The new Solid State X-ray Image Intensifier (SSXII) is a high-resolution, high-sensitivity, real-time region-ofinterest
(ROI) x-ray imaging detector. Evaluations were made of both standard linear systems metrics (MTF, DQE)
and total system performance with generalized linear systems metrics (GMTF, GDQE) including scatter and
geometric un-sharpness for simulated clinical conditions.
The SSXII is based on a 1k x 1k EMCCD sensor coupled to a 300 μm thick CsI(Tl) phosphor through a 2.88:1 fiber
optic taper resulting in a 37 μm effective pixel size and an effective 3.7 cm x 3.7 cm square field-of-view (FOV).
Standard methods were used to calculate MTF, NNPS and DQE. Generalized metrics were calculated and compared
for three different magnifications (1.03, 1.11 and 1.2) and three different focal spots (0.3 mm, 0.5 mm and 0.8 mm)
for a scatter fraction of 0.28.
For an RQA5 spectrum, at 5 cycles/mm the MTF was found to be 0.06 and DQE was 0.04, while the DQE(0) was
0.60. Focal spot un-sharpness and scatter significantly degrades the GMTF and GDQE performance of the detector.
A low frequency drop is caused by scatter and is almost independent of focal spot size and magnification. The
degradation for middle range frequencies is caused by geometric un-sharpness and increases with focal spot size and
magnification. This degradation was least in the case of the small focal spot and almost independent of
magnification.
In spite of this degradation, the high resolution SSXII with a small FOV may have a significant impact on ROI
image-guided neuro-interventions since it demonstrates far better performance than standard current detectors.
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.
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.
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