Imaging Catheter Research Articles

Intravascular photoacoustic imaging of human coronary atherosclerosis

We demonstrate intravascular photoacoustic imaging of human coronary atherosclerotic plaque. The data was obtained from two fresh human coronary arteries ex vivo, showing different stages of disease. A 1.25 mm diameter intravascular imaging catheter was built, comprising an angle-polished optical fiber adjacent to a 30 MHz ultrasound transducer. Specific photoacoustic imaging of lipid content, a key factor in vulnerable plaques that may lead to myocardial infarction, is achieved by spectroscopic imaging at different wavelengths between 1180 and 1230 nm. Simultaneous imaging with intravascular ultrasound was performed.

Dynamic tissue analysis using time- and wavelength-resolved fluorescence spectroscopy for atherosclerosis diagnosis.

Simultaneous time- and wavelength-resolved fluorescence spectroscopy (STWRFS) was developed and tested for the dynamic characterization of atherosclerotic tissue ex vivo and arterial vessels in vivo. Autofluorescence, induced by a 337 nm, 700 ps pulsed laser, was split to three wavelength sub-bands using dichroic filters, with each sub-band coupled into a different length of optical fiber for temporal separation. STWRFS allows for fast recording/analysis (few microseconds) of time-resolved fluorescence emission in these sub-bands and rapid scanning. Distinct compositions of excised human atherosclerotic aorta were clearly discriminated over scanning lengths of several centimeters based on fluorescence lifetime and the intensity ratio between 390 and 452 nm. Operation of STWRFS blood flow was further validated in pig femoral arteries in vivo using a single-fiber probe integrated with an ultrasound imaging catheter. Current results demonstrate the potential of STWRFS as a tool for real-time optical characterization of arterial tissue composition and for atherosclerosis research and diagnosis.

In vitro validation of new Fourier-domain optical coherence tomography

To validate the accuracy and evaluate the intra- and inter-observer variability of vascular measurements using novel Fourier-domain optical coherence tomography (FD-OCT) versus intravascular ultrasound (IVUS) in a coronary phantom model. A dedicated cylindrical phantom comprised of four sections with differing dimensions was used to compare images generated by five FD-OCT and five IVUS catheters. Each FD-OCT catheter was tested using three different consoles, generating 15 imaging pullbacks. Two independent experts, blinded to the phantom data, performed measurements. There were 180 FD-OCT and 60 IVUS cross-sectional measurements of mean lumen diameter (MeanLD), minimal lumen diameter (MLD), maximum lumen diameter (MaxLD) and lumen area (LA) at three points in each section. FD-OCT measurements had excellent correlations with IVUS (concordance correlation coefficient [CCC]: ≥0.9769 for MeanLD, LA or longitudinal length [LL]) and phantom dimensions (CCCs for FD-OCT: ≥0.9958 for MeanLD, LA or LL). FD-OCT measurements were larger than IVUS (p<0.0001), but showed less measurement errors compared to IVUS (p<0.0001). Moreover, FD-OCT caused less discrepancy between MaxLD and MLD versus IVUS (p<0.0001). Intra- and inter-observer variability was low for both FD-OCT (CCCs for MeanLD, LA and LL ≥0.9996) and IVUS (≥0.9935). Image catheter position did not influence FD-OCT measurements. FD-OCT was more accurate than IVUS and had similar high reproducibility to determine vascular dimensions in vitro. These results support the use of FD-OCT in the clinical setting.

Intravascular imaging of vulnerable coronary plaque: current and future concepts

Advances in coronary imaging are needed to enable the early detection of plaque segments considered to be 'vulnerable' for causing clinical events. Pathological studies have contributed to our current understanding of these vulnerable or unstable segments of plaque. Intravascular ultrasonography (IVUS) has provided insights into the morphology of atherosclerosis, the mediators of plaque progression and the factors associated with acute coronary syndrome (ACS). In addition, the demonstration of pancoronary arterial instability has highlighted that ACS involves a multifocal disease process. Various second-generation intravascular imaging technologies-employing advanced processing of ultrasound radiofrequency backscatter signals, light-based imaging, spectroscopic imaging and molecular targeting-possess inherent advantages for the identification of meaningful surrogates of plaque instability. The fusion of these imaging technologies within a single imaging catheter is likely to allow for greater synergism in image quality and early disease detection. However, natural-history studies to validate the use of these novel imaging tools for enhanced risk prediction are needed before these strategies can be incorporated into mainstream clinical practice.

Ultrasonic Imaging Catheters

An intravascular ultrasonic imaging catheter is provided with a flexible circuit electrically coupled to a transducer array mounted on the distal end of the catheter, a portion of the flexible circuit being helically wound about the catheter in order to enhance the flexibility of the circuit. The catheter may be a balloon catheter which is also provided with a stent mounted on the balloon, the stent carrying one or more drugs designed to be eluted or washed into a patient's blood stream after the stent ahs been delivered, by a the balloon catheter, into a target area within the patient's vascular system.

Systems and Methods for Reducing Noise in an Imaging Catheter System

The present invention provides systems and methods for reducing noise in an imaging catheter system. In an embodiment, a catheter comprises an imaging transducer and a transmission line within the catheter to transmit signals to and from the transducer. To reduce noise caused by exposure of the transmission line to external interference, a choke balun is coupled to the transmission line. In another embodiment, the signal from a rotating imaging transducer of the catheter is coupled to a motor drive unit by a slip ring assembly. The transducer signal is passed through first and second transformers placed on opposite sides of the slip ring assembly to reduce noise from the slip ring assembly. In another embodiment, the catheter includes a position sensor to track the position of the catheter. The position sensor is coupled to a second choke balun to further reduce noise.

Intravascular laser speckle imaging catheter for the mechanical evaluation of the arterial wall

Laser speckle imaging (LSI) is a novel technique for measuring the mechanical properties of atherosclerotic plaques. In LSI, the decorrelation time constant of speckle intensity fluctuations provides an index of viscoelasticity that is closely related to plaque microstructure and composition. Here, we demonstrate for the first time, the feasibility of conducting LSI in vivo using a prototype 1.5 mm (4.5 Fr) diameter intravascular catheter. Investigation of the catheter performance using human arterial samples ex vivo shows that plaque time constants measured by the LSI catheter correlate well with those measured using a free-space bulk optics system. To demonstrate LSI in vivo, the catheter is interfaced with a portable console for intravascular evaluation in the aorta of a living rabbit. Distinct differences in arterial time constants are identified at normal aortic and stented sites in vivo with intravascular LSI.

The Optical Design of Miniaturized Microscope Objective for CARS Imaging Catheter with Fiber Bundle

In coherent anti-Stokes Raman scattering (CARS) microscopy reported until now, conventional microscope objectives are used, so that they are limited for introduction into a living body. Gradient-index (GRIN) rod lenses might be a solution for miniaturized microscope objectives for in-vivo CARS microscopy. However, due to the inherent large amount of chromatic aberration, GRIN rod lenses cannot be utilized for this purpose. CARS imaging catheter, composed of miniaturized microscope objective and fiber bundle, can be introduced into a living body for minimally invasive diagnosis. In order to design the catheter, we have to first investigate design requirements. And then, the optical design is processed with design strategies and intensive computing power to achieve the design requirements. We report the miniaturized objective lens system with diffraction-limited performance and completely corrected chromatic aberrations for an in-vivo CARS imaging catheter.

HASTE MRI in the assessment of children with hydrocephalus

Background Recent reports and our clinical experience have shown the usefulness of rapid-acquisition MRI in evaluating children with hydrocephalus. An axial HASTE (i.e. Half-Fourier Acquisition Single-shot Turbo Spin Echo Magnetic Resonance Imaging) MRI study acquires clinically useful images in seconds without exposing children to the risks of ionizing radiation or sedation. The current report reviews the Seattle Children’s Hospital experience with rapid acquisition MRI in shunted children with attention to ventricular size, overall image quality, motion artifact, and catheter visualization. Materials and methods All HASTE MRIs obtained at Seattle Children’s Hospital over two-years were reviewed by two evaluators on scales of overall image quality, catheter visualization, motion artifact, and ventricular size. Relationships among these factors were sought. Results Overall image quality was rated very good or excellent in 94% of the studies reviewed, while only one study was graded as poor. Significant motion artifact was noted in 7% while 77% had little or no motion artifact. Catheter visualization was rated as good or excellent in 57% of studies reviewed, poor in 36%, and misleading in 7%. Small ventricular size showed a significant correlation with poor catheter visualization (Pearson correlation coefficient = .575; p<.00001). Ventricular enlargement concerning for shunt malfunction on HASTE imaging correlated with operative findings of shunt malfunction in 100% of cases taken to the OR based on HASTE imaging. Conclusions Our study adds further support to the emerging evidence that HASTE MRI is an adequate substitute for CT scanning allowing for reduced utilization of CT imaging and resultant exposure to ionizing radiation. Visualization of catheter position remains suboptimal with HASTE MRI, particularly when ventricles are small; however, shunt malfunction can be adequately determined based on ventricular size alone in the majority of cases.

Imaging and clinical findings in patients with aberrant course of the cervical internal carotid arteries.

Background and Purpose:Aberrrant course of the cervical internal carotid arteries (ICAs) may result in submucosal masses in the posterior pharyngeal wall, may cause confusion at physical examination, may be symptomatic, and can be at risk of surgical injury. The aim of this report is to present the clinical and imaging characteristics associated with aberrant course of the cervical portion of the ICAs.Methods:Imaging studies of 5.500 patients were prospectively selected from CT studies of the head and neck performed in a five years period, in which the course of the one or both ICAs at the level of the hypopharynx and oropharynx was assessed as aberrant by means of a proposed classification. We then reviewed the medical records to establish which symptoms were present and if these symptoms could be caused by these variations in the course of the ICAs. In selected cases, further studies including magnetic resonance (MR) imaging, MR angiography (MRA), or selective catheter angiography were obtained. Results:In our restricted classification, we found 14 (0.2%) patients who met the cervical ICA aberrancy criteria. In all patients contrast enhanced CT or CT angiography was performed, 4 also have had MRI and MRA, and in two additional catheter angiograms were performed. Mean age was 62 years. Eight patients were male and seven were female. Four patients (28%) were considered to have clinical symptoms related to aberrant course of the ICAs. In most of the symptomatic patients both ICAs had aberrant courses. Overall, the course of the right ICA was aberrant in 43%, the left ICA in 14%, and both in 43%. In 50% of the cases the aberrancy of the artery was focal (localized to the oropharynx or laryngopharynx) and in the other 50% it involved the entire cervical course of the ICA.Conclusions:In most of our patients variations in the course of the cervical portion of the ICA involved the right side and were asymptomatic, except with regard to potential surgical risks. However, in about 25% of our patients these variations were thought to be the culprit of patient complaints, particularly oropharyngeal pulsatile sensation. Furthermore, extreme degrees of medialization of the ICAs resulted in progressive symptoms including hoarseness and upper respiratory distress.

Dual-mode IVUS catheter for intracranial image-guided hyperthermia: feasibility study.

In this study, we investigated the feasibility of modifying 3-Fr IVUS catheters in several designs to potentially achieve minimally-invasive, endovascular access for image-guided ultrasound hyperthermia treatment of tumors in the brain. Using a plane wave approximation, target frequencies of 8.7 and 3.5 MHz were considered optimal for heating at depths (tumor sizes) of 1 and 2.5 cm, respectively. First, a 3.5-Fr IVUS catheter with a 0.7-mm diameter transducer (30 MHz nominal frequency) was driven at 8.6 MHz. Second, for a low-frequency design, a 220-μm-thick, 0.35 x 0.35-mm PZT-4 transducer--driven at width-mode resonance of 3.85 MHz--replaced a 40-MHz element in a 3.5-Fr coronary imaging catheter. Third, a 5 x 0.5-mm PZT-4 transducer was evaluated as the largest aperture geometry possible for a flexible 3-Fr IVUS catheter. Beam plots and on-axis heating profiles were simulated for each aperture, and test transducers were fabricated. The electrical impedance, impulse response, frequency response, maximum intensity, and mechanical index were measured to assess performance. For the 5 x 0.5-mm transducer, this testing also included mechanically scanning and reconstructing an image of a 2.5-cm-diameter cyst phantom as a preliminary measure of imaging potential.

Pulmonary Vein Contraction Before and After Radiofrequency Ablation for Atrial Fibrillation

Cardiovascular magnetic resonance imaging (cMRI) may provide a noninvasive method to test for pulmonary vein (PV) isolation after ablation for atrial fibrillation (AF) by detecting changes in PV contraction. PV contraction (the maximal percentage change in PV cross-sectional area [CSA] during the cardiac cycle) measured 1 month before and 2 months after PV isolation was compared in 63 PVs from 16 patients with medically refractory AF. Repeat cMRI imaging and invasive catheter mapping was performed prior to repeat PV ablation in 50 PVs from 14 additional patients with recurrent AF. Contraction in PVs with sustained isolation after the initial ablation was compared to contraction in PVs with electrical reconnection to adjacent atrium. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cutoff PV contraction value for prediction of PV-atrial reconnection after ablation. The cutoff value was then prospectively tested in 40 PVs from 12 additional patients. PV contraction decreased after AF ablation (22.4 ± 10% variation in CSA before ablation vs 10.1 ± 8% variation in CSA after ablation, P < 0.00001). PVs with sustained isolation on invasive mapping contracted less than PVs with electrical reconnection to adjacent atrium (13.7 ± 10.6% vs 21.4 ± 9.3%, P = 0.021). PV contraction produced a c-index of 0.74 for prediction of PV-atrial reconnection after ablation and >17% variation in PV CSA predicted reconnection with a sensitivity of 84.6% and specificity of 66.7%. PV contraction is reduced by ablation. PV contraction measurement may provide a noninvasive method to test for PV isolation after ablation procedures.

Evaluation of stent placement and outcomes with optical coherence tomography

Optical coherence tomography (OCT) is an imaging modality based on fiberoptic technology. OCT imaging systems use optical imaging catheters that emit near-infrared light to produce high resolution, real-time images. The frequencies and bandwidths of infrared light are far higher than medical ultrasound signals, resulting in greatly increased image resolution, which is approximately ten-times higher than that of intravascular ultrasound. Compared with conventional imaging modalities, OCT is superior for the evaluation of vulnerable plaque features, which may be associated with a higher risk of peri-interventional myocardial infarction, such as plaque rupture, thrombus, thin-capped fibroatheroma and macrophages within the fibrous caps. OCT can clearly visualize stent malapposition and tissue prolapse after stent deployment, as well as neointimal hyperplasia and persistent thrombus at follow-up. OCT provides new insight into the assessment and treatment of coronary artery disease with stent placement.

TU-D-BRB-02: Failure Modes and Effects Analysis Applied to HDR Treatment Planning

Purpose: To apply Failure Modes and Effects Analysis (FMEA) to HDR treatment planning in order to identify the most likely and significant sources of error in the process. Methods and Materials: We have made a list of 24 failure modes grouped into six categories (imaging, catheter reconstruction, dwell position activity, dose points/normalization, optimization/dose, and evaluation) based on our experience with the Nucletron Plato and Oncentra planning systems. Each mode was then rated on a 1–5 scale for severity, likelihood of occurrence, and probability of escaping detection. An overall ranking is formed from the product of the 3 scores (1–125). Severity was ranked according to potential harm to the patient (notably underdosing was not considered) and was based on the NCI Common Terminology Criteria for Adverse Events handbook v 4.0. The authors assigned scores independently and the resulting rankings were averaged. We have also analysed 36 recent reported medical events related to HDR treatment planning listed on the NRC website and compared with our own rankings. Results: Failure modes associated with image sets, catheter reconstruction, indexer length and incorrect dose points had the highest ranking in our analysis (scores > 20). The most often cited failure modes in the NRC reports examined were indexer length (17/36) and incorrect dose points (6/36). Several of our high‐ranking modes are not associated with reported events. Conclusion: It is a useful exercise to identify failure modes locally and analyse the efficacy of the local quality assurance program. Comparison with nationally reported failures can help direct the local analysis, but the absence or small number of reports for failure modes with a high score may be due to low detectability. Such modes obviously cannot be ignored.

Near-infrared fluorescence catheter system for two-dimensional intravascular imaging in vivo

Detection of high-risk coronary arterial plaques prior to rupture remains an unmet clinical challenge, in part due to the stringent resolution and sensitivity requirements for in vivo human coronary arterial imaging. To address this need, we have developed a near-infrared (NIR) fluorescence imaging catheter system for intra-vascular molecular imaging of atherosclerosis in coronary artery-sized vessels, capable of resolving two-dimensional fluorescence activity in hollow organs, such as blood vessels. Based on a rotational fiber design, the catheter system illuminates and detects perpendicular to the rotational axis, while an automated pullback mechanism enables visualization along blood vessels with a scan speed of up to 1.5 mm/sec. We demonstrate the previously undocumented capacity to produce intravascular NIR fluorescence images of hollow organs in vivo and showcase the performance metrics of the system developed using blood vessel mimicking phantoms. This imaging approach is geared toward in vivo molecular imaging of atherosclerotic biomarkers and is engineered to allow seamless integration into the cardiac catheterization laboratory.

Regional Anaesthesia for Bilateral Upper Limb Surgery: A Review of Challenges and Solutions

Regional anaesthesia for bilateral upper limb surgery can be challenging, yet surgeons are becoming increasingly interested in performing bilateral procedures at the same operation. Anaesthetists have traditionally avoided bilateral brachial plexus block due to concerns about local anaesthetic toxicity, phrenic nerve block and pneumothorax. We discuss these three concerns and review whether advances in ultrasound guidance and nerve catheter techniques should make us reconsider our options. A search of Medline and EMBASE from 1966 to January 2009 was conducted using multiple search terms to identify techniques of providing anaesthesia or analgesia for bilateral upper limb surgery and potential side-effects. Ultrasound imaging and nerve catheter techniques have led to a reduction in dose requirements for effective blocks without side-effects. Effective regional anaesthesia can be performed for bilateral surgery while remaining within recommended safe dose limits. Spacing blocks apart in time can further reduce potential toxicity issues, such that peak absorption rates for each block do not coincide. Since phrenic nerve block remains an issue even with low doses of local anaesthesia, bilateral interscalene blocks are still not recommended. Peripheral nerve blocks have excellent safety profiles and are ideal for ultrasound guidance. Regional anaesthesia can be a suitable option for bilateral upper limb surgery.

Abstract No. 263 EE: Portomesenteric thrombosis: Multiple approaches to percutaneous access and techniques for transcatheter treatment

Understand the disease entity portomesenteric thrombosis, its major underlying contributing factors, treatment options and interventional radiology's unique place within this spectrum. Understand specific techniques on how to successfully access the portomesenteric venous system for subsequent transcatheter therapy utilizing different approaches and imaging modalities through case examples. Understand the wide scope of specific percutaneous transcatheter treatment options through case examples. Portomesenteric venous thrombosis (PVT) is rare but potentially devastating condition accounting for 5% to 15% of all mesenteric ischemic events. This disease process includes a spectrum of clinical presentations ranging from incidental findings in an asymptomatic patient to fulminate liver failure and life-threatening bowel infarction with reported mortality rates of 13-50% for mesenteric thrombosis. Current therapy options for PVT involves a spectrum ranging from anticoagulation to invasive surgery including multivisceral transplantation in extreme cases. In recent years modern imaging guidance and catheter directed techniques have allowed percutaneous intervention to become an important treatment option for many patients. Cases will be highlighted demonstrating portomesenteric access from the transhepatic and bilateral transjugular routes as well as direct cannulation of the mesenteric vein during laparotomy. Examples of transhepatic access will be further divided by imaging modality including percutaneous puncture under fluoroscopy, ultrasound, and CT guidance. Examples of different transcatheter treatment options will include passive instillation of thrombolytics, pulse spray thrombolysis, use of pharmaco-mechanical combination as well as percutaneous mechanical thrombectomy devices such as Trellis-8 and AngioJet. Interventional radiology has a key role in administering effective, focused, minimally invasive treatment for the rare but potentially devastating disease entity of portomesenteric thrombosis by incorporating a spectrum of percutaneous options utilizing multiple approaches and treatment delivery techniques which can be tailored to specific patients needs.

In vivo measurement of proximal pulmonary artery elastic modulus in the neonatal calf model of pulmonary hypertension: development and ex vivo validation

Developing clinical work suggests that vascular stiffening plays a role in the progression of pulmonary hypertension (PH), while recent studies in animal models of hypoxic PH have found significant proximal vascular stiffening in the diseased population. Here, we develop and validate a minimally invasive, clinically realizable method to estimate the local elastic modulus of the proximal pulmonary arteries from pressure-diameter (PD) data. PD measurements were made in the main pulmonary arteries of 16 calves; lumen diameter was assessed using color M-mode tissue Doppler imaging ultrasound, while pressure was measured via catheter. Two methods corresponding to thin-walled pressure vessel theory ("thin") and Lame's equation for a thick-walled cylinder ("thick") were used to approximate the artery elastic modulus from PD measurements. The harvested arteries were tested independently to determine their "true" ex vivo elastic modulus and stiffness. Both approximations displayed excellent correlation with ex vivo elastic modulus of the calf main pulmonary artery (thin r(2) = 0.811; thick r(2) = 0.844; both P < 0.01). Bland-Altman analysis indicated that the thick-walled approximation has better overall agreement with ex vivo modulus. The approximations displayed quantitatively distinct regression slopes that were statistically different (P = 0.02). The elastic modulus of the main pulmonary artery can be reasonably estimated from combined color M-mode tissue Doppler imaging ultrasound and catheter pressure measurements in calves. Such measurements may be a valuable tool in the diagnosis and treatment of human PH.

Development of a catheter for combined intravascular ultrasound and photoacoustic imaging

Atherosclerosis is characterized by formation and development of the plaques in the inner layer of the vessel wall. To detect and characterize atherosclerotic plaques, we previously introduced the combined intravascular ultrasound (IVUS) and intravascular photoacoustic (IVPA) imaging capable of assessing plaque morphology and composition. The utility of IVUS/IVPA imaging has been demonstrated by imaging tissue-mimicking phantoms and ex vivo arterial samples using laboratory prototype of the imaging system. However, the clinical realization of a IVUS/IVPA imaging requires an integrated intravascular imaging catheter. In this paper, two designs of IVUS/IVPA imaging catheters--side fire fiber-based and mirror-based catheters--are reported. A commercially available IVUS imaging catheter was utilized for both pulse-echo ultrasound imaging and detection of photoacoustic transients. Laser pulses were delivered by custom-designed fiber-based optical systems. The optical fiber and IVUS imaging catheter were combined into a single device. Both designs were tested and compared using point targets and tissue-mimicking phantoms. The results indicate applicability of the proposed catheters for clinical use.

Intravascular Photoacoustic Imaging

Intravascular photoacoustic (IVPA) imaging is a catheter-based, minimally invasive, imaging modality capable of providing high-resolution optical absorption map of the arterial wall. Integrated with intravascular ultrasound (IVUS) imaging, combined IVPA and IVUS imaging can be used to detect and characterize atherosclerotic plaques building up in the inner lining of an artery. In this paper, we present and discuss various representative applications of combined IVPA/IVUS imaging of atherosclerosis, including assessment of the composition of atherosclerotic plaques, imaging of macrophages within the plaques, and molecular imaging of biomarkers associated with formation and development of plaques. In addition, imaging of coronary artery stents using IVPA and IVUS imaging is demonstrated. Furthermore, the design of an integrated IVUS/IVPA imaging catheter needed for in vivo clinical applications is discussed.