Micro-CT scan with virtual dissection of Left Ventricle is a non-destructive, reproducible alternative to dissection and weighing for Left Ventricular size




Doost, Ata

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Cardiac hypertrophy is a common condition and carries a substantial risk of cardiovascular morbidity and mortality. While there have been notable successes in the identification of monogenic diseases causing severe hypertrophic cardiomyopathy, the genes responsible for population variation in cardiac size have not been identified. Strategies to identify causative genes by genome wide-association studies have been implemented worldwide, but these studies are extensive with a vast cost. That makes an alternative, simpler and more practical approach that narrows the potential genes needing intensive evaluation appealing. Model systems such as inbred recombinant strains of mice provide such an alternate approach to identify a genetic basis for underlying susceptibility to common diseases. However, significantly reduced mouse cardiovascular structure presents a technical challenge when attempting to visualise anatomic features such as congenital defects or left ventricular (LV) hypertrophy. Histological analysis of sectioned soft tissues has been traditionally recognised as the gold standard in identification of cardiovascular diseases. Nonetheless histology only provides a two-dimensional view of a sectioned sample, requires intensive manual handling, and is prone to artefacts in sample processing and preparation. X-ray absorption micro-computed tomography (micro-CT) scan has recently attracted great attention in in-vivo and ex-vivo visualisation of small animal models and provides high resolution 3-Dimensional (3D) data, at a micrometre scale. The acquired images can be presented in multiple imaging planes and rapidly reconstructed thereby allowing a detailed assessment of cardiac anomalies without sample destruction. This technique is non-invasive and can be conducted without compromising the ability to further pursue downstream histological analysis. In this study we compared two common micro-CT scan staining agents for enhancement of soft tissues and their application for investigation of post-natal murine cardiac structures as part of a project on identifying genes that contribute to the left ventricular hypertrophy in the Collaborative Cross (CC) mice. The ability to study the CC strains using fixed tissue allows access to more strains at a greatly reduced cost compared to shipping live animals. Using micro-CT, we were able to show that it is technically feasible to do high-resolution and 3D visualisation of the whole murine heart with contrast staining without having to dissect and section them. Our data demonstrated that iodine staining compared to Phosphotungstic Acid (PTA) is easier and quicker to facilitate contrast enhancement of mouse cardiac tissue. Most importantly, stained samples are preserved for future histopathology and genotyping experiments. Virtual dissection of micro-CT 3D images provides non-destructive measurement of left-ventricular tissue volume allowing both secondary uses and repeated measurements neither of which are possible with physical dissection. We compared estimated LV mass with the directly measured LV mass after dissection as this has been the common comparator in many imaging studies. Although, for small volumes, histomorphometry has occasionally been used. Our results support the use of micro-CT to estimate LV tissue mass, particularly in circumstances where it is desirable to leave the preserved specimen intact for other subsequent use. Combining this technique with phenotypic information could provide a new, efficient way to identify genetic cardiac hypertrophic anomalies.






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