Factors influencing the absorbed dose in intraoral radiography

Investigating the Effect of Different Metal Sheets on Reducing Radiation Behind Intraoral Digital Phosphor Plates During Intraoral Radiography using Gray Value

Purpose:

To assess the efficacy of metal sheets with different thicknesses on reducing the radiation behind the photostimulable phosphor plate (PSP) during intraoral periapical examinations.

Materials and Methods:

In this study, a phantom head was used to investigate the effect of using metal sheets of aluminum, stainless steel, and copper with three thicknesses of 0.5, 0.75 and 1mm on reducing the radiation behind PSP. Images were acquired at 66 kVp 8 mA, and 0.16 s using the long-cone paralleling technique. The images were saved and exported to DICOM format without any post-processing. Then, they were transferred to an image processing software (Mimics, Materialize, Leuven, Belgium), and their mean gray values (MGV) were determined. The acquired data were statically analyzed for accessing the significant difference in groups means using ANOVA, and the means of groups were compared using Tukey’s test procedure.

Results:

The MGV of the second PSP differed significantly from those PSPs slotted with various metals (p<0.001). The MGV for lead and stainless steel at 0.5 mm thickness was insignificant (p = 0.852), but differed significantly from other metals. The MGV for PSPs with 0.75 mm stainless steel and 1 mm copper slots were varied significantly from those of all other PSP and metals. The 1 mm copper group was significantly different from all other groups (p<0.001).

Conclusion:

Using the mean gray value of the PSP, the use of various metal sheets of different thicknesses could effectively reduce the radiation behind the PSPs during periapical radiographs.

The use of radiographic imaging technologies by general dentists in Ontario, Canada

OBJECTIVE

The aim of this study was to determine the prevalence of 2-dimensional and 3-dimensional digital imaging technologies, the methods used by general dentists to limit patient exposure to ionizing radiation, and the impact of dentists' education on imaging technologies and patient dose-reducing techniques.

STUDY DESIGN

A cross-sectional, web-based survey of all general dentists in Ontario was conducted.

RESULTS

Responses from 1332 (14.7%) of the 9052 registered general dentists in Ontario were included in the analysis. Approximately 89% reported using digital intraoral technology, 81.1% reported owning panoramic imaging systems, 71.2% reported making referrals for cone beam computed tomography (CBCT), and 9.5% reported including CBCT in their practices. CBCT was most commonly used for dental implant treatment planning (85.8%), followed by endodontics (45.4%), evaluation of pathology (39.6%), and surgical assessment for impacted teeth or difficult extractions (36.8%). Approximately 32.7% used only collimators with a long focal point-receptor distance and 8% used only rectangular collimation; 86.9% reported using a thyroid collar when imaging patients. Differences in educational backgrounds correlated with differences in the use of imaging and dose-reducing techniques.

CONCLUSIONS

There is widespread adoption of digital imaging technologies by general dentists in Ontario, including CBCT. Greater implementation of long and/or rectangular collimation could markedly reduce the ionizing radiation dose to patients. Changes in dental education curricula and continuing education course offerings may address these issues.

Assessment of Adult Diagnostic Reference Levels for Panoramic Radiography in Tamil Nadu Region

Aim:

The aim of this study was to calculate dose area product (DAP) and to determine diagnostic reference level (DRL) for adult panoramic procedures in Tamil Nadu.

Materials and Methods:

In this study, air kerma on the front side of the secondary collimator was measured with a Black Piranha, RTI Electronics, Sweden and multiplied with the corresponding exposed area to calculate DAP. The obtained DAP values were further analyzed, and DRL was calculated using the Microsoft Excel software. The study was carried out with regular adult exposure parameters.

Results:

The mean, range, and 3^rd quartile values for 67 panoramic scanners in Tamil Nadu, India, were calculated as 94 mGycm², 41 mGycm²–165 mGycm², and 114.3 mGycm², respectively. The results are comparable with other international studies.

Conclusion:

The present study suggests that further optimization can be achieved in many centers by the recruitment of professionally qualified radiographers and conducting periodic training programs on the optimization of exposure parameters. Considering this as the first study for the dental DRL assessment, further studies are suggested to establish national dental DRL in India.

Efficacy of lead foil for reducing doses in the head and neck: a simulation study using digital intraoral systems

OBJECTIVES

To assess the efficacy of lead foils in reducing the radiation dose received by different anatomical sites of the head and neck during periapical intraoral examinations performed with digital systems.

METHODS

Images were acquired through four different manners: phosphor plate (PSP; VistaScan(®) system; Dürr Dental GmbH, Bissingen, Germany) alone, PSP plus lead foil, complementary metal oxide semiconductor (CMOS; DIGORA(®) Toto, Soredex(®), Tuusula, Finland) alone and CMOS plus lead foil. Radiation dose was measured after a full-mouth periapical series (14 radiographs) using the long-cone paralleling technique. Lithium fluoride (LiF 100) thermoluminescent dosemeters were placed in an anthropomorphic phantom at points corresponding to the tongue, thyroid, crystalline lenses, parotid glands and maxillary sinuses.

RESULTS

Dosemeter readings demonstrated the efficacy of the addition of lead foil in the intraoral digital X-ray systems provided in reducing organ doses in the selected structures, approximately 32% in the PSP system and 59% in the CMOS system.

CONCLUSIONS

The use of lead foils associated with digital X-ray sensors is an effective alternative for the protection of different anatomical sites of the head and neck during full-mouth periapical series acquisition.

Image optimization in digital dental radiography

Presented is a method for establishing the appropriate balance of image quality and radiation dose for dental imaging. Using the Monte Carlo N-Particle Extended (MCNPX) radiation transport code, the DC Planmeca radiographic unit and a dental bitewing phantom were modeled. The Carestream 6100 RVG sensor signal response, noise response, dose rate dependence, and reproducibility were determined experimentally, including uncertainties and inter/intraunit variabilities. The computationally varied parameters were peak kilovoltage and tube filtration. The entrance air kerma for the current clinical technique was used to establish reference image quality. Four figures of merit (FOM) were chosen to encompass parameter variation. With equal weighting of FOMs and no equipment limitations, the optimal parameters were 90 kVp with 0.1 mm added copper filtration. The optimal technique in the radiographic units' operating range was 70 kVp and 0.1 mm added copper filtration, resulting in a ∼50% (±17%) entrance dose and ∼40% effective dose savings.

Effect of Different Tube Potential Settings on Caries Detection using PSP Plate and Conventional Film

PURPOSE

To compare intraoral Phosphor Stimulable Plate digital system and intraoral film using different tube settings on incipient proximal caries detection.

MATERIALS AND METHODS

Five blocks, with five teeth each, were radiographically examined using phosphor plates and F-speed films. The images were acquired in 07 different tube potentials from 50-80 kV. The films were digitized. Three oral radiologists scored the images for the presence of caries using a 5-point rating scale. The areas under ROC curve were calculated. The influence of tube kilovoltage was verified by ANOVA and pair wise comparisons performed using Tukey test.

RESULTS

Mean ROC curve areas varied from 0.446-0.628 for digital images and 0.494-0.559 for conventional images. The tube setting of 70 kV presented the best result both for digital and conventional images. Considering the image type separately, 70 kV scored highest followed by 75 and 65 kV for digital images (p=0.084). For conventional image modality, even though 70 kV presented the best result, it did not differ significantly from 80 kV, not differing from 60 and 55 kV, which did not differ from 75, 65 and 50 kV (p=0.53).

CONCLUSION

Phosphor plate digital images seem to be more susceptible to tube setting potential variations then digitized film images.

The Effects on Absorbed Dose Distribution in Intraoral X-ray Imaging When Using Tube Voltages of 60 and 70 kV for Bitewing Imaging

Objectives

Efforts are made in radiographic examinations to obtain the best image quality with the lowest possible absorbed dose to the patient. In dental radiography, the absorbed dose to patients is very low, but exposures are relatively frequent. It has been suggested that frequent low-dose exposures can pose a risk for development of future cancer. It has previously been reported that there was no significant difference in the diagnostic accuracy of approximal carious lesions in radiographs obtained using tube voltages of 60 and 70 kV. The aim of this study was, therefore, to evaluate the patient dose resulting from exposures at these tube voltages to obtain intraoral bitewing radiographs.

Material and Methods

The absorbed dose distributions resulting from two bitewing exposures were measured at tube voltages of 60 and 70 kV using Gafchromic^® film and an anatomical head phantom. The dose was measured in the occlusal plane, and ± 50 mm cranially and caudally to evaluate the amount of scattered radiation. The same entrance dose to the phantom was used. The absorbed dose was expressed as the ratio of the maximal doses, the mean doses and the integral doses at tube voltages of 70 and 60 kV.

Results

The patient receives approximately 40 - 50% higher (mean and integral) absorbed dose when a tube voltage of 70 kV is used.

Conclusions

The results of this study clearly indicate that 60 kV should be used for dental intraoral radiographic examinations for approximal caries detection.

Diagnostic accuracy of Digora Optime storage phosphor plates for proximal subsurface demineralization: effect of different exposure times

OBJECTIVE

The aim of this study was to compare the diagnostic accuracy of F-speed film and storage phosphor plate (SPP) exposed with different exposure times for the detection of artificial enamel subsurface demineralization.

STUDY DESIGN

Standard enamel windows of extracted premolars were exposed to a demineralizing solution. All teeth were radiographed before and after acid application with F-speed films and SPPs. Films were exposed for 0.25 seconds and SPPs were exposed using 4 exposure times. Receiver operating characteristic analysis was used for diagnostic accuracy (A(z)).

RESULTS

Significant differences were obtained among A(z)s of 0.08- versus 0.12-seconds and 0.10- versus 0.12-second exposed SPPs (P < .05). A(z)s of films were higher than the SPPs exposed with 0.08, 0.10, and 0.12 seconds (P < .05). No difference was found between the A(z)s of the 2 systems when SPPs were exposed for 0.16 seconds (P > .05).

CONCLUSIONS

Diagnostic accuracy of films and SPPs was not impaired when exposure time was 36% reduced for the latter; however, diagnosis was impaired when reduced 52%.

Alternative X-ray filters for an intra-oral digital radiographic system

OBJECTIVE

The aim of this study was to evaluate the effect of the modulation of the radiation spectrum with the use of alternative X-ray filters in the quality of intra-oral digital images from storage phosphor plates.

METHODS

The radiographic exposures were performed in a GE 1000 X-ray machine (General Electric Co., Milwaukee, WI), operating at 65 kVp, 10 mA, 40 cm focus receptor distance using three different exposure times: 0.05 s, 0.16 s and 0.35 s. The control filter (GC) was 100% aluminium (Al) with a thickness of 1.5 mm. The tested filters were: G1, 97% Al and 3% copper (Cu) with 1.47 mm thickness; G2, 96% Al and 4% Cu with 1.53 mm thickness; G3, 95% Al and 5% zinc (Zn) with 1.56 mm thickness; G4, 98% Al and 2% Zn with 1.5 mm thickness; and G5, 95% Cu and 5% Zn with 1.6 mm thickness. For formation of the image, a 12-step Al wedge (each step with increments of 1 mm in thickness) was radiographed 10 times. Pixel values measured in digital images were converted into optical density (OD).

RESULTS

All replicates showed OD with high reproducibility (r > 0.95) for all exposure times and tested filters. In comparison between filters, statistically significant differences in density (p < 0.05) were observed. The OD curve of the G5 filter in all exposure times and G3 filter in an exposure time of 0.05 s showed changes in shape (p < 0.05).

CONCLUSIONS

Excluding the G5 filter, all others tested filters can be used as a substitute for GC without losses in image quality.

The effect of delayed scanning of storage phosphor plates on occlusal caries detection

OBJECTIVE

The aim of this study was to determine (1) the effect of various scan delays on pixel intensity measurements and (2) the diagnostic accuracy of occlusal caries detection.

METHODS

72 non-cavitated extracted human permanent molar teeth with sound and carious occlusal surfaces were radiographed using the DIGORA® storage phosphor plates (SPPs) (Soredex Corporation, Helsinki, Finland). Plates were scanned immediately and 10 min, 30 min, 60 min and 120 min after exposure. Three different plates were used for each scan delay. An aluminium (Al) wedge was used to evaluate the change in mean grey values (MGVs) for scan delays. Diagnostic accuracy for occlusal caries detection was performed by scoring all the digital images. The true presence of caries was determined by stereomicroscopy. Comparison of MGVs of the Al wedge for immediate and delayed scans was made using repeated measures analysis of variance (ANOVA) and Tukey-Kramer tests. The accuracy was expressed as the area under the receiver operating characteristics curves (A(z)). A(z)s were compared using two-way ANOVA and t-tests. Kappa was used to measure inter and intraobserver agreement.

RESULTS

The mean A(z)s of immediately scanned plates were higher than the A(z)s of plates scanned with four different delays (p < 0.05). The A(z) of immediately scanned images was significantly higher than the A(z)s of images with 60 min and 120 min scan delays (p < 0.05) but not for 10 min and 30 min delays (p > 0.05). MGVs of immediately scanned plates were significantly higher than the plates scanned with four different delays (p < 0.05). Agreement decreased with increasing scan delays.

CONCLUSION

Scanning of DIGORA SPPs should not be delayed beyond 30 min for accurate occlusal caries diagnosis.

Diagnostic accuracy of proximal enamel subsurface demineralization and its relationship with calcium loss and lesion depth

OBJECTIVE

The aim of this study was to determine the relationship between the amount of calcium loss, lesion depth, and the accuracy of storage phosphor plate (SPP) and film radiographs for the detection of artificial proximal demineralization.

METHODS

Standard enamel windows of extracted premolars were exposed to a demineralizing solution for 60 h, 80 h, 100 h and 120 h. Solutions were analysed for calcium concentration by atomic absorption spectrometer and the lesion depths were calculated by a specific formula. All teeth were radiographed with SPPs and F-speed films before and after acid application. Images were evaluated by five observers. Stereomicroscopic and scanning electron microscopic (SEM) observations were carried out to visualize enamel surfaces after acid exposure. Receiver operating characteristic analysis was used for diagnostic accuracy (A(z)). A(z)s were compared with factorial analysis of variance and t-tests. The relationship between A(z)s and lesion depths was determined with Pearson's correlation test.

RESULTS

Strong positive correlation was found between A(z)s of both radiographic methods and lesion depths. No difference was found between the A(z)s of two radiographic systems for any of the demineralization durations (p > 0.05). Pair-wise comparisons revealed no significant difference in A(z)s of SPPs (p > 0.05), while significant differences were obtained for the A(z)s of films for different demineralization periods (p < 0.05). Stereomicroscopic and SEM observations confirmed demineralizations from superficial to deeper layers of enamel.

CONCLUSION

Subsurface enamel demineralization was not accurately detectable with either storage phosphor plates or F-speed films. The amount of calcium loss and the depth of demineralization have a strong relationship with diagnostic accuracy with a significant effect particularly on F-speed films.

An Investigation into Dental Digital Radiography in Dental Practices in West Kent following the Introduction of the 2006 NHS General Dental Services Contract

Aims

The primary aims of the study were to investigate the use of digital radiography within primary dental care practices in the West Kent Primary Care Trust (PCT) area and general dental practitioners’ (GDPs) self-reported change in radiographic prescribing patterns following the introduction of the nGDS contract in 2006.

Methods

Data were gathered via a piloted, self-completed questionnaire, and circulated to all GDPs listed on the National Health Service (NHS) Choices website as practising in the West Kent PCT area. There were three mailings and follow-up telephone calls. The resulting data were entered into a statistical software database and, where relevant, statistically tested, using the chi-square test and Pearson correlation coefficient.

Results

Of 223 GDPs, 168 (75%) responded. There were 163 usable questionnaires. The respondents represented 85% of the general dental practices in West Kent. Eighty (49%) respondents were using digital intra-oral radiography. Of those who used digital radiography, 44 (55%) reported that they used phosphor plate systems and 36 (45%) that they used direct digital sensors. Eighty-three (51%) had a panoramic machine in their practice, 46 of whom (55%) were using digital systems; of these, 32 (67%) were using a direct digital system. Seventy-one GDPs reported that they worked exclusively or mainly in private practice. Forty (56%) of these ‘mainly private’ GDPs reported that they used digital radiographic systems, whereas only 40 (44%) of the 89 ‘mainly NHS’ GDPs reported using digital radiographic systems. On average, mainly private GDPs made the transition to a digital radiographic system six months before mainly NHS GDPs. Of those who provided NHS dentistry before and after April 2006, only 18 (14%) reported taking fewer radiographs and seven (6%) taking more.

Conclusions

In February 2010, of the West Kent GDPs who responded to the questionnaire, just under 50% used digital radiography. Mainly private GDPs were more likely to use digital radiography than their mainly NHS counterparts. A link between digital radiography and increased prescription of radiographs was not specifically apparent from this study. There was no evidence that West Kent GDPs were taking fewer radiographs than they did prior to the introduction of the new GDS contract in April 2006. Research is needed to investigate whether the uptake of digital radiography by GDPs in the rest of the country is similar to that in West Kent.

Effect of tube potential and image receptor on the detection of natural proximal caries in primary teeth

The aim of this study was to assess the detection of proximal caries in primary teeth at three different tube potentials using Ektaspeed films, storage phosphor plates (SPPs), and a charge-coupled device (CCD). Fifty-three extracted human primary molars with natural proximal caries were radiographed with three different imaging modalities--Digora Optime SPP system, RVGui CCD system, and Ektaspeed films--at 50-, 65-, and 70-kV tube potentials. Three observers scored the resultant images for the presence or absence of caries. The definitive diagnosis was determined by stereomicroscopic assessment. The diagnostic accuracy for each imaging modality was expressed as the area under the receiver operating characteristic curves (A(z)). Differences among the A(z) values were assessed using two-way ANOVA and t tests. Kappa was used to measure inter- and intra-observer agreement. Higher accuracy was found for SPPs compared to film and CCD images at all tube potentials. Accuracy was significantly different only at 50-kV tube setting in favor of SPPs (p < 0.05). Inter- and intra-observer agreement was high for all systems. A SPP system can be recommended for dental peadodontic clinics particularly with 50-kV tube potential for the diagnosis of proximal caries since further advantages include the elimination of chemical processing, image enhancement, and a better low-contrast detectability performance.

Work flow with digital intraoral radiography: a systematic review

OBJECTIVE

This systematic review evaluates the six most frequently emphasized advantages of working with digital radiography: less working time, lower radiation dose to the patient, fewer retakes and errors, wider dynamic range, easier access to patient information and easier image storage and communication. Moreover, some clinical aspects and possible disadvantages of digital imaging that were not foreseen at the beginning of the digital era, such as patient discomfort, damage to the receptor, degradation of the image, cross-contamination and viewing conditions, were assessed.

MATERIAL AND METHODS

The literature search used the PubMed database with no limits and was performed during June to August 2009. Search strategies are described in the text for each of the mentioned tasks. A hand search of task-specific journals supplemented the search strategies.

RESULTS

Time seems to be saved when switching from film to digital imaging in dental practice, a dose reduction may not be obtained, retakes and errors may be increased, the dynamic range may be wider with photostimulable storage phosphor (PSP) plates but not with sensors, the effect on patient information has not been well studied and storage and communication create new challenges with regard to handling large files and image compression. In addition, patient discomfort seems to be pronounced with sensors compared with PSP plates and film, the PSP plate may be scratched in clinical use and a two-layer barrier seems to be needed to prevent contamination of the receptor. The type of monitor may not be of major concern if the image is viewed in a room with subdued light.

CONCLUSIONS

Not all of the predicted advantages with digital compared to film-based radiography hold true in daily clinical work. Of particular interest is the relationship between number of images, retakes and the dose given to the patient.

Effect of two X-ray tube voltages on detection of approximal caries in digital radiographs. An in vitro study

This study evaluated the effect of two different tube voltages on clinicians' ability to diagnose approximal carious lesions in digital radiographs. One hundred extracted teeth were radiographed twice at two voltage settings, 60 and 70 kV, using a standardized procedure. Seven observers evaluated the radiographs on a standard color monitor pre-calibrated according to DICOM part 14. Evaluations were made at ambient light levels below 50 lx. All observations were analyzed with receiver operating characteristic curves. A histological examination of the teeth served as the criterion standard. A paired t test compared the effects of the two voltages. The significance level was set to p < 0.05. Weighted kappa statistics estimated intra-observer agreement. No significant difference in accuracy of approximal carious lesion diagnosis was found between the two voltage settings. But five observers rated dentin lesions on radiographs exposed at 70 kV better than on radiographs exposed at 60 kV. Intra-observer agreement differed from fair to moderate. There was no significant difference in accuracy of approximal carious lesion diagnosis between digital radiographs exposed with 60 or 70 kV.