Significance: For use in medical balloons and related clinical applications, polymers are usually designed for transparency under illumination with white-light sources. However, when illuminated with ultraviolet (UV) or blue light, most of these materials autofluoresce in the visible range, which can be a concern for modalities that rely on tissue autofluorescence for diagnostic or therapeutic purposes.
Aim: A search for published information on spectral properties of polymers that can be used for medical balloon manufacturing revealed a scarcity of published information on this subject. The aim of these studies was to address this gap.
Approach: The autofluorescence properties of polymers used in medical balloon manufacturing were examined for their suitability for hyperspectral imaging and related applications. Excitation-emission matrices of different balloon materials were acquired within the 320- to 620-nm spectral range. In parallel, autofluorescence profiles from the 420- to 620-nm range were extracted from hyperspectral datasets of the same samples illuminated with UV light. The list of tested polymers included polyurethanes, nylon, polyethylene terephthalate (PET), polyether block amide (PEBAX), vulcanized silicone, thermoplastic elastomers with and without talc, and cyclic olefin copolymers, known by their trade name TOPAS.
Results: Each type of polymer exhibited a specific pattern of autofluorescence. Polyurethanes, PET, and thermoplastic elastomers containing talc had the highest autofluorescence values, while sheets made of nylon, PEBAX, and TOPAS exhibited negligible autofluorescence. Hyperspectral imaging was used to illustrate how the choice of specific balloon material can impact the ability of principal component analysis to reveal the ablated cardiac tissue.
Conclusions: The data revealed significant differences between autofluorescence profiles of the polymers and pointed to the most promising balloon materials for clinical implementation of approaches that depend on tissue autofluorescence.
Atrial fibrillation is the most common cardiac arrhythmia. It is being effectively treated using the radiofrequency ablation (RFA) procedure, which destroys culprit tissue and creates scars that prevent the spread of abnormal electrical activity. Long-term success of RFA could be improved further if ablation lesions can be directly visualized during the surgery. We have shown that autofluorescence-based hyperspectral imaging (aHSI) can help to identify lesions based on spectral unmixing. We show that use of k-means clustering, an unsupervised learning method, is capable of detecting RFA lesions without a priori knowledge of the lesions’ spectral characteristics. We also show that the number of spectral bands required for successful lesion identification can be significantly reduced, enabling the use of increased spectral bandwidth. Together, these findings can help with clinical implementation of a percutaneous aHSI catheter, since by reducing the number of spectral bands one can reduce hypercube acquisition and processing times, and by increasing the spectral width of individual bands one can collect more photons. The latter is of critical importance in low-light applications such as intracardiac aHSI. The ultimate goal of our studies is to help improve clinical outcomes for atrial fibrillation patients.
Direct visualization of the ablated region in the left atrium during radiofrequency ablation (RFA) surgery for treating atrial fibrillation (AF) can improve therapy success rates. Our visualization approach is auto-fluorescence hyperspectral imaging (aHSI), which constructs each hypercube containing 31 auto-fluorescence images of the tissue. We wish to use the spectral information to characterize ablated lesions as being successful or not. In this paper, we reshaped one hypercube to a 2D matrix. Each row (sample) in the matrix represents a pixel in the spatial dimension, and the matrix has 31 columns corresponding to 31 spectral features. Then, we applied k-means clustering to detect ablated regions without a priori knowledge about the lesion. We introduced an accuracy index to evaluate the results of k-means by comparing with the reference truth images quantitatively. To speed-up the detection process, we implemented a grouping procedure to decrease the number of features. The 31 features were divided into four contiguous disjoint groups. In each group, the summation of values yielded a new feature. By the same evaluation method, we found the best 4-feature groups to adequately detect the lesions from all possible combinations. The average accuracy for detection by k-means (k=10) using 31 features was about 74% of reference truth images. And, for using the best grouped 4 features, it was about 95% of that using 31 features. The time cost of 4-feature clustering is about 41% of the 31-feature clustering. We expect that the reduction of time for both acquisition and processing will make possible intraoperative real-time display of ablation status.
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