Modeling the imaging performance of prototype organic x-ray imagers

A unified Monte Carlo and cascaded systems model for the simulation of active-matrix flat-panel imagers is presented. With few input parameters, the model simulated the imaging performance of previously measured flat-panel imagers with reasonable accuracy. The model is used to predict the properties of conceptual flat-panel imagers based on organic semiconductors on plastic substrates. The model suggests that significant improvements in resolution and detective quantum efficiency could be achieved by operating such a detector in a back-side illuminated configuration, or by employing two imaging arrays arranged face-to-face. The effect of semiconductor properties on the conceptual imagers is investigated. According to the model, a photodiode quantum efficiency of 25% and dark current of less than 100 pA mm(-2) would be satisfactory for a prototype imager, while a competitive imager would require a photodiode quantum efficiency of 40-50% with a dark current of less than 10 pA mm(-2) to be quantum limited over the radiographic exposure range.     

一种中药雾化熏鼻装置的设计

目的 鼻饲给药方式为呼吸系统疾病治疗的常用手段,但目前大多数鼻饲雾化给药装置均无法产生温热的药雾,冷雾容易引起气管痉挛、呛咳等不良反应,且对中药的雾化效率低下.本设计旨在研制一种中药雾化装置以解决目前药物雾化中存在的问题,为中医治疗呼吸道疾病提供一种现代仪器方法.方法 本装置分为中药煎煮、中药雾化2大功能模块.中药煎煮模块采用1200W大功率发热盘,可实现中药的文武火煎煮;雾化模块采用超声雾化与蒸汽雾化结合的方式,并利用非接触式红外加热的方式对药雾温度进行控制.通过装机调试后,进行中药雾化条件的实验,选用药材、药粉或药包等不同形式的中药,煎煮后根据普通纱布、细胞过滤器、细菌滤膜等过滤后的中药液雾化效果来确定中药的最佳雾化条件.结果 中药材选用药包形式的药材、过滤方式采用普通纱布与细胞过滤器结合的方式,所得药液雾化效果最佳.通过15例志愿者独立操作,证明本装置可方便有效地进行瑶医鼻饲疗法,有效避免传统的冷雾雾化方式带来的不良反应.结论 此药物雾化设备可直接使用中药材进行鼻饲治疗,产生的药雾粒径适于鼻饲治疗,且温热雾可避免临床上常用的冷雾给药带来的呛咳缺氧等不良反应;同时仪器具有友好的人机交互功能,可满足临床上对中药雾化治疗的需求.     

Pre-clinical assessment of a prototype non-invasive diagnostic device to detect aortic aneurysms

Journal of Artificial Organs - We have developed a non-invasive diagnostic device for treating thoracic aortic aneurysm that can be applied at a peripheral artery. This study aimed to examine how...     

Noise characteristics of a microchannel plate x-ray image intensifier

The noise performance of an experimental microchannel plate x-ray image intensifier has been evaluated. The intensifier, constructed for use with photons of energies between 20 and 150 keV, uses an MCP as the photon-to-electron converter. The influence of noise was determined by analysis of the optical-density fluctuations of a photograph of the viewing screen of the intensifier when the conversion layer was exposed to between 1 and 60 mR. Additionally, the contrast-detail performance of the experimental device was determined. The influence of both stochastic noise, due to quantum mottle and pulse-height variations, and structural noise, due to fluctuations in inherent gain from point to point, have been considered by using a model that adds these components.     

Development and preliminary evaluation of a prototype audiovisual biofeedback device incorporating a patient-specific guiding waveform

The aim of this research was to investigate the effectiveness of a novel audio-visual biofeedback respiratory training tool to reduce respiratory irregularity. The audiovisual biofeedback system acquires sample respiratory waveforms of a particular patient and computes a patient-specific waveform to guide the patient's subsequent breathing. Two visual feedback models with different displays and cognitive loads were investigated: a bar model and a wave model. The audio instructions were ascending/descending musical tones played at inhale and exhale respectively to assist in maintaining the breathing period. Free-breathing, bar model and wave model training was performed on ten volunteers for 5 min for three repeat sessions. A total of 90 respiratory waveforms were acquired. It was found that the bar model was superior to free breathing with overall rms displacement variations of 0.10 and 0.16 cm, respectively, and rms period variations of 0.77 and 0.33 s, respectively. The wave model was superior to the bar model and free breathing for all volunteers, with an overall rms displacement of 0.08 cm and rms periods of 0.2 s. The reduction in the displacement and period variations for the bar model compared with free breathing was statistically significant (p = 0.005 and 0.002, respectively); the wave model was significantly better than the bar model (p = 0.006 and 0.005, respectively). Audiovisual biofeedback with a patient-specific guiding waveform significantly reduces variations in breathing. The wave model approach reduces cycle-to-cycle variations in displacement by greater than 50% and variations in period by over 70% compared with free breathing. The planned application of this device is anatomic and functional imaging procedures and radiation therapy delivery.     

Direct analysis of molybdenum target generated x-ray spectra with a portable device

In routine applications, information about the photon flux of x-ray tubes is obtained from exposure measurements and cataloged spectra. This approach relies mainly on the assumption that the real spectrum is correctly approximated by the cataloged one, once the main characteristics of the tube such as voltage, target material, anode angle, and filters are taken account of. In practice, all this information is not always available. Moreover, x-ray tubes with the same characteristics may have different spectra. We describe an apparatus that should be useful for quality control in hospitals and for characterizing new radiographic systems. The apparatus analyzes the spectrum generated by an x-ray mammographic unit. It is based on a commercial CZT produced by AMPTEK Inc. and a set of tungsten collimator disks. The electronics of the CZT are modified so as to obtain a faster response. The signal is digitized using an analog to digital converter with a sampling frequency of up to 20 MHz. The whole signal produced by the x-ray tube is acquired and analyzed off-line in order to accurately recognize pile-up events and reconstruct the emitted spectrum. The energy resolution has been determined using a calibrated x-ray source. Spectra were validated by comparison of the HVL measured using an ionization chamber.     

The response of prototype plane-parallel ionization chambers in small megavoltage x-ray fields

Accurate small-field dosimetry has become important with the use of multiple small fields in modern radiotherapy treatments such as IMRT and stereotactic radiosurgery. In this study, we investigate the response of a set of prototype plane-parallel ionization chambers, based upon the Exradin T11 chamber, with active volume diameters of 2, 4, 10, and 20 mm, exposed to 6 MV stereotactic radiotherapy x-ray fields. Our goal was to assess their usefulness for accurate small x-ray field dose measurements. The relative ionization response was measured in circular fields (0.5 to 4 cm diameter) as compared to a 10 x 10 cm2 reference field. A large discrepancy (approximately 40%) was found between the relative response in the smallest plane-parallel chamber and other small volume dosimeters (radiochromic film, micro-metal-oxide-semiconductor field-effect transistor and diode) used for comparison. Monte Carlo BEAMnrc simulations were used to simulate the experimental setup in order to investigate the cause of the under-response and to calculate appropriate correction factors that could be applied to experimental measurements. It was found that in small fields, the air cavity of these custom-made research chambers perturbed the secondary electron fluence profile significantly, resulting in decreased fluence within the active volume, which in turn produces a chamber under-response. It is demonstrated that a large correction to the p(fl) correction factor would be required to improve dosimetric accuracy in small fields, and that these factors could be derived using Monte Carlo simulations.     

Performance characteristics of a real-time digital x-ray fluoroscopic system using an intensified charge injection device camera and CsI:Na crystal

A digital x-ray photoelectronic imaging system has been constructed using an optically flat 152-mm-diam, 2.5-mm-thick CsI:Na scintillating crystal. X-ray images formed by the scintillator are viewed by a single microchannel plate intensified charge injection device (ICID) camera and digitized at a real-time rate by a computerized frame-grabbing system. Video images are recorded and selected image frames are subjected to image processing and analysis schemes. Parameters governing the performance characteristics of the system are determined accordingly. For a 152-mm field size at the crystal plane, a spatial resolution limit of 1.50 +/- 0.10 1p/mm (1 sigma) measured at the 4% level of the modulation transfer function of the system has been obtained. This result is consistent with the measurements of the full width at half-maximum of the line spread function which is found to be 645 +/- 35 microns (1 sigma). Similarly, the intrinsic resolution of the CsI:Na scintillator only was found to be 6.5 +/- 0.5 1p/mm (1 sigma). Contrast ratio measurements, which are mainly determined by the quality of phosphor, have indicated a value of 12.1 +/- 0.6, whereas minimum visible details are observed at radiation exposure rates of 100 microR/s. This limit has been reduced to 10 microR/s using the single-scan integrating option provided by the ICID camera. A maximum contrast resolution of 1% corresponding to 100 statistically significant meaningful gray levels is achieved at a maximum exposure rate of 1000 microR/s. Consequently, although the imaging capability of the present system compares favorably with that of conventional x-ray video-fluoroscopic systems, a better performance may be achieved by using a higher resolution cooled dual-microchannel intensified CID camera in conjunction with a thinner CsI:Na crystal and a real-time digital image processing subsystem.     

Study of a prototype high quantum efficiency thick scintillation crystal video-electronic portal imaging device

Image quality in portal imaging suffers significantly from the loss in contrast and spatial resolution that results from the excessive Compton scatter associated with megavoltage x rays. In addition, portal image quality is further reduced due to the poor quantum efficiency (QE) of current electronic portal imaging devices (EPIDs). Commercial video-camera-based EPIDs or VEPIDs that utilize a thin phosphor screen in conjunction with a metal buildup plate to convert the incident x rays to light suffer from reduced light production due to low QE (<2% for Eastman Kodak Lanex Fast-B). Flat-panel EPIDs that utilize the same luminescent screen along with an a-Si:H photodiode array provide improved image quality compared to VEPIDs, but they are expensive and can be susceptible to radiation damage to the peripheral electronics. In this article, we present a prototype VEPID system for high quality portal imaging at sub-monitor-unit (subMU) exposures based on a thick scintillation crystal (TSC) that acts as a high QE luminescent screen. The prototype TSC system utilizes a 12 mm thick transparent CsI(Tl) (thallium-activated cesium iodide) scintillator for QE=0.24, resulting in significantly higher light production compared to commercial phosphor screens. The 25 X 25 cm2 CsI(Tl) screen is coupled to a high spatial and contrast resolution Video-Optics plumbicon-tube camera system (1240 X 1024 pixels, 250 microm pixel width at isocenter, 12-bit ADC). As a proof-of-principle prototype, the TSC system with user-controlled camera target integration was adapted for use in an existing clinical gantry (Siemens BEAMVIEW(PLUS)) with the capability for online intratreatment fluoroscopy. Measurements of modulation transfer function (MTF) were conducted to characterize the TSC spatial resolution. The measured MTF along with measurements of the TSC noise power spectrum (NPS) were used to determine the system detective quantum efficiency (DQE). A theoretical expression of DQE(0) was developed to be used as a predictive model to propose improvements in the optics associated with the light detection. The prototype TSC provides DQE(0)=0.02 with its current imaging geometry, which is an order of magnitude greater than that for commercial VEPID systems and comparable to flat-panel imaging systems. Following optimization in the imaging geometry and the use of a high-end, cooled charge-coupled-device (CCD) camera system, the performance of the TSC is expected to improve even further. Based on our theoretical model, the expected DQE(0)=0.12 for the TSC system with the proposed improvements, which exceeds the performance of current flat-panel EPIDs. The prototype TSC provides high quality imaging even at subMU exposures (typical imaging dose is 0.2 MU per image), which offers the potential for daily patient localization imaging without increasing the weekly dose to the patient. Currently, the TSC is capable of limited frame-rate fluoroscopy for intratreatment visualization of patient motion at approximately 3 frames/second, since the achievable frame rate is significantly reduced by the limitations of the camera-control processor. With optimized processor control, the TSC is expected to be capable of intratreatment imaging exceeding 10 frames/second to monitor patient motion.     

Effect of recombination in a high quantum efficiency prototype ionization-chamber-based electronic portal imaging device

The quantum efficiency (QE) of an imaging detector can be increased by utilizing a thick, high-density detection medium to increase the number of quantum interactions. However, image quality is more accurately described by the detection quantum efficiency (DQE). If a significant fraction of the increase in the number of detected quanta from a thick, dense detector were to result in useful imaging signal, this represents a favorable case where enhanced QE leads to increased DQE. However, for ionization-type detectors, one factor that limits DQE is the recombination between ion pairs that acts as a secondary quantum sink due to which enhancement in QE may not result in higher DQE depending on the extent of the signal loss from recombination. Therefore, an analysis of signal loss mechanisms or quantum sinks in an imaging system is essential for validating the overall benefit of high QE detectors. In this paper, a study of ion recombination as a secondary quantum sink is presented for a high QE prototype ion-chamber-based electronic portal imaging device (EPID): the kinestatic charge detector (KCD). The KCD utilizes a high pressure noble gas (krypton or xenon at 100 atm) and an arbitrarily large detector thickness (of the order of centimeters), resulting in a high QE imager. Compared with commercial amorphous silicon flat panel imagers that provide DQE(0) approximately 0.01, the KCD has much higher DQE. Studies indicated that DQE(0) = 0.20 for 6.1 cm thick, 100 atm (rho = 3.4 g/cm3) xenon chamber, and DQE(0)=0.34 for a 9.1 cm thick chamber. A series of experiments was devised and conducted to determine the signal loss due to recombination for a KCD chamber. The measurements indicated a fractional recombination loss of about 14% for a krypton chamber and about 18% for a xenon chamber under standard operating conditions (100 atm chamber pressure and 1275 V/cm electric field intensity). A theoretical treatment of the effect of recombination on imaging signal-to-noise ratio was applied to quantify the loss in DQE. These calculations indicated that recombination had a limited effect (<2%) on DQE under standard operating conditions. This was validated by good agreement between experimentally measured DQE and that obtained using Monte Carlo simulations that did not account for recombination.     

Performance characteristics of a widely used orthovoltage x-ray therapy machine

Experimental results sufficient to provide a data base for the Philips RT 250 x-ray machine are presented. A representative selection of operating conditions covering the working range of the machine from 75 to 250 kVp, were used. Beam quality, depth dose data, field flatness, and filtration characteristics were studied, and selected results are reported.     

克氏针折弯器的研制与应用

目的研制一种克氏针折弯器,解决现有技术中采用持针器、老虎钳完成折弯工作存在的费时费力、效果欠佳的问题。方法委托模具公司在一字形螺丝刀薄楔形头处依次钻取2.0mm、2.5mm及3.0mm直径圆孔,用于术中克氏针折弯,观察折弯效果。结果克氏针折弯器操作简单,省力,快速,折弯效果确切。结论本院研制的克氏针折弯器有一定的新颖性、实用性,值得临床推广使用。     

Development of a tapping device: a new needle insertion method for prostate brachytherapy

The purpose of this study is to develop and test a tapping device for needle insertion for prostate brachytherapy. This device will tap the needle into the prostate with a certain, well-defined, amount of momentum, instead of the currently used method of pushing the needle. Because of the high needle insertion velocity, we expect prostate motion and deformation to be less compared to current methods. We measured the momentum that is applied when manually tapping the needle into the prostate and found a mean momentum of 0.50 +/- 0.07 N s. The tapping device is pneumatically driven and we found that the delivered momentum increased linearly with the applied air pressure. The efficacy of the tapping device was tested on a piece of beef, placed on a freely moving and rotating platform. A significant correlation was found between the applied pressure and the rotation and displacement of the beef. Displacements and rotations were minimal for the highest pressure (4 bar) and amounted to only 2 mm and 6 degrees, respectively. Higher air pressures will further reduce displacements and rotations.     

Intra-operative evaluation of cementless hip implant stability: a prototype device based on vibration analysis

Cementless implants are mechanically stabilized during surgery by a press-fitting procedure. Good initial stability is crucial to avoid stem loosening and bone cracking, therefore, the surgeon must achieve optimal press-fitting. A possible approach to solve this problem and assist the surgeon in achieving the optimal compromise, involves the use of vibration analysis. The present study aimed to design and test a prototype device able to evaluate the primary mechanical stability of a cementless prosthesis, based on vibration analysis. In particular, the goal was to discriminate between stable and quasi-stable implants; thus the stem-bone system was assumed to be linear in both cases. For that reason, it was decided to study the frequency responses of the system, instead of the harmonic distortion. The prototype developed consists of a piezoelectric exciter connected to the stem and an accelerometer attached to the femur. Preliminary tests were performed on four composite femurs implanted with a conventional stem. The results showed that the input signal was repeatable and the output could be recorded accurately. The most sensitive parameter to stability was the shift in resonance frequency of the stem-bone system, which was highly correlated with residual micromotion on all four specimens.     

New device for accurate measurement of the x-ray intensity distribution of x-ray tube focal spots.

A new device has been developed with which the focal spot distribution can be measured accurately. The alignment and localization of the focal spot relative to the device are accomplished by adjustment of three micrometer screws in three orthogonal directions and by comparison of red reference light spots with green fluorescent pinhole images at five locations. The standard deviations for evaluating the reproducibility of the adjustments in the horizontal and vertical directions were 0.2 and 0.5 mm, respectively. Measurements were made of the pinhole images as well as of the line-spread functions (LSFs) and modulation transfer functions (MTFs) for an x-ray tube with focal spots of 1-mm and 50-mum nominal size. The standard deviations for the LSF and MTF of the 1-mm focal spot were 0.017 and 0.010, respectively.     

X-ray scalpel - a new device for targeted x-ray brachytherapy and stereotactic radiosurgery

The basic design and performance of a novel x-ray scalpel device for interstitial radiosurgery are reported. The x-ray scalpel is comprised of a capillary optics collimator conjugated with a high brilliance microfocus x-ray tube and a thin hollow needle (tip) attached to the collimator. The device is capable of producing a high dose rate (about 140 Gy min(-1) in water-like absorber at the exit window), 0.7 mm diameter, quasi-parallel beam that can be delivered to a targeted site by a minimally invasive procedure. Contrary to insertable x-ray tubes or radionuclides used in brachytherapy and complying with the 1/r(2) radiation attenuation law, the dose rate for a quasi-parallel beam decreases with distance as mu exp(-mu r), where mu is the energy-dependent linear attenuation coefficient in the exposed medium. Moreover, the shape, energy and the dose attenuation curve of the x-ray beam can be adjusted. Two versions of the x-ray scalpel device (5.4 keV and 20.2 keV) are described. We present results from our first test of the x-ray scalpel as a controllable source of focal radiation for producing radiation necrosis in rat brain tissue. Irradiation was transdurally delivered to the rat cerebral cortex for 10 min at a dose rate of 20 Gy min(-1).     

An x-ray CT polymer gel dosimetry prototype: I. Remnant artefact removal

In this study a new x-ray CT polymer gel dosimetry (PGD) filtering technique is presented for the removal of (i) remnant ring and streak artefacts, and (ii) 'structured' noise in the form of minute, intrinsic gel density fluctuations. It is shown that the noise present within x-ray CT PGD images is not purely stochastic (pixel by pixel) in nature, but rather is 'structured', and hence purely stochastic-based noise-removal filters fail in removing this significant, unwanted noise component. The remnant artefact removal (RAR) technique is based on a class of signal stripping (i.e. baseline-estimation) algorithms typically used in the estimation of unwanted non-uniform baselines underlying spectral data. Here the traditional signal removal algorithm is recast, whereby the 'signal' that is removed is the structured noise and remnant artefacts, leaving the desired polymer gel dose distribution. The algorithm is extended to 2D and input parameters are optimized for PGD images. RAR filter results are tested on (i) synthetic images with measured gel background images added, in order to accurately represent actual noise present in PGD images, and (ii) PGD images of a three-field gel irradiation. RAR results are compared to a top-performing noise filter (adaptive mean, AM), used in previous x-ray CT PGD studies. It is shown that, in all cases, the RAR filter outperforms the AM filter, particularly in cases where either (i) a low-dose gel image has been acquired or (ii) the signal-to-noise ratio of the PG image is low, as in the case when a low number of image averages are acquired within a given experiment. Guidelines for the implementation of the RAR filter are given.