Relation between denaturation time measured by optical coherence reflectometry and thermal lesion depth during radiofrequency cardiac ablation: Feasibility numerical study.

BACKGROUND/OBJECTIVE: Radiofrequency (RF) catheter ablation is a minimally invasive medical procedure used to thermally destroy the focus of cardiac arrhythmias. Novel optical techniques are now being integrated into RF catheters in order to detect the changes in tissue properties. Loss of birefringence due to fiber denaturation at around 70°C is related to changes in accumulated phase retardation and can be measured by polarization-sensitive optical coherence reflectometry (PS-OCR). Since irreversible thermal lesions are produced when the tissue reaches 50°C, our goal was to seek the mathematical relationship between both isotherms. MATERIALS AND METHODS: A two-dimensional model based on a coupled electric-thermal problem was built and solved using the finite element method. The model consisted of cardiac tissue, blood, and a non-irrigated electrode with a sensor embedded in its tip to maintain a specific target electrode temperature. Computer simulations were conducted by varying the tissue characteristics. Lesion depth was estimated by the 50°C isotherm, while the denaturation time (TD) was taken as the time at which the 70°C isotherm reached a depth of 0.75 mm (which corresponds to the optical depth reached by PS-OCR technology). RESULTS: A strong correlation (R2 > 0.83) was found between TD and lesion depth and an even stronger correlation (R2 > 0.96) was found between TD and the time required to achieve a specific lesion depth. For instance, the ablation time required to ensure a minimum lesion depth of 3 mm was 1.33 × TD + 3.93 × seconds. CONCLUSIONS: The computer results confirmed the strong relationship between denaturation time and lesion depth and suggest that measuring denaturation time by PS-OCR could provide information on the ablation time required to reach a specific lesion depth. Lasers Surg. Med. 50:222-229, 2018. © 2017 Wiley Periodicals, Inc.

Noninvasive identification of epicardial ventricular tachycardia substrate by magnetic resonance-based signal intensity mapping.

BACKGROUND: Endo-epicardial substrate ablation reduces ventricular tachycardia (VT) recurrences; however, not all patients in whom the epicardium is explored have a VT substrate. Contrast-enhanced magnetic resonance imaging (ceMRI) is used to characterize VT substrate after myocardial infarction. OBJECTIVE: The purpose of this study was to determine if epicardial VT substrate can be identified noninvasively by ceMRI-based endo-epicardial signal intensity (SI) mapping. METHODS: Myocardial infarction was induced in 31 pigs. Four or 16 weeks later, ceMRI was obtained, and the averaged subendocardial and subepicardial SIs were projected onto 3-dimensional endocardial and epicardial shells in which dense scar, heterogeneous tissue (HT), and normal tissue were differentiated. An HT channel was defined as a corridor of HT surrounded by dense scar and connected to normal tissue. A "patchy" scar pattern was defined as the presence of at least 3 dense scar islets surrounded by HT forming ≥2 HT channels. Electrophysiologic study was performed after ceMRI. RESULTS: Thirty-three different sustained monomorphic VTs (291 ± 49 ms) were induced in 25 pigs. Mid-diastolic electrograms were recorded in the endocardium (endocardial VT) in 17 and in the epicardium (epicardial VT) in 13. Epicardial SI mapping showed that scar area was similar in animals with and without epicardial VT (24 ± 6 cm2 vs. 25 ± 12 cm2), but HT covered a higher surface of the epicardial scar in animals with VT (76 ± 6% vs. 61 ± 10%, P = .03). A patchy scar pattern was observed in all animals with epicardial VT but only in 3 animals without VT (P < .001). CONCLUSION: CeMRI-based SI mapping allows identification of the epicardial VT substrate.

3D+t morphological processing: applications to embryogenesis image analysis.

We propose to directly process 3D + t image sequences with mathematical morphology operators using a new classification of the 3D+t structuring elements. Several methods (filtering, tracking, segmentation) dedicated to the analysis of 3D + t datasets of zebrafish embryogenesis are introduced and validated through a synthetic dataset. Then, we illustrate the application of these methods to the analysis of datasets of zebrafish early development acquired with various microscopy techniques. This processing paradigm produces spatio-temporal coherent results as it benefits from the intrinsic redundancy of the temporal dimension and minimizes the needs for human intervention in semi-automatic algorithms.

Do the spatial characteristics of myocardial scar tissue determine the risk of ventricular arrhythmias?

Sudden cardiac death is one of the main causes of mortality in patients with structural heart disease. Although an implantable cardioverter defibrillator significantly reduces the mortality rate, many patients never receive a shock. Identification of high-risk patients would reduce the costs associated with this therapy and prevent the deleterious effect of inappropriate discharges. As scar tissue is the substrate of ventricular arrhythmias in patients with structural heart disease, scar characterization could allow stratification of the risk. The objective of this article is to review the role of scar characteristics in the pathogenesis of ventricular arrhythmias in patients with structural heart disease.

Methodology for reconstructing early zebrafish development from in vivo multiphoton microscopy.

Investigating cell dynamics during early zebrafish embryogenesis requires specific image acquisition and analysis strategies. Multiharmonic microscopy, i.e., second- and third-harmonic generations, allows imaging cell divisions and cell membranes in unstained zebrafish embryos from 1- to 1000-cell stage. This paper presents the design and implementation of a dedicated image processing pipeline (tracking and segmentation) for the reconstruction of cell dynamics during these developmental stages. This methodology allows the reconstruction of the cell lineage tree including division timings, spatial coordinates, and cell shape until the 1000-cell stage with minute temporal accuracy and micrometer spatial resolution. Data analysis of the digital embryos provides an extensive quantitative description of early zebrafish embryogenesis.

Wavelet-based image fusion in multi-view three-dimensional microscopy.

MOTIVATION: Multi-view microscopy techniques such as Light-Sheet Fluorescence Microscopy (LSFM) are powerful tools for 3D + time studies of live embryos in developmental biology. The sample is imaged from several points of view, acquiring a set of 3D views that are then combined or fused in order to overcome their individual limitations. Views fusion is still an open problem despite recent contributions in the field. RESULTS: We developed a wavelet-based multi-view fusion method that, due to wavelet decomposition properties, is able to combine the complementary directional information from all available views into a single volume. Our method is demonstrated on LSFM acquisitions from live sea urchin and zebrafish embryos. The fusion results show improved overall contrast and details when compared with any of the acquired volumes. The proposed method does not need knowledge of the system's point spread function (PSF) and performs better than other existing PSF independent fusion methods. AVAILABILITY AND IMPLEMENTATION: The described method was implemented in Matlab (The Mathworks, Inc., USA) and a graphic user interface was developed in Java. The software, together with two sample datasets, is available at http://www.die.upm.es/im/software/SPIMFusionGUI.zip A public release, free of charge for non-commercial use, is planned after the publication of this article.

Noninvasive identification of ventricular tachycardia-related conducting channels using contrast-enhanced magnetic resonance imaging in patients with chronic myocardial infarction: comparison of signal intensity scar mapping and endocardial voltage mapping.

OBJECTIVES: We performed noninvasive identification of post-infarction sustained monomorphic ventricular tachycardia (SMVT)-related slow conduction channels (CC) by contrast-enhanced magnetic resonance imaging (ceMRI). BACKGROUND: Conduction channels identified by voltage mapping are the critical isthmuses of most SMVT. We hypothesized that CC are formed by heterogeneous tissue (HT) within the scar that can be detected by ceMRI. METHODS: We studied 18 consecutive VT patients (SMVT group) and 18 patients matched for age, sex, infarct location, and left ventricular ejection fraction (control group). We used ceMRI to quantify the infarct size and differentiate it into scar core and HT based on signal-intensity (SI) thresholds (>3 SD and 2 to 3 SD greater than remote normal myocardium, respectively). Consecutive left ventricle slices were analyzed to determine the presence of continuous corridors of HT (channels) in the scar. In the SMVT group, color-coded shells displaying ceMRI subendocardial SI were generated (3-dimensional SI mapping) and compared with endocardial voltage maps. RESULTS: No differences were observed between the 2 groups in myocardial, necrotic, or heterogeneous mass. The HT channels were more frequently observed in the SMVT group (88%) than in the control group (33%, p < 0.001). In the SMVT group, voltage mapping identified 26 CC in 17 of 18 patients. All CC corresponded, in location and orientation, to a similar channel detected by 3-dimensional SI mapping; 15 CC were related to 15 VT critical isthmuses. CONCLUSIONS: SMVT substrate can be identified by ceMRI scar heterogeneity analysis. This information could help identify patients at risk of VT and facilitate VT ablation.