Paediatric absorbed doses from rotational panoramic radiography.

OBJECTIVES: To determine the paediatric doses in rotational panoramic radiography with film/screen and photostimulable phosphor receptors. STUDY DESIGN: A paediatric anthropomorphic head and neck phantom was used. Absorbed doses were measured for two panoramic systems, the Orthophos (Sirona Dental Systems, Bensheim, Germany) and the PM 2002 CC (Planmeca Oy, Helsinki, Finland), with and without programmable child settings, using both screen/film and photostimulable phosphor receptors. RESULTS: Absorbed doses to the eye ranged from 5 to 24 micro Gy. Doses to the dental arches with the Orthophos unit ranged from 50 to 555 micro Gy with the adult and from 27 to 436 micro Gy with the child program; using the PM 2002 CC unit, doses ranged from 56 to 1040 micro Gy using the adult settings, and from 60 to 890 micro Gy with the paediatric settings. The paediatric exposure settings reduced doses at most locations for both panoramic systems. The highest doses were measured near the rotational axes of the X-ray beam. Paediatric settings with the Orthophos P10 resulted in the dose reduction more than 50% to the thyroid but not with the PM 2002 CC. When lower kVcp or mA settings were used, absorbed doses were effectively reduced for all combinations of machines, programs and detectors. CONCLUSIONS: Specific program settings for children reduced the absorbed doses from panoramic radiography irrespective of the machine or receptor used.

Digital imaging modalities for dental practice.

The introduction of the computed tomograph in the 1970s revolutionized medical diagnosis by initiating the transition from analogue to digital imaging. During this period, more specialized equipment for image processing was developed, such as cathode-ray tubes for image display, special sensors for image acquisition, and storage devices for image archiving. Digital imaging systems designed exclusively for use in dentistry were developed in the latter half of the 1980s. Some are now being clinically applied under conditions of close scrutiny to determine diagnostic accuracy, image quality, and radiation exposure to patients. This article reviews the enabling technologies of digital systems used in dentistry, and focuses upon intraoral digital imaging systems, concepts for digital image acquisition, and variations in radiation dose and their effects on diagnostic accuracy of caries detection.

Sensitometric properties of Agfa Dentus OrthoLux, Agfa Dentus ST8G, and Kodak Ektavision panoramic radiographic film.

OBJECTIVES: The purpose of this study was to compare the sensitometric properties of and visualization of anatomical structures with Agfa OrthoLux green-sensitive panoramic radiographic film, Agfa ST8G green sensitive panoramic radiographic film, and Kodak Ektavision green-sensitive panoramic radiographic film used in combination with an Agfa Ortho Regular 400 imaging screen, Kodak Ektavision imaging screen, and Kodak Lanex Regular imaging screen. METHODS: The density response and resolution of panoramic radiographic film/intensifying screen combinations was evaluated by means of Hunter and Driffield curves, modulation transfer functions, and noise-equivalent number of quanta. Image clarity of selected anatomical structures was rated independently by 6 oral and maxillofacial radiologists. RESULTS: The ISO speed for the Agfa OrthoLux panoramic radiographic film combinations was the fastest, and the ISO speed for the Kodak Ektavision green-sensitive panoramic radiographic film combinations was the slowest. The average gradient for the Agfa ST8G systems was relatively steep in comparison with those for the other film/screen combinations. The modulation transfer functions for the Kodak Ektavision film were higher than those for the other films, irrespective of the screen combination used, and those for Agfa OrthoLux film were slightly higher than those for Agfa ST8G film. The noise-equivalent number of quanta for the Agfa ST8G film/screen combinations was lower than those for the other film/screen combinations. The noise-equivalent number of quanta for the Kodak Ektavision film/screen combinations was well within the high-frequency range, whereas Agfa OrthoLux combined with either the Kodak Ektavision imaging screen or the Kodak Lanex Regular imaging screen produced a noise-equivalent number of quanta similar to those of the Kodak Ektavision film/screen combinations in the low-frequency range. Agfa OrthoLux was perceived to provide clearer images of the selected anatomical details than Agfa ST8G, and the Agfa OrthoLux/Agfa Ortho Regular 400 combination was not significantly different from the Kodak Ektavision/Kodak Lanex Regular combination in terms of perceived image quality. CONCLUSION: Agfa OrthoLux is an improvement over Agfa ST8G in film speed, spatial resolution, granularity, and perceived diagnostic image quality. The Agfa OrthoLux/Agfa Ortho Regular 400 combination did not exceed the Kodak Ektavision film/Kodak Ektavision imaging screen combination in resolution, granularity, or perceived image quality.

Comparison of three intra-oral storage phosphor systems using subjective image quality.

OBJECTIVE: To compare the subjective image quality of three intra-oral storage phosphor systems. METHODS: DenOptix (Dentsply/Gendex, Chicago, IL, USA), Digora (Soredex, Helsinki, Finland), and CD-Dent (DigiDent Digital Imaging Technologies, Nesher, Israel) were compared. Two different imaging plates (IPs), BAS300 and HR300 (Fuji Photo Film Co., Tokyo, Japan) were used with the DenOptix system. The specimen was the maxilla and surrounding soft tissues of an adult cadaver. Imaging was at 70 kVp and 8 mA with a focus-detector distance of 38 cm using an optical bench. The exposure times were varied and a panel of five dentists independently evaluated the images produced with each system/IP receptor for seven features; proximal caries, gingival soft tissues, cortical bone, root canal space, root apices, periodontal ligament space and endodontic instrument clarity on a three-interval confidence scale. The best three exposures were chosen according to the highest scores for each system. These images were re-read in random order a total of 10 times. Pair-wise comparisons were made by use of odd's ratio analysis. A 95% confidence interval was applied. RESULTS: Images made with the DenOptix system/BAS IP combination were perceived to have the best overall image quality. The DenOptix/HR IP combination and Digora were rated almost equally in second place. The DigiDent system was ranked inferior. The Digora was considered to be the best for demonstrating gingival soft tissues (P < 0.05) and the DenOptix/HR300 combination the best for clarity of endodontic instruments (P < 0.05). CONCLUSIONS: While the DenOptix/BAS 300 combination was rated highest overall, the ranking of image quality by modality was found to be task-dependent. Digora was rated best for demonstrating gingival soft tissues.

Effect of K-shell absorption edge filters on image quality in digital intraoral radiography.

OBJECTIVE: The purpose of this study was to investigate the effects of K-shell absorption edge filters on the image quality of a charge-coupled device-based digital intraoral radiographic system. STUDY DESIGN: NIOBI-X, Dental X-ray Beam Filter Kit, and KEY filter were added to a 1-mm thick aluminum filter. The half-value layer and the corresponding effective energy were measured. Digital x-ray images were obtained by using a Computed Dental Radiography (CDR). The sensitivity and the image contrast were compared for each filter. Visual detection tests were conducted to evaluate the depiction ability by using 2 kinds of phantoms. RESULTS: The highest effective energy was produced with the KEY filter, and this high effective energy tended to increase the sensitivity of the CDR. The KEY filter also produced the greatest contrast and had the best depiction ability. CONCLUSIONS: The appropriate combination of a charge-coupled device-based digital intraoral radiographic system and an additional filter can reduce the patient dosage and increase the diagnostic information.

Computed tomography of emphysema following tooth extraction.

Subcutaneous and tissue space emphysema following surgical extraction of mandibular third molars is a rare and serious complication of dental surgery. Recognition of mediastinal emphysema following surgical extraction is difficult because there are no absolute clinical symptoms and signs. We present two cases of emphysema following extraction of a lower third molar and discuss the contribution of CT to the early recognition of the presence and spatial migration of air and to clinical management.

Evaluation of tuned-aperture computed tomography depth discrimination for image series acquired variously with linear horizontal, linear vertical, and conical beam projection arrays.

OBJECTIVE: To compare depth discrimination by using tuned-aperture computed tomography (TACT) variously with linear horizontal, linear vertical, combined linear horizontal and linear vertical, and conical beam projection arrays. STUDY DESIGN: The first test object was a metallic mesh angled at 30 degrees to the surface of a computed dental radiography size No. 1 x-ray sensor. The second test object was a dry human mandible. The sensor was mounted on an optical bench constructed to permit free and precise geometrical settings for the horizontal and vertical angulations of the x-ray beam. The extent of blurring of horizontal and vertical wires in each TACT reconstructed image slice was observed for each of the tested beam projection arrays. RESULTS: With a linear horizontal beam projection array, it was not possible to determine the depth of structures parallel to the horizontal dimension, such as the mandibular canal. With a linear vertical beam projection, it was not possible to determine the depth of structures parallel to the vertical dimension. A conical array of beam projections was best suited to the task of depth discrimination of objects in all planes. The best second alternative was a combination of linear vertical and linear horizontal projections. CONCLUSIONS: Beam projection geometry is important for the accurate depth discrimination of TACT reconstructed images. A conical beam projection array is ideal.

Suitability of the general-purpose graphic printer as an image output device for digital dental x-ray images.

OBJECTIVES: The purpose of this study was to evaluate the suitability of the general-purpose graphic printer as an image output device for digital dental x-ray images. METHODS: The image quality as obtained by a thermal printer and by a dye sublimation printer was investigated. A grid pattern image was used to check parallelism and verticality of lines in each hard copy. A step-wedge image was printed with each printer, and the optical density, gradient, and root mean square granularity were compared. Depiction ability was also compared by using test images, including small signals. RESULTS: All of the lines were parallel and vertical on hard copies of both printers. The dye sublimation printer showed better results on optical density, gradient, root mean square granularity, and depiction ability. CONCLUSION: The dye sublimation printer produces images of the depiction ability comparable to the cathode ray tube display and seems suitable as an image output device for digital dental x-ray images.

Assessing the image quality of a CCD-based digital intraoral radiography system: application of perceptibility curve test.

The perceptibility curve test is a method for evaluating the psychophysical properties of radiographic systems. The concept of the perceptibility curve is based on the minimum perceptible exposure differences that are recorded by a particular imaging system. The perceptibility curve test was applied to a Charge-Coupled Device (CCD)-based digital intraoral radiography system in this study. A test object was made of a square aluminum block, 28 mm in both height and length and 10 mm in thickness. The test object had ten contrast details in the form of round holes with diameters of 1.5 mm. The depths of the holes ranged from 0.05 mm to 0.5 mm in steps of 0.05 +/- 0.01 mm. An X-ray unit was used that operated in the range of 60 to 90 kVp. Test radiographs were shown to observers in random order. Six observers were asked to rate them regarding the number of spots representing holes that they could perceive. The smallest perceptible difference in gray level on the computer monitor, a 15-inch cathode-ray tube (CRT), was then found. The minimum difference in gray level between a perceptible detail and the background was determined. Dose response functions were employed to determine exposures corresponding to these gray levels. For each case, delta logE as a function of the number of object details was calculated. Finally the reciprocal of all values of (delta logE)min were calculated. The number of details which the observers perceived decreased linearly with decreasing delta logE values. The maximum number of details that observers perceived was eight or nine. The perceptibility curves showed that their peaks shifted slightly with a change of the kVp but that their shapes were similar at different kVp settings.

Contrast-enhanced conventional CT in patients after surgery for malignant tumors: evaluation of the optimal method of the administration of the contrast medium.

Patients after ablative surgery for malignant tumors require computed tomography (CT) examination of a wide area on the head and neck to follow-up for recurrence and lymph metastasis. The aim of this study was to determine a more effective method for the infusion of the contrast medium into post-operative patients undergoing conventional CT, based on the relationship between the method of administering the contrast medium and the contrast-enhancing effect in the internal jugular vein. First eleven images were selected from the existing contrast-enhanced and plain CT images in a manner such that the CT values of the internal jugular vein were distributed evenly in a range of 50-180. Seven experienced observers evaluated the contrast-enhancing effect of each image set at a window value of 40 and window widths of 120, 200, and 280. Secondly, the CT values of the right internal jugular vein were measured in a total of 10 CT images from the thyroid to maxillary sinus level from each of 60 post-operative patients. The injection needles and contrast-enhancing techniques used in the 60 patients were drip infusion using an 18G injection needle in 20, drip infusion using a 21G injection needle with bolus intravenous injection immediately before scanning in 20, and drip infusion using a 23G injection needle with bolus intravenous injection immediately before scanning in 20. A CT value of 100 or above, preferably 120 or above, in the internal jugular vein was needed for the contrast-enhancing effect of a CT image to be judged as clinically significant. Our results found that, when a conventional CT was used in patients after surgery for malignant tumors, drip infusion using a 21G or 23G injection needle should be combined with bolus injections immediately before the beginning of scanning, and at the glottis or submandibular gland level during the scanning. A sufficient contrast-enhancing effect can also be obtained by drip infusion using an 18G injection needle without bolus injection.

An electronic survey of opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems.

OBJECTIVES: To assess opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems. METHODS: A questionnaire was posted in both English and in Japanese on oral and maxillofacial radiology electronic bulletin boards. The questionnaire was also mailed to selected researchers and manufacturers in oral and maxillofacial radiology. The replies were evaluated to determine opinion on the current and future status of digital intra-oral imaging with special reference to their compatibility with current X-ray generators. RESULTS: Seventy-one replies were received from 19 countries: 39% from Japan and Korea, 27% from North America, 25% from Europe and 8% from the rest of the world. Eighty per cent of respondents were from academia, 15% from industry and the remainder largely in private practice. Respondents' experience was equally divided between solid state, mainly charge-coupled devices (CCDs) and photostimulable phosphor (IP) technologies. Sixty-eight per cent considered that current X-ray generators are compatible with intra-oral digital systems and many believed this was due to their gray scale flexibility. Twenty-eight per cent believed that existing X-ray generators are inconsistent with low exposure times. Many of the replies suggested that in future pixel size would decrease and bit depth and receptor sensitivity increase. CONCLUSIONS: Most respondents are happy to use existing X-ray generators with digital X-ray systems. However, they also believe that increased sensitivity of receptors could lead to more stringent designs of X-ray generators to ensure more reliable outputs in the low exposure range.

Dependency of dose response of five charge-coupled device-based digital intra-oral radiographic systems on tube voltage.

OBJECTIVE: To compare the dependency of dose response of five CCD-based digital intra-oral radiographic systems on tube voltage. METHODS: Characteristic curves for Sens-A-Ray (old and new generations; Regam Medical Systems, Sundsvall, Sweden), Computed Dental Radiography (Schick Technologies, Long Island City, NY, USA), CompuRay (Yoshida, Tokyo, Japan), and VIXA (Dentsply/Gendex, Des Plaines, IL, USA) were generated between 60 and 90 kVp at intervals of 10 kVp and corrected by subtraction of dark current. Their sensitivities were compared. RESULTS: The sensitivity of the old generation Sens-A-Ray decreased with increase in tube voltage whereas in the other systems it increased. CONCLUSION: In the newer systems using a rare earth intensifying screen as a scintillator, the sensitivity increases with increase in tube voltage, thus reducing the radiation dose to the patient.

Effect of number of projections on accuracy of depth discrimination using tuned-aperture computed tomography for 3-dimensional dentoalveolar imaging of low-contrast details.

OBJECTIVE: The purpose of this study was to test the hypothesis that the number of projections influences the accuracy of a simple depth discrimination task when tuned-aperture computed tomography is used. STUDY DESIGN: In each of 4 partially edentulous mandibles, 2 radiopaque steel spheres were attached to the facial and lingual surfaces and 1 ceramic sphere was place in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned ceramic sphere relative to the 2 steel spheres were determined from 3-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently by means of an optical micrometer. Multiple projections were produced from radially symmetric exposures bearing an angular disparity of 15 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction was varied systematically (2, 4, 8, 12, and 16 projections). The consequences of this variable, as well as specimen and observer effects, were evaluated in a balanced factorial experimental design. Depth estimates were performed by 10 trained observers. The depth reported was that corresponding to the tuned-aperture computed tomography slice perceived to yield the image of the ceramic sphere in sharpest focus. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance. RESULTS: No statistically meaningful effects were found for the number of projections (P = .607) or for different observers (P = .093), but a significant specimen effect was demonstrated (P = .006). CONCLUSIONS: Factors other than high contrast limit the perception of image sharpness under these conditions. Depth may be estimated accurately from relatively small numbers of projections.

Intraoral radiographic storage phosphor image mean pixel values and signal-to-noise ratio: effects of calibration.

OBJECTIVE: The DIGORA intraoral radiographic storage phosphor system needs to be calibrated before images are made. Calibration involves inputting of the maximum exposure to be used. This investigation studied the effects of different maximum exposure calibration settings on the mean pixel value for selected regions of interest and the signal-to-noise ratio for images of a test phantom. STUDY DESIGN: A dental phantom containing a step wedge made of different thicknesses of homogeneously radiopaque bone-equivalent material was imaged at 70 kVp with exposures ranging from 12.8 to 105.2 microC.kg-1. Images were displayed through use of imaging software, and a region of interest was set for each bone-step. The mean pixel values and their standard deviations were measured. RESULTS: Except for very low exposures (< 10% of the calibrated maximum), there was a linear relationship between exposure and the pixel values within the regions of interest irrespective of the calibrated maximum exposure. Low exposures resulted in underexposed low-contrast images. Low calibrated maximum exposures (< 54.5 microC.kg-1) resulted in low-density images with poor signal-to-noise ratios. CONCLUSIONS: Because of the very wide image latitude of the DIGORA system, loss of image quality was not observed as a result of adjustments in the calibration setting over the range of exposure commonly used in dental practice. The highest accepted exposure was limited by prior calibration; hence, if diligence is applied, patient exposure can be minimized without detriment to image quality.

Effects of projection geometry and number of projections on accuracy of depth discrimination with tuned-aperture computed tomography in dentistry.

OBJECTIVE: The purpose of this study was to determine the degree to which the number and angular disparity of component projections influence depth discrimination with tuned-aperture computed tomography. STUDY DESIGN: Groups of three tiny steel spheres served as fiducial references on and in four partially edentulous mandibles. Two spheres were attached to the facial and lingual surfaces of each mandible, and the third was fixed in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned sphere relative to the other two spheres were determined from three-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently with an optical micrometer. Multiple projections required by the tuned-aperture computed tomography reconstruction algorithm were produced from radially symmetric exposures bearing angular disparities of 5, 15, 30, and 45 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction likewise was varied systematically (2, 4, 8, 12, and 16 projections). These variables were manipulated through the use of a balanced factorial design. Depth estimates were performed by trained observers; the estimates were based on the determination of tuned-aperture computed tomography slices perceived as imaging the respective apical spheres in sharpest focus. Specimen and observer effects were also considered as independent variables. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance. RESULTS: Significant differences (p < 0.005) were demonstrated for angular disparity and specimen effects, but the number of projections and the effect of the observer were not found to be statistically significant. CONCLUSIONS: In dentistry, angular disparities of 15 degrees or greater should be used when tuned-aperture computed tomography is being applied to diagnostic tasks requiring maximal depth discrimination accuracy.

A sensitometric comparison of Kodak Ektavision and Fuji Super HR-S panoramic radiographic films.

OBJECTIVES: The purpose of this study was to compare the combination of Ektavision film and Ektavision intensifying screen with the combination Super HR-S panoramic radiographic film and HR-4 intensifying screen with respect to sensitometric properties and the visualization of anatomic structures. METHODS: The density response and resolution of both panoramic radiographic film/intensifying screen combinations were evaluated through use of the generated characteristic curves and the modulation transfer function. The diagnostic clarity was evaluated by five oral and maxillofacial radiologists who used a rating scale to evaluate the image clarity of selected anatomic structures. RESULTS: The film speed and radiographic contrast, respectively, were 1.3 and 1.2 times higher for Ektavision than for Super HR-S. The image resolution with Ektavision was similar to that with Super HR-S. Ektavision was perceived to provide clearer images of the selected anatomic details than did Super HR-S. CONCLUSION: With respect to the clarity of anatomic structures, Ektavision film, with its higher speed and higher contrast, proved superior to Super HR-S film.

Distribution of scattered radiation during intraoral radiography with the patient in supine position.

OBJECTIVE: The purpose of this study was to investigate the spatial distribution of scattered radiation during intraoral radiography with the patient in a supine position to determine the exposure to an operator without a suitable barrier. STUDY DESIGN: A phantom was placed in the supine position on a dental chair with the occlusal plane perpendicular to the floor, and four intraoral periapical radiographic examinations in the anterior and posterior regions of the maxilla and mandible were performed. The scattered radiation was measured with an ionization chamber at distances ranging from 25 to 200 cm at 25 cm increments and at intervals of 45 degrees. Measurements were made at two different heights: level with the occlusal plane and 30 cm below it. The exposure was converted to an air-kerma/absorbed dose in air. RESULTS: The distribution of scattered radiation was symmetric during examinations of the anterior region. Circular iso-exposure curves of up to 0.5 microGy were observed at the level of the occlusal plane, and curves of up to 0.1 microGy were observed 30 cm below the plane. The lowest exposures were measured 30 cm below the occlusal plane and behind the chair. The distribution of scattered radiation was not symmetric during examinations of the posterior region. Iso-exposure curves of up to 0.25 microGy were observed at the level of the occlusal plane during exposure of the maxilla, and curves of up to 0.5 microGy were observed during exposure of the mandible. Circular iso-exposure curves of up to 0.1 microGy were observed 30 cm below the occlusal plane. Lower values for scattered radiation were observed 30 cm below the occlusal plane between 135 and 180 degrees behind the phantom. CONCLUSION: The spatial distribution of scattered radiation with the patient in a supine position was not the same in eight directions around the chair. Although the preferred position for the operator is behind a suitable barrier, the preferred position in the absence of a barrier is 200 cm behind the patient.

Sensitometric effects of varying the intensifying screens used with Agfa Dentus ST8G and RP6 panoramic radiographic films.

OBJECTIVES: To compare the sensitometric effects and information yield of varying the intensifying screens used with both Dentus ST8G and RP6 Agfa Gevaert, Dormagen, Germany panoramic radiographic films. MATERIAL AND METHODS: Four screen-film combinations were employed for each of the two film types. The screens used were blue fluorescing PX-III (Kasei Optonix, Tokyo, Japan) and Special (Siemens AG, Bensheim, Germany), as well as green fluorescing Lanex Regular (Eastman Kodak, Rochester, NY, USA) and Trimax T16 (3M, Mineapolis, Minnesota, USA). The density response for each screen-film combination was evaluated using the characteristic curves generated. Information yield, as determined by the radiographic detection of defects in an aluminium test object, was evaluated by nine observers. RESULTS: The characteristic curves for ST8G were different when green and blue fluorescing screens were used; however, those for RP6 varied little irrespective of the choice of intensifying screens. Observers were able to perceive defects at significantly lower radiation exposures for ST8G combined with green fluorescing screens compared with blue emitting screens. RP6 with all screen combinations provided similar image detail perceptibility at comparable exposures with ST8G with green-fluorescing screens. CONCLUSIONS: RP6 is suitable for use with either the spectrally matched blue emitting screens or green-emitting screens. ST8G radiographic film should always be matched to rare earth screens.

Evaluation of XD/A Plus and ST8G films for cephalometric radiography with Grenex G8 and BH-III screens.

OBJECTIVES: Sensitometric properties, clinical image quality, and patient dose requirements are important considerations when selecting film for cephalometrics. Two recently released films, XD/A Plus and ST 8G green sensitive films, were studied. METHODS: The films were each combined with Grenex G8 (Fuji Medical) green-fluorescing matched and BH-III (Kasei Optonix) blue-fluorescing mismatched intensifying screens. The density response and resolution for each screen-film combination were evaluated by use of the characteristic curve and modulation transfer function. The kilovoltage settings providing clinically acceptable images were assessed individually by 12 observers. Clinically acceptable images for each combination were also compared, and the skin entrance doses in the temporomandibular joint region were determined. RESULTS: The average contrast at the most effective density range was found to be slightly higher for the BH-III group than for the G8 group. The modulation transfer function for the BH-III group was inferior to that for the G8 screens. There were no significant differences in diagnostically acceptable image quality among the four combinations; nevertheless the BH-III screen group required two to three times more exposure than the G8 screen group. CONCLUSIONS: XD/A Plus and ST8G films provide acceptable image detail for cephalometrics. To minimize the patient dose they should be used with green-emitting screens.