Effects of rare-earth filters on patient exposure and image contrast

Minimizing patient exposure while maintaining a diagnostically acceptable radiograph is a major goal in diagnostic radiography. Rare-earth filters may be the means to achieve this goal due to their "band-pass effect". The purpose of this study was to examine the image contrast effects and exposure reductions for various thicknesses of aluminum, samarium, gadolinium, gadolinium oxysulfide, and gadolinium oxysulfide added to 2.5 mm of aluminum. Trials were conducted on an intra-oral dental x-ray unit (range, 65 to 90 kVp). When compared with conventional aluminum, all of the rare-earth filters provided lower radiation exposures, with gadolinium in the metallic or oxysulfide form providing the lowest exposures. Samarium, at a thickness of 0.127 mm, yielded the highest image contrast. Gadolinium or gadolinium oxysulfide added to 2.5 mm of aluminum resulted in a slight loss of contrast when compared with conventional aluminum filtration. This loss may not be clinically significant, and when coupled with the reduced exposure afforded by these filters, they become viable as acceptable alternatives to aluminum filtration.     

Beam quality and image contrast with VIXA-2

Purpose Current CCD-based intraoral radiographic systems permit the use of any dental X-ray generator. As a consequence, beam quality can be altered. This study was carried out to investigate studied the effects of varying beam quality on the VIXA-2 image contrast (Gendex Dental Systems srl Milan, Italy). Methods Images were made of a standard aluminum stepwedge and the pixel value of each step was measured. An optical bench was used to standardize geometric projection. Soft-tissue equivalent attenuation was effected using 1.75 cm plexiglass. Exposures were made at 2–48 impulses using 50–90 kVp settings at 10 kVp intervals. Exposures (μC/kg) were determined using a beryllium-windowed ionization chamber. Results The pixel values for each step decreased both with increased exposure (μC/kg) and with increased kVp. The relationship between exposure and pixel value was not linear. The longest scale of contrast was obtained at 17.3, 15.2, 13.5, 11.7, and 11.3 μC/kg respectively at 50, 60, 70, 80, and 90 kVp. The gradient for pixel values along the steps was steeper at lower kVp settings than at higher kVp settings. Conclusions The VIXA-2 can be operated at a wide range of kVp settings. Gamma conversion inherent in the VIXA-2 creates wide variations in the pixel values for different stepwedge thicknesses.     

The effects of beam quality and optical density on image quality in dental radiography

The literature relating to the choice of beam quality in dental radiography is reviewed. Twenty observers were asked to select radiographs of a test object at different beam qualities and densities. The same observers were asked to identify numbers of circular areas of small density differences in zones of high and low density. Subjectively, the observers favored radiographs produced with lower beam energies; 90 kVp aluminum filtration and 3.5 mm was least popular, and 70 kVp with 2.5 mm aluminum was most popular. Objectively, there was little difference in the success of identification between the beams of different energies. Masking of radiographs improved success apart from the low density zones in less exposed radiographs. Little evidence has been found within the range investigated for selecting one beam quality over another, other than subjective preference. However, low beam energies should be avoided because of reduced emulsion sensitivity.     

The use of added erbium filtration in intraoral radiography

Using D and E speed film, intraoral exposures were made of a phantom at 70 and 90 kVp, with and without erbium filtration. Measurement of surface exposures indicates substantial reduction when erbium filtration was used. However, there was a visible loss of contrast. The raters agreed that radiographs made with E speed and D speed film, both with and without erbium filtration, were all of adequate diagnostic quality. The radiographs with the highest contrast were consistently preferred by all of the raters.     

Effects of aluminum-copper alloy filtration on photon spectra, air kerma rate and image contrast

This study evaluated the performance of aluminum-copper alloy filtration, without the original aluminum filter, for dental radiography in terms of x-ray energy spectrum, air kerma rate and image quality. Comparisons of various thicknesses of aluminum-copper alloy in three different percentages were made with aluminum filtration. Tests were conducted on an intra-oral dental x-ray machine and were made on mandible phantom and on step-wedge. Depending on the thickness of aluminum-copper alloy filtration, the beam could be hardened and filtrated. The use of the aluminum-copper alloy filter resulted in reductions in air kerma rate from 8.40% to 47.33%, and indicated the same image contrast when compared to aluminum filtration. Aluminum-copper alloy filtration may be considered a good alternative to aluminum filtration.     

A perceptibility curve comparison of Ultra-speed and Ektaspeed Plus films

Objective. The purpose of this study was to evaluate the subjectively assessed contrast difference between Kodak's Ultra-speed and Ektaspeed Plus dental radiography films (Eastman Kodak, Rochester, N.Y.) through the use of perceptibility curves.Design. Four series of 22 radiographs were exposed at 70 and 90 kVp with each film type by means of a Gendex 1000 dental radiography unit (Gendex Corp., Milwaukee, Wis.) for times ranging from 0.05 to 5 seconds at 10 ma. The test object consisted of a 7-mm-thick rectangular aluminum block with 10 circular depth cuts, each 2 mm in diameter, which created wells varying in depth from 50 to 500 microns. The corresponding films were processed concurrently (for 4.5 minutes) in total darkness with fresh Kodak Readymatic solutions (Eastman Kodak) held at a constant temperature of 28° C. The resulting radiographs were viewed in a predetermined random order under ideal conditions by 10 dentists. The evaluators recorded the maximum number of perceptible images on each film. A pair of perceptibility curves were generated at 70 and 90 kVp by plotting the log relative exposure versus the mean number of perceptible images.Results. There was no statistical difference between the two film types with respect to the mean number of perceptible images, as analyzed by Wilcoxon's signed rank test (p = 0.22; p = 0.44).Conclusions. There is no subjectively assessed contrast difference between Kodak's Ultra-speed and Ektaspeed Plus films at 70 and 90 kVp.     

KVP meter errors induced by plastic wrap

The purpose of this study was to determine whether erroneous kVp meter readings, induced by plastic wrap, affected the actual kVp (output) of a dental X-ray machine. To evaluate the effect of plastic wrap on dental X-ray machine kVp meters, a radiation output device was used to measure output in mR/ma.s. An intraoral dental X-ray unit (S.S. White Model #90W) was used to make the exposures. First, the kVp meter was not covered with plastic wrap and output readings were recorded at various kVp settings with the milliamperage and time held constant. Secondly, the same kVp settings were selected before the plastic wrap was placed. Milliamperage and time were again held to the same constant. The X-ray console was then covered with plastic wrap prior to measuring the output for each kVp. The wrap possessed a static charge. This charge induced erroneous kVp meter readings. Out-put readings at the various induced kVp settings were then recorded. A kVp of 50 with no wrap present resulted in the same output as a kVp of 50 induced to read 40 or 60 kVp by the presence of wrap. Similar results were obtained at other kVp settings. This indicates that the plastic wrap influences only the kVp meter needle and not the actual kilovoltage of the X-ray machine. Dental X-ray machine operators should select kVp meter readings prior to placing plastic wrap and should not adjust initial settings if the meter is deflected later by the presence of wrap. The use of such a procedure will result in proper exposures, fewer retakes, and less patient radiation. If plastic wrap leads to consistent exposure errors, clinicians may wish to use a 0.5% sodium hypochlorite disinfectant as an alternative to the barrier technique.     

Frequent, low-dose, improved-contrast radiographic images with the use of narrow x-ray beams.

Conventional dental radiography uses 60 mm-wide x-ray beams that irradiate the cheeks. To reduce the dose of radiation, months or years can separate serial films and prevent short-term assessment of disease activity. A technique that uses a 13 mm narrow x-ray beam that avoids the cheeks was compared with a wide x-ray beam by using a contrast phantom, a cheek substitute, and a serially sectioned dry mandible. Phantom contrast was measured densitometrically at 50 kVp, 65 kVp, and 90 kVp with wide x-ray beam and narrow x-ray beam and with and without cheek scatter. The narrow x-ray beam without cheek scatter technique resulted in better contrast (0.06 to 0.04 OD) than the wide x-ray beam with cheek scatter (0.05 to 0.02 OD). A posterior interdental crest was irradiated and a trabecular rod was removed. The bone detail was best in the images produced with the narrow x-ray beam without cheek scatter. The area of the narrow x-ray beam was 4.35% of the area of the wide x-ray beam with approximately 5% of the dose. Short-interval (weekly), very-low-dose radiography should be possible with improved contrast to assess alveolar bone changes.     

Quantitative Performance Characterization of Radiation Dose for the Carestream CS9600 Cone-Beam Computed Tomography Machine

IntroductionCone-beam computed tomography (CBCT) machines produce relatively low levels of harmful ionizing radiation, as compared with the computed tomography devices used in medical practices. The Carestream CS9600 CBCT imaging device has been recently introduced into the marketplace, and the manufacturer reports the use of an increased x-ray tube voltage (120 kVp) for the device, along with a reduced patient dose that is achieved using added filtration. Independent dosimetry studies are performed to ensure appropriate radiation exposure dose levels are within recommended safety guidelines.The purpose of this study is to independently evaluate and measure the radiation exposure dose performance parameters of the CS9600 CBCT, including its multiple field of view, exposure settings, and filtration options.MethodsA thimble ionization chamber and PMMA phantom were used to characterize dose index using the established SEDENTEXTCT evaluation method.ResultsThe phantom-obtained radiation dose index measures ranged from 0.128782–13.848 milligrays (mGy) for the various scanning options evaluated. The field of view, type of filter used, and phantom size all had a direct impact on the relationship between the experimentally obtained dose index measures and the dose area product values reported by the manufacturer.ConclusionsA strong linear correlation was observed between the experimentally obtained dose index measures and the manufacturer-reported dose area product values. The 0.7 mm Cu filter that has been added to the CS9600 reduced the exposure dose index measures even with the x-ray tube kilovoltage peak (kVp) being increased to 120 kVp, as compared with the 0.15 mm Cu filter at 90 kVp.     

A laboratory evaluation of Ektaspeed Plus dental X-ray film

Objectives: The aim of this study was to make a laboratory evaluation of the image quality of a new dental X-ray film, Ektaspeed Plus, compared with Ektaspeed and Ultraspeed films.

Methods: Films of each emulsion type underwent a range of exposures at both 50 kVp and 70 kVp, and characteristic curves were constructed to give a comparison of fog, speed and contrast. Line pair and contrast detail test objects were used to assess the resolution of radiographs and the ability of the two film types to reproduce minor differences in subject contrast. The sensitivity of the emulsions to safelighting for a range of times was also tested.

Results: Ektaspeed Plus had the same speed, a slightly higher base plus fog density but a higher contrast (50 and 70 kVp) than Ektaspeed. The speed of Ektaspeed Plus was higher and the contrast similar to that of Ultraspeed film. Limiting resolutions of the three films were the same. There was a slightly better imaging of one contrast detail phantom with Ektaspeed Plus compared to Ektaspeed at 70 kVp only. All three emulsions were insensitive to recommended safelighting conditions.

Conclusion: The improved image contrast of Ektaspeed Plus may be more acceptable to dentists than Ektaspeed and lead to a greater acceptance of E-speed film, contributing to dose reduction.     

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.     

Detection of simulated osteoporosis in dog alveolar bone with the use of digital subtraction

The purpose of this in vitro study was to examine radiographic changes in dog alveolar bone during simulated osteoporosis (decalcification) and to determine the minimal amount of generalized bone loss that can be detected under optimal radiographic conditions with the use of digital subtraction. Five samples of dog maxillary alveolus were progressively decalcified at timed intervals with 0.1 N hydrochloric acid solutions. The percentage of calcium lost during each interval was quantified with calcium assays. Sets of four radiographs from each sample were exposed at 30 kVp and 50 kVp initially and after each decalcification interval. The radiographs were digitized and bone profiles (scan lines) were generated between images of lead markers. To suppress contaminating image noise each set of four profiles were superimposed and averaged on a pixel-by-pixel basis. The averaged profile from each stage of decalcification was subtracted from the averaged initial profile on a pixel-by-pixel basis, the mean profile intensity change for each decalcification stage calculated, and this mean change compared to the initial mean intensity to yield the percentage mean profile intensity change for each sample for each decalcification stage. Statistical analysis was performed with repeated measures analysis of variance. Results indicate that generalized decalcification of less than 7.5% was detected in all samples of dog maxillae with exposures of 30 kVp and that generalized decalcification of less than 19% was detected with exposures of 50 kVp.     

Evaluation of Niobi-X filtration in intraoral radiology.

This investigation studied the effect of adding niobium filtration to the dental x-ray beam assessing reduction in patient x-ray exposure and changes in image quality. Clinical radiographs were made with the use of D- or E-speed film with either aluminum or aluminum plus 25 microns or 30 microns of added niobium filtration. Similar exposures were made on a head phantom, measuring the absorbed dose to radiosensitive sites in the head and neck. Results indicated that the addition of 25 microns or 30 microns of niobium filtration does not significantly degrade the subjective image quality of diagnostic radiographs when D-speed film is used. With E-speed film, however, the addition of niobium filtration significantly degrades the diagnostic image quality. The addition of niobium filtration results in a 20% to 30% reduction in patient dose. We conclude that the use of niobium filtration with D-speed dental film is a positive contribution to patient care.     

Effect of mAs and kVp on resolution and on image contrast.

Two clinical experiments were conducted to study the effect of kVp and mAs on resolution and on image contrast percentage. The resolution was measured with a "test pattern." By using a transmission densitometer, image contrast percentage was determined by a mathematical formula. In the first part of the experiment, the density of the film was kept constant by changing the kVp and mAs. In the second part of the experiment, different mAs's were chosen, and for each mAs, several kVp's were used. Five observers read the radiographs. The first experiment showed that, when the film density is kept constant, the higher the kVp, the lower the resolution and image contrast percentage; also, the higher the mAs, the higher the resolution and image contrast percentage. The second experiment showed that when the film density is not kept constant, the correlation between kVp and resolution and between kVp and image contrast percentage was the same as in the first experiment. However, there was negligible correlation between mAs and resolution and between mAs and image contrast percentage. A high positive correlation was found between resolution and image contrast percentage, but a high negative correlation was found between resolution and film density.     

Image quality in digital radiographic systems

The aim of the present study was to evaluate the image quality of four direct digital radiographic systems. Radiographs were made of the maxillary central incisor and mandibular left molar regions of a dry skull, and an aluminum step-wedge. The X-ray generator operated at 10 mA. 60 and 70 kVp, and images were acquired with 3, 5, 8, 12, 24 and 48 exposure pulses. Six well-trained observers classified the images by means of scores from 1 to 3. Collected data were submitted to nonparametric statistical analysis using Fisher's exact test. Statistical analysis showed significant differences (p < 0.01) in image quality with the four systems. Based on the results, it was possible to conclude that: 1) all of the digital systems presented good performance in producing acceptable images for diagnosis, if the exposures of the step-wedge and the maxillary central incisor region were made at 5 pulses, as well as at 8 pulses for the mandibular left molar region, selecting 60 or 70kVp; 2) higher percentages of acceptable images were obtained with the administration of lower radiation doses in CCD-sensors (charge-coupled device); 3) the Storage Phosphor systems produced acceptable images at a large range of exposure settings, that included low, intermediate and high radiation doses.     

Variations in film exposure, effective kVp, and HVL among thirty-five dental x-ray units

Speed group "E" dental films were exposed in thirty-five dental x-ray units and processed under rigidly controlled conditions. The exposure, in milliroentgens required to produce an overall film density between 0.85 and 1.05 density units at the 9 mm. step of an aluminum step-wedge, ranged from 94 to 186 mR. The wide range in normalized exposure required to produce a standard density of 1.0 was associated with half-value layer and effective operating kilovoltage in only a general way. The half-value layer of thirty-five dental x-ray units ranged from 1.9 to 2.9 mm. Al, and their effective operating kilovoltages ranged from 62 to 77 kVp when units were set at 70 kVp. The exposure required to produce a specific radiographic density depended largely on the individual characteristics of the x-ray unit used.     

Pixel value modification using RVG-4 automatic exposure compensation for instant high-contrast images

The RVG-4 permits automatic exposure compensation (AEC). The purpose of this investigation was to determine the effects of AEC on image contrast. Images were made either with or without a dental QA jaw phantom using a fixed image projection geometry. Exposures were 6.3 through 27.3 μC/kg using an X-ray generator operated at 70 kVp. Region of interest pixel value distributions were measured at tissue thicknesses in this phantom, and the average pixel values and signal-to-noise ratios (SNR) were calculated. The use of AEC without an object in place resulted in a disproportionate relationship between pixel value and exposure with a marked reduction in SNR. The use of AEC on under- and over-exposed images of the phantom simultaneously enhanced image contrast and reduced SNR. Thus, AEC provides a convenient and quick method for achieving high-contrast images with sub-optimal exposures, however, this could lead to inappropriate patient dosages if the function is used for over-exposed images. AEC reduces the SNR and produces disproportionate pixel values relative to exposure.     

Radiation dose-reduction techniques in North American dental schools

OBJECTIVE: The purpose of this investigation was to describe the extent to which dental schools use materials, equipment, and quality-assurance protocols that reduce radiation exposure to patients. STUDY DESIGN: Questionnaires soliciting information regarding intraoral and extraoral radiographic practices and quality-assurance procedures were sent to the directors of oral and maxillofacial radiology (OMR) at the 65 schools of dentistry in the United States and Canada. RESULTS: The response rate was 100%. E-speed film is used at 86% of institutions. Direct digital radiography is used at 58% of institutions for intraoral imaging and 11% for extraoral radiography. Other dose-reducing techniques include long source-film distances (88%), rectangular beam limitation (47%), leaded aprons (95% for extraoral films; 85% with thyroid collars for intraoral films), and rare earth intensifying screens (100%). The most commonly used tube potential is 70 kVp (88%). The director of OMR is solely responsible for radiographic policies at approximately 75% of institutions. Regular tests for film fog, speed, and contrast are done at roughly 75% of schools, while over 90% test darkroom lighting and x-ray equipment. CONCLUSIONS: Some dose-reducing strategies are commonly used in dental schools, while others have not gained wide acceptance.     

E-speed dental films processed with rapid chemistry: a comparison with D-speed film

Image quality of E-speed film processed in four rapid chemistry solutions was evaluated and compared to that of D-speed film. One-hundred-twenty films (60 E-speed and 60 D-speed) were exposed with the use of a quality-control phantom and processed in four different rapid solutions. The images were evaluated for speed, contrast, fog and base, resolution, and granularity, and the useful lifetime of the solutions was determined. E-speed film processed with rapid chemistry produced images equal in quality to D-speed film in the range tested (70 to 90 kVp). Fog and base levels of E-speed film were greater than those of D-speed film. The resolution and granularity of the images were equal and were judged adequate in both film types, regardless of the chemistry used. Rapid processing solutions were found to have a 10% to 15% shorter useful lifetime with E-speed film than with D-speed film. The processing of E-speed film in rapid chemistry is recommended for emergency care and endodontics.     

Radiopacity of tantalum oxide nanoparticle filled resins.

OBJECTIVES: Radiopacity of composite resins allows radiographic distinction of existing restorations and recurrent caries. Current composites must be supplemented with heavy metal-containing glasses or minerals to achieve a desired radiopacity. The purpose of this study was to evaluate the radiopacity of Tantalum oxide (Ta2O5) filled resins at varying percentage loadings. METHODS: Methacrylate functionalized Ta2O5 nanoparticles (< 50 nm) in methanol-dissolved or powder forms were mixed into either glycerol dimethacrylate (GDMA) or a bisGMA, TEGDMA, bisEMA mixture (GTE). Specimens were made in a split brass mold (2 x 2 x 15 mm) and compared with an aluminum stepwedge (99.5% pure Al) and a dentin slice of the same thickness. Kodak Ultraspeed periapical X-ray film on a lead plate at a target distance of 45 cm was exposed at 70 kVp and 10 mA, for 0.5 s and processed automatically. Optical density was measured (n = 3) with an RMI Processor Control Densitometer. Radiopacity was calculated as percent relative linear attenuation coefficient (Alpha). ANOVA and Student-Newman-Keuls comparisons were used to determine significance at the 95% confidence level. RESULTS: Radiopacity increased significantly with Ta2O5 loading (p = 0.001). Ta2O5 nanoparticle filled resins enter the optimal range of diagnostic detectability (alpha = 150-250) at 50 wt.% and approach equivalence with enamel at approximately 70 wt.%. SIGNIFICANCE: The introduction of tantalum oxide nanoparticle filler has potential as a miscible component of a resin composite to provide radiopacity for microfiller-type restorative materials and to circumvent the need for hydrolysis-prone glass reinforcing fillers.