Bithiophene-Functionalized Infrared Two-Photon Absorption Metal Complexes as Single-Molecule Platforms for Synergistic Photodynamic, Photothermal, and Chemotherapy.

A planar conjugated ligand functionalized with bithiophene and its Ru(II), Os(II), and Ir(III) complexes have been constructed as single-molecule platform for synergistic photodynamic, photothermal, and chemotherapy. The complexes have significant two-photon absorption at 808 nm and remarkable singlet oxygen and superoxide anion production in aqueous solution and cells when exposed to 808 nm infrared irradiation. The most potent Ru(II) complex Ru7 enters tumor cells via the rare macropinocytosis, locates in both nuclei and mitochondria, and regulates DNA-related chemotherapeutic mechanisms intranuclearly including DNA topoisomerase and RNA polymerase inhibition and their synergistic effects with photoactivated apoptosis, ferroptosis and DNA cleavage. Ru7 exhibits high efficacy in vivo for malignant melanoma and cisplatin-resistant non-small cell lung cancer tumors, with a 100 % survival rate of mice, low toxicity to normal cells and low residual rate. Such an infrared two-photon activatable metal complex may contribute to a new generation of single-molecule-based integrated diagnosis and treatment platform to address drug resistance in clinical practice and phototherapy for large, deeply located solid tumors.

Improvement of performance for flexible film dosimeter by incorporating additive agents.

Objective.To evaluate the reduction in energy dependence and aging effect of the lithium salt of pentacosa-10,-12-diynoic acid (LiPCDA) films with additives including aluminum oxide (Al2O3), propyl gallate (PG), and disodium ethylenediaminetetracetate (EDTA).Approach. LiPCDA films exhibited energy dependence on kilovoltage (kV) and megavoltage (MV) photon energies and experienced deterioration over time. Evaluations were conducted with added Al2O3and antioxidants to mitigate these issues, and films were produced with and without Al2O3to assess energy dependence. The films were irradiated at doses of 0, 3, 6, and 12 cGy at photon energies of 75 kV, 105 kV, 6 MV, 10 MV, and 15 MV. For the energy range of 75 kV to 15 MV, the mean and standard deviation (std) were calculated and compared for the values normalized to the net optical density (netOD) at 6 MV, corresponding to identical dose levels. To evaluate the aging effect, PG and disodium EDTA were incorporated into the films: sample C with 1% PG, sample D with 2% PG, sample E with 0.62% disodium EDTA added to sample D, and sample F with 1.23% disodium EDTA added to sample D.Main results. Films containing Al2O3demonstrated a maximum 15.8% increase in mean normalized values and a 15.1% reduction in std, reflecting a greater netOD reduction at kV than MV energies, which indicates less energy dependence in these films. When the OD of sample 1-4 depending on the addition of PG and disodium EDTA, was observed for 20 weeks, the transmission mode decreased by 8.7%, 8.3%, 29.3%, and 27.3%, respectively, while the reflection mode was 5.4%, 3.0%, 37.0%, and 34.5%, respectively.Significance. Al2O3effectively reduced the voltage and MV energy dependence. PG was more effective than disodium EDTA in preventing the deterioration of film performance owing to the aging effect.

A simulation of a high-resolution cadmium zinc telluride positron emission tomography system.

BACKGROUND: A CZT (cadmium zinc telluride) PET (positron emission tomography) system is being developed at Stanford University. CZT has the promise of outperforming scintillator-based systems in energy and spatial resolution but has relatively poor coincidence timing resolution. PURPOSE: To supplement GATE (GEANT 4 Application for Emission Tomography) simulations with charge transport and electronics modeling for a high-resolution CZT PET system. METHODS: A conventional GATE simulation was supplemented with electron-hole transport modeling and experimentally measured single detector energy resolution to improve the system-level understanding of a CZT high-resolution PET system in development at Stanford University. The modeling used GATE hits data and applied charge transport in the crystal and RC-CR processing of the simulated signals to model the electronics, including leading-edge discriminators and peak pick-off. Depth correction was also performed on the simulation data. Experimentally acquired data were used to determine energy resolution parameters and were compared to simulation data. RESULTS: The distributions of the coincidence timing, anode energy, and cathode energy are consistent with experimental data. Numerically, the simulation achieved 153 ns FWHM coincidence time resolution (CTR), which is of the same order of magnitude as the raw 210 ns CTR previously found experimentally. Further, the anode energy resolution was found to be 5.9% FWHM (full width at half maximum) at 511 keV in the simulation, which is between the experimental value found for a single crystal of 3% and the value found for the dual-panel setup of 8.02%, after depth correction. CONCLUSIONS: Developing this advanced simulation improves upon the limitations of GATE for modeling semiconductor PET systems and provides a means for deeper analysis of the coincidence timing resolution and other complementary electron-hole dependent system parameters.

Photon spectra effects tested on the vegetal model Allium cepa.

The use of artificial light sources in plants is considered a type of photobiomodulation (PBM), a trend in agriculture and food industries, aiming at decontamination, pest control, and increased production yield. However, literature lacks a broader assessment to address the effects of photon light spectra on plant characteristics. Here, we aimed to describe the effects of visible light, infrared, and ultraviolet light upon Allium cepa, a known bioindicator, under various light doses. Samples irradiated under visible and infrared light did not show cytotoxicity, genotoxicity, or mutagenicity in any of the evaluated doses. Light induction at 460 and 635 nm significantly stimulated root development of the test organism. In contrast, 254 nm irradiation proved to be cytotoxic, genotoxic, and mutagenic. This work reveals and quantifies the spectral response of A. cepa seeds, suggesting that it can be proposed as a model for future research on mechanisms of PBM in plants.

An efficient quasi-Monte Carlo method with forced fixed detection for photon scatter simulation in CT.

Detected scattered photons can cause cupping and streak artifacts, significantly degrading the quality of CT images. For fast and accurate estimation of scatter intensities resulting from photon interactions with a phantom, we first transform the path probability of photons interacting with the phantom into a high-dimensional integral. Secondly, we develope a new efficient algorithm called gQMCFFD, which combines graphics processing unit(GPU)-based quasi-Monte Carlo (QMC) with forced fixed detection to approximate this integral. QMC uses low discrepancy sequences for simulation and is deterministic versions of Monte Carlo. Numerical experiments show that the results are in excellent agreement and the efficiency improvement factors are 4 ∼ 46 times in all simulations by gQMCFFD with comparison to GPU-based Monte Carlo methods. And by combining gQMCFFD with sparse matrix method, the simulation time is reduced to 2 seconds in a single projection angle and the relative difference is 3.53%.

Photons Induce Vesicular Exocytotic Release of Glutamate in a Power-Dependent Way.

Increasing evidence indicates that photobiomodulation, based on tissue irradiation with photons in the red to near-infrared spectrum, may be an effective therapeutic approach to central nervous system disorders. Although nervous system functionality has been shown to be affected by photons in animal models, as well as in preliminary evidence in healthy subjects or in patients with neuropsychiatric disorders, the mechanisms involved in the photobiomodulation effects have not yet been clarified. We previously observed that photobiomodulation could stimulate glutamate release. Here, we investigate mechanisms potentially involved in the glutamate-releasing effect of photons from adult mouse cerebrocortical nerve terminals. We report evidence of photon ability to induce an exocytotic vesicular release of glutamate from the terminals of glutamatergic neurons in a power-dependent way. It can be hypothesized that photobiomodulation, depending on the potency, can release glutamate in a potentially neurotoxic or physiological range.

Excellent ultraviolet optical limiting properties of Se nanosheets.

Selenium (Se) is located in the fourth period of the periodic table in group VIA (element 34). In this experiment, three different solvents (isopropyl alcohol, N-methyl-2-pyrrolidone, and ethanol) were used to prepare the two-dimensional Se nanosheets, which were manufactured by the liquid phase exfoliation method with a thickness of 3.35-4.64 nm and a transverse scale of several hundred nanometers. The nonlinear absorption properties at 355, 532, and 1064 nm were studied using the open apertureZ-scan technique. Final results showed that Se nanosheets exhibited optical limiting (OL) effect in all three wavebands and three solvents, and had large two-photon absorption coefficients, especially in ultraviolet (UV) waveband. Which proved that Se nanosheets had great potential application as excellent OL materials in UV waveband. Our research broadens the path for the semiconductor field of Se, inspires the application of Se in nonlinear optics field.

Development of a hydrated electron dosimeter for radiotherapy applications: A proof of concept.

BACKGROUND: Hydrated electrons, which are short-lived products of radiolysis in water, increase the optical absorption of water, providing a pathway toward near-tissue-equivalent clinical radiation dosimeters. This has been demonstrated in high-dose-per-pulse radiochemistry research, but, owing to the weak absorption signal, its application in existing low-dose-per-pulse radiotherapy provided by clinical linear accelerators (linacs) has yet to be investigated. PURPOSE: The aims of this study were to measure the optical absorption associated with hydrated electrons produced by clinical linacs and to assess the suitability of the technique for radiotherapy (⩽ 1 cGy per pulse) applications. METHODS: 40 mW of 660-nm laser light was sent five passes through deionized water contained in a 10 × 4 × $\times 4\times$ 2 cm3 glass-walled cavity by using four broadband dielectric mirrors, two on each side of the cavity. The light was collected with a biased silicon photodetector. The water cavity was then irradiated by a Varian TrueBeam linac with both photon (10 MV FFF, 6 MV FFF, 6 MV) and electron beams (6 MeV) while monitoring the transmitted laser power for absorption transients. Radiochromic EBT3 film measurements were also performed for comparison. RESULTS: Examination of the absorbance profiles showed clear absorption changes in the water when radiation pulses were delivered. Both the amplitude and the decay time of the signal appeared consistent with the absorbed dose and the characteristics of the hydrated electrons. By using literature value for the hydrated electron radiation chemical yield (3.0±0.3), we inferred doses of 2.1±0.2 mGy (10 MV FFF), 1.3±0.1 mGy (6 MV FFF), 0.45±0.06 mGy (6 MV) for photons, and 0.47±0.05 mGy (6 MeV) for electrons, which differed from EBT3 film measurements by 0.6%, 0.8%, 10%, and 15.7%, respectively. The half-life of the hydrated electrons in the solution was ∼ 24 µ $\umu$ s. CONCLUSIONS: By measuring 660-nm laser light transmitted through a cm-scale, multi-pass water cavity, we observed absorption transients consistent with hydrated electrons generated by clinical linac radiation. The agreement between our inferred dose and EBT3 film measurements suggests this proof-of-concept system represents a viable pathway toward tissue-equivalent dosimeters for clinical radiotherapy applications.

Seeing More with Less: Clinical Benefits of Photon-counting Detector CT.

Photon-counting detector (PCD) CT is an emerging technology that has led to continued innovation and progress in diagnostic imaging after it was approved by the U.S. Food and Drug Administration for clinical use in September 2021. Conventional energy-integrating detector (EID) CT measures the total energy of x-rays by converting photons to visible light and subsequently using photodiodes to convert visible light to digital signals. In comparison, PCD CT directly records x-ray photons as electric signals, without intermediate conversion to visible light. The benefits of PCD CT systems include improved spatial resolution due to smaller detector pixels, higher iodine image contrast, increased geometric dose efficiency to allow high-resolution imaging, reduced radiation dose for all body parts, multienergy imaging capabilities, and reduced artifacts. To recognize these benefits, diagnostic applications of PCD CT in musculoskeletal, thoracic, neuroradiologic, cardiovascular, and abdominal imaging must be optimized and adapted for specific diagnostic tasks. The diagnostic benefits and clinical applications resulting from PCD CT in early studies have allowed improved visualization of key anatomic structures and radiologist confidence for some diagnostic tasks, which will continue as PCD CT evolves and clinical use and applications grow. ©RSNA, 2023 Quiz questions for this article are available in the supplemental material. See the invited commentary by Ananthakrishnan in this issue.

Low-Intensity Visible and Near-Infrared Light-Induced Cell Signaling Pathways in the Skin: A Comprehensive Review.

Objective: To describe current knowledge regarding established and putative cell signaling pathways involved in skin photobiomodulation. Background: The skin is the largest and most accessible organ of the body. It is the first line of defense against the external environment, including solar radiation. Among solar rays, visible and infrared non-ionizing photons may reach human skin and trigger a cascade of non-thermal cell signaling pathways called photobiomodulation (PBM). The use of PBM using artificial light sources has been known for more than 50 years, but it has not yet been widely accepted due to uncertainty about the cellular mechanisms of action. However, much knowledge has been gained in this field in recent years, which will be summarized in this review. Methods: An extensive literature review was performed using Medline, Embase, and Google Scholar as research databases to acquire relevant publications in this particular field. Results: A comprehensive description of chromophores, primary and secondary effectors is provided in addition to a visual representation of known and putative cell signaling mechanisms involved in such complex light-skin interactions. Also, a summary of clinical indications of skin PBM, key light parameters, and promising skin applications (local and systemic) are mentioned. Conclusions: In PBM, skin cells are the first to absorb photons, triggering specific cell-signaling pathways through primary and secondary effectors, leading to enhanced cell repair and survival, notably in hypoxic or stressed cells. A better understanding of the mechanisms of action will help us optimize known indications and discover new ones.

CMOS Time-to-Digital Converters for Biomedical Imaging Applications.

Time-to-digital converters (TDCs) are high-performance mixed-signal circuits capable of timestamping events with sub-gate delay resolution. As a result of their high-performance, in recent years TDCs were integrated in complementary metal-oxide-semiconductor (CMOS) technology with highly sensitive photodetectors known as single-photon avalanche diodes (SPADs), to form digital silicon photomultipliers (dSiPMs) and SPAD imagers. Time-resolved SPAD-based sensors are capable of detecting the absorption of a single photon and timestamping it with picosecond resolution. As such, SPAD-based sensors are very useful in the field of biomedical imaging, using time-of-flight (ToF) information to produce data that can be used to reconstruct high-quality biological images. Additionally, the capability of integration in standard CMOS technologies, allows SPAD-based sensors to provide high-performance, while maintaining low cost. In this paper, we present an overview of fundamental TDC principles, and an analysis of state-of-the-art TDCs. Furthermore, the integration of TDCs into dSiPMs and SPAD imagers will be discussed, with an analysis of the current results of TDCs in different biomedical imaging applications. Finally, several important research challenges for TDCs in biomedical imaging applications are presented.

Two-Photon Excitation Spectra of Various Fluorescent Proteins within a Broad Excitation Range.

Two-photon excitation fluorescence laser-scanning microscopy is the preferred method for studying dynamic processes in living organ models or even in living organisms. Thanks to near-infrared and infrared excitation, it is possible to penetrate deep into the tissue, reaching areas of interest relevant to life sciences and biomedicine. In those imaging experiments, two-photon excitation spectra are needed to select the optimal laser wavelength to excite as many fluorophores as possible simultaneously in the sample under consideration. The more fluorophores that can be excited, and the more cell populations that can be studied, the better access to their arrangement and interaction can be reached in complex systems such as immunological organs. However, for many fluorophores, the two-photon excitation properties are poorly predicted from the single-photon spectra and are not yet available, in the literature or databases. Here, we present the broad excitation range (760 nm to 1300 nm) of photon-flux-normalized two-photon spectra of several fluorescent proteins in their cellular environment. This includes the following fluorescent proteins spanning from the cyan to the infrared part of the spectrum: mCerulean3, mTurquoise2, mT-Sapphire, Clover, mKusabiraOrange2, mOrange2, LSS-mOrange, mRuby2, mBeRFP, mCardinal, iRFP670, NirFP, and iRFP720.

Photobiomodulation therapy in mood disorders: a systematic review.

Mood disorders are common, debilitating and impose a high-cost burden on society. Side effects and resistance to psychiatric drugs justify finding new treatment methods. Photobiomodulation therapy (PBMT) uses photons of light to repair, modulate and improve the function of target tissue. The purpose of this study is to systematically review the use of PBMT for the treatment of mood disorders and to identify the useful parameters of PBMT, the level of evidence of its effectiveness, and the degree of its practical recommendation. "Google scholar," "Pub Med," "Scopus," and "Science direct" online databases were searched based on Preferred Reporting Items for Systematic Reviews and meta-analyses (PRISMA) guidelines. The human or animal studies written in English and published from January 2009 to August 2021 were included. Sixteen studies, which included four randomized controlled trials (RCTs), met the inclusion criteria. Infrared wavelength ranges from 800 to 830 nm, power density of 250 mW/cm2 and energy density of 60 to 120 J/ cm2 were the most used PBMT parameters. Bias risk assessment was performed to evaluate the quality of RCTs in which 2 out of 4 RCTs were evaluated as high quality. Based on grade practice recommendations, PBMT can be classified as strongly recommended for moderate grade of major depressive disorder (MDD) and recommended for anxiety disorder. In bipolar disorder, further studies are needed to recommend this therapeutic method.

Real-Time In Vivo Sensing of Nitric Oxide Using Photonic Microring Resonators.

Real-time in vivo detection of biomarkers, particularly nitric oxide (NO), is of utmost importance for critical healthcare monitoring, therapeutic dosing, and fundamental understanding of NO's role in regulating many physiological processes. However, detection of NO in a biological medium is challenging due to its short lifetime and low concentration. Here, we demonstrate for the first time that photonic microring resonators (MRRs) can provide real-time, direct, and in vivo detection of NO in a mouse wound model. The MRR encodes the NO concentration information into its transfer function in the form of a resonance wavelength shift. We show that these functionalized MRRs, fabricated using complementary metal oxide semiconductor (CMOS) compatible processes, can achieve sensitive detection of NO (sub-µM) with excellent specificity and no apparent performance degradation for more than 24 h of operation in biological medium. With alternative functionalizations, this compact lab-on-chip optical sensing platform could support real-time in vivo detection of myriad of biochemical species.

Material decomposition from photon-counting CT using a convolutional neural network and energy-integrating CT training labels.

Objective.Photon-counting CT (PCCT) has better dose efficiency and spectral resolution than energy-integrating CT, which is advantageous for material decomposition. Unfortunately, the accuracy of PCCT-based material decomposition is limited due to spectral distortions in the photon-counting detector (PCD).Approach.In this work, we demonstrate a deep learning (DL) approach that compensates for spectral distortions in the PCD and improves accuracy in material decomposition by using decomposition maps provided by high-dose multi-energy-integrating detector (EID) data as training labels. We use a 3D U-net architecture and compare networks with PCD filtered back projection (FBP) reconstruction (FBP2Decomp), PCD iterative reconstruction (Iter2Decomp), and PCD decomposition (Decomp2Decomp) as the input.Main results.We found that our Iter2Decomp approach performs best, but DL outperforms matrix inversion decomposition regardless of the input. Compared to PCD matrix inversion decomposition, Iter2Decomp gives 27.50% lower root mean squared error (RMSE) in the iodine (I) map and 59.87% lower RMSE in the photoelectric effect (PE) map. In addition, it increases the structural similarity (SSIM) by 1.92%, 6.05%, and 9.33% in the I, Compton scattering (CS), and PE maps, respectively. When taking measurements from iodine and calcium vials, Iter2Decomp provides excellent agreement with multi-EID decomposition. One limitation is some blurring caused by our DL approach, with a decrease from 1.98 line pairs/mm at 50% modulation transfer function (MTF) with PCD matrix inversion decomposition to 1.75 line pairs/mm at 50% MTF when using Iter2Decomp.Significance.Overall, this work demonstrates that our DL approach with high-dose multi-EID derived decomposition labels is effective at generating more accurate material maps from PCD data. More accurate preclinical spectral PCCT imaging such as this could serve for developing nanoparticles that show promise in the field of theranostics (therapy and diagnostics).

Use of gamma radiation and artificial neural network techniques to monitor characteristics of polyduct transport of petroleum by-products.

This study presents a methodology based on the dual-mode gamma densitometry technique in combination with artificial neural networks to simultaneously determine type and quantity of four different fluids (Gasoline, Glycerol, Kerosene and Fuel Oil) to assist operators of a fluid transport system in pipelines commonly found in the petrochemical industry, as it is necessary to continuously monitor information about the fluids being transferred. The detection system is composed of a 661.657 keV (137Cs) gamma-ray emitting source and two NaI(Tl) scintillation detectors to record transmitted and scattered photons. The information recorded in both detectors was directly applied as input data for the artificial neural networks. The proposed intelligent system consists of three artificial neural networks capable of predicting the fluid volume percentages (purity level) with 94.6% of all data with errors less than 5% and MRE of 1.12%, as well as identifying the pair of fluids moving in the pipeline with 95.9% accuracy.

Portable light detectors for bioluminescence biosensing applications: A comprehensive review from the analytical chemist's perspective.

Bioluminescence, that is the emission of light in living organisms, has been extensively explored and applied for diverse bioanalytical applications, spanning from molecular imaging to biosensing. The unprecedented technological evolution of portable light detectors opened new possibilities to implement bioluminescence detection into miniaturized devices. We are witnessing a number of applications, including DNA sequencing, reporter gene assays, DNA amplification for point-of care and point-of need analyses relying on BL. Several photon detectors are currently available for measuring low light emission, such as photomultiplier tubes (PMT), charge-coupled devices (CCD), complementary metal oxide semiconductors (CMOS), single photon avalanche diodes (SPADs), silicon photomultipliers (SiPMs) and smartphone-integrated CMOS. Each technology has pros and cons and several issues, such as temperature dependence of the instrumental specific noise, the power supply, imaging capability and ease of integration, should be considered in the selection of the most appropriate detector for the selected BL application. These issues will be critically discussed from the perspective of the analytical chemist together with relevant examples from the literature with the goal of helping the reader in the selection and use of the most suitable detector for the selected application and to introduce non familiar readers into this exciting field.

First Clinical Photon-counting Detector CT System: Technical Evaluation.

Background The first clinical CT system to use photon-counting detector (PCD) technology has become available for patient care. Purpose To assess the technical performance of the PCD CT system with use of phantoms and representative participant examinations. Materials and Methods Institutional review board approval and written informed consent from four participants were obtained. Technical performance of a dual-source PCD CT system was measured for standard and high-spatial-resolution (HR) collimations. Noise power spectrum, modulation transfer function, section sensitivity profile, iodine CT number accuracy in virtual monoenergetic images (VMIs), and iodine concentration accuracy were measured. Four participants were enrolled (between May 2021 and August 2021) in this prospective study and scanned using similar or lower radiation doses as their respective clinical examinations performed on the same day using energy-integrating detector (EID) CT. Image quality and findings from the participants' PCD CT and EID CT examinations were compared. Results All standard technical performance measures met accreditation and regulatory requirements. Relative to filtered back-projection reconstructions, images from iterative reconstruction had lower noise magnitude but preserved noise power spectrum shape and peak frequency. Maximum in-plane spatial resolutions of 125 and 208 µm were measured for HR and standard PCD CT scans, respectively. Minimum values for section sensitivity profile full width at half maximum measurements were 0.34 mm (0.2-mm nominal section thickness) and 0.64 mm (0.4-mm nominal section thickness) for HR and standard PCD CT scans, respectively. In a 120-kV standard PCD CT scan of a 40-cm phantom, VMI iodine CT numbers had a mean percentage error of 5.7%, and iodine concentration had root mean squared error of 0.5 mg/cm3, similar to previously reported values for EID CT. VMIs, iodine maps, and virtual noncontrast images were created for a coronary CT angiogram acquired with 66-msec temporal resolution. Participant PCD CT images showed up to 47% lower noise and/or improved spatial resolution compared with EID CT. Conclusion Technical performance of clinical photon-counting detector (PCD) CT is improved relative to that of a current state-of-the-art CT system. The dual-source PCD geometry facilitated 66-msec temporal resolution multienergy cardiac imaging. Study participant images illustrated the effect of the improved technical performance. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Willemink and Grist in this issue.

Design and modeling of a Laue lens for radiation therapy with hard x-ray photons.

We have designed and modeled a novel optical system composed of a Laue lens coupled to an x-ray tube that produces a focused beam in an energy range near 100 keV (λ= 12.4 picometer). One application of this system is radiation therapy where it could enable treatment units that are considerably simpler and lower in cost than present technologies relying on linear accelerators. The Laue lens is made of Silicon Laue components which exploit the silicon pore optics technology. The lens concentrates photons to a small region thus allowing high dose rates at the focal area with very much lower dose rates at the skin and superficial regions. Monte Carlo simulations with Geant4 indicate a dose deposition rate of 0.2 Gy min-1in a cylindrical volume of 0.7 mm diameter and 10 mm length, and a dose ratio of 72 at the surface (skin) compared to the focus placed 10 cm within a water phantom. Work is ongoing to newer generation crystal technologies to increase dose rate.

Tetrahedron beam imaging with a multi-pixel thermionic emission X-ray source and a photon-counting detector: A benchtop experimental study.

PURPOSE: A tetrahedron beam (TB) X-ray system with a linear X-ray source array and a linear detector array positioned orthogonal to each other may overcome the X-ray scattering problem of traditional cone-beam X-ray systems. We developed a TB imaging benchtop system using a linear array X-ray source to demonstrate the principle and benefits of TB imaging. METHODS: A multi-pixel thermionic emission X-ray (MPTEX) source with 48 focal spots in 4-mm spacing was developed in-house. The X-ray beams are collimated to a stack of fan beams that are converged to a 6-mm wide multi-row photon-counting detector (PCD). The data collected with a sequential scan of the sources at a fixed view angle were synthesized to a 2D radiography image by a shift-and-add algorithm. The data collected with a full rotation of the system were reconstructed into 3D TB CT (TBCT) images using an Feldkamp, Davis, and Kress (FDK)-based computed tomography (CT) algorithm modified for the TB geometry. RESULTS: With an 18.8-cm long source array and a 35-cm long detector array, the TB benchtop system provides a 25-cm cross-sectional and 8-cm axial field of view (FOV). The scatter-to-primary ratio (SPR) was approximately 17% for TB, as compared with 120% for cone beam geometry. The TBCT system enables reconstructions in two-dimensional radiography and three-dimensional volumetric CT. The TBCT images were free of "cupping" artifacts and have similar image quality as diagnostic helical CT. CONCLUSIONS: A TB imaging benchtop imaging system was successfully developed with MPTEX source and PCD. Phantom and animal cadaver imaging demonstrated that the TB system can produce satisfactory radiographic X-ray images and 3D CT images with image quality comparable to diagnostic helical CTs.