A Comparison of Four Methods for Distinguishing Doppler Signals From Gaseous and Particulate Emboli

Abstract

Background and Purpose-Many reports in the medical literature have proposed methods of differentiating between gaseous and particulate emboli detected with the use of transcranial Doppler ultrasound. The purpose of this study was to compare the previously published methods with our own sample volume length (SVL) parameter to assess the accuracy of each method in classifying emboli. Methods-A pure source of gaseous and particulate emboli was obtained from in vitro and in vivo studies, respectively, and recorded onto digital audiotape for off-line analysis. In total, 100 gaseous emboli and 215 particulate emboli were analyzed to measure four embolic parameters, namely, embolic duration, embolic velocity, relative signal intensity increase (measured embolic power [MEP]), and SVL of the embolic signal (ϭDurationϫVelocity). Receiver operator characteristic analysis was used to assess the optimum threshold for each parameter to differentiate between particulate and gaseous emboli, and levels of sensitivity and specificity were calculated. Results-Embolic duration and velocity produced the poorest levels of sensitivity and specificity compared with the MEP and SVL parameters. The optimum thresholds for embolic duration and velocity were 35 ms and 1 m/s, respectively, which produced a sensitivity (specificity) of 85.1% (87%) and 87% (67%), respectively. The optimum MEP and SVL thresholds were 30 dB and 12.8 mm, respectively, which produced a sensitivity (specificity) of 86.5% (95%) and 93% (97%), respectively. The SVL and MEP parameters were compared statistically ( 2 ) at chosen specificity values of 90%, 95%, 97%, 99%, and 100%, which showed that the SVL sensitivities were statistically greater than MEP sensitivities (PϽ0.01). Conclusions-SVL is the best parameter for differentiating between gaseous and particulate emboli but needs to be calculated with the use of a high-temporal-resolution spectral analyzer to measure embolic duration and velocity.

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

“…[13][14][15][16][17][18][19][20][21][22][23][24] In our study, the signals were reviewed by 2 observers, and for inclusion, both observers had to agree that the signal was a true embolic signal. The following definition for embolic signals was used: (1) typical visible, (2) short duration, (3) high-intensity signal, (4) within the Doppler spectrum, and (5) occurring at random within the cardiac cycle.…”

“…12 Previous attempts at producing an automated system for classifying HITS into artifacts or emboli have failed to achieve the same level of sensitivity (embolus detection) and specificity (artifact rejection) as the human expert, considered the current "gold standard." [13][14][15][16][17][18][19][20][21][22][23][24] Without an automated embolic signal detection system that is as effective as the human expert in terms of sensitivity and specificity, embolus detection remains a time-consuming process, restricted to research studies and unsuitable for clinical practice. 25 To separate artifacts from emboli, the best compromise is dual-gate TCD, which consists of tracing the embolus at 2 different depths in the same artery (time delay) ( Figure 1).…”

Relative Energy Index of Microembolic Signal Can Predict Malignant Microemboli

“…Distance of travel of MES may have some advantages over the MaxI on PMD display because it is not affected by amplifier overload. 13 However, it can be influenced by insonation status, such as bone window or the sonographer's skill. MES duration measurement is another promising approach, 14 which could be longer in the case of larger emboli.…”

“…11,12 Considerable work has been performed trying to distinguish between solid emboli vs air composition. 13,14 In addition, several studies have attempted to measure the size of emboli by their specific characteristics. 15 These efforts have been limited by the type of technology used in emboli detection because most studies relied on single-gate spectrogram TCD, which has limited sample volume that covers only a small part of the travel path of an embolus.…”

Occurrence and Clinical Impact of Microembolic Signals During or After Cardiosurgical Procedures

“…Studies conducted so far have used different monitoring times, ultrasound devices, and monitoring protocols, thus hampering the comparability of results. In addition, the overlapping physical properties of the microemboli do not yet allow us to unequivocally differentiate gaseous from solid MESs, despite promising technical progress, like multifrequency TCD, 100 a longer sample volume length for gaseous microemboli, 101 and Doppler time domain analysis. 39 Finally, there is a lack of large, prospective and long-term, follow-up studies in all fields of cardiosurgical procedures.…”