Abstract
BackgroundDominant frequency (DF) analysis of videocapsule endoscopy images is a new method to detect small intestinal periodicities that may result from mechanical rhythms such as peristalsis. Longer periodicity is related to greater image texture at areas of villous atrophy in celiac disease. However, extraneous features and spatiotemporal phase shift may mask DF rhythms.MethodThe robustness of Fourier and ensemble averaging spectral analysis to compute DF was tested. Videocapsule images from the distal duodenum of 11 celiac patients (frame rate 2/s and pixel resolution 576 × 576) were analyzed. For patients 1, 2, ... 11, respectively, a total of 10, 11, ..., 20 sequential images were extracted from a randomly selected time epoch. Each image sequence was artificially repeated to 200 frames, simulating periodicities of 0.2, 0.18, ..., 0.1Hz, respectively. Random white noise at four different levels, spatiotemporal phase shift, and frames with air bubbles were added. Power spectra were constructed pixel-wise over 200 frames, and an average spectrum was computed from the 576 × 576 individual spectra. The largest spectral peak in the average spectrum was the estimated DF. Error was defined as the absolute difference between actual DF and estimated DF.ResultsFor Fourier analysis, the mean absolute error between estimated and actual DF was 0.032 ± 0.052Hz. Error increased with greater degree of random noise imposed. In contrast, all ensemble average estimates precisely predicted the simulated DF.ConclusionsThe ensemble average DF estimate of videocapsule images with simulated periodicity is robust to noise and spatiotemporal phase shift as compared with Fourier analysis. Accurate estimation of DF eliminates the need to impose complex masking, extraction, and/or corrective preprocessing measures.
Highlights
Dominant frequency (DF) analysis of videocapsule endoscopy images is a new method to detect small intestinal periodicities that may result from mechanical rhythms such as peristalsis
It was shown that when spatiotemporal phase noise, random white noise, and air bubbles are imposed on videocapsule series acquired from the distal duodenum of celiac patients (Figures 1 and 4), spectral analysis using the ensemble averaging method was useful to detect the dominant frequency (Figures 3 and 6)
Since prior results suggest a relationship between long periodicity and regions of villous atrophy [8], accurate measurement of the dominant periodicity will be important in future efforts to correlate these parameters to location in the small intestine, and to determine their actual relationship to small intestinal motility
Summary
Dominant frequency (DF) analysis of videocapsule endoscopy images is a new method to detect small intestinal periodicities that may result from mechanical rhythms such as peristalsis. Extraneous features including air bubbles and opaque fluids in the small intestinal lumen, as well as random imaging noise, are ubiquitous in videocapsule data [4,5,6] These distorting factors can in part be remediated by their delineation followed by masking or extraction; such systems can be complex, computationally unwieldy, and their sensitivity is somewhat modest [7]. Longer periodicity in the frequency spectra would possibly be indicative of slower motility, while shorter periodicity may suggest faster motility [8] To validate such measurements, it should be determined whether known, periodic changes in videocapsule image frames, in the presence of image degradation, can be detected using methods of spectral analysis
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