The Effects of Additional Filtration on Image Quality and Radiation Dose in Cone Beam CT: An In Vivo Preliminary Investigation.

Purpose: The aim of this study was to investigate the effect of reduced radiation doses on the image quality of cone-beam computed tomography scans and the suitability of such imaging for orthodontics, oral surgery, dental implantology, periodontology, and endodontology. Materials and Methods: Cone-beam computed tomography scans of a live patient were performed using seven attenuation filters with increased thickness to decrease the effective radiation dose from 22.4 to 1.8 µSv, and the effects of different radiation doses on image quality were further analysed. Quantitative image quality was calculated using dedicated measures, such as signal and contrast-to-noise ratio and sharpness. A panel of five certified raters assessed the cone-beam computed tomography scans qualitatively. Nine anatomical structures relevant to dentistry were identified, and the overall acceptance was assessed. Results: Linear reduction of the effective radiation dose had a nonlinear effect on image quality. A 5-fold reduction in the effective dose led to acceptable quantitative and qualitative image quality measures, and the identification rate of dental anatomical structures was 80% or greater. The use of less than 40% of the reference dose was unacceptable for all dental specialties. Conclusions: The ideal radiation dose for specific diagnostic requirements remains a patient-related and specialty-related decision that must be made on an individual basis. Based on the results of this study, it is possible to reduce exposure in selected patients, and at the same time obtain sufficient quality of images for clinical purposes.

Ultra short time to Echo (UTE) MRI for cephalometric analysis-Potential of an x-ray free fast cephalometric projection technique.

OBJECTIVES: A novel magnetic resonance imaging (MRI) scan protocol is presented on the basis of ultra-short time to echo (UTE). By this MRI cephalometric projections (MCPs) can be acquired without the need of post processing in one shot. Different technical parameterizations of the protocol are performed. Their impact on the performance of MCPs is evaluated in comparison to the gold standard-the lateral cephalometric radiography (LCR) for cephalometric analysis (CA) in orthodontics. METHODS: Seven MCPs with various scan parameters influencing the scan duration and one LCR are used from one subject. 40 expert assessors performed CA for 14 predefined cephalometric landmarks. Relative metric distances and absolute angular measurements were calculated. Statistical analysis is presented and the deviations are highlighted to demonstrate the potential of the method for further analysis. RESULTS: The MCPs are acquired in 5-154 seconds, depending on resolution and contrast. Mean relative distances were 2.4-2.7 mm in MCPs and 1.6 mm in LCR, which demonstrate the accuracy and level of agreement of the expert assessors in identifying anatomical landmarks. In comparison to other studies, the presented MCP performed similar in angular analysis and demonstrated on average deviation of 1.2° ±1.1° in comparison to LCR. Despite the point articulare (Ar) and the related gonial angle the calculate distances and angles show outcomes in the range of ±2°/2mm. CONCLUSIONS: MCPs can be acquired much faster in comparison to other techniques known from literature for CA. This study demonstrated the potential of the new method and showed first feasible results. Further research is needed to analyze the performance on a broad range of patients.

Virtual intensive care unit (ICU): real-time simulation environment applying hybrid approach using dynamic Bayesian Networks and ODEs.

Combining deterministic (e.g. differential equations) and probabilistic (Bayesian Networks) approaches to model physiological processes in a real-time software environment leads to a novel model for simulation of human patient physiology especially relevant for intensive care units (ICU). Using dedicated HW/SW interfaces simulated patient signals are measurable with standard monitoring systems. Therefore, this system, based on realistic simulations, is very well suited for teaching and education. Additionally, the environment is usable for inferring patient-specific model structures and parameters. We introduce a hierarchical modeling approach, which allows building complex models based on aggregation of simple sub models. The simulation is controlled to run in real-time with typical sampling times of 1-10 ms (depending on model complexity) on a standard PC (Pentium 2.66 GHz CPU).

Real-time ECG emulation: a multiple dipole model for electrocardiography simulation.

A new model for describing electrocardiography (ECG) is presented, which is based on multiple dipoles compared to standard single dipole approaches in vector electrocardiography. The multiple dipole parameters are derived from real data (e.g. four dipoles from 12-channel ECG) by solving the backward problem of ECG numerically. Results are transformed to a waveform description based on Gaussian mixture for every dimension of each dipole. These compact parameterized descriptors are used for a very realistic real-time simulation applying the forward solution of the proposed model.

Simulation of dynamic ultrasound based on CT models for medical education.

In our approach, we first specify a 3D model of the image structure by segmenting a CT dataset into the respective tissues followed by assigning the acoustic properties (velocity, impedance, scattering mean and standard deviation, damping factor and packing factor). Given that model, we simulate the ray propagation, beam forming, and finally the backscattering. Due to the inhomogenities of tissue, different physical models for ultrasound simulation are required: Rayleigh scattering is applied for homogenous regions and ray tracing techniques handle abrupt changes in acoustic impedance on tissue boundaries. The latter leads to different phenomena like refraction (Snell's law), reflection and transmission (Fresnel equation). The gradients needed for these methods are precomputed for each model using a central-difference method with multiple neighbours. Absorption is calculated by the Beer-Lambert law.