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We present herein a custom-made, in situ, multimodal spin coater system with an integrated heating stage that can be programmed with spinning and heating recipes and that is coupled with synchrotron-based, grazing-incidence wide- and small-angle x-ray scattering. The spin coating system features an adaptable experimental chamber, with the ability to house multiple ancillary probes such as photoluminescence and visible optical cameras, to allow for true multimodal characterization and correlated data analysis. This system enables monitoring of structural evolutions such as perovskite crystallization and polymer self-assembly across a broad length scale (2 Å-150 nm) with millisecond temporal resolution throughout a complete thin film fabrication process. The use of this spin coating system allows scientists to gain a deeper understanding of temporal processes of a material system, to develop ideal conditions for thin film manufacturing.
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BACKGROUND: Radiofrequency (RF) ablation has become a mainstay of treatment for ventricular tachycardia, yet adequate lesion formation remains challenging. This study aims to comprehensively describe the composition and evolution of acute left ventricular (LV) lesions using native-contrast cardiovascular magnetic resonance (CMR) during CMR-guided ablation procedures. METHODS: RF ablation was performed using an actively-tracked CMR-enabled catheter guided into the LV of 12 healthy swine to create 14 RF ablation lesions. T2 maps were acquired immediately post-ablation to visualize myocardial edema at the ablation sites and T1-weighted inversion recovery prepared balanced steady-state free precession (IR-SSFP) imaging was used to visualize the lesions. These sequences were repeated concurrently to assess the physiological response following ablation for up to approximately 3 h. Multi-contrast late enhancement (MCLE) imaging was performed to confirm the final pattern of ablation, which was then validated using gross pathology and histology. RESULTS: Edema at the ablation site was detected in T2 maps acquired as early as 3 min post-ablation. Acute T2-derived edematous regions consistently encompassed the T1-derived lesions, and expanded significantly throughout the 3-h period post-ablation to 1.7 ± 0.2 times their baseline volumes (mean ± SE, estimated using a linear mixed model determined from n = 13 lesions). T1-derived lesions remained approximately stable in volume throughout the same time frame, decreasing to 0.9 ± 0.1 times the baseline volume (mean ± SE, estimated using a linear mixed model, n = 9 lesions). CONCLUSIONS: Combining native T1- and T2-based imaging showed that distinctive regions of ablation injury are reflected by these contrast mechanisms, and these regions evolve separately throughout the time period of an intervention. An integrated description of the T1-derived lesion and T2-derived edema provides a detailed picture of acute lesion composition that would be most clinically useful during an ablation case.
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Edema Cardíaco/diagnóstico por imagen , Ventrículos Cardíacos/diagnóstico por imagen , Ventrículos Cardíacos/cirugía , Imagen por Resonancia Cinemagnética , Imagen por Resonancia Magnética Intervencional/métodos , Ablación por Radiofrecuencia/métodos , Animales , Edema Cardíaco/etiología , Edema Cardíaco/patología , Edema Cardíaco/fisiopatología , Ventrículos Cardíacos/patología , Ventrículos Cardíacos/fisiopatología , Modelos Animales , Valor Predictivo de las Pruebas , Ablación por Radiofrecuencia/efectos adversos , Sus scrofa , Factores de Tiempo , Función Ventricular IzquierdaRESUMEN
PURPOSE: Elongated implanted conductors can interact with the radiofrequency (RF) transmission field during MRI, posing safety concerns of excessive heating in patients with deep brain stimulators. A technique using parallel RF transmission (pTx) is evaluated on an anthropomorphic heterogeneous model with bilateral and unilateral curved wires. METHODS: Amplitude and phase were optimized by simulation to minimize heating surrounding the implanted wires and to minimize B1+ inhomogeneity for four-channel and eight-channel pTx in a heterogeneous model. MRI experiments were conducted in an equivalent test phantom created from a common digital mesh file. RESULTS: In four-channel pTx, maximum local specific absorption rate (SAR) was reduced in both unilateral and bilateral wires by 47% and 59%, respectively, but with compromised B1+ homogeneity. Optimized eight-channel pTx substantially reduced local SAR compared with birdcage coil RF excitation in both unilateral and bilateral wires (reduction of maximum local SAR of 79% and 87%, respectively). B1+ inhomogeneity was limited to 17% and 26%, respectively. Experimental validation with four-channel pTx showed 80% and 92% temperature reduction at the tips of wire 1 and wire 2, respectively. CONCLUSION: This pTx approach yields promising reductions in local SAR at the tips of unilateral and bilateral implanted wires while maintaining image quality in simulation and experiment. Magn Reson Med 78:2408-2415, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
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Encéfalo/diagnóstico por imagen , Imagen por Resonancia Magnética , Ondas de Radio , Algoritmos , Antropometría , Simulación por Computador , Estimulación Encefálica Profunda , Diseño de Equipo , Cabeza/diagnóstico por imagen , Calor , Humanos , Modelos Teóricos , Seguridad del Paciente , Fantasmas de Imagen , Prótesis e ImplantesRESUMEN
OBJECTIVE: MRI in the area of cardiovascular catheter-based interventional procedures is an active field. A common intervention-revascularization of chronic total occlusions, requires a conductive guidewire for revascularization. The mechanical properties of guidewires are paramount to the successful execution of such procedures. Furthermore to benefit from MRI techniques, additional conductors are required to transmit signal from the tip of a catheter. Long thin conductors in MRI systems pose a safety risk in the form of RF heating due to induced RF currents on the conductors. Unfortunately many existing techniques to mitigate this risk require physical modification of the conductors, inevitably resulting in detrimental mechanical tradeoffs in the guidewire. This manuscript proposes a novel application and miniaturization of an existing device, the floating RF trap. The RF trap couples strongly to any thin conductor passing through the trap lumen inducing significant series impedance. This results in reduction of induced RF currents, and thus, heating. METHODS AND RESULTS: This study shows theoretical and experimental analysis of induced impedance as well as theoretical reduction in heating due to various distributions of traps along the length of a catheter. Results of measuring induced current and heating in phantom experiments are also presented. Through comparison with commercial simulation packages and results of phantom experiments, it is shown that miniaturized RF traps can be modeled accurately, including their induced series impedance and effect on induced RF current. CONCLUSION AND SIGNIFICANCE: It was demonstrated that floating RF traps present a feasible method to mitigate RF heating while maintaining important mechanical properties of guidewires.
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Cateterismo Cardíaco/instrumentación , Imagen por Resonancia Magnética/instrumentación , Cirugía Asistida por Computador/instrumentación , Impedancia Eléctrica , Diseño de Equipo , Calor , Fantasmas de Imagen , Ondas de RadioRESUMEN
GOAL: The purpose of this study is to improve the accuracy of interventional catheter guidance during intracardiac procedures. Specifically, the use of preprocedural magnetic resonance roadmap images for interventional guidance has limited anatomical accuracy due to intraprocedural respiratory motion of the heart. Therefore, we propose to build a novel respiratory motion model to compensate for this motion-induced error during magnetic resonance imaging (MRI)-guided procedures. METHODS: We acquire 2-D real-time free-breathing images to characterize the respiratory motion, and build a smooth motion model via registration of 3-D prior roadmap images to the real-time images within a novel principal axes frame of reference. The model is subsequently used to correct the interventional catheter positions with respect to the anatomy of the heart. RESULTS: We demonstrate that the proposed modeling framework can lead to smoother motion models, and potentially lead to more accurate motion estimates. Specifically, MRI-guided intracardiac ablations were performed in six preclinical animal experiments. Then, from retrospective analysis, the proposed motion modeling technique showed the potential to achieve a 27% improvement in ablation targeting accuracy. CONCLUSION: The feasibility of a respiratory motion model-based correction framework has been successfully demonstrated. SIGNIFICANCE: The improvement in ablation accuracy may lead to significant improvements in success rate and patient outcomes for MRI-guided intracardiac procedures.
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Procedimientos Quirúrgicos Cardíacos/métodos , Imagen por Resonancia Magnética/métodos , Movimiento/fisiología , Respiración , Cirugía Asistida por Computador/métodos , Algoritmos , Animales , Diseño de Equipo , Estudios de Factibilidad , Imagenología Tridimensional , Imagen por Resonancia Magnética/instrumentación , Modelos Biológicos , Cirugía Asistida por Computador/instrumentación , PorcinosRESUMEN
Deep Brain Stimulation (DBS) is increasingly used to treat a variety of brain diseases by sending electrical impulses to deep brain nuclei through long, electrically conductive leads. Magnetic resonance imaging (MRI) of patients pre- and post-implantation is desirable to target and position the implant, to evaluate possible side-effects and to examine DBS patients who have other health conditions. Although MRI is the preferred modality for pre-operative planning, MRI post-implantation is limited due to the risk of high local power deposition, and therefore tissue heating, at the tip of the lead. The localized power deposition arises from currents induced in the leads caused by coupling with the radiofrequency (RF) transmission field during imaging. In the present work, parallel RF transmission (pTx) is used to tailor the RF electric field to suppress coupling effects. Electromagnetic simulations were performed for three pTx coil configurations with 2, 4, and 8-elements, respectively. Optimal input voltages to minimize coupling, while maintaining RF magnetic field homogeneity, were determined for all configurations using a Nelder-Mead optimization algorithm. Resulting electric and magnetic fields were compared to that of a 16-rung birdcage coil. Experimental validation was performed with a custom-built 4-element pTx coil. In simulation, 95-99% reduction of the electric field at the tip of the lead was observed between the various pTx coil configurations and the birdcage coil. Maximal reduction in E-field was obtained with the 8-element pTx coil. Magnetic field homogeneity was comparable to the birdcage coil for the 4- and 8-element pTx configurations. In experiment, a temperature increase of 2±0.15°C was observed at the tip of the wire using the birdcage coil, whereas negligible increase (0.2±0.15°C) was observed with the optimized pTx system. Although further research is required, these initial results suggest that the concept of optimizing pTx to reduce DBS heating effects holds considerable promise.
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Estimulación Encefálica Profunda/instrumentación , Electrodos Implantados , Imagen por Resonancia Magnética/instrumentación , Ondas de Radio , Simulación por Computador , Diseño de Equipo , Calor , Campos Magnéticos , Imagen por Resonancia Magnética/métodos , Fantasmas de ImagenRESUMEN
PURPOSE: Many procedures involving catheters and implanted medical devices could benefit from MRI guidance but are currently contraindicated due to risk of significant heating near linear conductive structures. A priori safety prediction is impossible in vivo and thus, safety is typically investigated in vitro by directly measuring temperature rise. Existing methods of investigating safety are inflexible and provide few data. Furthermore, they are fundamentally limited because dangerous temperatures rises can only be investigated if induced. A method of remotely predicting safety is necessary for ensuring safety in patients. THEORY AND METHODS: Electric current induced on the metallic object causes any dangerous heating; thus a remote method of safely characterizing the induced radiofrequency (RF) current distribution would suffice to evaluate safety assuming conservative estimates for local tissue properties. Here we propose a method of analyzing induced phase artifacts seen in low-specific absorption rate characterization images, to determine induced current on an interventional device. This induced current distribution can then be used to predict RF heating behavior under application of any other imaging sequence. RESULTS: This method has been successfully used to reproduce numerical simulations in a phantom. Furthermore, the heating behavior around a conductive wire produced by a scan other than that used to characterize current was successfully predicted. CONCLUSION: It has been shown in phantom experiments that remote current characterization can safely prevent dangerous scans as well as enable safe scans that previously would not have been attempted.
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Conductometría/métodos , Calor , Imagen por Resonancia Magnética/métodos , Metales , Ondas de Radio , Radiometría/métodos , Interpretación de Imagen Asistida por Computador/métodos , Imagen por Resonancia Magnética/instrumentación , Fantasmas de Imagen , Dosis de Radiación , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
AIMS: To create a large animal coronary chronic total occlusion (CTO) model. Presence of microvessels within the CTO lumen facilitates guidewire crossing. The patterns and time profiles of matrix changes and microvessel formation during coronary CTO maturation are unknown. METHODS AND RESULTS: CTO were created in 15 swine by percutaneous deployment of a collagen plug. Matrix changes were assessed by histology. Intraluminal neovascularisation was assessed by histology and several imaging modalities, including conventional and 3D spin angiography, micro-computed tomography (micro-CT) imaging, and contrast-enhanced magnetic resonance imaging (MRI), at six and 12 weeks following CTO creation. Matrix changes included an intense inflammatory reaction at six weeks which had partially abated by 12 weeks. A proteoglycan-rich matrix at six weeks was partially replaced with collagen by 12 weeks. Similar changes were noted in the proximal cap which was acellular. Three patterns of microvessel formation were identified and defined based on the presence and extent of a "lead" neovessel. No major differences in pattern or extent of neovascularisation were noted between six and 12 weeks. CONCLUSIONS: Heterogeneity in neovascularisation patterns occurs during coronary CTO development in a porcine model. Non-invasive imaging to determine the predominant type of neovascularisation prior to and during CTO revascularisation may improve guidewire crossing success rates. This model may be useful for further exploration of CTO pathophysiology, and may aid in further refinements of in vivo imaging of CTO and development of novel therapeutic approaches to revascularisation of CTO, such as manipulations of the proximal cap, matrix composition, neovessel induction, and device testing.
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Oclusión Coronaria/etiología , Modelos Animales de Enfermedad , Animales , Enfermedad Crónica , Oclusión Coronaria/diagnóstico por imagen , Oclusión Coronaria/patología , Oclusión Coronaria/terapia , Femenino , Imagen por Resonancia Magnética , Porcinos , Tomografía Computarizada por Rayos XRESUMEN
The manufacturing of intravascular imaging coils poses several challenges. Due to their size, it can be difficult to incorporate local matching networks and signal amplifiers. The goal of this study is to investigate tuning and amplification strategies for intravascular coils and to assess the signal-to-noise benefits of incorporating a matching network and/or miniature amplifier into catheter-based intravascular imaging devices at various locations in the signal chain. The results suggest that the use of a low-noise amplifier close to the receiving coil enables the use of miniature coaxial cables to be used despite being noisy. Moreover, an improvement in the signal-to-noise ratio of over 75% is presented over conventional intravascular coil configurations where the matching circuit and low-noise amplifier are placed at the proximal end. Therefore, designing devices for intravascular applications capable of generating high signal-to-noise ratio images becomes more feasible, also allowing for significant reductions in scan time.
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Amplificadores Electrónicos , Procedimientos Endovasculares/instrumentación , Aumento de la Imagen/instrumentación , Imagen por Resonancia Magnética Intervencional/instrumentación , Imagen por Resonancia Magnética/instrumentación , Magnetismo/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
The purpose of this study is to describe a new active technique for accurately determining both the position and orientation of the tip of a catheter during magnetic resonance (MR)-guided percutaneous cardiovascular procedures. The technique utilizes phase information introduced into the MR signal from a small receive coil located on the distal tip of the catheter. Phase patterns around a small receive coil are rich in information that is directly related to position and orientation. This information can be collected over a large spherical volume with a diameter several times that of the receive coil. The high degree of redundancy yields the potential for an accurate and robust method of catheter tracking. A tracking algorithm is presented that performs catheter tip localization using phase images acquired in two orthogonal planes without any a priori knowledge of catheter position. Associated experimentation demonstrating feasibility is also presented.
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Cateterismo Cardíaco/instrumentación , Cateterismo Cardíaco/métodos , Imagen por Resonancia Magnética Intervencional/instrumentación , Imagen por Resonancia Magnética Intervencional/métodos , Magnetismo/instrumentación , Reconocimiento de Normas Patrones Automatizadas/métodos , Diseño de Equipo , Análisis de Falla de Equipo , Magnetismo/métodos , Fantasmas de Imagen , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
PURPOSE: Functional magnetic resonance imaging (fMRI) is limited by sensitivity to millimetre-scale head motion. Adaptive correction is a strategy to adjust the imaging plane in response to measured head motion, thereby suppressing motion artifacts. This strategy should correct for motion in all six degrees of freedom and also holds promise for through-plane motion that creates "spin-history" artifact that cannot easily be removed by postprocessing methods. Improved quantitative understanding of the MRI signal behavior associated with spin-history artifact would be useful for implementing adaptive correction robustly. METHODS: A numerical simulation was developed to predict MRI artifact signal amplitude in a single-slice for simple motions, implemented with and without adaptive correction, and compared with experiment by imaging a phantom at 3.0 T. Functional MRI was also performed of a human volunteer to illustrate adaptive correction in the presence of spin-history artifact. RESULTS: Good agreement was achieved between simulation and experimental results. Although time-averaged artifact signal amplitude was observed to correlate linearly with motion speed, artifact time-courses were nonlinearly related to motion waveforms. In addition, experimental results demonstrated effective adaptive correction of spin-history artifact when the phantom underwent complex motions. Adaptive correction during human fMRI suppressed spin-history artifacts and spurious activations associated with task-correlated motion. CONCLUSIONS: Overall, this work suggests that adaptive correction, especially when implemented with minimal lag between motion measurement and scan plane update, may help to expand the populations for which fMRI can be performed robustly.
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Imagen por Resonancia Magnética/estadística & datos numéricos , Algoritmos , Artefactos , Fenómenos Biofísicos , Encéfalo/anatomía & histología , Encéfalo/fisiología , Mapeo Encefálico/estadística & datos numéricos , Movimientos de la Cabeza , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Movimiento (Física) , Fantasmas de Imagen , Adulto JovenRESUMEN
OBJECTIVES: The purpose of this study was to characterize the 3-dimensional structure of intravascular and extravascular microvessels during chronic total occlusion (CTO) maturation in a rabbit model. BACKGROUND: Intravascular microchannels are an important component of a CTO and may predict guidewire crossability. However, temporal changes in the structure and geographic localization of these microvessels are poorly understood. METHODS: A total of 39 occlusions were created in a rabbit femoral artery thrombin model. Animals were sacrificed at 2, 6, 12, and 24 weeks (n > or =8 occlusions per time point). The arteries were filled with a low viscosity radio-opaque polymer compound (Microfil) at 150 mm Hg pressure. Samples were scanned in a micro-computed tomography system to obtain high-resolution volumetric images. Analysis was performed in an image processing package that allowed for labeling of multiple materials. RESULTS: Two distinct types of microvessels were observed: circumferentially oriented "extravascular" and longitudinally oriented "intravascular" microvessels. Extravascular microvessels were evident along the entire CTO length and maximal at the 2-week time point. There was a gradual and progressive reduction in extravascular microvessels over time, with very minimal microvessels evident beyond 12 weeks. In contrast, intravascular microvessel formation was delayed, with peak vascular volume at 6 weeks, followed by modest reductions at later time points. Intravascular microvessel formation was more prominent in the body compared with that in the proximal and distal ends of the CTO. Sharply angulated connections between the intravascular and extravascular microvessels were present at all time points, but most prominent at 6 weeks. At later time points, the individual intravascular microvessels became finer and more tortuous, although the continuity of these microvessels remained constant beyond 2 weeks. CONCLUSIONS: Differences are present in the temporal and geographic patterns of intravascular and extravascular microvessel formation during CTO maturation.
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Arteriopatías Oclusivas/diagnóstico por imagen , Arteriopatías Oclusivas/fisiopatología , Arteria Femoral/diagnóstico por imagen , Arteria Femoral/fisiopatología , Microvasos/diagnóstico por imagen , Microvasos/fisiopatología , Neovascularización Fisiológica , Microtomografía por Rayos X , Animales , Arteriopatías Oclusivas/inducido químicamente , Enfermedad Crónica , Constricción Patológica , Modelos Animales de Enfermedad , Masculino , Conejos , Interpretación de Imagen Radiográfica Asistida por Computador , Elastómeros de Silicona/administración & dosificación , Trombina , Factores de TiempoRESUMEN
OBJECTIVES: We sought to perform the first systematic study of the natural history of chronic total arterial occlusions (CTOs) in an experimental model. BACKGROUND: Angioplasty of CTOs has low success rates. The structural and perfusion changes during CTO maturation, which may adversely affect angioplasty outcome, have not been systematically studied. METHODS: Occlusions were created in 63 rabbit femoral arteries by thrombin injection. Histology, contrast-enhanced magnetic resonance imaging, relative blood volume (RBV) index, and micro-computed tomography imaging were analyzed at 2, 6, 12, and 18 to 24 weeks. RESULTS: Early changes were characterized by an acute inflammatory response and negative arterial remodeling, with >70% reduction of arterial cross-sectional area (CSA) from 2 to 6 weeks. Intraluminal neovascularization of the CTO occurred with a 2-fold increase in total (media + intima) microvessel CSA from 2 to 6 weeks (0.014 +/- 0.002 mm2 to 0.023 +/- 0.005 mm2, p = 0.0008) and a 3-fold increase in RBV index (5.1 +/- 1.9% to 16.9 +/- 2.7%, p = 0.0008). However at later time periods, there were significant reductions in both RBV (3.5 +/- 1.1%, p < 0.0001) and total microvessel CSA (0.017 +/- 0.002 mm2, p = 0.011). Micro-computed tomography imaging demonstrated a corkscrew-like recanalization channel at the proximal end at 6 weeks that regressed at later time points. These vascular changes were accompanied by a marked decrease in proteoglycans and accumulation of a collagen-enriched extracellular matrix, particularly at the entrance ("proximal fibrous cap"). CONCLUSIONS: This study is the first to systematically analyze compositional changes occurring during CTO maturation, which may underlie angioplasty failure. Negative remodeling, regression of intraluminal channels, and CTO perfusion, together with the accumulation of dense collagen, may represent important targets for novel therapeutic interventions.
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Trombosis/fisiopatología , Angioplastia , Animales , Volumen Sanguíneo , Enfermedad Crónica , Modelos Animales de Enfermedad , Matriz Extracelular/patología , Arteria Femoral , Imagen por Resonancia Magnética , Masculino , Neovascularización Patológica , Conejos , Trombosis/patología , Tomografía Computarizada por Rayos X/métodosRESUMEN
Recent intravascular imaging coil configurations have focused on side-viewing catheters capable of imaging the vessel wall of a patent vessel. These designs suffer from the presence of signal nulls and the inability to image in front of a device when it is oriented along the main static field. This is of particular importance when a device is being navigated through an occlusive lesion. To address these limitations we propose a new intravascular coil design consisting of two independent orthogonal solenoids located at the catheter tip. The two coils are oriented in such a way that signal nulls are eliminated and imaging is possible in planes located directly in front of the catheter. Complete characterization of the spatial signal-to-noise ratio (SNR) distribution of the design is presented. The coil configuration was fabricated on a 6F guide catheter, and its use is demonstrated in phantoms and in vivo.
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Arteriopatías Oclusivas/diagnóstico , Aumento de la Imagen/instrumentación , Imagen por Resonancia Magnética/instrumentación , Magnetismo/instrumentación , Cirugía Asistida por Computador/instrumentación , Transductores , Animales , Diseño de Equipo , Análisis de Falla de Equipo , Humanos , Imagen por Resonancia Magnética/métodos , Fantasmas de Imagen , Cirugía Asistida por Computador/métodos , PorcinosRESUMEN
A novel flexible scanning optical probe is constructed with a finely etched optical fiber strung through a platinum coil in the lumen of a dissipative polymer. The packaged probe is 2.2 mm in diameter with a rigid length of 6mm when using a ball lens or 12 mm when scanning the fiber proximal to a gradient-index (GRIN) lens. Driven by constant high voltage (1-3 kV) at low current (< 5 microA), the probe oscillates to provide wide forward-viewing angle (13 degrees and 33 degrees with ball and GRIN lens designs, respectively) and high-frame-rate (10-140 fps) operation. Motion of the probe tip is observed with a high-speed camera and compared with theory. Optical coherence tomography (OCT) imaging with the probe is demonstrated with a wavelength-swept source laser. Images of an IR card as well as in vivo Doppler OCT images of a tadpole heart are presented. This optomechanical design offers a simple, inexpensive method to obtain a high-frame-rate forward-viewing scanning probe.
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Óptica y Fotónica , Polímeros/química , Electricidad Estática , Tomografía de Coherencia Óptica/instrumentación , Cateterismo , Efecto Doppler , Electrodos , Electrónica , Diseño de Equipo , Espectrofotometría Infrarroja/métodos , Factores de Tiempo , Tomografía de Coherencia Óptica/métodos , Tomografía Computarizada por Rayos XRESUMEN
Chronic total occlusions (CTOs) are a subset of lesions that present a considerable burden to cardiovascular patients. There exists a strong clinical desire to improve non-surgical options for CTO revascularization. While several techniques, devices, and guide wires have been developed and refined for use in CTOs, the inability of angiography to adequately visualize occluded arterial segments makes interventions in this setting technically challenging. This review describes the current status of several invasive and non-invasive imaging techniques that may facilitate improved image guidance during CTO revascularization, with the goals of improving procedure safety and efficacy while reducing the time required to complete these interventions. Cardiac imaging also has important potential roles in selecting patients most likely to benefit from revascularization as well as pre-procedural planning, post-procedural assessment of revascularized segments and long-term outcomes studies. Modalities discussed include non-invasive techniques, such as CT(computed tomography) angiography and cardiac magnetic resonance imaging (MRI), as well as invasive techniques, such as intravascular ultrasound, optical coherence tomography, intravascular MRI, and conventional angiography. While some of these techniques have some evidence to support their use at present, others are at earlier stages of development. Strategies that combine imaging techniques with the use of interventional therapies may provide significant opportunities to improve results in CTO interventions and represent an active area of investigation.
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Enfermedad Coronaria/diagnóstico , Diagnóstico por Imagen/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Animales , Enfermedad Crónica , Angiografía Coronaria/métodos , Enfermedad Coronaria/terapia , Humanos , Angiografía por Resonancia Magnética/métodos , Tomografía de Coherencia Óptica/métodos , Tomografía Computarizada por Rayos X/métodos , Ultrasonografía Intervencional/métodosRESUMEN
The aim of the current study is to investigate the ability of micro-ultrasound (microUS) to identify microvasculature in CTOs in vivo. Results are compared with MRI studies. CTOs were developed in nine porcine superficial femoral arteries (SFA) by percutaneous insertion of a dissolvable polymer plug. This model is characterized by acute thrombosis that later organizes into a fibrotic CTO containing abundant microchannels. 3D microUS images with Power Doppler (PD) overlays from the arteries were acquired at two timepoints: one and eight weeks after placement ofthe polymerplug. Phase contrast MRI and contrast enhanced MRI was also performed. Imaging was performed transcutaneously. Microvessels were identified in vivo in six of eight CTOs using microUS, and in three of seven CTO vessels with MRI, compared with five of seven seen histologically. PW Doppler profiles showed pulsatile blood velocities of approximately 2 cm/s. Intraluminal microvessels within CTOs can be consistently identified by 3D microUS. This technique appears to be more sensitive than MRI. MicroUS may play a role in guiding CTO interventions.
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Arteriopatías Oclusivas/diagnóstico por imagen , Microcirculación , Ultrasonografía Doppler/métodos , Animales , Arteriopatías Oclusivas/patología , Modelos Animales de Enfermedad , Arteria Femoral/diagnóstico por imagen , Arteria Femoral/patología , Imagen por Resonancia Magnética , PorcinosRESUMEN
Arterial chronic total occlusions (CTO) are a common and clinically relevant problem in patients with coronary artery disease. Percutaneous coronary intervention (PCI) success rates in a wide range of CTO are low, primarily due to inability of guidewire crossing. The pathophysiology of CTO is poorly understood and limits our ability to introduce innovative therapies. Recent studies from our laboratory have suggested that microvessel formation within arterial CTO is a complex process with temporal and regional differences. Moreover, there is evidence from pilot studies that the presence of either microvessels or the particular extracellular matrix environment in the adjacent perivascular tissue can facilitate guidewire crossing and successful PCI. Currently, studies are underway in our experimental CTO model to delineate the pathophysiology of microvessel formation in CTO and its potential role in PCI.