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.
X-ray equipment testing using phantoms that mimic the specific human anatomy, morphology, and structure is a very
important step in the research, development, and routine quality assurance for such equipment. Although the NEMA
XR21 phantom exists for cardiac applications, there is no such standard phantom for neuro-, peripheral and cardiovascular
angiographic applications. We have extended the application of the NEMA XR21-2000 phantom to evaluate
neurovascular x-ray imaging systems by structuring it to be
head-equivalent; two aluminum plates shaped to fit into the
NEMA phantom geometry were added to a 15 cm thick section. Also, to enable digital subtraction angiography (DSA)
testing, two replaceable central plates with a hollow slot were made so that various angiographic sections could be
inserted into the phantom. We tested the new modified phantom using a flat panel C-arm unit dedicated for endovascular
image-guided interventions. All NEMA XR21-2000 standard test sections were used in evaluations with the new "headequivalent"
phantom. DSA and DA are able to be tested using two standard removable blocks having simulated arteries
of various thickness and iodine concentrations (AAPM Report 15). The new phantom modifications have the benefits of
enabling use of the standard NEMA phantom for angiography in both neuro- and cardio-vascular applications, with the
convenience of needing only one versatile phantom for multiple applications. Additional benefits compared to using
multiple phantoms are increased portability and lower cost.
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)
KEYWORDS: Angiography, Neck, Scanning electron microscopy, Arteries, Polyurethane, In vivo imaging, Animal model studies, Electron microscopy, Hemodynamics, Domes
Image-guided endovascular intervention (EIGI), using new flow modifying endovascular devices for intracranial
aneurysm treatment is an active area of stroke research. The new polyurethane-asymmetric vascular stent (P-AVS), a
vascular stent partially covered with a polyurethane-based patch, is used to cover the aneurysm neck, thus occluding
flow into the aneurysm. This study involves angiographic imaging of partially covered aneurysm orifices. This
particular situation could occur when the vascular geometry does not allow full aneurysm coverage. Four standard in-vivo
rabbit-model aneurysms were investigated; two had stent patches placed over the distal region of the aneurysm
orifice while the other two had stent patches placed over the proximal region of the aneurysm orifice. Angiographic
analysis was used to evaluate aneurysm blood flow before and immediately after stenting and at four-week follow-up.
The treatment results were also evaluated using histology on the aneurysm dome and electron microscopy on the
aneurysm neck. Post-stenting angiographic flow analysis revealed aneurysmal flow reduction in all cases with faster
flow in the distally-covered case and very slow flow and prolonged pooling for proximal-coverage. At follow-up,
proximally-covered aneurysms showed full dome occlusion. The electron microscopy showed a remnant neck in both
distally-placed stent cases but complete coverage in the proximally-placed stent cases. Thus, direct flow (impingement
jet) removal from the aneurysm dome, as indicated by angiograms in the proximally-covered case, was sufficient to
cause full aneurysm healing in four weeks; however, aneurysm healing was not complete for the distally-covered case.
These results support further investigations into the treatment of aneurysms by flow-modification using partial
aneurysm-orifice coverage.
A graphical user interface based on LabVIEW software was developed to enable clinical evaluation of a new High-Sensitivity Micro-Angio-Fluoroscopic (HSMAF) system for real-time acquisition, display and rapid frame transfer of
high-resolution region-of-interest images. The HSMAF detector consists of a CsI(Tl) phosphor, a light image intensifier
(LII), and a fiber-optic taper coupled to a progressive scan,
frame-transfer, charged-coupled device (CCD) camera which
provides real-time 12 bit, 1k × 1k images capable of greater than 10 lp/mm resolution. Images can be captured in
continuous or triggered mode, and the camera can be programmed by a computer using Camera Link serial
communication. A graphical user interface was developed to control the camera modes such as gain and pixel binning as
well as to acquire, store, display, and process the images. The program, written in LabVIEW, has the following
capabilities: camera initialization, synchronized image acquisition with the x-ray pulses, roadmap and digital subtraction
angiography acquisition (DSA), flat field correction, brightness and contrast control, last frame hold in fluoroscopy,
looped play-back of the acquired images in angiography, recursive temporal filtering and LII gain control. Frame rates
can be up to 30 fps in full-resolution mode. The user friendly implementation of the interface along with the high frame-rate
acquisition and display for this unique high-resolution detector should provide angiographers and interventionalists
with a new capability for visualizing details of small vessels and endovascular devices such as stents and hence enable
more accurate diagnoses and image guided interventions.
New advances in catheter technology and remote actuation for minimally invasive procedures are continuously
increasing the demand for better x-ray imaging technology. The new x-ray high-sensitivity Micro-Angiographic
Fluoroscope (HS-MAF) detector offers high resolution and real-time image-guided capabilities which are unique when
compared with commercially available detectors. This detector consists of a 300 μm CsI input phosphor coupled to a
dual stage GEN2 micro-channel plate light image intensifier (LII), followed by minifying fiber-optic taper coupled to a
CCD chip. The HS-MAF detector image array is 1024X1024 pixels, with a 12 bit depth capable of imaging at 30 frames
per second. The detector has a round field of view with 4 cm diameter and 35 microns pixels. The LII has a large
variable gain which allows usage of the detector at very low exposures characteristic of fluoroscopic ranges while
maintaining very good image quality. The custom acquisition program allows real-time image display and data storage.
We designed a set of in-vivo experimental interventions in which placement of specially designed endovascular stents
were evaluated with the new detector and with a standard x-ray image intensifier (XII). Capabilities such fluoroscopy,
angiography and ROI-CT reconstruction using rotational angiography data were implemented and verified. The images
obtained during interventions under radiographic control with the HS-MAF detector were superior to those with the XII.
In general, the device feature markers, the device structures, and the vessel geometry were better identified with the new
detector. High-resolution detectors such as HS-MAF can vastly improve the accuracy of localization and tracking of
devices such stents or catheters.
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