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Purpose: The purpose of this study is to investigate the feasibility of increasing the system spatial resolution and scanning speed of Hologic Selenia Dimensions digital breast tomosynthesis (DBT) scanner by replacing the rotating mammography x-ray tube with a specially designed carbon nanotube (CNT) x-ray source array, which generates all the projection images needed for tomosynthesis reconstruction by electronically activating individual x-ray sources without any mechanical motion. The stationary digital breast tomosynthesis (s-DBT) design aims to (i) increase the system spatial resolution by eliminating image blurring due to x-ray tube motion and (ii) reduce the scanning time. Low spatial resolution and long scanning time are the two main technical limitations of current DBT technology. Methods: A CNT x-ray source array was designed and evaluated against a set of targeted system performance parameters. Simulations were performed to determine the maximum anode heat load at the desired focal spot size and to design the electron focusing optics. Field emission current from CNT cathode was measured for an extended period of time to determine the stable life time of CNT cathode for an expected clinical operation scenario. The source array was manufactured, tested, and integrated with a Selenia scanner. An electronic control unit was developed to interface the source array with the detection system and to scan and regulate x-ray beams. The performance of the s-DBT system was evaluated using physical phantoms. Results: The spatially distributed CNT x-ray source array comprised 31 individually addressable x-ray sources covering a 30 angular span with 1 pitch and an isotropic focal spot size of 0.6 mm at full width at half-maximum. Stable operation at 28 kV(peak) anode voltage and 38 mA tube current was demonstrated with extended lifetime and good source-to-source consistency. For the standard imaging protocol of 15 views over 14, 100 mAs dose, and 2 × 2 detector binning, the projection resolution along the scanning direction increased from 4.0 cycles/mm [at 10% modulation-transfer-function (MTF)] in DBT to 5.1 cycles/mm in s-DBT at magnification factor of 1.08. The improvement is more pronounced for faster scanning speeds, wider angular coverage, and smaller detector pixel sizes. The scanning speed depends on the detector, the number of views, and the imaging dose. With 240 ms detector readout time, the s-DBT system scanning time is 6.3 s for a 15-view, 100 mAs scan regardless of the angular coverage. The scanning speed can be reduced to less than 4 s when detectors become faster. Initial phantom studies showed good quality reconstructed images. Conclusions: A prototype s-DBT scanner has been developed and evaluated by retrofitting the Selenia rotating gantry DBT scanner with a spatially distributed CNT x-ray source array. Preliminary results show that it improves system spatial resolution substantially by eliminating image blur due to x-ray focal spot motion. The scanner speed of s-DBT system is independent of angular coverage and can be increased with faster detector without image degration. The accelerated lifetime measurement demonstrated the long term stability of CNT x-ray source array with typical clinical operation lifetime over 3 years.

Studies have shown that digital breast tomosynthesis (DBT) can improve breast cancer diagnosis by reconstructing 3D images. However, DBT scanners based on rotation gantry prolong the imaging time and reduce spatial resolution due to motion comparing with the regular two-view mammography. To obtain three dimension reconstruction images and maintain the high image quality of conventional mammography, we proposed a prototype stationary digital breast tomosynthesis system (s-DBT). The proposed s-DBT system acquires projection images without mechanical movement. The core component of the s-DBT system is a specially designed spatially distributed multi-beam x-ray tube based on the carbon nanotube field emission x-ray technology. The multi-beam x-ray source array enables collection of all projection images from different viewing angles without mechanical motion. Preliminary results show the s-DBT system can achieve a scan time comparable to the regular two-view mammography, and improve the spatial resolution comparing with rotating gantry DBT.

We report the progress in development of carbon nanotube (CNT) field emission micro-focus x-ray tubes for dynamic small animal imaging with high spatial and temporal resolution. Extensive electron optics simulations were performed to study the focusing structure and optimize the tube design. 3D finite element analysis was used for modeling and simulating electron beam optics. A simple and intuitive model is developed to model the field emission properties of CNT cathodes. The dependence of focus spot size and the anode current on the gate extracting voltage, the focusing voltages, the gate mesh geometry, and other geometric parameters were studied. Several tubes were built according to the optimal design. The experimentally measured focus spot size and its dependence on the focus voltages were found to be in quantitative agreement with simulations.

We have previously reported the development of a dynamic micro-CT scanner with a stationary mouse bed using a compact carbon nanotube (CNT) field emission x-ray tube and preliminary results on its utility for prospectively gated cardiac imaging. In this paper we report the recent progress in improving the perf ormance characteristics of this scanner. Through optimization of the CNT cathode, the stable emission current has been increased. The output power of the CNT x-ray source has reached ~100W peak power at 100 P m focal spot size. The higher flux enables improvement of the x-ray energy spectrum to minimize the beam hardening effect and increasing the system temporal resolution by using shorter x-ray exposure time. The scanner’s temporal resoluti on has been increased to ~10 msec, which is sufficient for high-resolution micro-CT imaging of mouse heart and lung under free-breathing setting. The spatial resolution is maintained at 6.2 lp per mm at 10% system MTF. The nanotube micro-CT scanner’s application in mouse cardiac imaging has been demonstrated with high-resolution (80 P m and 15 msec) micro-CT of the mouse heart under free-breathing setting. Keywords: cardiac imaging, micro-CT, x-ray, carbon nanotube

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.

Tomosynthesis imaging requires projection images from different viewing angles. Conventional systems use a moving xray source to acquire the individual projections. Using a stationary distributed x-ray source with a number of sources that equals the number of required projections, this can be achieved without any mechanical motion. Advantages are a potentially faster image acquisition speed, higher spatial and temporal resolution and simple system design. We present distributed x-ray sources based on carbon nanotube (CNT) field emission cathodes. The field emission cathodes deliver the electrons required for x-ray production. CNT emitters feature a stable emission at high current density, a cold emission, excellent temporal control of the emitted electrons and good configurability. We discuss the use of stationary sources for two applications: (i) a linear tube for stationary digital breast tomosynthesis (sDBT), and (ii) a square tube for on-board tomosynthesis image-guided radiation therapy (IGRT). Results from high energy distributed sources up to 160kVp are also presented.

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.

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.

Digital breast tomosynthesis (DBT) is a limited angle computed tomography technique that can distinguish tumors from its overlying breast tissues and has potentials for detection of cancers at a smaller size and earlier stage. Current prototype DBT scanners are based on the regular full-field digital mammography systems and require partial isocentric motion of an x-ray tube over certain angular range to record the projection views. This prolongs the scanning time and, in turn, degrades the imaging quality due to motion blur. To mitigate the above limitations, the concept of a stationary DBT (s-DBT) scanner has been recently proposed based on the newly developed spatially distributed multibeam field emission x-ray (MBFEX) source technique using the carbon nanotube. The purpose of this article is to evaluate the performance of the 25-beam MBFEX source array that has been designed and fabricated for the s-DBT system. The s-DBT system records all the projection images by electronically activating the multiple x-ray beams from different viewing angles without any mechanical motion. The configuration of the MBFEX source is close to the published values from the Siemens Mammomat system. The key issues including the x-ray flux, focal spot size, spatial resolution, scanning time, beam-to-beam consistency, and reliability are evaluated using the standard procedures. In this article, the authors describe the design and performance of a distributed x-ray source array specifically designed for the s-DBT system. They evaluate the emission current, current variation, lifetime, and focal spot sizes of the source array. An emission current of up to 18 mA was obtained at 0.5×0.3 mm effective focal spot size. The experimentally measured focal spot sizes are comparable to that of a typical commercial mammography tube without motion blurring. Trade-off between the system spatial resolution, x-ray flux, and scanning time are also discussed. Projection images of a breast phantom were collected using the x-ray source array from 25 different viewing angles without motion. These preliminary results demonstrate the feasibility of the proposed s-DBT scanner. The technology has the potential to increase the resolution and reduce the imaging time for DBT. With the present design of 25 views, they demonstrated experimentally the feasibility of achieving 11 s scanning time at full detector resolution with 0.5×0.3 mm source resolution without motion blur. The flexibility in configuration of the x-ray source array will also allow system designers to consider imaging geometries that are difficult to achieve with the conventional single-source rotating approach.

A prototype physiologically gated micro-computed tomography (micro-CT) system based on a “eld emissionmicro-focus x-ray sour ce has been developed for in vivo imaging of small animal models. The novel x-raysource can generate radiation with a programmable waveform that can be readily synchronized and gated withnon-periodic physiological signals. The system performance is evaluated using phantoms and sacri“ced andanesthetized mouse models. Prospect ive respiratory-gated CT images of a nesthetized free-breathing mice arecollected using this scanner at 100msec temporal resolution and 10lp/mm of 10% system MTF.Keywords: micro-CT, in vivo imaging, respiratory gating, x-ray source, carbon nanotube 1. INTRODUCTION Micro-computed tomography (micro-CT) is an important tool in non-invasive screening of small animals suchas mice and rats for pre-c linical cancer studies. 1–3 Compared to clinical CT scanners, a much higher spatialresolution is needed in order to image the anatomy of small animals with research interest. Current commercialmicro-CT scanners oer the capability of imaging objects ex-vivo with high spatial resolution. Studies on lungand colon cancer models have shown that micro-CT is capable of sequentially tracking tumors of larger than2mm in diameter with high “delity. Small tumors are still hardly distinguishable from the normal tissue, whichis partially attributed to the motion-induced artifacts created by peristalsis, respiration and cardiac motion.The motion-induced artifacts can in principle be minimized by prospective gating where the image acquisition issynchronizedwith the physiological signals, as commonly done in clinical CT scanners. However, performing suchmeasurements on small animals is challenging because their physiological motions are at least ten times fasterthan those of human. Motion-induced artifacts blur the micro-CT image resulting in signi“cantly deterioratedspatial resolution than the nominal values.Several new designs have been considered for high-resolution CT imaging of live animals. One is to use ahigh power rotating anode x-ray source instead of a “xed-anode micro-focus x-ray tube.

Carbon Nanotubes (CNTs) have been shown excellent field emission emitters due to their unique properties. CNTs are a stable form of carbon; a graphite sheet rolls up forming a cylindrical shape with high aspect ratio, low turn-on field, high current density, high strength (1) and can generate quality x-ray radiation (2). These properties make carbon nanotubes very attractive for field emission applications. Field emission cathodes are the central part of field emission displays (FED) and carbon nanotubes field emission x-ray source. FED is a new flat panel display technology; this technology enables much thinner, lighter, and highest resolution displays than the cathode ray tubes (CRT). CNTs field emission x-ray source technology has applications in medical imaging and homeland security (2–7). The current thermionic cathodes have several disadvantages over CNT based field emission x-ray source such as slow response time, high power consumption, high operation temperature that reduces the lifetime of the x-ray tube (4) and large device size (3). Also CNT based field emission x-ray source offers improvement in high temporal resolution and capabilities for spatial and temporal modulation (7). CNT field emission x-ray source technology is available in single- and multi-beam imaging system. Multi-beam imaging system offers image of an object from multiple projection angles without mechanical motion (7).

Purpose: We recently demonstrated the feasibility of generating high current and high energy x‐ray radiation using field emitted electrons from the carbon nanotubes(CNTs). The purpose of the present work is to develop a spatially distributed multiple beam x‐ray array technology for stationary tomographyimaging, including digital breast tomosynthesis, with the goal of increasing the spatial resolution and scanning speed. Method and Materials:CNTcathodesfabricated by patterned electrophoretic deposition were used as the field emission electron source for x‐ray generation. Computer simulations and experimental measurements were carried out to design the electrostatic lens to focus the field emitted electrons to the predetermined area on the metal anode. Finite element analysis was performed to determine the anode heat load under the desired operation conditions. Spatially distributed x‐ray source arrays with one‐ and two‐dimensionally distributed focal spots were constructed using matrix addressable multi‐pixel CNTcathode, and corresponding focusing and anode structures. By varying the extraction electrical field, x‐ray radiation with programmable waveform was readily generated which can be gated with external triggers such as physiological signals with sub‐microsecond response time. Dedicated control electronics were designed and manufactured to switch, scan, and regulate the x‐ray beams. Results: Several spatially distributed field emission x‐ray source arrays with different configurations and performance parameters have been fabricated and characterized for different imaging systems. Stable operation at anode voltage up to 160kVp has been achieved. Through improvement of the CNTcathode and electronic regulation beam‐to‐beam consistency in intensity and focal spot size has been demonstrated. A dedicated x‐ray source array has been designed and fabricated for stationary digital breast tomosynthesis. The source comprises 31 individually controllable x‐ray beams covering 30 degrees viewing angle, allowing collection of the all the projection images from different angles without any mechanical motion blur. It is operated up to 50KVp anode voltage at an effective focal size comparable to that of the traditional mammography tube. Tomosynthesisimages of a breast phantom were obtained using the new source array and a flat‐panel x‐ray detector. Conclusion: The distributed field emission x‐ray source array technology offers unique capabilities that are attractive for tomographyimaging and potentially for radiotherapy. The flexibility in source configuration opens up new possibilities in system design. Conflict of Interest: Zhou is a board director of XinRay Systems which develops and commercializes the CNT X‐Ray source technology.

Carbon nanotube (CNT) field emitters are now being evaluated for a wide range of vacuum electronic applications. However, problems including short lifetime at high current density, instability under high voltage, poor emission uniformity, and pixel-to-pixel inconsistency are still major obstacles for device applications. We developed an electrophoretic process to fabricate composite CNT films with controlled nanotube orientation and surface density, and enhanced adhesion. The cathodes have significantly enhanced macroscopic field emission current density and long-term stability under high operating voltages. The application of this CNT electron source for high-resolution x-ray imaging is demonstrated.

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.

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.

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 system's 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.