Applying synthetic radiography to intraoral tomosynthesis: a step towards achieving 3D imaging in the dental clinic.

OBJECTIVES: A practical approach to three-dimensional (3D) intraoral imaging would have many potential applications in clinical dentistry. Stationary intraoral tomosynthesis (sIOT) is an experimental 3D imaging technology that holds promise. The purpose of this study was to explore synthetic radiography as a tool to improve the clinical utility of the images generated by an sIOT scan. METHODS: Extracted tooth specimens containing either caries adjacent to restorations (CAR) or vertical root fractures (VRF) were imaged by sIOT and standard dental radiography devices. Qualitative assessments were used to compare the conspicuity of these pathologies in the standard radiographs and in a set of multi-view synthetic radiographs generated from the information collected by sIOT. RESULTS: The sIOT-based synthetic 2D radiographs contained less artefact than the image slices in the reconstructed 3D stack, which is the conventional approach to displaying information from a tomosynthesis scan. As a single sIOT scan can be used to generate synthetic radiographs from multiple viewing angles, the interproximal space was less likely to be obscured in the synthetic images compared to the standard radiograph. Additionally, the multi-view synthetic radiographs can potentially improve the display of CAR and VRFs as compared to a single standard radiograph. CONCLUSIONS: This preliminary experience combining synthetic radiography and sIOT in extracted tooth models is encouraging and supports the ongoing study of this promising approach to 3D intraoral imaging with many potential applications.

Characterization and preliminary imaging evaluation of a clinical prototype stationary intraoral tomosynthesis system.

PURPOSE: Technological advancements in dental radiography have improved oral care on many fronts, yet diagnostic efficacy for some of the most common oral conditions, such as caries, dental cracks and fractures, and periodontal disease, remains relatively low. Driven by the clinical need for a better diagnostic yield for these and other dental conditions, we initiated the development of a stationary intraoral tomosynthesis (s-IOT) imaging system using carbon nanotube (CNT) x-ray source array technology. Here, we report the system characterization and preliminary imaging evaluation of a clinical prototype s-IOT system approved for human use. METHODS: The clinical prototype s-IOT system is comprised of a multibeam CNT x-ray source array, high voltage generator, control electronics, collimator cone, and dynamic digital intraoral detector. During a tomosynthesis scan, each x-ray source is operated sequentially at fixed, nominal tube current of 7 mA and user-specified pulse width. Images are acquired by a digital intraoral detector and the reconstruction algorithm generates slice information in real time for operator review. In this study, the s-IOT system was characterized for tube output, dosimetry, and spatial resolution. Manufacturer specifications were validated, such as tube current, kVp, and pulse width. Tube current was measured with an oscilloscope on the analog output of the anode power supply. Pulse width, kVp, and peak skin dose were measured with a dosimeter with ion chamber and high voltage accessory. In-plane spatial resolution was evaluated via measurement of MTF and imaging of a line pair phantom. Spatial resolution in the depth direction was evaluated via artifact spread measurement. The size of the collimated radiation field was evaluated for compliance with FDA regulations. A dental phantom and human specimens of varying pathologies were imaged on a clinical 2D intraoral imaging system as well as s-IOT for comparison and to explore potential clinical applications. RESULTS: The measured tube current, kVp, and pulse width values were within 3% of the set values. A cumulative peak skin dose of 1.12 mGy was measured for one complete tomosynthesis scan using a 50-ms pulse per projection view. Projection images and reconstruction slices revealed MTF values ranging from 8.1 to 9.3 cycles/mm. Line pair imaging verified this result. The radiation field was found to meet the FDA requirements for intraoral imaging devices. Tomosynthesis reconstruction slice images of the dental phantom and human specimens provided depth resolution, allowing visibility of anatomical features that cannot be seen in the 2D intraoral images. CONCLUSIONS: The clinical prototype s-IOT device was evaluated and found to meet all manufacturer specifications. Though the system capability is higher, initial investigations are targeting a low-dose range comparable to a single 2D radiograph. Preliminary studies indicated that s-IOT provides increased image quality and feature conspicuity at a dose comparable to a single 2D intraoral radiograph.

MRI for Dental Applications.

Imaging of hard and soft tissue of the oral cavity is important for dentistry. However, medical computed tomography, cone beam computed tomography (CBCT), nor MRI enables soft and hard tissue imaging simultaneously. Some MRI sequences were shown to provide fast soft and hard tissue imaging of hydrogen, which increased the interest in dental MRI. Recently, MRI allowed direct visualization of cancellous bone, intraoral mucosa, and dental pulp despite that cortical bone and dental roots are indirectly visualized. MRI seems to be adequate for many indications that CBCT is currently used for: implant treatment and inflammatory diseases of the tooth.