Development of a clinically applicable tool for bone density assessment.

OBJECTIVES: To assess the accuracy and reliability of new software for radiodensitometric evaluations. METHODS: A densitometric tool developed by MevisLab was used in conjunction with intraoral radiographs of the premolar region in both in vivo and laboratory settings. An aluminum step wedge was utilized for comparison of grey values. After computer-aided segmentation, the interproximal bone between the premolars was assessed in order to determine the mean grey value intensity of this region and convert it to a thickness in aluminum. Evaluation of the tool was determined using bone mineral density (BMD) values derived from decalcified human bone specimens as a reference standard. In vivo BMD data was collected from 35 patients as determined with dual X-ray absorptiometry (DXA). The intra and interobserver reliability of this method was assessed by Bland and Altman Plots to determine the precision of this tool. RESULTS: In the laboratory study, the threshold value for detection of bone loss was 6.5%. The densitometric data (mm Al eq.) was highly correlated with the jaw bone BMD, as determined using dual X-ray absorptiometry (r = 0.96). For the in vivo study, the correlations between the mm Al equivalent of the average upper and lower jaw with the lumbar spine BMD, total hip BMD and femoral neck BMD were 0.489, 0.537 and 0.467, respectively (P < 0.05). For the intraobserver reliability, a Bland and Altman plot showed that the mean difference +/- 1.96 SD were within +/-0.15 mm Al eq. with the mean difference value small than 0.003 mm Al eq. For the interobserver reliability, the mean difference +/-1.96 SD were within +/-0.11 mm Al eq. with the mean difference of 0.008 mm Al eq. CONCLUSIONS: A densitometric software tool has been developed, that is reliable for bone density assessment. It now requires further investigation to evaluate its accuracy and clinical applicability in large scale studies.

Comparison between effective radiation dose of CBCT and MSCT scanners for dentomaxillofacial applications.

OBJECTIVES: To compare the effective dose levels of cone beam computed tomography (CBCT) for maxillofacial applications with those of multi-slice computed tomography (MSCT). STUDY DESIGN: The effective doses of 3 CBCT scanners were estimated (Accuitomo 3D, i-CAT, and NewTom 3G) and compared to the dose levels for corresponding image acquisition protocols for 3 MSCT scanners (Somatom VolumeZoom 4, Somatom Sensation 16 and Mx8000 IDT). The effective dose was calculated using thermoluminescent dosimeters (TLDs), placed in a Rando Alderson phantom, and expressed according to the ICRP 103 (2007) guidelines (including a separate tissue weighting factor for the salivary glands, as opposed to former ICRP guidelines). RESULTS: Effective dose values ranged from 13 to 82 microSv for CBCT and from 474 to 1160 microSv for MSCT. CBCT dose levels were the lowest for the Accuitomo 3D, and highest for the i-CAT. CONCLUSIONS: Dose levels for CBCT imaging remained far below those of clinical MSCT protocols, even when a mandibular protocol was applied for the latter, resulting in a smaller field of view compared to various CBCT protocols. Considering this wide dose span, it is of outmost importance to justify the selection of each of the aforementioned techniques, and to optimise the radiation dose while achieving a sufficient image quality. When comparing these results to previous dosimetric studies, a conversion needs to be made using the latest ICRP recommendations.

Image quality vs radiation dose of four cone beam computed tomography scanners.

OBJECTIVES: To evaluate image quality by examining segmentation accuracy and assess radiation dose for cone beam CT (CBCT) scanners. METHODS: A skull phantom, scanned by a laser scanner, and a contrast phantom were used to evaluate segmentation accuracy. The contrast phantom consisted of a polymethyl methacrylate (PMMA) cylinder with cylindrical inserts of air, bone and PMMA. The phantoms were scanned on the (1) Accuitomo 3D, (2) MercuRay, (3) NewTom 3G, (4) i-CAT and (5) Sensation 16. The structures were segmented with an optimal threshold. Thicknesses of the bone of the mandible and the diameter of the cylinders in the contrast phantom were measured across lines at corresponding places in the CT image vs a ground truth. The accuracy was in the 95th percentile of the difference between corresponding measurements. The correlation between accuracy in skull and contrast phantom was calculated. The radiation dose was assessed by DPI(100,c) (dose profile integral (100,c)) at the central hole of a CT dose index (CTDI) phantom. RESULTS: The results for the DPI(100,c) were 107 mGy mm for (1), 1569 mGy mm for (2), 446 mGy mm for (3), 249 mGy mm for (4) and 1090 mGy mm for (5). The segmentations in the contrast phantom were submillimeter accurate in all scanners. The segmentation accuracy of the mandible was 2.9 mm for (1), 4.2 mm for (2), 3.4 mm for (3), 1.0 mm for (4) and 1.2 mm for (5). The correlation between measurements in the contrast and skull phantom was below 0.37 mm. CONCLUSIONS: The best radiation dose vs image quality was found for the i-CAT.

Comparative study of image quality for MSCT and CBCT scanners for dentomaxillofacial radiology applications.

The image quality of four cone-beam computed tomography (CBCT) scanners dedicated for dentomaxillofacial imaging and one multi-slice computed tomography (MSCT) scanner was compared. For the MSCT scanner, a clinical and a low-dose protocol for oral indications were evaluated. The image quality was assessed by dedicated software that allows an automated analysis of accuracy measurements and evaluation of metal artefacts on two image quality phantoms. Bone was segmented with sub-millimetre accuracyin all scanners.

Comparative localized linear accuracy of small-field cone-beam CT and multislice CT for alveolar bone measurements.

OBJECTIVES: To compare the accuracy of cone-beam computerized tomography (CBCT) and multislice CT (MSCT) for linear jaw bone measurements. STUDY DESIGN: An ex vivo formalin-fixed human maxilla was imaged with both CBCT (Accuitomo 3D; Morita, Kyoto, Japan) and MSCT (4-slice Somatom VolumeZoom and 16-slice Somatom Sensation 16; Siemens, Erlangen, Germany). The MSCT images were reconstructed using different reconstruction filters to optimize bone visualization (U70u and U90u for VolumeZoom, H30s and H60s for Sensation 16). Before scanning, triplets of small gutta-percha markers were glued onto the soft tissues overlying the maxillary bone on the top and on both sides of the alveolar ridge to define a set of reproducible linear measurements in 11 planes. Image measurements were performed by 2 observers. The gold standard was determined by means of physical measurements with a caliper by 3 observers. RESULTS: The accuracy of the linear measurements was 0.35 +/- 1.31 mm (U70u) and 0.06 +/- 1.23 mm (U90u) for the Somatom VolumeZoom, 0.24 +/- 1.20 mm (H60s) and 0.54 +/- 1.14 mm (H30s) for the Sensation 16, and -0.09 +/- 1.64 mm for the Accuitomo 3D. Statistical analysis with 2-way analysis of variance showed no significant inter- or intraobserver disagreement for the physical or the radiologic measurements. There was also no significant difference for the measurements on the different reconstruction filters. CONCLUSION: Both CBCT and MSCT yield submillimeter accuracy for linear measurements on an ex vivo specimen.

Radiation dose vs. image quality for low-dose CT protocols of the head for maxillofacial surgery and oral implant planning.

The goal of this study was to determine the acquisition parameters for a low-dose multi-slice CT protocol and to compare the effective dose and the image quality of this low-dose protocol with the image quality of a clinical multi-slice CT protocol, routinely used for visualisation of the head. The low-dose protocol was derived from a clinical multi-slice CT protocol by lowering mA s and kV and increasing the pitch. The low-dose protocol yielded a dose reduction from 1.5 to 0.18 mSv for a multi-slice CT scan of the whole head, whereas noise in the low-dose CT images was increased. For bone segmentation, noise could be reduced by use of a non-linear edge preserving smoothing filter. Tests on ESP and skull phantom indicated that the accuracy of the measurements on low-dose CT is acceptable for image-based planning of maxillofacial and oral implant surgery, reducing the dose by a factor of 8.