Photostimulable Phosphor Systems Research Articles

Effect of beam quality and readout direction in the edge profile on the modulation transfer function of photostimulable phosphor systems via the edge method.

Purpose: The objective of this study was to investigate the effects of (i) the difference in the beam qualities on the presampled modulation transfer function (MTF) using the edge method and (ii) the readout direction of the edge profile for the photostimulable phosphor (PSP) system. Approach: The International Electrotechnical Commission (IEC) defined a technique using the "radiation qualities based on a phantom made up of an aluminum added filter" (RQA). A general radiographic system with a tube voltage of 50kV and 9.7mm of additional aluminum filtration was used to conform the x-ray to the IEC-specified beam quality definition RQA3. Additionally, we employed two different beams with tube voltages of 60 and 70kV using a dental x-ray unit. The MTF was measured in the readout direction from low-to-high exposure regions and vice versa with respect to the scanning and subscanning directions of the PSP system. Results: The difference in the 50%MTF value for all directions between 60 and 70kV averaged less than . The 50%MTF of RQA3 was on average 0.2 lower than the value for 60kV for each direction. For all beam qualities, no difference was observed between the MTFs measured in the readout direction from the low-to-high exposure regions and vice versa. Conclusions: The MTFs, measured using the dental x-ray unit, were unaffected by the tube voltage, and they were slightly higher than those measured using the RQA3. Furthermore, the MTF was unaffected by the differences in the readout directions of the edge profile.

Effect of image acquisition parameters on the radiopacity of bulk-fill and nanocomposite resins

This study evaluated the radiopacity of 2 bulk-fill resins (SonicFill and Filtek Bulk Fill) and a nanocomposite (Filtek Z350 XT) resin compared with enamel, dentin, and aluminum as measured with different exposure parameters. Resin disks were radiographed together with a 1-mm human tooth section and an aluminum stepwedge, at exposure times of 0.2 and 0.32 s, and source-image (S-I) distances of 30 and 40 cm, using complementary metal oxide semiconductor (CMOS) and photostimulable phosphor systems. Grayscale values were measured using ImageJ software. Paired Student t tests were used to compare the effect of the receptor on grayscale values for each material. Analysis of variance was used to evaluate the effects of receptor, exposure parameters, and the resins on radiopacity. All resins exhibited greater radiopacity scores than enamel and were significantly different from each other. Filtek Z350 produced the lowest radiopacity values, whereas SonicFill produced the highest. The radiopacity values were higher on images acquired with CMOS receptors. Receptor type, exposure time, S-I distance, and material, as well as many interactions of these parameters, affected the radiopacity of the resins. The tested resins complied with ISO 4049. Exposure parameters and digital receptors affected their radiopacity.

History of Digital Detectors in Intraoral Radiography

The first digital sensor used in intraoral radiography, RadioVisioGraphy was introduced in 1987. It was based on the activity of a charged-Coupled Device (CCD) sensor. Later on, other digital sensors became commercially available, including the Digora featuring an imaging plate coated with photostimulable phosphor (PSP) in 1994 and the complementary metal-oxide semiconductorbased sensor, CDR active pixel sensor, in 1998. These technologies have recently undergone considerable improvement, and several dental clinics have switched from film-based systems to digital imaging. In the early days, digital sensors were considered inferior to film in clinical diagnostics, but according to recent research results, there is no longer any significant difference because of the improvement in performance. However, our latest research using a new evaluation method and a precise phantom model indicated some differences between the performance of CCD and PSP systems and further differences between PSP systems of different function and performance.

Accuracy of scanography using storage phosphor plate systems and film for assessment of mandibular third molars

The aim of this study was to compare the diagnostic accuracy of two digital photostimulable storage phosphor (PSP) systems and film for assessment of mandibular third molars before surgery. 110 patients were referred to have both their mandibular third molars removed. Each patient underwent a radiographic examination with scanography using either Digora (Soredex, Helsinki, Finland) and film or VistaScan (Dürr Dental, Beitigheim-Bissingen, Germany) and film in a randomized paired design. Two observers examined the following variables on the scanograms: bone coverage, angulation of the tooth in the bone, number of roots, root morphology and the relationship to the mandibular canal. In 75 of the pairs (Digora/film pair = 38 and Vista/film pair = 37) both third molars were eventually removed. During and after surgery the same variables were assessed, which served as reference standard for the radiographic assessments. The Wilcoxon signed-rank test tested differences in accuracy (radiographic compared with surgical findings) between Digora/film and between Vista/film. There was no statistically significant difference between the diagnostic accuracy of film and either of the two digital receptors for assessment of mandibular third molars before surgery (P > 0.05), although Digora obtained a higher accuracy than film. Scanography is a valuable method for examination of mandibular third molars before removal and the PSP digital receptors in this study were equal to film for this purpose.

A comprehensive in vitro study of image accuracy and quality for periodontal diagnosis. PART 1: The influence of X-ray generator on periodontal measurements using conventional and digital receptors

The aim of this study was the determination of image accuracy and quality for periodontal diagnosis using various X-ray generators with conventional and digital radiographs. Thirty-one in vitro periodontal defects were evaluated on intraoral conventional (E-, F/E-speed) and digital images (three indirect, two direct sensors). Standardised radiographs were made with an alternating current (AC), a high-frequency (HF) and a direct current (DC) X-ray unit at rising exposure times (20-160ms with 20-ms interval) with a constant kV of 70. Three observers assessed bone levels for comparison to the gold standard. Lamina dura, contrast, trabecularisation, crater and furcation involvements were evaluated. Irrespective X-ray generator-type, measurement deviations increased at higher exposure times for solid-state, but decreased for photostimulable storage phosphor (PSP) systems. Accuracy for HF or DC was significantly higher than AC (p < 0.0001), especially at low exposure times. At 0.5- to 1-mm clinical deviation, 27-53% and 32-55% dose savings were demonstrated when using HF or DC generators compared to AC, but only for PSP. No savings were found for solid-state sensors, indicating their higher sensitivity. The use of digital sensors compared to film allowed 15-90% dose savings using the AC tube, whilst solid-state sensors allowed approximately 50% savings compared to PSP, depending on tube type and threshold level.. Accuracy of periodontal diagnosis increases when using HF or DC generators and/or digital receptors with adequate diagnostic information at lower exposure times.

The use of high-resolution digital imaging technology for small diameter K-file length determination in endodontics

To assess the reliability of high resolution intra-oral photostimulable storage phosphor (PSP) and complementary metal-oxide semiconductor (CMOS) imaging systems for working length (WL) assessment of small K-files in narrow and curved root canals. Eleven narrow and curved canals from extracted molars were used as pre-test for sample-size calculation. Nineteen canals from four cadavers were used for endodontic length assessment in the final study. Small K-files (ISO size 6, 8, and 10) were introduced into the canals at prepared length. Digital intra-oral radiographs were obtained using high-resolution Vistascan PSP plates and Sigma M CMOS active pixel sensor with a DC X-ray tube at 70 kV, 7 mA, and 0.16 s. Both image series were assessed with and without use of a dedicated endodontic filter. Three observers measured WLs for comparison to the gold standards of a digital millimeter ruler. Multiple regression analysis of the dependent measurements revealed no significant influence of imaging sensor (PSP or CMOS, p = 0.34) and image processing (p = 0.97). For ISO file size, however, there was a significant difference (p = 0.08) at a level of 10%. Observers mostly underestimated lengths using PSP but overestimated them on CMOS. Almost all radiographic measurements (96-98%) were within 2-mm deviation, while 71% to 82% deviated within 1 mm. Dedicated filtering and sensor type did not influence the outcome of WL determination of small file sizes when using high-resolution imaging sensors. WL determination with ISO file 6 did show a significant difference compared to ISO 8 and 10 but mostly for deviations <1.5 mm.

The use of photostimulable phosphor systems for periodic quality assurance in radiotherapy

The fusion of radiological and optical images can be achieved through charging a photostimulable phosphor plate (PSP) with an exposure to a field of X- or gamma-rays, followed by exposure to an optical image which discharges the plate in relation to the amount of incident light. According to this PSP characteristic, we developed a simple method for periodic quality assurance (QA) of light/radiation field coincidence, distance indicator, field size indicators, crosshair centering, coincidence of radiation and mechanical isocenter for linear accelerators. The geometrical accuracy of radiological units can be subjected to the same QA method. Further, the source position accuracy for an HDR remote afterloader can be checked by taking an autoradiography of the radioactive source and simultaneously an optical image of a reference geometrical system.

Time and motion study: a comparison of two photostimulable phosphor imaging systems used in dentistry

To compare two photostimulable phosphor (PSP) dental radiographic systems in terms of time efficiency in making full mouth intraoral X-ray surveys (FMS). PSP systems compared were (1) DenOptix) (Kavo/Gendex, Des Plaines, IL) and (2) ScanX) (Air Techniques, Hicksville, NY). Twenty one FMS of a DXTRR) Manikin (Dentsply, Des Plaines, IL) were made with each of the systems. Time for each procedural step was determined using a stopwatch. Steps studied were: (1) plate erasure; (2) packaging; (3) positioning/exposure; (4) unpacking, loading processor, scanning; and (5) image transfer to virtual FMS mount. The first six test runs for each system were excluded to eliminate the learning curve period influencing results. An independent groups t-test was employed for statistical analysis. The a priori was set at P< or =0.05. The total time involved in producing a FMS was not proven to be statistically significant comparing DenOptix) and ScanX). The mean procedure time for DenOptix) was 31.2 min; for ScanX) it was 27.1 min. While the processing time with ScanX) (mean time: 3.9 min) was shorter than for DenOptix) (mean time =7.8 min), the opposite was true for the image transfer to FMS format with the time much shorter with DenOptix) using VixWin) software (mean time =2.0 min) compared with ScanX) using Vipersoft) (mean time =3.9 min). The differences between the systems for these two steps did prove to be statistically significant (P< or =0.05). Although the mean time to make a FMS was slightly shorter on average with ScanX) than DenOptix), this difference was not proven to be statistically significant (P>0.05) in terms of time efficiency in producing a FMS.

Bitewing examination with four digital receptors.

To evaluate recording errors and patient discomfort during bitewing examinations using four digital receptors. Seventy-eight patients had two bitewings taken on each side of the mouth with the intention of displaying the tooth surfaces from the distal surface of the canine to the distal surface of the most posterior molar, using four digital receptors, two charge-coupled device (CCD) and two photostimulable phosphor (PSP) systems. The patients scored their feelings of discomfort during the examination on a visual analogue scale. Receptor positioning errors in the sagittal plane were determined from the tooth surfaces present on each image and in the vertical plane from the presence of the alveolar bone crest. Cone positioning errors were determined from cone cuts. Canine and premolar surfaces were more often not depicted on the CCD images than on the PSP images (P<0.05). Cone cuts occurred in 19% of DenOptix images, in 9% of Digora images and in one Planmeca image. The bone crest was more often missing in the upper jaw on Planmeca images than on PSP images (P<0.01). In the lower jaw, Trophy images more often missed the bone crest than the other systems (P<0.05). Patients ranked the receptors as follows (with increasing discomfort): DenOptix, Planmeca, Digora and Trophy, with all being significantly different (P<0.05). It was more difficult to correctly position CCD sensors than PSP plates in the vertical plane, resulting in more images with missing alveolar bone crest. CCD sensors most often did not display the most anterior surfaces in a bitewing examination.

Precise image–receptor calibration and monitoring of beam quality with a step wedge

OBJECTIVE To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. METHODS Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. RESULTS The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. CONCLUSIONS The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.

Precise image-receptor calibration and monitoring of beam quality with a step wedge.

To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.

Subjective image quality of solid-state and photostimulable phosphor systems for digital intra-oral radiography

Subjective image quality of solid-state and photostimulable phosphor systems for digital intra-oral radiography

Comparison of a photostimulable phosphor system with film for dental radiology

This study compared the imaging performance of a photostimulable phosphor system with E speed film for dental radiography. The response of each imaging system was measured as a function of radiation exposure. Measurements were also made of imaging performance in terms of the limiting spatial resolution and low contrast detectability. Photostimulable phosphors had a wider dynamic range in comparison with film. The limiting spatial resolution of the photostimulable phosphor was approximately 6.5 lp/mm and independent of image magnification. For film, the limiting spatial resolution was in the range 11 to 20 lp/mm depending on image magnification. At the same radiation exposure, low contrast detectability of the photostimulable phosphor was superior to that of film. Major benefits of photostimulable phosphor systems include the elimination of chemical processing and an improved low contrast detectability performance.