Charge-coupled device panoramic radiography: effect of beam energy on radiation exposure

OBJECTIVE

To determine the consequences for entrance exposure of varying the beam energy and operating current for panoramic radiography using a charge-coupled device receptor.

MATERIAL AND METHODS

Images were made of a RANDO average man phantom (Alderson Research Laboratories, Stamford, CT) at kVcp settings of 60, 66, 70 and 80 and an mA of 2.0, 3.2, 6.4 and 10.0. The exposure cycle was set as recommended by the manufacturer at 17.6 s. Diagnostic image quality was rated by a panel of two oral and maxillofacial radiologists and one oral and maxillofacial pathologist. Entrance exposures were assessed using a 3 cc ionization chamber placed at the beam entry points while imaging the molar, premolar, and anterior teeth both using the DigiPan (Trophy Radiologie, Vincennes, France) CCD receptor and conventional T-Mat G film/Lanex Regular screens (Eastman Kodak, Rochester, NY, USA).

RESULTS

Acceptable image quality was attained with combinations of 60 kVcp and 3.2, 6.4 or 10 mA, 70 kVcp and 2.0, 3.2 or 6.4 mA; at 80 kVcp irrespective of the mA it was unacceptable. The maximum reduction in entrance dose was 77%, averaged over the three sites, at 70 kVcp and 2 mA.

CONCLUSION

The DigiPan receptor produces satisfactory images with saving in entry exposure saving of approximately 70% when compared with a conventional film/rare earth screen combination.

Tissue radiation dosages using the RVG-S with and without niobium filtration

Tissue doses for a modified Rando head- and-neck phantom were measured for imaging with speed group E film with standardized aluminium filtration and the RVG-S both with and without added niobium filtration. Cylindrical holes drilled into the phantom's tissue-equivalent material permitted the placement of a small ionization chamber into anatomically correct sites representing the thyroid, parotid, submandibular and sublingual glands. To establish the necessary cone positions, angulations and time settings for each exposure, diagnostically acceptable images of six teeth, representative of different intraoral regions, were made for a DXXTR mannequin. Entrance and exit points were marked and transferred to the phantom to allow reproducible repeat exposures. The RVG-S provided reductions in average skin entrance dose of 31 per cent to 39 per cent with standard aluminium filtration and 51 per cent to 60 per cent with the addition of niobium filtration to attenuate the beam. While dose reductions relative to E-speed film usage were found for deep tissue sites, these were site and projection specific. The cumulative reduction from use of the RVG-S without niobium filtration was 32 per cent. It was 42 per cent with additional niobium filtration. It should be noted, however, that adding niobium filtration resulted in increased dosages to the deeper soft tissues such as the thyroid gland.

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.

The OP 100 Digipan: evaluation of the image layer, magnification factors, and dosimetry

OBJECTIVES

The purpose of this study was to describe the Orthopantomograph OP 100 Digipan modification and to determine the image-layer and dosimetric characteristics of this system.

RESEARCH DESIGN

Image-layer contours for the Digipan were determined at resolution limits of 4.0, 3.0, and 1.5 line pairs (Ip) mm(-1) using a resolution grid positioned at intervals along the beam projection paths. A hexagonal test device was placed above the grid to determine the magnification factors at the selected resolution limits. For dosimetry, a 30 mm2 ionization chamber was placed at the beam entry points while imaging the molar, premolar, and anterior teeth using both the Digipan and conventional film receptors.

RESULTS

The maximum resolution exceeded 4.0 Ip mm(-1)in the center of the image layer. Using a 1.5 Ip mm(-1) resolution limit, the focal trough width was 14 mm at 0-degree horizontal angulation, 20 mm at 37 degrees, and 36 mm at 83 degrees. At 1.5 Ip mm(-1), the horizontal magnification was -21% facial and +42% lingual to the center of the image layer in the incisor region; -25% facial and +19% lingual to the center of the image layer at a horizontal angulation of 83 degrees. At 4.0 Ip mm(-1), horizontal magnifications in the incisor region were -2.0% facially and +0.5% lingually; at 83 degrees they were -3.9% facially and +1.1% lingually. The neck entrance dose for imaging the anterior and premolar regions averaged 89.5 (+/-5.6) microGy. The cheek entrance doses for imaging the molar region averaged 220.6 (+/-8.0)microGy with the Digipan. With film the average entrance doses were 297.9 (+/-8.6) microGy (anterior and premolar regions) and 682.1 (+/-16.9) microGy (molar region).

CONCLUSIONS

The Digipan image layer is similar, but slightly narrower than that previously reported for the Orthopantomograph OP 100 using standard film-screen combinations. The resolution at the center of the image layer exceeded 4.0 Ip mm(-1). The Digipan produced images with an entry dose savings of approximately 70% when compared with photo-timed exposures using conventional film with the Orthopantomograph OP 100.

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.

Measurement algorithm accuracy of the RVG-PCi in vertical and diagonal assessments at various beam energies

The Trophy RadioVisioGraphy model PCi was compared to Kodak Ektaspeed Plus film for accurate recording and estimation of the length of size 15 files placed vertically and diagonally across the receptor surface. Variations in kilovoltage (50, 70, and 75) and exposure were also factored. Eight observers estimated file lengths using the proprietary software measurement algorithm for the RVG-PCi and a millimeter rule for the film-based radiographs. Both modalities resulted in slight magnification for vertically oriented files; however, the RVG-PCi caused overestimation in the order of 6 to 8% with diagonally oriented instruments. Measurement interobserver variability was least when using the RVG-PCi. It was concluded that the proprietary software supplied with RVG-PCi is not sufficiently accurate for endodontic assessment. Furthermore, exposures above 0.15 s at 75 kVp resulted in pixel saturation resulting in apparent shortening of the instrument; hence, length calculations are particularly sensitive to overexposure when using the RVG-PCi.

Optical densities of dental resin composites: a comparison of CCD, storage phosphor, and Ektaspeed plus radiographic film

Density versus exposure was determined for digital and film radiographic images of various thicknesses of six dental resin composites. The curves were relatively parallel; saturation at the black end of the contrast scale occurred at lower exposures with Computed Dental Radiography (CDR, Schick Industries, Long Island City, NY) than with the Sens-A-Ray (Regam AB, Sundsvall, Sweden). Ektaspeed Plus film (Kodak Dental Products, Rochester, NY) was the least sensitive modality tested. The DIGORA storage phosphor system (Soredex-Orion, Helsinki) had a wide exposure latitude with significantly less steep characteristic slopes than for images from the charge-coupled devices (CCDs). Slopes generated for the Sens-A-Ray and the CDR were not significantly different. Slopes generated for each resin composite were not significantly different for each of the modalities. Relative radiopacities of the resin materials with respect to each other were constant across all modalities; hence, in these systems, sensor type is unlikely to affect differentiation between resin composites and dental enamel or recurrent caries.

Identification of the temporomandibular joint and adjacent cephalometric landmarks using a dual sensitivity screen-cassette system

OBJECTIVES

Clinical evaluation of a cassette with dual speed screens for cephalometric radiography.

METHODS

Two lateral cephalometric radiographs were taken on 20 consenting subjects using the TMJ Orthoceph Slimline Cassette System (TOSCS), incorporating circular Trimax 12 screens in the area adjacent to the temporomandibular joint, and a control cassette (Trimax 8 screens). Ten pairs of radiographs with optimal image quality were randomly presented to 10 observers trained in cephalometric interpretation. Observers rated the overall diagnostic quality of each radiograph and of the TMJ region on an ordinal scale. They then located specific landmarks and traced the TMJ anatomy using acetate overlays. Overlays were digitized by a single operator who repeated tracing placements and digitizations to determine the error of recording method. Landmark variability was compared in the x- and y-axis by the Wilcoxon matched-pairs signed ranks test (p < 0.05). Six repeat tracings were performed and assessed by percentage of repeated observations above the maximum affordable error. Fossa space values were analyzed by the coefficient of variation (CV). The variability of the angular and linear values was also compared.

RESULTS

TOSCS image quality was perceived as significantly better than the control. Method error was 0.34 mm in the x-axis and 0.4 mm in the y-axis. Interobserver variability was 2 to 3 times greater than intraobserver. There was less variability with TOSCS for identification of basion (x-axis), center-of-rotation (x-axis) and condyle (posterior) (x-axis). However, this was clinically insignificant. Accurate determination of the fossa space was not possible as CV varied from 23 to 84%. No differences in the variability of angular or linear values variability were found.

CONCLUSIONS

While observers preferred TOSCS, no significant clinical differences could be demonstrated between the two systems.

Technical note. Modulation transfer function analysis of a newly revised rotational panoramic machine

OBJECTIVES

To determine the modulation transfer function (MTF) and noise equivalent passband (NE) values for a newly revised rotational panoramic X-ray machine, the PC-1000 (Panoramic Corp., Fort Wayne, Indiana, USA).

METHODS

Images of a 10 microns test slit were taken at various locations along the X-ray beam projection path using a Lanex Regular/T-Mat G image receptor. Line spread functions were obtained at specific beam paths by scanning slit images with a microdensitometer.

RESULTS

MTF values were highest around the central plane of the image layer, with a maximum near the centre of 0.25 at 4 cycles/mm. The NE values near the central plane of image layer were 1.4 cycles/mm. MTF and NE values in the anterior region were low, 0.2 and 1.2, respectively. The width of the image layer was narrower in the anterior and wider in the posterior segments. Rapid decreases in MTF and NE values were found on the X-ray tube side compared with the receptor side of the central plane. Using a spatial frequency of 0.25 MTF the shape of the image layer was coincident with that determined visually.

CONCLUSION

On the basis of the MTF and NE values the image resolution produced by this machine is considered acceptable for panoramic dental radiography.

Observer differentiation of proximal enamel mechanical defects versus natural proximal dental caries with computed dental radiography

OBJECTIVES

Various models have been used to study the accuracy of imaging systems for detection of dental caries. This study compares the ability of dentists to detect mechanically created defects versus natural dental caries cavitations on the proximal surfaces of extracted teeth with Computed Dental Radiography (Schick Industries, Long Island City, N.Y.). Detection rates are investigated according to lesion depth to permit comparisons to be made between studies in the literature with other mechanical defects or natural caries models. Discrimination of natural caries versus artificial defects with Computed Dental Radiography is also compared with a previous report that used standard dental film.

STUDY DESIGN

Fifty-two extracted molar and premolar teeth were mounted into representative sets of maxillary and mandibular posterior arches for bite-wing radiography. There were 16 proximal surfaces with natural caries and 28 proximal surfaces with mechanical defects. An optical bench was used to ensure constant beam geometry. A 1.8 cm acrylic soft tissue equivalent attenuator was placed in front of the receptor. Thirty dentists acted independently as observers to differentiate between sound proximal tooth surfaces, natural dental caries, and mechanical defects. Evaluation of intra- and interobserver variability was made with use of the kappa statistic. The Zelen test of odds ratios was used to test for homogeneity, and the Mantel-Haenszel analysis plus stratified logistic regression were used for inference about the common odds ratio. Significance was set at p < 0.05.

RESULTS AND CONCLUSIONS

Ignoring stipulation of cavity type, detection was 74% for mechanical defects and 67% for natural caries. The odds of detecting a mechanical defect were 1.40 times the odds of finding natural dental caries cavitation of the same depth. Lesion depth did influence the probability of correctly identifying the presence of a lesion; the odds of identifying cavitation increased 1.41 times with every 0.1 mm increase in lesion depth. Correct designation of lesion type was 1.42 times more likely with mechanical defects than with natural caries (p = 0.003). Intraobserver (kappa = 0.65) and interobserver (kappa = 0.43) agreements were fair to good. Discrimination between natural and artificial lesions was less with the Computed Dental Radiography than that found in our previous study with standard direct emulsion x-ray film.

Technical report. Processing to achieve high-contrast images with computed dental radiography

OBJECTIVES

To determine the effects of equalization on image contrast and signal-to-noise ratio (SNR) with Computed Dental Radiography (CDR).

METHODS

Pixel value distributions were measured for various tissue thicknesses of a dental quality assurance jaw phantom and the average pixel values and SNR calculated.

RESULTS

Equalization resulted in enhanced image contrast of underexposed images by effecting pixel value adjustment with little change in SNR. Overexposed images demonstrated minimal difference in contrast or SNR when equalization was applied.

CONCLUSION

The equalize function of CDR is a convenient method to provide high-contrast images from underexposed images without detriment to the SNR. As it does not compensate for overexposure, the function will not lead to inappropriate overdosage of the patient.

Optimum exposure ranges for computed dental radiography

OBJECTIVE

Computed dental radiography (CDR; Schick Technologies Inc, Lond Island City, NY, USA) can be used with any dental X-ray generator. The optimum exposure at various tube voltage settings was studied.

METHODS

Images were made of a dental QA jaw phantom and a standard aluminium stepwedge. Exposures were made between 50 and 90 kVp at 10 kVp intervals. Two contrast indices were calculated from the bone stepwedge pixel values: CI(1), the ratio between the highest and lowest pixel values, and CI(2), the difference between them.

RESULTS

Contrast indices were greatest at low kVp. The gradual decrease in CI(1) with increased exposure demonstrated that the optimum exposure range was always relatively wide. Maximum CI(2) values were found at exposures of 27, 17, 15, 11 and 9microC kg-1 at 50, 60, 70, 80 and 90 kVp, respectively, at the centre of the optimum exposure range. Pixel values for each aluminium step increased both with increased exposure and with increased kVp. The longest contrast scale was obtained at 11.0, 9.6, 8.7, 7.2 and 7.0 microC kg-1 at 50, 60, 70, 80 and 90 kVp. The steepest slopes were obtained either with thin aluminium steps or at low kVp.

CONCLUSIONS

CDR is a fast CCD-based system and is capable of operating at a wide range of kVp settings.

Effects of instruction on the knowledge, attitudes and beliefs of dental students towards digital radiography

OBJECTIVE

To investigate the effects of a course of instruction in intraoral digital radiology on the knowledge, attitudes and beliefs of dental students.

METHODS

A questionnaire was administered to dental students at two institutions with (UL) and without (MCG) formal instruction in digital dental radiology, investigating their understanding of the principles of digital radiography, their attitudes to its use in the near future, and on the timing and suitability of the topic in the undergraduate dental curriculum. Differences in the responses between preclinical and clinical students at the two institutions were statistically assessed.

RESULTS

The overall response rate was 66% (277) with rates of 52% (103) at MCG and 76% (174) at UL. UL students knew significantly more about digital radiography but they also had some significant misconceptions and differed in their perception of its future role. Most students (93%) believed that digital radiography should be included in the curriculum or offered as an elective course.

CONCLUSIONS

Dental students want digital radiology to be introduced into the dental radiology curriculum, regardless of whether it is examined or not. The teaching methods and content of such a course need careful consideration.

Low-cost teleradiology for dentistry

The performance of a low-cost teleradiology system was studied. The time needed for radiographic transmission between computers and the image integrity following transmission were measured. The image resolution was analyzed with a line-pair test chart. Images were transmitted through computers that had a video-processing board and a modem at both the transmission and receiving sites. Intraoral radiographs were captured with a black and white charge-coupled device camera. The time required for image transmission was less than 1 minute (46 to 56 seconds), an effective transmission speed of 1.73 kbyte/s (13.9 kbit/s). No changes were observed in pixel value distributions; hence, there was no loss of image detail. The maximal resolution of the system was 4 line-pairs/mm. The performance of the teleradiology system demonstrated its potential as an effective, low-cost telenetwork for dentistry.

Sensitometric response of the Sens-A-Ray, a charge-coupled imaging device, to changes in beam energy

OBJECTIVES

To evaluate image density (pixel values) and image contrast due to variations in beam energy (kVp) for the Sens-A-Ray intra-oral radiographic sensor.

METHOD

Images of an aluminium step wedge were made at 50, 70 and 90 kVp. Mean pixel values (with standard deviations) for representative attenuator thicknesses were measured using region-of-interest histogram analysis. Corresponding entrance doses were measured using a beryllium-windowed ionization chamber.

RESULTS

The steepest response slopes were found with the lowest kVp settings; hence the CCD results mimic the behaviour of standard radiographic film, with the high contrast being found with low kVp. The entrance dose resulting in pixel saturation was less with low kVp than high kVp. It is suggested that this is due to the CCD receptor being most sensitive to X-ray photons of relatively low keV.

CONCLUSION

While the kVp needs to be selected in relation to both tissue and receptor characteristics, it is possible to use low kVp techniques with the Sens-A-Ray without increasing the entrance dosage.

Mechanical defects in dental enamel vs. natural dental caries: observer differentiation using Ektaspeed Plus film

The value of imaging modalities in enabling the observer to detect proximal dental caries has been tested previously using both natural carious cavitations and mechanical defects. This study compared the ability of dentists to detect mechanically created defects and natural dental carious cavitations on the proximal surfaces of extracted teeth, and to differentiate between the two. Detection rates according to lesion depth were also investigated. There was a difference in the ability of readers to detect natural proximal dental carious cavities and mechanical defects in the proximal enamel. The odds of detecting artificial cavities was 2.92 times the odds of diagnosing natural caries cavitations. There was great variation in the ability of the dentists to identify natural and artificial lesions. According to logistic regression, when the cavity depths are equal, the mechanical defects in the proximal dental enamel are easier to identify than are natural enamel dental caries cavitations. The odds ratio charts provided from this study show the depths of mechanical and natural lesions that are comparable in diagnostic challenge. These charts might permit rough approximations to be made when comparing previously published papers that variously use both mechanical defects and natural caries. Use of poorly designed in vitro models for testing can produce a false guide to the clinical performance of diagnostic systems.

Measurement accuracy: a comparison of two intra-oral digital radiographic systems, RadioVisiography-S and FlashDent, with analog film

OBJECTIVES

To compare the accuracy of measurement algorithms incorporated into the software provided with two CCD-based digital radiographic systems and compare assessments using intra-oral film.

METHODS

A test object with three radiopaque reference points was imaged using Ektaspeed intra-oral film, both with and without an overlaid 1 mm reference grid, the RVG-S, the measurement software of which overlays a 2 mm grid, and the FlashDent, which uses a mouse-driven cursor to estimate distances. Geometric factors, including source-to-object and receptor-to-object distances, vertical and horizontal cone angulation, and vertical angulation of receptor, were successively altered. Six viewers estimated vertical, horizontal and diagonal distances for each image.

RESULTS

Increased source-to-object distance resulted in a 5-10% reduction in image dimensions, whereas increased receptor-to-object distance produced a magnification of 15-20% with all techniques. Increased vertical and horizontal cone angulation resulted in slight increases in magnification (0-5%) whereas greater receptor angulation resulted in noticeable magnification under all test conditions (10-15%). Estimated values for vertical, horizontal and diagonal measurements were approximately 5-10% higher than the actual dimensions, irrespective of the technique used. The FlashDent mouse-driven cursor system and direct measurement of distances from conventional film were more accurate in horizontal and diagonal dimension estimates than using an overlaid grid. Intra-observer and inter-observer differences were found for specific situations.

CONCLUSION

The mouse-driven computerized measurement cursor and intra-oral film assessment using a ruler provided the most accurate, reliable and consistent dimensional measurements.

Perceptibility of defects in an aluminum test object: a comparison of the RVG-S and first generation VIXA systems with and without added niobium filtration

OBJECTIVE

To compare the first generation VIXA (Gendex, Milan, Italy) and the RVG-S (Trophy Radiologie, Vincennes, France) for detection of defects in an aluminium test object at various exposures both with and without added niobium filtration.

METHODS

Images of a 7 mm aluminium test object with defects ranging from 0.1 to 1.5 mm with standardized projection geometry. Seven dentists acted as observers. Perceptibility curves were developed for both sensors under the various filtration conditions and exposures.

RESULTS

At optimum exposures both the VIXA and the RVG-S permitted the same number of defects to be observed. The optimum exposures were similar for the two systems, but the dynamic range was greater for the RVG-S. Addition of niobium filtration did not appreciably alter the radiation dose required to perceive a given number of defects using either system.

CONCLUSIONS

The two systems performed equally at optimum exposure when the dose is approximately the same irrespective of the presence or absence of niobium filtration. Beyond the optimal level, the RVG-S outperformed the VIXA system.

Accuracy of dimensional and angular measurements from panoramic and lateral oblique radiographs

OBJECTIVES

Dimensional and angular measurements from radiographs can be used in clinical dentistry to determine the inclination of impacted teeth, the relative position of roots and restorative abutments, and for implant site assessment. This study was carried out to assess the in-vitro accuracy of such measurements obtained from three rotational panoramic systems and two standardized lateral oblique projections (45 degrees and 60 degrees) using two cephalometric systems.

METHODS

Acrylic test models with wires positioned to represent the position and angulations of the teeth were used. Ten images were taken with Oralix Pan DC/1, Panelipse and Orthophos panoramic machines. Fourteen lateral oblique radiographs were also taken using two cephalometric units: an Orthophos and a Quint Sectograph. The models were repositioned between each exposure. Horizontal, vertical and angular dimensions of every tooth position on each radiograph were measured by three evaluators and compared using ANOVA at an a priori significance level of alpha = 0.05.

RESULTS

Assessment of vertical dimensions was consistently more accurate on lateral oblique projections than on the panoramic radiographs. In general, the most accurate horizontal measurements could also be made with the lateral oblique projections. No differences in angular measurement accuracy were found between any of the projections. The use of statistical means and standard deviations can be misleading in ranking accuracy where a consistent conversion factor can be applied.

CONCLUSIONS

While panoramic radiography is convenient for dimensional and angular assessments, lateral oblique radiographs taken with a standard cephalometric apparatus are an alternative when greater clinical accuracy is needed.

A dual sensitivity screen system for TMJ image enhancement in cephalometric radiography: sensitometric evaluation

OBJECTIVES

An in vitro evaluation of the image quality of the TMJ OrthoCeph Slimline Cassette System (TOSCS).

METHODS

The density response, resolution and clarity of the system were evaluated by use of the characteristic curve, modulation transfer function and root mean square quantum mottle. Relative sharpness was evaluated qualitatively by five observers.

RESULTS

Increased density with Trimax 12 gave almost the same contrast as that with Trimax 8 in the diagnostic range, whereas MTF and RMS for Trimax 12 were inferior.

CONCLUSIONS

The dual-sensitivity screen system should lead to improved radiographic contrast of the TMJ region in cephalometric radiography. The reduction in sharpness is probably clinically insignificant.