R Peng

A dynamic micro-CT scanner based on a carbon nanotube field emission x-ray source

Current commercial micro-CT scanners have the capability of imaging objects ex vivo with high spatial resolution, but performing in vivo micro-CT on free-breathing small animals is still challenging because their physiological motions are non-periodic and much faster than those of humans. In this paper, we present a prototype physiologically gated micro-computed tomography (micro-CT) scanner based on a carbon nanotube field emission micro-focus x-ray source. The novel x-ray source allows x-ray pulses and imaging sequences to be readily synchronized and gated to non-periodic physiological signals from small animals. The system performance is evaluated using phantoms and sacrificed and anesthetized mice. Prospective respiratory-gated micro-CT images of anesthetized free-breathing mice were collected using this scanner at 50 ms temporal resolution and 6.2 lp mm(-1) at 10% system MTF. The high spatial and temporal resolutions of the micro-CT scanner make it well suited for high-resolution imaging of free-breathing small animals.

A carbon nanotube field emission multipixel x-ray array source for microradiotherapy application

The authors report a carbon nanotube (CNT) field emission multipixel x-ray array source for microradiotherapy for cancer research. The developed multipixel x-ray array source has 50 individually controllable pixels and it has several distinct advantages over other irradiation source including high-temporal resolution (millisecond level), the ability to electronically shape the form, and intensity distribution of the radiation fields. The x-ray array was generated by a CNT cathode array (5×10) chip with electron field emission. A dose rate on the order of >1.2 Gy∕min per x-ray pixel beam is achieved at the center of the irradiated volume. The measured dose rate is in good agreement with the Monte Carlo simulation result.

Stationary micro-CT scanner using a distributed multi-beam field emission x-ray source: a feasibility study

Current micro-CT scanners use either one or two x-ray tubes that are mechanically rotated around an object to collect the projection images for CT reconstruction. The rotating gantry design hinders the performance of the micro-CT scanner including the scanning speed. Based on the newly emerged carbon nanotube based distributed multi-beam x-ray array technology, we have proposed to build a stationary gantry-free multi-beam micro-CT (MBμCT) scanner. To investigate the feasibility of this concept, a prototype system using a source array with 20 individually controlled x-ray beams has been designed and tested. The prototype CT scanner can generate a scanning x-ray beam to image an object from different viewing angles (coverage of 36°) without any rotation. The electronics and software for system control and data have been implemented. The projected performance of the prototype MBμCT imaging system was discussed and some preliminary imaging results were presented.

Respiratory-gated micro-CT using a carbon nanotube based micro-focus field emission x-ray source

A prototype physiologically gated micro-computed tomography (micro-CT) system based on a field emission micro-focus x-ray source has been developed for in vivo imaging of small animal models. The novel x-ray source can generate radiation with a programmable waveform that can be readily synchronized and gated with non-periodic physiological signals. The system performance is evaluated using phantoms and sacrificed and anesthetized mouse models. Prospective respiratory-gated CT images of anesthetized free-breathing mice are collected using this scanner at 100msec temporal resolution and 10 lp/mm of 10% system MTF.

Design, optimization and testing of a multi-beam micro-CT scanner based on multi-beam field emission x-ray technology

As a widely adopted imaging modality for pre-clinical research, micro-CT is constantly facing the need of providing better temporal as well as spatial resolution for a variety of imaging applications. Faster CT scanning speed is also preferred for higher imaging throughput. We recently proposed a gantry-free multi-beam micro-CT (MBμCT) design which has the potential to overcome some of the intrinsic limitations of current rotating-gantry CT technology. To demonstrate its feasibility, we have constructed a testing system with a multi-beam field emission x-ray (MBFEX) source array with a linear array of 20 individually controllable x-ray emitting pixels. Based on simulations of the electron optics and preliminary experimental measurements the design of the MBFEX source has been further optimized. The newly designed imaging system has been characterized and commissioned following our standard imaging protocol. It has clearly shown improved system stability and enhanced imaging capability. As a result of reduced mechanical rotation during imaging acquisition, we are expecting to achieve higher CT scanning speed without significantly sacrificing imaging quality. This prototype MBμCT system, although still in its early development phase, has been proved to be an ideal testing platform for the proposed gantry-free micro-CT scanner.

WE‐E‐201C‐05: Performance of Multiplexing X‐Ray Imaging Based on Multi‐Beam X‐Ray Source Technology

Purpose:Multiplexing technique has been widely used in telecommunication,magnetic resonance imaging(MRI), and various spectroscopic applications to drastically increase system throughput. The recent development of carbon nanotube(CNT)field emission based multi‐beam x‐ray source technology provides us an opportunity to adopt multiplexing for x‐ray imaging. In this study we report our recent simulation work on the imaging quality assessment of multiplexing x‐ray imaging under different noise environments. Method and Materials: A computer model was built to simulate the imaging behavior of a multi‐beam x‐ray system. The imaging parameters, including x‐ray tube current, exposure time, number of x‐ray beams and noise composition (quantum noise and electronic noise), can be easily controlled to evaluate the system performance under different imaging environments. In the simulation, the noise composition was varied from the photonnoise limited case (100% photonnoise) to the electronic noise limited case (100% electronic noise).Results: Our results indicated that the performance of multiplexing x‐ray imaging is closely related to the noise composition of the imaging system. Under the photonnoise limit, multiplexing/demultiplexing procedure magnifies the noise and degrades the imaging quality and multiplexing x‐ray imaging is always outperformed by its sequential counterpart. However the performance of multiplexing x‐ray imaging gradually improves as the fraction of electronic noise in the total noise increases. In the electronic noise limited case, multiplexing is indeed able to speed up system imaging throughput. Conclusion: Under appropriate imaging conditions, multiplexing x‐ray radiography has the potential to achieve higher imaging speed without significantly sacrificing the imaging quality. It could be used for applications such as image‐guided radiation therapy (IGRT) for which imaging speed instead of imaging quality is the main concern of the task. We are hoping that this study can provide us a guideline to better identify future multiplexing x‐ray imaging related applications.

SU-GG-J-130: Recent Development of a Carbon Nanotube Field Emission Based X-Ray Micro-Radiotherapy System for Small Animal Radiotherapy

Purpose: To develop a novel multi‐pixel x‐ray beam micro‐radiotherapy (micro‐RT) system for high‐resolution small animal image‐guidedradiotherapy(IGRT) using carbon nanotube(CNT)field emissiontechnology.Materials and Methods: We have developed a prototype multi‐pixel x‐ray beam micro‐RT device for feasibility demonstration. The micro‐RT design uses a pixel beam array which consists of fifty individually addressable x‐ray pixel beams, each beam is ∼2 mm in size. The pixel beam array can form a maximum field size of 1 cm × 2 cm with arbitrary field shapes and intensity modulation patterns. Potential advantages of the multi‐pixel micro‐RT system over the single source micro‐RT systems are stationary flexibility and real‐time nature of the electronic field shaping.CNTfield emission based imaging and irradiation systems have also ultrahigh temporal resolution, which can be very important for small animal IGRT. Previously we have demonstrated the feasibility of the system using lower beam energy and here we report the recent progress in CNT FE based micro‐RT development with higher energy beams. Results: A 100 kV prototype CNTfield emission based micro‐RT system is developed. The prototype device can generate 75 individual addressable multi‐pixel x‐ray beams. Each beam is expected to produce a dose rate on the order of >1 Gy/min at the center of the irradiated object. We also integrated our CNTfield emission based micro‐RT and micro‐CT devices for small animal IGRT.Conclusions: We have made significant progress in developing the novel multi‐pixel micro‐RT system using CNTfield emissiontechnology. It remains to be a challenge to achieve high voltage (>100 kV) and high dose rate using this highly original prototype device in an academic research laboratory environment. The CNT‐based micro‐RT can be integrated with the CNTfield emission based micro‐CT already developed for real time small animal IGRT.

SU‐FF‐J‐156: High Throughput Micro‐CT Scanner Using a Distributed Multi‐Beam Field Emission X‐Ray Source

Purpose: To investigate the feasibility of a stationary gantry‐free micro‐CT scanner using spatially distributed multi‐beam x‐ray source. A prototype multi‐beam micro‐CT (MBμCT) scanner has been developed and its imaging performance characterized. Method and Materials: The MBμCT system consists of a 20‐beam carbon nanotube(CNT)field emission x‐ray source; an object table; a flat panel x‐ray detector; a MOSFET based control circuitry and a control console with a customized software user interface written in LabVIEW for data acquisition and processing. The x‐ray beams are individually controlled and can generate a scanning beam covering an angle span of 36°. It takes merely 9 steps to finish a full rotation in less than 10s. The projection images are acquired and stored for imaging processing and CTreconstruction.Results: The performance (focal spot size, field emission I‐V characteristics and current stability) of the multi‐beam x‐ray source has been characterized. The control circuitry and LabVIEW based controlsoftware have been implemented and tested. A mouse carcass has been scanned using the prototype MBμCT system and the acquired projection images showed decent imaging quality. We are currently working on refining the system geometry calibration and developing the corresponding CTreconstruction algorithm for this novel MBμCT imagingsystem, and some preliminary data will be presented. Conclusion: The feasibility of a stationary gantry‐free MBμCT has been evaluated based on the study of the as‐developed prototype system. Our preliminary results showed that the MBμCT scanner has the potential to deliver fast CT scan speed as a result of its novel scanning configuration. As a prototype system, it will be used to perform various feasibility tests for the future development of a fully stationary multi‐beam micro‐CT scanner. Once fully developed, this system would potentially provide fast screening, image registration and guidance for radiotherapy in pre‐clinical studies as well.

TH‐C‐BRC‐03: An Image‐Guided Micro‐Radiotherapy System Based On Carbon Nanotube Field Emission Technology for Small Animal Irradiation for Cancer Research

Purpose: To demonstrate the feasibility of a nanotechnology‐based micro‐computed tomography (micro‐CT) and micro‐radiotherapy (micro‐RT) integrated system (micro‐CT‐RT) that delivers real‐time image‐guided intensity‐modulated radiation therapy(IMRT) for small animal irradiation. Materials and Methods:Carbon nanotube(CNT)field emission (FE) based x‐ray technology is used for the development of the multi‐pixel x‐ray beam array micro‐RT system. The multi‐pixel x‐ray beam array has individual pixel control to electronically shape the radiation field and form intensity modulation patterns in the irradiated object. Monte Carlo based dosimetric simulations and electro‐optical simulations have been performed to guide the micro‐RT system design. Results: A prototype multi‐pixel beam array micro‐RT system was designed and fabricated. The prototype can successfully generate a 5 × 10 x‐ray beam array which offers a maximum radiation field size of 10 mm x 20 mm . Each beam can produce a dose rate on the order of 1 Gy/min at the center of the irradiated object. Conclusions: The feasibility to fabricate a multi‐pixel beam array micro‐RT system based on CNT FE technology is demonstrated. The prototype micro‐RT can generate a 5 × 10 x‐ray beam array which offers a maximum radiation field size of 10 mm × 20 mm in the irradiated object. The system is still under testing and performance improvement. Once fully developed, the micro‐RT system will be integrated with the nanotechnology‐based prototype micro‐CT already developed for real time image‐guided IMRT and treatment response observation in small animals.

SU‐GG‐J‐16: A Physiologically Gated Micro‐CT Scanner for Dynamic Small Animal Imaging Based On a Carbon Nanotube X‐Ray Source

Purpose: Current commercial micro‐CT scanners have the capability of imaging objects ex vivo with high spatial resolution, but performing in vivo micro‐CT on small animals is still challenging because their physiological motions are at least ten times faster than those of human. The purpose of this research is to develop a respiratory and cardiac gated micro‐CT scanner with both enhanced spatial and temporal resolutions, and more versatile imaging capabilities for in vivoimaging of small animal models. Method and Materials: A physiologically gated micro‐CT scanner was constructed based on a carbon nanotube micro‐focus x‐ray source. The scanner consists of a carbon nanotube x‐ray source, a flat panel x‐ray detector, and a rotation sample stage aligned in cone‐beam geometry. The dynamic gating was achieved from a small animal physiological monitor system plus some home‐made gating electronics. The spatial and temporal resolutions of the scanner were evaluated by MTF analysis and temporal analysis, respectively. Cardiopulmonary gated micro‐CT images were collected and analyzed on several anesthetized free‐breathing mice to evaluate the systems performance. Results: The scanner was found to have 50 microns spatial resolution and ∼20 milliseconds temporal resolution. Imaging sequences were readily synchronized and gated to non‐periodic physiological signals of free‐breathing mice. Quantitative physiological measurements can be obtained from the four‐dimensional micro‐CT results for the cardiopulmonary organs of the mice. Conclusion: We have developed a physiologically gated micro‐CT scanner based on a carbon nanotube micro‐focus x‐ray source. The scanner can easily acquire images at the desired cardiopulmonary phases with fast temporal resolution and minimized delay. The high spatial and temporal resolutions of the micro‐CT scanner make it well suited for in vivoimaging of small animal models. The system performance can be potentially enhanced through further development of a carbon nanotube micro‐focus x‐ray tube with higher flux.