Original ContributionsCerebral arteriovenous transit time (cTT): a sonographic assessment of cerebral microcirculation using ultrasound contrast agents
Introduction
Neurological deficits due to disorders of small vessels are common, encompassing up to one third of all cerebral infarctions Chamorro et al 1991, Bogousslavsky et al 1988, Ostrow and Miller 1993, Olsson et al 1996. Clinically, these patients present with focal neurological deficits, gait disorders, progressive cognitive impairment or urinary incontinence (Miller Fisher 1989). The structural lesions due to small vessel disease may be detected by CT (computed tomography) and MRI (magnetic resonance imaging). Brain perfusion deficits due to altered microcirculation are determined by radionuclear perfusion techniques such as PET (positron emission tomography) or SPECT (single photon emission computed tomography) Sabri et al 1995, Reiche and Weiller 1990.
Here, we describe a new and more easily applicable assessment of impaired microcirculation and brain perfusion in patients with microangiopathy, using contrast-enhanced transcranial color-coded duplex sonography (TCCS). The method is based on the assumption that the time an ultrasound contrast agent requires to pass from the cerebral arteries to the veins (cerebral transit time, cTT) should be prolonged in patients with small vessel disorders.
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Patients and methods
We examined 27 patients (median age: 65 y, range 46 and 84 y, 10 women, 17 men) with clinical and radiological evidence of cerebral microangiopathy. Inclusion criteria were: (a) history of focal neurological deficits due to at least one lacunar stroke; (b) multiple (more than three) lacunes identified by MRI or CT; (c) arterial hypertension (repeated systolic results > 160 mmHg in the past); and (d) availability of an acoustic bone window suitable for transcranial sonography. Exclusion criteria
Results
The following focal neurological deficits were identified in patients with cerebral microangiopathy: hemi- or central monoparesis of arm or leg (n = 16), dysarthria (n = 7), sensory deficits (n = 4), gait disorders (n = 12). Age, heart rate and blood pressure, as well as frequency of nycturia, walking speed and results of neuropsychiological performance are given in Table 1. Doppler measurements of the extracranial and basal arteries revealed normal findings in both patients and controls.
Discussion
TCCS is a new ultrasound application enlarging the scope of ultrasound in the diagnosis of neurological disorders, particulary of cerebrovascular diseases. Here, we describe a further new sonographic parameter, cTT, assessable with TCCS and ultrasound contrast agents, that may provide a view of the cerebral microcirculation. CTT is defined as the time that an ultrasound agent requires to pass from the cerebral arteries to the veins. We hypothesized that cTT should be related to the vascular
Acknowledgements
The study was supported by the Siemens AG, Germany, and Schering Deutschland GmbH. The authors thank Frau Schlieβer for her continuous support and technical assistence and Prof. Dr. K. Reiners for helpful comments on the manuscript.
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