KEYWORDS: Sensors, X-rays, CMOS sensors, Electrons, X-ray detectors, Digital filtering, X-ray imaging, Scintillators, Signal to noise ratio, Imaging systems
The detectors that are used for endovascular image-guided interventions (EIGI), particularly for neurovascular
interventions, do not provide clinicians with adequate visualization to ensure the best possible treatment outcomes.
Developing an improved x-ray imaging detector requires the determination of estimated clinical x-ray entrance
exposures to the detector. The range of exposures to the detector in clinical studies was found for the three modes of
operation: fluoroscopic mode, high frame-rate digital angiographic mode (HD fluoroscopic mode), and DSA mode.
Using these estimated detector exposure ranges and available CMOS detector technical specifications, design
requirements were developed to pursue a quantum limited, high resolution, dynamic x-ray detector based on a CMOS
sensor with 50 μm pixel size. For the proposed MAF-CMOS, the estimated charge collected within the full exposure
range was found to be within the estimated full well capacity of the pixels. Expected instrumentation noise for the
proposed detector was estimated to be 50-1,300 electrons. Adding a gain stage such as a light image intensifier would
minimize the effect of the estimated instrumentation noise on total image noise but may not be necessary to ensure
quantum limited detector operation at low exposure levels. A recursive temporal filter may decrease the effective total
noise by 2 to 3 times, allowing for the improved signal to noise ratios at the lowest estimated exposures despite
consequent loss in temporal resolution. This work can serve as a guide for further development of dynamic x-ray
imaging prototypes or improvements for existing dynamic x-ray imaging systems.
Present day treatment for neurovascular pathological conditions involves the use of devices with
very small features such as stents, coils, and balloons; hence, these interventional procedures demand high resolution xray
imaging under fluoroscopic conditions to provide the capability to guide the deployment of these fine endovascular
devices. To address this issue, a high resolution x-ray detector based on EMCCD technology is being developed. The
EMCCD field-of-view is enlarged using a fiber-optic taper so that the detector features an effective pixel size of 37 μm
giving it a Nyquist frequency of 13.5 lp/mm, which is significantly higher than that of the state of the art Flat Panel
Detectors (FPD). Quantitative analysis of the detector, including gain calibration, instrumentation noise equivalent
exposure (INEE) and modulation transfer function (MTF) determination, are presented in this work. The gain of the
detector is a function of the detector temperature; with the detector cooled to 50 C, the highest relative gain that could be
achieved was calculated to be 116 times. At this gain setting, the lowest INEE was measured to be 0.6 μR/frame. The
MTF, measured using the edge method, was over 2% up to 7 cycles/ mm. To evaluate the performance of the detector
under clinical conditions, an aneurysm model was placed over an anthropomorphic head phantom and a coil was guided
into the aneurysm under fluoroscopic guidance using the detector. Image sequences from the procedure are presented
demonstrating the high resolution of this SSXII.
A high resolution (up to 11.2 lp/mm) x-ray detector with larger field of view (8.5 cm x 8.5 cm) has been
developed. The detector is a 2 x 2 array of individual imaging modules based on EMCCD technology. Each module
outputs a frame of size 1088 x 1037 pixels, each 12 bits. The frames from the 4 modules are acquired into the processing
computer using one of two techniques. The first uses 2 CameraLink communication channels with each carrying
information from two modules, the second uses a application specific custom integrated circuits, the Multiple Module
Multiplexer Integrated Circuit (MMMIC), 3 of which are used to multiplex the data from 4 modules into one
CameraLink channel. Once the data is acquired using either of the above mentioned techniques, it is decoded in the
graphics processing unit (GPU) to form one single frame of size 2176 x 2074 pixels each 16 bits. Each imaging module
uses a fiber optic taper coupled to the EMCCD sensor. To correct for mechanical misalignment between the sensors and
the fiber optic tapers and produce a single seamless image, the images in each module may be rotated and translated
slightly in the x-y plane with respect to each other.
To evaluate the detector acquisition and correction techniques, an aneurysm model was placed over an anthropomorphic
head phantom and a coil was guided into the aneurysm under fluoroscopic guidance using the detector array. Image
sequences before and after correction are presented which show near-seamless boundary matching and are well suited for
fluoroscopic imaging.
KEYWORDS: Attenuators, X-rays, Signal attenuation, Fluoroscopy, Image filtering, Image quality, Digital filtering, Electronic filtering, Signal to noise ratio, Arteries
A novel dose reduction technique for fluoroscopic interventions involving a combination of a material x-ray
region of interest (ROI) attenuator and spatially different, temporally variable ROI temporal recursive filter, was used to
guide the catheter to the ROI in three live animal studies, two involving rabbits and one involving a sheep. In the two
rabbit studies presented , a catheter was guided to the entrance of the carotid artery. With the added ROI attenuator the
image under the high attenuation region is very noisy. By using temporal filtering with a filter weight of 0.6 on previous
frames, the noise is reduced. In the sheep study the catheter was guided to the descending aorta of the animal. The sheep
offered a relatively higher attenuation to the incident x-rays and thus a higher temporal filter weight of 0.8 on previous
frames was used during the procedure to reduce the noise to levels acceptable by the interventionalist.
The image sequences from both studies show that significant dose reduction of 5-6 times can be achieved with
acceptable image quality outside the ROI by using the above mentioned technique. Even though the temporal filter
weighting outside the ROI is higher, the consequent lag does not prevent perception of catheter movement.
We demonstrate a novel approach for achieving patient dose savings during image-guided neurovascular
interventions, involving a combination of a material x-ray region of interest (ROI) attenuator and a spatially different
ROI temporal filtering technique. The part of the image under the attenuator is reduced in dose but noisy and less bright
due to fewer x-ray quanta reaching the detector, as compared to the non-attenuating (or less attenuating) region. First the
brightness is equalized throughout the image by post processing and then a temporal filter with higher weights is applied
to the high attenuating region to reduce the noise, at the cost of increased lag; however, in the regions where less
attenuation is present, a lower temporal weight is needed and is applied to preserve temporal resolution.
A simulation of the technique is first presented on an actual image sequence obtained from an endovascular
image guided interventional (EIGI) procedure. Then the actual implementation of the technique with a physical ROI
attenuator is presented. Quantitative analysis including noise analysis and integral dose calculations are presented to
validate the proposed technique.
We have designed and developed from the discrete component level a high resolution dynamic x-ray detector to be used
for fluoroscopic and angiographic medical imaging. The heart of the detector is a 1024 ×1024 pixel electron multiplying
charge coupled device (EMCCD) with a pixel size of 13 × 13 μm2 (Model CCD201-20, e2v Technologies, Inc.), bonded
to a fiber optic plate (FOP), and optically coupled to a 350 μm thick micro-columnar CsI(TI) scintillator via a fiber optic
taper (FOT). Our aim is to design an array of these detectors that could be extended to any arbitrary X × Y size in two
dimensions to provide a larger field of view (FOV). A physical configuration for a 3×3 array is presented that includes
two major sub-systems. First is an optical front end that includes (i) a phosphor to convert the x-ray photons into light
photons, and (ii) a fused array of FOTs that focuses light photons from the phosphor onto an array of EMCCD's optically
coupled using FOPs. Second is an electronic front end that includes (i) an FPGA board used for generating clocks and
for data acquisition (ii) driver boards to drive and digitize the analog output from the EMCCDs, (iii) a power board, and
(iv) headboards to hold the EMCCD's while they are connected to their respective driver board using flex cables. This
configuration provides a larger FOV as well as region-of-interest (ROI) high-resolution imaging as required by modern
neurovascular procedures.
We present the image processing upgrades implemented on a Graphics Processing Unit (GPU) in the Control,
Acquisition, Processing, and Image Display System (CAPIDS) for the custom Micro-Angiographic Fluoroscope (MAF)
detector. Most of the image processing currently implemented in the CAPIDS system is pixel independent; that is, the
operation on each pixel is the same and the operation on one does not depend upon the result from the operation on the
other, allowing the entire image to be processed in parallel. GPU hardware was developed for this kind of massive
parallel processing implementation. Thus for an algorithm which has a high amount of parallelism, a GPU
implementation is much faster than a CPU implementation. The image processing algorithm upgrades implemented on
the CAPIDS system include flat field correction, temporal filtering, image subtraction, roadmap mask generation and
display window and leveling. A comparison between the previous and the upgraded version of CAPIDS has been
presented, to demonstrate how the improvement is achieved. By performing the image processing on a GPU, significant
improvements (with respect to timing or frame rate) have been achieved, including stable operation of the system at 30
fps during a fluoroscopy run, a DSA run, a roadmap procedure and automatic image windowing and leveling during each
frame.
A novel method for achieving trichromatic color detection using a single photodetector with less than three p-n junctions
is presented. This new method removes the constraints of color sensing in buried-double-junction (BDJ) photodiode,
eliminates the need for a priori light source knowledge or for changing color intensity. After using a single visible light
optical filter to block irradiance external of visible spectrum, the color detection is achieved by taking the difference in
depletion region photocurrent generated by different reverse bias voltages. This "difference output" effectively forms the
"third" optical wavelength specific depletion region required for trichromatic color sensing. This method is based on
exploiting the relationship between photon absorption and photon penetration depth of silicon, and the basic property of
p-n junction photodiode which states that only photons absorbed within depletion region generate current. The theory is
validated experimentally using BDJ photodiodes fabricated through MOSIS Inc. in the AMI-ABN 1.5um technology and
ON-SEMI 0.5um technology. A commercial p-i-n photodiode is also being investigated for contrast and comparison.
In this paper, we describe the development of a novel, retina-like neuromorphic chip that has an array of two types of
retina 'cells' arranged to mimic the fovea structure in certain animals. One of the two retina cell types performs
irradiance detection and the other can perform color detection. Together, via the two parallel pathways the retina chip
can perform color change intensity change disambiguation (CCICD). The irradiance detection cell has a wide-dynamic
detection range that spans almost 3 orders of magnitude. The color detection cell has a buried double junction (BDJ)
photodiode as the photoreceptor followed by two parallel logarithmic I-V convertors. The output from this is a color
response which has at least a 50nm resolution for wavelengths from 400nm to 900nm. With these two cells, the array
can perform color change -intensity change disambiguation (CCICD) to determine if a change in the output of the
irradiance pathway is because of irradiance change, color change, or both. This biological retina-like neuromorphic
sensor array is implemented in ON-SEMI 0.5μm technology, a standard CMOS fabrication process available at MOSIS.
A methodology for enabling biochemical sensing applications using porous polymer photonic bandgap structures is presented. Specifically, we demonstrate an approach to encapsulation of chemical and biological recognition elements within the pores of these structures. This sensing platform is built on our recently demonstrated nanofabrication technique using holographic interferometry of a photo-activated mixture that includes a volatile solvent as well as monomers, photoinitiators, and co-initiators. Evaporation of the solvent after polymerization yields nanoporous polymeric 1D photonic bandgap structures that can be directly integrated into optical sensor systems that we have previously developed. More importantly, these composite structures are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of biochemical recognition elements. As a specific example of a prototype device, we demonstrate an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Finally, we report initial results of extending this technique to the development of a hydrophilic porous polymer photonic bandgap structure for sensing in aqueous environments. The ability to control the hydrophilic/hydrophobic nature of these materials has direct impact on chemical and biological sensing.
Rapid advances in point-of-care devices for medical and biomedical diagnostic and therapeutic applications have
increased the need for low cost, low power, high throughput, and miniaturized systems. To this end, we developed
several optical sensor systems using CMOS detection and processing components and sol-gel derived xerogel
recognition elements for monitoring various biochemical analytes. These sensors are based either on the measurement of
the luminescence intensity or the excited-state lifetimes of luminophores embedded in the nanostructured xerogel
matrices. Specifically, the design and development of CMOS detection and signal processing components and their
system integration will be described in detail. Additionally, we will describe the factors that limit the performance of
these sensor systems in terms of sensitivity, response time, and dynamic range. Finally, the results obtained for
monitoring important biochemical analytes such as oxygen (O2) and glucose will be discussed.
We report on a new strategy for producing self-contained sensor elements for protein detection. The method exploits molecular imprinting, sol-gel-derived xerogels, and selective installation of the fluorescent reporter molecule within the template site. There are no biological reagents used. We term these new xerogel-based sensor elements as Protein Imprinted Xerogels with Integrated Emission Sites (PIXIES). The analytical figures of merit are described.
KEYWORDS: Sensors, Very large scale integration, Analog electronics, System integration, Head, Optical engineering, Eye, Integrated circuits, Laser systems engineering, Visualization
We describe the development of an analog very large scale integration (AVLSI) system for perceiving depth of a stationary object, termed the depth through motion parallax (DTMP) system. The system consists of an AVLSI smart focal plane array and an optical lens, with a laser system for the object. The DTMP integrated circuit is implemented using the AMI Semiconductor 1.5-µm process available through the MOSIS integrated circuit fabrication service. The DTMP chip and the lens are mounted on a single motion-controlled stage to mimic the human head and eye. The object is mounted on a different motion stage and is manually moved to different depths with respect to the lens. We report experimental results obtained for depth perception with the head being stationary and the object moving with a constant velocity that is geometrically equivalent to the object being stationary and the head moving with a constant velocity. Our results show that the transit time across the DTMP chip, which is equivalent to the perceived velocity, can be used to determine the depth of an object, and uses less than 2 mW of average power.
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