Angiographic Phantom Research Articles

Comparing visualization performance of liquid embolic agents using a novel injectable phantom.

Radiographic visualization of liquid embolic agents (LEAs) during embolization procedures in neurovascular territory represents a crucial feature to ensure efficacy and safety for the patients during endovascular treatment of arteriovenous shunting lesions. Radiopacity of available LEAs varies significantly and limited methods are currently available for comparison. The purpose of this study was to compare the contrast resolution (CR) during injection under blank roadmap of various LEAs, as well as standard contrast material. An injectable angiographic phantom was designed consisting of parallel tubings between 313 and 1000 micron. Under roadmap, eight radiopaque liquid agents were injected and analyzed: Onyx18®, 34® Squid®12, 18, PHIL®25% (PHIL®25), PHIL®30% (PHIL®30).TrufillTM (NBCA), 30% dilution and Omnipaque®300. CR was evaluated as a contrast to noise ratio (CNR) and calculated as mean peak signal (Sa) minus mean background signal (Sb) divided by the standard deviation of the background signal (Std) . Omnipaque 300 and NBCA were found to have the highest CR. PHIL®25 demonstrated the lowest CNR (45% of Omnipaque CNR). Onyx 18 and 34 (Both around 82% of Omnipaque CNR) demonstrated higher CNR compared to Squid®12 and 18 (52-55% of Omnipaque CNR). On average, at 500 micron there is a >70% reduction in CNR, and at 313 micron there is a 90% reduction in CNR compared to 1000 micron. Significantly different CNR between most LEAs and iodinated contrast media was evident under roadmap conditions and should be considered prior to injection.

Impacts of photon counting CT to maximum intensity projection (MIP) images of cerebral CT angiography: theoretical and experimental studies

While CTA is an established clinical gold standard for imaging large cerebral arteries and veins, an important challenge that currently remains for CTA is its limited performance in imaging small perforating arteries with diameters below 0.5 mm. The purpose of this work was to theoretically and experimentally study the potential benefits of using photon counting detector (PCD)-based CT (PCCT) to improve the performance of CTA in imaging these small arteries. In particular, the study focused on an important component of the CTA image package known as the maximum intensity projection (MIP) image. To help understand how the physical properties of a detector quantitatively influence the MIP image quality, a theoretical model on the statistical properties of MIP images was developed. After validating this model, it was used to explore the individual and joint contribution of the following detector properties to the MIP signal-to-noise ratio (SNR): inter-slice noise covariance, spatial resolution along the z direction, and native pixel pitch along z. The model demonstrated that superior slice sensitivity, reduced inter-slice noise correlation, and smaller native pixel pitch along z provided by PCDs lead to improved vessel SNR in MIP images. Finally, experiments were performed by scanning an anthropomorphic cerebral angiographic phantom using a benchtop PCCT system and a commercial MDCT system. The experimental MIP results consistently demonstrated that compared with MDCT, PCCT provides superior vessel conspicuity and reduced artifactual stenosis.

A theoretical comparison of x-ray angiographic image quality using energy-dependent and conventional subtraction methods

X-ray digital subtraction angiography (DSA) is widely used for vascular imaging. However, the need to subtract a mask image can result in motion artifacts and compromised image quality. The current interest in energy-resolving photon-counting (EPC) detectors offers the promise of eliminating motion artifacts and other advanced applications using a single exposure. The authors describe a method of assessing the iodine signal-to-noise ratio (SNR) that may be achieved with energy-resolved angiography (ERA) to enable a direct comparison with other approaches including DSA and dual-energy angiography for the same patient exposure. A linearized noise-propagation approach, combined with linear expressions of dual-energy and energy-resolved imaging, is used to describe the iodine SNR. The results were validated by a Monte Carlo calculation for all three approaches and compared visually for dual-energy and DSA imaging using a simple angiographic phantom with a CsI-based flat-panel detector. The linearized SNR calculations show excellent agreement with Monte Carlo results. While dual-energy methods require an increased tube heat load of 2× to 4× compared to DSA, and photon-counting detectors are not yet ready for angiographic imaging, the available iodine SNR for both methods as tested is within 10% of that of conventional DSA for the same patient exposure over a wide range of patient thicknesses and iodine concentrations. While the energy-based methods are not necessarily optimized and further improvements are likely, the linearized noise-propagation analysis provides the theoretical framework of a level playing field for optimization studies and comparison with conventional DSA. It is concluded that both dual-energy and photon-counting approaches have the potential to provide similar angiographic image quality to DSA.

X-ray imaging with a silicon microstrip detector coupled to the RX64 ASIC

A single photon counting X-ray imaging system, with possible applications to dual energy mammography and angiography, is presented. A silicon microstrip detector with 100μm pitch strips is coupled to RX64 ASICs, each of them including 64 channels of preamplifier, shaper, discriminator and scaler. The system has low noise, good spatial resolution and high counting rate capability. Results on energy resolution have been obtained with a fluorescence source and quasi-monochromatic X-rays beams. Preliminary images obtained with an angiographic phantom are presented.

Performance of angiographic catheters.

Simple methods of quantifying selected physical characteristics of angiographic catheters, which are likely to influence their in vivo performance, have been developed. The torsional stiffness ('torque') of catheters was measured, and tip control ('manoeuvrability') in an angiographic phantom was studied. Both braided and unbraided catheters were investigated all having the 'headhunter' tip shape. Significant differences between measurements made at 20 and 37 degrees C were found. Torsional stiffness was not a good predictor of performance in the angiographic phantom. Ethylene oxide re-sterilization has only a limited effect on the physical characteristics studied.

Region of interest fluoroscopy.

In some medical imaging applications, it is necessary to visualize only the center of the field of view with optimal quality. For example, often in interventional radiographic procedures only the region directly adjacent to the catheter tip must be well seen. A new imaging approach which reduces the number of photons exposing the patient outside a region of interest (ROI), while allowing the photon fluence to be maintained or increased in the ROI, may make more optimal use of the total integral radiation dose to the patient as well as enable increased contrast and reduced artifacts in the ROI. A demonstration is given with an angiographic phantom, for an ROI which is less than 10% of the total field of view and where the periphery receives 6% of the ROI exposure. Contrast is improved about 30% in the ROI, and yet the images are adequate in the periphery for visualizing high contrast reference features while there is a reduction in total integral patient dose. Details of the technique are discussed along with requirements for clinical implementation.

Phantom evaluation of angiographer performance using low frame rate acquisition fluoroscopy.

The authors have investigated the effect of 5 frames/s television fluoroscopy on the time required to selectively catheterize five test arteries in an angiographic phantom. Here, 5 frames/s acquisition was accomplished by sampling frames from a 30 frames/s video signal. Sampled frames were stored in a video memory which provided continuous display to the fluoroscopist between samples. The test phantom was a plastic model of an aorta with branching vessels immersed in an isodense suspension of barium in water. For four of the five vessels there was no significant difference in time required for catheter placement between 30 frames/s and 5 frames/s.

A photodiode array x-ray imaging system for digital angiography.

A line scanning imaging system that can be used to make low-noise x-ray images to detect low-contrast structure is described. The system makes use of a 1024-element, self-scanning, photodiode array (Reticon RL 1024S) optically coupled to an x-ray image intensifier tube. Low-noise images are obtained by imaging only small areas of interest at a time to reduce the noise resulting from the detection of scattered radiation, and by making use of the very large dynamic range (8000:1) solid-state photodetector. Some performance characteristics of the diode array system are discussed. It was found that while sensitivities of individual elements differed by up to +/- 15% from the average, they could be corrected with a precision of 0.02% to 0.04% of the maximum signal. The limiting spatial resolution of the system in the direction of the diode array was 2.0 cycles/mm, limited by the image intensifier. The system linearity was studied by measuring the attenuation of a monoenergetic x-ray beam by Plexiglas. The measured attenuation agreed with the expected exponential decrease over a range of approximately 1000 to within experimental error. The imaging capabilities of the system were demonstrated by imaging an angiographic phantom consisting of an iodine-filled tube with an asymmetric 20% stenosis. The stenosis was oriented on the tube surface furthermost from the detector resulting in an image with a 2% radiographic contrast change but no decrease of the tube width. The stenosis was clearly imaged using a temporal subtraction technique.