Digital intraoral radiographic quality assurance and control in private practice.

At present, the American Dental Association and the American Academy of Oral Maxillofacial Radiology have guidelines for the dental environment that include quality assurance and control of film-based radiography. Approximately 19%-30% of US dental offices currently use some form of digital intraoral radiography, and growth is expected to continue. It is anticipated that new tools and guidelines will be needed to aid in the development of quality assurance (QA) and control of digital intraoral radiographic images.

Evaluation of image quality parameters of representative intraoral digital radiographic systems.

Objective: The aim of this study was to compare imaging properties of 20 intraoral digital systems objectively.

Study Design: Using a direct current x-ray source and a radiographic phantom, a series of radiographs was made from the lowest exposure time until the sensor saturated. Images were captured and stored.

Deriving Hounsfield units using grey levels in cone beam CT: a clinical application.

Objective: To present a clinical study demonstrating a method to derive Hounsfield units from grey levels in cone beam CT (CBCT).

Methods: An acrylic intraoral reference object with aluminium, outer bone equivalent material (cortical bone), inner bone equivalent material (trabecular bone), polymethlymethacrylate and water equivalent material was used. Patients were asked if they would be willing to have an acrylic bite plate with the reference object placed in their mouth during a routine CBCT scan.

Characterization and correction of cupping effect artefacts in cone beam CT.

Objective: The purpose of this study was to demonstrate and correct the cupping effect artefact that occurs owing to the presence of beam hardening and scatter radiation during image acquisition in cone beam CT (CBCT).

Methods: A uniform aluminium cylinder (6061) was used to demonstrate the cupping effect artefact on the Planmeca Promax 3D CBCT unit (Planmeca OY, Helsinki, Finland). The cupping effect was studied using a line profile plot of the grey level values using ImageJ software (National Institutes of Health, Bethesda, MD).

Quality assurance phantom for digital dental imaging.

Objective: The purpose of this research was to develop a simple quality assurance phantom that could be used for the initial calibration and follow-up testing of commercially available intraoral digital imaging systems.

Study Design: A radiographic phantom was constructed that contains a calibrated step wedge for measuring dose response, an etched pattern of slits in a metallic background for measuring the spatial resolution in line pairs per millimeter, and 2 rows of wells of varying diameter and depth in an acrylic background for contrast-detail analysis. Quality assurance protocols were developed and validated.

Pre-clinical evaluation of a new dental panoramic radiographic system based on tomosynthesis method.

Objectives: The purpose of the study was to compare the image generated by a classic panoramic machine equipped with a cadmium telluride sensor capable of digital tomosynthesis and special software with images produced by other popular panoramic X-ray machines using a charge-coupled device and native software for image capture.

Methods: Panoramic images were made using a phantom of a human skull on Planmeca ProMax, Planmeca EC Proline, Kodak 8000 and PC-1000. With the last machine we used the PanoACT® software to adjust the entire arch and to adjust the image in selected regions of interest (ROIs).

Deriving Hounsfield units using grey levels in cone beam computed tomography.

Objectives: an in vitro study was performed to investigate the relationship between grey levels in dental cone beam CT (CBCT) and Hounsfield units (HU) in CBCT scanners.

Methods: a phantom containing 8 different materials of known composition and density was imaged with 11 different dental CBCT scanners and 2 medical CT scanners. The phantom was scanned under three conditions: phantom alone and phantom in a small and large water container.

Development of a new dental panoramic radiographic system based on a tomosynthesis method.

The objective of this study was to develop a new practical method to reconstruct a high-quality panoramic image in which radiographers would be free from the onerous task of correctly locating the patient's jaws within the image layer of the panoramic unit. In addition, dentists would be able to freely select any panoramic plane to be reconstructed after the acquisition of the raw scan data. A high-speed data acquisition device was used with a CdTe (cadmium telluride) semiconductor detector and a sophisticated digital signal-processing technique based on tomosynthesis was developed.

Transtomography: a new tomographic scanning technique.

Objectives: To introduce and test a new tomographic technique, namely transtomography, making it possible to expose tomographic images employing the narrow beam of an advanced panoramic machine.

Methods: The working principle of the new technique is described. It combines a translational movement with a pendular movement of the beam that creates motion unsharpness analogous to that of conventional tomography.

Comparison of the psychophysical properties of various intraoral film and digital systems by means of the perceptibility curve test.

Objectives: To compare psychophysical properties of two intraoral films and three digital systems using the perceptibility curve (PC) test.

Materials And Methods: A test object was used to determine the exposures and exposure differences between the total thickness of the test object and details consisting of holes of increasing depth. The PCs for the two intraoral films, UltraSpeed and EktaSpeed Plus, were constructed employing exposure and exposure differences from dose response functions.

Evaluation of endodontic files in digital radiographs before and after employing three image processing algorithms.

Objectives: Two digital image processing algorithms, one aimed at correction for exponential attenuation and one at correction for visual response, have been developed. The aims of the present study were to test whether digital radiographs processed with these algorithms improve determination of the length of endodontic files and whether such processed radiographs are comparable with the radiographs processed with a default image processing method employed by one commercially available digital intraoral system.

Methods: A dried human skull embedded in an acrylic compound was used for exposing radiographs of the upper and lower premolars and molars with endodontic files (Kerr files size 10 and size 15) positioned to the full length of the roots or 1.

Perceptibility curve test for digital radiographs before and after correction for attenuation and correction for attenuation and visual response.

Objective: Two digital image processing methods, correction for X-ray attenuation and correction for attenuation and visual response, have been developed. The aim of the present study was to compare digital radiographs before and after correction for attenuation and correction for attenuation and visual response by means of a perceptibility curve test.

Material And Methods: Radiographs were exposed of an aluminium test object containing holes ranging from 0.

Determination of the resolution of a digital system for panoramic radiography based on CCD technology.

Objectives: To determine Line Spread Functions (LSFs) and Modulation Transfer Functions (MTFs) for a digital system for panoramic radiography: the Dimax I (Planmeca Oy, Helsinki, Finland) based on Charge-Coupled Device (CCD) technology.

Study Design: A test object was specially designed having a gold foil positioned vertically. Images of the gold foil created edge functions that were used to determine LSFs and MTFs.

Perceptibility curves for the Digora system.

Objectives: To construct perceptibility curves (PCs) for given calibration settings in order to define psychophysical properties of the Digora storage phosphor system and to evaluate the effects of automatic exposure correction (AEC) on the PCs.

Methods: The Digora system was calibrated at two exposures, 80 microC kg(-1) (high calibration) and 40 microC kg(-1) (low calibration). Since the grey levels displayed in the radiographs are adjusted by AEC, dose-response functions at high calibration were obtained using AEC on and off modes.

Visual linearization of the display of digital radiographs.

Objectives: To derive and test a method to linearize the visual response of the display of digital radiographs so that equal steps in gray levels will be perceived as equal steps in brightness.

Method: A mathematical analysis was performed and expressions for visual linearization were derived. Twenty-four test images were computer generated to confirm that visual linearization may be achieved.

Correction for attenuation and visual response in digital radiography.

Objectives: To derive a method to correct for the exponential attenuation adding visual linearization for digital radiography and to perform an experimental test to study effects on observer performance.

Method: A theoretical analysis was performed and expressions were derived to correct radiographic data for the attenuation. An experiment was performed exposing an aluminum step wedge with holes of increasing depths behind each step plus soft tissue simulation.

Detection of approximal caries in digital radiographs before and after correction for attenuation and visual response. An in vitro study.

Objective: To evaluate if digital compensation for exponential attenuation and the characteristics of the human visual system improves the diagnosis of approximal caries from digital radiographs.

Material And Methods: Forty premolar teeth were mounted in plaster blocks. Radiographs of the teeth were exposed with the Dixi digital intraoral system employing a Prostyle Intra dental X-ray unit (Planmeca Oy, Helsinki, Finland).

Conventional and predicted perceptibility curves for contrast-enhanced direct digital intraoral radiographs.

Objectives: To construct Perceptibility Curves (PCs) for contrast-enhanced digital intraoral radiographs.

Methods: Radiographs of a test object having holes of increasing depths were exposed using three digital systems, the CDR (Schick Technologies, Long Island, NY, USA), the Dixel (J Morita MFG, Kyoto, Japan) and the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). The radiographs were contrast-enhanced and PCs constructed in the conventional way using 10 observers.

Comparison of five methods for the derivation of spectra for a constant potential dental X-ray unit.

Objectives: To compare the diagnostic X-ray spectra derived by different methods for a constant potential dental X-ray unit.

Materials And Methods: Five methods of deriving X-ray spectra for a constant potential dental X-ray unit were compared: measurement by spectrometer using cadmium-zinc-telluride (CZT) detector, calculation by Monte Carlo simulation, calculation by two different, semi-empirical methods and estimation from transmission data. The dental X-ray set was a Heliodent MD unit (Sirona, Charlotte, NC, USA) operable at 60 or 70 kV.

An improved method for rapid objective measurement of gamma camera resolution.

An improved method for an easy, rapid measurement of the intrinsic spatial resolution of a gamma camera is presented. A simplified model was previously developed based solely on mean and standard deviation measurements taken from a region of interest in bar pattern images. This led to an estimate of the modulation transfer function and the full width at half maximum (FWHM) of a line spread function (LSF).

Modification and benchmarking of MCNP for low-energy tungsten spectra.

The MCNP Monte Carlo radiation transport code was modified for diagnostic medical physics applications. In particular, the modified code was thoroughly benchmarked for the production of polychromatic tungsten x-ray spectra in the 30-150 kV range. Validating the modified code for coupled electron-photon transport with benchmark spectra was supplemented with independent electron-only and photon-only transport benchmarks.

Measurement and validation of benchmark-quality thick-target tungsten X-ray spectra below 150 kVp.

Pulse-height distributions of two constant potential X-ray tubes with fixed anode tungsten targets were measured and unfolded. The measurements employed quantitative alignment of the beam, the use of two different semiconductor detectors (high-purity germanium and cadmium-zinc-telluride), two different ion chamber systems with beam-specific calibration factors, and various filter and tube potential combinations. Monte Carlo response matrices were generated for each detector for unfolding the pulse-height distributions into spectra incident on the detectors.

Using measured 30-150 kVp polychromatic tungsten x-ray spectra to determine ion chamber calibration factors, Nx (Gy C(-1)).

Two methods for determining ion chamber calibration factors (Nx) are presented for polychromatic tungsten x-ray beams whose spectra differ from beams with known Nx. Both methods take advantage of known x-ray fluence and kerma spectral distributions. In the first method, the x-ray tube potential is unchanged and spectra of differing filtration are measured.

Analysis of sensitivity and specificity of a new digital subtraction system: an in vitro study.

Objective: The purpose of this study was to compare a new digital subtraction system with conventional radiograph images for the detection of periapical and periodontal bone lesions.

Study Design: Periapical and periodontal bone lesions were simulated with cortical bone chips of varying sizes placed on a human dry mandible. Radiographic film images were acquired from varying projections and were subsequently digitized, registered, and subtracted.

Physical properties of a photostimulable phosphor system for intra-oral radiography.

Objectives: To determine physical properties of the Digora digital intra-oral radiographic system (Soredex Orion Corporation, Helsinki, Finland) for different calibration settings and beam energies.

Methods: The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of a slit. Noise power spectra (NPS) were determined from radiographs exposed to homogeneous radiation fields at 10, 50 and 100% of the calibration exposure for three tube potentials.