Left Atrium Wall-mapping Application for Wall Thickness Visualisation

Abstract

The measurement method for the LA wall thickness (WT) using cardiac computed tomography (CT) is observer dependent and cannot provide a rapid and comprehensive visualisation of the global LA WT. We aim to develop a LA wall-mapping application to display the global LA WT on a coplanar plane. The accuracy, intra-observer, and inter-observer reproducibility of the application were validated using digital/physical phantoms, and CT images of eight patients. This application on CT-based LA WT measures were further validated by testing six pig cardiac specimens. To evaluate its accuracy, the expanded maps of the physical phantom and pig LA were generated from the CT images and compared with the expanded map of the digital phantom and LA wall of pig heart. No significant differences (p > 0.05) were found between physical phantom and digital phantom as well as pig heart specimen and CT images using our application. Moreover, the analysis was based on the LA physical phantom or images of clinical patients; the results consistently demonstrated high intra-observer reproducibility (ICC > 0.9) and inter-observer reproducibility (ICC > 0.8) and showed good correlation between measures of pig heart specimen and CT data (r = 0.96, p < 0.001). The application can process and analyse the LA architecture for further visualisation and quantification.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1

Sectional views of the LA digital phantoms with (A) a homogeneous wall thickness of 1.0 mm from the roof to the base, (B) a homogeneous wall thickness of 2.0 mm, (C) an inhomogeneous gradient wall thickness with a wall thickness of 0.5 mm at the roof and a gradual increase to 1.6 mm at the base. (D) Sectional view of the physical acryl phantom corresponding to LA digital phantom (A). (E) LA physical phantom fixed in a cylindrical water phantom with a 10-cm diameter. (F) Cylindrical water phantom placed in the QRM cardio phantom. H: height; CCL: central circumference length; BCL: basal circumference length; LSPV: left superior pulmonary vein; LIPV: left inferior pulmonary vein; RSPV: right superior pulmonary vein; RIPV: right inferior pulmonary vein.

Figure 2

The study design flowchart.

Figure 3

Schematic diagram of the image-space transformation. (A) The 3D image-space. White voxels belong to the LA wall, grey voxels belong to the background, and the blue voxel is the initial tracking point for the location of the LA wall thickness in the 3D image space. The red rectangleis the weighting matrix controlling the moving direction of the tracking point. (B) The 2D mapping space. The red arrow indicates the moving direction of mapping the LA wall thickness data onto the 2D mapping space in a certain slice.

Figure 4

Procedures for processing and analysing the LA physical phantom using the LA wall-mapping application. (A) LA delineation; (B) inner-boundary segmentation; (C) outer-boundary segmentation; (D) wall thickness calculation; and (E) 2D wall map generation (four holes on the map are the pulmonary vein ostium). The colour bar shows the wall thickness.

Figure 5

Comparison of the LAgold standard (first column) with the LAmeasurement (second column). The third column shows the corresponding wall-map profile. The blue dashed line is for LAgold standard andthe red solid line for LAmeasurement. The last column showsthe difference map between the LAgold standard and LAmeasurement. The results for the 1 mm, 2 mm, and gradient wall thicknessare shown in the top, middle, and bottom row, respectively. The colour bar shows thewall thickness.

Figure 6

Partial volume effect on the LA wall. The horizontal bar indicates a CT slice, and the blue voxelsshow the LA wall thickness is overestimated, especially in the roof region.

Figure 7

Comparison of (A) the pig heart specimen and (B) the fusion image with (C) the LA wall map. The LA wall thickness between specimen and CT image was (a) 0.31 mm vs. 0.51 mm, (b) 2.88 mm vs 2.76 mm, (c) 1.51 mm vs 1.53 mm, and (d) 3.13 mm vs 3.21 mm.

Figure 8

The correlation of LA wall thickness between the pig heart specimen and cardiac CT image.

Figure 9

Procedures for processing and analysing a set of clinical CT images using the LA wall-mapping application. (A) LA delineation; (B) inner-boundary segmentation; (C) outer-boundary segmentation; (D) wall thickness calculation; and (E) 2D wall map generation. The colour bar shows the wall thickness. 1: right superior pulmonary vein (RSPV); 2 right inferior pulmonary vein (RIPV); 3 left superior pulmonary vein (LSPV); and 4: left inferior pulmonary vein (LIPV). The red dashed line indicates the annulus of mitral valve (MV).

Figure 10

Sampleclinical results. The columns (A) and (B) show the results of the two patients without AF, and the columns (C) and (D) show the results of the two AF patients.The axial CT images, the LA surface-rendered model, and the wall map results are shown in the top, middle, and bottom row, respectively. The LA wall is marked in blue, and the black solid line represents the intersectionbetween the LA and PV. Labels 1-4 indicatethe ostium of pulmonary veins.The colour bar shows the wall thickness.

Figure 11

A specific position on the (A) LA wall map can be simultaneously localised on the corresponding cardiac CT images in (B) a 4-chamber view, (C) a 2-chamber view, and (D) a short-axis view. RIPV: right inferior pulmonary vein.