Polarization image segmentation of radiofrequency ablated porcine myocardial tissue

Abstract

Optical polarimetry has previously imaged the spatial extent of a typical radiofrequency ablated (RFA) lesion in myocardial tissue, exhibiting significantly lower total depolarization at the necrotic core compared to healthy tissue, and intermediate values at the RFA rim region. Here, total depolarization in ablated myocardium was used to segment the total depolarization image into three (core, rim and healthy) zones. A local fuzzy thresholding algorithm was used for this multi-region segmentation, and then compared with a ground truth segmentation obtained from manual demarcation of RFA core and rim regions on the histopathology image. Quantitative comparison of the algorithm segmentation results was performed with evaluation metrics such as dice similarity coefficient (DSC = 0.78 ± 0.02 and 0.80 ± 0.02), sensitivity (Sn = 0.83 ± 0.10 and 0.91 ± 0.08), specificity (Sp = 0.76 ± 0.17 and 0.72 ± 0.17) and accuracy (Acc = 0.81 ± 0.09 and 0.71 ± 0.10) for RFA core and rim regions, respectively. This automatic segmentation of parametric depolarization images suggests a novel application of optical polarimetry, namely its use in objective RFA image quantification.

Review of the emerging role of optical polarimetry in characterization of pathological myocardium

“…13,14 Importantly, polarimetry has earned a reputation by enabling the visualization of clinically important rim region, characterization of which usually presents a major challenge to the conventional medical imaging tools such as US and CT and other large pool of optical imaging techniques. Specifically, these imaging modalities have only focused to distinguish the RFA lesion core from the surrounding healthy myocardium and have not investigated the sandwiched rim region, despite its potential clinical importance, as the residual viable myocytes in this region might complicate or resist the targeted "electric isolation," resulting in RFA treatment failure.…”

“…Other quantitative evaluation indices for the comparison of the two segmentation schemes were: Dice similarity coefficient (0.78 AE 0.02 and 0.80 AE 0.02), specificity (S p ¼ 0.76 AE 0.17 and 0.72 AE 0.17), sensitivity (S n ¼ 0.83 AE 0.10 and 0.91 AE 0.08), and accuracy (Acc ¼ 0.81 AE 0.09 and 0.71 AE 0.10) for the RFA core and rim regions, respectively. 13 Despite the technological advances in the available pool of imaging tools, such quantitative analysis of RFA lesion in three zones remains elusive. The computer-assisted segmentation of parametric depolarization images suggests another application of optical polarimetry, namely its extended use in objective RFA image quantification.…”

“…To this end, a variety of the prevailing medical imaging techniques such as ultrasound (US), magnetic resonance (MR), and computed tomography (CT) have been explored; however, each of these imaging modalities has its own advantages and limitations, as discussed elsewhere. 13,14 Alternatively optical imaging, including optical polarimetry, represents a powerful tool in the investigation of structural characteristics of myocardial tissues, particularly those bearing structural remodeling such as infarction, stem cell regeneration, and RFA ablation. In particular, cardiac tissue comprises fibrous constituents (e.g., cardiomyocytes and collagen fibers), which are highly anisotropic in nature, a feature of prime significance for optical polarimetry evaluation of cardiac pathology.…”

“…It is worth mentioning that such applications of polarized light are not limited to cardiac tissues, [13][14][15][16][17] rather have been described in the investigation of several other tissue types with various pathology platforms; indicative examples include skin and colon cancers, 18,19 structural disorders of bladder wall, 20 etc. Recently, many studies have investigated polarized light measurements for the characterization of various pathologies pertaining to cardiac tissue, proving the growing interest of the research community for such applications.…”

“…13 In addition, the orientation of cardiomyocytes in cardiac muscle has previously been explored accurately with optical polarimetry. 15,22 Collectively, these studies illustrate that the optical polarimetry holds much promise for the characterization of myocardial pathologies, including sketching of myofiber organization.…”