Purpose: To provide improved MAF image guidance during intracranial aneurysm treatment (IAT) with detachable coils. Method and Materials:The MAF is an ultra-high resolution (35 μm pixels), high speed detector mounted on a clinical Flat Panel (FP) C-arm used whenever high resolution is needed in a small field of view. During IATˈs the interventionalists fill the aneurysm dome with platinum or highly x-ray attenuating detachable micro-coils. For medium and large aneurysms, the coil mass becomes increasingly dense making any additional coil nearly impossible to visualize with the standard FP. Thus estimation of dome filling relies heavily only on experience rather than actual imagery. The MAF gain is capable of adjusting dynamically during the procedure based on the average pixel value indicated in a custom or preset ROI. In this study we selected an ROI fitted over the aneurysm, so that as the aneurysm fills with coils, the MAF gain increases to keep the ROI average pixel value the same even with increased x-ray attenuation. The aneurysm was coiled using MAF fluoroscopic guidance for an elastomer aneurysm phantom superimposed on an anthropomorphic head phantom. The technique was repeated for the FP for comparison purposes. Results: The MAF used with dynamically adjustable gain offered excellent coil visualization during the entire process while the microcatheter tip position and deployment in the aneurysm within the coil mass was visible at all times even though background values increased during deployment to saturation. For the FP, imaging of the catheter tip was not distinguishable after 1/3 coil filling. Conclusions: Improved image guidance for coil deposition in aneurysms is presented. Catheter tip visualization was possible during the entire process which could result in better aneurysm dome coil filling due to improved image guidance with the MAF. NIH Grants R01-EB008425, R01-EB002873.

During image guided interventional procedures, superior resolution and image quality is critically important. Operating the MAF in the new High Definition (HD) fluoroscopy mode provides high resolution and increased contrast-to-noise ratio. The MAF has a CCD camera and a 300 micron cesium iodide x-ray convertor phosphor coupled to a light image intensifier (LII) through a fiber-optic taper. The MAF captures 1024 × 1024 pixels with an effective pixel size of 35 microns, and is capable of real-time imaging at 30 fps. The HD mode uses the advantages of higher exposure along with a small focal spot effectively improving the contrast-to-noise ratio (CNR) and the spatial resolution. The Control Acquisition Processing and Image Display System (CAPIDS) software for the MAF controls the LII gain. The interventionalist can select either fluoroscopic or angiographic modes using the two standard foot pedals. When improved image quality is needed and the angiography footpedal is used for HD mode, the x-ray machine will operate at a preset higher exposure rate using a small focal spot, while the CAPIDS will automatically adjust the LII gain to achieve proper image brightness. HD mode fluoroscopy and roadmapping are thus achieved conveniently during the interventional procedure. For CNR and resolution evaluation we used a bar phantom with images taken in HD mode with both the MAF and a Flat Panel Detector (FPD). It was seen that the FPD could not resolve more than 2.8 lp/mm whereas the MAF could resolve more than 5 lp/mm. The CNR of the MAF was better than that of the FPD by 60% at lower frequencies and by 600% at the Nyquist frequency of the FPD. The HD mode has become the preferred mode during animal model interventions because it enables detailed features of endovascular devices such as stent struts to be visualized clearly for the first time. Clinical testing of the MAF in HD mode is imminent.

Purpose: Immediate treatment assessment of intracranial aneurysms using flow modifying stents, can be done using comparative analysis of pre‐ and post‐stented normalized time density curves (NTDC). Previous study showed poor correlation of the time‐related NTDC parameters with the treatment outcome. A parameter normalization method to improve the NTDC parameters‐treatment outcome correlation, is proposed and investigated. Method and Materials: Elastase animal aneurysms model were treated using Asymmetric Vascular Stent prototypes. Angiograms were acquired pre‐ and post‐treatment and after four‐weeks. NTDC's parameters: time‐to‐peak TTP, mean‐transit‐time MTT and wash‐out‐time WOT, were measured and normalized to the corresponding quantities derived from main artery bolus TDC. Aneurysms displaying small area with contrast filling localized at the aneurysm neck were dropped from the analysis. The results are further presented in terms of pre‐stented/post‐stented ratios to describe the flow changes due to stent treatment. Based on a four week follow‐up angiogram, a five grade scale was used to generate a “healing” grade. The correlation between the parameter ratios and healing grade was calculated using Spearman correlation factor (SCF). Results: The pre‐/post‐stented ratio parameters after normalization were: TTP=0.30±0.28, MTT=0.42±0.42 and WOT=0.29±0.28. The SCF's between the time‐related ratios and the healing grade before the correction were under 0.52. After corrections implementation, all SCF's were above 0.82. Conclusion: After implementation of the proposed adjustments the measured parameters agree better with the treatment outcome, hence a better treatment assessment scale can be built for accurate aneurysm occlusion prediction (Support: R01NS43924 and R01EB002873 and Toshiba Medical Systems Corp)

As the field of minimally invasive endovascular image‐guided interventions (EIGI) advances, there has been progress in the development of new endovascular devices such as the asymmetric vascular stent for treatment of aneurysms as well as progress in the image guidance systems needed to improve both the diagnoses and interventions and the methods used to evaluate the improved imaging performance. High resolution imaging systems with MTFs extending past 8 Lp/mm and with ability to visualize not only radioopaque markers but the detailed structure of devices such as stents have motivated the development of new asymmetric devices such as the blood flow modifying asymmetric vascular stent (AVS). The AVS has now come through a number of generations from balloon expandable stainless steel strutted structures with laser micro‐welded mesh flow diverters to new super‐elastic nitinol closedcell self‐expanding stents with organic material flow diverters. The methods of laser machining, surface finishing, and deployment will be described with progress in animal models reported. In parallel with advances in EIGI devices has come new high resolution detector development. The detectors have a unique combination of features such as far superior spatial resolution compared with conventional dynamic flat panel detectors, large dynamic range of sensitivity with negligible lag and ghosting to enable both fluoroscopy and angiography, and low noise to enable quantum limited performance over the full useful range including during lowdose fluoroscopy. The Micro‐Angiographic Fluoroscope (MAF) consists of an x‐ray converter phosphor sensed by a micro‐channel plate light image intensifier which is in turn coupled to a high performance CCD camera using a fiber optic taper. The MAF is a region of interest (ROI) imager with 4 cm field of view centered at the interventional site and may be moved in front of a larger conventional detector when improved resolution is needed. The Solid State X‐ray Image Intensifier (SSXII) while having much of the benefits of the MAF in superior imaging capability achieves its great sensitivity using only electron multiplying CCD sensors. An array design is being developed so that the imaging FOV may be expanded by adding modules each with its own EMCCD‐based detector. To more fully characterize detectors, new evaluation methods are being explored. For example, the accurate determination of MTF from measurements of noise only, without the need for a slit or edge will be reported. Also from a careful analysis of noise, the exposure range for detector quantum limited performance can be well demarcated by the instrumentation noise equivalent exposure (INEE). Finally, more realistic linear system parameters that include focal‐spot size, geometry, and scatter provide generalized MTFs and DQEs or GMTFs and GDQEs. All told, there is much happening in EIGI.Learning Objectives1. Appreciate the progress being made in improved EIGI devices and in particular flow modifiers such as the asymmetric vascular2. stent (AVS) for aneurysm treatment.3. Understand the operation of new high‐resolution micro‐angiographic systems including the MAF and SSXII.4. Understand new objective image detector evaluations including INEE, GMTF, GDQE, and determination of MTF from noise5. measurements alone.(Supported in part by NIH Grants R01EB002873, R01 NS43924, R01EB008425, and the Toshiba Medical Systems Corp.)

Purpose: To demonstrate the effects of variation of focal‐spot size and magnification on the spatial resolution of reconstructed images of a micro‐computed tomography (μCT) system which is attached to a standard angiographic C‐arm gantry to enable Region‐of‐Interest cone‐beam CT (ROI‐CBCT). Method and Materials: High‐resolution ROI projection data of a vascular phantom were acquired using a new high‐sensitivity, microangiographic fluoroscope (HSMAF) detector (35 μm pixels), which was attached to the C‐arm gantry and able to be positioned in front of a standard full field‐of‐view, low‐resolution commercial flat‐panel detector (FPD) (194 μm pixels). The HSMAF consists of a CsI phosphor viewed by a 4‐cm diameter light image‐intensifier with large variable dynamic range whose output is coupled via a fiber‐optic taper to a CCD camera. The test objects in the vascular phantom were a stent (100 micron struts) inside of a catheter in a cylindrical water bath. The phantom was placed on a portable test platform (PTP) enabling CBCT image acquisition by the HSMAF every 1°. Six μCT runs were performed using two focal‐spot sizes (0.3 and 0.6 mm) and three magnification factors (1.15, 1.29, and 1.48). Profiles were extracted from the reconstructed struts, and the full width half‐maximum (FWHM) were measured. Results: The reconstructed data show that using the optimal configuration (smallest magnification with small focal spot) compared to the worst configuration (largest magnification and the large focal spot) resulted in a 47% reduction in the FWHM in the object plane (175 μm versus 375 μm). Conclusion: Micro‐CBCT can provide more accurate visualization of fine device features; however, geometric unsharpness and/or large focal spots can substantially degrade resolution reducing the quality of the μCBCT reconstructions.(Research sponsored by: NIH Grants R01‐NS43924, R01‐EB002873, Toshiba Medical Systems Corporation)