Transcranial Doppler and computed tomography angiography for detecting cerebral vasospasm post-aneurysmal subarachnoid hemorrhage

Cerebral vasospasm is a life-threatening complication following aneurysmal subarachnoid hemorrhage (aSAH). While digital subtraction angiography (DSA) is the current gold standard for detection, the diagnostic performance of computed tomography angiography (CTA) and transcranial Doppler (TCD) remains controversial. We aimed to summarize the available evidence and provide recommendations for their use based on GRADE criteria. A literature search was conducted for studies comparing CTA or TCD to DSA for adults ≥ 18 years with aSAH for radiographic vasospasm detection. The DerSimonian-Laird random-effects model was used to pool sensitivity and specificity and their 95% confidence intervals (CI) and derive positive and negative pooled likelihood ratios (LR + /LR -). Out of 2070 studies, seven studies (1646 arterial segments) met inclusion criteria and were meta-analyzed. Compared to the gold standard (DSA), CTA had a pooled sensitivity of 82% (95%CI, 68-91%) and a specificity of 97% (95%CI, 93-98%), while TCD had lower sensitivity 38% (95%CI, 19-62%) and specificity of 91% (95%CI, 87-94%). Only the LR + for CTA (27.3) reached clinical significance to rule in diagnosis. LR - for CTA (0.19) and TCD (0.68) approached clinical significance (< 0.1) to rule out diagnosis. CTA showed higher LR + and lower LR - than TCD for diagnosing radiographic vasospasm, thereby achieving a strong recommendation for its use in ruling in or out vasospasm, based on the high quality of evidence. TCDs had very low LR + and a reasonably low LR - , thereby achieving a weak recommendation against its use in ruling in vasospasm and weak recommendation for its use in ruling out vasospasm.

Prevalence of Patent Foramen Ovale in North Indian Cryptogenic Young Strokes

BACKGROUND

: Strokes of the undetermined cause or cryptogenic strokes (CS) account for 30-40% of ischemic strokes. Paradoxical embolism secondary to patent foramen ovale (PFO) may be associated with CS. Transcranial Doppler (TCD) with bubble contrast is a noninvasive bedside tool for diagnosis of right-to-left shunt (RLS) with high sensitivity and specificity. Data on the prevalence of PFO in CS in India are lacking. We determined the prevalence of RLS likely secondary to PFO in cryptogenic young strokes of the north Indian population using TCD with bubble contrast.

PATIENTS AND METHODS

: In this hospital-based prospective cross-sectional study, TCD with bubble contrast was performed in 57 young (age 15 > 45 years) CS and 50 healthy controls for the detection of RLS. The risk of paradoxical embolism (RoPE) score was calculated from various variables such as age, presence of cortical stroke on neuroimaging, and absence of vascular risk factors.

RESULTS

: 57 young CS and 50 healthy controls were recruited. TCD with bubble contrast was positive in 31% cases vs 6% in controls (P = 0.001). All patients with TCD positive for RLS had superficial cortical infarcts (P = 0.03). The median RoPE score of our patients was 9 (range: 7-10).

CONCLUSIONS

: There is a high prevalence of RLS likely secondary to PFO in cryptogenic young strokes in north India. TCD with bubble contrast is an excellent bedside tool for the detection of RLS.

Impact of Stellate Ganglion Block in the Management of Cerebral Vasospasm: A Prospective Interventional Study

BACKGROUND

Stellate ganglion block (SGB) causes blockage of sympathetic nerve activity, which may lead to intracerebral vessel dilatation and relieve cerebral vasospasm in patients of aneurysmal subarachnoid hemorrhage (aSAH).

OBJECTIVE

The aim of this study was to evaluate the efficacy and safety of SGB to relieve cerebral vasospasm on clinicoradiological parameters.

MATERIALS AND METHODS

We prospectively included 20 patients with clinical and angiographic evidence of vasospasm post aneurysmal clipping. Cerebral blood flow velocity and Lindegaard ratio were assessed using transcranial Doppler (TCD). Location of vasospasm, vessel diameter, vasospasm severity, parenchymal filling time, and venous sinus filling time were assessed on digital subtraction angiography (DSA). Patients received ultrasound-guided SGB with 10 mL of 0.5% bupivacaine on the ipsilateral side of the vasospasm. After 30 minutes, the neurological status, TCD, and DSA parameters were reevaluated.

RESULTS

After SGB, there was statistically significant reduction in the middle cerebral artery (MCA) peak systolic velocity (P = 0.005), mean flow velocity (P = 0.025), and Lindegaard ratio (P = 0.022) on TCD. We observed significant dilatation in the mean vessel diameter measured at the mid-M1 segment of MCA (P = 0.003) and mid-A1 segment of ACA (P = 0.002) on DSA. The mean parenchymal filling time and mean venous sinus filling time decreased nonsignificantly after SGB (P = 0.163/0.104). Neurological improvement was observed in five (25%) patients.

CONCLUSION

SGB has positive clinicoradiological influence in the management of cerebral vasospasm of large vessels. However, its effect on cerebral microvasculature is limited and needs a larger database for further analysis.

Effects of 2D-Shear Wave Elastography on Brain-Derived Neurotrophic Factor (BDNF) in the Brains of Neonatal Mice and Exploration of the Mechanism

BACKGROUND The aim of this study was to explore the effect and duration of 2-dimensional shear wave elastography (2D-SWE) irradiation on the expression of brain-derived neurotrophic factor (BDNF) in the brains of neonatal mice and to preliminarily investigate whether its mechanism is neuronal apoptosis. MATERIAL AND METHODS Neonatal mice (within 48 hours of birth) were subjected to 2D-SWE irradiation of the brain for 10 minutes (group S1), 20 minutes (group S2), and 30 minutes (group S3). The mice were sacrificed immediately after irradiation or 24 hours after irradiation. Brains were collected for real-time polymerase chain reaction (RT-PCR) and western blot experiments to determine the expression of BDNF in each group. TdT-mediated dUTP nick-end labeling (TUNEL) was performed to observe neuronal apoptosis in the brain. RESULTS The results of PCR and western blots from the brains of neonatal mice that were sacrificed immediately after irradiation show that S1, S2, and S3 were significantly different from those in the control group. The PCR and western blot results of brain tissues from neonatal mice sacrificed at 24 hours after irradiation showed that there was no significant difference between the S1, S2, S3, and control groups. The results of TUNEL experiments showed that there was no statistically significant difference in the number of apoptotic neurons between the S1, S2, S3, and control groups. CONCLUSIONS 2D-SWE irradiation of neonatal mice for more than 10 minutes downregulated the expression of BDNF. This effect disappeared within 24 hours after the irradiation, and the 2D-SWE scan seemed not to induce neuronal apoptosis.

Transtemporal ultrasound application potentially elevates brain temperature: results of an anthropomorphic skull model

PURPOSE

Transtemporal sonothrombolysis is a tool for a more effective treatment in acute stroke patients. However, some reports revealed side effects, which might be potentially connected to temperature elevation. To gain better insight into cerebral temperature changes during transtemporal sonication, diagnostic and therapeutic ultrasound (US) applications were evaluated using an anthropomorphic skull model.

MATERIALS AND METHODS

The impact of diagnostic (PW-Doppler, 1.8-MHz, 0.11 W/cm², TIC 1.2) and therapeutic (1-MHz and 3-MHz, 0.07 - 0.71 W/cm², continuous and pulsed mode) US application on temperature changes was evaluated at the level of muscle/temporal bone (TB), TB/brain, brain and at the middle cerebral artery (MCA) using 4 miniature thermocouples along the US beam. Sonication lasted 120 minutes.

RESULTS

Diagnostic ultrasound revealed a maximum temperature increase of 1.45°/0.60°/0.39°/0.41°C (muscle/TB, TB/brain, brain, MCA) after 120 minutes. Therapeutic-1-MHz ultrasound raised temperature by 4.33°/2.02°/1.05 °C/0.81°C (pulsed 1:20) and by 10.38°/4.95°/2.43°/2.08°C (pulsed 1:5) over 120 minutes. Therapeutic-3-MHz US raised temperature by 4.89°/2.56°/1.24/1.25°C (pulsed 1:20) and by 14.77°/6.59°/3.56°/2.86°C (pulsed 1:5) over 120 minutes, respectively. Continuous application of therapeutic US (1-MHz and 3-MHz) led to a temperature increase of 13.86°/3.63°/1.66°/1.48°C and 17.09°/4.28°/1.38/0.99°C within 3 minutes.

CONCLUSION

Diagnostic PW-Doppler showed only a moderate temperature increase and can be considered as safe. Therapeutic sonication is very powerful in delivering energy so that even pulsed application modes resulted in significant and potentially harmful temperature increases.

Thermal effects of diagnostic ultrasound in an anthropomorphic skull model

PURPOSE

Exposure to diagnostic ultrasound (US) can significantly heat biological tissue although conventional routine examinations are regarded as safe. The risk of unwanted thermal effects increases with a high absorption coefficient and extended insonation time. Certain applications of transcranial diagnostic US (TC-US) require prolonged exposure. An anthropomorphic skull model (ASM) was developed to evaluate thermal effects induced by TC-US of different modalities. The objective was to determine whether prolonged continuous TC-US application results in potentially harmful temperature increases.

MATERIALS AND METHODS

The ASM consists of a human skull with tissue mimicking material and exhibits acoustic and anatomical characteristics of the human skull and brain. Experiments are performed with a diagnostic US device testing four different US modalities: Duplex PW (pulsed wave) Doppler, PW Doppler, color flow Doppler and B-mode. Temperature changes are recorded during 180 minutes of insonation.

RESULTS

All measurements revealed significant temperature increases during insonation independent of the US modality. The maximum temperature elevation of + 5.25° C (p < 0.001) was observed on the surface of the skull exposed to duplex PW Doppler. At the bone-brain border a maximum temperature increae of + 2.01 °C (p < 0.001) was noted. Temperature increases within the brain were < 1.23 °C (p = 0.001). The highest values were registered using the duplex PW Doppler modality.

CONCLUSION

TC-US induces significant local heating effects in an ASM. An application duration that extends routine clinical periods causes potentially harmful heating especially in tissue close to bone. TC-US elevates the temperature in the brain mimicking tissue but is not capable of producing harmful temperature increases during routine examinations. However, the risk of thermal injury in brain tissue increases significantly after an exposure time of > 2 hours.

Does routine transcranial duplex ultrasound heat up the patient brain?

PURPOSE

The effect of transcranial duplex ultrasound (US) on the intraventricular temperature in patients was analyzed. Temperature increases during examination have been identified as a potential risk factor but only data from model studies is currently available.

MATERIALS AND METHODS

Patients who had an intracranial pressure/temperature transducer implanted and underwent US assessment were included. In an examination series (B-mode, combined B- and color mode, combined B- and color mode plus Doppler, 3 min for each mode), the intracranial thermodilution thermistor was focused while intraventricular temperature and body temperature (bladder catheter or rectal probe) were recorded continuously and temperature changes were analyzed.

RESULTS

Thirty-one US examinations were performed in 14 patients. Twenty-six examinations in 9 patients in which the intracranial temperature probe was depicted were included. Initial patient temperatures ranged from 35.1dgC to 38.7dgC. No significant increase or decrease in intracranial temperature was seen after the first (B-mode), second (B- and color mode) and third (B- and color mode plus Doppler) duplex US examination. T-test for paired samples showed a constant temperature throughout US examination (two-sided significance: 1.000, 1.000, 0.731).

CONCLUSION

Routine transcranial duplex ultrasound does not increase the intracranial temperature in patients.

Safety and efficacy of the sonographic acceleration of the middle cerebral artery recanalization: results of the pilot thrombotripsy study

The aim was to demonstrate the safety and efficacy of continuous ultrasound monitoring of the artery occlusion area (sonothrombotripsy) in patients with acute middle cerebral artery (MCA) occlusion. A total of 52 consecutive patients with acute MCA occlusion were included in the thrombotripsy group. Doppler monitoring of the region of occlusion was performed for up to 45 min. The control group was created from the NAIS study database. Patients were matched for their vascular status, age, sex, artery occlusion, NIHSS at admission, rt-PA treatment and time to the first ultrasound examination. The number of recanalized arteries at 6 and 24 h after the onset of symptoms, the number of independent patients (mRS 0-2 versus 3-6) after 90 d, and the number of serious adverse events were statistically evaluated. In the thrombotripsy group, 19 patients (36.5%) had complete recanalization and 27 (51.9%) patients had partial recanalization at 1 h after the start of the TCCS monitoring. Higher recanalization rates at 6 and 24 h after stoke onset were also seen compared with controls (69.2% versus 7.7% and 92.3% versus 61.5% complete recanalizations, respectively, p < 0.05). Independence (mRS 0-2) at day 90 was achieved by 61.5% of the thrombotripsy patients and 32.7% controls, p < 0.05, odds ratio 1.88 (95% confidence interval = 1.23 - 2.90). In both groups, two symptomatic intracerebral hemorrhages and one symptomatic brain edema occurred. Sonothrombotripsy with diagnostic transcranial duplex technology is safe and may offer benefit in addition to standard of care stroke treatment.

Diagnostic transcranial ultrasound perfusion-imaging at 2.5 MHz does not affect the blood-brain barrier

The purpose was to assess whether standard ultrasound (US) perfusion-imaging by means of contrast-enhanced transcranial color-coded sonography (TCCS) affects the blood-brain barrier (BBB) in patients with small-vessel disease (SVD). One week after a screening MRI to exclude a preexisting BBB disruption, unilateral TCCS phase inversion harmonic imaging (PIHI) was performed in an axial diencephalic plane after intravenous bolus application of 2.5 mL SonoVue (IGEA, Bracco, Italy). Magnetic resonance imaging (MRI) was performed immediately after US. In five patients, PIHI was performed applying a mean mechanical index (MI) of 0.7 +/- 0.1 for a time period of 2.5 min. MRI was started 12 +/- 2 min after US contrast injection. Comparisons of initial and post-US MRI by four blinded readers did not show any signs of BBB disruption. It is concluded that standard contrast-enhanced US perfusion imaging in patients with SVD did not lead to MRI-detectable BBB changes. This gives further evidence for safety of diagnostic US. Future investigations with larger sample sizes and higher-field MRI might give further insights into potential bioeffects of diagnostic, as well as therapeutic, contrast-enhanced transcranial US.

Changes in haemocoagulation in healthy volunteers after a 1-hour thrombotripsy using a diagnostic 2–4 MHz transcranial probe

INTRODUCTION

The aim was to monitor the changes in haemocoagulation parameters in healthy volunteers after a thrombotripsy with 1-hour transcranial Doppler monitoring using a 2-4 MHz probe.

MATERIALS AND METHODS

About 10 healthy volunteers underwent a 1-hour thrombotripsy of the middle cerebral artery (MCA), thrombotripsy of the radial artery and a standard 20-min neurosonologic examination (NSE) in 2-week intervals. Platelet count, aPTT, prothrombin time, fibrinogen, D-dimers, tPA, FDP, alpha-2-antiplasmin (AP), plasminogen, PAI-1 antigen, time of euglobulin clot lysis (ECL), homocysteine, and lipoprotein (a) were examined before, at the end and 24 h after a thrombotripsy. All adverse events were monitored.

RESULTS

After a thrombotripsy of the MCA, PAI-1 antigen, tPA antigen, fibrinogen and AP activity were significantly decreased by a mean of 32, 23, 7, and 4% respectively (P < 0.05 in all cases). After a thrombotripsy of the RA, there was a significant decrease in tPA antigen alone by an average of 14% (P < 0.05). Standard NSE did not affect any of the measured factors.

CONCLUSIONS

Thrombotripsy with 1-hour TCD monitoring using a 2-4 MHz diagnostic probe may affect the fibrinolytic system in humans.

Does Long-Term Continuous Transcranial Doppler Monitoring Require a Pause for Safer Use?

BACKGROUND

Transcranial Doppler sonography (TCD) has been used widely for long-term monitoring of cerebral blood flow without adverse reports. However, attention has not been adequately paid to the fact that an increase in the time period of TCD insonation causes brain temperature to rise due to ultrasound absorption by tissue and the skull. We measured the actual temperature rise in local brain tissue induced by TCD insonation over a long time period during in vivo animal experiments in order to verify whether or not a pause is required in long-term, continuous TCD monitoring.

METHODS

We inserted thermocouples into the skull-brain interface (SBI) of 15 New Zealand White rabbits (10: TCD application group; 5: control group, TCD non-application group). The TCD probe was placed on the parietal bone, and changes in SBI temperature (SBIT) were measured for 90 min. TCD was set at maximum output level (0.2 W, 2 MHz).

RESULTS

SBIT in the TCD group increased rapidly to 3.47 degrees C within 25 min and then reached a plateau. The maximum time for safe continuous TCD application is estimated to be 33 min.

CONCLUSIONS

Even though there are large differences in factors, such as brain volume and environmental conditions, between rabbits and humans, there is less difference in their cerebral blood flow per brain weight, which is the parameter that is mainly associated with heat reduction. Accordingly, the findings of the present experiment suggest that long-term TCD monitoring in clinical use should include a pause after every 30 min of insonation to avoid thermal damage to the brain surface.

Acute stroke: therapeutic transcranial color duplex sonography

The enhancement of thrombolysis by ultrasound energy (sonothrombolysis) is an emerging field of interest in the treatment of acute ischemic stroke. Recent in vitro and clinical studies have investigated the effects of using transcranially applied 'diagnostic' ultrasound for this purpose. Using transcranial color duplex sonography (TCDS) allows an examiner to identify the site of occlusion and focus the ultrasound beam on it. Clinical studies using TCDS to enhance thrombolysis in acute middle cerebral artery occlusions have revealed an accelerating effect on recanalization, as well as a tendency for a better outcome. Data from small sample studies suggest that this effect on recanalization is present not only in combination with recombinant tissue plasminogen activator (rt-PA), but also with any thrombolytic drug. However, when TCDS was used in combination with rt-PA, an increase in the rate of asymptomatic and symptomatic intracerebral hemorrhages tended to occur compared to patients treated with thrombolysis alone. Larger sample-sized clinical studies should be conducted in the future to evaluate the safety and efficacy of using TCDS for sonothrombolysis. This method should also be further developed to determine its effect when used in combination with other types of ultrasound and thrombolytic drugs.

Acute stroke: therapeutic transcranial Doppler sonography

Ultrasound (US) has emerged as a new tool to treat ischemic stroke. The potential advantage of US is decreased risk of systemic bleeding complications due to its site-specific effect. Moreover, external application is noninvasive and is readily available. Experimental studies showed that low intensity (<or=2W/cm2) US safely enhanced thrombolytic drug activity within a wide range of frequencies (0.04-3.4 MHz). In humans, transcranial sonothrombolysis with mid-kHz frequencies showed an unacceptably high rate of intracranial bleeding, while the use of 2MHz yielded promising results in The Combined Lysis of Thrombus in Brain Ischemia Using Transcranial Ultrasound and Systemic TPA (CLOTBUST) study. This study was a phase II randomized clinical trial that included patients with middle cerebral artery (MCA) occlusion within 3 h of stroke onset, who were treated with standard dose of tissue plasminogen activator (t-PA). Residual flow in MCA was monitored with 2MHz US in one group, and the rate of complete recanalization and dramatic clinical recovery significantly increased as compared to t-PA alone. This chapter further discusses diagnosis of an acute occlusion and recanalization using the thrombolysis in brain ischemia (TIBI) waveform flow grading scale, application of fast track insonation protocol, and administration of US. Also, the potential enhancement of sonothrombolysis with microbubbles is discussed.

Transcranial Low-Frequency Ultrasound-Mediated Thrombolysis in Brain Ischemia

Background— Clinical studies using ultrasound at diagnostic frequencies in transcranial Doppler devices provided encouraging results in enhancing thrombolysis with tissue plasminogen activator (tPA) in acute stroke. Low-frequency ultrasound does not require complex positioning procedures, penetrates through the skull better, and has been demonstrated to accelerate thrombolysis with tPA in animal experiments in wide cerebrovascular territories without hemorrhagic side effects. We therefore conducted the first multicenter clinical trial to investigate safety of tPA plus low-frequency ultrasound (300 kHz).

Methods— Acute stroke patients within a 6-hour time window were included (National Institutes of Health Stroke Scale scores >4). Magnetic resonance imaging (MRI) was used to document vascular occlusion and to rule out cerebral hemorrhage. Patients were allocated to combination therapy alternately; the first patient received tPA only, the second patient received tPA plus ultrasound, etc. Follow-up included serial MRI directly thereafter and 24 hours later to confirm recanalization and tissue imaging. Clinical recovery was measured after treatment and 3 months later.

Results— 26 patients (70.4±9.7 years) entered the trial (12 tPA, 14 tPA plus ultrasound). The study was prematurely stopped because 5 of 12 patients from the tPA only group but 13 of 14 patients treated with the tPA plus ultrasound showed signs of bleeding in MRI ( P <0.01). Within 3 days of treatment, 5 symptomatic hemorrhages occurred within the tPA plus ultrasound group. At 3 months, neither morbidity nor treatment-related mortality or recanalization rates differed between both groups.

Conclusions— This study demonstrated bioeffects from low-frequency ultrasound that caused an increased rate of cerebral hemorrhages in patients concomitantly treated with intravenous tPA.

The threshold for brain damage in rabbits induced by bursts of ultrasound in the presence of an ultrasound contrast agent (Optison)

The purpose of this study was to test the hypothesis that burst ultrasound (US) in the presence of a US contrast agent using parameters similar to those used in brain blood flow measurements causes tissue damage. The brains of 10 rabbits were sonicated in 3-8 locations with 1.5-MHz, 10- micro s bursts repeated at a frequency of 1 kHz at temporal peak acoustic pressure amplitudes ranging from 2 to 12.7 MPa. The total sonication time for each location was 20 s. Before each sonication, a bolus of US contrast agent was injected IV. Contrast-enhanced magnetic resonance (MR) images were obtained after the sonications to detect local enhancement in the brain. Whole brain histological evaluation was performed, and the sections were stained with hematoxylin and eosin (H and E), TUNEL, and vanadium acid fuchsin (VAF) staining to evaluate tissue effects, including apoptosis and ischemia. Both the magnetic resonance imaging (MRI) contrast enhancement and histology findings indicated that brain tissue damage was induced at a pressure amplitude level of 6.3 MPa. The damage included vascular wall damage, hemorrhage and, eventually, necrosis. Mild vascular damage was observed localized in a few microscopic tissue volumes in about half of the sonicated locations at all pressure values tested (down to 2 MPa). However, these sonications did not induce any detectable tissue effects, including ischemia or apoptosis. As a conclusion, the study showed that the US exposure levels currently used for blood flow measurements in brain are below the threshold of blood-brain barrier opening or brain tissue damage. However, one should be aware that brain damage can be induced if the exposure level is increased.

Potential pitfalls in cranial sonography

BACKGROUND

We present several anatomic variants of the brain and artifacts related to scanning techniques which could be misinterpreted as lesions on neonatal cranial sonography.

MATERIALS AND METHODS

The findings were derived from US studies performed on 176 premature infants and 26 full-term newborns, using the anterior, posterior and mastoid fontanelles as acoustic windows.

RESULTS

The pseudolesions are divided into three groups: ventricular system (asymmetric lateral ventricle size and coarctation of the lateral ventricles); choroid plexus ("split" choroid, "truncated" choroid and choroid cyst); and brain parenchyma (peritrigonal blush, thalamic pseudolesion, pseudo-absence of the inferior vermis, occipital pseudomass and calcar avis simulating intraventricular clot). We provide images of these pseudolesions and clues to their differentiation from true brain pathology. Images of several brain disorders are included for comparison. Knowledge of these potential pitfalls is essential for proper interpretation of US brain studies and will help to avoid the use of other more invasive diagnostic tests.

CONCLUSIONS

Misleading images seen on US examination of the neonatal brain that could be misinterpreted as pathology are presented, with clues to their differentiation from true lesions.

Sonographic characterisation of radiation-induced carotid artery stenosis

BACKGROUND AND PURPOSE

To study the distribution, extent and sonographic characterisation of radiation-induced carotid artery stenosis in nasopharyngeal carcinoma (NPC) patients.

METHODS

The distribution of plaques, the extent of stenosis, and the sonographic characterisation of the plaque at maximum stenosis were recorded in 71 NPC patients. The results were compared with the ultrasound results of a control group of 142 patients presenting with symptoms of cerebrovascular disease or carotid bruit.

RESULTS

NPC patients had a higher incidence of carotid stenosis (77 vs. 50.7%). The common carotid arteries were most commonly affected by radiation-induced stenosis (93/142 vs. 37/284 in the control group), whereas the carotid bulb was the most commonly affected (56/284) site in the control group. Significantly more NPC patients had moderate-to-severe stenosis (21/71 vs. 27/142). Analysis of the sonographic appearance of radiation-induced and atherosclerotic plaques showed more diffuse involvement in the post-radiation group. Non-calcified plaques and intraplaque hypoechoic foci were also more frequent in the post-radiation group.

CONCLUSIONS

Radiation-induced carotid stenosis is more diffuse in distribution, is associated with more severe luminal stenosis and has different sonographic plaque characterisation compared with carotid stenosis without radiation exposure.

What is the most sensitive non-invasive imaging strategy for the diagnosis of intracranial aneurysms?

OBJECTIVES

To determine whether combining non-invasive tests for intracranial aneurysms together would significantly improve aneurysm detection over individual tests.

METHODS

114 patients undergoing intra-arterial digital subtraction angiography to confirm or exclude an intracranial aneurysm were also examined by CT angiography, MR angiography, and transcranial power Doppler ultrasound. The reviewers and ultrasonographers were blinded to the angiogram result, other imaging results and all clinical information.

RESULTS

The combination of non-invasive tests did improve diagnostic performance on a per patient basis. The combination of power Doppler and CT angiography had the greatest sensitivity for aneurysm detection (0.83; 05% confidence interval (95% CI) 0.66-0.93) and the level of agreement for this strategy with the reference angiographic standard was excellent (kappa 0.84; 95% CI 0.72-0.95). The improvement in sensitivity of adding power Doppler to CT angiography was not significant (p=0.55) but the improvement in the level of agreement with the reference standard was substantial. However, even the most sensitive combination strategy performed poorly in the detection of small (3-5 mm) and very small (<3 mm) aneurysms with a sensitivity of 0.43 (95% CI 0.23-0.66) and 0.00 (95% CI 0.00-0.31) respectively.

CONCLUSIONS

The addition of transcranial power Doppler ultrasound to either CT angiography or MR angiography does improve diagnostic performance on a per patient basis but aneurysms of 5 mm or smaller can still not be reliably identified by current standard clinical non-invasive imaging modalities.

Evaluation of posterior cerebral artery blood flow with transcranial Doppler sonography: value and risk of common carotid artery compression

PURPOSE

Investigations of the posterior cerebral arteries (PCA) by transcranial Doppler sonography (TCD) may be less reliable than investigations of the anterior part of the circle of Willis. Nevertheless, a true PCA may be identified by manual compression of the proximal common carotid artery (CCA) during TCD. Therefore, we used CCA compression in clinically indicated TCD studies and assessed retrospectively its risks and prospectively its benefits for PCA evaluations.

METHODS

Using the transtemporal approach, we prospectively assessed flow velocities in posteriorly located blood vessels in 180 consecutive patients before and during CCA compression. The complications of CCA compression were retrospectively reviewed in all 3,383 clinical TCD investigations performed over an 8-year period.

RESULTS

Decreased flow velocities during ipsilateral CCA compression occurred in 17% of patients. A PCA-like vessel with perfusion from the carotid artery or PCA supply from the carotid circulation was unmasked. Mixed distal PCA support by the posterior communicating artery and proximal PCA could not be shown by TCD. Transient cerebral symptoms occurred in less than 0.4% of the 3,383 retrospectively reviewed TCD investigations; no other adverse effects were seen.

CONCLUSIONS

TCD without CCA compression may lead to false identification of the PCA. Since transient cerebral symptoms during CCA compression are rare, CCA compression can be used when a clinical TCD investigation of intracranial collateral blood flow compensation is indicated or when the identification of a cerebral artery is uncertain.

Physiologic, histologic, and neurologic responses to simultaneous bilateral cerebral vessel Doppler imaging at high beam intensity

This study evaluates physiological fluid heating during continuous bilateral insonation at 530 mW/cm2 for 8 h in a bench simulation. It also examines the physiologic, histopathologic, and neurologic effects of bilateral Doppler imaging of middle cerebral artery (MCA) blood flow velocity using ultrasonic beams with 530 mW/cm2 intensity in a canine model immediately after and 2 weeks after insonation. In saline-filled containers, instrumented with opposing Doppler probes angled 10 degrees off axis, temperature was recorded at 15-min intervals for approximately 8 h at the intersection of the Doppler probe axes. Three conditions were tested: 1) an ambient control, 2) continuous bilateral insonation at 530 mW/cm2 per channel with the thermistor in position, and 3) intermittent thermistor insertion. In one group of canines, physiopathologic responses during continuous bilateral insonation of the MCAs for 8 h at 2 MHz and 530 mW/cm2 were studied. Brains were prepared for histologic examination immediately after insonation. Cerebral temperature; arterial, venous, pulmonary artery, and capillary wedge pressures; electrocardiogram; cardiac output; MCA velocity; and arterial blood gases were monitored. In a second group of canines, a neurologic evaluation was performed before and after insonation and again after 2 weeks. Brain tissue was evaluated histologically after the last neurologic examination. Light microscopic study was used for all histologic evaluations. In the bench experiments, a net temperature rise in the fluid of the simulation amounted to 0.0075 degrees C/h in the overlap region after correction for ambient temperature effects and artifact thermistor heating. In canines, brain temperature (after correction for core body temperature changes and artifact heating of the thermistor) rose a mean of 0.2 degrees C (p < 0.05) by the first hour, thereafter unchanging. No significant changes in the physiologic, neurologic, or histologic evaluations were observed in either of the experimental groups.