Absorbed dose and noise in intensity-modulated dental computed tomography

Abstract

For a dental cone-beam computed tomography (CBCT) with a reduced patient dose, we have considered the tube-current modulation, and tube-current and voltage, or beam intensity, modulation techniques. For various modulation scenarios to the dental CBCT with various fields of view (FOVs), we assessed the absorbed dose using the Monte Carlo method. We also applied the scenarios to a laboratory bench-top CBCT system and evaluated the voxel noise. While the modulation techniques reduced the effective dose, more effectively as increasing FOV, they increased the voxel noise. The gain from their combinations was therefore none or slightly less, compared to the CBCT with the conventional uniform power scanning. We used the filtered-backprojection and the simultaneous algebraic reconstruction technique for image reconstructions, and we ignored the correction for data truncation in smaller FOVs. Therefore, there is enough room for the enhancement of image quality performance using advanced reconstruction methods. In addition, the modulation scenarios considered only the field around the cervical spine. Nevertheless we have found meaningful dose reductions in dental CBCTs in corporation with the modulation techniques.

Frequency‐dependent signal and noise in spectroscopic x‐ray imaging

“…To simulate photon transport and the resulting deposited energy, we used the particle‐tracking function (pTrac), which provides a report on the entire interaction history for each simulated photon 22,68,69 . For each interaction event, pTrac records the interaction type, the location of the interaction, (e.g., for the j ‐th interaction of the i ‐th x‐ray photon transport in a simulation) and the energy remaining after the interaction (e.g., ).…”

“…To simulate photon transport and the resulting deposited energy, we used the particle-tracking function (pTrac), which provides a report on the entire interaction history for each simulated photon. 22,68,69 For each interaction event, pTrac records the interaction type, the location of the interaction, (e.g., x i j for the j-th interaction of the i-th x-ray photon transport in a simulation) and the energy remaining after the interaction (e.g., e i j ). To validate our model of transport and reabsorption of fluorescent photons, we assumed photons deposit all of their energy at the interaction sites, that is, we ignored the range of photoelectrons.…”

X-ray interaction characteristic functions in semiconductor detectors

“…In order to determine A(x) and C(x) within CdTe detectors, we use the commercial radiation transport simulation code (MCNP version 5, RSICC, Oak Ridge, TN). To describe A i (x) and C i (x), we use a built-in function of the MCNP5, called the particle-tracking function (pTrac), which reports every interaction experienced by a single photon during its transport [16,20,21]. For every interaction event, the pTrac reports the interaction type, the coordinates representing the interaction site, the energy remained after the interaction at the site, etc.…”