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. 2012 Feb;25(1):110-20.
doi: 10.1007/s10278-011-9384-z.

Locating the reference point of symphysis pubis in axial CT images

Jiyong Oh  1 , Dae Chul Jung, Chong-Ho Choi
Affiliations

Locating the reference point of symphysis pubis in axial CT images

Jiyong Oh et al. J Digit Imaging. 2012 Feb.

Abstract

In this paper, we present an effective method to determine the reference point of symphysis pubis (SP) in an axial stack of CT images to facilitate image registration for pelvic cancer treatment. In order to reduce the computational time, the proposed method consists of two detection parts, the coarse detector, and the fine detector. The detectors check each image patch whether it contains the characteristic structure of SP. The coarse detector roughly determines the location of the reference point of SP using three types of information, which are the location and intensity of an image patch, the SP appearance, and the geometrical structure of SP. The fine detector examines around the location found by the coarse detection to refine the location of the reference point of SP. In the experiment, the average location error of the propose method was 2.23 mm, which was about the side length of two pixels. Considering that the average location error by a radiologist is 0.77 mm, the proposed method finds the reference point quite accurately. Since it takes about 10 s to locate the reference point from a stack of CT images, it is fast enough to use in real time to facilitate image registration of CT images for pelvic cancer treatment.

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Figures

Fig. 1
Fig. 1
Successive CT images with the structure of SP and their levels in an axial stack
Fig. 2
Fig. 2
Overall structure of the proposed method
Fig. 3
Fig. 3
Detection window and image patches in an image of 128 × 128 pixels
Fig. 4
Fig. 4
The hybrid cascade detector in the coarse detection
Fig. 5
Fig. 5
Four types of Haar-like features
Fig. 6
Fig. 6
Some of the SP patches
Fig. 7
Fig. 7
Negative samples
Fig. 8
Fig. 8
Distributions of dW
Fig. 9
Fig. 9
Clustering of the base points. Each point denotes a base point
Fig. 10
Fig. 10
The R-points detected from a pair of CT image stacks of the same patient
Fig. 11
Fig. 11
Errors of the 49 stacks in the test set. These figures show the level errors, the location errors in the xy plane, and the cumulative distribution of the location errors in three-dimensional space, respectively
See this image and copyright information in PMC

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