Effect of transcranial Doppler intensity on successful recording in Japanese patients

Transcranial volumetric imaging using a conformal ultrasound patch

Accurate and continuous monitoring of cerebral blood flow is valuable for clinical neurocritical care and fundamental neurovascular research. Transcranial Doppler (TCD) ultrasonography is a widely used non-invasive method for evaluating cerebral blood flow1, but the conventional rigid design severely limits the measurement accuracy of the complex three-dimensional (3D) vascular networks and the practicality for prolonged recording2. Here we report a conformal ultrasound patch for hands-free volumetric imaging and continuous monitoring of cerebral blood flow. The 2 MHz ultrasound waves reduce the attenuation and phase aberration caused by the skull, and the copper mesh shielding layer provides conformal contact to the skin while improving the signal-to-noise ratio by 5 dB. Ultrafast ultrasound imaging based on diverging waves can accurately render the circle of Willis in 3D and minimize human errors during examinations. Focused ultrasound waves allow the recording of blood flow spectra at selected locations continuously. The high accuracy of the conformal ultrasound patch was confirmed in comparison with a conventional TCD probe on 36 participants, showing a mean difference and standard deviation of difference as -1.51 ± 4.34 cm s-1, -0.84 ± 3.06 cm s-1 and -0.50 ± 2.55 cm s-1 for peak systolic velocity, mean flow velocity, and end diastolic velocity, respectively. The measurement success rate was 70.6%, compared with 75.3% for a conventional TCD probe. Furthermore, we demonstrate continuous blood flow spectra during different interventions and identify cascades of intracranial B waves during drowsiness within 4 h of recording.

Noninvasive Brain Stimulation Therapies to Promote Recovery of Consciousness: Where We Are and Where We Should Go

Therapeutic options for patients with disorders of consciousness (DoC) are still underexplored. Noninvasive brain stimulation (NIBS) techniques modulate neural activity of targeted brain areas and hold promise for the treatment of patients with DoC. In this review, we provide a summary of published research using NIBS as therapeutic intervention for DoC patients, with a focus on (but not limited to) randomized controlled trials (RCT). We aim to identify current challenges and knowledge gaps specific to NIBS research in DoC. Furthermore, we propose possible solutions and perspectives for this field. Thus far, the most studied technique remains transcranial electrical stimulation; however, its effect remains moderate. The identified key points that NIBS researchers should focus on in future studies are (1) the lack of large-scale RCTs; (2) the importance of identifying the endotypes of responders; and (3) the optimization of stimulation parameters to maximize the benefits of NIBS.

Factors affecting transtemporal window quality in transcranial sonography

OBJECTIVE

To assess the influencing factors of transtemporal window quality and identify patients suitable for transcranial sonography (TCS) examination in two-dimensional imaging.

METHODS

In this cross-sectional study, TCS was performed in 161 consecutive patients through the temporal bone window (TBW) in the neurology or neurosurgery department. Each patient's sex, age, height, weight, and temporal bone thickness (TBT) were collected. After examination, the patients were divided into two groups: TBW success and TBW failure. The data were statistically compared between the two groups.

RESULTS

Among the studied population, the total TBW success rate was 80.1% (95% confidence interval [CI]: 74-86). The TBW success rate was 91.4% (95% CI: 85-98) in males and 70.9% (95% CI: 61-81) in females (p = .001). Sex (p = .001), age (p = .002), height (p = .047), and TBT (p < .001) showed significant differences between the TBW success and failure groups. In males, only TBT (p = .001) showed a significant difference; in females, age (p < .001) and TBT (p = .003) showed a significant difference. The area under the receiver operating characteristic curve (AUC) of sex, age, and TBT and their combination was 0.686, 0.659, 0.842, and 0.922 (p < .001), respectively. The AUC of the combination of parameters was significantly greater than that of age and sex alone (p = .007; p = .0002) but not greater than that of TBT (p = .090).

CONCLUSIONS

The TBW success rate varied with sex, age, height, and TBT. Males, younger patients, taller patients, and patients with a thinner temporal bone tended to be more suitable for the examination by TCS.

Non-invasive Detection of Diffuse Intracranial Vertebrobasilar Artery Stenosis: A Prospective Comparison with Digital Subtraction Angiography

The aim of this study was to prospectively evaluate diffuse intracranial vertebrobasilar artery stenosis by ultrasonic examination with digital subtraction angiography as the reference. Five hundred forty-one vertebrobasilar arteries with a normal lumen or intracranial stenosis were enrolled. Peak systolic velocity, mean flow velocity and end-diastolic velocity (EDV) at the intracranial vertebrobasilar arteries and extracranial vertebral arteries (VAs) were measured. The resistance index (RI) at extracranial VAs and the difference between the RI of extracranial VAs and the RI of the extracranial internal carotid artery (RI_ica) were calculated. Compared with normal arteries, all stenotic arteries were divided into the high-velocity group (focal stenosis, multiple-segment stenosis and multiple-artery stenosis) and low-velocity group (critical stenosis and long stenosis). The consistency between ultrasonic examination and digital subtraction angiography for evaluation of vertebrobasilar arteries with multiple-segment stenosis and multiple-artery stenosis was not favorable when applying the widely used Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis criteria (κ = 0.442 and 0.438, respectively). The optimal low-velocity criteria for identifying intracranial vertebrobasilar arteries with critical stenosis and long stenosis were determined by receiver operating characteristic curve analysis and were as follows: EDV ≤15 cm/s and RI ≥0.68 at the extracranial VA and RIica ≥0.10.

Effect of the Acoustic Impedance Mismatch at the Bone-Soft Tissue Interface as a Function of Frequency in Transcranial Ultrasound: A Simulation and In Vitro Experimental Study

The transcranial Doppler (TCD) ultrasound is a method that uses a handheld low-frequency (2-2.5 MHz), pulsed Doppler phased array probe to measure blood velocity within the arteries located inside the brain. The problem with TCD lies in the low ultrasonic energy penetrating inside the brain through the skull, which leads to a low signal-to-noise ratio. This is due to several effects, including phase aberration, variations in the speed of sound in the skull, scattering, the acoustic impedance mismatch, and absorption of the three-layer medium constituted by soft tissues, the skull, and the brain. The goal of this article is to study the effect of transmission losses due to the acoustic impedance mismatch on the transmitted energies as a function of frequency. To do so, wave propagation was modeled from the ultrasonic transducer into the brain. This model calculates transmission coefficients inside the brain, leading to a frequency-dependent transmission coefficient for a given skin and bone thickness. This approach was validated experimentally by comparing the analytical results with measurements obtained from a bone phantom plate mimicking the skull. The average position error of the occurrence of the maximum amplitude between the experiment and analytical result was equivalent to a 0.06-mm error on the skin thickness given a fixed bone thickness. The similarity between the experimental and analytical results was also demonstrated by calculating correlation coefficients. The average correlation between the experimental and analytical results came out to be 0.50 for a high-frequency probe and 0.78 for a low-frequency probe. Further analysis of the simulation showed that an optimized excitation frequency can be chosen based on skin and bone thicknesses, thereby offering an opportunity to improve the image quality of TCD.

Autodetect extracranial and intracranial artery stenosis by machine learning using ultrasound

BACKGROUND

and Purpose: This study proposed a machine learning method for identifying ≥50% stenosis of the extracranial and intracranial arteries.

PATIENTS AND METHODS

A total of 8211 patients with both carotid ultrasound and cerebral angiography were enrolled. Support vector machine (SVM) was employed as the machine learning classifier. Carotid Doppler parameters and transcranial Doppler parameters were used as the input features. Feature selection was performed using the Extra-Trees (extremely randomized trees) method.

RESULTS

For the machine learning method, the sensitivities and specificities of identifying stenosis of the extracranial arteries were 88.5%-100% and 96.0%-100%, respectively. The sensitivities and specificities of identifying stenosis of the intracranial arteries were 71.7%-100% and 88.9%-100%, respectively.

CONCLUSIONS

The SVM classifier with feature selection is an efficient method for identifying the stenosis of both intracranial and extracranial arteries. Comparing with traditional Doppler criteria, this machine learning method achieves up to 20% higher in accuracy and 45% in sensitivity, respectively.

Dynamic Cerebral Autoregulation Assessment Using Extracranial Internal Carotid Artery Doppler Ultrasonography

Transcranial Doppler ultrasonography of the middle cerebral artery (MCA) is frequently used to assess dynamic cerebral autoregulation (dCA); however, this is difficult in patients with poor temporal bone windows. In the study described here, we investigated the agreement and sensitivity of dCA indices determined from the extracranial internal carotid artery (ICA) and those determined from the MCA. Measurements for 32 stroke patients and 59 controls were analyzed. Measurement of the mean flow correlation index (Mx) and transfer function analysis based on spontaneous blood pressure fluctuation were simultaneously performed for the extracranial ICA and MCA. The mean values of Mx and phase shift did not significantly differ between the ICA and MCA (mean difference: Mx = 0.01; phase shift of very low frequency [VLF] = 0.7°, low frequency [LF] = 3.3° and high frequency = 4.5°), but the gains in VLF and LF in the ICA were significantly lower than those in the MCA (mean difference: gain of VLF = -0.13, gain of LF = -0.10). The intra-class correlation coefficient between the dCA indices of the ICA and MCA was favorable in Mx (0.76) and the phase shift of VLF (0.72). The area under the receiver operating characteristic curve for stroke diagnosis did not differ among the dCA indices. We conclude that dCA assessed from the ICA is as effective as that from the MCA, but the results are not interchangeable.

Temporal bone thickness and texture are major determinants of the high rate of insonation failures of transcranial Doppler in Amerindians (the Atahualpa Project)

PURPOSE

To assess the role of temporal bone characteristics in transcranial Doppler (TCD) insonation failures in Amerindians living in rural Ecuador.

METHODS

We evaluated thickness and texture of temporal bones in community-dwelling Amerindians ≥65 years old undergoing TCD. Using receiver operator characteristics curve analysis and generalized estimating equations, we investigated factors associated with insonation failures.

RESULTS

Of 65 participants (mean age 74.7 ± 6.7 years, 60% women), 32 (49%) had uni- or bilateral insonation failure through temporal windows. Considering temporal bones independently, 57 of 130 (44%) had poor insonation. Mean thickness was higher (4.7 ± 1.2 versus 2.7 ± 0.9, p < 0.0001), and texture more often heterogeneous (93% versus 22%, p < 0.0001) in bones with poor acoustic windows. Thickness, better predicting poor insonation, was ≥3.6 mm if used alone, and ≥2.7 mm if used together with heterogeneous texture. For every millimeter of increase in thickness, subjects were 2.9 times more likely to have insonation failures. Per se, heterogeneous texture increased by 3.2 times the odds for poor insonation. In all models, being woman increased the odds for poor insonation by six to nine times.

CONCLUSIONS

Temporal bone thickness and texture are independent predictors of TCD insonation failure in Amerindians.

Cranioplasty and Duraplasty with Transcranial Color-Coded Duplex Sonography after Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Transcranial color-coded duplex sonography (TCCS) is a noninvasive technique for monitoring of cerebral vasospasm after neurosurgery for aneurismal subarachnoid hemorrhage. In this surgery, surgical materials are used. The goal of the study was to identify materials that can be used with ultrasound and to propose methods for cranioplasty and duraplasty using materials that permit TCCS.

METHODS

The chosen neurosurgical materials were titanium mesh plate (TMP), Gore-tex, SEAMDURA, gelatinous sponge, and oxidized cellulose. B-mode imaging was recorded with the materials placed between urethane resin 10 mm in diameter and the urethane phantom model. TCCS was performed to detect middle cerebral artery flow through TMP and Gore-tex.

RESULTS

TMP and SEAMDURA permitted penetration of ultrasound in B-mode and Doppler imaging, but the other materials did not do so.

CONCLUSIONS

A postcraniotomy window (PCW) on a line extending from the horizontal portion of M1 using only TMP permitted flow imaging with TCCS. In external decompression, TCCS was effective only without use of Gore-tex around the postcraniotomy window. This method allows the middle cerebral artery flow to be detected easily.

Technical difficulties due to poor acoustic insonation during transcranial Doppler recordings in Amerindians and individuals of European origin. A comparative study

BACKGROUND

There is no information on transcranial Doppler (TCD) failures due to poor insonation among native inhabitants of Latin America.

METHODS

Seventy Ecuadorian natives and 70 age- and sex-matched individuals of European origin underwent TCD. The same investigators performed all exams using the same equipment and protocol. Using the McNemar's test for correlated proportions, we compared TCD failures related to poor insonation across ethnic groups.

RESULTS

Out of 140 participants, 56 (40%) had one or more suboptimal/absent acoustic windows. These persons were older (p = 0.01) and were more often women (p < 0.0001) than those with all optimal windows (irrespective of race/ethnicity). In the matched-pair analysis, Amerindians were more likely to have suboptimal/absent acoustic windows than individuals of European origin (OR: 2.8, 95% CI: 1.3-6.5, p = 0.006).

CONCLUSION

Amerindians are almost three times more likely to have insonation failures related to poor acoustic windows than their European counterparts.

Image guidance to improve reliability and data integrity of transcranial Doppler sonography

BACKGROUND

Principles and accuracy of image-guided transcranial Doppler (IG TCD) sonography have been published recently. However, it remains open whether combination of image guidance and TCD offers an additional clinical advantage. This study scores the accuracy of conventional TCD examinations and investigates the potential improvement of TCD data integrity and reliability regarding the additional use of IG.

METHODS

Conventional TCD was performed by a group of experienced investigators, who were blinded to images of a navigation system tracking the Doppler probe, whereas an independent observer documented the TCD findings, acquired by the investigators, due to saving spatial data of the TCD sample volume using IG for subsequent analysis. In a second set of experiments, image guidance was available to investigators without any previous TCD experience.

RESULTS

The analysis of 3D data of vessels (n=173) labeled by experienced investigators in conventional TCD, revealed a rate of 37% misinterpreted Doppler signals regarding the target vessel. Correctness of labeling was comparable between the different vascular segments. The rate of correct labeling was higher for right- (69%) than for left-sided vessels (57%). In comparison, by using IG, TCD investigators without any previous TCD experience achieved a significantly lower rate of 10% (n=39) mislabeled vessels.

CONCLUSIONS

Our data suggest, that misinterpretation of the vascular source of the Doppler signal is a common source of errors in conventional TCD. Visualization of the vascular anatomy by image guidance offers improved accuracy and reliability of TCD results and may positively influence the learning curve for inexperienced investigators.

Transcranial Doppler in a Hispanic-Mestizo population with neurological diseases: a study of sonographic window and its determinants

Between 5% and 37% of patients are not suitable for transtemporal insonation with transcranial Doppler (TCD). This unsuitability is particularly frequent in elderly females and non-Caucasians. We aim to evaluate TCD efficiency in a mixed Hispanic population in Santiago, Chile and to determine whether factors associated with the presence of optimal windows depend exclusively on patient-related elements. Seven hundred forty-nine patients were evaluated with power mode TCD. Optimal temporal windows (TWs) included detection of the middle, anterior, posterior cerebral arteries and terminal carotid. The patient's age and sex, the location of the examination, the time of day, whether the test was conducted on weekends and whether mechanical ventilation was used were recorded. Percentages of optimal windows were calculated. Examinations were deemed ideal if both TWs were optimal. TWs were obtained in 82% of cases. In univariate analyses, male sex (P < 0.001), an age below 60 years (P < 0.0001) and mechanical ventilation (P= 0.04) correlated with ideal TWs. Using logistic regression where dependent variable was a non-ideal window only male sex odds ratio (OR) 2.3 (1.51-3.45) and age below 60 OR 13.8 (7.8-24.6) were statistically significant. Our findings indicate that Hispanic populations have detection rates for TWs similar to Europeans and are affected by patient-related elements.

A review of low-intensity focused ultrasound pulsation

With the recent approval by the Food and Drug Administration (FDA) of Deep Brain Stimulation (DBS) for Parkinson's Disease, dystonia and obsessive compulsive disorder (OCD), vagus nerve stimulation (VNS) for epilepsy and depression, and repetitive transcranial magnetic stimulation (rTMS) for the treatment of depression, neuromodulation has become increasingly relevant to clinical research. However, these techniques have significant drawbacks (eg, lack of special specificity and depth for the rTMS, and invasiveness and cumbersome maintenance for DBS). This article reviews the background, rationale, and pilot studies to date, using a new brain stimulation method-low-intensity focused ultrasound pulsation (LIFUP). The ability of ultrasound to be focused noninvasively through the skull anywhere within the brain, together with concurrent imaging (ie, functional magnetic resonance imaging [fMRI]) techniques, may create a role for research and clinical use of LIFUP. This technique is still in preclinical testing and needs to be assessed thoroughly before being advanced to clinical trials. In this study, we review over 50 years of research data on the use of focused ultrasound (FUS) in neuronal tissue and live brain, and propose novel applications of this noninvasive neuromodulation method.

Frontal bone window improves the ability of transcranial color-coded sonography to visualize the anterior cerebral artery of Asian patients with stroke

The frontal bone window (FBW) is a promising approach in evaluating the anterior cerebral artery. The goal of the present study was to determine the rates of detection of the basal cerebral arteries by using the FBW alone and a combination of the FBW with the temporal bone window (TBW) in 163 patients. The combined application improved detection rates of A1 (58.6% versus 46.0%, P = .001) and A2 (43.6% versus 6.7%, P < .001) compared with the TBW alone.

Suitability of Temporal Bone Acoustic Window: Conventional TCD Versus Transcranial Color-Coded Duplex Sonography

PURPOSE AND BACKGROUND

To determine whether the proportion of patients with suitable temporal bone acoustic windows is different for conventional transcranial Doppler sonography (TCD) and transcranial color-coded duplex sonography (TCCS), based on a head-to-head comparison in the same population of patients.

SUBJECTS AND METHODS

Ninety patients, age 22-88 years (mean 57.1 +/- 11.7 years), 46 women and 44 men, 66 Caucasian, 19 African-American, and five Hispanic, underwent routine conventional TCD and the TCCS examination close in time to each other. Suitability of temporal bone acoustic window was defined by ability to insonate the middle and posterior and/or anterior cerebral arteries, while partial suitability was defined by ability to detect the posterior cerebral artery but not the middle cerebral artery. To compare proportions of suitable temporal bone windows for both sonographic methods, exact sign test by Liddell was used.

RESULTS

Bilateral absence of temporal bone acoustic window was reported in six patients when studied with both conventional TCD and TCCS, whereas at least unilateral absence was reported in 10 patients. Partial, at least unilateral, suitability was reported in 11 patients with conventional TCD, and in 7 with TCCS. All differences in proportions were not significant (two-sided P>0.05).

CONCLUSIONS

This study suggests that success rate of insonating the intracranial vessels through the temporal bone acoustic window is the same for conventional TCD and imaging TCCS.

Carotid Ultrasound Criteria for Detecting Intracranial Carotid Stenosis

BACKGROUND/AIMS

This study attempted to establish carotid ultrasound criteria for identifying stenosis of the intracranial internal carotid artery (ICA) and middle cerebral artery (MCA).

METHODS

Two hundred and fifty-five patients were enrolled. Ultrasound measurements for common carotid artery (CCA) and ICA were as follows: flow volume (FV), peak systolic velocity (PSV), end-diastolic velocity (EDV), pulsatility index (PI) and resistance index (RI). The sensitivity and specificity of the ultrasound criteria for determining intracranial ICA or MCA>or=50% stenosis were calculated.

RESULTS

The criteria identified for detecting intracranial ICA>or=50% stenosis were ICA FV<159 ml/min, ICA PSV<33 cm/s and CCA PSV<42 cm/s. When ICA PSV<33 cm/s was combined with CCA PSV<42 cm/s, sensitivity increased to 82%, with 91% specificity. The criteria identified for detecting MCA>or=50% stenosis were CCA FV<285 ml/min, ICA FV<179 ml/min, ICA PSV<33 cm/s, >35% reduction in FV in the CCA, >40% reduction in FV in ICA, and >35% reduction in PSV in ICA. When these criteria were combined, sensitivity increased to 69%, with 85% specificity.

CONCLUSION

This study demonstrated that ultrasound criteria are sensitive and specific for detecting intracranial ICA and MCA significant obstruction.

Transcranial sonography of the substantia nigra in Japanese patients with Parkinson's disease or atypical parkinsonism: clinical potential and limitations

OBJECTIVE

There is growing interest in the use of transcranial sonography (TCS) of the substantia nigra (SN) in patients with Parkinson's disease (PD), as it has been reported that SN hyperechogenicity may be present in about 90% of PD patients. However, TCS of the SN has not been applied in Japanese patients, and its clinical potential has not been determined.

PATIENTS AND METHODS

TCS of the SN was performed in patients with PD, progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and essential tremor (ET), and age-matched controls. Ultrasound images of the SN were assessed using semi-qualitative estimation criteria by two investigators unaware of clinical diagnosis.

RESULTS

SN hyperechogenicity was observed in approximately 83% of accessible SNs in Japanese PD patients. In comparison, SN hyperechogenicity was less frequently observed in healthy subjects or in patients with PSP, MSA, and ET. However, the rate of successful recording of the SN by TCS decreased prominently with advancing age, particularly in females.

CONCLUSION

The present study confirmed that TCS of the SN is potentially useful in the investigation of Japanese patients, and it provides a better differential diagnosis between PD and atypical parkinsonism. The recording failure of TCS in aged, particularly female subjects, may limit the clinical potential of TCS of the SN in Japanese patients.

Low-frequency, low-intensity ultrasound accelerates thrombolysis through the skull

Systemic thrombolysis of acute ischemic stroke with recombinant tissue plasminogen activator (rt-PA) has been established recently. Whereas the delay to and the rate of vessel recanalization are unknown, they are likely slower and smaller than for local application of rt-PA. This may contribute to the small benefits of recovery reported and stimulate further investigations to improve clot lysis. Pilot studies indicate that continuous-wave low-frequency ultrasound (US) can accelerate rt-PA-mediated recanalization of peripheral thrombotic vessel occlusion. For the hypothesized therapeutical purpose in stroke treatment, we measured the attenuation of ultrasound through the skull at different frequencies and intensities (33.3 and 71.4 kHz; 0.5 and 3.4 W/cm2), and investigated thrombolysis in vitro (n = 125 clots). Attenuation was lowest by transtemporal insonation of 33.3 kHz, 0.1 dB (0.9). Thrombolysis (artificial fibrin-rich clots) was significantly increased after 1 h (p < 0.025) and after 3 h (p < 0.01) for US treatment in combination with rt-PA vs. rt-PA alone. Results suggest that US increases rt-PA-mediated thrombolysis through the skull and may improve benefits of thrombolytic stroke treatment in vivo.

Diagnostic yield of a 1-MHz transducer in evaluation of the basal cerebral arteries

The authors examined the efficacy of a 1-MHz transducer in routine ultrasound monitoring. Fifty outpatients (34 women, 16 men; mean age, 65 +/- 2) with inadequate temporal bone window for examination with 2-MHz transducers were re-examined with a 1-MHz transducer. Additionally, 50 controls (34 men, 16 women; mean age 49 +/- 2) with adequate temporal bone window were examined with both the 1- and 2-MHz transducers. Signal quality was classified as good (GQ), adequate (AQ), or poor (PQ). Finally, 30 normal controls were examined with both transducers under standardized conditions, to evaluate potential differences in velocity measurements. A total of 90 temporal windows were lacking in the 50 patients. Use of the 1-MHz transducer resulted in identification of the middle cerebral artery in 68 cases (76%; PQ, n = 13; AQ, n = 29; GQ, n = 26), the anterior cerebral artery in 51 cases (57%; PQ, n = 23; AQ, n = 17; GQ, n = 11) and the posterior cerebral artery in 46 cases (51%; PQ, n = 12; AQ, n = 21; GQ, n = 13). Examination was feasible with both transducers in the 50 controls, with minimal differences in signal quality between the two transducers. Correlation between velocity values acquired with the 1- and 2-MHz transducers was significant for all vessels examined. Best values were measured for the middle cerebral artery, followed by the anterior cerebral artery and posterior cerebral artery. The authors conclude that the use of the 1-MHz transducer increases the yield of transcranial Doppler sonography.