Photoacoustics for Cardiovascular Applications

In the thesis entitled Photoacoustic imaging for Cardiovascular Applications, two cardiovascular diseases were tackled, namely atrial fibrillation and coronary atherosclerosis. An imaging algorithm was also devised to enhance imaging target super-localization. Photoacoustic imaging is an imaging modality which provides molecular information, based on optical absorption and subsequent thermoelastic expansion resulting in detectable pressure waves with common ultrasonic detectors. Capability of imaging tissue molecular changes was shown relevant to enable real-time monitoring of lesion formation in catheter-based ablation for atrial fibrillation as well as to assess lipid content of atherosclerotic plaques in an animal model in vivo. This thesis describes the development and design of the photoacoustic imaging system from instrumentation to realization in clinically translatable setups

Spectroscopic photoacoustic imaging of radiofrequency ablation in the left atrium

Catheter-based radiofrequency ablation for atrial fibrillation has long-term success in 60-70% of cases. A better assessment of lesion quality, depth, and continuity could improve the procedure’s outcome. We investigate here photoacoustic contrast between ablated and healthy atrial-wall tissue in vitro in wavelengths spanning from 410 nm to 1000 nm. We studied single-and multi-wavelength imaging of ablation lesions and we demonstrate that a two-wavelength technique yields precise detection of lesions, achieving a diagnostic accuracy of 97%. We compare this with a best single-wavelength (640 nm) analysis that correctly identifies 82% of lesions. We discuss the origin of relevant spectroscopic features and perspectives for translation to clinical imaging

Real-time volumetric lipid imaging in vivo by intravascular photoacoustics at 20 frames per second

Lipid deposition can be assessed with combined intravascular photoacoustic/ultrasound (IVPA/US) imaging. To date, the clinical translation of IVPA/US imaging has been stalled by a low imaging speed and catheter complexity. In this paper, we demonstrate imaging of lipid targets in swine coronary arteries in vivo, at a clinically useful frame rate of 20 s−1. We confirmed image contrast for atherosclerotic plaque in human samples ex vivo. The system is on a mobile platform and provides real-time data visualization during acquisition. We achieved an IVPA signal-to-noise ratio of 20 dB. These data show that clinical translation of IVPA is possible in principle

Real-time photoacoustic assessment of radiofrequency ablation lesion formation in the left atrium

In interventional electrophysiology, catheter-based radiofrequency (RF) ablation procedures restore cardiac heart rhythm by interrupting aberrant conduction paths. Real-time feedback on lesion formation and post-treatment lesion assessment could overcome procedural challenges related to ablation of underlying structures and lesion gaps. This study aims to evaluate real-time visualization of lesion progression and continuity during intra-atrial ablation with photoacoustic (PA) imaging, using clinically deployable technology. A PA-enabled RF ablation catheter was used to ablate and illuminate porcine left atrium, both excised and intact in a passive beating heart ex-vivo, for photoacoustic signal generation. PA signals were received with an intracardiac echography catheter. Using the ratio of PA images acquired with excitation wavelengths of 790 nm and 930 nm, ablation lesions were successfully imaged through c

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Center-by-center results of a multicenter prospective trial to determine the inter-observer correlation of the simplified POP-Q in describing pelvic organ prolapse

This study was conducted to determine the differences in the inter-observer agreement of the simplified Pelvic Organ Prolapse Quantification (POP-Q) system from center to center in a large international multicenter study.This is a secondary analysis of the results of a large prospective single blind multicenter trial studying the inter-observer agreement of a simplified POP-Q exam. Twelve centers from four continents with a total of 511 subjects were included in this study. The number of subjects recruited per center ranged from 20 to 81. Each patient was independently examined by two investigators, with examination order randomly assigned and investigators blinded to each other’s result. The weighted kappa statistic was used to evaluate the inter-observer agreement.Good and significant associations were observed on the anterior, posterior, and apical segments. Six out of 11 sites did not provide adequate number of subjects with prior hysterectomy for weighted kappa statistics or achieve significance regarding vaginal cuff measurement.The simplified POP-Q demonstrated good inter-examiner agreement across multiple centers

Multicenter inter-examiner agreement trial for the validation of simplified POPQ system

The primary aim of this study was to evaluate the inter-examiner agreement of a previously described simplified pelvic organ prolapse quantification (S-POP) system in a multicenter, prospective, randomized, blinded fashion. Pelvic organ prolapse quantification (POPQ) system's use in daily practice is hampered due to perceived complexity and difficulty of use. The S-POP was introduced in order to make the POPQ user-friendly and increase its usage (Swift et al. in Int Urogynecol J 17(6):615-620, 2006). Five hundred eleven subjects underwent two separate pelvic exams in random order by two blinded examiners employing the S-POP at 12 centers around the world. Data were compared using weighted kappa statistics. The weighted kappa statistics for the inter-examiner reliability of the S-POP were 0.87 for the overall stage, 0.89 and 0.81 for the anterior and posterior vaginal walls, 0.82 for the apex/cuff 0.89, and 0.84 for the cervix and vaginal fornix, respectively

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical science. © The Author(s) 2019. Published by Oxford University Press