Endovascular Image-guided Interventions Research Articles

Imaging Recommendations for Diagnosis, Staging, and Management of Sinonasal Tumors

AbstractSinonasal tumors are a relatively rare and heterogeneous group of tumors. Owing to their nonspecific presentation and rarity, they can be potentially overlooked resulting in delayed diagnosis and management, and increased patient morbidity. Imaging is crucial for the detection, staging, surgical planning, follow-up as well as surveillance of sinonasal masses, wherein computed tomography (CT) and magnetic resonance imaging (MRI) play complementary roles. CT is better at depicting bony changes, while MRI is useful for delineating the extent of soft tissue lesion, detect perineural, intracranial, or intraorbital spread as well as differentiate trapped sinus secretions from tumor tissue. Other modalities like fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) and arteriography can be selectively employed. FDG-PET is useful for metastatic workup and detection of residual/ recurrent disease. Arteriography and endovascular image-guided interventions are useful to delineate supply of vascular tumors and perform preoperative embolization. A systematic evidence-based approach to a possible case of sinonasal tumor can go a long way in streamlining the detection and management of these tumors, while optimizing the use of available healthcare resources.

A CMOS-based high resolution fluoroscope (HRF) detector prototype with 49.5 μm pixels for use in endovascular image guided interventions (EIGI).

X-ray detectors to meet the high-resolution requirements for endovascular image-guided interventions (EIGIs) are being developed and evaluated. A new 49.5-micron pixel prototype detector is being investigated and compared to the current suite of high-resolution fluoroscopic (HRF) detectors. This detector featuring a 300-micron thick CsI(Tl) scintillator, and low electronic noise CMOS readout is designated the HRF-CMOS50. To compare the abilities of this detector with other existing high resolution detectors, a standard performance metric analysis was applied, including the determination of the modulation transfer function (MTF), noise power spectra (NPS), noise equivalent quanta (NEQ), and detective quantum efficiency (DQE) for a range of energies and exposure levels. The advantage of the smaller pixel size and reduced blurring due to the thin phosphor was exemplified when the MTF of the HRF-CMOS50 was compared to the other high resolution detectors, which utilize larger pixels, other optical designs or thicker scintillators. However, the thinner scintillator has the disadvantage of a lower quantum detective efficiency (QDE) for higher diagnostic x-ray energies. The performance of the detector as part of an imaging chain was examined by employing the generalized metrics GMTF, GNEQ, and GDQE, taking standard focal spot size and clinical imaging parameters into consideration. As expected, the disparaging effects of focal spot unsharpness, exacerbated by increasing magnification, degraded the higher-frequency performance of the HRF-CMOS50, while increasing scatter fraction diminished low-frequency performance. Nevertheless, the HRF-CMOS50 brings improved resolution capabilities for EIGIs, but would require increased sensitivity and dynamic range for future clinical application.

Comparison of High Resolution X-Ray detectors with Conventional FPDs using Experimental MTFs and Apodized Aperture Pixel Design for Reduced Aliasing.

Apodized Aperture Pixel (AAP) design, proposed by Ismailova et. al, is an alternative to the conventional pixel design1. The advantages of AAP processing with a sinc filter in comparison with using other filters include non-degradation of MTF values and elimination of signal and noise aliasing, resulting in an increased performance at higher frequencies, approaching the Nyquist frequency3. If high resolution small field-of-view (FOV) detectors with small pixels used during critical stages of Endovascular Image Guided Interventions (EIGIs) could also be extended to cover a full field-of-view typical of flat panel detectors (FPDs) and made to have larger effective pixels, then methods must be used to preserve the MTF over the frequency range up to the Nyquist frequency of the FPD while minimizing aliasing. In this work, we convolve the experimentally measured MTFs of an Microangiographic Fluoroscope (MAF) detector, (the MAF-CCD with 35μm pixels) and a High Resolution Fluoroscope (HRF) detector (HRF-CMOS50 with 49.5μm pixels) with the AAP filter and show the superiority of the results compared to MTFs resulting from moving average pixel binning and to the MTF of a standard FPD. The effect of using AAP is also shown in the spatial domain, when used to image an infinitely small point object. For detectors in neurovascular interventions, where high resolution is the priority during critical parts of the intervention, but full FOV with larger pixels are needed during less critical parts, AAP design provides an alternative to simple pixel binning while effectively eliminating signal and noise aliasing yet allowing the small FOV high resolution imaging to be maintained during critical parts of the EIGI.

TU-FG-209-05: Demonstration of the Line Focus Principle Using the Generalized Measured-Relative Object Detectability (GM-ROD) Metric

Purpose: Demonstrate and quantify the augmented resolution due to focalspot size decrease in images acquired on the anode side of the field, for both small and medium (0.3 and 0.6mm) focal-spot sizes using the experimental task-based GM-ROD metric. Theoretical calculations have shown that a medium focal-spot can achieve the resolution of a small focal-spot if acquired with a tilted anode, effectively providing a higher-output small focal-spot. Methods: The MAF-CMOS (micro-angiographic fluoroscopic complementary-metal-oxide semiconductor) detector (75µm pixel pitch) imaged two copper wire segments of different diameter and a pipeline stent at the central axis and on the anode side of the beam, achieved by tilting the x-ray C-arm (Toshiba Infinix) to 6° and realigning the detector with the perpendicular ray to correct for x-ray obliquity. The relative gain in resolution was determined using the GM-ROD metric, which compares images on the basis of the Fourier transform of the image and the measured NNPS. To emphasize the geometric unsharpness, images were acquired at a magnification of two. Results: Images acquired on the anode side were compared to those acquired on the central axis with the same target-area focal-spot to consider the effect of an angled tube, and for all three objects the advantage of the smaller effective focal-spot was clear, showing a maximum improvement of 36% in GM-ROD. The images obtained with the small focal-spot at the central axis were compared to those of the medium focal-spot at the anode side and, for all objects, the relative performance was comparable. Conclusion: For three objects, the GM-ROD demonstrated the advantage of the anode side focal-spot. The comparable performance of the medium focal-spot on the anode side will allow for a high-output small focal-spot; a necessity in endovascular image-guided interventions. Partial support from an NIH grant R01EB002873 and an equipment grant from Toshiba Medical Systems Corp.

Simultaneous 3D-2D image registration and C-arm calibration: Application to endovascular image-guided interventions.

Three-dimensional to two-dimensional (3D-2D) image registration is a key to fusion and simultaneous visualization of valuable information contained in 3D pre-interventional and 2D intra-interventional images with the final goal of image guidance of a procedure. In this paper, the authors focus on 3D-2D image registration within the context of intracranial endovascular image-guided interventions (EIGIs), where the 3D and 2D images are generally acquired with the same C-arm system. The accuracy and robustness of any 3D-2D registration method, to be used in a clinical setting, is influenced by (1) the method itself, (2) uncertainty of initial pose of the 3D image from which registration starts, (3) uncertainty of C-arm's geometry and pose, and (4) the number of 2D intra-interventional images used for registration, which is generally one and at most two. The study of these influences requires rigorous and objective validation of any 3D-2D registration method against a highly accurate reference or "gold standard" registration, performed on clinical image datasets acquired in the context of the intervention. The registration process is split into two sequential, i.e., initial and final, registration stages. The initial stage is either machine-based or template matching. The latter aims to reduce possibly large in-plane translation errors by matching a projection of the 3D vessel model and 2D image. In the final registration stage, four state-of-the-art intrinsic image-based 3D-2D registration methods, which involve simultaneous refinement of rigid-body and C-arm parameters, are evaluated. For objective validation, the authors acquired an image database of 15 patients undergoing cerebral EIGI, for which accurate gold standard registrations were established by fiducial marker coregistration. Based on target registration error, the obtained success rates of 3D to a single 2D image registration after initial machine-based and template matching and final registration involving C-arm calibration were 36%, 73%, and 93%, respectively, while registration accuracy of 0.59 mm was the best after final registration. By compensating in-plane translation errors by initial template matching, the success rates achieved after the final stage improved consistently for all methods, especially if C-arm calibration was performed simultaneously with the 3D-2D image registration. Because the tested methods perform simultaneous C-arm calibration and 3D-2D registration based solely on anatomical information, they have a high potential for automation and thus for an immediate integration into current interventional workflow. One of the authors' main contributions is also comprehensive and representative validation performed under realistic conditions as encountered during cerebral EIGI.

Treatment Planning for Image-Guided Neuro-Vascular Interventions Using Patient-Specific 3D Printed Phantoms.

Minimally invasive endovascular image-guided interventions (EIGIs) are the preferred procedures for treatment of a wide range of vascular disorders. Despite benefits including reduced trauma and recovery time, EIGIs have their own challenges. Remote catheter actuation and challenging anatomical morphology may lead to erroneous endovascular device selections, delays or even complications such as vessel injury. EIGI planning using 3D phantoms would allow interventionists to become familiarized with the patient vessel anatomy by first performing the planned treatment on a phantom under standard operating protocols. In this study the optimal workflow to obtain such phantoms from 3D data for interventionist to practice on prior to an actual procedure was investigated. Patient-specific phantoms and phantoms presenting a wide range of challenging geometries were created. Computed Tomographic Angiography (CTA) data was uploaded into a Vitrea 3D station which allows segmentation and resulting stereo-lithographic files to be exported. The files were uploaded using processing software where preloaded vessel structures were included to create a closed-flow vasculature having structural support. The final file was printed, cleaned, connected to a flow loop and placed in an angiographic room for EIGI practice. Various Circle of Willis and cardiac arterial geometries were used. The phantoms were tested for ischemic stroke treatment, distal catheter navigation, aneurysm stenting and cardiac imaging under angiographic guidance. This method should allow for adjustments to treatment plans to be made before the patient is actually in the procedure room and enabling reduced risk of peri-operative complications or delays.

3D-2D Registration of Cerebral Angiograms: A Method and Evaluation on Clinical Images

Endovascular image-guided interventions (EIGI) involve navigation of a catheter through the vasculature followed by application of treatment at the site of anomaly using live 2D projection images for guidance. 3D images acquired prior to EIGI are used to quantify the vascular anomaly and plan the intervention. If fused with the information of live 2D images they can also facilitate navigation and treatment. For this purpose 3D-2D image registration is required. Although several 3D-2D registration methods for EIGI achieve registration accuracy below 1 mm, their clinical application is still limited by insufficient robustness or reliability. In this paper, we propose a 3D-2D registration method based on matching a 3D vasculature model to intensity gradients of live 2D images. To objectively validate 3D-2D registration methods, we acquired a clinical image database of 10 patients undergoing cerebral EIGI and established "gold standard" registrations by aligning fiducial markers in 3D and 2D images. The proposed method had mean registration accuracy below 0.65 mm, which was comparable to tested state-of-the-art methods, and execution time below 1 s. With the highest rate of successful registrations and the highest capture range the proposed method was the most robust and thus a good candidate for application in EIGI.

A theoretical and experimental evaluation of the microangiographic fluoroscope: A high‐resolution region‐of‐interest x‐ray imager

The increasing need for better image quality and high spatial resolution for successful endovascular image-guided interventions (EIGIs) and the inherent limitations of the state-of-the-art detectors provide motivation to develop a detector system tailored to the specific, demanding requirements of neurointerventional applications. A microangiographic fluoroscope (MAF) was developed to serve as a high-resolution, region-of-interest (ROI) x-ray imaging detector in conjunction with large lower-resolution full field-of-view (FOV) state-of-the-art x-ray detectors. The newly developed MAF is an indirect x-ray imaging detector capable of providing real-time images (30 frames per second) with high-resolution, high sensitivity, no lag and low instrumentation noise. It consists of a CCD camera coupled to a Gen 2 dual-stage microchannel plate light image intensifier (LII) through a fiber-optic taper. A 300 microm thick CsI(T1) phosphor serving as the front end is coupled to the LII. The LII is the key component of the MAF and the large variable gain provided by it enables the MAF to operate as a quantum-noise-limited detector for both fluoroscopy and angiography. The linear cascade model was used to predict the theoretical performance of the MAF, and the theoretical prediction showed close agreement with experimental findings. Linear system metrics such as MTF and DQE were used to gauge the detector performance up to 10 cycles/mm. The measured zero frequency DQE(0) was 0.55 for an RQA5 spectrum. A total of 21 stages were identified for the whole imaging chain and each stage was characterized individually. The linear cascade model analysis provides insight into the imaging chain and may be useful for further development of the MAF detector. The preclinical testing of the prototype detector in animal procedures is showing encouraging results and points to the potential for significant impact on EIGIs when used in conjunction with a state-of-art flat panel detector (FPD).

TU‐C‐211‐03: Increasing X‐Ray Tube Output for Small Focal Spot, Region‐Of‐Interest Imaging

Purpose: High‐resolution region‐of‐interest (ROI) imaging requires the use of a small focal spot with sufficient output to maintain spatial and contrast resolution. We investigate methods to increase the x‐ray output while maintaining the focal‐spot size for a small field‐of‐view (FOV) as needed for endovascular‐image‐guided interventions (EIGIs).Materials and Methods: We evaluated the increase in tube output made possible by reducing the anode angle and lengthening the filament for the small focal spot to maintain a constant effective focal‐spot size. Since the area of heat deposition on the anode is increased, tube‐loading capacity increases and the mA can be increased proportionally if the electron flux density at the target is unchanged. “Spek Calc” software was used to calculate the change in inherent tube filtration and in x‐ray spectrum and intensity as a function of anode angle. The gain in tube output achievable while maintaining focal‐spot size was determined for the small‐FOV of our custom high‐resolution, ROI imager. When the same tube is used for both large‐FOV imager and the small‐FOV ROI imager, angling the tube and adjusting filament length can allow a tradeoff between spatial resolution, tube loading and FOV. Results: For the 5‐cm FOV needed in neurovascular ROI imaging, the x‐ray output could be increased substantially with decreasing anode angle while the focal‐spot size and FOV is maintained. Considering both increased anode‐target area and increased inherent anode filtration, a net output increase of 3.3 times could be achieved with a 2‐ degree anode angle compared to the standard 8‐degree target with an increase of 4 times in filament length. Conclusions: For EIGIs where high resolution is essential but only over a small FOV, higher tube output while maintaining a small focal spot should be achievable with only small modification of standard x‐ray tube geometry.Support: NIH Grants R01‐EB008425, R01‐EB002873

TH‐C‐210A‐04: New High Resolution Dynamic Detectors and Flow Modifying Stents for Neuro‐Endovascular Image Guided Interventions

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.)

TU‐C‐342‐04: Advances in Endovascular Image‐Guided Interventions

In a recent Medical Physics “Vision 2020” paper (Medical Physics 35(1): 301–309, Jan 2008), the authors reviewed the state of endovascular image‐guided interventions (EIGI) and offered some predictions for the future. Here we review the current status of the field and of some of these advances. First, endovascular devices (such as clot busting tools, stents and their catheter delivery systems, and blood flow modifiers) are becoming finer, more complex, and are enabling the replacement of invasive surgical procedures with minimally invasive EIGI procedures. Innovative methods of actuating motion at the catheter tip, such as the use of external magnetic fields, are being introduced. Second, along with improvements in devices, imaging systems that provide real‐time high‐resolution image guidance are being developed including a Solid State X‐ray Image Intensifier based on electron multiplying charge coupled devices (EMCCDs) that provide large on‐chip gain to overcome instrumentation noise such as that characteristic of current flat panel detectors. SSXIIs also have very high resolution capable of exceeding 10 lp/mm yet with no lag or ghosting. Third, the new high‐resolution region‐of‐interest (ROI) detectors can be used in combination with large conventional detectors for dual‐detector cone‐beam computer tomography (CB‐CT) to visualize ROIs within larger objects yet with minimal truncation artifact and with reduced integral dose. Fourth, during an interventional procedure, limited projection views can be taken to generate full 3D representations of the vasculature with accurate determination of vessel lumen morphology to enable computer fluid dynamic (CFD) calculations which in turn can be used to plan further EIGI treatment within the patient treatment time. Finally, as EIGI procedures become more complex, the consequent patient dose especially where improved image quality is implemented must be more carefully monitored. For example, we found that patient dose actually increased for certain electro‐physiology (EP) procedures performed in our EP Lab following replacement of a mobile c‐arm with a fixed unit capable of generating improved image quality. In conclusion, while progress is being made toward fulfilling the predictions made by the authors in the Vision 2020 paper published early in 2008, EIGI remains open to continuing exciting advancements.Educational Objectives:1. Appreciate the progress being made in improved EIGI devices and imaging systems.2. Understand the operation of new high‐resolution micro‐angiographic systems including the SSXII and the operation of dual‐detector ROI CB‐CT systems.3. Understand the role of limited view acquisition for providing 3D images.4. Appreciate the patient exposure burden during EIGI procedures.[Supported in part by NIH Grants R01 EB002873, R01 NS43924, R01 EB00842501, R01 HL52567, UB Foundation IRDF, and an equipment grant from Toshiba Medical Systems Corp.].

Endovascular image‐guided interventions (EIGIs)

Minimally invasive interventions are rapidly replacing invasive surgical procedures for the most prevalent human disease conditions. X-ray image-guided interventions carried out using the insertion and navigation of catheters through the vasculature are increasing in number and sophistication. In this article, we offer our vision for the future of this dynamic field of endovascular image-guided interventions in the form of predictions about (1) improvements in high-resolution detectors for more accurate guidance, (2) the implementation of high-resolution region of interest computed tomography for evaluation and planning, (3) the implementation of dose tracking systems to control patient radiation risk, (4) the development of increasingly sophisticated interventional devices, (5) the use of quantitative treatment planning with patient-specific computer fluid dynamic simulations, and (6) the new expanding role of the medical physicist. We discuss how we envision our predictions will come to fruition and result in the universal goal of improved patient care.