Automatic Classification of HITS Into Artifacts or Solid or Gaseous Emboli by a Wavelet Representation Combined With Dual-Gate TCD

Abstract

Background and Purpose-Transcranial Doppler (TCD) can detect high-intensity transient signals (HITS) in the cerebralcirculation. HITS may correspond to artifacts or solid or gaseous emboli. The aim of this study was to develop an offline automated Doppler system allowing the classification of HITS. Methods-We studied 600 HITS in vivo, including 200 artifacts from normal subjects, 200 solid emboli from patients with symptomatic internal carotid artery stenosis, and 200 gaseous emboli in stroke patients with patent foramen ovale. The study was 2-fold, each part involving 300 HITS (100 of each type). The first 300 HITS (learning set) were used to construct an automated classification algorithm. The remaining 300 HITS (validation set) were used to check the validity of this algorithm. To classify HITS, we combined dual-gate TCD with a wavelet representation and compared it with the current "gold standard," the human experts. Results-A combination of the peak frequency of HITS and the time delay makes it possible to separate artifacts from emboli. On the validation set, we achieved a sensitivity of 97%, a specificity of 98%, a positive predictive value (PPV) of 99%, and a negative predictive value (NPV) of 94%. To distinguish between solid and gaseous emboli, where positive refers now to the solid emboli, we used the peak frequency, the relative power, and the envelope symmetry of HITS.On the validation set, we achieved a sensitivity of 89%, a specificity of 86%, a conditional PPV of 89%, and a conditional NPV of 89%. Conclusions-An

Is Hypoperfusion an Important Cause of Strokes? If So, How?

“…Transcranial Doppler ultrasound (TCD) monitoring has now shown that signals identified in the Fast Fourier Transformation (FFT) of the spectrum may represent ‘microembolic’ particles and are very often detectable in patients with potential sources of embolism, although they hardly ever cause any associated clinical events [22,23,24,25,26,27,28,29,30]. Thus, these signals should be described as high-intensity transient signals (HITS) within the Doppler spectra rather than microembolic signals.…”

“…Patients with atrial fibrillation, those with coronary atherosclerotic heart disease with ejection fractions of <30%, dilated cardiomyopathy, and valvular heart disease have the highest frequency. However, quite often these signals are produced by microgaseous cavitations that can be differentiated from solid thromboembolic material detected during and shortly after cardiac surgery [26, 27]. Many HITS are detected in the MCAs and in the lumen of the aorta during and after cardiac surgery when patients are monitored using TCD and transesophageal echocardiography [41,42,43,44,45].…”

Improved Detection of Microbubble Signals Using Power M-Mode Doppler

“…Emboli detection has been improved by using dual-gate, reference-gate, and multifrequency Doppler, which help distinguish artifact from real emboli. 11,12 In this study we showed that when compared with spectral TCD, the transcranial PMD detected more microbubble signals, thereby improving the diagnostic accuracy of PMD in detecting cardiac right-to-left shunt.…”

“…Emboli detection has been improved by using dual-gate, reference-gate, and multifrequency Doppler, which help distinguish artifact from real emboli. 11,12 In this study we showed that when compared with spectral TCD, the transcranial PMD detected more microbubble signals, thereby improving the diagnostic accuracy of PMD in detecting cardiac right-to-left shunt.The reason for the increased yield of MBS counts with transcranial PMD is increased sampling due to the simultaneous insonation of both MCA and ACA, allowing detection of emboli traveling in either artery. This effect persists after Valsalva maneuver.…”

Multigate transcranial doppler ultrasound system with real-time embolic signal identification and archival

“…7 and 9 shows how, in the case of simple events, there are clear differences between the characteristics of embolic signals and artifacts. Embolic signals show a progressive time delay between their arrivals in adjacent gates and are unidirectional, and artifacts appear simultaneously in all gates (including the gate placed outside the vessel) and are bidirectional [8], [11], [14], [22]- [27]. The inclusion of these properties as inputs into our expert reasoning system will further enhance its high performance levels.…”