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ã Dentomaxillofacial Radiology (2001) 30, 56 ± 58 2001 Macmillan Publishers Ltd. All rights reserved 0250 ± 832X/01 $15.00 www.nature.com/dmfr 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 insucient 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 eectiveness. 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. 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