Image processing of head CT images using neuro best contrast (NBC) and lesion detection performance

Purpose: The purpose of this study was to objectively compare lesion detection performance of head CT images reconstructed using filtered back projection (FBP) algorithms with those reconstructed using NBC. Method: The observer study was conducted using the 2-AFC methodology. An AFC experiment consists of 128 observer choices and permits the computation of the intensity needed to achieve 92% correct (I92%). High values of I92% corresponds to a poor level of detection performance, and vice versa. Head CT images were acquired at an x-ray tube voltage of 120 kVp with a CTDIvol value of 75 mGy in a helical scan. Nine randomly selected normal images from three patients and at three anatomical head locations were reconstructed using filtered back projection (FBP) and neuro-best-contrast (NBC) processing. Circular lesions were generated by projecting spheres onto the image plane, followed by blurring function, with lesion sizes of 2.8 mm, 6.5 mm and 9.8 mm used in these experiments. Four readers were used, with 18 experiments performed by each observer (2 processing techniques × 3 lesion sizes × 3 repeats). The experimental order of the 18 experiments was randomized to eliminate learning curve and/or observer fatigue. The ratio R of the I92% value for NBC to the corresponding I92% value for FBP was calculated for each observer and each lesion size. Values of R greater than unity indicate that NBC is inferior to FBP, and vice versa. Results: Analysis of data from each observer showed that a total of four data points had R less than unity, and eight data points were greater than unity. Eleven of the twelve individual observer R values with one standard deviation of unity. When data for the four observers were pooled, the resultant average R values were 0.98 ± 0.38, 0.96 ± 0.33 and 1.15 ± 0.45, for the 2.8 mm, 6.5 mm and 9.8 mm lesions respectively. The overall average R for all three lesions sizes was 1.03 ± 0.67. Conclusion: Our AFC investigation has shown no evidence that use of Neuro Best Contrast to process head CT images improves detection of circular, low contrast lesions less than 10 mm.