Automated mitral annulus annotation over 4D-CT for transcatheter mitral valve replacement

Abstract

The morphological assessment of the geometry and the deformation of the mitral annulus has the potential to support the development of minimally invasive solutions for patients suffering from mitral valve regurgitation. Cardiac 4D-CT allows such a morphological assessment, which is, however, often performed manually, by annotating the mitral annulus and other cardiac landmarks. The goal of this study is to automate the annotation of cardiac landmarks in 4D-CT by propagating them from one reference phase to all others. The method proposed is based on non-rigid image registration, and four alternative variations have been tested, based on pairwise and groupwise registration. Their accuracy is evaluated against inter-observer variability on eight 4D-CTs. The results show that the pairwise and groupwise approaches using independent 3D transforms have a comparable performance, with an accuracy comparable with the inter-observer variability; however, the latter approach was computationally more expensive. Instead, the spatio-temporal groupwise approach obtained significantly worse results. The technology has, therefore, the potential to make an efficient analysis of the deforming heart more attainable. Moreover, the manual annotation process confirms that the mitral annulus deforms significantly during the cardiac contraction, supporting the use of 4D imaging for a reliable morphological assessment.