Two-dimensional Detector Array Research Articles

Preliminary study of luminescence phenomena from various materials under ultra-high dose rate proton beam irradiation for dose management

This research aimed to identify materials capable of emitting visible light useful for dose management at ultra-high dose rate (uHDR). Various materials were irradiated with proton beams at a normal dose rate (NDR) and uHDR, and the resulting surface luminescence was captured using a high-sensitivity camera. The luminescence images were compared with the corresponding dose distributions. The luminescence of Tough Water Phantoms (Kyoto Kagaku Co. Ltd.) with various thicknesses was also observed to evaluate the depth distributions. Dose distributions were measured using two-dimensional ionization chamber detector arrays. The Tough Bone Phantom (Kyoto Kagaku Co. Ltd.) exhibited the strongest luminescence among the materials, followed by the Tough Water Phantom. The metals exhibited relatively weak luminescence. The luminescence profiles of the Tough Water Phantom, water, the Tough Lung Phantom (Kyoto Kagaku Co. Ltd.), and an acrylic were similar to the dose profiles. The luminescence distribution of the Tough Water Phantom in the depth direction was similar to that of the dose distributions. The luminescence at uHDR and NDR were approximately equivalent. The Tough Water Phantom was found to be a suitable material for dosimetry, even at uHDR. More detailed measurement data, such as wavelength data, must be collected to elucidate the luminescence mechanism.

Cross-waveband optical computing imaging.

A novel, to the best of our knowledge, cross-spectral optical computing imaging experiment has been achieved through a single exposure of a charge-coupled device. The experimental setup integrates single-pixel imaging (SPI) with ghost imaging (GI) through a photoelectric conversion circuit and a synchronous modulation system. The experimental process involves modulation in one wavelength band (in SPI) and demodulation using the GI algorithm in another. Significantly, our approach utilizes optical computing demodulation, a departure from the conventional electronic demodulation in GI (SPI), which involves the convolution between the bucket optical signals and the modulated patterns on the digital micromirror device. A proof-of-concept cross-band imaging experiment from near-infrared to visible light has been carried out. The results highlight the system's ability to capture images at up to 20 frames per second using near-infrared illumination, which are then reconstructed in the visible light spectrum. This success not only validates the feasibility of our approach but also expands the potential applications in the SPI or GI fields, particularly in scenarios where two-dimensional detector arrays are either unavailable or prohibitively expensive in certain electromagnetic spectra such as x-ray and terahertz.

Modeling of Gamma Index for Prediction of Pretreatment Quality Assurance in Stereotactic Body Radiation Therapy of the Liver.

The purpose of this study was to develop a predictive model to evaluate pretreatment patient-specific quality assurance (QA) based on treatment planning parameters for stereotactic body radiation therapy (SBRT) for liver carcinoma. We retrospectively selected 180 cases of liver SBRT treated using the volumetric modulated arc therapy technique. Numerous parameters defining the plan complexity were calculated from the DICOM-RP (Radiotherapy Plan) file using an in-house program developed in MATLAB. Patient-specific QA was performed with global gamma evaluation criteria of 2%/2 mm and 3%/3 mm in a relative mode using the Octavius two-dimensional detector array. Various statistical tests and multivariate predictive models were evaluated. The leaf speed (MILS) and planning target volume size showed the highest correlation with the gamma criteria of 2%/2 mm and 3%/3 mm (P < 0.05). Degree of modulation (DoM), MCSSPORT, leaf speed (MILS), and gantry speed (MIGS) were predictors of global gamma pass rate (GPR) for 2%/2 mm (G22), whereas DoM, MCSSPORT, leaf speed (MILS) and robust decision making were predictors of the global GPR criterion of 3%/3 mm (G33). The variance inflation factor values of all predictors were <2, indicating that the data were not associated with each other. For the G22 prediction, the sensitivity and specificity of the model were 75.0% and 75.0%, respectively, whereas, for G33 prediction, the sensitivity and specificity of the model were 74.9% and 85.7%%, respectively. The model was potentially beneficial as an easy alternative to pretreatment QA in predicting the uncertainty in plan deliverability at the planning stage and could help reduce resources in busy clinics.

Multi-pixel photon counter-based gamma camera with pinhole collimator to locate Cs-137 sources at high dose rates for the Fukushima nuclear power plant

The Fukushima Daiichi Nuclear Power Plant was severely damaged during the 2011 Great East Japan Earthquake. However, the ongoing decommissioning work has been limited by the complexity of the reactor's internal structure and very high radiation levels; locating radioactive sources is essential for efficient decommissioning. Conventional gamma cameras are mainly designed for low radiation dose (∼mSv/h) and using them under high radiation conditions is difficult (>Sv/h). Therefore, we developed a pinhole gamma camera with a gamma radiation detector consisting of a high-speed YGAG scintillator array and multi-pixel photon counters to locate radioactive sources at high dose rates. The gamma-ray photon signals captured by the developed two-dimensional detector array can be processed at a speed as high as >1 MHz/pixel using the developed large scale integrated circuit. Herein, we report the measurement results of an extremely high radioactivity of 137Cs (∼34 TBq) using the developed gamma camera. The gamma-ray source position was determined using an angular size of ∼4.6°, with images obtained at 2 m from the radioactive source and at a dose rate of 0.3 Sv/h. The direct gamma rays with a photoelectric peak at 662 keV and scattered component of gamma rays can be distinguished from the measured spectrum. We also characterize the imaging capability of the 137Cs depending on the detected gamma-ray energies and discuss related details.

Point spread function modeling for photoacoustic tomography - II: two-dimensional detection geometries.

Point spread function (PSF) modeling is important for the characterization of the imaging performance of a photoacoustic computed tomography (PACT) system. This work aims to study the degradation mechanism of PSF in PACT and investigate the impact of the shape of detection geometry on PSF. PSF modeling of three typical two-dimensional detection geometries, including circular, curved, and linear detector arrays, is presented. Based on the non-ideal detection geometries, the effect of detector bandwidth and detector aperture on PSF is also investigated. Moreover, PSFs of each geometry with typical detector bandwidths and typical detector aperture sizes are presented. Experiments are conducted to validate the results. The proposed PSF modeling approach and corresponding results can help predict and interpret the quality of photoacoustic images produced by a practical PACT system. It is beneficial for the design of detector arrays for enhanced imaging performance.

Super-resolution of dose distributions from a two-dimensional array detector using a convolutional neural network

Super-resolution of dose distributions from a two-dimensional array detector using a convolutional neural network

Validation of an EGSnrc-based Monte Carlo model for a complex 2D-array for technical QA measurements of a linear accelerator.

Multi-axis ionization chamber arrays can be used for quality assurance (QA) and measurement of linear accelerator (linac) specific data. In this work, the ability of the IC Profiler (Sun Nuclear Corp., Melbourne, Florida) detector array to measure the photon beam quality specifier %dd(10) and TPR20, 10 was investigated. To investigate the method for beam energy QA using a two-dimensional detector array, a Monte Carlo-based model of the detector array was developed and validated. A Monte Carlo-based model of the IC Profiler detector array with Quad Wedge accessories was developed in detail from drawings provided by the manufacturer using the egs++ class library from the EGSnrc code system. Monte Carlo simulations were used to calculate the absorbed dose in the 251 ionization chambers of the IC profiler in the 6 MV Elekta Precise radiation field. To validate the results from the Monte Caro simulations, measurements were performed on clinical 6 MV linacs. To vary the photon beam quality of the Elekta 6 MV linac, the current of the bending magnet was varied. Furthermore, the area ratio was calculated from IC Profiler measurements with the Quad Wedgeaccessories. Measurements as well as Monte Carlo simulations confirmed the linear relationship between the area ratio and the investigated photon beam quality specifier %dd(10) and TPR20, 10 for the investigated radiation source. Furthermore, the Monte Carlo-simulated data were within the 95% confidence interval of the linear fit to the measured data. This enabled the Monte Carlo-based IC Profiler model to be used for further investigations. The values were calculated for various electron beam sizes and the angle of incidence on the target of thelinac. A Monte-Carlo-based model of the detector array was developed, which could successfully reproduce measurements, demonstrating that even very complex geometries can be modeled in EGSnrc. Moreover, the study showed that the validated Monte Carlo model has the potential to investigate variations in beam parameters and their effects on AR ratios and %dd(10) that may not be investigated experimentally. While these findings may help users gain a deeper understanding of the QA method, the Monte Carlo model enables other complex investigations, such as the simulation of measurements in the presence of magnetic fields, or the simulation of measurements on novel treatment delivery techniques anddevices.

Commissioning and Performance Evaluation of Varian TrueBeam Linear Accelerator

Aim: The aim of this study is to present a report on the commissioning results of the Varian TrueBeam machine with available photon energies so that it can benefit medical physicists during the entire commissioning process. Subjects and Methods: All tests were performed as per the recommendation of the Atomic Energy Regulatory Board. The beam profiles and percentage depth dose of both photon and electron beams were measured with Sun nuclear Radiation Field Analyzer and 0.125 cc ionization chamber. Output accuracy and consistency of photon and electron beams were measured using 0.6 cc cylindrical ionization chamber and 0.350 cc parallel plate ionization chamber, respectively. To measure the congruency of radiation and optical field and isocenter check with respect to gantry, collimator, and couch, self-developed films were used. Results: Isocenter shift due to gantry, collimator, and couch, rotation was found to be within ± 2-mm diameter circle. Congruency of optical and radiation fields was measured for symmetric fields 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, and 30 cm × 30 cm for all available energy and was within ± 2 mm. Dosimetric leaf gap value for the multi-leaf collimator was measured with 0.125 cc ionization chamber and values are −0.853 mm, −1.106 mm, −1.097 mm, −0.765 mm, and −1.005 mm for energies 6 MV, 10 MV, 15 MV, 6 flattening filter free (FFF), and 10 FFF, respectively. Conclusions: All electrical, mechanical, dosimetric, and safety measurement were found to be within permissible limits. Before clinical use, the beam data are crosschecked with point dosimetry, portal dosimetry, and MapCHECK two-dimensional detector array and results are within tolerance.

Evaluation of the feasibility of cardiac gating for SBRT of ventricular tachycardia based on real-time ECG signal acquisition.

To investigate the feasibility of cardiac synchronized gating in stereotactic body radiation therapy (SBRT) of ventricular tachycardia (VT) using a real-time electrocardiogram (ECG) signal acquisition. Stability of beam characteristics during simulated ECG gating was examined by developing a microcontroller interface to a Varian Clinac iX linear accelerator allowing gating at frequencies and duty cycles relevant to cardiac rhythm. Delivery accuracy was evaluated by measuring dose linearity with an ionization chamber, and flatness and symmetry with a two-dimensional detector array, for different gating windows within typical human cardiac cycle periods. To establish a practical method of gating based on actual ECG signals, an AD8232 Heart Monitor board was used to acquire the ECG signal and synchronize the beam delivery. Real-time cardiac gated delivery measurements were performed for a single 10×10cm2 field and for a VT-SBRT plan using intensity-modulated radiation therapy (IMRT). Dose per monitor unit (MU) values were found to be linear within most gating windows investigated with maximum differences relative to non-gated delivery of <2% for gating windows ≥200ms and for >10MUs. Beam profiles for both gated and non-gated modes were also found to agree with maximum differences of 0.5% relative to central axis dose for all sets of beam-on/beam-off combinations. Comparison of dose distributions for intensity-modulated SBRT plans between non-gating and cardiac gating modes provided a gamma passing rate of 97.2% for a 2% 2mm tolerance. Beam output is stable with respect to linearity, flatness, and symmetry for gating windows within cardiac cycle periods. Agreement between dose distributions for VT-SBRT using IMRT in non-gated and cardiac cycle gated delivery modes shows that the proposed methodology is feasible. Technically, gating for delivery of SBRT for VT is possible with regard to beam stability.

Evaluation of a High-Resolution Large-Area Two-Dimensional Detector Array for Pre-Treatment Verification of Multiple-Target SRS Plans Using a Single Isocenter

<h3>Purpose/Objective(s)</h3> Pre-treatment verification of multiple-target SRS plans using a single isocenter is challenging because of small target sizes and multiple off-isocenter targets. Targets located further away from the isocenter are more sensitive to rotational setup variations, increasing the risk of geometrical miss. It demands high-resolution detector for small target sizes and large detector area for measuring multiple targets at once. The purpose of this study is to evaluate a high-resolution large-area two-dimensional (2D) detector array for pre-treatment verification of multiple-target SRS plans using a single isocenter. <h3>Materials/Methods</h3> A 2D detector array was evaluated for this purpose. It is based on a silicon complementary metal-oxide-semiconductor platform, which enables a compact design, fast read-out, and high pixel density with each pixel comprising a radiation-sensitive photodiode, a capacitor and three transistors. Its spatial resolution is 0.4 mm, with 105,000 pixels across a large active area of 120 × 140 mm². Ten multiple-target SRS plans were selected such that each plan has at least 2 targets appear on a longitudinal plane cross the isocenter. All plans were created in a treatment planning system using 6 MV flattening filter free photon beam. The typical plan consisted of one or two coplanar arcs, and two to three non-coplanar arcs. All plans were delivered in patient geometry with the detector center aligned to the plan isocenter. The detector plane was rotated to the corresponding desired longitudinal plane to measure the composite dose in a single measurement. The smallest target measured was 0.12 cc. The largest center-to-center target separation measured was 12 cm. Six of the plans in which the target separations were relatively short were able to be cross verified with a patient-specific quality assurance (PSQA) tool, whose detector area is of 77 × 77 mm². The measured 2D dose distributions in true composite were compared with the calculated dose distributions. Gamma index analysis was performed using 3%/1 mm criteria with a 10% dose threshold. <h3>Results</h3> With the 2D detector array, the gamma passing rates are all greater than 95% except one, which is 93%. The average gamma-passing rate is 97.7%. For the 6 plans cross verified, the average gamma-passing rates are 98.2% and 96.1% with the 2D detector array and PSQA tool, respectively. <h3>Conclusion</h3> The 2D detector array was demonstrated to be suitable and offers an efficient way for pre-treatment verification of multiple-target SRS plans using a single isocenter. The advantages of this 2D array include: 1) High-resolution of 0.4 mm avoids dose interpolations for plans calculated with 0.5 -1.0 mm dose grid and potentially avoids "false positive" results due to more measured points; 2) Large active area of 120 × 140 mm² allows simultaneous verification of multiple targets in true composite in patient geometry.

Monolithic Integration of Gesn on Si for IR Camera Demonstration

Due to the development of cost-efficient detector technologies in the NIR (Near Infrared), new areas of application are constantly being addressed. This affects autonomous driving, where LiDAR (Light Detection and Ranging) systems with better eye safety are being developed, as well as low-cost night vision cameras. Another area of application is NIR spectroscopy, e.g. in the areas of food monitoring, environmental research or medical technology. The increasing need for portable, low-cost analysis devices, for example for "on-site" measurements or for everyday life, is driving the development of highly miniaturized and low-cost lab-on-a-chip systems. The NIR detectors and NIR cameras available on the market are primarily based on materials from group III/V compound semiconductors, e.g. InGaAs. However, the CMOS (Complementary Metal Oxide Semiconductor) standard process cannot be used for the production of this technology, which significantly increases the cost factor and thus limits its use on the market. A promising alternative is offered by group IV based detectors, in particular Ge and GeSn detectors, which can be monolithically integrated on a Si substrate. As a result, such detector systems can be processed much more cost-efficiently with CMOS compatible standard technology. The NIR absorption properties are also comparable to III/V components.This paper reports on the monolithic integration of Ge and GeSn detector arrays on Si substrates for the realization of a camera system. The entire system consists of a photonic chip, a readout chip and a standard microcontroller, which is connected to a laptop via USB. The SNR (signal-to-noise ratio) is an important parameter for such an integrated system. The quantum efficiency of each individual pixel sensor has to be maximized and a high fill factor per pixel is aimed for. A particularly high fill factor is achieved here with optical light coupling via the substrate back-side, since the front-side metallization does not interfere with the optical coupling area. Furthermore, the metallization acts then as a mirror, the light thus passes through the absorption area twice and leads to a higher quantum efficiency.However, the main obstacle of Ge and GeSn, compared to III/V devices, is the higher intrinsic charge carrier concentration, which leads to a significantly higher dark current. A possible solution is the zero bias operation of the detector at the expected dark current minimum. The dark current is 3 orders of magnitude smaller at 0 V compared to an operating point at -1 V. Another criterion for the circuit is that a signal range or photocurrent supports a wide dynamic range (between nA and µA). For this purpose, the photocurrent is fed into the evaluation electronics via a triple cascaded current mirror. The measured value is output to a 12-bit ADC (Analog Digital Converter) integrated in the microcontroller via a current/voltage converter, two buffers and a sample hold element. With the help of additional multiplexers, the circuit can be used to read out several detectors and thus address a pixel matrix.We report on the fabrication of the photonic chip, which is carried out using CMOS compatible processes and MEMS (Micro-Electro-Mechanical System) processes in combination with an epitaxial growth of the active device structures. The photonic chip is based on 150 mm Si substrates, which were prepared first with multiple ion implantation steps. The active pin detector layers, consisting of Si and Ge or GeSn, were grown by means of molecular beam epitaxy. Afterwards, deep trenches were now etched between the detectors in a MEMS process to minimize crosstalk between neighboring pixels. The detectors were structured then using CMOS processes, and the backside is polished or structured. Finally, a two layer frontside-metallization is applied for the contacts. We demonstrate the functionality of both two-dimensional and linear detector arrays and show possible applications such as NIR cameras or NIR spectrometers.

A two-dimensional array detector for determining the direction to gamma-ray source

With increasing demand in the nuclear technology field for locating isolated radioactive sources, numerous studies have focused on the array detector. Given the concerns over the limited performance that only determined the horizontal direction of traditional direction algorithms, an improved algorithm based on the two-dimensional (2D) array detector is proposed for determining the gamma-source direction in the full 2π hemisphere field of view. Coupling a 2 × 2 Cesium Iodide Thallium [CsI(Tl)] crystal array with a silicon photomultiplier array, a prototype of the array detector was designed and implemented. For verification of its directional performance, Geant4 simulations and experiments were performed. The results verified that the detector is capable of simultaneously determining the horizontal and vertical direction of gamma-ray source with an accuracy around 1∘∼5∘. In addition, the simulation results showed that the detector can determine the direction of gamma-ray sources with a wide energy range from 30 keV to 3000 keV.

Design Study of Broadband and Ultrahigh-Resolution Imaging Spectrometer Using Snapshot Multimode Interference in Fiber Bundles

Imaging spectrometry plays a significant role in various scientific realms. Although imaging spectrometers based on different schemes have been proposed, the pursuit of compact and high-performance devices is still ongoing. A compact broadband and ultrahigh-resolution imaging spectrometer (CBURIS) is presented, which comprises a microlens array, multiple fiber bundles, a microscope, and a two-dimensional detector array. The principle of the device is to spatially sample and integrate the field information via the front microlens array and then further process with the fiber bundles and imaging system based on the multimode interference theory. From both the theoretical and numerical analysis, this CBURIS design is a superior concept that not only achieves a 0.17° spatial resolution and ultrahigh spectral resolution (resolving power exceeds 2.58 × 106 at 1.55 µm) from the visible to mid-infrared region but also has the advantages of snapshot measurement, thermal stability, and a compact footprint compared with most existing imaging spectrometers.

Saturated-excitation image scanning microscopy.

Image scanning microscopy (ISM) overcomes the trade-off between spatial resolution and signal volume in confocal microscopy by rearranging the signal distribution on a two-dimensional detector array to achieve a spatial resolution close to the theoretical limit achievable by infinitesimal pinhole detection without sacrificing the detected signal intensity. In this paper, we improved the spatial resolution of ISM in three dimensions by exploiting saturated excitation (SAX) of fluorescence. We theoretically investigated the imaging properties of ISM, when the fluorescence signals are nonlinearly induced by SAX, and show combined SAX-ISM fluorescence imaging to demonstrate the improvement of the spatial resolution in three dimensions. In addition, we confirmed that the SNR of SAX-ISM imaging of fluorescent beads and biological samples, which is one of the challenges in conventional SAX microscopy, was improved.

Spatially modulated scene illumination for intensity-compensated two-dimensional array photon-counting LiDAR imaging

Photon-counting LiDAR using a two-dimensional (2D) array detector has the advantages of high lateral resolution and fast acquisition speed. The non-uniform intensity profile of the illumination beam and non-uniform quantum efficiency of the detectors in the 2D array deteriorate the imaging quality. Herein, we propose a photon-counting LiDAR system that uses a spatial light modulator to control the spatial intensity to compensate for both the non-uniform intensity profile of the illumination beam, and the variation in the quantum efficiency of the detectors in the 2D array. By using a 635 nm peak wavelength and 4 mW average power semiconductor laser, lab-based experiments at a 4.27 m stand-off distance are performed to verify the effectiveness of the proposed method. Compared with the unmodulated method, the standard deviation of the intensity image of the proposed method is reduced from 0.109 to 0.089 for a whiteboard target, with an average signal photon number of 0.006 per pixel.

Use of the Fully Spectroscopic Pixelated Cadmium Telluride Detector for Benchtop X-Ray Fluorescence Computed Tomography.

In this work, we integrated a commercially-available fully-spectroscopic pixelated cadmium telluride (CdTe) detector system as a two-dimensional (2D) array detector into our existing benchtop cone-beam x-ray fluorescence computed tomography (XFCT) system. After integrating this detector, known as High-Energy X-ray Imaging Technology (HEXITEC), we performed quantitative imaging of gold nanoparticle (GNP) distribution in a small animal-sized phantom using our benchtop XFCT system. Owing to the upgraded detector component within our benchtop XFCT system, we were able to conduct this phantom imaging in an unprecedented manner by volumetric XFCT scans followed by XFCT image reconstruction in 3D. The current results showed that adoption of HEXITEC, in conjunction with a custom-made parallel-hole collimator, drastically reduced the XFCT scan time/dose. Compared with the previous work performed with our original benchtop XFCT system adopting a single crystal CdTe detector, the currently observed reduction was up to a factor of 5, while achieving comparable GNP detection limit under similar experimental conditions. Overall, we demonstrated, for the first time to the best our knowledge, the feasibility of benchtop XFCT imaging of small animal-sized objects containing biologically relevant GNP concentrations (on the order of 0.1 mg Au/cm3 or 100 parts-per-million/ppm), with the scan time (on the order of 1 minute)/x-ray dose (on the order of 10 cGy) that are likely meeting the minimum requirements for routine preclinical imaging applications.

Focused Ultrasound Thermometry: A Two-Dimensional Resistance Temperature Detector Array in a Tissue-Mimicking Material

A two-dimensional resistance temperature detector (RTD) array sensor for the measurement of temperature distribution inside a tissue-mimicking material was proposed to validate focused ultrasound (FUS) devices. The fully two-dimensional $10\times10$ RTD array sensor with 1 mm inter-RTD distance was fabricated on the $2.5~ \boldsymbol {\mu } \text{m}$ thick film and placed inside the tissue-mimicking material. The measurement uncertainty for the RTD array was 0.18 K. The temperature distribution inside the phantom caused by a FUS transducer was measured and compared depending on the input power and focal plane. A tissue-mimicking phantom with an implanted RTD array can be applied to validate the performance and safety of both high- and low-intensity focused ultrasound (HIFU and LIFU) devices.

Reformatted method for two-dimensional detector arrays measurement data in proton pencil beam scanning

Reformatted method for two-dimensional detector arrays measurement data in proton pencil beam scanning

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance

Dosimetric characterization of a new two-dimensional diode detector array used for stereotactic radiosurgery quality assurance