JBR–BTR, 2006, 89: 264-265.
SPECIAL ARTICLE
AN ANCIENT ROMAN BOWL EMBEDDED IN A SOIL SAMPLE: SURFACE
SHADED THREE DIMENSIONAL DISPLAY USING DATA FROM A MULTIDETECTOR CT
M. De Maeseneer1, N. Buls2, N. Cleeren3, L. Lenchik1, J. De Mey2
We present an unusual application of multidetector CT and shaded surface rendering in the investigation of a soil
sample, containing an ancient Roman bronze bowl. The CT findings were of fundamental importance in helping the
archaeologists study the bronze bowl from the soil sample.
Key-words: Radiography, in art
The city of Oudenburg, located
on the Belgian shore, in the vicinity
of Oostende is an important archaeological site for study of ancient
Rome. At this site, a Roman army
base dating from 2nd to 5th century
A.D. was uncovered. It is estimated
that up to 500 soldiers at a time
inhabited the base which served to
defend the northern border of the
Roman Empire against invasion
from Germanic tribes. The Institute
for the Archaeological Patrimonium
of Flanders has been involved with
excavations at this site. Unfortunately, the site is scheduled to be
destroyed in order to make room for
a shopping mall.
Recently, at this site, a sample of
soil (Fig. 1) was uncovered containing remnants of what appeared to
be a bronze bowl. The sample was
removed in its entirety for further
study. Visual inspection of the surface of the sample revealed fragments of bronze with typical greenish discoloration and evidence of
corrosion. The impression was that
several portions of different bowls
were present. Radiography (Fig. 2)
and multislice CT (Fig. 3) was then
performed to better characterize the
contents of the soil sample.
Materials and methods
After excavation, the sample of
earth measuring 50 x 50 x 30 cm
was placed in a wooden crate
(Fig. 1). Before imaging the wooden
crate was removed and the sample
was placed in a large plastic bag.
Permission to image the archaeo-
Fig. 1. — Soil sample containing bronze bowl. Note central
ring (white arrows).
logical sample was waived from the
ethical committee of the hospital.
Standard radiography was obtained
using a DR system (Hologic,
Bedford, USA) equipped with a
direct a-Se detector (Fig. 2). The
sample was then scanned on a multidetector CT scanner (Siemens,
Erlangen, Germany) using the
following scanning parameters:
120 kVp, 160 mAs per rotation, slice
thickness: 16 0.75 mm pitch: 0.75.
The radiographs and CT images
were evaluated in concert by a radiologist, physicist, and archaeologist.
Subsequently, three dimensional
reconstructions (Figs. 4, 5) were
performed on a Leonardo VB30
workstation (Siemens, Erlangen,
Germany). The technique of surface
From: 1. Department of Radiology, Wake Forest University, Winston Salem, NC, USA,
2. Department of Radiology, Vrije Universiteit Brussel, 3. Instituut voor het Arcehologisch Patrimonium Flanders, Belgium.
Address for correspondence: Dr M. De Maeseneer, MD, Wake Forest University
Hospital Division of Radiologic Sciences, Medical Center Boulevard, Winston-Salem,
NC 27157. E-mail: [email protected].
shaded display was used with a
Hounsfield Units range of +2200 to
+3071.
Results
Standard radiographs could only
be obtained along the smallest
dimension of the archaeological
sample because of the high attenuation along other dimensions. The
images suggested that at least two
bowls were present (Fig. 2).
The CT images suggested that
only one fragmented bowl was present in the soil sample. In addition,
deep to the bowl, a few dense and
irregular curved and linear structures, measuring several centimetres, were present. These were less
dense than the bronze bowl and
were assumed to represent sea
shells, as the archaeological site is
located in a coastal region (Fig. 3).
The surface shaded 3D CT
images were the most informative
(Fig. 4). They showed clear evidence
SURFACE SHADED THREE DIMENSIONAL DISPPLAY — DE MAESENEER et al
265
Fig. 3. — Coronal CT image of sample. Note that only one
bowl is present (large arrows). On one side, wall is collapsed
centripetally.Note central ring (white arrows), and peripheral
ring (black arrows). Seashells are seen (white arrowhead), as
well as supporting sand bags (S).
Fig. 2. — Craniocaudal radiograph of soil sample. Central
ring-like structure us seen (white arrows). Note more peripheral ring (black arrows).
that only one bowl was present. The
impression on standard radiography that multiple bowls were
present was due to two circular
ridges present in the bowl. One
ridge was located centrally and
another between the margin of the
bowl and this central ridge.
Perpendicular to and connecting
both ridges, multiple smaller ridges
were observed. Some portions
showed considerable fragmentation, whereas other portions were
relatively intact. Along a 70-degree
region, the outer margin of the bowl
also was collapsed in a centripetal
direction. The collapsed portion, as
well as the ridges gave the impression on standard radiography that
several bowls were present.
The specimen was further stored
without undertaking an attempt to
remove the bowl from the specimen. At this point it is not clear if
this will be done in the future.
Removing the bowl is a time consuming and complex procedure
given the considerable fragmentation present.
Discussion
With the advent of multidetector
CT, three dimensional datasets are
commonly employed in various
radiological specialties. For example, musculoskeletal radiologists
commonly use surface rendered
images to allow better understanding of three dimensional relationships of complex bony structures
such as the pelvis (1).
Fig. 4. — Surface shaded display CT. One bowl is seen with
outer margin (large arrows), and two other ridges more centrally (large thin arrows, short thin arrows).
The application of multidetector
CT combined with surface rendering
in the evaluation of metallic archaeological findings has not been previously described. Whereas previously the presence of metal was a contraindication for CT scanning due to
presence of artefacts, such artefacts
are now minimized due to advances
in CT technology (2).
Standard radiography of the
archaeological sample was only
possible in the short axis direction.
The thickness of the lump in other
directions prevented sufficient penetration by the x-ray beam.
In contrast, CT scanning was able
to penetrate the sample of soil containing the bowl without any problems, and yielded images with
minimal metal artefacts. It was still
very difficult, however, from the
native CT images, to understand
three dimensional relationships.
Surface shaded rendering with
views from different angles, however allowed a detailed understanding of the shape of the bronze bowl,
and the location of the different
fragments. This information was
valuable to the archaeologists. It can
help them in retrieving the bronze
bowl from the soil sample as intact
as possible. If retrieval is not possible, line drawings from the bowl can
be made based on the surface
shaded displays, giving valuable
archaeological information.
References
1.
Haveri M., Junila J., Suramo I.,
Lahde S.: Multiplanar and 3D CT of
acetabular fractures. Acta Radiol,
1998, 39: 257-264.
2. Total hip prosthesis metal-artifac
suppression using iterative deblurring reconstruction. J Comput Assist
Tomogr, 1997, 21: 293-298.