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Micro-CT Scanning:

Updated: Mar 1

Innovations in the recording of cremation burials

Conventionally, potential cremation vessels are block lifted on site – upon arrival at the Finds Department, the soil within the urn is excavated in spits to reveal what the urn contains. Simultaneously, plans are hand-drawn and pictures are taken to indicate the exact positions of materials found within the urn. This is a complex task that must be done slowly and carefully as the location, depth and extent of materials such as cremated human bones or other pyre goods are unknown. There also looms the possibility of human error – in case of cremation urns, there is a high chance of destroying cremated bone fragments during excavation, since they are already quite soft and brittle due to extensive exposure to high temperatures. This can skew the findings.


In 1993, the Trust’s osteoarchaeologist Trevor Anderson carried out the first ever

Computerised Tomography (CT) scans of cremation urns from Each End, Ash – a method that had previously been used for examining mummified material or facial reconstruction but never for cremated human remains. CT scans are a non-destructive imaging procedure whereby ‘slices’ or sections of the material being scanned are obtained using high-resolution X-rays. This pin-points, with certainty, the position and expanse of the materials within the vessel. With current advancements in projection, 3-dimentional volumetric models of the urn can also be produced with high accuracy. Furthermore, specific components of interest within the scan can also be isolated and visualised as a 3-D object, that reveals the textured details of its surface. Exact measurements can be taken virtually while rotating these objects around. Different materials can be distinguished by varying shades in these contrasting grayscale scans, with lighter shades depict denser compositions. Although the risk of damage during consequent excavation remains, the whole procedure is more efficient and accurate

since data for assessment is collected before dismantling the urn and taking its contents

apart.


Although, the Updated Guidelines to the Standards for Recording Human Remains published by CIfA in 2017 acknowledges CT scans as an aid to initial examinations of urned cremated remains, it discusses the scarce availability of the expensive equipment, especially in the commercial sector. Subsequently, it points out the exceptional use of CT scans for recording fragile bone fragments that are likely to be destroyed during excavation. For example, if the soil within the urn is highly acidic, it can decimate the delicate, sponge-like internal trabecular bone, leaving the cortical bone flimsy, weak, and thus, highly susceptible to breakage during excavation. If scanned, the bone fragments can be visualised as a whole.


The School of Anthropology and Conservation at the University of Kent has newly acquired a micro-CT scanner for their ‘Imaging Centre for Life Sciences’. Prof. Mathew Skinner, the Director of the lab, offered to scan some cremations from the Trust’s projects. We decided to test the scanner for four potential cremation urns from Thanet Parkway and an interesting Roman pot from Slatters Hotel. The Roman vessel was recovered from a pit within a Roman building from around 2nd-3rd Century AD. Initial studies indicated that the vessel might have been placed there as a 'closure' deposit, marking the end of the use of the building. Table 1 contains the details and dimensions of all the vessels. We could not scan one of the vessels (2402) from Thanet Parkway since it was too heavy.


Table 1: Dimensions of the vessels
Table 1: Dimensions of the vessels.

Out of the four contexts scanned from Thanet Parkway, three contained what seems to be cremated human remains. Vessel (2807) seems to contain considerable amounts of human bones in its lower segment; the urn also seems to be almost complete. Vessel (5461) is a large urn, almost complete, with substantial quantity of potential cremated bones (Image 1) scattered throughout the matrix of the soil. Context (6279) seems to only have a few broken sherds of pottery, but it surely contains some cremated human remains in the upper segment of the soil (Image 2). Although vessel (2707) does not seem to contain human remains, it has an interesting feature that would have been difficult to determine during manual excavation. There are small burrow-like cavities (Image 3) extending downwards through the soil – the largest one ends in a small, hollow pit with miniscule consolidations. There could have been organic material in the vessel that decomposed and left the voids with small pebbles that visualise as darker consolidations, or it could be taphonomic – an organism burrowed down through the soil within the vessel and the smaller opacities detected in the

pit are bones. The urn itself is well preserved.


3D model of vessel (2807).

View from the top of vessel (5461) showing the cremated bones at the bottom of the vessel.


CT scan
Image 1: CT scan of vessel (5461) – a cross-section of the long bones can be seen in the lower segment.
CT scan
Image 2: CT scan of a part of vessel (6279) – shaft of long bones can be visualised clearly.
CT scan
Image 3: CT scan of vessel (2707) clearly depicts a burrow with small densities at the base.

The vessel (2729) from Slatters Hotel has a distinct shape (Image 4); it is fragmented but mostly well preserved. It has no obvious pieces of cremated bone but there seems to be some small concretions scattered throughout the lower segment of the pot – the somewhat round shape of the dense material suggests they are pebbles. It could also be a sample of well-cremated human bones – the excavation followed by wet sieving of the soil will confirm and identify the contents of the pot.


CT scan
Image 4: CT scan of vessel (2729) – concretions visible at base.

These preliminary scans provided us with some good visualisations and 3-Dimentional

volumetric models (Images 5 and 6). Due to the lack of established methodological standards the images required multiple scans with various exploratory settings; the haziness visible in some images was potentially caused by the high density of soil within the vessels. This was the first time such dense material was being scanned using the micro-CT scanner, therefore, further calibrations might be needed for clearer imaging. Increased current and voltage might provide increased penetration. The noise in the images can potentially be reduced by better adjustment – changing filters or increasing the number of projections might prove beneficial.


CT scan
Image 5 and 6: 3-Dimentional rendering bone fragments from within the scanned cremation (6279).

For further use, regularised CT scanning of potential cremations might prove to be beneficial in various aspects. For fragile cremated human bones, the scans would be a marvellous way to visualise them without causing any damage whatsoever from excavating. It can provide an excellent and accurate view of the concentration and distribution of materials within the urn – with exact location, depth and measurements of each isolated fragment. The texture of the materials can also be visualised in great detail, which would be essential for assessing the nature of the burnt bone (animal or human). Such accuracy will allow for lesser chance of bias in data collection and subsequent statistical tests. Furthermore, detailed texture visualization of the bone elements will aid the assessment of heat induced fissure pattern and fragmentation which will allow inferences regarding the initial state of the remains (dry or wet), pyre temperature as well as the degree of manipulation. Additionally, scanned empty vessels would not require excavation, saving precious time and effort – the most important component of it, the vessel itself, will already have been scanned and we would have a 3-D volumetric, interactive image of it for further analysis.

Adelina Teoaca

Ihini Aambreen

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