With the development of computer-aided detection of polyps (CADpolyp), various features have been extracted to detect
the initial polyp candidates (IPCs). In this paper, three approaches were utilized to reduce the number of false positives
(FPs): the multiply linear regression (MLR) and two modified machine learning methods, i.e., neural network (NN) and
support vector machine (SVM), based on their own characteristics and specific learning purposes. Compared to MLR,
the two modified machine learning methods are much more sophisticated and well-adapted to the data provided. To
achieve the optimal sensitivity and specificity, raw features were pre-processed by the principle component analysis
(PCA) in the hope of removing the second-order statistical correlation prior to any learning actions. The gain by the use
of PCA was evidenced by the collected 26 patient studies, which included 32 colonic polyps confirmed by both optical
colonoscopy (OC) and virtual colonoscopy (VC). The learning and testing results showed that the two modified
machine-learning methods can reduce the number of FPs by 48.9% (or 7.2 FPs per patient) and 45.3% (or 7.7 FPs per
patient) respectively, at 100% detection sensitivity in comparison with that of traditional MLR method. Generally, more
than necessary number of features were stacked as input vectors to machine learning algorithms, dimensionality
reduction for a more compact feature combination, i.e., how to determine the remaining dimensionality via PCA linear
transform was considered and discussed in this paper. In addition, we proposed a new PCA-scaled data pre-processing
method to help reduce the FPs significantly. Finally, fROC (free-response receiver operating characteristic) curves
corresponding to three FP-reduction approaches were acquired, and comparative analysis was conducted.
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