Automatic classification of HITS into artifacts or solid or gaseous emboli by a wavelet representation combined with dual-gate TCD

BACKGROUND AND PURPOSE

Transcranial Doppler (TCD) can detect high-intensity transient signals (HITS) in the cerebral circulation. 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 automated wavelet representation combined with dual-gate TCD can reliably reject artifacts from emboli. From a clinical standpoint, however, this approach has only a fair accuracy in differentiating between solid and gaseous emboli.

Absence of circulating microemboli in patients with atrial fibrillation undergoing electric cardioversion

Electrical cardioversion (CV) of atrial fibrillation (AF) is associated with an increased risk of stroke, and its appropriate prevention is still a matter of debate. It is known that, besides dislodgement of pre-existing intra-atrial thrombi, the "stunned" atrium after CV is an important cause of thrombus formation and subsequent embolism. We investigated whether CV of AF is associated with occurrence of circulating microemboli (ME) representing a sensitive marker of the actual thromboembolic activity. Twenty-nine patients (22 men) aged 54 +/- 13 years suffering from valvular (n = 5) or nonvalvular (n = 24) AF were studied. All but 1 patient (with recent-onset AF) had been put on oral anticoagulation (INR >2.0) for at least 3 weeks before and 4 weeks after successful CV. In all patients, exclusion of internal carotid artery stenosis and atrial thrombus was performed prior to CV. Five unilateral 1-hour transcranial Doppler ME monitorings over the middle cerebral artery were performed (1) before CV, and (2) immediately, (3) 4-6 h, (4) 24 h, and (5) 2-4 weeks after CV. Total absence of circulating ME was found before CV as well as during a cumulative monitoring time of 115 h after successful CV. Electrical CV of AF after at least 3 weeks of effective anticoagulation is not associated with occurrence of cerebral circulating ME. This finding requires further investigation including high-risk patients with AF undergoing CV based on different treatment protocols.

Microembolus detections at follow-up in 19 patients with acute stroke: correlation with stroke etiology and antithrombotic treatment

The present study was designed to perform follow-up transcranial Doppler investigations for microembolic signals (MES) in acute stroke patients by means of a strict protocol. The number of MES was correlated with stroke etiology and the strength of antithrombotic treatment. Concurrently, we wanted to demonstrate that MES in acute stroke patients are solid in nature and not gaseous. Nineteen patients with middle cerebral artery ischemic events, 16 with completed stroke and 3 with transient ischemic attack (TIA) were investigated within 24 h following the onset of symptoms. Six 1-hour recordings on days 1, 2, 3, 4, 7 and 14 were performed from the affected middle cerebral artery. The four-gate technique and recently established criteria for the identification of MES were used. Eight of 19 patients showed MES in at least one recording. Variability was high and showed no uniform tendency with respect to time since onset of symptoms or treatment. All 3 patients with internal carotid artery dissection showed MES. In 3 patients with lacunar stroke, no MES were detected. Two patients with MES suffered recurrent TIAs during the observation period, whereas none of the patients without MES suffered a recurrent ischemic event. In the acute phase following stroke, ongoing, emerging and vanishing embolization in some patients may reflect individual active processes of remodelling, healing and disruption or disappearance of the embolic source.

Contrast transcranial doppler ultrasound in the detection of right-to-left shunts : time window and threshold in microbubble numbers

BACKGROUND AND PURPOSE

Cardiac right-to-left shunts can be identified by transesophageal echocardiography (TEE) and by transcranial Doppler ultrasound (TCD) with the use of contrast agents and a Valsalva maneuver (VM) as provocation procedure. Currently, data on the appropriate timing of the VM, the use of a diagnostic time window, and a threshold in contrast agent microbubbles detected are insufficient.

METHODS

Fifty-eight patients were investigated by both TEE and bilateral TCD of the middle cerebral artery. The following protocol with injections of 10 mL of the commercial galactose-based contrast agent Echovist was applied in a randomized way: (1) no VM, (2) VM for 5 seconds starting 2 seconds after the beginning of contrast injection, (3) VM for 5 seconds starting 5 seconds after the beginning of contrast injection, (4) VM for 5 seconds starting 8 seconds after the beginning of contrast injection, and (5) repetitive short VMs in between 2 and 13 seconds after the beginning of contrast injection. In addition to the single tests, we also tested the sensitivity and specificity of combined results of the tests with VM.

RESULTS

In 21 patients, a right-to-left shunt was demonstrated by TEE and contrast TCD (shunt positive). Twenty-one patients were negative in both investigations, no patient was positive on TEE and negative on TCD, and 16 patients were only positive on at least 1 TCD investigation but negative during TEE. Test 3 was the most appropriate test when combined with the results of 1 of the other tests with VM. The highest sensitivities were achieved with a diagnostic time window of 40 seconds and when the presence of a single microbubble was sufficient for the diagnosis of a shunt.

CONCLUSIONS

TCD performed twice with 2 provocation maneuvers with Echovist is a sensitive method to identify TEE-proven cardiac right-to-left shunts. The VM should be performed for 5 seconds starting at 5 seconds after the beginning of contrast injection.

Preoperative B-mode ultrasound plaque appearance compared with carotid endarterectomy specimen histology

In carotid artery stenosis both the degree of the lesion and its plaque morphology are thought to be associated with the carrier's thromboembolic risk. In this study we evaluated the diagnostic preciseness of non-invasively B-mode ultrasound in predicting the histopathological plaque structure. We examined 44 patients with > 50% ICA stenosis by B-mode within 6 weeks prior to carotid endarterectomy. At the affected bifurcations, up to 10 different regions of interest (ROI) per artery were investigated. Plaque appearance was classified according to 6 subtypes considering different ultrasonic plaque features. Postoperatively, plaque specimens were examined histopathologically for their relative content of calcification, fibrous tissue and different soft tissue. B-mode ultrasound was compared with histopathological features in ROI. A total of 265 regions of interest were evaluated. In mainly echolucent types of plaques, atheromatous debris was most frequently seen, whereas fibrosis was rare. Homogeneous echolucent plaques showed a high proportion of cholesterol and/or recent haemorrhage. Thrombosis at the plaque surface was often seen in "completely echolucent" plaque type (each P<0.001). Carotid B-mode ultrasonography is able to predict the histopathological components and the texture of carotid plaques.

Middle cerebral artery blood flow velocity, end-tidal pCO2 and blood pressure in patients with obstructive sleep apnea and in healthy subjects during continuous positive airway pressure breathing

There is conflicting evidence in the literature as to the potential effect of continuous positive airway pressure (CPAP) on cerebral perfusion. Compromising cerebral perfusion could possibly outweigh the benefit of improved oxygenation. Patients with the obstructive sleep apnea syndrome (OSAS) have been claimed to have a higher cerebrovascular reactivity to changes in end-tidal pCO2. In this study, we investigated 23 patients with OSAS and 16 healthy young adults in the waking state. Both groups performed a series of 10 min of normal breathing, 20 min with 9 cmH2O nasal CPAP, and then 10 min of normal breathing while wearing a nasal CPAP mask. The following parameters were assessed: bilateral transcranial Doppler signal of the middle cerebral artery, systolic and diastolic blood pressure assessed manually, and cerebrovascular reactivity to changes in pCO2 during hyperventilation and rebreathing into an airbag. Continuous end-tidal pCO2 measurements were performed in 14 subjects. As compared with normal breathing middle cerebral artery blood flow velocity and pCO2 remained unchanged during CPAP. Systolic and diastolic blood pressure increased slightly by 1.2 mmHg (p = 0.015) and 1.1 mmHg (p = 0.007), respectively. Cerebrovascular reactivity did not differ in the two groups. Nasal CPAP of 9 cmH2O is a safe treatment with respect to the maintenance of cerebral blood flow. Our study gives further evidence for the autoregulation's capacity to maintain cerebral blood flow velocity constant during different levels of intrathoracic pressure and different cerebral perfusion pressures. We could not demonstrate any difference in cerebrovascular reactivity between patients with OSAS and healthy persons.

Abundance of microembolic signals detected by transcranial doppler ultrasound in a patient with Eisenmenger's syndrome

BACKGROUND

Clinically silent circulating microemboli can be detected by transcranial Doppler sonography.

CASE DESCRIPTION

We report the case of a 45-year-old man with congenital cyanotic heart disease, elevated haematocrit, low platelet count and decreased protein C and protein S activity. Before and following several haemodilutions, we performed 5 1-hour transcranial Doppler recordings from one or both middle cerebral arteries (MCAs) on different days. The number of microembolic signals per hour varied from 54 to 134. During the bilateral recording, the microemboli occurred on both sides (55 in the right and 45 in the left MCA, respectively). There was no relation to red blood cell count, platelet count, the spontaneously lowered prothrombin time or the spontaneously prolonged activated partial thromboplastin time.

CONCLUSIONS

The origin of the large number of microembolic signals found in this patient remains unclear, but may be presumed in the intra-abdominal or crural venous system.

Prevalence and frequency of microembolic signals in 105 patients with extracranial carotid artery occlusive disease

Besides the established factors "presence of symptoms" and "degree of stenosis", plaque echolucency is considered to be associated with increased risk of stroke in patients with carotid artery disease. An evaluation was carried out as to whether the prevalence and number of microembolic signals (MES) detected by transcranial Doppler ultrasound were higher in patients with echolucent carotid plaques. One hundred and five patients with carotid artery stenosis from 20%-99% or occlusion underwent clinical investigations, duplex ultrasound of the carotid arteries, and a 1 hour recording from the middle cerebral artery downstream to the carotid artery pathology using the four gate technique. The presence of MES was more frequent and the number greater in symptomatic patients (21 out of 64 patients (33%); mean number of MES in all 64 patients 3.1) than in asymptomatic patients (four out of 41 patients (10%); mean number of MES in all 41 patients 0.3) (p=0.007, and p=0.006, respectively). Echogenicity of the lesions did not affect either number or presence of MES. Positivity for MES and the number of MES increased with increasing degree of stenosis (both p=0.002). Four out of 12 patients with carotid artery occlusion showed MES. No MES could be detected in carotid artery stenosis below 80%. There was a decline in positivity of MES and of the number of MES with the time after the ischaemic event. After 80 days or more after the index event, only one patient showed MES. In conclusion, increasing degree of stenosis and presence of symptoms similarly affect macroembolic and microembolic risk. Thus MES may be a surrogate parameter for risk of stroke. The presence of MES in a few asymptomatic patients suggests that clinically silent circulating microemboli may give additional information on the pending embolic potential of carotid artery stenoses. Echolucency of the plaque was not related to an increased number of MES.

Four-gated transcranial Doppler ultrasound in the detection of circulating microemboli

OBJECTIVE

Embolus detection by transcranial Doppler ultrasound is very time consuming and semi-automated detection is mandatory. The device studied, a TC4040, Nicolet-EME, uses the four-gate technique and allows for audiovisual off-line verification of the recorded events.

METHODS

Twenty controls, 10 patients with mechanical prosthetic heart valves and 12 patients with occlusive carotid artery disease were investigated by transcranial colour-coded duplex sonography and, subsequently, underwent a 1-h unilateral embolus detection from the middle cerebral artery using four-gate TCD. We investigated the Doppler spectrum background, microembolic signals (MES) and artefacts produced. A detection threshold of 5 dB or more was defined taking into account natural fluctuations of the Doppler spectrum.

RESULTS

Sensitivity of the software was 91.9% and observer-software agreement on MES was 7.8% in the valve patients, and 77.7% and 7.5% in the carotid artery disease patients, respectively. Weaker MES were more likely not to be detected in all four channels. The artefact signal rejection rate was 62%. MES produced either positive or zero time delays in adjacent channels. Artefact signals produced either no delay, or a positive or a negative time delay. Duration of MES ranged from 1-88 ms.

CONCLUSIONS

Besides refined recognition of MES using the time delay, four gates give faint MES no less than four opportunities to overcome the detection threshold. With this device's satisfying sensitivity, regions of interest in a 1-h recording can audiovisually be evaluated off-line in a few minutes by an investigator.

Contrast transcranial Doppler ultrasound in the detection of right-to-left shunts. Reproducibility, comparison of 2 agents, and distribution of microemboli

BACKGROUND AND PURPOSE

Cardiac right-to-left shunts can be identified by transcranial Doppler ultrasound (TCD) with the use of different contrast agents and by transesophageal echocardiography (TEE). Systematic data are available on neither the reproducibility of contrast TCD, the comparison of different contrast agents, nor the comparison of simultaneous bilateral to unilateral recordings. Furthermore, we assessed the side distribution of thus provoked artificial cardiac emboli.

METHODS

Fifty-four patients were investigated by TEE and by bilateral TCD of the middle cerebral artery. The following protocol was performed twice: injection of 9 mL of agitated saline without Valsalva maneuver, injection of 9 mL of agitated saline with Valsalva maneuver, injection of 5 mL of a commercial galactose-based contrast agent without Valsalva maneuver, and injection of 5 mL of the galactose-based contrast agent with Valsalva maneuver.

RESULTS

In 18 patients, a right-to-left shunt was demonstrated by TEE and contrast TCD (shunt positive). Twenty-nine patients were negative in both investigations, 1 was positive on TEE and negative on TCD, and 6 patients were only positive on TCD. Both bilateral and repeated recordings increased the sensitivity of contrast TCD. There was a symmetrical distribution of microembolic signals in the right and left middle cerebral artery.

CONCLUSIONS

TCD performed twice and with the use of saline or a galactose-based contrast agent is a sensitive method in the identification of cardiac right-to-left shunts also identified by TEE. The cardiac microemboli in this study did not show any side preference for one of the middle cerebral arteries.

Cerebral vasculopathy in HIV infection revealed by transcranial Doppler: A pilot study

BACKGROUND AND PURPOSE

There is growing evidence for affection of cerebral vessels during human immunodeficiency virus (HIV) infection. We prospectively evaluated cerebrovascular reserve capacity (CRC) in HIV-seropositive patients by transcranial Doppler sonography (TCD) after systemic administration of acetazolamide. We hypothesized that a disturbed vasoreactivity would reflect the cerebral arteries' involvement in HIV infection.

METHODS

We assessed the mean blood flow velocity (BFV) of the middle cerebral artery and its increase after intravenous administration of 1 g acetazolamide (CRC) in 31 HIV-infected individuals without symptoms of cerebrovascular disease (mean+/-SD age, 39+/-11 years). Stenotic or occlusive lesions of the large brain-supplying arteries were excluded by color-coded duplex and transcranial imaging. BFV and CRC were also measured in an age-matched group of 10 healthy control subjects. Patients were classified according to clinical, laboratory, and neurophysiological parameters. We also performed cerebral MRI (n=25) and rheumatological blood tests (n=26).

RESULTS

Baseline BFV and CRC both were significantly reduced in HIV-infected patients as compared with control subjects (P<0.05, Student's t test). These findings did not correlate with duration of seropositivity, helper cell count, or other clinical, rheumatological, and neuroradiological findings.

CONCLUSIONS

Our findings support the hypothesis of a cerebral vasculopathy etiologically associated with HIV infection.

Automatic embolus detection by a neural network

BACKGROUND AND PURPOSE

Embolus detection using transcranial Doppler ultrasound is a useful method for the identification of active embolic sources in cerebrovascular diseases. Automated embolus detection systems have been developed to reduce the time of evaluation in long-term recordings and to provide more "objective" criteria. The purpose of this study was to evaluate the critical conditions of automated embolus detection by means of a trained neural network (EMBotec V5.1 One, STAC GmbH, Germany).

METHODS

In 11 normal volunteers and in 11 patients with arterial or cardiac embolic sources, we performed simultaneous recordings from both middle or both posterior cerebral arteries. In the normal subjects, we produced 1342 additional artifacts to use the latter as false-positives. Detection of microembolic signals (MES) was done offline from digital audiotapes (1) by an experienced blinded investigator used as a reference and (2) by a trained 3-layer-feed-forward neural network.

RESULTS

From the 1342 provoked artifacts the neural network labeled 216 events as microemboli, yielding an artifact rejection of 85%. In microembolus-positive patients the neural network detected 282 events as emboli, among these 122 signals originating from artifacts; 58 "real" events were not detected. This result revealed a sensitivity of 73.4% and a positive predictive value of 56.7. The spectral power of the detected artifact signals was 16.5+/-5 dB above background signal. MES from patients with artificial heart valves had a spectral power of 6.4+/-2.1 dB; however, in patients with other sources of emboli, MES had an averaged energy reflection of 2.7+/-0.9 dB.

CONCLUSIONS

The neural network is a promising tool for automated embolus detection, the formal algorithm for signal identification is unknown. However, extreme signal qualities, eg, strong artifacts, lead to misdiagnosis. Similar to other automated embolus detection systems, good signal quality and verification of MES by an experienced investigator is still mandatory.

Diagnostic benefit of echocontrast enhancement for the insufficient transtemporal bone window

Echocontrast agents (ECA) are known to improve transcranial color-coded duplex (TCCD) imaging, but its diagnostic benefit in the routine clinical setting has not clearly been defined. The authors investigated the diagnostic benefit of ECA application in 54 patients with insufficient transtemporal bone window, consecutively referred to their ultrasound laboratory. According to the precontrast imaging quality, patients were assigned to three categories: A, no intracranial structures or vessel segments visible on B-mode imaging and TCCD (n = 5); and intracranial structures visible on B-mode imaging and vessel segments less than 5 mm in length (B, n = 21), or larger than 5 mm in length (C, n = 28) visible on TCCD. The effect of the echocontrast enhancement was assessed with respect to signal enhancement, imaging quality, and diagnostic confidence. In 49 out of 54 patients (91%), a significant improvement of the imaging quality was noted, enabling 43 (80%) neurovascular diagnoses of sufficient diagnostic confidence. The diagnostic ECA effect was strongly dependent on the precontrast imaging quality: upon echoenhancement, a satisfactory image quality was obtained in none of the patients of category A, as opposed to 16 (76%) and 27 (96%) patients of categories B and C, respectively. In summary, in 80% of our consecutive patient series with insufficient transtemporal bone window, application of ECA allowed for a conclusive TCCD study. Properties of the transtemporal precontrast scans are strongly predictive of the diagnostic benefit and should be taken into the decisive consideration.

[Clinical significance of echocontrast enchancement in neurovascular diagnosis. Review of experience following a year of use]

AIM OF THE STUDY

To evaluate the potential and limitations of echocontrast enhancement using Levovist in a non selected consecutive cohort of neurological patients with insufficient native ultrasound investigations.

METHODS

In 91 patients an indication for echocontrast application was seen after an insufficient extracranial (n = 17), transtemporal (n = 54), and transforaminal (n = 20) Doppler- und color-coded Duplex sonography. Levovist was injected at a concentration of 400 mg/ml and 200-400 mg/ml for the transcranial and extracranial approach, respectively. The effect of the echocontrast enhancement was assessed semiquantitatively with respect to signal enhancement, imaging quality, and diagnostic confidence.

RESULTS

In a total of 83 patients (91%) the signal enhancement led to a moderate to high imaging quality allowing to reach 67 definite neurovascular diagnoses (74%). In subgroup analysis, the amount of sufficiently confident examinations was significantly higher for the transtemporal and transforaminal (both 80%) than for the extracranial approach (47%). The latter was mostly due to artificial signals derived from adjacent neck vessels.

CONCLUSION

Levovist constitutes a safe and highly effective diagnostic tool especially for the transtemporal and transforaminal neurosonographical imaging. By means of a differentiated application of echocontrast agents, its cost-effectiveness can be increased and the need for other potential invasive and expansive neuroimaging methods can be further reduced.

Echocontrast enhanced transcranial colour-coded duplex offers improved visualization of the vertebrobasilar system

OBJECTIVES

By means of transcranial colour-coded duplex sonography (TCCD) through the foramen magnum, the intracranial vertebral arteries (VAs) and the basilar artery (BA) can be investigated. In this study we evaluated the additional diagnostic value of echocontrast administration in patients with an insufficient pre-contrast TCCD investigation of the vertebrobasilar system.

MATERIAL AND METHODS

In 22 patients the intracranial VAs and the proximal, middle and distal BA were evaluated before and after the application of 4 g of the echocontrast agent Levovist. The length of the different vessel segments visualized on colour mode before and after echocontrast, and the diagnostic benefit and the diagnostic confidence were assessed.

RESULTS

Echocontrast enlarged in each vessel segment the length that could be visualized. Using echocontrast, in 5/22 patients (23%) definite and probable pathological findings unnoted in the native scans were detected. In 12 additional patients (55%) the investigator and the clinician became confident with the vascular diagnosis by echocontrast to a degree that angiography could be avoided. In only 3/22 patients (14%) no gain and in 2/22 patients (9%) an insufficient diagnostic gain was noted.

CONCLUSIONS

Our study demonstrates that echocontrast provides effective Doppler signal enhancement and considerably increases the diagnostic gain of TCCD in the intracranial vertebral and basilar vasculature.

Microembolic load in asymptomatic patients with cardiac aneurysm, severe ventricular dysfunction, and atrial fibrillation. Clinical and hemorheological correlates

Transcranial Doppler sonography has become a widely used method for detecting cerebral circulating microemboli (ME) arising from the carotid arteries or the heart. Yet, studies on subgroups of patients with distinct cardiac sources of embolism are still limited. The same holds true for investigation on the relationship between microembolization and hemorheological parameters. A total of 142 patients suffering from left ventricular aneurysm (LVA, n = 52), severe left ventricular dysfunction (LVD, n = 43), or chronic atrial fibrillation (AF, n = 47) were enrolled in this study. All patients had been neurologically asymptomatic for at least 1 month. Further relevant embolic disorders of the carotid arteries and the heart had been excluded. Unilateral monitoring for ME over the middle cerebral artery was performed for 30 min. Blood was drawn after each monitoring for determination of plasmatic coagulation parameters, as well as plasma viscosity, and platelet reactivity. The overall prevalence of ME was 31%, with a slightly higher prevalence in patients with LVA (37%) compared to patients suffering from AF (30%) or LVD (26%). With single-factor analysis, a trend towards higher ME prevalences was found with (a) a history of remote embolic events, (b) ineffective anticoagulation, (c) increased platelet aggregation, or (d) increased plasma viscosity (all p > 0.1). The combination of ineffective anticoagulation in conjunction with increased platelet aggregation, however, was significantly associated with higher ME rates even after adjustment for other factors by logistic regression analysis. Our results demonstrate a low ongoing microembolic activity in asymptomatic patients suffering from LVA, LVD and AF. An activated plasmatic coagulation system together with increased platelet aggregation contributes to ME generation.

Potential and limitations of echocontrast-enhanced ultrasonography in acute stroke patients: a pilot study

BACKGROUND AND PURPOSE

Ultrasonography (US) is a well-established method used to assess the brain-supplying arteries in the acute stroke setting. However, several technical and anatomic limitations are known to reduce its diagnostic accuracy and confidence level. Echocontrast agents (ECA) are known to improve the signal-to-noise ratio by enhancing the intensity of the reflecting Doppler signal. We undertook this prospective study to evaluate the diagnostic value of ECA in a consecutive, nonselected cohort of acute stroke patients with insufficient native US investigations.

METHODS

During a 1-year period, 25 patients were examined within 48 hours of the onset of stroke. The need for ECA was due to an insufficient transtemporal (n=18), transforaminal (n=4), or extracranial (n=3) imaging of arteries potentially involved in the ischemic event. In 12 patients, a diagnostic suspicion could natively be raised, whereas in the other 13 patients, the strongly reduced image quality did not allow for any neurovascular conclusions. Four grams of Levovist was injected at a concentration of 200 mg/mL and 400 mg/mL for the extracranial and transcranial insonations, respectively. The effect of the echocontrast enhancement was assessed with respect to (1) signal enhancement, (2) image quality, (3) final diagnostic confidence, and (4) the need for additional neurovascular imaging methods.

RESULTS

In all but one patient (96%), a strong signal enhancement was noted, leading to a moderate (n=11) or strong improvement (n=10) of the transcranial image quality. Thus in a total of 18 patients (72%), the echoenhancement provided a neurovascular diagnosis of sufficient confidence. This led to the confirmation of the previously suspected findings and disclosed three further occlusions and four stenoses of the intracranial arteries. In contrast, for the three extracranial examinations the image quality was not sufficiently improved because of persistent color artifacts derived from adjacent neck vessels. Besides the seven patients with inconclusive examinations, five patients with conclusive echoenhanced US studies (48% in total) demanded additive neurovascular imaging studies, based on the clinical decision of the attending physicians. This led to confirmation of all high-confident sonographic diagnoses.

CONCLUSIONS

In summary, in approximately three fourths of our acute stroke patients with insufficient native US investigations, echocontrast enhancement enabled a reliable neurovascular diagnosis, allowing the cancellation of additive neurovascular imaging procedures in half of our cohort. Our preliminary results suggest that ECA can reasonably support the early cerebrovascular workup in the acute stroke setting.

Collateralization of an occluded internal carotid artery via a vas vasorum

BACKGROUND

Reopening of an occluded internal carotid artery (ICA) is often seen in dissections but only rarely occurs in atherothrombotic occlusion of the internal carotid artery.

CASE DESCRIPTION

A 60-year-old man suffered a minor stroke with dysphasia in March 1995. Color-coded duplex ultrasonography of his neck arteries revealed a left ICA occlusion. He was placed on a regimen of aspirin and followed up clinically and with ultrasonography. At follow-up 18 months later, the patient was asymptomatic. On duplex ultrasonography his left occluded ICA was found to be reopened, with a residual, proximal, high-grade stenosis. However, intra-arterial digital subtraction angiography demonstrated a persistent ICA occlusion and a vas vasorum originating from the carotid bulb and draining into the ICA distal to the occlusion.

CONCLUSIONS

The rare collateralization of an occluded ICA by vasa vasorum seems to take several months. It can be a pitfall in the ultrasound diagnosis of carotid artery occlusive disease.

Oxygen inhalation can differentiate gaseous from nongaseous microemboli detected by transcranial Doppler ultrasound

BACKGROUND AND PURPOSE

Clinically silent circulating microemboli can be detected by transcranial Doppler sonography. The composition of these emboli in different clinical conditions is unclear.

METHODS

We performed 1-hour transcranial Doppler sonographic recordings from the middle cerebral or posterior cerebral artery in 20 patients with mechanical prosthetic heart valves, in 78 patients with an arterial embolic source, and in 20 control subjects. During 30 minutes of this recording, the patients inspired room air and 6 L of oxygen per minute via a loosely fitting facial mask; during the remaining 30 minutes, they breathed room air only.

RESULTS

There was a significant decline of embolic signals (ES) under oxygen in the patients with mechanical prosthetic cardiac valves (144 ES without oxygen versus 63 ES with oxygen; P = .002) but not in the patients with arterial embolic sources (145 ES without oxygen versus 135 ES with oxygen; P = NS). In the control subjects, no ES were found.

CONCLUSIONS

ES in patients with mechanical prosthetic cardiac valves correspond mainly to gas bubbles. Oxygen inhibits the cavitation process of mechanical prosthetic heart valves or speeds up redissolution of gas bubbles generated by cavitation. In contrast, solid microemboli originating from thrombus or atheroma cannot be suppressed by oxygen inhalation. This simple method of oxygen inhalation should help to clarify the composition of microemboli in various clinical and experimental settings.

Oxazepam esters. 1. Correlation between hydrolysis rates and brain appearance of oxazepam

Esters of the centrally acting oxazepam were investigated to find quantitative correlations between the pharmacokinetics of the parent drug and in vitro biotransformation rates and physicochemical properties of its prodrugs. The 14C-labeled aliphatic and omega-phenyl-substituted esters were administered intravenously to mice. Brain levels of the esters and oxazepam were determined and the latter was fitted to a simplified exponential equation. In vitro hydrolysis rate of the esters catalyzed by the hepatic microsomal fraction was measured with a pH stat. Pharmacokinetic constants characterizing the rising part of oxazepam brain levels correlate well with the chromatographic RM values and with in vitro maximal hydrolysis rates of the esters. The hydrolysis is capacity limited in the liver. In a closely related set of aliphatic esters, oxazepam brain penetration also correlates with the steric constant (ES) of its esters.