New Imaging Signatures of Cardiac Alterations in Ischaemic Heart Disease and Cerebrovascular Disease Using CMR Radiomics

Background: Ischaemic heart disease (IHD) and cerebrovascular disease are two closely inter-related clinical entities. Cardiovascular magnetic resonance (CMR) radiomics may capture subtle cardiac changes associated with these two diseases providing new insights into the brain-heart interactions.Objective: To define the CMR radiomics signatures for IHD and cerebrovascular disease and study their incremental value for disease discrimination over conventional CMR indices.Methods: We analysed CMR images of UK Biobank's subjects with pre-existing IHD, ischaemic cerebrovascular disease, myocardial infarction (MI), and ischaemic stroke (IS) (n = 779, 267, 525, and 107, respectively). Each disease group was compared with an equal number of healthy controls. We extracted 446 shape, first-order, and texture radiomics features from three regions of interest (right ventricle, left ventricle, and left ventricular myocardium) in end-diastole and end-systole defined from segmentation of short-axis cine images. Systematic feature selection combined with machine learning (ML) algorithms (support vector machine and random forest) and 10-fold cross-validation tests were used to build the radiomics signature for each condition. We compared the discriminatory power achieved by the radiomics signature with conventional indices for each disease group, using the area under the curve (AUC), receiver operating characteristic (ROC) analysis, and paired t-test for statistical significance. A third model combining both radiomics and conventional indices was also evaluated.Results: In all the study groups, radiomics signatures provided a significantly better disease discrimination than conventional indices, as suggested by AUC (IHD:0.82 vs. 0.75; cerebrovascular disease: 0.79 vs. 0.77; MI: 0.87 vs. 0.79, and IS: 0.81 vs. 0.72). Similar results were observed with the combined models. In IHD and MI, LV shape radiomics were dominant. However, in IS and cerebrovascular disease, the combination of shape and intensity-based features improved the disease discrimination. A notable overlap of the radiomics signatures of IHD and cerebrovascular disease was also found.Conclusions: This study demonstrates the potential value of CMR radiomics over conventional indices in detecting subtle cardiac changes associated with chronic ischaemic processes involving the brain and heart, even in the presence of more heterogeneous clinical pictures. Radiomics analysis might also improve our understanding of the complex mechanisms behind the brain-heart interactions during ischaemia.

Polarization-Sensitive Second Harmonic Generation Microscopy for Investigations of Diseased Collagenous Tissues

The advancement of non-invasive quantitative optical diagnosis techniques such as polarization-sensitive second harmonic generation microscopy (PSHG) for diseases such as cancer presents opportunities for improving disease understanding and survival rates. Here, novel and developing techniques in PSHG microscopy applied for the differentiation of cancerous or diseased tissues are presented, including circular dichroism, modulation of laser linear polarization, detection of outgoing linear laser polarization, and double-Stokes Mueller. Typically, initial cancer diagnosis is performed by visual inspection of stained biopsy or surgical resection tissue sections under bright-field microscopy, however, early diagnosis is challenging due to variability in morphological interpretation of the tissues, and because cancer initiation regions can be small and easy to miss. Therefore, pathologists could benefit in identifying cancer on biopsy or surgical resection sections by using unbiased quantitative automated technologies with high spatial resolution and improved disease specificity that can check the entire slide pixel-by-pixel. Second harmonic generation microscopy offers the opportunity to measure ultrastructural alterations in collagenous scaffolds of organ tissues virtually background free on submicron-sized tissue regions. The approach is particularly interesting for cancer diagnosis applications, because during cancer initiation and progression, the collagen in the affected tissue extracellular matrix is often deregulated and becomes disorganized. This mini-review contains a thorough summary of PSHG techniques that have interrogated diseased tissues, and discusses their technical variations and successes in disease discrimination.