3. Cross-sections Preparation

The selection of the appropriate set of cross-sections from the complete VHD had to be done first. The VHD files a_vm1350.raw to a_vm1505.raw were selected. Then a cropping of the selected cross-sections was implemented in order to extract only the heart area. The size of the cropped picture was 512 x 512 pixels. It was noticed that all the cross-sections were not positioned correctly in the Z direction. Some picture elements had to be trimmed into the axial position of the cross-sections. The white circle on the top-right side of each cross-section was selected for this purpose. A simple program counted the number of pixels belonging to the circle and found the centre of the circle and with this, an absolute position on each cross-section. Examples from some successive files were:

Cross-section 1358; X:1661 Y: 200; Detected points in circle:1264

Cross-section 1359; X:1661 Y: 200; Detected points in circle:1273

Cross-section 1360; X:1661 Y: 200; Detected points in circle:1264

Cross-section 1361; X:1647 Y: 200; Detected points in circle:1290

Cross-section 1362; X:1648 Y: 200; Detected points in circle:1147

Cross-section 1363; X:1648 Y: 200; Detected points in circle:1150

indicating a shift from 1661 to 1648 in the X direction from cross-section 1360 to cross-section 1362 (See Figure 2.). In the sequence from 1300 to 1539, four important shifts were found. The used offset for the cropped sections were as follows:

Cross-sections 1350-1360; X offset: 699; Y offset: 344

Cross-sections 1361-1390; X offset: 686; Y offset: 344

Cross-sections 1391-1416; X offset: 699; Y offset: 344

Cross-sections 1417-1505; X offset: 686; Y offset: 344

Cross-sections 1506-1509; X offset: 678; Y offset: 346.

Figure 2. Graphical presentation of X shifts visible on the circles that were used as a position marker.

Figure 3. Cropped original VHD cross-section 1450.

The result of this step was a box of 156 cross-sections containing aligned pictures of the heart with a resolution of 512 x 512 pixels.