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

Cone-beam computed tomography evaluation of the pterygomaxillary fissure and pterygopalatine fossa using 3D rendering programs

PURPOSE

The aim of this study was to investigate the detailed anatomy of the pterygomaxillary fissure (PMF) and pterygopalatine fossa (PPF) and variations therein using three-dimensional (3D) cone-beam computed tomography (CBCT) software.

METHODS

This study was based on a retrospective evaluation of CBCT scans. A total of 825 CBCT images of patients (448 females, 377 males) who met the inclusion criteria were analyzed. PMF shapes were classified, and morphometric measurements (PMF area and PPF volume) were performed according to age, right/left side, and gender using 3D rendering programs. Maxillary and sphenoid sinus pathologies were also classified to reveal possible correlations between morphometric measurements. Analysis of variance was used for comparisons. Multiple comparisons were assessed using the Bonferroni test. Pearson's test was used to assess correlations between parameters. A p value < 0.05 was considered to indicate statistical significance.

RESULTS

Six types of PMF shapes were defined. There were no significant differences in types according to gender, age or sinus pathology. Males had a significantly larger PMF area than females (p < 0.001). Left/right comparison of the PMF area revealed that the mean PMF coronal, axial, and sagittal area dimensions were significantly higher on the right side in all patients. Our results also indicated that the PMF area and PPF volume increased significantly after 40 years of age.

CONCLUSION

Various PMF shapes were defined and classified. PMF and PPF dimensions increased with age. Knowledge of these anatomical variations will allow surgeons to avoid damage to the neurovascular structures passing through the area.

Effect of patient anxiety on image motion artefacts in CBCT

BACKGROUND

Artefacts in images related to patient movement decrease image quality, potentially necessitating re-scanning, which leads to an extra radiation dose for the patient. Thus, avoiding patient motion reduces patient exposure to radiation. The aim of this study was to analyse image motion artefacts (MAs) and how they are affected by patient anxiety during cone beam computed tomography (CBCT) examination.

METHODS

A total of 100 patients undergoing CBCT examination were investigated. The State Trait Anxiety Inventory (STAI-S and STAI-T) form was used to measure patient anxiety. Patient's age, gender, dental anxiety score, diagnostic reason for CBCT examination, field of view (FOV), acquisition time, anatomical area, and presence of motion artefacts on images were recorded. Comparisons of the parameters were evaluated using Pearson's correlation, the chi-square test, the Mann-Whitney U test, the Kruskal-Wallis test and t-tests. The significance level was set at 0.05.

RESULTS

The mean values of the scores for the total population were 37.2 for the STAI-S and 41.6 for the STAI-T. Women exhibited higher anxiety levels than men. The patients' anxiety scores were significantly correlated with dental fear. The prevalence of patients showing motion artefacts was 6%. The mean age of patients with motion artefacts on their images (56.83) was higher than that of patients without (39.14). There was no relationship between motion artefact presence and patient gender, anxiety score, diagnostic reason for CBCT examination, FOV, acquisition time, or anatomical area. Patients showing motion artefacts on their images had higher STAI scores than those with no motion artefacts (non-significant).

CONCLUSIONS

The population in this study experienced anxiety before CBCT scanning. Excessive anxiety did not clearly affect whether image motion artefacts were generated during CBCT examination, although a non-significant increase in STAI scores was noticed in patients with motion artefacts on their images.

In vivo CT dosimetry during CT colonography

OBJECTIVE

The purpose of this study was to develop a method of measuring rectal radiation dose in vivo during CT colonography (CTC) and assess the accuracy of size-specific dose estimates (SSDEs) relative to that of in vivo dose measurements.

MATERIALS AND METHODS

Thermoluminescent dosimeter capsules were attached to a CTC rectal catheter to obtain four measurements of the CT radiation dose in 10 volunteers (five men and five women; age range, 23-87 years; mean age, 70.4 years). A fixed CT technique (supine and prone, 50 mAs and 120 kVp each) was used for CTC. SSDEs and percentile body habitus measurements were based on CT images and directly compared with in vivo dose measurements.

RESULTS

The mean absorbed doses delivered to the rectum ranged from 8.8 to 23.6 mGy in the 10 patients, whose mean body habitus was in the 27th percentile among American adults 18-64 years old (range, 0.5-67th percentile). The mean SSDE error was 7.2% (range, 0.6-31.4%).

CONCLUSION

This in vivo radiation dose measurement technique can be applied to patients undergoing CTC. Our measurements indicate that SSDEs are reasonable estimates of the rectal absorbed dose. The data obtained in this pilot study can be used as benchmarks for assessing dose estimates using other indirect methods (e.g., Monte Carlo simulations).

Low-dose protocol of the spiral CT in orthodontics: comparative evaluation of entrance skin dose with traditional X-ray techniques

BACKGROUND

The aim of this study was to evaluate the amount of radiation doses absorbed by soft tissues (entrance skin dose) with a low-dose spiral computed tomography (CT) protocol compared to conventional X-ray techniques commonly used in orthodontics.

METHODS

The amount of skin dose has been evaluated using a tissue-equivalent head-neck radiotherapy humanoid phantom with thermoluminescent dosimeters placed at the level of eye lens, parotid glands, and thyroid glands. CT images have been taken using a Sensation 16 Siemens CT scan and a low-dose protocol (15 mAs, 1 pitch, 2.5 mGy (CTDIvol), 80 kV, 1-mm slice thickness).

RESULTS

The difference in image quality between traditional X-ray techniques and low-dose spiral CT was statistically significant (P<0.05). The difference in mean absorbed dose instead was not statistically significant.

CONCLUSIONS

Our protocol allows a more accurate orthodontic diagnosis without an increase of radiological risk for the patients in comparison to traditional X-ray techniques.

Significant reduction in dental cone beam computed tomography (CBCT) eye dose through the use of leaded glasses

OBJECTIVE

In light of the increased recognition of the potential for lens opacification after low-dose radiation exposures, we investigated the effect of leaded eyeglasses worn during dental cone-beam computerized tomography (CBCT) procedures on the radiation absorbed dose to the eye and suggest simple methods to reduce risk of radiation cataract development.

STUDY DESIGN

Dose measurements were conducted with the use of 3 anthropomorphic phantoms: male (Alderson radiation therapy phantom), female (CIRS), and juvenile male (CIRS). All exposures were performed on the same dental CBCT machine (Imtec, Ardmore, OK) using 2 different scanning techniques but with identical machine parameters (120 kVp, 3.8 mA, 7.8 s). Scans were performed with and without leaded glasses and repeated 3 times. All measurements were recorded using calibrated thermoluminescent dosimeters and optical luminescent dosimetry.

RESULTS

Leaded glasses worn by adult and pediatric patients during CBCT scans may reduce radiation dose to the lens of the eye by as much as 67% (from 0.135 ± 0.004 mGy to 0.044 ± 0.002 mGy in pediatric patients).

CONCLUSIONS

Leaded glasses do not appear to have a deleterious effect on the image quality in the area of clinical significance for dental imaging.

Evaluation of distracted mandibular bone using computed tomography scan and ultrasonography: technical note

OBJECTIVES

Distraction osteogenesis is considered an important reconstruction armamentarium in the management of mandibular deformities and deficiency disorders. The duration of the consolidation period is still a debatable issue among the clinicians. Evaluation of the newly formed bone is the cornerstone for terminating the consolidation period safely. The aim of this study is to find a more conservative protocol for the evaluation of callus distraction by monitoring bone healing using two different examination tools: ultrasonography and dental CT.

METHODS

Four adult patients (three women and one man) underwent mandibular distraction (using two intraoral and two extraoral devices). The latency period was 5-7 days and the distraction was at a rate of 2 mm per day, with 12-14 weeks of consolidation. All patients were evaluated during activation, 3 months, 6 months and 1 year post-distraction. Evaluation included clinical examination, plain radiographs, CT and ultrasonography examinations.

RESULTS

Ultrasonographic examination of the healing callus revealed four different phases of maturation. These phases were similar to the degree of tissue calcification as measured by CT. Tissue density across the distraction wound at the time of distractor removal (12-14 weeks) was equal to or less than one-third of normal bone density.

CONCLUSIONS

Clinical monitoring of mandibular distraction wounds can be successfully achieved through frequent use of ultrasonographic examinations. Standardization of ultrasonography based on CT findings will expand the reliability of ultrasound in monitoring callus maturation. An algorithm for evaluation of distraction wound healing is suggested.

Comparison of radiation dose for implant imaging using conventional spiral tomography, computed tomography, and cone-beam computed tomography

OBJECTIVE

The objective of this study was to compare typical patient radiation dose delivered in implant imaging with spiral computed tomography (CT), conventional spiral tomography, and cone-beam CT (CBCT).

STUDY DESIGN

The Scanora (Orion Corporation Soredex, Helsinki, Finland), Spiral HiSpeed/Fxi (General Electric, Milwaukee, WI), and Classic iCAT (Imaging Sciences International, Hatfield, PA) units were selected to represent conventional spiral tomography, spiral CT, and CBCT, respectively. Thermoluminescent dosimeters were used in a Rando phantom to measure radiation-absorbed doses to the lenses, parotid glands, submandibular glands, sublingual gland, and the thyroid for maxillary and mandibular implant imaging techniques.

RESULTS

Spiral CT delivered the highest absorbed dose, whereas CBCT delivered the lowest in both maxillary and mandibular implant scans. The salivary glands received the highest absorbed doses. Scanora delivered lower radiation doses than CBCT when the anterior region of the maxilla or mandible was irradiated.

CONCLUSION

In implant imaging, CT delivers the highest radiation dose to the salivary glands, whereas the CBCT system studied delivers the lowest dose. Irrespective of imaging modality, during implant imaging as conducted for this study, salivary glands receive most radiation.

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.

Dose reduction in maxillofacial imaging using low dose Cone Beam CT

OBJECTIVES

(a) To measure the absorbed dose at certain anatomical sites of a RANDO phantom and to estimate the effective dose in radiographic imaging of the jaws using low dose Cone Beam computed tomography (CBCT) and (b) to compare the absorbed and the effective doses between thyroid and cervical spine shielding and non-shielding techniques.

STUDY DESIGN

Thermoluminescent dosimeters (TLD-100) were placed at 14 sites in a RANDO phantom, using a Cone Beam CT device (Newtom, Model QR-DVT 9000, Verona, Italy). Dosimetry was carried out applying two techniques: in the first, there was no shielding device used while in the second one, a shielding device (EUREKA!, TRIX) was applied for protection of the thyroid gland and the cervical spine. Effective dose was estimated according to ICRP(60) report (E(ICRP)). An additional estimation of the effective dose was accomplished including the doses of the salivary glands (E(SAL)). A Wilcoxon Signed Ranks Test was used for statistical analysis.

RESULTS

In the non-shielding technique the absorbed doses ranged from 0.16 to 1.67 mGy, while 0.32 and 1.28 mGy were the doses to the thyroid and the cervical spine, respectively. The effective dose, E(ICRP), was 0.035 mSv and the E(SAL) was 0.064 mSv. In the shielding technique, the absorbed doses ranged from 0.09 to 1.64 mGy, while 0.18 and 0.95 mGy were the respective values for the thyroid and the cervical spine. The effective dose, E(ICRP), was 0.023 mSv and E(SAL) was 0.052 mSv.

CONCLUSIONS

The use of CBCT for maxillofacial imaging results in a reduced absorbed and effective dose. The use of lead shielding leads to a further reduction of the absorbed doses of thyroid and cervical spine, as well as the effective dose.

Radiation doses of indirect and direct digital cephalometric radiography

AIM

The aim of this study was to measure organ doses and calculate the effective dose for indirect and direct digital cephalometric exposures.

MATERIAL AND METHODS

Indirect digital cephalometric exposures were made of a Rando phantom head using a Cranex Tome multipurpose unit with storage phosphor plates from Agfa and the direct digital (Charge Coupled Device, CCD) exposures were made with a Proline Ceph CM unit. Exposure settings were 70 kV and 4 mAs for indirect digital exposures. Direct digital exposures were made with 70 kV, 10 mA and a total scanning time of 23 s. TLD700 dosemeters were used to measure organ doses, and the effective doses were calculated with (effective dose(sal)) and without inclusion of the salivary glands. A pilot study was carried out to compare diagnostic image quality of both imaging modalities.

RESULTS

Effective doses were 1.7 microSv for direct digital and 1.6 microSv for indirect digital cephalometric imaging. When salivary glands were included in the calculation, effective doses(sal) were 3.4 microSv and 2.2 microSv respectively. Organ doses were higher for direct digital imaging, except for the thyroid gland, where the organ doses were comparable. Diagnostic image quality of indirect and direct digital cephalometric images seemed comparable.

CONCLUSION

Effective dose and effective dose(sal) were higher for direct digital cephalometric exposure compared with indirect digital exposure. Organ doses were higher for direct digital cephalography. From preliminary data, it may be presumed that diagnostic image quality of indirect and direct digital cephalometric images are comparable.

Morphology and dimensions of the mandibular jaw bone in the interforaminal region in patients requiring implants in the distal areas

This study aimed to analyse variations in the mandibular interforaminal morphology in an attempt to identify potential risks or contraindications for surgery, especially implant installation, in this particular region. A total of 210 spiral computer tomography (CT) examinations of patients requiring endosseous implant installation in the lower jaw were re-evaluated to explore anatomical variations in bone morphology (shape and contour), and to measure parameters concerning height, width and inclination of the bone in the symphyseal atrea. All measurements were performed on the cross-sectional reformatted images mesial to the mental foramina. A lingual concavity (with a depth of 6 +/- 2.6 mm) was observed in 2.4% of the jaws, with a remaining bone height in that area ranging from 4.2 to 11.9 mm. A clearly lingual tilted/inclined morphology was seen in 28.1% of jaws with a mean angle of 67.6 +/- 6.5 degrees, but a relatively constant width (> 8.8 mm). The remaining jaws (69.5%) showed a slight broadening in the caudal direction. The morphologic parameters were influenced neither by age nor by gender. In conclusion, mandibles with a lingual concavity or a severe slope of the lingual cortex might confer increased risks of lingual perforations during trepanation surgery or graft harvesting as well as fenestrations during implant installation. The detection frequency of such variations within the lower jaw seems to advocate a profound dissection of the lingual site and, in the case of some special treatment strategies, additional cross-sectional radiography.

Imaging technique selection for the preoperative planning of oral implants: a review of the literature

BACKGROUND

As the use of oral implants for the treatment of partially as well as fully edentulous patients has increased the past two decades, more specialized radiographic techniques have become available for the preoperative planning of oral implant placement.

PURPOSE

The goal of this article was to enable clinicians to select the appropriate imaging techniques when planning for oral implants.

MATERIALS AND METHODS

This artide reviews the available literature about various imaging techniques and their indication for the preoperative planning of oral implants. The advantages and drawbacks of each technique are described. A dosimetric overview is given relative to different radiologic techniques used in various clinical situations.

RESULTS

For preoperative planning of implant placement, advantages and drawbacks of the available imaging techniques have been considered, which allows guidelines for image technique selection to be formulated based on the clinical situation provided, considering the diagnostic yield of each technique and the radiation doses involved.

CONCLUSIONS

From the available literature, it can be stated that many clinical situations demand the use of cross-sectional imaging techniques for optimal preoperative planning of implant placement. Nevertheless, such techniques are not required in cases in which the clinical examination reveals sufficient bone width and where standard radiographic examinations, such as intraoral and panoramic radiography, reveal adequate bone height and space for implant placement.