Quantitative electron density characterization of soft tissue substitute plastic materials using grating-based x-ray phase-contrast imaging

Entrance Skin Dose (ESD) and Bucky Table Induced Backscattered Dose (BTI-BSD) in Abdominal Radiography With nanoDot Optically Stimulated Luminescence Dosimeter (OSLD)

In radiography, inconsistencies in patients' measured entrance skin dose (ESD) exist. There is no published research on the bucky table induced backscattered radiation dose (BTI-BSD). Thus, we aimed to ascertain ESD, calculate the BTI-BSD in abdominal radiography with a nanoDot OSLD, and compare the ESD results with the published data. A Kyoto Kagaku PBU-50 phantom (Kyoto, Japan) in an antero-posterior supine position was exposed, selecting a protocol used for abdominal radiography. The central ray of x-ray beam was pointed at the surface of abdomen at the navel, where a nanoDot dosimeter was placed to measure ESD. For the BTI-BSD, exit dose (ED) was determined by placing a second dosimeter on the exact opposite side (backside) of the phantom from the dosimeter used to determine (ESD) with and without bucky table at identical exposure parameters. The BTI-BSD was calculated as the difference between ED with and without bucky table. The ESD, ED, and BTI-BSD were measured in milligray (mGy). ESD mean values with and without bucky table were 1.97 mGy and 1.84 mGy, whereas ED values were 0.062 mGy and 0.052 mGy, respectively. Results show 2-26% lower ESD values with nanoDot OSLD. The BTI-BSD mean value was found to be approximately 0.01 mGy. A local dose reference level (LDRL) can be established using ESD data to safeguard patients from unnecessary radiation. In addition, to minimize the risk of BTI-BSD in patients in radiography, the search for the use or fabrication of a new, lower atomic number material for the bucky table is suggested.

High-resolution multicontrast tomography with an X-ray microarray anode-structured target source

Talbot–Lau interferometry (TLI) holds remarkable potential for multicontrast X-ray imaging but suffers from technical challenges associated with microfabrication and limited efficiency. We tackle the frontier challenges in this field by developing a microarray anode–structured target source with a built-in structured illumination scheme. Our development facilitates high-resolution and high-sensitivity TLI imaging without the absorption source grating. We demonstrate the tri-contrast tomography capability with a Drum fish tooth specimen and separate the biological features with different combinations of physical properties. Our approach not only addresses the long-standing challenges in the field of X-ray TLI phase-contrast imaging but also features a compact setup that can potentially be made broadly available to academia research and industrial applications.

Multicontrast X-ray imaging with high resolution and sensitivity using Talbot–Lau interferometry (TLI) offers unique imaging capabilities that are important to a wide range of applications, including the study of morphological features with different physical properties in biological specimens. The conventional X-ray TLI approach relies on an absorption grating to create an array of micrometer-sized X-ray sources, posing numerous limitations, including technical challenges associated with grating fabrication for high-energy operations. We overcome these limitations by developing a TLI system with a microarray anode–structured target (MAAST) source. The MAAST features an array of precisely controlled microstructured metal inserts embedded in a diamond substrate. Using this TLI system, tomography of a Drum fish tooth with high resolution and tri-contrast (absorption, phase, and scattering) reveals useful complementary structural information that is inaccessible otherwise. The results highlight the exceptional capability of high-resolution multicontrast X-ray tomography empowered by the MAAST-based TLI method in biomedical applications.

Recent Progress in X-ray and Neutron Phase Imaging with Gratings

Under the JST-ERATO project in progress to develop X-ray and neutron phase-imaging methods together, recent achievements have been selected and reviewed after describing the merit and the principle of the phase imaging method. For X-ray phase imaging, recent developments of four-dimensional phase tomography and phase microscopy at SPring-8, Japan are mainly presented. For neutron phase imaging, an approach in combination with the time-of-flight method developed at J-PARC, Japan is described with the description of new Gd grating fabrication.

Accurate effective atomic number determination with polychromatic grating-based phase-contrast computed tomography

The demand for quantitative medical imaging is increasing in the ongoing digitalization. Conventional computed tomography (CT) is energy-dependent and therefore of limited comparability. In contrast, dual-energy CT (DECT) allows for the determination of absolute image contrast quantities, namely the electron density and the effective atomic number, and is already established in clinical radiology and radiation therapy. Grating-based phase-contrast computed tomography (GBPC-CT) is an experimental X-ray technique that also allows for the measurement of the electron density and the effective atomic number. However, the determination of both quantities is challenging when dealing with polychromatic GBPC-CT setups. In this paper, we present how to calculate the effective atomic numbers with a polychromatic, laboratory GBPC-CT setup operating between 35 and 50\,kVp. First, we investigated the accuracy of the measurement of the attenuation coefficients and electron densities. For this, we performed a calibration using the concept of effective energy. With the reliable experimental quantitative values, we were able to evaluate the effective atomic numbers of the investigated materials using a method previously shown with monochromatic X-ray radiation. In detail, we first calculated the ratio of the electron density and attenuation coefficient, which were experimentally determined with our polychromatic GBPC-CT setup. Second, we compared this ratio with tabulated total attenuation cross sections from literature values to determine the effective atomic numbers. Thus, we were able to calculate two physical absolute quantities -- the electron density and effective atomic number -- that are in general independent of the specific experimental conditions like the X-ray beam spectrum or the setup design.

Implementation of a double-grating interferometer for phase-contrast computed tomography in a conventional system nanotom® m

Visualizing the internal architecture of large soft tissue specimens within the laboratory environment in a label-free manner is challenging, as the conventional absorption-contrast tomography yields a poor contrast. In this communication, we present the integration of an X-ray double-grating interferometer (XDGI) into an advanced, commercially available micro computed tomography system nanotom® m with a transmission X-ray source and a micrometer-sized focal spot. The performance of the interferometer is demonstrated by comparing the registered three-dimensional images of a human knee joint sample in phase- and conventional absorption-contrast modes. XDGI provides enough contrast (1.094 ± 0.152) to identify the cartilage layer, which is not recognized in the conventional mode (0.287 ± 0.003). Consequently, the two modes are complementary, as the present XDGI set-up only reaches a spatial resolution of (73 ± 6) μm, whereas the true micrometer resolution in the absorption-contrast mode has been proven. By providing complimentary information, XDGI is especially a supportive quantitative method for imaging soft tissues and visualizing weak X-ray absorbing species in the direct neighborhood of stronger absorbing components at the microscopic level.

Liquid tissue surrogates for X-ray and CT phantom studies

PURPOSE

To develop a simple method for producing liquid-tissue-surrogate (LTS) materials that accurately represent human soft tissues in terms of density and X-ray attenuation coefficient.

METHODS AND MATERIALS

We evaluated hypothetical mixtures of water, glycerol, butanol, methanol, sodium chloride, and potassium nitrate; these mixtures were intended to emulate human adipose, blood, brain, kidney, liver, muscle, pancreas, and skin. We compared the hypothetical densities, effective atomic numbers (Z_eff ), and calculated discrete-energy CT attenuation [Hounsfield Units (HU)] of the proposed materials with those of human tissue elemental composition as specified in International Commission on Radiation Units (ICRU) Report 46. We then physically produced the proposed LTS materials for adipose, liver, and pancreas tissue, and we measured the polyenergetic CT attenuation (also expressed as HU) of these materials within a 32 cm phantom using a 64-slice clinical CT scanner at 80 kVp, 100 kVp, 120 kVp, and 140 kVp.

RESULTS

The predicted densities, Z_eff , and calculated discrete-energy CT attenuation of our proposed formulations generally agreed with those of ICRU within < 1% or < 10 HU. For example, the densities of our hypothetical materials agreed precisely with ICRU's reported values and were 0.95 g/mL for adipose tissue, 1.04 g/mL for pancreatic tissue, and 1.06 g/mL for liver tissue; the discrete-energy CT attenuation at 60 keV of our hypothetical materials (and ICRU-specified compositions) were -107 HU (-113 HU) for adipose #3, -89 HU (-90 HU) for adipose #2, 56 HU (55 HU) for liver tissue, and 31 HU (31 HU) for pancreatic tissue. The densities of our physically produced materials (compared to ICRU-specified compositions) were 0.947 g/mL (0.0%) for adipose #2, 1.061 g/mL (+2.0%) for pancreatic tissue, and 1.074 g/mL (+1.3%) for liver tissue. The empirical polyenergetic CT attenuation measurements of our LTS materials (and the discrete-energy HU of the ICRU compositions at the mean energy of each spectrum) at 80 kVp were -104 HU (-113 HU) for adipose #3, -87 HU (-90 HU) for adipose #2, 59 HU (55 HU) for liver tissue, and 33 HU (31 HU) for pancreatic tissue; at 120 kVp, these were -83 HU (-83 HU) for adipose #3, -68 HU (-63 HU) for adipose #2, 55 HU (52 HU) for liver tissue, and 35 HU (33 HU) for pancreatic tissue.

CONCLUSION

Our method for formulating tissue surrogates allowed straightforward production of solutions with CT attenuation that closely matched the target tissues' expected CT attenuation values and trends with kVp. The LTSs' inexpensive and widely available constituent chemicals, combined with their liquid state, should enable rapid production and versatile use among different phantom and experiment types. Further study is warranted, such as the inclusion of contrast agents. These liquid tissue surrogates may potentially accelerate development and testing of advanced CT imaging techniques and technologies.

Polychromatic X-ray effects on fringe phase shifts in grating interferometry

In order to quantitatively determine the projected electron densities of a sample, one needs to extract the monochromatic fringe phase shifts from the polychromatic fringe phase shifts measured in the grating interferometry with incoherent X-ray sources. In this work the authors propose a novel analytic approach that allows to directly compute the monochromatic fringe shifts from the polychromatic fringe shifts. This approach is validated with numerical simulations of several grating interferometry setups. This work provides a useful tool in quantitative imaging for biomedical and material science applications.

Mass Density Measurement of Mineralized Tissue with Grating-Based X-Ray Phase Tomography

Establishing the mineral content distribution in highly mineralized tissues, such as bones and teeth, is fundamental in understanding a variety of structural questions ranging from studies of the mechanical properties to improved pathological investigations. However, non-destructive, volumetric and quantitative density measurements of mineralized samples, some of which may extend several mm in size, remain challenging. Here, we demonstrate the potential of grating-based x-ray phase tomography to gain insight into the three-dimensional mass density distribution of tooth tissues in a non-destructive way and with a sensitivity of 85 mg/cm³. Density gradients of 13 − 19% over 1 − 2 mm within typical samples are detected, and local variations in density of 0.4 g/cm³ on a length scale of 0.1 mm are revealed. This method proves to be an excellent quantitative tool for investigations of subtle differences in mineral content of mineralized tissues that can change following treatment or during ageing and healing.

Experimental Realisation of High-sensitivity Laboratory X-ray Grating-based Phase-contrast Computed Tomography

The possibility to perform high-sensitivity X-ray phase-contrast imaging with laboratory grating-based phase-contrast computed tomography (gbPC-CT) setups is of great interest for a broad range of high-resolution biomedical applications. However, achieving high sensitivity with laboratory gbPC-CT setups still poses a challenge because several factors such as the reduced flux, the polychromaticity of the spectrum, and the limited coherence of the X-ray source reduce the performance of laboratory gbPC-CT in comparison to gbPC-CT at synchrotron facilities. In this work, we present our laboratory X-ray Talbot-Lau interferometry setup operating at 40 kVp and describe how we achieve the high sensitivity yet unrivalled by any other laboratory X-ray phase-contrast technique. We provide the angular sensitivity expressed via the minimum resolvable refraction angle both in theory and experiment, and compare our data with other differential phase-contrast setups. Furthermore, we show that the good stability of our high-sensitivity setup allows for tomographic scans, by which even the electron density can be retrieved quantitatively as has been demonstrated in several preclinical studies.

Low-dose, phase-contrast mammography with high signal-to-noise ratio

Differential phase-contrast X-ray imaging using a Talbot-Lau interferometer has recently shown promising results for applications in medical imaging. However, reducing the applied radiation dose remains a major challenge. In this study, we consider the realization of a Talbot-Lau interferometer in a high Talbot order to increase the signal-to-noise ratio for low-dose applications. The quantitative performance of π and π/2 systems at high Talbot orders is analyzed through simulations, and the design energy and X-ray spectrum are optimized for mammography. It is found that operation even at very high Talbot orders is feasible and beneficial for image quality. As long as the X-ray spectrum is matched to the visibility spectrum, the SNR continuously increases with the Talbot order for π-systems. We find that the optimal X-ray spectra and design energies are almost independent of the Talbot order and that the overall imaging performance is robust against small variations in these parameters. Discontinuous spectra, such as that from molybdenum, are less robust because the characteristic lines may coincide with minima in the visibility spectra; however, they may offer slightly better performance. We verify this hypothesis by realizing a prototype system with a mean fringe visibility of above 40% at the seventh Talbot order. With this prototype, a proof-of-principle measurement of a freshly dissected breast at reasonable compression to 4 cm is conducted with a mean glandular dose of only 3 mGy but with a high SNR.