Page 34 - Craniomaxillofacial Implant Surgery - Jeroen P.J. Dings

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Chapter 2
Image acquisition
To prevent movement artefacts the cadaver skulls were stabilized in an upright position for the CBCT scan and in a supine position for the MDCT scan like in the real clinical situation. CBCT images were obtained using the KaVo 3D eXam Imaging System® (KaVo Dental GmbH, Biberach, Germany). 3D imaging data were acquired at 120 kV and pulses of 1.2 mA. The scan time was 40 seconds. The field of view was set to an 23 cm diameter and a 17 cm height with a voxel size of 0.3 mm. Data were converted into DICOM format (Digital Imaging and Communications in Medicine).
MDCT examination was carried out with a commercially available 320-detector row CT- system (Toshiba Aquilion ONE; Toshiba Medical Systems Corporation, Tochigi, Japan) with the following scan parameters kept identical for all specimens: tube voltage 120 kV, slice thickness 0.5 millimetre (increment, 0.3 mm) with a radiation exposure per slide of 61.8 mGy and a total exposure of 1619.1 mGy with a 26.2 cm diameter circular field of view.
Physical measurements
After volumetric image data acquisition the cuts in the skulls were sectioned into small skull blocks since most anatomical landmarks prevented direct access for caliper measurement. Indelible ink marker lines were drawn from the drill holes perpendicular to the cut surface indicating the points of physical measurement with a high precision digital caliper (Digimatic Caliper 0-150 mm, Mitutoyo, Kawasaki, Japan) (Figure 3). Three oral and maxillofacial surgeons independently conducted three measurements at each marked point on the cut surface at three different days with minimum intervals of seven days to determine the inter-observer and intra-observer variability. Each measurement was recorded with an accuracy of 0.01 mm. Means of these measurements were used as the physical reference standards.
Radiological measurements
The radiological data were rendered using commercially available software tools for DICOM data review (Maxilim, v2.3.0.3, Medicim Medical Image Computing, Mechelen, Belgium). All images were reconstructed using multiplanar reformatting. After localizing cuts and bony reference holes, cross-sectional planes were placed parallel to the cuts on the 3D surface rendered reconstructions using the planning software (Figure 4). A software module was developed to create perpendicular planes on these cross-sectional planes parallel to the cut surfaces. On this perpendicular plane the reference holes were localized. Digital markers