Improved Detection of Microbubble Signals Using Power M-Mode Doppler

Abstract

Background-Power motion-mode transcranial Doppler (TCD) (PMD) is a new, multigated technique that may simplify and enhance detection of embolus. We developed criteria for emboli detection using PMD. Then, we performed a blinded comparison of transcranial PMD with single-gate spectral TCD in TCD bubble study patients. Methods-Patients with right-to-left shunt as detected with standard TCD were selected for this study. The international emboli criteria for spectral TCD were used. We defined novel PMD criteria for detecting emboli signature on PMD as follows: (1) signature at least 3 dB higher than the highest spontaneous PMD display of background blood flow; (2) embolic signature reflects motion in one direction at a minimum spatial extent of 7.5 mm and temporal extent of 30 ms; (3) embolus must traverse a prespecified depth. Each study was blindly assessed for microbubble signals (MBS) count on either modality. Results-Thirty-six patients were included in the study. Mean age was 44.4 (SD 14.4), 50% were male, and median time from stroke onset to TCD bubble test was 12 days. Median MBS count in middle cerebral arteries (MCA) was 4 on both modalities. Spectral TCD MBS counts were highly correlated (ϭ0.97) with PMD MBS counts in MCA and similarly in anterior cerebral arteries (ACA) (ϭ0.79). When PMD microbubble counts in the ACA and MCA were summed, a clear 2-fold difference emerged between 2 modalities (PϽ0.001). In younger patients (Ͻ55 years), paradoxical embolization through cardiac right-to-left shunts has been proposed as etiology for ischemic stroke and transient ischemic attack (TIA). 4 A recent transesophageal echocardiography (TEE) study showed that patient with both patent foramen ovale (PFO) and atrial septal aneurysm (ASA) are at increased risk of recurrent stroke. 5 TCD detects right-to-left shunts via the "TCD bubble study," in which microbubble signals (MBS) are identified in the intracranial arteries several seconds after venous injection of a contrast agent or agitated saline. When performed with a validated protocol, this test has a sensitivity of Ͼ90% and specificity of 70% to 75% for identifying PFO when compared with TEE. 6 When both TCD bubble studies and TEE are used in all patients suspected to have PFO, PFO detection rate is higher than when using either method alone. 7 A portable 2 MHz Power M-mode digital transcranial Doppler (TCD) system (PMD) has been recently introduced. 8 Transcranial PMD may enhance the detection of MBS during the TCD bubble study. We compared standard single-gate spectral TCD with multiple-gated PMD to detect MBS during TCD bubble studies. Conclusion-When MethodsStroke and TIA patients from 2 academic stroke centers participated in the study. All patients had positive TCD bubble studies with right-to-left shunts on spectral TCD. In both centers, a technician and an expert neurosonologist performed the procedure.Transcranial PMD (Spencer Technologies, Inc; PMD 100 mol/L) was used in all TCD bubble studies. This technology collects (1) 2-MHz spectral single-gate TCD i...

Applications and Advantages of Power Motion-Mode Doppler in Acute Posterior Circulation Cerebral Ischemia

“…Also, the PMD display has been shown to be more sensitive for the detection of embolic flow signatures than the singlegate spectral display, because it allows simultaneous display of flow over long arterial segments as well as more than one vessel. 13 In our series, we noted PMD embolic tracks in the cerebellar arteries (depicted as red bands on PMD display over different depths), whereas our sample volume interrogation was set in depths corresponding to VA or BA. Because the cerebellar arteries are not routinely insonated during the assessment of posterior circulation vessels with single-gate TCD, the presence of embolization distal to an extracranial or intracranial stenoocclusive arterial lesion may have not been identified without PMD-TCD.…”

“…The brighter PMD colors reflect stronger intensities, and this "road map" can serve as a guide for more complete spectral analysis. Our group and other investigators have described potential applications and advantages of PMD-over single-gate TCD in detecting acoustic windows 12 and microembolic flow signatures, 13 in diagnosing acute middle cerebral artery occlusions, 14 and for evaluating cervical internal carotid artery stenosis. 15 In the present study, we aimed to evaluate the diagnostic accuracy of PMD-TCD against angiography for the detection of acute posterior circulation stenoocclusive arterial disease.…”

Malignant Emboli on Transcranial Doppler During Carotid Stenting Predict Postprocedure Diffusion-Weighted Imaging Lesions

“…5 Embolic signals on power M-mode were identified as at least 3 dB higher than the highest spontaneous power M-mode background blood flow, which reflect motion in 1 direction at a minimum spatial extent of 7.5 mm and temporal extent of 30 ms and must traverse a prespecified depth. 6 Signals detected during contrast injections were excluded. Emboli were recorded quantitatively for each step, and their sizes were estimated using the relative energy index of micro emboli signals, as described previously.…”

Valsalva maneuver procedures in the diagnosis of right-to-left shunt by contrast-enhanced transcranial doppler using agitated saline solution with blood as a contrast agent

“…The ET criteria were a unidirectional, typically visible and audible, short duration, high-intensity signal within the doppler flow spectrum with a movement toward the MCA as time progresses and a positively-sloped track in the Mmode image (Fig 1) 1, [7][8][9] . The ET counts were obtained individually for each MCA during an offline analysis.…”