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.
The solid-state x-ray image intensifier (SSXII) is an EMCCD-based x-ray detector designed to satisfy an increasing need
for high-resolution real-time images, while offering significant improvements over current flat panel detectors (FPDs)
and x-ray image intensifiers (XIIs). FPDs are replacing XIIs because they reduce/eliminate veiling glare, pincushion or s-shaped
distortions and are physically flat. However, FPDs suffer from excessive lag and ghosting and their performance
has been disappointing for low-exposure-per-frame procedures due to excessive instrumentation-noise. XIIs and FPDs
both have limited resolution capabilities of ~3 cycles/mm. To overcome these limitations a prototype SSXII module has
been developed, consisting of a 1k x 1k, 8 μm pixel EMCCD with a fiber-optic input window, which views a 350 μm
thick CsI(Tl) phosphor via a 4:1 magnifying fiber-optic-taper (FOT). Arrays of such modules will provide a larger field-of-
view. Detector MTF, DQE, and instrumentation-noise equivalent exposure (INEE) were measured to evaluate the
SSXIIs performance using a standard x-ray spectrum (IEC RQA5), allowing for comparison with current state-of-the-art
detectors. The MTF was 0.20 at 3 cycles/mm, comparable to standard detectors, and better than 0.05 up to 7 cycles/mm,
well beyond current capabilities. DQE curves indicate no degradation from high-angiographic to low-fluoroscopic
exposures (< 2% deviation in overall DQE from 1.3 mR to 2.7 μR), demonstrating negligible instrumentation-noise,
even with low input signal intensities. An INEE of < 0.2 μR was measured for the highest-resolution mode (32 μm
effective pixel size). Comparison images between detector technologies qualitatively demonstrate these improved
imaging capabilities provided by the SSXII.
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.
A new high-resolution, high-sensitivity, low-noise x-ray detector based on EMCCDs has been developed. The EMCCD detector module consists of a 1kx1k, 8μm pixel EMCCD camera coupled to a CsI(Tl) scintillating phosphor via a fiber optic taper (FOT). Multiple modules can be used to provide the desired field-of-view (FOV). The detector is capable of acquisitions over 30fps. The EMCCD's variable gain of up to 2000x for the pixel signal enables high sensitivity for fluoroscopic applications. With a 3:1 FOT, the detector can operate with a 144μm effective pixel size, comparable to current flat-panel detectors. Higher resolutions of 96 and 48μm pixel size can also be achieved with various binning modes. The detector MTFs and DQEs were calculated using a linear-systems analysis. The zero frequency DQE was calculated to be 59% at 74 kVp. The DQE for the 144μm pixel size was shown to exhibit quantum-noise limited behavior down to ~0.1μR using a conservative 30x gain. At this low exposure, gains above 30x showed limited improvements in DQE suggesting such increased gains may not be necessary. For operation down to 48µm pixel sizes, the detector instrumentation noise equivalent exposure (INEE), defined as the exposure where the instrumentation noise equals the quantum-noise, was <0.1μR for a 20x gain. This new technology may provide improvements over current flat-panel detectors for applications such as fluoroscopy and angiography requiring high frame rates, resolution, dynamic range and sensitivity while maintaining essentially no lag and very low INEE. Initial images from a prototype detector are also presented.
A new microangiographic system (MA) integrated into a c-arm gantry has been developed allowing precise placement of a MA at the exact same angle as the standard x-ray image intensifier (II) with unchanged source and object position. The MA can also be arbitrarily moved about the object and easily moved into the field of view (FOV) in front of the lower resolution II when higher resolution angiographic sequences are needed. The benefits of this new system are illustrated in a neurovascular study, where a rabbit is injected with contrast media for varying oblique angles. Digital subtraction angiographic (DSA) images were obtained and compared using both the MA and II detectors for the same projection view. Vessels imaged with the MA appear sharper with smaller vessels visualized. Visualization of ~100 μm vessels was possible with the MA whereas not with the II. Further, the MA could better resolve vessel overlap. Contrast to noise ratios (CNR) were calculated for vessels of varying sizes for the MA versus the II and were found to be similar for large vessels, approximately double for medium vessels, and infinitely better for the smallest vessels. In addition, a 3D reconstruction of selected vessel segments was performed, using multiple (three) projections at oblique angles, for each detector. This new MA/II integrated system should lead to improved diagnosis and image guidance of neurovascular interventions by enabling initial guidance with the low resolution large FOV II combined with use of the high resolution MA during critical parts of diagnostic and interventional procedures.
The new Multi-View Reconstruction (MVR) method for generating 3D vascular images was evaluated experimentally. The MVR method requires only a few digital subtraction angiographic (DSA) projections to reconstruct the 3D model of the vessel object compared to 180 or more projections for standard CBCT. Full micro-CBCT datasets of a contrast filled carotid vessel phantom were obtained using a Microangiography (MA) detector. From these datasets, a few projections were selected for use in the MVR technique. Similar projection views were also obtained using a standard x-ray image intensifier (II) system. A comparison of the 2D views of the MVRs (MA and II derived) with reference micro-CBCT data, demonstrated best agreement with the MA MVRs, especially at the curved part of the phantom. Additionally, the full 3D MVRs were compared with the full micro-CBCT 3D reconstruction resulting for the phantom with the smallest diameter (0.75 mm) vessel, in a mean centerline deviation from the micro-CBCT derived reconstructions of 29 μm for the MA MVR and 48 μm for the II MVR. The comparison implies that an MVR may be substituted for a full micro-CBCT scan for evaluating vessel segments with consequent substantial savings in patient exposure and contrast media injection yet without substantial loss in 3D image content. If a high resolution system with MA detector is used, the improved resolution could be well suited for endovascular image guided interventions where visualization of only a small field of view (FOV) is required.
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