Cone-beam Computed Tomography Protocols Research Articles

3D Assessment of Endodontic Lesions with a Low-Dose CBCT Protocol.

Background: Cone beam computed tomography (CBCT) is often used in different fields of dental science, especially in complex anatomical districts like the endodontic one. The aim of this study is to propose a low-dose CBCT protocol useful in cases of endodontic lesions. Methods: The device used was a MyRay Hyperion X9-11x5; the low dose setting of the machine was 90 Kv, 27 mAs, CTDI/Vol 2.89 mGy. The absorbed organ doses have been evaluated with an anthropomorphic phantom loaded with thermoluminescent dosimeters positioned at the level of sensitive organs like brain, bone marrow, salivary glands, thyroid, esophagus, oral mucosa, extrathoracic airways, and lymph nodes. Equivalent and effective doses have been calculated; the last one has been calculated using the recommendations approved by the Main Commission of ICRP (International Commission Radiological Protection) in March 2007. For the assessment of image quality, five senior clinicians, independent and experienced clinicians, were asked to state if CBCT scans were accurate enough to assess endodontic lesions. Results: The use of a low-dose CBCT acquisition produced the lowest organ dose (5.01 microSv) at the level of the esophagus. Image quality has been considered accurate enough for endodontic diagnostic needs. Conclusions: CBCT low-dose protocol can be used over the standard one in endodontic special cases because it provides a significantly lower radiation dose to the patients while ensuring good image quality. However, further studies are necessary to evaluate the opportunity of low-dose CBCT exams in endodontic clinical practice.

Assessment of Eye Lens Dose Reduction When Using Lateral Lead Shields on the Patient's Head during Neurointerventional Fluoroscopic Procedures and Cone-beam Computed Tomography (CBCT) Scans.

The purpose of this study was to evaluate the effect of placing small lead shields on the temple region of the skull to reduce radiation dose to the lens of the eye during interventional fluoroscopically-guided procedures and cone-beam computed tomography (CBCT) scans of the head. EGSnrc Monte-Carlo code was used to determine the eye lens dose reduction when using lateral lead shields for single x-ray projections, CBCT scans with different protocols, and interventional neuroradiology procedures with the Zubal computational head phantom. A clinical C-Arm system was used to take radiographic projections and CBCT scans of anthropomorphic head phantoms without and with lead patches, and the images were compared to assess the effect of the shields. For single lateral projections, a 0.1 (0.3)-mm-thick lead patch reduced the dose to the left-eye lens by 40% to 60% (55% to 80%) from 45° to 90° RAO and to the right-eye lens by around 30% (55%) from 70° to 90° RAO. For different CBCT protocols, the reduction of lens dose with a 0.3-mm-thick lead patch ranged from 20% to 53% at 110 kVp. For CBCT scans of the anthropomorphic phantom, the lead patch introduced streak artifacts that were mainly in the orbital regions but were insignificant in the brain region where most neurointerventional activity occurs. The dose to the patient's eye lens can be reduced considerably by placing small lead shields over the temple region of the head without substantially compromising image quality in neuro-imaging procedures.

Evaluation of a low-dose protocol for cone beam computed tomography of the temporomandibular joint.

Objective:Evaluation of cone beam CT (CBCT) examination with a low-dose scanning protocol for assessment of the temporomandibular joint (TMJ).Methods:34 adult patients referred for CBCT imaging of the TMJ underwent two examinations with two scanning protocols, a manufacturer-recommended protocol (default) and a low-dose protocol where the tube current was reduced to 20% of the default protocol. Three image stacks were reconstructed: default protocol, low-dose protocol, and processed (using a noise reduction algorithm) low-dose protocol. Four radiologists evaluated the images. The Sign test was used to evaluate visibility of TMJ anatomic structures and image quality. Receiver operating characteristic analyzes were performed to assess the diagnostic accuracy. κ values were used to evaluate intraobserver agreement.Results:With the low-dose and processed protocols, visibility of the TMJ anatomical structures and overall image quality were comparable to the default protocol. No significant differences in radiographic findings were found for the two low-dose protocols compared to the default protocol. The area under the curves (Az) averaged for the low-dose and processed protocols, according to all observers, were 0.931 and 0.941, respectively. Intraobserver agreement was good to very good.Conclusion:For the CBCT unit used in this study, the low-dose CBCT protocol for TMJ examination was diagnostically comparable to the manufacturer-recommended protocol, but delivered a five times lower radiation dose. There is an urgent need to evaluate protocols for CBCT examinations of TMJ in order to optimize them for a radiation dose as low as diagnostically acceptable (the as low as diagnostically acceptable principle recommended by NCRP).

Dosimetric Feasibility of Cone-Beam CT in Pediatric Image-Guided Retrograde Gastrostomy Tube Insertions.

Cone-beam computed tomography (CBCT) in interventional radiology allows volumetric imaging with open patient access. This work aimed to assess radiation dose metrics of CBCT in simulated image-guided retrograde gastrostomy (IGRG) tube insertions in pediatric anthropomorphic phantoms and to compare them to measured radiation dose metrics obtained using fluoroscopy during clinical IGRG tube insertions in children. Radiation dose indices obtained from radiation dose structured reports of fluoroscopic IGRG tube insertions were retrospectively evaluated in a consecutive cohort of 30 children. Dose indices were fractionated into 3 clinical stages for each procedure (planning, insertion, and confirmation). These 3 stages in 30 patients (3 × 30 = 90 patient stages) were compared to dose indices measured from 4 CBCT acquisition protocols acquired in pediatric phantoms. The mean proportion of radiation dose during planning, insertion, and confirmation was 35%, 38% and 27%, with mean reference-point air kerma (range) measured to be 1.0 (0.02-6.0) mGy, 0.9 (0.03-4.1) mGy, and 0.7 (0.04-3.7) mGy, respectively. Cone-beam computed tomography dose varied greatly depending on technical parameters and protocol selection, ranging from 0.7 to 39.3 mGy. In 19% of patient stages, the most dose-sparing CBCT protocol evaluated on phantoms delivered less radiation than the radiation dose indices recorded from patient's fluoroscopy. From a dosimetric perspective, radiation delivered in CBCT can vary widely, yet can be appreciably low. With appropriate CBCT protocol selection, the radiation dose delivered may be sufficiently low to warrant consideration for use, if clinically needed during difficult IGRG tube insertions, and satisfy the interventionalist's benefit-risk assessment.

Low-Dose Image-Guided Pediatric CNS Radiation Therapy: Final Analysis From a Prospective Low-Dose Cone-Beam CT Protocol From a Multinational Pediatrics Consortium.

Background:Lower-dose cone-beam computed tomography protocols for image-guided radiotherapy may permit target localization while minimizing radiation exposure. We prospectively evaluated a lower-dose cone-beam protocol for central nervous system image-guided radiotherapy across a multinational pediatrics consortium.Methods:Seven institutions prospectively employed a lower-dose cone-beam computed tomography central nervous system protocol (weighted average dose 0.7 mGy) for patients ≤21 years. Treatment table shifts between setup with surface lasers versus cone-beam computed tomography were used to approximate setup accuracy, and vector magnitudes for these shifts were calculated. Setup group mean, interpatient, interinstitution, and random error were estimated, and clinical factors were compared by mixed linear modeling.Results:Among 96 patients, with 2179 pretreatment cone-beam computed tomography acquisitions, median age was 9 years (1-20). Setup parameters were 3.13, 3.02, 1.64, and 1.48 mm for vector magnitude group mean, interpatient, interinstitution, and random error, respectively. On multivariable analysis, there were no significant differences in mean vector magnitude by age, gender, performance status, target location, extent of resection, chemotherapy, or steroid or anesthesia use. Providers rated >99% of images as adequate or better for target localization.Conclusions:A lower-dose cone-beam computed tomography protocol demonstrated table shift vector magnitude that approximate clinical target volume/planning target volume expansions used in central nervous system radiotherapy. There were no significant clinical predictors of setup accuracy identified, supporting use of this lower-dose cone-beam computed tomography protocol across a diverse pediatric population with brain tumors.

Radiation dose in cone beam CT guided ERCP

PurposeTo evaluate the practical and radiation safety considerations in utilization of 3-D imaging through cone beam computed tomography (CBCT) in endoscopic retrograde cholangiopancreatography (ERCP). MethodERCP procedures were performed using an Artis Q interventional suite (Siemens Healthineers), including 42 procedures with CBCT. Some CBCT cases used the standard “DR” exposure protocol and some used the low dose protocol “DR care”. Data on x-ray radiation doses were retrospectively collected and to help optimize technical factors surrounding the procedure and compared to radiation exposure data of patients undergoing conventional ERCP. ResultsThe median dose area product was 24.4 Gycm2 for one DR volume and 5.07 Gycm2 for one DR care volume. The median total dose area product was 6.52 Gycm2 for conventional ERCP, 48.9 Gycm2 for procedures using DR and 19.7 Gycm2 when using DR care. Conventional ERCP resulted in a significantly lower radiation dose than procedures using either CBCT protocols (p < 0.001). However, conventional ERCP showed a large number of outliers with higher dose at the level of, or surpassing, CBCT procedures. ConclusionsFor less complex procedures with small x-ray doses and short fluoroscopy times conventional 2-D x-ray technique is clinically sufficient and utilizes less radiation dose than CBCT methods, but there is a wide range of doses and extreme outliers have been observed. CBCT can facilitate ERCP in cases with difficult ducal anatomy, possibly reducing procedural time, x-ray exposure time and need for contrast injections. Methods for prediction on high radiation ERCPs are needed to standardize and optimize patient selection for CBCT-ERCP.

Twin Robotic X-Ray System for 3D Cone-Beam CT of the Wrist: An Evaluation of Image Quality and Radiation Dose.

OBJECTIVE. The purpose of this study was to assess image quality and radiation dose of a novel twin robotic x-ray system's 3D cone-beam CT (CBCT) function for the depiction of cadaveric wrists. MATERIALS AND METHODS. Sixteen cadaveric wrists were scanned using dedicated low-dose and standard-dose CBCT protocols as well as clinical MDCT for comparison. Three readers assessed overall image quality, noise, and artifacts in bone and soft tissue on 5-point Likert scales. For radiation dose analysis, volume CT dose indexes (CTDIvol) were compared. RESULTS. Overall image quality of most studies was very good or excellent in MDCT (for readers 1, 2, and 3: 100%, 100%, and 88%, respectively), standard-dose CBCT (100%, 100%, and 94%), and low dose CBCT (100%, 94%, and 88%) with two readers favoring standard-dose CBCT over MDCT image quality (readers 1 and 2; p ≤ 0.046). In soft tissue, standard-dose (readers 1, 2, and 3; p ≤ 0.021) and low-dose (all p ≤ 0.001) CBCT images had more noise than MDCT in all cases. Standard-dose (all p ≤ 0.003) and low-dose (all p < 0.001) CBCT images also displayed more artifacts. In osseous tissue, one reader observed more noise (p < 0.001) and artifacts (p = 0.020) for low-dose CBCT than for MDCT, whereas no difference was found between standard-dose CBCT and MDCT. Mean CTDIvol was significantly lower for standard-dose (5.2 ± 0.6 mGy; p < 0.001) and low-dose CBCT (1.8 ± 0.2 mGy; p < 0.001) than for clinical MDCT without automatic dose modulation (15.0 ± 0.0 mGy). CONCLUSION. The tested CBCT function delivers suitable image quality for clinical wrist imaging at significantly lower radiation levels than conventional MDCT. In combination with comfortable positioning options and the ability to perform additional radiographic and fluoroscopic examinations, the twin robotic x-ray system may hold the potential to be a one-stop shop device for trauma-associated wrist imaging.

Comparison of MRI with dedicated head and neck signal amplification coil and cone beam computed tomography: MRI is a useful tool in diagnostics of cranio-facial growth disorders

ObjectiveMagnetic resonance imaging (MRI) shows excellent image quality for the depiction of soft tissues and is therefore an important imaging technique in medical diagnostics. However, the practical simultaneous presentation of hard and soft tissue structures of the mouth, jaw and facial area is not fully satisfactory at this time. We investigated the image quality of 1.5 T MRI using a dedicated signal amplifying coil for the application in the oral and maxillofacial field of and compared it with cone beam computed tomography (CBCT). We hypothesized that imaging quality for growth disorders of the facial skull does not differ significantly between the two imaging techniques. Materials and methods12 patients were consecutively enrolled into this study between 01/2016 and 12/2017. Patients received diagnostic imaging for clinical indications using 1,5 T MRI using a dedicated head and neck coil for signal amplification as well as an CBCT. For each patient 5 different MRI sequences and one CBCT protocol were assessed. Images were evaluated by a radiologist and a dentist in consensus. On the basis of 51 anatomical structures and orthodontic, cephalometric reference points, the five datasets were subjectively rated and compared to the CBCT dataset. ResultsPatient age was in the range of 19–78 years. 2614 (69.8%) out of 3744 possible valuations were assessable. Compared to CBCT, MRI images were rated to have a superior image quality of presentation for 42 out of 51 anatomic structures (p < 0.05). Notably, 5 out of 51 structures were not assessable due to missing values. T1-weighted MRI images were rated superiorly to T2-weighted images in displaying anatomically relevant landmarks in the oral and maxillofacial field. MRI datasets were inferior in imaging cephalometric and orthodontic reference points in comparison to CBCT images. ConclusionIn conclusion, this pilot study demonstrates that radiation-free dental MRI enables a reliable detection of important anatomical structures. Thus, the signal amplified MRI presents a radiation-free imaging alternative to established CBCT in craniofacial growth disorders protocols. However, imaging quality in MRI datasets remains inferior to CBCT images for cephalometric and orthodontic reference points.

Dual-energy material decomposition for cone-beam computed tomography in image-guided radiotherapy

Background: Dual-energy (DE) diagnostic computed tomography (CT) combines two scans of different photon energy spectra which can provide additional image information as compared to standard CT. We developed a DE material decomposition scan protocol for daily cone-beam CT (CBCT) of head-and-neck patients receiving radiotherapy and tested it in a clinical trial.Material and methods: Our DE CBCT protocol consisted of an 80 and 140 kVp scan. The material decomposition algorithm split the low and high energy scan into components of two basis materials, aluminum and acrylic. Scans of different thicknesses and overlap of the basis materials were acquired to calibrate the model which decomposed the CBCT projections into thicknesses of aluminum and acrylic on a per-pixel basis. Pseudo monochromatic projections were created from these thicknesses and the known energy dependence of the attenuation coefficient of the basis materials. A frequency selective de-noising method was further applied to the basis material projections. The DE CBCT protocol was tested on seven patients. Two DE images were chosen, one at low (50–60) keV to evaluate soft tissue image quality and one at 150 keV to assess metal artifact reduction as compared to standard CBCT.Results: The de-noising algorithm reduced noise by 41% and 69% in the 60 and 150 keV images, respectively, compared to images without the de-noising. The low keV image showed an increase in soft tissue contrast-to-noise ratio of 7–43% compared to the standard clinical CBCT for six of the seven patients. The 150 keV DE CBCT image reduced metal artifacts. Enhanced streaking from metal artifacts were observed in some of the DE CBCT images.Conclusion: Monochromatic DE images from material decomposition can improve soft tissue contrast-to-noise ratio and metal artifact reduction. Improvements are limited, however, and new artifacts were also introduced by the DE algorithm.

Accuracy of Different Imaging CBCT Systems for the Detection of Natural External Radicular Resorption Cavities: An Ex Vivo Study

ObjectiveThe aim of this study was to compare the sensitivity and specificity of 3 different systems of cone-beam computed tomography (CBCT) in the detection of natural external root resorption (ERR) cavities using microtomography as the gold standard. MethodA sample of 126 ex vivo teeth were submitted to a microtomography examination to verify the presence/absence of ERR cavities. Then, they were divided into the control group: 85 teeth that did not present with an ERR cavity; and experimental group: 41 teeth that presented with 1 or more ERR cavities. The size of the natural ERR cavities varied from 2.46 mm3 to 3.11 mm3, which corresponded to cavities of 1.67 mm and 1.81 mm in diameter, respectively. The teeth were placed on a dry human mandible for scanning in each of the 3 protocols with different voxel sizes: 0.25 mm, 0.20 mm, and 0.166 mm. ResultsThe accuracy of the 3 protocols evaluated in this study are listed in decreasing order: 60.3% for a voxel size of 0.20 mm, 56.7% for a voxel size of 0.166 mm, and 46.7% for a voxel size of 0.25 mm; these are smaller values than previous studies have obtained using artificial ERR cavities. Statistically significant results were not found among the 3 CBCT protocols that were used (P > .05), and the receiver operating characteristic curve shows the small differences found between the protocols. ConclusionThe results indicate that CBCT presents, for natural ERR, lower sensitivity and specificity values than those detected in previous studies of artificial cavities. The results demonstrate that natural ERR is neither easily observed nor accurately located by CBCT, as previous studies using artificial ERR indicated.

Precision of 2 Low-dose Abdomen/Pelvis Cone Beam Computed Tomography Protocols for Alignment to Bone and Soft Tissue in Pediatric Patients Receiving Image Guided Radiation Therapy

PurposeTo evaluate the precision of 2 low-dose cone (LD) beam computed tomography (CBCT) protocols to align to bone and soft tissue for pediatric patients receiving image guided radiation therapy (IGRT) to the abdomen and pelvis. Methods and MaterialsImage-quality evaluation was done for 858 CBCT scans from 46 pediatric patients treated with IGRT from January 2015 to December 2017. The evaluations guided the development of 2 significantly dose-reduced protocols, LD-CBCT1 and a further dose-reduced LD-CBCT2. Representative scans from LD-CBCT1 and LD-CBCT2 from 8 patients with at least 1 CBCT scan from both protocols were registered separately to a bone and soft-tissue landmark on the simulation computed tomography scan. Eighteen identical blinded random offsets were applied to each patient's LD-CBCT1 and LD-CBCT2 from a starting registration that was then realigned using rigid registration. The residual offset between the baseline registration and the final registration attempt was calculated and analyzed using a 1-sided, 1 sample t test to evaluate whether LD-CBCT1, delivering a higher dose, was superior to the lower-dose LD-CBCT2 for bone and soft-tissue alignment. ResultsIn comparing 288 registrations with a bone landmark across 8 patients, no difference was found in the vector magnitude offsets using LD-CBCT 1 (mean [x¯], 0.73 mm; standard deviation [σ], 0.39 mm) and LD-CBCT2 (x¯, 0.74 mm; σ, 0.40 mm; P = .425). Comparing 216 registrations with a soft-tissue landmark across 6 patients, alignment using LD-CBCT2 (x¯, 1.55 mm; σ, 1.08 mm) resulted in larger differences in the vector magnitude of the offsets compared with LD-CBCT1 (x¯, 1.37 mm; σ, 0.74 mm; P = .049). ConclusionsClinics treating pediatric patients should consider implementing a protocol mirroring LD-CBCT2 for abdomen and pelvis IGRT bone alignment. Further evaluation of the precision of LD-CBCTs for soft-tissue alignment is necessary.

Accuracy of linear measurements using low dose cone beam computed tomography protocol versus direct skull linear measurements: An in vitro study

Background: Cone beam computed tomography (CBCT) imaging has been widely used for different dental applications over the last few years. It delivers a high dose of radiation compared to conventional imaging modalities. This study aimed to compare the accuracy of linear measurements conducted using a low dose CBCT protocol in comparison with direct skull linear measurements. Methods: Ten dry human skulls were included in the study. 12 linear measurements were measured directly on each skull between 23 chosen anatomical landmarks using a digital calliper. Radio-opaque markers were then glued on these anatomical landmarks. Each skull was then scanned using low dose CBCT protocol operated at 90 kVp, 7.1 mA, for 9 sec. Results: There was no statistically significant difference in the accuracy of linear measurements conducted using the low dose CBCT protocol when compared with direct linear measurements. Relative Dahlberg Error value ranged from 0.8% to 1.9%. Conclusion: Reducing mAs using a low dose CBCT protocol does not affect the accuracy of linear measurements used in craniofacial imaging tasks as compared with those taken directly on the skull by a digital calliper.

53. IGRT Cone Beam CT: Patient specific organ dose evaluation

Purpose Daily images from CBCT could deliver significant dose to the patient, which should be considered and evaluated. It is essential to associate the absorbed dose delivered by the imaging procedures to the treatment of each patient. Aim of this work is to calculate organ doses for patients undergoing Cone Beam CT (CBCT) when treated with radiotherapy. Methods The system in use was an Elekta CBCT (XVI) and the protocols analysed were four: head, pelvis, chest and chest 4D with different parameters. The formula for organ dose calculation was obtained from Rampado et al. [1] where dose to organs were evaluated by means of Monte Carlo simulation in phantom; the effect of patient size were also accounted for. Dose to organs involved in CBCT scans is: D T = D W , 1 Ph · ( D T / D W , 1 Ph ) tab · a · e - bx where D W , 1 Ph is the measured dose in a phantom for the specific protocol, x is the effective diameter of the patient, ( D T / D W , 1 Ph ) tab , a and b are tabulated data from the article cited above. Patients were analyzed from March to June 2017. For each case were registered: the effective diameter from simulation CT, CBCT protocol, number of CBCT scans. Results Two hundred patients were considered. For head protocol, the mean CBCT doses were about 20 ± 10 mGy for all organs. Instead, doses of about 400 ± 150 mGy were evaluated for pelvis protocol. CBCT Doses for Chest 4D protocol were lower than other chest ones (about 50 ± 25 mGy vs 400 ± 150 mGy). This difference was due to number of CBCT scans/treatment fractions. Conclusions Doses from CBCT procedures should be accounted for; based on organ doses calculation, a program of dose optimization could be performed.

Оценка индекса дозы при использовании протоколов сканирования компьютерной томографии в коническом пучке для пациентов детского возраста

Purpose: Cone-beam computed tomography (CBCT) is an indispensable procedure for accurate patient positioning during radiation therapy (RT) in many clinical cases. However, the patients get an additional dose using CBCT. This dose is neither therapeutic nor diagnostic. It is very difficult to obtain the reliable information about the dose distribution within the patient using the CBCT. Despite this, there is a need to control the additional dose for the pediatric patients and reduce it. There are different approaches of imaging dose evaluation. Most accurate methods are based on the Monte-Carlo calculation and thermoluminescent dosimeters-based measurements. However, the implementation of these methods is complex and cumbersome, that makes impossible their application in routine clinical practice. The evaluation of dose indexes is an accessible and convenient alternative. The purpose of this study is evaluation of the cone beam computed tomography dose indexes for different imaging protocols and object sizes. Material and methods: The technique based on absolute and relative dose measurements for CBCT was used in this study. Absolute dose measurements were performed at the periphery and center of the FREEPOINT (CIRS) phantom using the Farmer type chamber FC65-P for each CBCT protocols. FREEPOINT (20 cm height, 30 cm width, 30 cm length) was used for imitation big chest and pelvis. Inner insert (16 cm diameter) of the phantom was used for imitation head, small chest and pelvis. The dose profiles were measured using I’mRT MatriXX (IBA) and analyzed by OmniPro-I’mRT software, dose indexes DLP (dose–length product) were calculated. Results: The dose indexes were identified for five protocols corresponding three scanning areas (Head and Neck, Chest and Pelvis). The dose indexes were 51.82 and 90.25 mGy×cm using Head and Neck S20 and Head and Neck M20 protocols respectively. The lowest dose index was obtained 13.28 mGy×cm for Fast Head and Neck S20. It was established that the scanning object size strongly affects on the dose index values and, as result, on the absorbed dose within the patient. The dose indexes were 305.42 and 187.53 mGy×cm using scanning protocol Chest M20 for small and big phantoms respectively. The similar results were obtained for scanning protocol Pelvis M15. The highest dose index was obtained 846.93 mGy×cm for the small phantom, while the dose index was 563.79 mGy×cm for the big phantom. The necessity of several clinical protocols to scan different areas was shown. Using of the Pelvis M15 protocol for head scanning may increase the additional point dose 96 times in comparison with Fast Head and Neck S20 protocol. Conclusion: The dose indexes were evaluated taking into account the size of the scanning object for different imaging protocols. Routine use of CBCT in clinical practice requires a sensible choice of the scanning protocol based on the results of the dose index estimation.

Dose area product in estimation of effective dose of the patients undergoing dental cone beam computed tomography examinations

Objective: To investigate the relationship of the effective dose and dose area product (DAP) in dental cone beam computed tomography (CBCT) examinations and to propose conversion factors for estimation of effective doses of the patients using DAP. Dependence of organ doses on DAP was also investigated. Materials and Methods: Different exposure geometries in Cranex3Dx CBCT device were simulated using Monte Carlo simulation and computational anthropomorphic phantom. Then organ doses and effective dose for every exposure geometry was compared to DAP and analysed. Results: The effective dose in all simulated CBCT protocols and positions with 180° tube rotation ranged from 5 μSv for 50 × 50 mm2 field of view (FOV) localised on one tooth using lowest resolution to 265 μSv for the largest FOV and highest resolution. In case of 360° tube rotation the effective dose ranges from 6 to 332 μSv for the same FOV sizes and positions as well as resolutions as in 180° tube rotation. Conclusions: Though the DAP introduces a large uncertainty in the risk measure in dental CBCT, it represents the dose and FOV size which are the most important scanning parameters affecting the dose. To decrease uncertainty in the risk measure, the effective dose has to be estimated for usual clinical positions of the FOV.

Optimizing contrast-enhanced cone-beam CT protocol to facilitate simultaneous visualization of neurovascular pathologies and surrounding structures of interest.

Contrast-enhanced cone-beam computed tomography (CBCT) imaging is commonly used for evaluating neurovascular stents and their relationship to the parent artery or vascular pathologies such as arteriovenous malformations (AVMs) and dural arteriovenous fistulas (dAVFs) in the context of surrounding anatomical structures. The purpose of this study was to understand the effects of varying concentrations of contrast medium used in CBCT imaging for optimal visualization of various endovascular devices and anatomical pathologies. Thirty-five patients with various neurovascular pathologies were included in the study. Contrast-enhanced CBCT images (20 s DR, Siemens syngo DynaCT, Siemens AG, Forchheim, Germany) were acquired in all cases, with varying dilutions of contrast medium, from 1% to 30%. The injection rate was kept constant at 3 cc/sec with an X-ray delay of two sec, and a total volume of 66 cc of diluted contrast was administered. Results from visual and quantitative analysis were reported. Ten percent dilution of contrast medium resulted in the best image differentiation between flow-diverter devices and the parent artery. Concentrations as low as 2.5% contrast medium also resulted in identifying AVMs in the context of the surrounding brain parenchyma, whereas 20% to 30% dilution provided the best visualization of residual AVMs with prior Onyx embolization and dAVFs in the presence of bony structures. Simultaneous visualization of brain parenchyma, bony structures, devices, and pathological anatomy using contrast-enhanced CBCT imaging is feasible with appropriate doses of iodinated contrast, and should be tailored to the individual case based on the goals of CBCT.

P261] Image quality assessment of filtered dual energy cone beam CT for radiotherapy

Purpose Dual energy (DE) computed tomography (CT), combines two scans obtained with different photon energy spectra. It is known from diagnostic CT to reduce metal artefacts. This study investigates the feasibility of developing a DE protocol for cone-beam CT (CBCT) in radiotherapy. Methods The DE efficacy depends on the ability to separate the energy spectra of the two scans. Therefore, different thickness of copper (Cu) filtration was added to the high energy scan. The DE CBCT scanning protocol consists of two scans at 80 (low) and 140 (high) kV, respectively. Two different DE protocols with 1 and 2 mm added Cu filtration were created. The filtration was done by physically adding Cu plates onto the kV source of the CBCT system. The mAs was adjusted to keep the doses of both DE protocols on the same level as the standard CBCT. The dose was measured using a CTDI phantom. The DE images, I DE , were created in image space from the high, I high , and low, I low , energy images using I DE ( E ) = w ( E ) ∗ I low + ( 1 - w ( E ) ) ∗ I high where w(E) is a weighting factor dependent on the (pseudo) monochromatic energy, E, of the I DE images. Scans of a Catphan phantom were acquired with the DE CBCT protocols as well as a standard CBCT scan at 100 kV. The Cu filtered DE CBCT scans were investigated with respect to soft tissue image quality as the potential benefit of image artefact reduction should not compromise overall image quality or increase radiation dose compared to the standard CBCT. To quantify the image quality, contrast-to-noise (CNR) measurements were done in regions resembling muscle and fat in the phantom. Results The radiation dose was 100.1% and 101.4% of the standard CBCT dose for the 1 and 2 mm Cu protocols, respectively. The CNR was found to be 1.3 (standard), 1.4 (DE, 1 mm Cu) and 1.3 (DE, 2 mm Cu). Conclusions The filtered DE and standard CBCT protocols showed similar performance in radiation dose and soft tissue image quality. Hence it is feasible to explore the potential benefits of increased soft tissue contrast and artefact reduction for DE CBCT protocols.

Dose estimate for cone beam CT equipment protocols using Monte Carlo simulation in computational adult anthropomorphic phantoms

Cone beam computed tomography (CBCT) has become essential for dental diagnoses in the last decade. This is supported by its low cost and low doses, when compared to medical CT. Following this increase in CBCT procedures, it is necessary to ensure the image quality within low radiation doses to the patients. This is an especially difficult challenge in CBCT, given the number of equipment models (more than 50), radiographic techniques that may be employed, and technical information not available to the users by the manufacturers. The objective of this study was to estimate the cancer risk, effective and absorbed doses in tissues and organs for CBCT protocols intended for dental use. Monte Carlo (MC) simulations were used to estimate these quantities in tissues and organs with radiological importance, as those suggested by the International Commission of Radiological Protection (ICPR) report ICRP 103. Five different fields of view (FOV) were simulated to i-Cat Classic CBCT, using the MCNPX code. The virtual anthropomorphic phantoms FASH3 (Female Adult MeSH) and MASH3 (Male Adult MeSH) were also used. The effective dose estimative was in the range 75.15–142.20 μSv. The largest contribution to the effective dose was from the salivary glands (17%), thyroid (27%) and remainder tissues (28%). The results of this work showed that the effective and absorbed doses in tissues/organs vary according to the FOV, exposure parameters, and the positioning of the beam, relative to the radiosensitive organs. Furthermore, for the same exposure conditions, women can exceed the total risk of cancer by 26–34%, when compared to men.

Cone beam computed tomography in implant dentistry: recommendations for clinical use

BackgroundIn implant dentistry, three-dimensional (3D) imaging can be realised by dental cone beam computed tomography (CBCT), offering volumetric data on jaw bones and teeth with relatively low radiation doses and costs. The latter may explain why the market has been steadily growing since the first dental CBCT system appeared two decades ago. More than 85 different CBCT devices are currently available and this exponential growth has created a gap between scientific evidence and existing CBCT machines. Indeed, research for one CBCT machine cannot be automatically applied to other systems.MethodsSupported by a narrative review, recommendations for justified and optimized CBCT imaging in oral implant dentistry are provided.ResultsThe huge range in dose and diagnostic image quality requires further optimization and justification prior to clinical use. Yet, indications in implant dentistry may go beyond diagnostics. In fact, the inherent 3D datasets may further allow surgical planning and transfer to surgery via 3D printing or navigation. Nonetheless, effective radiation doses of distinct dental CBCT machines and protocols may largely vary with equivalent doses ranging between 2 to 200 panoramic radiographs, even for similar indications. Likewise, such variation is also noticed for diagnostic image quality, which reveals a massive variability amongst CBCT technologies and exposure protocols. For anatomical model making, the so-called segmentation accuracy may reach up to 200 μm, but considering wide variations in machine performance, larger inaccuracies may apply. This also holds true for linear measures, with accuracies of 200 μm being feasible, while sometimes fivefold inaccuracy levels may be reached. Diagnostic image quality may also be dramatically hampered by patient factors, such as motion and metal artefacts. Apart from radiodiagnostic possibilities, CBCT may offer a huge therapeutic potential, related to surgical guides and further prosthetic rehabilitation. Those additional opportunities may surely clarify part of the success of using CBCT for presurgical implant planning and its transfer to surgery and prosthetic solutions.ConclusionsHence, dental CBCT could be justified for presurgical diagnosis, preoperative planning and peroperative transfer for oral implant rehabilitation, whilst striving for optimisation of CBCT based machine-dependent, patient-specific and indication-oriented variables.

Assessment of a training programme on detection of temporomandibular joint osseous changes applying pre-defined 2D multiplane cone beam computed tomography reconstructions.

Osseous changes in temporomandibular joint disorders (TMD) are common indications for cone beam computed tomography (CBCT). The number of such cases is increasing while a number of qualified oral radiologists is limited. This study investigated the usefulness of a training programme for general dental practitioners (GDPs) regarding temporomandibular joint (TMJ) osseous changes detection in CBCT images. We selected CBCT images of 35 TMD cases and chose 5 of them to use in training 7 GDPs on detecting osseous changes in the TMJ. In evaluation directly following training, GDPs assessed the 30 remaining cases. Three qualified radiologists served as reference standard. A 2-month follow-up of training comprising evaluation of the same cases. The cases are assessed according to Ahmad etal (Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 107, 2009, 844) protocol of TMJ osseous changes in CBCT images. Sensitivity and specificity of the CBCT protocol were high, except for some criteria that did not appear in the cases. Average observer sensitivity was 65% while specificity was 87%. Average correct individual response rate was 84%. Mean agreement among the GDPs was 73%. Observer performance had improved at the 2-month follow-up. The present educational programme could be a helpful material on recognising possible osseous changes of TMJ and it can be used as a part of a training programme for GDP and for specialist candidates.