Absorbed doses from spiral CT and conventional spiral tomography: a phantom vs. cadaver study

For several radiological examinations, a clinician can select between conventional and spiral computed tomography. Using both techniques, this study aimed at evaluating the difference in absorbed doses when examining a single lateral jaw segment in a human cadaver head and Rando phantom. The present study involved the placement of thermoluminescent dosimeter (TLD) chips (GR-200) in the thyroid gland, and bilaterally, in the parotid and submandibular glands and the lenses of the eyes in both a human cadaver and a Rando phantom at corresponding locations. Consecutive conventional spiral tomographic examinations were carried out in both the left upper and lower premolar area, using a Cranex TOME multifunctional unit. Each examination consisted of 4 slices with a 2 mm slice thickness and exposure parameters of 57 kV, 56 seconds and 1.6-2.0 mA. Regarding spiral computed tomography (CT), a Somatom Plus S scanner (Siemens, Erlangen, Germany), with a slice thickness of 1 mm with settings at 120 kV and 165 mA, was used on both phantoms and separately in the upper and lower jaw. With conventional tomography, the findings of the present study showed that the parotid and submandibular glands on the side near the X-ray tube received the highest dose, both for the cadaver head (doses ranging from 0.5 to 1.3 mGy) and the phantom (doses ranging from 0.6 to 2.6 mGy). For CT of the upper jaw, the highest doses were delivered to the parotid glands with an average absorbed dose of 9.2 and 10.6 mGy for the cadaver head and phantom, respectively. The submandibular glands received the highest doses during CT examination of the lower jaw with an average of 7.8 and 12.9 mGy for the cadaver head and phantom, respectively. It appears from the present investigation that if small edentulous regions are examined, radiation doses during conventional tomography remain much lower than during CT imaging. However, when multiple tomographic cuts are required, a spiral CT examination can replace a series of conventional examinations, especially in cases such as the rehabilitation of an edentulous upper jaw or a more complex surgery.     

Absorbed Radiation Doses During Tomographic Examinations in Dental Implant Planning: A Study in Humans

Objective: The aim of this human study was to evaluate the radiation doses in the buccal cavity and face, during panoramic, spiral conventional tomography, and helicoidal computerized tomography exams. Material and Methods: Lithium fluoride TL detectors (TLD‐100) were placed on the skin at anatomic points such as parotid glands, submandibular glands, thyroid glands, and crystalline to assess the skin entrance dose in 19 patients who were to undergo dental implant surgery. Results: In the panoramic exam, maximum doses were observed near the parotid glands at 1.57 (±18%) mGy on the right and 1.89 (±18%) mGy on the left. In the spiral conventional tomography exam, the maximum dose was 4.41 (±21%) mGy near the right and left parotid glands, whereas near the right or left submandibular glands, the maximum doses reached 40.7 (±18%) mGy. In the helicoidal computerized tomography for mandibular and maxilla exams, the maximum dose was 40.9 (±15%) mGy near the parotid glands and 41.0 (±18%) mGy near the submandibular glands. Near the thyroid and eye lens, doses were lower than 0.23 (±21%) in all exams. Conclusion: Regardless of the exam target area, the submandibular and parotid glands represented the most irradiated organs. This data suggests that efforts should be made by professionals to improve and optimize methods in order to reduce doses without losing the information necessary for treatment planning.     

Localisation of the mandibular canal using conventional spiral tomography: a human cadaver study

For certain surgical procedures (e.g. placement of implants), an accurate localisation of the mandibular canal is of utmost importance to avoid injuries to the neurovascular bundle. The aim of the present study was to evaluate, on human fresh cadavers (n = 6), the accuracy of conventional spiral tomography for the localisation of the mandibular canal. By means of the Cranex TOME multifunctional unit (Orion Corporation Soredex, Helsinki, Finland), tomographic slices were taken at 3 different locations in the left posterior mandible (distal to the mental foramen). The mandibles were then sectioned at these 3 sites with a microtome. With a digital sliding caliper, the following 3 measurements were performed both on the tomograms and the bone sections at the three sites: 1) distance from the crest to mandibular canal, 2) overall bone height and 3) bone width. Overestimations of the distance to the mandibular canal (8/18) ranged from 1.05 to 0.10 mm and underestimations from 0.30 to 1.36 mm. The same number of over- and underestimations occurred for the bone height (1.14 to 0.14 mm and 0.15 to 1.40 mm, respectively). The bone width scored more overestimations (10/18), ranging from 1.40 to 0.12 mm, while underestimations ranged from 0.25 to 1.35 mm. From the present results, it is concluded that spiral tomography using the Cranex TOME multifunctional X-ray unit provides accurate information and sufficient detail for preoperative planning of implant placement in the posterior mandible.     

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口腔颌面锥形束CT是口腔医学领域一种新型影像摄取技术。本文从以下5个方面对其放射剂量及如何进行有效防护进行了系统阐述:(1)放射量的测定;(2)口腔颌面锥形束CT与螺旋CT有效剂量比较;(3)口腔颌面锥形束CT与口腔常规X线平片检查有效剂量比较;(4)现有口腔颌面锥形束CT间有效剂量比较;(5)口腔颌面锥形束CT的放射防护。     

口腔颌面锥形束CT放射剂量与放射防护

提要：口腔颌面锥形束CT是口腔医学领域一种新型影像摄取技术。本文从以下5个方面对其放射剂量及如何进行有效防护进行了系统阐述：（1）放射量的测定;（2）口腔颌面锥形束CT与螺旋CT有效剂量比较;（3）口腔颌面锥形束CT与口腔常规X线平片检查有效剂量比较;（4）现有口腔颌面锥形束CT间有效剂量比较;（5）口腔颌面锥形束CT的放射防护。     

Hypothetical mortality risk associated with spiral computed tomography of the maxilla and mandible

In the present study, dose measurements have been conducted following examination of the maxilla and mandible with spiral computed tomography (CT). The measurements were carried out with 2 phantoms, a head and neck phantom and a full body phantom. The analysis of applied thermoluminescent dosimeters yielded radiation doses for organs and tissues in the head and neck region between 0.6 and 16.7 mGy when 40 axial slices and 120 kV/165 mAs were used as exposure parameters. The effective dose was calculated as 0.58 and 0.48 mSv in the maxilla and mandible, respectively. Tested methods for dose reduction showed a significant decrease of radiation dose from 40 to 65%. Based on these results, the mortality risk was estimated according to calculation models recommended by the Committee on the Biological Effects of Ionizing Radiations and by the International Commission on Radiological Protection. Both models resulted in similar values. The mortality risk ranges from 46.2×10-6 for 20-year-old men to 11.2×10⁻⁶ for 65-year-old women. Using 2 methods of dose reduction, the mortality risk decreased by ∼ 50 to 60% to 19.1×10⁻⁶ for 20-year-old men and 5.5×10⁻⁶ for 65-year-old women. It can be concluded that a CT scan of the maxillofacial complex causes a considerable radiation dose when compared with conventional radiographic examinations. Therefore, a careful indication for this imaging technique and dose reduction methods should be considered in daily practice.     

Changes in the pre-surgical treatment planning using conventional spiral tomography

OBJECTIVE: To investigate variation in the pre-surgical treatment planning after using conventional spiral tomography in addition to conventional radiographic exams. MATERIAL AND METHODS: Twenty-nine partial or fully edentulous patients referred to implant therapy were selected and submitted to periapical, panoramic and conventional cross-sectional tomography exams. Pre-surgical treatment planning of 120 potential implant sites in 69 edentulous areas was performed by two independent experienced dental implant surgeons. After clinical examination, pre-surgical planning was made using only periapical and panoramic exams. Examiners were requested to reformulated initial planning after assessing tomographic images. Four treatment parameters were evaluated: length and width of implants, need of bone grafting and need of other surgical procedures. RESULTS: Implant length and width remained unchanged in 60.2% and 87.2% of cases, respectively. No difference in length (P=0.576) and width (P=1) scores was observed in treatment planning with and without tomography. Variation in implant dimension was not affected by location of edentulous areas. Bone grafting and other surgical procedures significantly changed after tomograms (P<0.001), independent of the location of edentulous areas. In 15.8% and 5.3% of cases bone grafting and other procedures were planned only after tomograms, respectively. Significant differences were observed in all maxillary and mandibular regions. CONCLUSION: Conventional spiral tomography plays an important role in pre-surgical treatment planning, increasing clinician's certainty of the need of additional surgical procedures (bone grafting, sinus lifting, and others) in pre-surgical treatment stage.     

Accuracy of linear measurement provided by cone beam computed tomography to assess bone quantity in the posterior maxilla: a human cadaver study

Purpose: The aim of this study was to assess, for implant placement in the posterior maxilla, the accuracy of linear measurements provided by cone beam computed tomography (CBCT) using an image intensifier tube and television (TV) chain as an X‐ray detector despite a loss of contrast resolution. The NewTom® 9000 (Quantitative Radiology, Verona, Italy) was used to explore the posterior maxilla. Materials and Methods: Fourteen measurements were taken in three dry maxillaries. On every anatomical site, three fiducial markers were placed on the bony crest to define a plane. Dry maxillaries were submitted to CBCT imaging examination. The maxillaries were then sawn according to the previously defined planes, and bone height and width were assessed using a caliper. The same measurements were taken on images. Results: Clinical analysis demonstrated no difference between real measurements and image measurements. Conclusions: Although cadaver bone density may not correspond to the density of vital bone, this in vitro study indicates that CBCT images provided by technique using image intensifier tube and TV chain as an X‐ray detector are reliable to define the bone volume of the posterior maxilla for the purpose of planning the implant axis.     

腮腺少见肿瘤的增强CT表现及其病理基础

目的 探讨腮腺少见肿瘤增强CT表现特征与病理的相关性,以提高影像诊断水平。方法 对22例经手术病理证实的少见腮腺肿瘤进行回顾性分析,包括基底细胞瘤6例,肌细胞上皮瘤5例,脉管瘤4例,淋巴上皮囊肿及腮腺脂肪瘤各3例,软骨肉瘤1例。在增强CT图像上,从病变所在腮腺的位置、病变大小和形态、病变密度以及其与周围结构的关系进行总结分析。结果 基底细胞瘤发生在腮腺浅叶,边界清楚,病变内易囊变。增强扫描呈不均匀中度-明显强化肿块,边缘或内部可见结节状强化,可伴有增大的淋巴结。肌细胞上皮瘤多发于腮腺浅叶,易发生小囊变,少数病变内可有小点状钙化。实性部分增强后中度-明显强化,多有典型的动脉期强化结节和边缘显著强化。血管瘤为软组织肿块,病变较大可占据整个腮腺,密度均匀或不均匀,可见静脉石,突出于腮腺表面,增强后轻度-明显强化。淋巴上皮囊肿囊液较黏稠,CT值密度较高。软骨肉瘤以囊性为主的肿块,含边缘钙化、骨化成分的肿块。腮腺脂肪瘤可见脂肪密度肿块,边界清晰,无强化,病变内可见纤维分隔。结论 腮腺少见肿瘤的增强CT表现具有一定的影像学特征,可揭示其病理基础;增强CT是诊断腮腺少见肿瘤病变性质有效的影像检查手段。     

Hypothetical mortality risk associated with spiral tomography of the maxilla and mandible prior to endosseous implant treatment

Radiation dose delivered from the SCANORA® radiography unit during the cross-sectional mode for dentotangential projections was determined. With regard to oral implantology, patient situations of an edentulous maxilla and mandible as well as a single tooth gap in regions 16 and 46 were simulated. Radiation doses were measured between 0.2 and 22.5 mGy to organs and tissues in the head and neck region when the complete maxilla or mandible was examined. When examining a single tooth gap, only 8% to 40% of that radiation dose was generally observed. Based on these results, the mortality risk was estimated according to a calculation model recommended by the Committee on the Biological Effects of Ionizing Radiations. The mortality risk ranged from 31.4 × 10⁻⁶ for 20-year-old men to 4.8 × 10⁻⁶ for 65-year-old women when cross-sectional imaging of the complete maxilla was performed. The values decreased by 70% when a single tooth gap in the molar region of the maxilla was radiographed. The figures for the mortality risk for examinations of the complete mandible were similar to those for the complete maxilla, but the mortality risk decreased by 80% if only a single tooth gap in the molar region of the mandible was examined. Calculations according to the International Commission on Radiological Protection carried out for comparison did not reveal the decrease of the mortality risk with age and resulted in a higher risk value in comparison to the group of 35-year old individuals in calculations according to the Committee on the Biological Effects of Ionizing Radiations.     

Effects of dose reduction on multi‐detector computed tomographic images in evaluating the maxilla and mandible for pre‐surgical implant planning: a cadaveric study

Objective: To assess effects of dose reduction on image quality in evaluating maxilla and mandible for pre‐surgical implant planning using cadavers. Materials and methods: Six cadavers were used for the study using multi‐detector computed tomography (CT) operated at 120 kV and the variable tube current of 80, 40, 20 and 10 mA. A slice thickness of 0.625 mm and pitch 1 were used. Multi‐planar images perpendicular and parallel to dentitions were created. The images were evaluated by five oral radiologists in terms of visibility of the anatomical landmarks including alveolar crest, mandibular canal, floors of the maxillary sinus and nasal cavity, contours/cortical layer of jaw bones and the details of trabecular bone. Observers were asked to determine the quality of the images in comparison with 80 mA images based on the criteria: excellent, good, fair or non‐diagnostic. The average scores of all observers were calculated for each specimen in all exposure conditions. Results: The 40 mA images could visualize such landmarks and were evaluated to be same or almost equivalent in quality to the 80 mA images. Even the 20 mA images could be accepted just for diagnostic purpose for implant with substantial deterioration of the image quality. The 10 mA images may not be accepted because of the obscured contour caused by image noise. Conclusion: Significant dose reduction by lowering mA can be utilized for pre‐surgical implant planning in multi‐detector CT. To cite this article:
Koizumi H, Sur J, Seki K, Nakajima K, Sano T, Okano T. Effects of dose reduction on multi‐detector computed tomographic images in evaluating the maxilla and mandible for pre‐surgical implant planning: a cadaveric study.
Clin. Oral Impl. Res. 21 , 2010; 830–834.
doi: 10.1111/j.1600‐0501.2010.01925.x     

Cone beam computed tomography for imaging orbital trauma—image quality and radiation dose compared with conventional multislice computed tomography

We compared the image quality and radiation dose to the lens of the eye in patients with suspected orbital fractures who were imaged using cone beam computed tomography (CBCT) or conventional multislice computed tomography (CT). Although CBCT has a lower radiation dose than conventional CT, it is not known whether the image quality is comparable for diagnostic purposes. We identified fractures of the orbit (floor or roof, or both) in 6/10 patients who were scanned using CBCT and in 5/10 patients who were scanned using multislice CT (orbital floor and medial wall). Impingement of the rectus muscle on fracture lines was identified with both techniques, but retro-orbital haemorrhage was detected only on multislice CT. The mean radiation dose to the lens of the eye was 42% lower (range 23–53, SD 10) for CBCT than for multislice CT (p < 0.001), and the effective dose (a measure of the risk of developing a radiation-induced cancer) was also significantly lower. CBCT can therefore be used to diagnose orbital fractures, and is associated with a significantly lower radiation dose than multislice CT.     

Comparison of panoramic and conventional cross-sectional tomography for preoperative selection of implant size

Objective: To compare panoramic and conventional cross‐sectional tomography for preoperative selection of implant size for three implant systems (Brånemark, Straumann^®, 3i). Material and methods: Presurgical panoramic (Pan) and cross‐sectional tomograms (Tomo) of 121 implant sites in 121 patients scheduled for single‐tooth implant treatment were recorded; in 70 of the Pans (Pan‐B), a metal ball was placed in the edentulous area. By means of dedicated software, an implant with subjectively determined proper dimensions for the respective site was outlined by manually placing four reference points in each image by three observers. Additionally, four reference points corresponding to the margins of the metal ball were manually placed in Pan‐Bs. The length and width of the implant were calculated after calibration to the reference ball (true magnification) in Pan‐Bs and to a “standard” calibration method in all images (magnification factor 1.25 in Pans and 1.7 in Tomos). Based on the corrected dimensions, the nearest, smaller implant size was selected among those available in each of the three implant systems. Results: When comparing Pans with Tomos, selected implant size differed in on average 89% of the cases. The length differed in 69% and the width in 66%. Implants planned on Tomos were longer than those planned on Pans in 47% and narrower in 30% (<10% in posterior regions). The Straumann^® system, with the smallest range of available implant sizes was significantly less affected by the radiographic method compared with the other two systems. Conclusion: The selected implant size differed considerably when planned on panoramic or cross‐sectional tomographs. To cite this article:
Schropp L, Stavropoulos A, Gotfredsen E, Wenzel A. Comparison of panoramic and conventional cross‐sectional tomography for preoperative selection of implant size.
Clin. Oral Impl. Res. 22 , 2011; 424–429.     

Implant design and intraosseous stability of immediately placed implants: a human cadaver study

Objective: The objective of this study was to explore effects of implant macrodesign and diameter on initial intraosseous stability and interface mechanical properties of immediately placed implants. Material and method: Mandibular premolars of four fresh‐frozen human cadavers were extracted. Ø 4.1/4.8 mm ITI® TE®, Ø 4.1 and 4.8 mm solid screw synOcta® ITI® implants were placed into freshly prepared extraction sockets. Resonance frequency analysis was conducted to quantify primary implant stability quotient (ISQ). Installation torque value (ITV) and removal torque value (RTV) of the implants were measured using a custom‐made strain‐gauged torque wrench connected to a data acquisition system at a sample rate of 10,000 Hz. The vertical defect depth around the collar of each implant was measured directly by an endodontic spreader. The bone–implant contact was determined in digitalized images of periapical radiographs and expressed as percentage bone contact. Results: The ISQ values of the TE® implant was higher than the Ø 4.1 mm implant (P<0.01), and comparable with the Ø 4.8 mm implants (P>0.05). ITVs and RTVs of TE® and Ø 4.8 mm implants were higher than the Ø 4.1 mm implant, although the differences between groups were statistically insignificant (P>0.05). The vertical defect depths around all types of implants were similar. In the radiographic analyses, percentage bone–implant contact of the TE® and Ø 4.8 mm implants were comparable at the marginal bone region and both were higher than that of the Ø 4.1 mm ITI® implant. Nonparametric correlations between groups revealed a significant correlation between ITV and RTV (r=0.838; P<0.001), but not between ISQ values and ITVs and RTVs (P>0.05). Conclusion: Immediately placed ITI® TE® implant leads to initial intraosseous stability and interface mechanical properties comparable with a wide diameter implant.     

Biomechanical aspects of primary implant stability: a human cadaver study

Background: The quality of bone is an important factor in the successful implant treatment, and it is evident that higher implant failure is more likely in poor quality of bone. The primary stability of oral implants related to resistance to micromotion during healing is influenced by bone quality, surgical technique, and implant design.
Purposes: The aims of this biomechanical study were to explore the effect of bone quality on initial intraosseous stability of implants, and to determine the correlations between the bone quality and implant stability parameters.
Materials and Methods: Twenty-four implants (Neoss Ltd., Mölnlycke, Sweden) were placed into anterior and posterior regions of three human cadaver mandibles. The bone densities of implant recipient sites were preoperatively determined using computerized tomography (CT) in Hounsfield unit (HU). The maximum insertion torque values were recorded, and primary implant stability measurements were noninvasively performed by means of resonance frequency analysis (RFA).
Results: The bone density values ranged from −267 HU to 553 HU. It was found that mean bone density, insertion torque, and RFA values were 113 ± 270 HU, 41.9 ± 5 Ncm, and 70 ± 7 implant stability quotient (ISQ), respectively. Statistically significant correlations were found between bone density and insertion torque values ( r  = 0.690, p  < .001); bone density and ISQ values ( r  = 0.557, p  < .05); and insertion torque and ISQ values ( r  = 0.853, p  < .001).
Conclusion: CT is a useful tool to assess bone quantity and quality in implant recipient sites, and bone density has a prevailing effect on implant stability at placement.