Medical X-ray Source Research Articles

On the thermal response of LuAG:Ce single crystals

It is well known that the luminescence efficiency of single crystals is affected by external parameters, such as the environmental temperature, especially in harsh environments. Due to this, it is of worth to examine the influence of temperature on the luminescence output of single-crystal scintillators. In this study lutetium aluminum garnet (Lu3Al5O12:Ce-LuAG:Ce) was examined, against previously published data for cadmium tungstate (CdWO4) and calcium fluoride doped with europium (CaF2:Eu) single crystals. Experiments were carried using a medical X-ray source, set to fixed high voltage (90kVp) and tube current/exposure time product (63mAs), in order to record the produced light, under different temperature conditions (20-120 Celsius). An interesting finding is that temperature, in the examined range, appear to have minimal influence on the light output of LuAG:Ce, in the contrary to the previously examined crystals (CdWO4 and CaF2:Eu) where the luminescence output constantly decreased with increasing temperature. The thermal stability of LuAG:Ce, in the examined temperature range, renders it a good choice, besides medical imaging, also for application in harsh environments as well as for long-term operation in high power LEDs.

Abstract 3941: Novel cancer therapy approach based on Auger effect mediated by monoenergetic x-ray

Abstract The Auger effect is a physical phenomenon in which the filling of an inner-shell vacancy of an atom is accompanied by the emission of an electron from the same atom. An Auger electron is estimated to have a travel distance around 2-100 μm, within which an energy up to 106 gray is released. Therefore, if Auger effect can be induced in cancer cell DNA, it could mediate immense damage concentrated in cancer genome, providing a potential approach for cancer therapy. Auger effect can be induced by radioactive isotope itself, like 125I, or monoenergetic X-Ray in combination with specific heavy atom. Conventionally, monoenergetic X-Ray can be produced only in a synchrotron radiation accelerator, which hinders its application in medical use. Here, our study showed that a novel design of X-Ray tube allowing electron beams to pass through the target metal can generate monoenergetic X-ray efficiently. This design substantially minimizes the size of X-Ray generator to be portable, and can generate 3-fold higher X-Ray production than traditional X-ray tube under the same voltage and current-exposure time. The monoenergetic X-Ray generated by the novel design (denominated as NanoRay hereafter) contains >20% of K-characteristic photon, up to 29-fold higher than traditional X-Ray in the same energy range. For anti-cancer analysis, 14 and 33 keV NanoRays were combined with Thymidine analogues BrdU and IdU, respectively, in cancer cell treatment. The results showed that while single treatments showed low cytotoxicity, the combination of Nanorays with BrdU or IdU induced significant cancer cell death synergistically in vitro. In contrast, combined treatments of conventional radiation with BrdU or IdU did not show any synergistic effect. In vivo tumor treatment combining 33 keV NanoRay and IdU showed a tumor reduction rate up to 80% as compared to Nanoray alone. Likewise, combination of conventional radiation with IdU showed no synergistic anti-tumor effect. DNA damage analysis found that NanoRay produced 2-fold more double-strand breaks (DSBs) in cancer cells incorporating BrdU or IdU than control cells, validating the Auger effect induced and applied in cancer genome damage. In summary, the current study presents that NanoRay, a new generation of medical X-Ray with highly specific monoenergetic spectrum, can be generated from a transmission tube within a portable apparatus. When NanoRay is applied to cancer DNA incorporating specific heavy atoms, such as BrdU or IdU, it induced significantly more pronounced DNA DSBs and cell death through Auger effect, thus lowering the dose necessary for corresponding anti-tumor effect induced by conventional radiation. NanoRay serves as a novel medical X-Ray source with low dose, low cost, and high efficiency, holding great promise in future cancer therapy. Citation Format: Erh-Hsuan Lin, Wen-Wong Kuo, Wan-Ting Tseng, Chi-Chieh Cheng, Shih-Feng Tseng, Wei-Li Chen, Chia-Gee Wang, Cheng-Wen Wu. Novel cancer therapy approach based on Auger effect mediated by monoenergetic x-ray [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3941.

Simulation study on X-ray phase contrast imaging with dual-phase gratings.

Two phase gratings in an X-ray grating interferometers can solve several technical challenges for clinical use of X-ray phase contrast. In this work, we adapt and evaluate this setup design to clinical X-ray sources and detectors in a simulation study. For a given set of gratings, we optimize the remaining parameter space of a dual-phase grating setup using a numerical wave front simulation. The simulation results are validated with experimentally obtained visibility measurements on a setup with a microfocus tube and a clinical X-ray detector. We then confirm by simulation that the Lau condition for the [Formula: see text] grating also holds for two phase gratings. Furthermore, we use a [Formula: see text] grating with a fixed period to search for periods of matching phase grating configurations. Simulated and experimental visibilities agree very well. We show that the Lau condition for a dual-phase grating setup requires the interference patterns of the first phase grating to constructively overlay at the second phase grating. Furthermore, a total of three setup variants for given [Formula: see text] periods were designed with the simulation, resulting in visibilities between 4.5 and 9.1%. Dual-phase gratings can be used and optimized for a medical X-ray source and detector. The obtained visibilities are somewhat lower than for other Talbot-Lau interferometers and are a tradeoff between setup length and spatial resolution (or additional phase stepping, respectively). However, these disadvantage appears minor compared to the overall better photon statistics, and the fact that dual-phase grating setups can be expected to scale to higher X-ray energies.

Medical X-ray sources now and for the future

This paper focuses on the use of X-rays in their largest field of application: medical diagnostic imaging and image-guided therapy. For this purpose, vacuum electronics in the form of X-ray tubes as the source of bremsstrahlung (braking radiation) have been the number one choice for X-ray production in the range of photon energies between about 16 keV for mammography and 150 keV for general radiography. Soft tissue on one end and bony structures on the other are sufficiently transparent and the contrast delivered by difference of absorption is sufficiently high for this spectral range. The dominance of X-ray tubes holds even more than 120 years after Conrad Roentgen’s discovery of the bremsstrahlung mechanism. What are the specifics of current X-ray tubes and their medical diagnostic applications? How may the next available technology at or beyond the horizon look like? Can we hope for substantial game changers? Will flat panel sources, less expensive X-ray “LED’s”, compact X-ray Lasers, compact synchrotrons or equivalent X-ray sources appear in medical diagnostic imaging soon? After discussing the various modalities of imaging systems and their sources of radiation, this overview will briefly touch on the physics of bremsstrahlung generation, key characteristics of X-ray tubes, and material boundary conditions, which restrict performance. It will discuss the deficits of the bremsstrahlung technology and try to sketch future alternatives and their prospects of implementation in medical diagnostics.

Effect of substrate material on the growth and field emission characteristics of large-area carbon nanotube forests

Carbon nanotubes (CNTs) are a promising replacement for tungsten filaments as electron emitters in conventional x-ray sources, owing to their higher aspect ratio, superior mechanical stability, chemical inertness, and high electrical and thermal conductivities. Conditions for realizing the best emission behavior from CNTs have been formulated over the last few years. In this paper, we report the relatively less-investigated factor, namely, the influence of the nature of substrate material on the growth as well as field emission characteristics of large-area multiwalled CNTs for their practical application in medical x-ray sources. We compare the morphology of CNTs on a variety of substrates such as stainless steel, copper, molybdenum, graphite, few-layer graphene, and carbon nanowalls grown by thermal chemical vapor deposition following a simple drop-coating of catalyst. We find that CNTs grown on stainless steel and graphite show the best combination of emission characteristics under pulsed operation mode. These studies are helpful in selecting the optimum substrate material for field emission applications. Ex situ studies on field emission degradation of CNTs are presented towards the end.

Correction of data truncation artifacts in differential phase contrast (DPC) tomosynthesis imaging

The use of grating based Talbot–Lau interferometry permits the acquisition of differential phase contrast (DPC) imaging with a conventional medical x-ray source and detector. However, due to the limited area of the gratings, limited area of the detector, or both, data truncation image artifacts are often observed in tomographic DPC acquisitions and reconstructions, such as tomosynthesis (limited-angle tomography). When data are truncated in the conventional x-ray absorption tomosynthesis imaging, a variety of methods have been developed to mitigate the truncation artifacts. However, the same strategies used to mitigate absorption truncation artifacts do not yield satisfactory reconstruction results in DPC tomosynthesis reconstruction. In this work, several new methods have been proposed to mitigate data truncation artifacts in a DPC tomosynthesis system. The proposed methods have been validated using experimental data of a mammography accreditation phantom, a bovine udder, as well as several human cadaver breast specimens using a bench-top DPC imaging system at our facility.

The Dosepix detector—an energy-resolving photon-countingpixel detector for spectrometric measurements

The Dosepix detector is a hybrid photon-counting pixel detector based on ideas of the Medipix and Timepix detector family. 1 mm thick cadmium telluride and 300 μm thick silicon were used as sensor material. The pixel matrix of the Dosepix consists of 16 x 16 square pixels with 12 rows of (200 μm)2 and 4 rows of (55 μm)2 sensitive area for the silicon sensor layer and 16 rows of pixels with 220 μm pixel pitch for CdTe. Besides digital energy integration and photon-counting mode, a novel concept of energy binning is included in the pixel electronics, allowing energy-resolved measurements in 16 energy bins within one acquisition. The possibilities of this detector concept range from applications in personal dosimetry and energy-resolved imaging to quality assurance of medical X-ray sources by analysis of the emitted photon spectrum. In this contribution the Dosepix detector, its response to X-rays as well as spectrum measurements with Si and CdTe sensor layer are presented. Furthermore, a first evaluation was carried out to use the Dosepix detector as a kVp-meter, that means to determine the applied acceleration voltage from measured X-ray tubes spectra.

Bragg accelerator optimization

Abstract We present the first steps of a design of the optimal parameters for a full Bragg X-Ray free electron laser (BX-FEL). Aiming towards a future source of coherent X-ray radiation, operating in the strong Compton regime, we envisage the system to be the seed for an advanced light source or compact medical X-ray source. Here we focus on the design of the accelerator parameters: maximum gradient, optimal accelerated charge, maximum efficiency, and ‘wake coefficient’, which relates to the decelerating electric field generated due to the motion of a charged-line or train of charged-lines. Specifically, we demonstrate that the maximum efficiency has optimal value and given the fluence of the materials, the maximum accelerated charge in the train is constant. These two results might be important in any future design.

Design and characterization of electron beam focusing for X-ray generation in novel medical imaging architecture

A novel electron beam focusing scheme for medical X-ray sources is described in this paper. Most vacuum based medical X-ray sources today employ a tungsten filament operated in temperature limited regime, with electrostatic focusing tabs for limited range beam optics. This paper presents the electron beam optics designed for the first distributed X-ray source in the world for Computed Tomography (CT) applications. This distributed source includes 32 electron beamlets in a common vacuum chamber, with 32 circular dispenser cathodes operated in space charge limited regime, where the initial circular beam is transformed into an elliptical beam before being collected at the anode. The electron beam optics designed and validated here are at the heart of the first Inverse Geometry CT system, with potential benefits in terms of improved image quality and dramatic X-ray dose reduction for the patient.

Time-resolved X-ray tomography of a fluidized bed

This paper discusses first results of bubbles moving through a fluidized bed imaged with an X-ray Tomographic Scanner. The scanner is made of 3 medical X-ray sources equipped with 30 CdWO 4 detectors each. The fluidized bed has a diameter of 23 cm and is filled with Geldart B powder. The scanner measures the attenuation in a thin slice perpendicular to the column axis at a sampling frequency of 2500 Hz. The data collected during 2 s are reconstructed using the SART algorithm with a one-step-late correction. The reconstructions show the distribution of the bubbles in the 2-dimensional cross-section. By stacking these images, a 3-dimensional view of the bubbles in the column is represented.

Feasibility study of a time-resolving x-ray tomographic system

This paper discusses the possibilities for developing a tomographic scanner for studying the phase distribution of fluidized beds. The system is based on a medical x-ray source equipped with 30 CdWO4 detectors. We mimic a five-source system via simulation and in experiments of voids in a 23 fluidized bed filled with polystyrene particles. Both static voids and moving ones are studied. The reconstruction uses the simultaneous algebraic reconstruction technique with regularization. We find that it is possible to reconstruct objects with a spatial resolution of about 5 mm at a frame rate of 200 Hz. It is concluded that noise levels should be kept below 2%.

X-ray tests of a microchannel plate detector and amorphous silicon pixel array readout for neutron radiography

High-performance large area imaging detectors for fast neutrons in the 5–14MeV energy range do not exist at present. The aim of this project is to combine microchannel plates or MCPs (or similar electron multiplication structures) traditionally used in image intensifiers and X-ray detectors with amorphous silicon (a-Si) pixel arrays to produce a composite converter and intensifier position sensitive imaging system. This detector will provide an order of magnitude improvement in image resolution when compared with current millimetre resolution limits obtained using phosphor or scintillator-based hydrogen rich converters. In this study we present the results of the initial experimental evaluation of the prototype system. This study was carried out using a medical X-ray source for the proof of concept tests, the next phase will involve neutron imaging tests. The hybrid detector described in this study is a unique development and paves the way for large area position sensitive detectors consisting of MCP or microsphere plate detectors and a-Si or polysilicon pixel arrays. Applications include neutron and X-ray imaging for terrestrial applications. The technology could be extended to space instrumentation for X-ray astronomy.

Radiation protection standards: their evolution from science to philosophy

The concept of applying constraints on individual sources to a small fraction of the public dose limit has been deemed inappropriate when shielding the medical X-ray sources. This represents a broad-based consensus of medical physics and radiological societies in the United States, and the report series on the shielding design for medical X-ray sources (including dental, X-ray imaging and therapeutic X ray) from the National Council on Radiation Protection and Measurements (NCRP) utilises 1 mSv y(-1) as a source control limit. In the present study, the rationale for such a conclusion is discussed, and a somewhat critical look at the current model of radiation protection of the public is made.