Spectrogram analysis of arterial Doppler signals for off-line automated hits detection

Recently, a time processing of arterial Doppler signals was proposed to det ect automatically high-intensity transient signals (HITS). This technique p rovided satisfactory detection results, but was not always constantly accur ate, particularly with high-resistance blood velocity profiles. A time-freq uency processing, based on the spectrogram, is presented to detect the pres ence of emboli in the arterial Doppler signals. The method uses the narrow- band hypothesis and extracts the detection criterion from the time-frequenc y representation (TFR). A first database of 560 peripheral arterial Doppler HITS was created to study microemboli and to define the normal limits to b e used in our method. A threshold was experimentally defined using this dat abase, and then applied to 38 recordings from 12 patients. Using another da tabase, 6 human expert Doppler users reported 140, 176, 155, 161, 161 and 1 46 HITS, corresponding to a total of 197 different observed HITS. When an e vent was detected by at least 6, 5, 4, 3, 2 and 1 of the observers, sensiti vity of the automatic detection was 93.9, 91.7, 89.6, 88.7, 84.7 and 73.1%, respectively. The sensitivity of our automatic detection is, thus, highly associated with the number of observers in agreement. A preliminary experim ent has been performed to test the method in the case of long recording dur ation. In 15 patients, 6 h 24 min of recordings have been analyzed. The pro posed automated processing provided an overall sensibility of 91.5%. The pr esent work shows that this detection scheme preserves good sensibility and improves the positive predictive value compared with the time-processing re cently proposed. (C) 1999 World Federation for Ultrasound in Medicine & Bio logy.