Fig 1.
Flow chart of methodology.
Fig 2.
Selection of surface points with GM and EB of them.
An object is created using threshold segmentation and the marching cubes algorithm. (a) A ray going through the center of the ball (C) is fired and the P, i.e., the ray-object intersection point, is computed. The center of the ball is continuously adjusted to keep the distance between C and P a constant ratio of the ball radius so that the ball can be moved along the surface of the object of interest properly. The ROI is defined by the surface points inside the range of ball along its path. Then the EB of the ROI is implemented by emitting rays from screen to the object surface at the viewing direction, removing voxels one layer at a time and forming a new surface (green dash lines). (b) A 3D grid cube containing the surface is evaluated as the black cube in (a). A marching cube triangle will intersect the cube with marching cube vertex between voxels 1 and 0 representing the inside and outside the object. In GM algorithm, the grey level value of voxel 1 is applied to marching cube vertex to construct a surface. The same application can be used in the new surface after the EB.
Fig 3.
A 60-year-old female with descending colon cancer diagnosed by colonoscopy.
CTC found a polypoid lesion in the sigmoid colon. (a) The polyp appears suspicious in traditional SR CTC. (b) Rough surface and heterogeneous hypo-densities of the polypoid lesion are suspicious in the initial EB image. Stool is suspicious but not a polyp. (c) EB of the polypoid lesion 4 voxels beneath the surface. Persistent and more apparent hypodensities (cross) are found in EB. Small cavitation (arrow) is also noted in EB. These findings are characteristic of stool. (d) The corresponding 2D position of the hypo-densities (cross) in EB below surface (HU, −110). The corresponding 2D position of cavitation (arrow).
Fig 4.
CTC images of a 60-year-old male with surgically proven rectal cancer.
Comparison of SR and EB of colon cancer on CTC. (a) SR of the polypoid rectal cancer (b) Beginning of EB in the first layer of the lesion shows mildly homogeneous, increased density that is on the contrary in Fig 3(B). (c) EB of the lesion shows persistently homogeneous and increased density up to 5 pixels deep to the surface. No low-density areas or cavitation inside the lesion were found during the EB procedure. (d) The correlated 2D position of the Fig 4(c) (cross) in the EB (HU, 57).
Fig 5.
Images from a 62-year-old male.
Colonography revealed swelling of the ileocecal valve with narrowing of the terminal ileum. CTC of the prominent ileocecal fold: (a) SR of the fold. (b) Beginning of EB reveals multiple hypodensities on the fold (arrow). (c) Further EB study shows the same hypodensities in the subsequent layer beneath the surface. (d) The original 2D position in c (cross). The density indicates fat (HU, −88).
Fig 6.
CTC evaluation of an endoluminal lesion below tagging agents.
A 72-year-old female with a biopsy-proven cecal adenocarcinoma diagnosed at the local medical department. (a) SR shows only the spatial shape of the polypoid lesion. (b) GM shows not only a polypoid lesion but also contrast coating its surface and layering in its inferior portion. (c) EB exploration of the lesion up to 5 voxels below the surface shows gray-level changes from contrast to soft tissue densities. (d) The correlated 2D position (cross) of the 3D EB image in c (cross). The density indicates enhanced soft tissue (HU, 77).
Table 1.
Image features and classification scores of endoluminal lesions on CTC.
Table 2.
Diagnostic performance of SR, GM, TGM and EB.
Fig 7.
Noncontrast CTC Images of a 74-year-old female with a descending colon cancer.
(a) An SR image of an annular colon mass and a proximal impacted polypoid lesion. (b) An initial EB image shows a mass with higher density and smooth surface (arrow). Another polypoid lesion with heterogeneous lower densities (cross), shaggy and porous appearance proximal to the above mass. (c) An EB image up to 4–5 voxel depth to the surface shows the persistent and apparent above features (arrow and cross) corresponding to those of (b). The cavitation of the polypoid lesion becomes more apparent (arrow head) compared with that of (b). An annular colon cancer and proximal impacted stool were proved by the colonoscopy. The non-contrast EB features are similar to the contrast Figs 3(C) and 4(C) images.