An In Vitro Comparison of Embolus Differentiation Techniques for Clinically Significant Macroemboli: Dual-Frequency Technique versus Frequency Modulation Method

Abstract

The ability to distinguish harmful solid cerebral emboli from gas bubbles intra-operatively has potential to direct interventions to reduce the risk of brain injury. In this in vitro study, two embolus discrimination techniques, dual-frequency (DF) and frequency modulation (FM) methods, are simultaneously compared to assess discrimination of potentially harmful large pieces of carotid plaque debris (0.5–1.55 mm) and thrombus-mimicking material (0.5–2 mm) from gas bubbles (0.01–2.5 mm). Detection of plaque and thrombus-mimic using the DF technique yielded disappointing results, with four out of five particles being misclassified (sensitivity: 18%; specificity: 89%). Although the FM method offered improved sensitivity, a higher number of false positives were observed (sensitivity: 72%; specificity: 50%). Optimum differentiation was achieved using the difference between peak embolus/blood ratio and mean embolus/blood ratio (sensitivity: 77%; specificity: 81%). We conclude that existing DF and FM techniques are unable to confidently distinguish large solid emboli from small gas bubbles (<50 μm).

Neurological impact of emboli during adult cardiac surgery

“…A technical limitation is that no technology currently exists to reliably distinguish between thrombus, lipid, and gaseous emboli [ 30 ]; so any weak embolic signals from lipids or thrombus particles would have been misclassified by our sizing algorithm as small bubbles. Misclassification of thrombus and lipid emboli as small bubbles will have influenced our bubble parameter estimates, and limits our ability to draw firm conclusions relating to the separate contributions of thrombus, lipid and gas emboli to cognitive and MRI outcomes.…”

Cerebral High‐Intensity Transient Signals during Pediatric Cardiac Catheterization: A Pilot Study Using Transcranial Doppler Ultrasonography

“…Further development of advanced Doppler techniques using multigated and multifrequency methods may help identify a potential "window of opportunity" in particular subgroups of patients who are at highest risk of neurologic sequelae from cerebral embolism. 39 We did not detect any major perturbations in cerebrovascular hemodynamics in association with HITS. Although we found a significant elevation in peak CBFV during HITS within clusters, this finding is likely a type 1 error considering the small sample size and large amount of variability in CBFV measurements within and between subjects.…”

“…Because there were no adverse neurologic events in our small study, clinical correlates for HITS could not be evaluated. Further development of advanced Doppler techniques using multigated and multifrequency methods may help identify a potential “window of opportunity” in particular subgroups of patients who are at highest risk of neurologic sequelae from cerebral embolism …”

Operative strategies to reduce cerebral embolic events during on- and off-pump coronary artery bypass surgery: A stratified, prospective randomized trial

“…The number and timing of HITS were monitored and recorded by dedicated research coordinators who were trained and experienced in TCD (e-video). Differentiation between solid and gaseous HITS was not performed because the overall clinical accuracy of dual frequency and frequency modulation analyses were not able to accurately separate gas from solid emboli 5–7 . All TCD data were reviewed and adjudicated by a staff neurologist at Emory University with expertise in TCD ultrasonography who was blinded to the treatment group.…”