Visualization of droplets and aerosols in simulated dental treatments to clarify the effectiveness of oral suction devices.

PURPOSE: The hazards of aerosols generated during dental treatments are poorly understood. This study aimed to establish visualization methods, discover conditions for droplets/aerosols generated in simulating dental treatments and identify the conditions for effective suction methods. METHODS: The spreading area was evaluated via image analysis of the droplets/aerosols generated by a dental air turbine on a mannequin using a light emitting diode (LED) light source and high-speed camera. The effects of different bur types and treatment sites, reduction effect of intra-oral suction (IOS) and extra-oral suction (EOS) devices, and effect of EOS installation conditions were evaluated. RESULTS: Regarding the bur types, a bud-shaped bur on the air turbine generated the most droplets/aerosols compared with round-shaped, round end-tapered, or needle-tapered burs. Regarding the treatment site, the area of droplets/aerosols produced by an air turbine from the palatal plane of the anterior maxillary teeth was significantly higher. The generated droplet/aerosol area was reduced by 92.1% by using IOS alone and 97.8% by combining IOS and EOS. EOS most effectively aspirated droplets/aerosols when placed close (10 cm) to the mouth in the vertical direction (0°). CONCLUSIONS: The droplets/aerosols generated by an air turbine could be visualized using an LED light and a high-speed camera in simulating dental treatments. The bur shape and position of the dental air turbine considerably influenced droplet/aerosol diffusion. The combined use of IOS and EOS at a proper position (close and perpendicular to the mouth) facilitated effective diffusion prevention to protect the dental-care environment.

Revealing the origins of vortex cavitation in a Venturi tube by high speed X-ray imaging.

Hydrodynamic cavitation is useful in many processing applications, for example, in chemical reactors, water treatment and biochemical engineering. An important type of hydrodynamic cavitation that occurs in a Venturi tube is vortex cavitation known to cause luminescence whose intensity is closely related to the size and number of cavitation events. However, the mechanistic origins of bubbles constituting vortex cavitation remains unclear, although it has been concluded that the pressure fields generated by the cavitation collapse strongly depends on the bubble geometry. The common view is that vortex cavitation consists of numerous small spherical bubbles. In the present paper, aspects of vortex cavitation arising in a Venturi tube were visualized using high-speed X-ray imaging at SPring-8 and European XFEL. It was discovered that vortex cavitation in a Venturi tube consisted of angulated rather than spherical bubbles. The tangential velocity of the surface of vortex cavitation was assessed considering the Rankine vortex model.

Insights into the cavitation morphology of rubber reinforced with a nano-filler.

Notwithstanding the various uses of rubber, the fracture mechanism of filler-reinforced rubber remains unclear. This study used four-dimensional computed tomography (4D-CT) involving monochromatic synchrotron X-rays to examine the cavitation within silica-reinforced rubber quantitatively and systematically. The results suggested a threshold value of silica content for the cavitation morphology. Macroscopic fractures, such as those developed by void formation, occurred below the threshold value of silica content. Above this threshold, the density of rubber decreased but macroscopic voids rarely occurred. The lower-density rubber area in the high-silica-content rubber was reversible at the effective pixel size for 4D-CT. These results suggest that the growth of the damage points to macrosized voids could be stopped by the formation of a network of rigid polymer layers. This study allows the elucidation of the reinforcing mechanism and the cavitation morphology of filler-reinforced rubber.

Dynamic X-ray elastography using a pulsed photocathode source.

X-ray absorption of breast cancers and surrounding healthy tissue can be very similar, a situation that sometimes leads to missed cancers or false-positive diagnoses. To increase the accuracy of mammography and breast tomosynthesis, we describe dynamic X-ray elastography using a novel pulsed X-ray source. This new imaging modality provides both absorption and mechanical properties of the imaged material. We use a small acoustic speaker to vibrate the sample while a synchronously pulsed cold cathode X-ray source images the mechanical deformation. Using these stroboscopic images, we derive two-dimensional stiffness maps of the sample in addition to the conventional X-ray image. In a breast phantom composed of ZrO2 powder embedded in gel, dynamic elastography derived stiffness maps were able to discriminate a hard inclusion from surrounding material with a contrast-to-noise ratio (CNR) of 4.5. The CNR on the corresponding absorption image was 1.1. This demonstrates the feasibility of dynamic X-ray elastography with a synchronously pulsed X-ray source.

High-speed rotating device for X-ray tomography with 10 ms temporal resolution.

The temporal resolution of X-ray tomography, using a synchrotron radiation X-ray source, has been improved to millisecond order in recent years. However, the sample must be rotated at a speed of more than a few thousand revolutions per minute, which makes it difficult to control the environment around the sample. In this study, a high-speed rotation device has been developed, comprising two synchronized coaxial motors movable along the direction of the axis, which can stretch or compress the rotating sample. Using this device, tomograms of breaking rubber were successfully obtained at a temporal resolution of 10 ms.

Probing Surface Morphology using X-ray Grating Interferometry.

X-ray reflectometry (XRR), a surface-sensitive technique widely used for characterizing surfaces, buried interfaces, thin films, and multilayers, enables determination of the electron density distribution perpendicular to a well-defined surface specularly reflecting X-rays. However, the electron density distribution parallel to the surface cannot be determined from an X-ray reflectivity curve. The electron density correlation in the lateral direction is usually probed by measuring the grazing-incidence small-angle X-ray scattering (GISAXS). GISAXS measurement, however, typically requires using a collimated X-ray point beam to distinguish the GISAXS from the specularly reflected X-rays, and so the sample must be scanned in the lateral direction with the point beam to investigate variations in the surface and interface morphology for a region larger than the size of the beam. In this paper, we report a new approach based on X-ray grating interferometry: an X-ray sheet beam is used instead of an X-ray point beam. A method using this approach can simultaneously provide one-dimensional real-space images of X-ray reflectivity, surface curvature, and 'dark-field' contrast with a field-of-view of more than a few millimetres. As a demonstration, a sample having a 400 nm line and space SiO2 pattern with a depth of 10 nm on its surface was used, and the dark-field contrast due to the unresolved line and space structure, creating GISAXS in the lateral direction, was successfully observed. Quantitative analysis of these contrasts provided the real-space distribution of the structural parameters for a simple model of the grating structure. Our study paves the way to a new approach to structure analysis, providing a quantitative way to investigate real-space variations in surface and interface morphology through wavefront analysis.

Hard X-ray imaging microscopy with self-imaging phenomenon.

The self-imaging phenomenon referred to as the Talbot effect in the field of optics was discovered by H.F. Talbot in the 1830s, and is now widely used for imaging using not only visible light but also X-rays, electrons, neutrons, and matter waves. In this review, the author introduces the current progress being made in hard-X-ray imaging microscopy based on the self-imaging phenomenon. Hard-X-ray imaging microscopy is a promising technique for non-destructively visualizing internal structures in specimens with a spatial resolution up to a few tens of nanometers. The use of the self-imaging phenomenon makes it possible to realize highly sensitive phase-contrast X-ray imaging microscopes. These approaches have several advantages over conventional X-ray imaging microscopes, including the widely used Zernike X-ray phase-contrast microscopes, and can provide a powerful way of quantitative visualization with a high spatial resolution and a high sensitivity even for thick specimens.

Effect of insufficient temporal coherence on visibility contrast in X-ray grating interferometry.

X-ray grating interferometry, which has been spotlighted in the last decade as a multi-modal X-ray imaging technique, can provide three independent images, i.e., absorption, differential-phase, and visibility-contrast images. We report on a cause of the visibility contrast, an effect of insufficient temporal coherence, that can be observed when continuous-spectrum X-rays are used. This effect occurs even for a sample without unresolvable random structures, which are known as the main causes of visibility contrast. We performed an experiment using an acrylic cylinder and quantitatively explained the visibility contrast due to this effect.

Edge-illumination x-ray phase contrast imaging with Pt-based metallic glass masks.

Edge-illumination x-ray phase contrast imaging (EI XPCI) is a non-interferometric phase-sensitive method where two absorption masks are employed. These masks are fabricated through a photolithography process followed by electroplating which is challenging in terms of yield as well as time- and cost-effectiveness. We report on the first implementation of EI XPCI with Pt-based metallic glass masks fabricated by an imprinting method. The new tested alloy exhibits good characteristics including high workability beside high x-ray attenuation. The fabrication process is easy and cheap, and can produce large-size masks for high x-ray energies within minutes. Imaging experiments show a good quality phase image, which confirms the potential of these masks to make the EI XPCI technique widely available and affordable.

Osteocyte-directed bone demineralization along canaliculi.

The mammalian skeleton stores calcium and phosphate ions in bone matrix. Osteocytes in osteocyte lacunae extend numerous dendrites into canaliculi less than a micron in diameter and which are distributed throughout bone matrix. Although osteoclasts are the primary bone-resorbing cells, osteocytes also reportedly dissolve hydroxyapatite at peri-lacunar bone matrix. However, robust three-dimensional evidence for peri-canalicular bone mineral dissolution has been lacking. Here we applied a previously reported Talbot-defocus multiscan tomography method for synchrotron X-ray microscopy and analyzed the degree of bone mineralization in mouse cortical bone around the lacuno-canalicular network, which is connected both to blood vessels and the peri- and endosteum. We detected cylindrical low mineral density regions spreading around canaliculi derived from a subset of osteocytes. Transmission electron microscopy revealed both intact and demineralized bone matrix around the canaliculus. Peri-canalicular low mineral density regions were also observed in osteopetrotic mice lacking osteoclasts, indicating that osteoclasts are dispensable for peri-canalicular demineralization. These data suggest demineralization can occur from within bone through the canalicular system, and that peri-canalicular demineralization occurs not uniformly but directed by individual osteocytes. Blockade of peri-canalicular demineralization may be a therapeutic strategy to increase bone mass and quality.

Osteogenic capillaries orchestrate growth plate-independent ossification of the malleus.

Endochondral ossification is a developmental process by which cartilage is replaced by bone. Terminally differentiated hypertrophic chondrocytes are calcified, vascularized, and removed by chondroclasts before bone matrix is laid down by osteoblasts. In mammals, the malleus is one of three auditory ossicles that transmit vibrations of the tympanic membrane to the inner ear. The malleus is formed from a cartilaginous precursor without growth plate involvement, but little is known about how bones of this type undergo endochondral ossification. Here, we demonstrate that in the processus brevis of the malleus, clusters of osteoblasts surrounding the capillary loop produce bone matrix, causing the volume of the capillary lumen to decrease rapidly in post-weaning mice. Synchrotron X-ray tomographic microscopy revealed a concentric, cylindrical arrangement of osteocyte lacunae along capillaries, indicative of pericapillary bone formation. Moreover, we report that overexpression of Fosl1, which encodes a component of the AP-1 transcription factor complex, in osteoblasts significantly blocked malleal capillary narrowing. These data suggest that osteoblast/endothelial cell interactions control growth plate-free endochondral ossification through 'osteogenic capillaries' in a Fosl1-regulated manner.

Effect of beam hardening on a visibility-contrast image obtained by X-ray grating interferometry.

X-ray grating interferometry has been highlighted in the last decade as a multi-modal X-ray phase-imaging technique for providing absorption, differential phase, and visibility-contrast images. It has been mainly reported that the visibility contrast in the visibility-contrast image originates from unresolvable random microstructures. In this paper, we show that the visibility contrast is even reduced by a uniform sample with flat surfaces due to the so-called "beam-hardening effect", which has to be taken into account when X-rays with a continuous spectrum is used. We drive a criterion for determining whether the beam-hardening effect occurs or not, and propose a method for correcting the effect of beam hardening on a visibility-contrast image.

Effects of unresolvable edges in grating-based X-ray differential phase imaging.

We investigated effects of unresolvable sharp edges on images obtained in a grating-based X-ray differential phase imaging technique. Results of numerical calculations for monochromatic X-rays show that an unresolvable sharp edge generates not only differential-phase contrast but also visibility contrast. The latter shows that the visibility contrast has another major origin other than ultra-small-angle X-ray scattering (USAXS) from randomly distributed unresolvable microstructures, which has been considered the main origin for the contrast. The effects were experimentally confirmed using a synchrotron X-ray source.

X-ray phase imaging: from synchrotron to hospital.

With the aim of clinical applications of X-ray phase imaging based on Talbot-Lau-type grating interferometry to joint diseases and breast cancer, machines employing a conventional X-ray generator have been developed and installed in hospitals. The machine operation especially for diagnosing rheumatoid arthritis is described, which relies on the fact that cartilage in finger joints can be depicted with a dose of several milligray. The palm of a volunteer observed with 19 s exposure (total scan time: 32 s) is reported with a depicted cartilage feature in joints. This machine is now dedicated for clinical research with patients.

Talbot-defocus multiscan tomography using the synchrotron X-ray microscope to study the lacuno-canalicular network in mouse bone.

The three-dimensional network of lacunae and canaliculi that regulates metabolism in bone contains osteocytes and their dendritic processes. We constructed a synchrotron radiation X-ray microscope for sequential tomography of mouse tibia first by using a Talbot interferometer to detect the degree of bone mineralization and then by using absorption contrast under a slightly defocused setting to enhance outline contrast thereby visualizing structures of the osteocyte lacuno-canalicular network. The resultant pair of tomograms was precisely aligned with each other, allowing evaluation of mineral density in the vicinity of each osteocyte lacuna and canaliculus over the entire thickness of the cortical bone. Thus, multiscan microscopic X-ray tomography is a powerful tool for analyzing bone mineralization in relation to the lacuno-canalicular network at the submicron resolution level.

Wavefront measurement for a hard-X-ray nanobeam using single-grating interferometry.

Wavefront measurement for a hard-X-ray nanobeam using single-grating interferometry based on the Talbot effect and the Fourier transform method was demonstrated in the 1-km-long beamline of SPring-8. 10 keV X-rays were one-dimensionally focused down to 32 nm using a total-reflection elliptical mirror. An intentionally distorted wavefront was generated using a deformable mirror placed just upstream of the focusing mirror. The wavefront measured by interferometry was cross-checked with the phase retrieval method using intensity profiles around the beam waist. Comparison of the obtained wavefront errors revealed that they are in good agreement with each other and with the wavefront error estimated from the shape of the deformable mirror at a ~0.5 rad level.

Iterative reconstruction in x-ray computed laminography from differential phase measurements.

Phase-contrast X-ray computed laminography is demonstrated for the volume reconstruction of extended flat objects, not suitable to the usual tomographic scan. Using a Talbot interferometer, differential phase measurements are obtained and used to reconstruct the real part of the complex refractive index. The specific geometry of laminography leads to unsampled frequencies in a double cone in the reciprocal space, which degrades the spatial resolution in the direction normal to the object plane. First, the filtered backprojection formula from differential measurements is derived. Then, reconstruction is improved by the use of prior information of compact support and limited range, included in an iterative filtered backprojection algorithm. An implementation on GPU hardware was required to handle the reconstruction of volumes within a reasonable time. A synchrotron radiation experiment on polymer meshes is reported and results of the iterative reconstruction are compared with the simpler filtered backprojection.

Four-dimensional X-ray phase tomography with Talbot interferometry and white synchrotron radiation: dynamic observation of a living worm.

X-ray Talbot interferometry is attractive as a method for X-ray phase imaging and phase tomography for objects that weakly absorb X-rays. Because X-ray Talbot interferometry has the advantage that X-rays of a broad energy bandwidth can be used, high-speed X-ray phase imaging is possible with white synchrotron radiation. In this paper, we demonstrate time-resolved three-dimensional observation with X-ray Talbot interferometry (namely, four-dimensional X-ray phase tomography). Differential phase images, from which a phase tomogram was reconstructed, were obtained through the Fourier-transform method, unlike the phase-stepping method that requires several (at least three) moiré images to be measured sequentially in order to generate one differential phase image. We demonstrate dynamic observation of a living worm in three dimensions with a time resolution of 0.5 s, visualizing a drastic change in the respiratory tract.

High-speed X-ray phase imaging and X-ray phase tomography with Talbot interferometer and white synchrotron radiation.

X-ray Talbot interferometry, which uses two transmission gratings, has the advantage that broad energy bandwidth x-rays can be used. We demonstrate the use of white synchrotron radiation for high-speed X-ray phase imaging and tomography in combination with an X-ray Talbot interferometer. The moiré fringe visibility over 20% was attained, enabling quantitative phase measurement. X-ray phase images with a frame rate of 500 f/s and an X-ray phase tomogram with a scan time of 0.5 s were obtained successfully. This result suggests a breakthrough for time-resolved three-dimensional observation of objects that weakly absorb X-rays, such as soft material and biological objects.

Efficiency of capturing a phase image using cone-beam x-ray Talbot interferometry.

We assesses the efficiency of x-ray Talbot interferometry (XTI), a technique based on the Talbot effect for measuring a wavefront gradient, in terms of how quickly it can capture a high-quality phase image with a large signal-to-noise ratio for a given incident photon number. Photon statistics cause errors in the phase of the moiré fringes and impose a detection limit on the wavefront gradient. The relation between the incident photon number and the detection limit is determined, and a figure of merit of XTI for a monochromatic cone beam is then defined. The dependence of the figure of merit on optical system parameters, such as grating pitch and position, is then discussed. The effects of varying the pattern height and linewidth of the second grating are shown for rectangular and trapezoidal teeth. Finally, we show how to design a practical cone-beam Talbot interferometer for certain boundary conditions.