Due to the need for high-resolution angiographic and interventional vascular imaging, a Micro-Angiographic
Fluoroscope (MAF) detector with a Control, Acquisition, Processing, and Image Display System (CAPIDS) was
installed on a detector changer, which was attached to the C-arm of a clinical angiographic unit at a local hospital. The
MAF detector provides high-resolution, high-sensitivity, and
real-time imaging capabilities and consists of a 300 μm thick
CsI phosphor, a dual stage micro-channel plate light image intensifier (LII) coupled to a fiber optic taper (FOT),
and a scientific grade frame-transfer CCD camera, providing an image matrix of 1024×1024 35 μm effective square
pixels with 12 bit depth. The changer allows the MAF
region-of-interest (ROI) detector to be inserted in front of the
Image Intensifier (II) when higher resolution is needed during angiographic or interventional vascular imaging
procedures, e.g. endovascular stent deployment. The CAPIDS was developed and implemented using Laboratory
Virtual Instrumentation Engineering Workbench (LabVIEW) software and provides a user-friendly interface that enables
control of several clinical radiographic imaging modes of the MAF including: fluoroscopy, roadmapping, radiography,
and digital-subtraction-angiography (DSA). The total system has been used for image guidance during endovascular
image-guided interventions (EIGI) for diagnosing and treating artery stenoses and aneurysms using self-expanding
endovascular stents and coils in fifteen patient cases, which have demonstrated benefits of using the ROI detector. The
visualization of the fine detail of the endovascular devices and the vessels generally gave the clinicians confidence on
performing neurovascular interventions and in some instances contributed to improved interventions.
A new Graphical User Interface (GUI) was developed using Laboratory Virtual Instrumentation Engineering Workbench
(LabVIEW) for a high-resolution, high-sensitivity Solid State X-ray Image Intensifier (SSXII), which is a new x-ray
detector for radiographic and fluoroscopic imaging, consisting of an array of Electron-Multiplying CCDs (EMCCDs)
each having a variable on-chip electron-multiplication gain of up to 2000x to reduce the effect of readout noise. To
enlarge the field-of-view (FOV), each EMCCD sensor is coupled to an x-ray phosphor through a fiberoptic taper. Two
EMCCD camera modules are used in our prototype to form a computer-controlled array; however, larger arrays are
under development. The new GUI provides patient registration, EMCCD module control, image acquisition, and patient
image review. Images from the array are stitched into a 2kx1k pixel image that can be acquired and saved at a rate of 17
Hz (faster with pixel binning). When reviewing the patient's data, the operator can select images from the patient's
directory tree listed by the GUI and cycle through the images using a slider bar. Commonly used camera parameters
including exposure time, trigger mode, and individual EMCCD gain can be easily adjusted using the GUI. The GUI is
designed to accommodate expansion of the EMCCD array to even larger FOVs with more modules. The high-resolution,
high-sensitivity EMCCD modular-array SSXII imager with the new user-friendly GUI should enable angiographers and
interventionalists to visualize smaller vessels and endovascular devices, helping them to make more accurate diagnoses
and to perform more precise image-guided interventions.
To treat or prevent some of the 795,000 annual strokes in the U.S., self-expanding endo-vascular stents deployed under
fluoroscopic image guidance are often used. Neuro-interventionalists need to know the deployment behavior of each
stent in order to place them in the correct position. Using the Micro-Angiographic Fluoroscope (MAF) which has about
3 times higher resolution than commercially available flat panel detectors (FPD) we studied the deployment mechanics
of two of the most important commercially available nitinol stents: the Pipeline embolization device (EV3), and the
Enterprise stent (Codman). The Pipeline stent's length extends to about 3 times that of its deployed length when it is
contained inside a catheter. From the high-resolution images with the MAF we found that upon the sudden release of the
distal end of the Pipeline from a helical wire cap, the stent expands radially but retracts to about 30% (larger than for
patient deployments) of its length. When released from the catheter proximally, it retracts additionally about 50%
contributing to large uncertainty in the final deployed location. In contrast, the MAF images clearly show that the
Enterprise stent self expands with minimal length retraction during deployment from its catheter and can be retrieved
and repositioned until the proximal markers are released from clasping structures on its guide-wire thus enabling more
accurate placement at the center of an aneurysm or stenosis. The high-resolution imaging demonstrated in this study
should help neurointerventionalists understand and control endovascular stent deployment mechanisms and hence
perform more precise treatments.
Due to the high-resolution needs of angiographic and interventional vascular imaging, a Micro-Angiographic Fluoroscope (MAF) detector with a Control, Acquisition, Processing, and Image Display System (CAPIDS) was installed on a detector changer which was attached to the C-arm of a clinical angiographic unit. The MAF detector
provides high-resolution, high-sensitivity, and real-time imaging capabilities and consists of a 300 μm-thick CsI phosphor, a dual stage micro-channel plate light image intensifier (LII) coupled to a fiber optic taper (FOT), and a
scientific grade frame-transfer CCD camera, providing an image matrix of 1024×1024 35 μm square pixels with 12 bit
depth. The Solid-State X-Ray Image Intensifier (SSXII) is an EMCCD (Electron Multiplying charge-coupled device)
based detector which provides an image matrix of 1k×1k 32 μm square pixels with 12 bit depth. The changer allows the
MAF or a SSXII region-of-interest (ROI) detector to be inserted in front of the standard flat-panel detector (FPD) when higher resolution is needed during angiographic or interventional vascular imaging procedures. The CAPIDS was developed and implemented using LabVIEW software and provides a user-friendly interface that enables control of several clinical radiographic imaging modes of the MAF or SSXII including: fluoroscopy, roadmapping, radiography,
and digital-subtraction-angiography (DSA). The total system has been used for image guidance during endovascular
image-guided interventions (EIGI) using prototype self-expanding asymmetric vascular stents (SAVS) in over 10 rabbit aneurysm creation and treatment experiments which have demonstrated the system's potential benefits for future clinical use.
The Asymmetric Vascular Stent (AVS) for intracranial aneurysm (IA) treatment is an experimental device, specially
designed for intra-aneurysmal blood flow diversion and thrombosis promotion. The stent has a low-porous patch to
cover only the aneurysm neck while the rest of the stent is very porous to avoid blockage of adjacent branches. The latest
AVS design is similar to state-of-art, closed-cell, self-expanding, neurovascular stent. The stents were used to treat
sixteen rabbit-elastase aneurysm models. The treatment effect was analyzed using normalized-time-density-curves
(NTDC) measured by pixel-value integration over a region-of-interest containing the aneurysm. Normalization constant
was the total bolus injection determined angiographically. Based on NTDC measurement, five quantities were derived to
describe the contrast flow. Two are related to the amount of contrast entering the aneurysm: NTDC peak and NTDC
input slope. The other three are related to contrast presence in the aneurysmal dome: time-to-peak (TTP), wash-out-time
(WOT) and mean-transit-time (MTT). Flow modification descriptions using the contrast related quantities were
expressed as a pre-/post-stented NTDC parameter ratio, while the time related quantities were expressed as a post-/prestented
ratio, so that ratios smaller than one indicate a desired effect. Thirteen aneurysms were treated successfully and
achieved significant aneurysm occlusion. For these cases, the resulting average parameters were: peak-ratio=0.17+0.21;
input-slope-ratio=0.19±0.24, TTP-ratio=0.17+0.21, WOT-ratio=0.58±0.73 and MTT-ratio=0.65±0.97). All the quantities
revealed decreased aneurysmal flow due to blood flow diversion using the new self-expanding asymmetrical vascular
stent (SAVS). Treatment outcome results and angiographic analysis indicate that the new self-deploying stent design has
great potential for clinical implementation.
The new Solid State X-ray Image Intensifier (SSXII) is being designed based on a modular imaging array of Electron
Multiplying Charge Couple Devices (EMCCD). Each of the detector modules consists of a CsI(Tl) phosphor coupled to
a fiber-optic plate, a fiber-optic taper (FOT), and an EMCCD sensor with its electronics. During the optical coupling and
alignment of the modules into an array form, small orientation misalignments, such as rotation and translation of the
EMCCD sensors, are expected. In addition, barrel distortion will result from the FOTs. Correction algorithms have been
developed by our group for all the above artifacts. However, it is critical for the system's performance to correct these
artifacts in real-time (30 fps). To achieve this, we will use
two-dimensional Look-Up-Tables (LUT) (each for x and y
coordinates), which map the corrected pixel locations to the
acquired-image pixel locations. To evaluate the feasibility of
this approach, this process is simulated making use of parallel coding techniques to allow real-time distortion corrections
for up to sixteen modules when a standard quad processor is used. The results of this simulation confirm that tiled
field-of-views (FOV) comparable with those of flat panel detectors can be generated in ~17 ms (>30 fps). The increased FOV
enabled through correction of tiled images, combined with the EMCCD characteristics of low noise, negligible lag and
high sensitivity, should make possible the practical use of the SSXII with substantial advantages over conventional
clinical systems. (Support: NIH Grants R01EB008425, R01NS43924, R01EB002873)
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