Search

In proton therapy, a highly conformal proton dose can be delivered to the tumor by means of the steep distal dose penumbra at the end of the beam range. The proton beam range, however, is highly sensitive to range uncertainty, which makes accurately locating the proton range in the patient difficult. In-vivo range verification is a method to manage range uncertainty, one of the promising techniques being prompt gamma imaging (PGI). In earlier studies, we proposed gamma electron vertex imaging (GEVI), and constructed a proof-of-principle system. The system successfully demonstrated the GEVI imaging principle for therapeutic proton pencil beams without scanning, but showed some limitations under clinical conditions, particularly for pencil beam scanning proton therapy. In the present study, we upgraded the GEVI system in several aspects and tested the performance improvements such as for range-shift verification in the context of line scanning proton treatment. Specifically, the system showed better performance in obtaining accurate prompt gamma (PG) distributions in the clinical environment. Furthermore, high shift-detection sensitivity and accuracy were shown under various range-shift conditions using line scanning proton beams.

Proton therapy for cancer treatment has a precise dose deposition capability owing to the nature of the interactions of heavy charge particles with matter resulting in a Bragg Peak. Uncertainties in the proton range can limit the scope of proton therapy. Academia Sinica PET employs a modular design for In-beam detection using SiPMs and crystals read out by STiC asic for range verification. In this work we report the depth distribution of the positron emitters from a PMMA sample irradiated with 130 MeV protons at the Chang Gung Memorial Hospital measured using a compact 32-channel setup. The timing capabilities of this system are assessed and presented. The depth dependence of the positron activity measured using coincidences agrees well with the Geant4 simulated distributions. Using a multi-exponential fit function we estimate and compare the relative amounts of different positron emitting isotopes with the relative cross sections. The application of this method can be useful to estimate the anatomical changes between different treatment sessions. The modular design of the AS-PET currently under development at Academia Sinica is presented and the simulated images of the reconstructed positron activity for the palm sized modules are used to assess the range verification capability.

Novel technological solutions for the design of positron emission tomography (PET) systems to be used in the in-beam beam-on monitoring of proton tracks within biological tissues represent the frontier of the instrumentation in proton therapy. We report a novel all-digital PET dual heads prototype based on the multivoltage threshold (MVT) technology, able to operate in beam-on modality. We demonstrate in phantom and animal experiments that, by using an event selection based on the energy of singles and on the delay with respect to the radio-frequency period of the proton beam bunches, the monitoring PET system is able to image the induced activity by both pristine and pencil proton beam with energy ranging between 70 and 150 MeV during irradiation.

Purpose In proton therapy, the potential of using high-dose rates in the cancer treatment is being explored. High-dose rates could improve efficiency and throughput in standard clinical practice, allow efficient utilization of motion mitigation techniques for moving targets, and potentially enhance normal tissue sparing due to the so-called FLASH effect. However, high-dose rates are difficult to reach when lower energy beams are applied in cyclotron-based proton therapy facilities, because they result in large beam sizes and divergences downstream of the degrader, incurring large losses from the cyclotron to the patient position (isocenter). In current facilities, the emittance after the degrader is reduced using circular collimators; however, this does not provide an optimal matching to the acceptance of the following beamline, causing a low transmission for these energies. We, therefore, propose to use a collimation system, asymmetric in both beam size and divergence, resulting in symmetric emittance in both beam transverse planes as required for a gantry system. This new emittance selection, together with a new optics design for the following beamline and gantry, allows a better matching to the beamline acceptance and an improvement of the transmission. Methods We implemented a custom method to design the collimator sizes and shape required to select high emittance, to be transported by the following beamline using new beam optics (designed with TRANSPORT) to maximize acceptance matching. For predicting the transmission in the new configuration (new collimators + optics), we used Monte Carlo simulations implemented in BDSIM, implementing a model of PSI Gantry 2 which we benchmarked against measurements taken in the current clinical scenario (circular collimators + clinical optics). Results From the BDSIM simulations, we found that the new collimator system and matching beam optics results in an overall transmission from the cyclotron to the isocenter for a 70 MeV beam of 0.72%. This is an improvement of almost a factor of 6 over the current clinical performance (0.13% transmission). The new optics satisfies clinical beam requirements at the isocenter. Conclusions We developed a new emittance collimation system for PSI's PROSCAN beamline which, by carefully selecting beam size and divergence asymmetrically, increases the beam transmission for low-energy beams in current state-of-the-art cyclotron-based proton therapy gantries. With these improvements, we could predict almost 1% transmission for low-energy beams at PSI's Gantry 2. Such a system could easily be implemented in facilities interested in increasing dose rates for efficient motion mitigation and FLASH experiments alike., Medical Physics, 48 (12), ISSN:0094-2405, ISSN:2473-4209, ISSN:1522-8541

Unlike the conventional optical needle directed along the optical axis, we propose an approach to generate an optical needle with prescribed polarization direction and length by inversely focusing ...

Magnetic fluids belong to the class of nanomaterials with a high gain of light absorption, aggregative and sedimentation stability as well as controllability by external fields, which is of interest to use in the field of optoacoustics. The purpose of the work was to experimentally study the effect of the optoacoustic transformation in a magnetic fluid, depending on the concentration of magnetic colloidal particles, boundary conditions, intensity of the laser as well as to identify the possibilities of using the magnetic fluid as an element of the optoacoustic transformation in a number of applications.A brief analysis of the optoacoustic transformation mechanism in a magnetic fluid was carried out and a technique and an installation that implements the shadow measurement variant developed. A Lotis type laser was used as a source of ultrasonic pulse-laser excitation in magnetic fluids. A quartz and air were used as a material transmitting the energy of laser radiation in a magnetic fluid. Receiving of ultrasound signals was made by a piezoelectric probe at a working frequency of 5 MHz. In the measurement process, the concentration of the dispersed phase in tmagnetic fluid was varied from zero to 8 % and the energy in the impulse – from zero to 10 mJ.For the first time, it was established that: a) an amplitude of the function of the optoacoustic transformation in a magnetic fluid, depending on the concentration of the dispersed phase, has a maximum determined by the fluid physical properties and boundary conditions; b) for all samples within the measurement error, a quasilinear dependence of the specified amplitude of energy in the laser pulse in the range of 0–8 MJ has been established.A number ways of the optoacoustic effects in magnetic fluids to use in ultrasonic testing, measuring the intensity of the laser radiation had been suggested.

We report an elliptical beam design for aberration mitigation in high-resolution optical coherence tomography (OCT). We polished a large angle on the fiber terminal facet in the sample arm to make a non-rotational symmetric beam with different numerical apertures (NA) for the two axes vertical to the optical axis. By sacrificing the resolution in the out-of-plane transverse direction, the elliptical beam mitigated the aberration introduced by the focusing optics in the OCT system. The elliptical beam with a doubled NA in the in-plane transverse direction promoted the axial field-of-view (FOV) by about 50% and increased the signal back-coupling efficiency by about 25%. We verified the feasibility of the design by imaging the USAF 1951 resolution chart, swine cornea ex vivo, and human skin in vivo. Results show that the proposed method relieves aberration-related problems in high-resolution OCT. Ministry of Education (MOE) Ministry of Health (MOH) National Medical Research Council (NMRC) Published version This work was supported in part by China Railway Siyuan Survey and Design Group Company Ltd. under Grant 2020K183, in part by National Medical Research Council under Grant MOH-OFIRG19may-0009, and in part by Ministry of Education Singapore under Grant MOE-T2EP30120-0001.

Background and Aim: Beam shaper applicator is one of the dedicated applicators for intraoperative electron radiotherapy which is usually employed for large tumors irradiation. Due to the high weight and lack of possibility of direct placement on the patient’s body, a considerable air gap exists between the applicator and patient. Therefore, determination of the effective position of electron source (SSDeff) is absolutely necessary to correct the applicator output for air gap effect and accurate delivery of the prescribed dose to the patient. The aim of this study was to determine the SSDeff for all square fields of beam shaper applicator at different electron energies using Monte Carlo (MC) simulation. Materials and Methods: At first, the head of LIAC accelerator and beam shaper applicator were simulated by MCNPX MC code and then, the validity of the simulated model was evaluated through comparing the calculated percentage depth dose (PDD) curves at different field sizes and energies with the corresponding practiacal values. After verifying the simulated model, the SSDeff was determined for different field sizes and electron energies using inverse square law (ISL) method. Results: The results showed that the SSDeff is a function of electron energy and radiation field size. Dependency of SSDeff on field size variations was much more than that on the alterations in the electron energy. Generally, increase in the field size or electron energy led to increase in SSDeff. Conclusion: The determined SSDeff values for the electron beam of the beam shaper applicator in our study, can be used to correct the electron beam output for clinical purposes.

Optical Coherence Tomography (OCT) is a high-resolution, non-invasive technique to image subsurface tissue and tissue functions. A broadband light source illuminates an object and the reflected photons are processed using an interferometer, demodulated into inphase and quadrature components and then digitized. The captured data contains information about the velocity of the moving scatterers but current Doppler estimation algorithms have a limited velocity detection range. Here we demonstrate Doppler OCT (DOCT) detection of in vivo of blood flow in a rat aorta with over 1 m/s peak velocity through an esophageal DOCT probe using a new processing technique. Previous methods have used a transverse Kasai (TK) autocorrelation estimation to estimate the velocity. By calculating the Kasai autocorrelation with a lag in the depth or axial direction, backscattered frequency information is obtained. Through subtraction with stationary backscattered information, the Doppler shift is obtained by the axial Kasai (AK) technique. Maximum non-aliased Doppler frequency estimation using a time domain DOCT system increased from +/-4 kHz to =+/-1.6 MHz. The TK has better velocity resolution in the low flow rate range and when combined with the AK we demonstrate a dynamic frequency range over 100 dB with a velocity detection range from 10 [micro]m/s to over 1 m/s. This velocity range spans from microcirculation to cardiac blood flow velocities.

Electron and photon beams demonstrate extraordinary characteristics useful for the treatment of cancer. These characteristics are essential to analyze before the calibration of the linear accelerator with dual energies. This study focused on the dosimetric characteristics of the different energies of electron beam for different field sizes. The basic objective of this work was to calculate the dosimetric parameters and characteristics of the electron beam, especially depth dose characteristics along the central axis. In this work, 6 MeV, 9 MeV, 12 MeV, 15 MeV and 18 MeV of electron beam and 6 MV and 15 MV of photon beam with different field sizes were used. The characteristics of the depth dose of electron and photon beams in water were analyzed to optimize the radiation quality for radiation treatment planning. The different beam characteristics are due to different interactions that occur between electron beams giving them a definite range, whereas photon beams are attenuated leading to dose deposition and a much larger range with no definite end. Depth dose characteristics of electron and photon beams are not similar since the interaction of these beams with matter depends on their quality. Attenuation and penetration factors change with changing dosimetric parameters. A complete analysis of the dosimetric characteristics of electron and photon beams helps to choose the more accurate beam for the treatment of cancer. This work helps to increase accuracy in the treatment of cancer with radiotherapy. Copyright(c) The Authors

The greatest advantage of scattering theory-based ultrasound tomography (UT) is its ability to investigate small structures. DBIM is the Distorted Born Iterative Method. The nearest neighbour inter...

The aim of this work is to analyze existing detectors for the relative dosimetry of small radiation fields in external beam radiation therapy and the requirements for them, consider the problems in carrying out dosimetry of small radiation fields, determine the physical conditions under which an external photon beam can be designated as a small field. In modern radiation therapy, there is an increase in the use of small static fields, which is facilitated by the general availability of standard and optional multileaf collimators and new generation treatment machines of various designs. There is growing interest in the use of such radiation techniques as stereotactic radiosurgery, stereotactic body radiotherapy, intensity modulated radiotherapy, which are widely used small fields. This has increased the uncertainties in clinical dosimetry, especially for small fields. Accurate dosimetry of small fields is important when commissioning linear accelerators and is a difficult task, especially for very small fields used in stereotactic radiotherapy. In the course of the work, a study of topical problems in the dosimetry of small radiation fields in external beam radiation therapy has been carried out. The physical conditions under which the external photon beam can be designated as a small field are considered. A review and analysis of existing detectors for the relative dosimetry of small radiation fields, as well as an analysis of the requirements for the character. The analysis revealed that liquid ionization chambers, silicon diodes, diamond detectors, organic scintillators, radiochromic films, thermoluminescent dosimeters and optically stimulated luminescence detectors are considered suitable for relative dosimetry of small photon fields and are recommended for use in clinics where radiotherapy is performed.

A technique for Doppler flow mapping in optical coherence tomography is described. The proposed technique allows obtaining data on the location, direction, and velocity of biological fluid flows by analyzing fluctuations in the speckle pattern and estimating phase shifts in the interference signal. It can be used in ophthalmic optical coherence tomography for functional imaging of the blood circulation in the vessels of the retina and optic nerve.

Recently developed x-ray transmittance modeling-based three-step algorithm compensates for the spectral distortion in the photon-counting detector (PCD) and estimates the line-integrals of the basis materials. The x-ray transmittance modeling linearizes the nonlinear forward imaging model and derives a computationally efficient three-step algorithm that achieves almost unbiased and minimum variance estimator. In this article, we apply the algorithm to the experimental data from a research whole-body PCD-computed tomography (CT) system. We perform pixel-by-pixel calibration using water-equivalent phantoms to fit the output of the scanner to the forward model and then feed the calibrated data into the three-step algorithm. Experimental data from iodine phantom and swine abdomen scans demonstrate that the proposed algorithm compensates for the spectral distortion effectively and estimates the line-integrals of two basis materials, water and iodine, efficiently. The proposed method substantially reduces the beam hardening and ring artifacts present in the test phantom compared to those of the image-based material decomposition method and the images directly reconstructed from the raw data of the system. The algorithm also exhibits less bias and comparable noise to those of the other methods for various x-ray energies.

A new experimental setup to continuously and automatically measure ultrasonic elastic wave velocities, X-ray radiography, and X-ray diffraction in large volume press is developed to explore structu...

Ultrasound vascular imaging based on ultrafast plane wave imaging and singular value decomposition (SVD) clutter filtering has demonstrated superior sensitivity in blood flow detection. However, ultrafast ultrasound vascular imaging is susceptible to electronic noise due to the weak penetration of unfocused waves, leading to a lower signal-to-noise ratio (SNR) at larger depths. In addition, incoherent clutter artifacts originating from strong and moving tissue scatterers that cannot be completely removed create a strong mask on top of the blood signal that obscures the vessels. Herein, a method that can simultaneously suppress the background noise and incoherent artifacts is proposed. The method divides the tilted plane or diverging waves into two sub-groups. Coherent spatial compounding is performed within each sub-group, resulting in two compounded datasets. An SVD-based clutter filter is applied to each dataset, followed by a correlation between the two datasets to produce a vascular image. Uncorrelated noise and incoherent artifacts can be effectively suppressed with the correlation process, while the coherent blood signal can be preserved. The method was evaluated in wire-target simulations and phantom, in which around 7 dB to 10 dB SNR improvement was shown. Consistent results were found in a flow channel phantom with improved SNR by the proposed method (39.9 ± 0.2 dB) against conventional power Doppler (29.1 ± 0.6 dB). Last, we demonstrated the effectiveness of the method combined with block-wise SVD clutter filtering in a human liver, breast tumor and inflammatory bowel disease datasets. The improved blood flow visualization may facilitate more reliable small vessel imaging for a wide range of clinical applications, such as cancer and inflammatory diseases.

Doppler ultrasound is the premier modality to analyze blood flow dynamics in clinical practice. With conventional systems, Doppler can either provide a time-resolved quantification of the flow dynamics in sample volumes (spectral Doppler) or an average Doppler velocity/power [color flow imaging (CFI)] in a wide field of view (FOV) but with a limited frame rate. The recent development of ultrafast parallel systems made it possible to evaluate simultaneously color, power, and spectral Doppler in a wide FOV and at high-frame rates but at the expense of signal-to-noise ratio (SNR). However, like conventional Doppler, ultrafast Doppler is subject to aliasing for large velocities and/or large depths. In a recent study, staggered multi-pulse repetition frequency (PRF) sequences were investigated to dealias color-Doppler images. In this work, we exploit the broadband nature of pulse-echo ultrasound and propose a dual-wavelength approach for CFI dealiasing with a constant PRF. We tested the dual-wavelength bandpass processing, in silico , in laminar flow phantom and validated it in vivo in human carotid arteries ( ${n} = 25$ ). The in silico results showed that the Nyquist velocity could be extended up to four times the theoretical limit. In vivo , dealiased CFI were highly consistent with unfolded Spectral Doppler ( ${r}^{2}=0.83$ , ${y}=1.1{x}+0.1$ , ${N}=25$ ) and provided consistent vector flow images. Our results demonstrate that dual-wavelength processing is an efficient method for high-velocity CFI.

Cosine response is an important characteristic of an optical detector for irradiance measurements. The non-ideal cosine response of a detector may lead to errors in irradiance measurements. In this paper, a theoretical simulation of irradiance generated due to isotropic point light sources is carried out for different illumination conditions. Simulation results show that the errors in irradiance measurements due to the cosine error of detectors become significantly high at the edges and corners of the floor when a light source is placed at the center of the roof. Further, it is observed that the errors are more in the enclosures having a height smaller than the floor dimensions. Even calibrated detectors measure erratic values of irradiance for a wider angle of incidence. Therefore, cosine errors in irradiance measurements are of great importance especially during the current scenarios of the COVID-19 pandemic, for ensuring the correct dose of Ultraviolet Germicidal Irradiation (UVGI).

Positron Emission Tomography (PET) is a widely-used imaging modality for medical research and clinical diagnosis. Here we demonstrate, through detailed experiments and simulations, an exploration of the benefits of exploiting the quantum entanglement of linear polarisation between the two positron annihilation photons utilised in PET. A new simulation, which includes the predicted influence of quantum entanglement on the interaction of MeV-scale photons with matter, is validated by comparison with experimental data from a cadmium zinc telluride (CZT) PET demonstrator apparatus. In addition, a modified setup enabled the first experimental constraint on entanglement loss for photons in the MeV regime. Quantum-entangled PET offers new methodologies to address key challenges in next generation imaging. As an indication of the potential benefits, we present a simple method to quantify and remove in-patient scatter and random backgrounds using only the quantum entanglement information in the PET events., Comment: 39 pages, 12 figures

In ultrahigh field magnetic resonance imaging (MRI) using a static magnetic field over 7 T, the inhomogeneity in the time-varying magnetic field ( $B_{1}$ ), which is caused by its short wavelength, is mitigated by using a multichannel radio frequency (RF) coil as an antenna. However, the conventional multichannel RF coil has a fixed configuration; consequently, its transmit efficiency (TE) changes according to the head shape of the patient. In this study, a geometrically adjustable eight-channel RF transmitter head coil for 7-T MRI was proposed. All resonators and supporting structures (called bridges) in the coil have interlocking teeth at their sides, allowing each channel to adjust its geometric location according to the head shape of the patient. Scenarios for conventional and proposed coils in three different configurations were simulated and compared in terms of the transmitted component of the $B_{1}$ field ( $B_{1}^{+}$ field) and specific absorption rate (SAR) maps. The simulation results indicate that, for a given configuration and head shape, the TE of the proposed coil was higher than that of the conventional coil, while the SAR efficiency remained unchanged. Furthermore, the S-parameter matrix of the proposed coil and the measured $B_{1}$ field produced by the two channels facing each other show that the proposed coil resonates at 298 MHz with acceptable mutual coupling and effectively improves the $B_{1}$ field intensity. Moreover, the obtained signal-to-noise ratio (SNR) maps and magnetic resonance (MR) images prove that the proposed coil is an efficient candidate for an RF transmitter or transceiver head coil used in 7-T MRI.

The present study verified and evaluated the dosimetric effects of protons scattered from a snout and an aperture in clinical practice, when a range compensator was included. The dose distribution calculated by a treatment planning system (TPS) was compared with the measured dose distribution and the dose distribution calculated by Monte Carlo simulation at several depths. The difference between the measured and calculated results was analyzed using Monte Carlo simulation with filtration of scattering in the snout and aperture. The dependence of the effects of scattered protons on snout size, beam range, and minimum thickness of the range compensator was also investigated using the Monte Carlo simulation. The simulated and measured results showed that the additional dose compared with the results calculated by the TPS at shallow depths was mainly due to protons scattered by the snout and aperture. This additional dose was filtered by the structure of the range compensator so that it was observed under the thin region of the range compensator. The maximum difference was measured at a depth of 16 mm (8.25%), with the difference decreasing with depth. Analysis of protons contributing to the additional dose showed that the contribution of protons scattered from the snout was greater than that of protons scattered from the aperture when a narrow snout was used. In the Monte Carlo simulation, this effect of scattered protons was reduced when wider snouts and longer‐range proton beams were used. This effect was also reduced when thicker range compensator bases were used, even with a narrow snout. This study verified the effect of scattered protons even when a range compensator was included and emphasized the importance of snout‐scattered protons when a narrow snout is used for small fields. It indicated that this additional dose can be reduced by wider snouts, longer range proton beams, and thicker range compensator bases. These results provide a better understanding of the additional dose from scattered protons in clinical practice.

A combination of high-resolution neutron powder diffraction, energy-dependent cold-neutron radiography, and synchrotron-based X-ray diffraction radiography on two pouch bag cells of different dimen...

Background and purpose: Three-dimensional dosimetry of proton therapy (PT) with chemical dosimeters is challenged by signal quenching, which is a lower dose-response in regions with high ionization density due to high linear-energy-transfer (LET) and dose-rate. This study aimed to assess the viability of an empirical correction model for 3D radiochromic silicone-based dosimeters irradiated with spot-scanning PT, by parametrizing its LET and dose-rate dependency. Materials and methods: Ten cylindrical radiochromic dosimeters (Ø50 and Ø75 mm) were produced in-house, and irradiated with different spot-scanning proton beam configurations and machine-set dose rates ranging from 56 to 145 Gy/min. Beams with incident energies of 75, 95 and 120 MeV, a spread-out Bragg peak and a plan optimized to an irregular target volume were included. Five of the dosimeters, irradiated with 120 MeV beams, were used to estimate the quenching correction factors. Monte Carlo simulations were used to obtain dose and dose-averaged-LET (LETd) maps. Additionally, a local dose-rate map was estimated, using the simulated dose maps and the machine-set dose-rate information retrieved from the irradiation log-files. Finally, the correction factor was estimated as a function of LETd and local dose-rate and tested on the different fields. Results: Gamma-pass-rates of the corrected measurements were >94% using a 3%-3 mm gamma analysis and >88% using 2%-2 mm, with a dose deviation of

A technique has been developed to characterize the doping concentration distribution of inertial confinement fusion capsules based on a method combining absorption retrieval, computerized tomograph...

3D Filtered Back Projection (FBP) is a three-dimensional reconstruction algorithm usually used in Cone Beam Computed Tomography (CBCT) system. FBP is one of the most popular algorithms due to its reconstruction is fast while quality of the result is acceptable. It can also handle a more considerable amount of data with same computer performance with other algorithms. However, the quality of a reconstructed image by the FBP algorithm strongly depends on spatial filters and denoising filters applied to projections. In this paper an evaluation of the reconstructed image quality of the CBCT system by using different denoising filters and spatial filters to find out the best filters for the CBCT system is performed. The result shows that, there is a significantly decrease of the noise of projection with the combination of Median and Gaussian filters. The reconstructed image has high resolution with Cosine filter and becomes more sharpen with Hanning filter.

An optically read-out glass gas electron multiplier (G-GEM) detector is expected to simplify complicated quality assurance measurements for hadron therapies by imaging the dose distribution of the ...

Ambient dose equivalent rates were measured in the environment of the Fukushima prefecture using NaI(Tl)/CsI(Tl) scintillation detectors and CdZnTe/Ge semiconductor detectors. The dose rates obtained at the same locations varied beyond uncertainty (1σ). By replacing the spectrum-dose conversion operators obtained from the anterior–posterior geometry with those from the rotational geometry, the dose rates agreed with each other within uncertainties, except for a CsI(Tl) scintillation detector with a considerably flat crystal configuration, due to its excessive directional dependence.

Magnetic hyperthermia is a promising cancer therapy gaining great interest in recent years. In this therapy, in addition to magnetic particles, important elements include techniques for detecting the position and temperature of magnetic particles in a tumor region in determining the effectiveness of therapeutic heating. In previous studies, we developed a low invasive heating and wireless temperature measurement system for magnetic hyperthermia using a ferromagnetic implant with low Curie temperature (FILCT). To make this approach feasible in clinical settings, a challenge remains when the FILCT injected into the tumor region deviates from the central axis of drive coil. As a result, the heating efficiency of FILCT and the temperature measurement accuracy of FILCT decrease. In this study, we develop an automatic localization system for magnetic particles. Using the constructed system, it was possible to automatically locate the position of magnetic particles with an accuracy below 1 mm in vitro by operating magnetic field supply and detection (MFSD) unit in two modes of coarse scanning (rotary scanning) and fine-tuned scanning (linear scanning) based on three pickup voltages induced in three pickup coils symmetrically installed inside drive coil.

The Kansai BNCT Medical Center has a cyclotron based epithermal neutron source for clinical Boron Neutron Capture Therapy. The system accelerates a proton to an energy of 30 MeV which strikes a beryllium target producing fast neutrons which are moderated down to epithermal neutrons for BNCT use. While clinical studies in the past have shown BNCT to be highly effective for malignant melanoma of the skin, to apply BNCT for superficial lesions using this system it is necessary to shift the thermal neutron distribution so that the maximum dose occurs near the surface. A dose distribution shifter was designed to fit inside the collimator to further moderate the neutrons to increase the surface dose and reduce the dose to the underlying normal tissue. Pure polyethylene was selected, and a Monte Carlo simulation was performed to determine the optimum thickness of the polyethylene slab. Compared with the original neutron beam, the shifter increased the thermal neutron flux at the skin by approximately 4 times. The measured and simulated central axis depth distribution and off axis distribution of the thermal neutron flux were found to be in good agreement. Compared with a 2 cm thick water equivalent bolus, a 26% increase in the thermal neutron flux at the surface was obtained, which would reduce the treatment time by approximately 29%. The DDS is a safe, simple and an effective tool for the treatment of superficial tumours for BNCT if an initially fast neutron beam requires moderation to maximise the thermal neutron flux at the tissue surface.

Background: Symmetry and flatness are two quantities which should be evaluated in the commissioning and quality control of an electron beam in electron beam radiotherapy. The aim of this study is to compare symmetry and flatness obtained using three different dosimeters for various small and large fields in electron beam radiotherapy with linac. Materials and methods: Beam profile measurements were performed in a PTW water phantom for 10, 15 and 18 MeV electron beams of an Elekta Precise linac for small and large beams (1.5 × 1.5 cm 2 to 20 × 20 cm 2 field sizes). A Diode E detector and Semiflex-3D and Advanced Markus ionization chambers were used for dosimetry. Results: Based on the obtained results, there are minor differences between the responses from different dosimeters (Diode E detector and Semiflex-3D and Advanced Markus ionization chambers) in measurement of symmetry and flatness for the electron beams. The symmetry and flatness values increase with increasing field size and electron beam energy for small and large field sizes, while the increases are minor in some cases. Conclusions: The results indicate that the differences between the symmetry and flatness values obtained from the three dosimeter types are not practically important.

Intensity correlations in turbulent biological tissues are evaluated when collimated Gaussian laser beam is used. Variations of the intensity correlations in biological tissues are investigated ver...

The technology of magnetic resonance imaging is developing towards higher magnetic fields to improve resolution and contrast. However, whole-body imaging at 7 T or even higher flux densities remains challenging due to wave interference, tissue inhomogeneities, and high RF power deposition. Nowadays, proper RF excitation of a human body in prostate and cardiac MRI is only possible to achieve by using phased arrays of antennas attached to the body (so-called surface coils). Due to safety concerns, the design of such coils aims at minimization of the local specific absorption rate (SAR), keeping the highest possible RF signal in the region of interest. Most previously demonstrated approaches were based on resonant structures such as e.g. dipoles, capacitively-loaded loops, TEM-line sections. In this study, we show that there is a better compromise between the transmit signal \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\bf{B}}}_{{\bf{1}}}^{{\boldsymbol{+}}}$$\end{document}B1+ and the local SAR using non-resonant surface coils generating a low electric field in the proximity of their conductors. With this aim, we propose and experimentally demonstrate a leaky-wave antenna implemented as a periodically-slotted microstrip transmission line. Due to its non-resonant radiation, it induces only slightly over half the peak local SAR compared to a state-of-the-art dipole antenna but has the same transmit efficiency in prostate imaging at 7 T. Unlike other antennas for MRI, the leaky-wave antenna does not require to be tuned and matched when placed on a body, which makes it easy-to-use in prostate imaging at 7 T MRI., Magnetic resonance imaging of the prostate is challenging due to the trade-off between a high magnetic field and safety concern of local specific absorption rate. Here, the authors demonstrate that a leaky-wave antenna design can reduce local heating due to non-resonant radiation.

Atomic magnetometers operated in spin-exchange relaxation-free (SERF) have the potential to replace superconducting quantum interference devices (SQUIDs) in the field of biomagnetism. Here, we demonstrate the dual-axis closed-loop control of a single-beam SERF magnetometer that allows sensing of two orthogonal magnetic fields simultaneously and independently with suppressed crosstalk effect, achieved by applying a rotating modulation field and using the negative feedback. Operating in the dual-axis closed-loop mode with a miniature 4 $\times $ 4 $\times $ 4 mm 87Rb cell, we achieve the magnetic field sensitivity of 20 fT/Hz1/2 and a bandwidth of 1.8 kHz. In addition to the experimental study of the sensitivity and bandwidth, we perform a theoretical analysis of the dual-axis response and develop an effective decoupling method. The implementation of closed-loop control enables the magnetometer to be robust against the disturbance of the ambient field, which could enlarge the dynamic range, enhance the systematic stability, and suppress the crosstalk effect. Such a simple, yet high-performance SERF magnetometer could be suitable as a promising candidate in the field of biomagnetism, allowing for a denser sensor array and opening up new possibilities for noninvasive biomagnetic imaging.

The penetration depth of photoacoustic imaging in biological tissues has been fundamentally limited by the strong optical attenuation when light is delivered externally through the tissue surface. To address this issue, we previously reported internal-illumination photoacoustic imaging using a customized radial-emission optical fiber diffuser, which, however, has complex fabrication, high cost, and non-uniform light emission. To overcome these shortcomings, we have developed a new type of low-cost fiber diffusers based on a graded-scattering method in which the optical scattering of the fiber diffuser is gradually increased as the light travels. The graded scattering can compensate for the optical attenuation and provide relatively uniform light emission along the diffuser. We performed Monte Carlo numerical simulations to optimize several key design parameters, including the number of scattering segments, scattering anisotropy factor, divergence angle of the optical fiber, and reflective index of the surrounding medium. These optimized parameters collectively result in uniform light emission along the fiber diffuser and can be flexibly adjusted to accommodate different applications. We fabricated and characterized the prototype fiber diffuser made of agarose gel and intralipid. Equipped with the new fiber diffuser, we performed thorough proof-of-concept studies on ex vivo tissue phantoms and an in vivo swine model to demonstrate the deep-imaging capability (~10 cm achieved ex vivo) of photoacoustic tomography. We believe that the internal light delivery via the optimized fiber diffuser is an effective strategy to image deep targets (e.g., kidney) in large animals or humans.

A method for controlling the synchrotron beam intensity during proton irradiation of patients is proposed. The control is based on the installation of two precision “warm-liquid” pad chambers, one at the exit from the last scanning magnet and the other in front of the patient. The intensity density of the beam directed to the irradiated target using two pad chambers is measured. The measured intensity density profiles are compared with specified parameters; the beam is turned off if the measured parameters deviate from the permissible ones. The result is an increase in the proton therapy conformity due to the continuous dose and dose field boundary control in the target for each accelerator pulse.

Accurate gain control of PET detectors is a prerequisite for quantitative accuracy. A shift in the 511 keV peak position can lead to errors in scatter correction, degrading quantitation. The PET detectors in a PET/MR scanner are subject to thermal transients due to eddy currents induced during gradient-intensive MRI sequences. Since the gain of silicon photomultiplier-based detectors changes with temperature, good gain control is particularly challenging. In this paper we describe a method that utilizes information from the entire singles spectrum to create a real-time gain control method that maintains gain of PET detectors stable within approximately ±0.5% (±2.5 keV) with varying levels of scatter and in the presence of significant thermal transients. We describe the methods used to combine information about multiple peaks and how this algorithm is implemented in a way that permits real-time processing on a field-programmable gate array. Simulations demonstrate rapid response time and stability. A method (“virtual scatter filter”) is also described that extracts unscattered photopeak events from phantom data and demonstrates the accuracy of the photopeak for various radionuclides that emit energies in addition to the pure 511 keV annihilation peak. Radionuclides 52 Mn, 55 Co, 64 Cu, 89 Zr, 90 Y, and 124 I are included in the study for their various forms of spectral contamination.

In emergency situations with the release of radioactivity to the environment, possible radiation doses to the affected public are estimated with computational modeling. However, it should be noted that the estimates to a certain degree depend on various calculation parameters that may make the predicted radiation doses inconclusive. To reduce occurring uncertainties is possible by adjusting estimated outcomes with measurement data. The gamma-radiation spectra from the released radioactive cloud is measured by systems for radiation situation monitoring in the area surrounding the source of radioactive materials release. The feasibility study aimed at obtaining information needed for improvement of radiation doses estimates quality should be carried out. Due to certain problems related to performance of experimental work, there is the need to devel-op new approach to calculate gamma-spectra of radioactivity emitted from the released cloud. The solution of this problem will allow to select the parameters of equipment and measurement parameters necessary for adjusting the forecasts of radiation doses to the population in a case of accidents with a radiation factor based on the results of processing gamma radiation spectra.

This study evaluated the non-thermal effects of microwave on bovine lens by measuring the S-parameters induced by the dielectric coefficient variation in bovine lens. A closed, integrated biological experiment system was designed to expose bovine lens to microwave radiation quantitatively, and S-parameters were measured. Morphological evaluations were also performed during microwave radiation to evaluate the reaction mechanism of the non-thermal effects of microwave on the bovine lens. The results showed that the bovine lens became gradually cloudy and its refractive index changed significantly with increasing doses of microwave radiation. A comparison of experimental and control bovine lenses stained with hematoxylin and eosin revealed that the change in bovine lens might be a result of the nuclear fragmentation of lens epithelial cells and disorderly arrangement of lens fiber cells, which were induced by the vibration and friction of fiber tissues upset by microwave radiation. Further, the fluctuating decrements of 3.8 dB in S21 showed that the non-thermal effects of microwave could lead to the variations in the bovine lens dielectric coefficient. These findings suggest that the dielectric coefficient may quantitatively describe the physiological state of bovine lens. This study might be the valuable reference for the establishment of new electromagnetic radiation safety standard.

The design features of a multichannel pad (position-sensitive) ionization-chamber camera (PC) based on a warm liquid are considered. The PC is intended for joint operation with a TV-type detector (DTeT) in simulation of dose fields in a water phantom in the mode of a scanning (modulated) pencil proton beam. The electronic section of the PC has been tested with a pulsed X-ray source. As a detector, the PC measures the absolute value of the dose released in a specified target voxel by the pencil proton beam in a single pulse.

We propose and investigate an efficient terahertz radiation scheme using low-energy electron beams, including a single-electron bunch and a train of bunches, to excite cascaded gratings. It combines the mechanisms of wakefield radiation and of Smith–Purcell radiation (SPR) by transforming a series of surface waves into coherent SPR. Compared with the conventional wakefield radiation and SPR schemes, its radiation efficiency and power can be remarkably higher. In addition, it changes the conventional incoherent SPR into coherent emission with frequency being continuously tunable. Thus, it affords a promising way of developing the high power, coherent, and tunable terahertz radiation sources.

A magnetically coupled three-coil system to have one transmitting and two receiving coils is considered. We show that the position of the transmitting coil can be estimated from the ratio of received wave amplitudes and its angular derivative when the two receiving coils are strongly coupled to each other and each of the receiving coils is weakly coupled to the transmitting coil, i.e., a Fano resonance phenomenon. A coupled mode theory is developed to elucidate the midrange position sensing mechanism, where the ratio of received wave amplitudes is inversely proportional to the ratio of the coupling strengths of each receiving coil to the transmitting coil at the intrinsic resonance frequency of the receiving coils.

Optical Coherence Tomography (OCT) imaging technique has emerged as a non- or minimally invasive modality in the clinical pathogenesis such as deep tissue examining and optical biopsy etc. The OCT imaging increases the Depth of Focus (DoF) by devising mechanisms to increase an Optical Transfer Function (OTF) of the imaging system. This is achieved through an apodization technique on the surface of lens in conjugation with the femtosecond Bessel-type laser beam. An investigation on postulation of OTF through a masked aperture, or specifically a micro-dot is investigated to measure variations of intensity profile at the optical coordinates in the radial as well as axial directions. The intensity variations in the radial and axial coordinates are calibrated to obtain the information, which significantly helps in devising of OCT imaging system. A theoretical investigation of OTF matching the experimental relationship between spot size and DoF in response to obscuration ratio is presented in this paper. This mathematical approach could be applied to different types of masking functions by meticulously exploring the parameters of optical coordinates.

The results of designing a printed ultra-wideband antenna intended for use as a part of a multichannel microwave radiometer are presented. The design of a ring-shaped antenna with a built-in infrared sensor for measuring skin temperature is proposed. The results of numerical simulation of the electromagnetic field of the antenna in tissues of a biological object are presented. The results of calculating the voltage standing wave ratio, measurement depth of the antenna, the resolution, and the distribution of radiation power over the tissue volume under study are presented.

Photon-counting detectors are a promising new technology for computed tomography (CT) systems. They provide energy-resolved CT data at very high spatial resolution without electronic noise and with improved tissue contrasts. This review article gives an overview of the principles of photon-counting detector CT, of potential clinical benefits and limitations, and of the experience gained so far in pre-clinical installations.

We present an ultrasound algorithm [lesion imaging and target detection in multiple scattering (LITMUS)] suited to image lesions (hypoechoic) or targets (hyperechoic) in highly complex structures. In such media, standard ultrasound imaging techniques fail to detect lesions or targets due to aberrations and the loss of linearity between propagation distance and propagation time, caused by multiple scattering of ultrasound waves. The present algorithm (LITMUS) has the capability to predict the location as well as the size of such lesions/targets by using the multiple scattered ultrasound signals to its advantage. In this experimental and computational study, we use an ultrasound linear array. Lesions/targets are embedded at varying depths inside multiple scattering media with varying density of scatterers. In the simulations, plastic scatterers are used as the source of multiple scattering in a propagation medium (water). In the experiments, melamine sponges are used, with air alveoli as the scattering source. For multiple locations along the transducer, the incoherent backscattered intensity of the backscattered signals is extracted and the linear growth of the diffusive halo over time is tracked. Sudden changes in this growth indicate the presence of a region with reduced heterogeneity, indicative of the presence of a lesion/target. This methodology is combined with a depression detection algorithm to predict the size and location of the lesion/targets with high fidelity, despite the presence of strong heterogeneity and multiple scattering.

Ultra-low field magnetic resonance imaging (ULF MRI) is an effective imaging technique that applies the ultrasensitive detector of superconducting quantum interference device (SQUID) sensor to detect the MR signal at a microtesla field range. In this work, we designed and developed a SQUID-based ULF MRI system with a frequency-adjustable measurement field, the performance of which was characterized via water phantoms. In order to enhance the MR signals, a 500 mT Halbach magnet was used to prepolarize the magnetization of the sample prior to excitation. The signal-to-noise-ratio (SNR) of the spin-echo- (SE-) based pulse sequence can reach up to 70 in a single scan. The images were then reconstructed successfully by using the maximum likelihood expectation maximization (MLEM) algorithm based on the backprojection imaging method. It was demonstrated that an in-plane resolution of 1.8 × 1.8 mm2 can be achieved which indicated the feasibility of SQUID-based MRI at the ULF.

The application of optical methods for tissue diagnosis, activation, and treatment suffers dramatically from the low accessible depths due to strong light scattering in tissues. Here we demonstrate a method to address this issue by utilizing transient ultrasound waves, travelling transversally to the light propagation direction, to guide light into deeper tissue regions. We study the formation of the ultrasound-induced refractive index structures and waveguides using simple ultrasound field configurations and analyze their effects on the propagation of short light pulses. As a proof of concept, we demonstrate using 5 ns pulses of 532 nm light and Intralipid-20%-based phantoms with $$\mu _{\mathrm{s}}^\prime$$ μ s ′ up to 4.5 cm−1 a waveguide supported light intensity increase up to the depths of at least 90 mean free paths.

Optical coherence tomography (OCT) with a robust depth-resolved attenuation compensation method for a wide range of imaging applications is proposed and demonstrated. The proposed novel OCT attenuation compensation algorithm introduces an optimized axial point spread function (PSF) to modify existing depth-resolved methods and mitigates under and overestimation in biological tissues, providing a uniform resolution over the entire imaging range. The preliminary study is implemented using A-mode numerical simulation, where this method achieved stable and robust compensation results over the entire depth of samples. The experiment results using phantoms and corneal imaging exhibit agreement with the simulation result evaluated using signal-to-noise (SNR) and contrast-to-noise (CNR) metrics.

Purpose To explain the concept behind the Castrop toric lens (tIOL) power calculation formula and demonstrate its application in clinical examples. Methods The Castrop vergence formula is based on a pseudophakic model eye with four refractive surfaces and three formula constants. All four surfaces (spectacle correction, corneal front and back surface, and toric lens implant) are expressed as spherocylindrical vergences. With tomographic data for the corneal front and back surface, these data are considered to define the thick lens model for the cornea exactly. With front surface data only, the back surface is defined from the front surface and a fixed ratio of radii and corneal thickness as preset. Spectacle correction can be predicted with an inverse calculation. Results Three clinical examples are presented to show the applicability of this calculation concept. In the 1st example, we derived the tIOL power for a spherocylindrical target refraction and corneal tomography data of corneal front and back surface. In the 2nd example, we calculated the tIOL power with keratometric data from corneal front surface measurements, and considered a surgically induced astigmatism and a correction for the corneal back surface astigmatism. In the 3rd example, we predicted the spherocylindrical power of spectacle refraction after implantation of any toric lens with an inverse calculation. Conclusions The Castrop formula for toric lenses is a generalization of the Castrop formula based on spherocylindrical vergences. The application in clinical studies is needed to prove the potential of this new concept.

Monochromatic hard X-rays with high brightness are desired for medical applications including Auger therapy. One can generate such X-rays through laser-Compton scattering (LCS) by allowing photons from a compact laser system to interact with electrons accelerated by a compact electron accelerator. In this paper, after a brief description of laser-Compton X-ray sources, a scheme called crab crossing to enhance the X-ray intensity is proposed. The effect of crab crossing is evaluated, and we report our dedicated laser system for the crab crossing LCS research.The luminosity enhancement factor by crab crossing is evaluated. For the electron beam, a rf deflector will be used to generate a tilted electron beam. For the laser system, chirped pulsed amplification is adopted. Yb-doped optical fibers and a Yb:YAG thin-disk is used for the laser gain media.The luminosity enhancement factor by crab crossing is expected to be 3.8 when the crossing angle is 45 degrees. 10mJ pulse energy was achieved by thin-disk regenerative amplifier. The pulse duration after the pulse compressor was about 1.5 ps.We are going to demonstrate the LCS X-ray enhancement by crab crossing of electron beam and laser pulse. The expected enhancement factor is 3.8. We have successfully finished the laser development and the proof-of-principle experiment will be conducted soon.