Histogram of values calculated for each of the test image realignments. The rightmost bin shows 23 additional realignments with .
shown in reference to the subject motion measured by the Vicra system for the same image frame for all 256 images in the test dataset. Subject motion is presented as the 3D distance between the position of the image frame and the target frame.
Data flow for the proposed realignment assessment tool. The choice of the threshold value (1.0 mm) is discussed in Sec.III C. The path of each of the 256 test images are followed through the protocol with the number of images passed from one step to the next indicated in brackets.
(a) A histogram of values for the operator-accepted Vicra realignments. The rightmost bin represents two additional realignments with . (b) A histogram of values for the operator-flagged realignments. The rightmost bin represents 21 additional realignments with .
ROC curve for the range of thresholds described in Table I for all images in the training set. The point on the curve closest to the upper left corner (largest true-positive rate for the smallest false-positive rate) is at .
TACs for two representative ROIs placed on the right caudate and putamen in a sample human RAC PET scan. The TACs for the original, well-aligned, dataset are shown with a solid connecting line. TACs for ROIs misplaced by 1.2 mm in each of the , , and axes in frame 11 (at ) are shown with a long dashed connecting line. The impact of the modeled realignment error resulted in a change in of less than 1.2% from the original data. TACs for ROIs misplaced by 3.6 mm in the axis and 1.2 mm in the axis in frame 11 are shown with a short dashed connecting line. The values for these TACs were 5% different from those calculated for the original data.
The number of protocol-accepted realigned images , incorrect-acceptances , protocol-flagged , and incorrect-flags out of 192 realignments in the training set for several values of threshold. The bold numbers represent the optimal value based on the ROC analysis (Fig. 5).
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