Impact of ultrasound contrast agents in cerebrovascular diagnostics

Improved modelling of ultrasound contrast agent diminution for blood perfusion analysis

Ultrasound contrast imaging is increasingly used to analyze blood perfusion in cases of ischemic or cancerous diseases. Among other imaging methods, the diminution harmonic imaging (DHI), which modells the diminution of contrast agent due to ultrasound pulses, is the most promising because of its speed. However, the current imaging quality of DHI is insufficient for reliable diagnoses. In this paper, we extend the mathematical DHI model to include the part of the intensity signal which is due to tissue reflections and other effects not based on the contrast agent and its concentration in the blood. We show in a phantom experiment with available perfusion ground truth the vast improvements in accuracy of the new model. Our findings also strongly support the theory of a linear relationship between the perfusion speed and the determined perfusion coefficient, which is a large step towards quantitative perfusion measurements.

Transcranial color-coded duplex sonography for detection of distal internal carotid artery stenosis

BACKGROUND AND PURPOSE

Gradation of high-grade intracranial internal carotid artery (ICA) stenosis poses a challenge to noninvasive neurovascular imaging, which seems critical for angioplasty in the ICA segments C1 and C5. We investigated cutoff values of intracranial ICA stenosis for transcranial color-coded sonography (TCCS) and compared this method with the "gold standard," digital subtraction angiography (DSA).

MATERIALS AND METHODS

Forty patients (mean age, 58.9 +/- 13.8 years) with intracranial ICA lesions were prospectively examined by using TCCS and DSA. Two standard TCCS coronal imaging planes were used to evaluate the intracranial ICA. In addition, a control group of 128 volunteers without cerebrovascular disease (mean age, 48.8 +/- 15.9 years) was investigated to establish standard velocity values.

RESULTS

DSA confirmed 96 stenoses and 8 occlusions of the intracranial ICA in the study population. In 9% and 7% of cases, stenosis confined to the C1 or C5 segment was >50% and 70%, respectively. Receiver-operating curves demonstrated cutoff values for >70% stenosis in C1 when the peak systolic velocity (PSV) was >200 cm/s (specificity, 100%; sensitivity, 71%) or the C1/submandibular ICA index was >3 (specificity, 93%; sensitivity, 86%).

CONCLUSIONS

TCCS is a reliable adjunctive method to detect and quantify significant stenosis of the intracranial ICA. The assessment of the C1/ICA index and peak systolic velocities maximizes the diagnostic accuracy of C1 stenosis to >70% when extracranial ICA stenosis coexists. Further studies need to be performed to compare the diagnostic accuracies of MR angiography and TCCS with that of DSA.

Intraoperative real-time contrast-enhanced ultrasound angiography: a new adjunct in the surgical treatment of arteriovenous malformations

Object

The goal of this study was to combine the use of ultrasound contrast agents with intraoperative ultrasound techniques to identify intraoperatively a patient's vascular anatomy, including feeding arteries and draining veins of an intracranial arteriovenous malformation (AVM).

Methods

The authors examined 12 consecutive patients with AVMs that had been diagnosed on the basis of preoperative findings on magnetic resonance images and digital subtraction angiograms obtained between September 2003 and December 2005. After each patient had undergone a routine craniotomy, a bolus of contrast agent was injected intravenously, and a real-time microbubble perfusion process was observed to identify the feeding arteries and draining veins of the AVM in a single cross-section. The so-called burst–refill technique was used to sweep the lesion in multiple sections and orientations to obtain information on the surrounding vascular anatomy, after which the findings were compared with those obtained during preoperative imaging.

Results

Intraoperative ultrasonography provided high-quality images in every case. Although plain imaging failed to show an identifiable AVM boundary, color Doppler flow imaging clearly delineated the shape and margin of the AVM. Nevertheless, neither mode of imaging enabled the surgeons to categorically distinguish between feeding and draining vessels.

The real-time perfusion process of microbubbles was first visualized 20 to 30 seconds after the SonoVue bolus injection, and the burst–refill technique made possible identification of the vascular anatomy of malformation lesions in multiple planes.

Conclusions

Using both an ultrasound contrast agent and the burst–refill technique provided a rapid, convenient, and precise way of locating AVM feeding arteries intraoperatively. The combined technique seems warranted in the intraoperative treatment of AVMs.

Quantitative evaluation of cerebrovascular reactivity in brain tissue by a refill kinetic method of transcranial ultrasonic perfusion imaging: a comparison with Doppler sonography

To confirm the reliability of a refill kinetic method of ultrasonic harmonic perfusion imaging (HPI) capable of quantifying separate parameters of microvascular blood flow velocity and volume in brain tissue, we evaluated acetazolamide (ACZ) cerebrovascular reactivity by transcranial HPI in comparison with Doppler sonography (TCD). Methods. HPI during continuous Levovist infusion with changing pulsing intervals (t) and TCD time-averaged maximum velocity (TAMX) in the middle and posterior cerebral arteries were evaluated before and after ACZ administration in 12 patients, 8 without and 4 with a temporal skull defect. Plateau value (A) and rise rate (beta) of intensity (I) represented by HPI time-intensity curves of I(t) = A(1 - e(-beta*t)) were analyzed on the axial diencephalic plane.

RESULTS

1) A significantly decreased in proportion to the region of interest location depth only in the intact skull cases. 2) Despite inter- and intra-individual data scattering, in correspondence with TAMX increases after ACZ, significant beta increases were more frequently identified than increases of A.

CONCLUSIONS

Cerebral vasoreactivity analysis utilizing refill kinetics of transcranial HPI can potentially provide separate quantification based on microvascular blood velocity and volume (capillary patency) with consideration of depth-dependant ultrasound attenuation. This should be suitable for bedside evaluation of neurointensive care patients.