A comparative study of the effective radiation doses from cone beam computed tomography and plain radiography for sialography

Objectives

As a first step in developing a protocol for multidimensional sialography using cone beam CT (CBCT), the objective of this study was to compare the effective radiation doses from sialography of the parotid and submandibular glands using plain radiography and CBCT.

Methods

The effective doses were calculated from dose measurements made at 25 selected locations in the head and neck of a radiation analogue dosimeter (RANDO) phantom, using International Commission on Radiological Protection 2007 tissue weighting factors.

Results

The effective dose (E) changed in relationship to changes in CBCT field of view (FOV), peak kilovoltage (kVp) and milliamperage (mA). Specifically, E decreased from a maximum of 932 μSv (30 cm FOV, 120 kVp, 15 mA) to 60 μSv (15 cm FOV, 80 kVp, 10 mA) for a parotid gland study and to 148 μSv (15 cm FOV, 80 kVp, 10 mA) for a submandibular study. The collective series of plain radiographs made during sialography of the parotid and submandibular glands yielded effective doses of 65 μSv and 156 μSv, respectively. The plain parotid gland series included one panoramic, two anterior–posterior skull and four lateral skull radiographs, whereas the submandibular gland series included one panoramic, one standard mandibular occlusal and four lateral skull radiographs.

Conclusion

The effective doses from CBCT examinations centred on the parotid and submandibular glands were similar to those calculated for plain radiograph sialography when a 15 cm FOV was chosen in combination with exposure conditions of 80 kVp and 10 mA.     

Optimization of exposure parameters for cone beam computed tomography sialography

Objectives

The assessment of image quality is a crucial step in the development of a new imaging protocol. Having proposed and reported on a preliminary protocol for sialography using cone beam CT (CBCT), the purpose of this study was to further optimize this protocol by maximizing the image signal difference-to-noise ratio (SDNR) and to relate these new data to previously published dosimetric data for CBCT sialography.

Methods

An imaging phantom was constructed using samples with different concentrations of iodine and a water-immersed mandible. The CB MercuRay (Hitachi Medical Systems, Tokyo, Japan) was used to image the phantom using different peak kilovoltage (kVp) and milliamperage (mA) settings. SDNR was then calculated using the raw images based on mean pixel values (MPV) measured in selected regions of interest (ROI). Finally, a figure of merit (FOM) was calculated to examine the trade-off between image SDNR and effective radiation dose.

Results

The SDNR demonstrated an expected increase as the kVp increased from 60 to 120. Also, images made with the higher mA setting (15) had greater SDNR. The iodine concentration also influenced the image quality such that SDNR increased with increased amounts of iodine. The calculated FOM was greatest for the technique using 80 kVp, with equivalent results for 10 mA and 15 mA.

Conclusion

An optimized protocol for CBCT sialography using CB MercuRay entails a 6 inch field of view with 80 kVp and 10 mA.     

Cone beam CT sialography of Stafne bone cavity

Stafne bone cavity (SBC) was mostly described as a small oval radiolucency in the posterior mandibular region. To the best of our knowledge, the literature does not contain any report of the use of cone beam CT (CBCT) sialography for the diagnosis of this entity. The aim of this paper is to present a large, irregular and expanded atypical SBC, which made diagnosis difficult. A CBCT sialography was performed to get a definite diagnosis of this rare entity.     

A comparative study of accuracy of detection of surface osseous changes in the temporomandibular joint using multidetector CT and cone beam CT

Objective

The aim of this study was to assess the accuracy and reliability of cone beam CT (CBCT) images compared with multidetector CT (MDCT) images for the detection of surface osseous changes in temporomandibular joints (TMJs).

Methods

Naked-eye inspection of 110 sites in 10 TMJs from 5 dry human skulls provided the gold standard. Two radiologists interpreted the images. Sensitivity, specificity and kappa statistics were used for analysis.

Results

The sensitivities of both modalities were low and comparable whereas the specificities were high and comparable. Intraobserver reliabilities for CBCT (p=0.0005) and for MDCT (p=0.0001) showed significant agreement. Interobserver reliability was higher for CBCT than for MDCT.

Conclusion

CBCT and MDCT accuracy was comparable in detecting surface osseous changes with comparable intraobserver reliabilities. However, since CBCT requires less radiation exposure, it should be encouraged for imaging TMJ with suspected surface osseous changes.     

Intracranial physiological calcifications evaluated with cone beam CT

Objectives

The purpose of this study was to evaluate cone beam CT (CBCT) scans for the presence of physiological and pathological intracranial calcifications.

Methods

CBCT scans from male and female patients that met our ascertainment criteria were evaluated retrospectively (n = 500) for the presence of either physiological or pathological intracranial calcifications.

Results

Out of the 500 patients evaluated, 176 had evidence of intracranial physiological calcification (35.2% prevalence), and none had evidence of pathological calcification. There was a 3:2 male-to-female ratio and no ethnic predilection; the ages of affected patients ranged from 13 years to 82 years with a mean age of 52 years. The majority of calcifications appeared in the pineal/habenular region (80%), with some also appearing in the choroid plexus region bilaterally (12%), and a smaller subset appearing in the petroclinoid ligament region bilaterally (8%).

Conclusions

Intracranial physiological calcifications can be a common finding on CBCT scans, whereas pathological intracranial calcifications are rare.     

Effective doses from cone beam CT investigation of the jaws

Objectives

The purpose of the study was to calculate the effective dose delivered to the patient undergoing cone beam (CB) CT of the jaws and maxillofacial complex using the i-CAT Next Generation CBCT scanner (Imaging Sciences International, Hatfield, PA).

Methods

A RANDO® phantom (The Phantom Laboratory, Salem, NY) containing thermoluminence dosemeters were scanned 10 times for each of the 6 imaging protocols. Effective doses for each protocol were calculated using the 1990 and approved 2007 International Commission on Radiological Protection (ICRP) recommended tissue weighting factors (E1990, E2007).

Results

The effective dose for E1990 and E2007, respectively, were: full field of view (FOV) of the head, 47 μSv and 78 μSv; 13 cm scan of the jaws, 44 μSv and 77 μSv; 6 cm standard mandible, 35 μSv and 58 μSv; 6 cm high resolution mandible, 69 μSv and 113 μSv; 6 cm standard maxilla, 18 μSv and 32 μSv; and 6 cm high resolution maxilla, 35 μSv and 60 μSv.

Conclusions

Using the new generation of CBCT scanner, the effective dose is lower than the original generation machine for a similar FOV using the ICRP 2007 tissue weighting factors.     

Metal artefact reduction with cone beam CT: an in vitro study

Background

Metal in a patient''s mouth has been shown to cause artefacts that can interfere with the diagnostic quality of cone beam CT. Recently, a manufacturer has made an algorithm and software available which reduces metal streak artefact (Picasso Master 3D® machine; Vatech, Hwaseong, Republic of Korea).

Objectives

The purpose of this investigation was to determine whether or not the metal artefact reduction algorithm was effective and enhanced the contrast-to-noise ratio.

Methods

A phantom was constructed incorporating three metallic beads and three epoxy resin-based bone substitutes to simulate bone next to metal. The phantom was placed in the centre of the field of view and at the periphery. 10 data sets were acquired at 50–90 kVp. The images obtained were analysed using a public domain software ImageJ (NIH Image, Bethesda, MD). Profile lines were used to evaluate grey level changes and area histograms were used to evaluate contrast. The contrast-to-noise ratio was calculated.

Results

The metal artefact reduction option reduced grey value variation and increased the contrast-to-noise ratio. The grey value varied least when the phantom was in the middle of the volume and the metal artefact reduction was activated. The image quality improved as the peak kilovoltage increased.

Conclusion

Better images of a phantom were obtained when the metal artefact reduction algorithm was used.     

Ex vivo comparison of Galileos cone beam CT and intraoral radiographs in detecting occlusal caries

Objective

The aim of this study was to compare the accuracy of cone beam CT (CBCT) with intraoral radiographs for detection of occlusal caries.

Methods

A set of 60 extracted teeth were imaged using a Sirona Galileos CBCT system (Sirona Dental Systems, Bensheim, Germany) and an intraoral Planmeca® system (Planmeca OY, Helsinki, Finland). Six observers looked at both modalities and used a five-point confidence scale to evaluate presence or absence of occlusal caries. Histology was used as the gold standard. Receiver operating characteristic analysis and weighted kappa statistics were used for statistical analysis. Differences in the area under the curve (AUC) values between observers and modalities were analysed using analysis of variance (ANOVA). Differences in sensitivity and specificity were analysed using the Wilcoxon test. Interobserver and intraobserver reliability was assessed by weighted kappa scores.

Results

The mean value and standard deviation of AUC was 0.719 ± 0.038 for CBCT and 0.649 ± 0.062 for the intraoral radiographs. The ANOVA results demonstrated that there was no significant difference between the modalities and the observers. The interobserver kappa for pairs of observers ranged from fair to substantial for bitewings (0.244–0.543) and CBCT (0.152–0.401). Four out of six observers reported higher sensitivity but lower specificity with CBCT. The Wilcoxon exact p-value showed no difference in sensitivity (0.175) or specificity (0.573) between the two modalities.

Conclusion

Based on the results we conclude that the Sirona CBCT unit cannot be used for the sole purpose of looking at occlusal caries.     

Evaluation of a cone beam CT artefact reduction algorithm

Objectives

An algorithm and software to reduce metal artefact has been developed recently and is available in the Picasso Master 3D® (VATECH, Hwaseong, Republic of Korea), which under visual assessment produces better quality images than were obtainable previously. The objective of this in vitro study was to investigate whether the metal artefact reduction (MAR) algorithm of the Picasso Master 3D machine reduced the incidence of metal artefacts and increased the contrast-to-noise ratio (CNR) while maintaining the same gray value when there was no metallic body present within the scanned volume.

Methods

20 scans with a range of 50–90 kVp were acquired, of which 10 had a metallic bead inserted within a phantom. The images obtained were analysed using public domain software (ImageJ; NIH Image, Bethesda, MD). Area histograms were used to evaluate the mean gray level variation of the epoxy resin-based substitute (ERBS) block and a control area. The CNR was calculated.

Results

The MAR algorithm increased the CNR when the metallic bead was present; it enhanced the ERBS gray level independently of the presence of the metallic bead. The image quality also improved as peak tube potential was increased.

Conclusion

Improved quality of images and regaining of the control gray values of a phantom were achieved when the MAR algorithm was used in the presence of a metallic bead.     

Dose reduction of cone beam CT scanning for the entire oral and maxillofacial regions with thyroid collars

Objective

The aim of this study was to evaluate the influence of thyroid collars on radiation dose during cone beam CT (CBCT) scanning.

Methods

Average tissue-absorbed dose for a NewTom 9000 CBCT scanner (Quantitative Radiology, Verona, Italy) was measured using thermoluminescent dosemeter chips in a phantom. The scans were carried out with and without thyroid collars. Effective organ dose and total effective dose were derived using International Commission on Radiological Protection 2007 recommendations.

Results

The effective organ doses for the thyroid gland and oesophagus were 31.0 µSv and 2.4 µSv, respectively, during CBCT scanning without a collar around the neck. When the thyroid collars were used loosely around the neck, no effective organ dose reduction was observed. When one thyroid collar was used tightly on the front of the neck, the effective organ dose for the thyroid gland and oesophagus were reduced to 15.9 µSv (48.7% reduction) and 1.4 µSv (41.7% reduction), respectively. Similar organ dose reduction (46.5% and 41.7%) was achieved when CBCT scanning was performed with two collars tightly on the front and back of the neck. However, the differences to the total effective dose were not significant among the scans with and without collars around the neck (p = 0.775).

Conclusions

Thyroid collars can effectively reduce the radiation dose to the thyroid and oesophagus if used appropriately.     

Evaluation of juxta-apical radiolucency in cone beam CT images

Objectives:

The aim of this study was to analyse the position and relationship of juxta-apical radiolucency (JAR) to the mandibular canal and buccal and/or lingual cortical plates using cone beam CT (CBCT).

Methods:

A retrospective study was carried out to analyse the JAR on CBCT for 27 patients. These findings were compared with 27 age- and sex-matched patients without the presence of JAR, which acted as the control group. The CBCT images were analysed according to a checklist, to evaluate the position of the JAR and its relationship to the mandibular canal. Then, any thinning or perforation of either the buccal or lingual cortical plate due to JAR was noted, and a classification to quantify the thinning of cortical plates was proposed. The findings in the two groups were analysed using a paired comparison by McNemar test.

Results:

A statistical increased thinning of cortical plates was seen in the JAR group compared with the control group, and most of the cases were in the J3 group. None of the patients in either the JAR or the control group showed perforation of the buccal and/or lingual cortical plate on CBCT images.

Conclusions:

A classification to quantify the thinning of cortical plates was proposed, which may be used for objective evaluation of the thinning of the cortical plates in future studies. The present study gives an insight into the relationship of the juxta-apical area with the mandibular canal and cortical plates in the mandible using CBCT.     

Foramen tympanicum or foramen of Huschke: anatomical cone beam CT study

Objective

The foramen of Huschke (foramen tympanicum) represents a developmental defect in the antero-inferior aspect of the bony external auditory meatus. The foramen is located at the antero-inferior aspect of the external auditory canal, posteromedial to the temporomandibular joint. The aim of this study is to define the prevalence and location of the foramen of Huschke.

Methods

We retrospectively examined 207 cone beam CT (CBCT) studies (414 ears). We used flat panel detector (FPD)-based CBCT (New Tom FP; Quantitative Radiology, Verona, Italy) for imaging in our department. We noted the location of the foramen tympanicum and calculated its prevalence as a percentage.

Results

We found a foramen tympanicum in 37 (17.9%) of 207 patients. This was unilateral in 24 patients (11.6%) and bilateral in 13 patients (6.3%). Mean axial diameter was 5 mm and mean sagittal diameter was 2 mm.

Conclusion

The foramen tympanicum is an uncommon disorder and is well demonstrated on CBCT. This is the first study to detect the foramen tympanicum using FPD-based CBCT.     

Dental cone beam CT image quality possibly reduced by patient movement

Patient artefacts in dental cone beam CT scans can happen for various reasons. These range from artefacts from metal restorations to movement. An audit was carried out in the Glasgow Dental Hospital analysing how many scans showed signs of “motion artefact”, and then to assess if there was any correlation between patient age and movement artefacts. Specific age demographics were then analysed to see if these cohorts were at a higher risk of “movement artefacts”.     

Comparative study between conventional and cone beam CT-synthesized half and total skull cephalograms

Objectives

The aim of this study was to compare cephalometric measurements obtained from conventional cephalograms with total and half-skull synthesized cone beam CT (CBCT) cephalograms.

Methods

Cephalometric analyses of 30 clinically symmetric patients were conducted by a calibrated examiner on conventional and CBCT-synthesized cephalograms (total, right and left). Reproducibility was investigated using the intraclass correlation coefficient (ICC). The Bland–Altman analysis was used to assess the agreement of the measurements from each factor obtained by conventional, total, right and left CBCT-synthesized cephalograms.

Results

The ICC was above 0.9 for most of the 40 cephalometric factors analysed, revealing similar levels of reproducibility. When the measurements obtained from conventional and CBCT-synthesized cephalograms were compared, the Bland–Altman analysis showed a strong agreement between them.

Conclusions

Half-skull CBCT-synthesized cephalograms offer the same diagnostic performance and equivalent reproducibility in terms of cephalometric analysis as observed in conventional and total CBCT-synthesized cephalograms.     

Radiological examination of the articular eminence morphology using cone beam CT

Objective

The purpose of the present study was to investigate the articular eminence inclination and height according to age and gender in patients with temporomandibular joint (TMJ) dysfunction and healthy controls using cone beam CT (CBCT).

Methods

The measurements were performed on CBCT records of 52 TMJ dysfunction patients (11 males and 41 females) and 41 control patients (17 males and 24 females). The eminence inclination and height were measured on the CBCT images.

Results

The eminence inclination and height values were higher in males than in females in both TMJ dysfunction patient and control groups; however, these differences were not statistically significant (p>0.05). While no statistically significant differences were found in the eminence inclination and height values between the age groups (p>0.05) in the TMJ dysfunction patient group, there were statistically significant differences in the control group. The eminence inclination was highest between the ages of 21 and 30 years and showed a decrease after the age of 30 years. Additionally, the eminence inclinations of the control patients were statistically higher than those of the TMJ dysfunction patients.

Conclusion

There were no statistically significant differences in eminence inclination and height according to gender. The eminence inclination reaches its highest value between the ages of 21 and 30 years and shows a decrease after the age of 31 years in healthy patients. The eminence inclination was steeper in healthy control patients than in patients with TMJ dysfunction.     

Cervical vertebral column morphology in patients with obstructive sleep apnoea assessed using lateral cephalograms and cone beam CT. A comparative study

Objectives:

Few studies have described morphological deviations in obstructive sleep apnoea (OSA) patients on two-dimensional (2D) lateral cephalograms, and the reliability of 2D radiographs has been discussed. The objective is to describe the morphology of the cervical vertebral column on cone beam CT (CBCT) in adult patients with OSA and to compare 2D lateral cephalograms with three-dimensional (3D) CBCT images.

Methods:

For all 57 OSA patients, the cervical vertebral column morphology was evaluated on lateral cephalograms and CBCT images and compared according to fusion anomalies and posterior arch deficiency.

Results:

The CBCT assessment showed that 21.1% had fusion anomalies of the cervical column, i.e. fusion between two cervical vertebrae (10.5%), block fusions (8.8%) or occipitalization (1.8%). Posterior arch deficiency occurred in 14% as partial cleft of C1 and in 3.5% in combination with block fusions. The agreement between the occurrence of morphological deviations in the cervical vertebral column between lateral cephalograms and CBCT images showed good agreement (κ = 0.64).

Conclusions:

Prevalence and pattern in the cervical column morphology have now been confirmed on CBCT. The occurrence of morphological deviations in the cervical vertebral column showed good agreement between lateral cephalograms and CBCT images. This indicates that 2D lateral cephalograms (already available after indication in connection with, e.g. treatment planning) are sufficient for identifying morphological deviations in the cervical vertebral column. For a more accurate diagnosis and location of the deviations, CBCT is required. New 3D methods will suggest a need for new detailed characterization and division of deviations in cervical vertebral column morphology.     

The importance of cone beam CT in the radiological detection of osteomalacia

Although osteomalacia is one of the most common osteometabolic diseases among the elderly, there is no case in the literature that presents the effects of osteomalacia in detail using cone beam CT (CBCT). While thin and porous bones are the most common radiographic sign of the disease, the radiological hallmarks are pseudofractures (Looser's zone). We coincidentally detected osteomalacia in a 23-year-old female and we showed the pseudofracture on CBCT images. In the present case, we aim to present the images of osteomalacia that were detected by CBCT in detail. CBCT has an important value in screening for osteomalacia.     

Small field of view cone beam CT temporomandibular joint imaging dosimetry

Objectives:

Cone beam CT (CBCT) is generally accepted as the imaging modality of choice for visualisation of the osseous structures of the temporomandibular joint (TMJ). The purpose of this study was to compare the radiation dose of a protocol for CBCT TMJ imaging using a large field of view Hitachi CB MercuRay™ unit (Hitachi Medical Systems, Tokyo, Japan) with an alternative approach that utilizes two CBCT acquisitions of the right and left TMJs using the Kodak 9000^® 3D system (Carestream, Rochester, NY).

Methods:

25 optically stimulated luminescence dosemeters were placed in various locations of an anthropomorphic RANDO^® Man phantom (Alderson Research Laboratories, Stanford, CT). Dosimetric measurements were performed for each technique, and effective doses were calculated using the 2007 International Commission on Radiological Protection tissue weighting factor recommendations for all protocols.

Results:

The radiation effective dose for the CB MercuRay technique was 223.6 ± 1.1 μSv compared with 9.7 ± 0.1 μSv (child), 13.5 ± 0.9 μSv (adolescent/small adult) and 20.5 ± 1.3 μSv (adult) for the bilateral Kodak acquisitions.

Conclusions:

Acquisitions of individual right and left TMJ volumes using the Kodak 9000 3D CBCT imaging system resulted in a more than ten-fold reduction in the effective dose compared with the larger single field acquisition with the Hitachi CB MercuRay. This decrease is made even more significant when lower tube potential and tube current settings are used.     

Evaluation of the effective dose of cone beam CT and multislice CT for temporomandibular joint examinations at optimized exposure levels

Objectives:

To compare the effective dose to patients from temporomandibular joint examinations using a dental CBCT device and a multislice CT (MSCT) device, both before and after dose optimization.

Methods:

A Promax^® 3D (Planmeca, Helsinki, Finland) dental CBCT and a LightSpeed VCT^® (GE Healthcare, Little Chalfont, UK) multislice CT were used. Organ doses and effective doses were estimated from thermoluminescent dosemeters at 61 positions inside an anthropomorphic phantom at the exposure settings in clinical use. Optimized exposure protocols were obtained through an optimization study using a dry skull phantom, where four observers rated image quality taken at different exposure levels. The optimal exposure level was obtained when all included criteria were rated as acceptable or better by all observers.

Results:

The effective dose from a bilateral examination was 184 µSv for Promax 3D and 113 µSv for LightSpeed VCT before optimization. Post optimization, the bilateral effective dose was 92 µSv for Promax 3D and 124 µSv for LightSpeed VCT.

Conclusions:

At optimized exposure levels, the effective dose from CBCT was comparable to MSCT.