Shabana Sultana

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.

High resolution stationary digital breast tomosynthesis using distributed carbon nanotube x-ray source array

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.

Prospective-gated cardiac micro-CT imaging of free-breathing mice using carbon nanotube field emission x-ray

PURPOSE Carbon nanotube (CNT) based field emission x-ray source technology has recently been investigated for diagnostic imaging applications because of its attractive characteristics including electronic programmability, fast switching, distributed source, and multiplexing. The purpose of this article is to demonstrate the potential of this technology for high-resolution prospective-gated cardiac micro-CT imaging. METHODS A dynamic cone-beam micro-CT scanner was constructed using a rotating gantry, a stationary mouse bed, a flat-panel detector, and a sealed CNT based microfocus x-ray source. The compact single-beam CNT x-ray source was operated at 50 KVp and 2 mA anode current with 100 microm x 100 microm effective focal spot size. Using an intravenously administered iodinated blood-pool contrast agent, prospective cardiac and respiratory-gated micro-CT images of beating mouse hearts were obtained from ten anesthetized free-breathing mice in their natural position. Four-dimensional cardiac images were also obtained by gating the image acquisition to different phases in the cardiac cycle. RESULTS High-resolution CT images of beating mouse hearts were obtained at 15 ms temporal resolution and 6.2 lp/mm spatial resolution at 10% of system MTF. The images were reconstructed at 76 microm isotropic voxel size. The data acquisition time for two cardiac phases was 44 +/- 9 min. The CT values observed within the ventricles and the ventricle wall were 455 +/- 49 and 120 +/- 48 HU, respectively. The entrance dose for the acquisition of a single phase of the cardiac cycle was 0.10 Gy. CONCLUSIONS A high-resolution dynamic micro-CT scanner was developed from a compact CNT microfocus x-ray source and its feasibility for prospective-gated cardiac micro-CT imaging of free-breathing mice under their natural position was demonstrated.

Stationary digital breast tomosynthesis system with a multi-beam field emission x-ray source array

A stationary digital breast tomosynthesis (DBT) system using a carbon nanotube based multi-beam field emission x-ray (MBFEX) source has been designed. The purpose is to investigate the feasibility of reducing the total imaging time, simplifying the system design, and potentially improving the image quality comparing to the conventional DBT scanners. The MBFEX source consists of 25 individually programmable x-ray pixels which are evenly angular spaced covering a 48° field of view. The device acquires the projection images by electronically switching on and off the individual x-ray pixels without mechanical motion of either the x-ray source or the detector. The designs of the x-ray source and the imaging system are presented. Some preliminary results are discussed.

Distributed source x-ray tube technology for tomosynthesis imaging.

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.

A dynamic micro-CT scanner with a stationary mouse bed using a compact carbon nanotube field emission x-ray tube

In this paper we report the development of a high resolution dynamic micro-computed tomography (CT) scanner with a stationary mouse bed using a compact carbon nanotube (CNT) x-ray tube. The scanner comprises a rotating x-ray tube and detector pair and a stationary and a horizontally positioned small animal bed. The system is optimized for in vivo mouse cardiac imaging. Its performance is evaluated with CT scans of phantoms and free-breathing mice. The modulation transfer function (MTF) at 10% is 5 lp/mm. At single frame acquisition, mouse cardiac micro-CT at 20msec temporal resolution has been demonstrated by prospectively gating the imaging acquisitions to both respiration and cardiac signals.

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.

Design and characterization of a carbon-nanotube-based micro-focus x-ray tube for small animal imaging

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.

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.

SU-FF-I-40: A Novel Gantry-Free DBT System Using a Stationary Multi-Beam Field Emission X-Ray Source Array Based On Carbon Nanotubes (CNTs)

Purpose: To test the feasibility of a novel gantry‐free digital breast tomosynthesis (DBT) system using a stationary multi‐beam field emission X‐ray source array based on carbon nanotubes(CNTs) and to compare the system performance with the conventional devices.Method and Materials: Two tomosynthesisimagingsystems have been built: a compact model and a full scale model, which contain 9 and 25 individual X‐ray pixels, respectively. The compact model can only image a partial breast phantom due to the limited span of the X‐ray source array and the small FOV of the detector. The full scale system is capable of full field digital mammography by utilizing a detector with 20‐cm FOV. The geometry of the full scale system is also comparable to the conventional DBT devices (refer to the supporting material). The system geometry, such as the source to detector distance (SDD) and X‐ray source position, is calibrated. The slice images at different depths are reconstructed using ordered subset convex (maximum likelihood) method. The system performance is evaluated by measuring parameters such as MTF and SNR. Results: By eliminating the rotary gantry, the system design is simplified and the issue if image blurring due to x‐ray source motion is removed. The total scan time can potentially be further shortened with a faster detector readout speed. Conclusion: By eliminating the rotary gantry, the system noise and equipment cost of the tomosynthesisimagingsystem are reduced. The total scan time can be further shortened with faster detector readout speed. The novel stationary tomosysthesis system shows great potential in clinical imaging.