autopsy visualization. 12 The resulting software laid the groundwork for the initial versions of the Inside Explorer Visualization table. It essentially addressed the challenges by adjusting the local level of detail based on the perceived visual impact on the final image and adapting image quality at runtime during interactive exploration. Much research has been devoted over the past 20 years to developing and refining DVR, as well as managing increasingly large and complex datasets, as surveyed by Beyer et al. 3 in 2015.

In the virtual autopsy project, we put each forensic case with casualties through a full-body CT scan prior to the traditional clinical autopsy of the cadaver. Since inception of the virtual autopsy project in 2003, approximately 800 cases have been processed at the Center for Medical Imaging and Visualization, and all cadavers now routinely undergo postmortem full-body CT imaging when there is suspicion of murder. A large body of knowledge has been established, and various studies have been conducted for specific types of autopsy examinations, including classification of dental fillings. This work has been beneficial, if not pivotal, for the subsequent scanning of mummified cadavers. The knowledge gained from scanning and visualizing cadavers could be translated and adapted into scanning and visualizing mummies and other interesting artifacts at the world’s premier museums.

Historical Notes on
Virtual Autopsy

Figure 3. The volume-rendering integral. On a modern GPU, thousands of these ray integrals can be computed in parallel. enabling full HD resolution rendering at 30Hz–60Hz.