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Dentomaxillofacial Radiology (2001) 30, 56 ± 58
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TECHNICAL REPORT
Radiographic imaging of the mastoid process with conventional
tomography: a novel positioning technique
G Kaeppler*,1, B Nestle2 and S Reinert2
1
Department of Oral Radiology, School of Dental Medicine, University of TuÈbingen, Germany; 2Department of Maxillofacial
Surgery, University of TuÈbingen, Germany
The Scanora1 (Soredex, Helsinki, Finland) is a multimodal unit for maxillofacial imaging
combining narrow beam radiography and pluridirectional spiral tomography. We describe a
novel technique for imaging the mastoid process based on a modi®cation of the program for
coronal tomography of the ear. This technique is of potential clinical value for implant
planning and postoperative evaluation in the temporal bone.
Keywords: tomography, X-ray; dental implants; mastoid; temporal bone
Introduction
The Scanora1 is a multimodal X-ray unit for
maxillofacial imaging which combines the principles
of narrow beam radiography with linear and rotational
scanning and conventional pluridirectional spiral
tomography.1,2 Conventional tomography with the
Scanora1 is widely used to solve a range of imaging
problems in the maxillofacial region and in implantology.3 ± 7 However, there are no speci®c programs for
imaging the temporal bone. In this study we report a
novel technique to achieve this by modifying the
positioning of the patient for coronal tomography of
the ear.
provided insucient information about the potential
implant sites.
The ear programs of the Scanora1 X-ray unit which
provide conventional coronal tomography in the
postero-anterior plane were selected to image the
mastoid process. Images were obtained with Lanex1
Imaging technique
Case 1 involved a patient with right microtia and
agenesis of the ear. It was planned to retain an arti®cial
ear on implants. However, the available bone could not
be assessed clearly with either a conventional submentovertex radiograph or axial (Figure 1) and 3DCT.
Case 2 involved a patient following carcinoma of the
external ear who required implants in the left mastoid.
The lateral and frontal cephalometric radiographs
*Correspondence to: Dr Gabriele Kaeppler, Department of Oral Radiology,
School of Dental Medicine, University of TuÈbingen, Osianderstr. 2-8, D-72076
TuÈbingen, Germany
Received 10 March 2000; accepted 5 September 2000
Figure 1 Case 1: Axial CT scan showing the limited amount of bone
in the right ear
Tomography of the mastoid process
G Kaeppler et al
medium screens combined with T-MAT G ®lm
(Eastman Kodak Company, Rochester, NY, USA) at
63 kV, 5 mA and an exposure time of 99 s in the ®rst
case (program 997-357 for the right side) and at 60 kV,
6.4 mA and 98 s in the second case (program 997-358
for the left side) for a complete sequence of four
tomograms on one ®lm. A 2 mm slice thickness with a
2 mm interval was chosen. In the ®rst case, a metal ball
was ®xed to the patient's skin over the mastoid process
to aid orientation of the tomograms.
Positioning the patient for cross-sectional imaging
with the Scanora1 is based on orientation of three light
lines in the X, Y and Z planes (Figure 2). Normally,
the frontal light line (X) is adjusted to the midsagittal
a
plane and the dotted vertical light line (Y) and the
horizontal line (Z) to the anterior edge of the external
auditory meatus.
The ear program was therefore modi®ed as follows:
The head was positioned with the orbitomeatal plane
parallel to a horizontal plane (Figure 2). The coronal
light beam (X) was ®xed so as to coincide with a
vertical line through the lateral margin of the orbit on
the same side.
The light line Y was adjusted in a posterior direction
so that the dotted vertical line coincided with the
mastoid process. The horizontal line Z was adjusted to
coincide with the centre of the maxillary sinus and
therefore with the centre of the mastoid (Figure 2a,b).
The position of the image layer in relation to
anatomical structures (viewed from above) is shown
in diagrammatic form in Figure 3. To allow for better
contrast of the pneumatized mastoid, a single 55 mm
thick sheet of patternless lead foil from an intra-oral
®lm packet was placed in front of the primary
collimator.
This process has now been used successfully in the
two cases described above (Figure 4a,b).
57
Discussion
The range of indications for the Scanora1 multimodal
radiographic system can be extended by modifying the
existing positioning techniques, as has already been
achieved for imaging bony lesions in the middle of the
hard palate and ectopic maxillary third molars.8
b
Figure 2 (a) Patient positioning for the left side in Case 2. (b)
Diagram of patient positioning. The orbitomeatal line is parallel to a
horizontal plane. The frontal line (X) was adjusted to coincide with
the vertical line through the lateral margin of the left orbit; the Y
light line was adjusted in a posterior direction so that it coincided
with a vertical line through the mastoid process; the Z light line was
aligned with the centre of the maxillary sinus and therefore the centre
of the mastoid process
Figure 3 Diagram indicating the position of the image layer relative
to the adjacent anatomical structures (viewed from above)
Dentomaxillofacial Radiology
Tomography of the mastoid process
G Kaeppler et al
58
a
b
Figure 4 (a) Case 1: Coronal tomogram of the mastoid process. A metal ball has been ®xed to the patient's skin. (b) Case 2: Postoperative
coronal tomogram of the temporal bone and mastoid process showing the more anterior of the two implants
We completely covered the primary aperture of the
Scanora1 with lead foil to improve the contrast.
Measurements with an ionisation chamber ®xed to
the upper lip showed that we achieved a dose reduction
of about 45% (11.0 vs 20.4 mGy).
The great advantages of conventional tomography
compared with CT are ease and cost e€ectiveness. It
gives a good overview with four tomograms on one
®lm with a de®ned magni®cation factor of 1.7.5,6
Metallic artefacts which may often degrade the
postoperative CT of implants are avoided.
The present modi®cation of frontal tomography
demonstrates the mastoid process and temporal bone
better than conventional radiography.
References
1. Tammisalo EH, Hallikainen D, Kanerva H, Tammisalo T.
Comprehensive oral x-ray diagnosis: Scanora1 multimodal
radiography. Dentomaxillofac Radiol 1992; 21: 9 ± 15.
2. GroÈndahl HG, Ekestubbe A. A new, multi-purpose X-ray
machine for dento-maxillo-facial radiology. Phillip J 1992; 9:
97 ± 103.
3. Ekestubbe A, Thilander A, GroÈndahl HG. Absorbed doses and
energy imparted from tomography for dental implant installation. Spiral tomography using the Scanora1 technique
compared with hypocycloidal tomography. Dentomaxillofac
Radiol 1992; 21: 65 ± 69.
4. GroÈndahl K, Lekholm U. The predictive value of radiographic
diagnosis of implant instability. Int J Oral Maxillofac Implants
1997; 12: 59 ± 64.
Dentomaxillofacial Radiology
5. Ekestubbe A, GroÈndahl HG. Reliability of spiral tomography
with the Scanora1 technique for dental implant planning. Clin
Oral Impl Res 1993; 4; 195 ± 202.
6. Kaeppler G, Axmann-Krcmar D, Schwenzer N. Anwendungsbereiche transversaler Schichtaufnahmen (Scanora) in der zahnaÈrztlichen Implantologie. Z ZahnaÈrztl Implantol 1997; 13: 18 ±
26.
7. Wenzel A, Aagaard E, Sindet-Pedersen S. Evaluation of a new
radiographic technique: diagnostic accuracy for mandibular
third molars. Dentomaxillofac Radiol 1998; 27: 255 ± 263.
8. Kaeppler G, Meyle J, Schulte W. Radiographic imaging of the
hard palate and of upper third molars with spiral tomography: a
novel technique of patient positioning. Quintessence International 1996; 27: 455 ± 463.