Ultrasonic evaluation of pathological brain perfusion in acute stroke using second harmonic imaging

Objective-To evaluate the use of transient response second harmonic imaging (HI) by means of ultrasound to assess abnormalities of cerebral echo contr ast agent enhancement in patients with acute stroke. Methods-The study comprised 25 patients with acute onset of hemispheric str oke (<24 h) with sufficient insonation conditions and 14 control subjects w ithout cerebrovascular disease. All stroke patients had HI, extracranial an d transcranial colour coded duplex examinations of the arteries supplying t he brain, and clinical examinations (European stroke scale) performed in th e acute phase, on day 2, and within I week. Acute CT was repeated within 1 week and facultatively accompanied by angiography. Examinations using HI we re performed in an axial diencephalic plane of section using the transtempo ral acoustic bone window. After bolus application of galactose based microb ubbles, 61 ultrasound images with a cardiac cycling triggering frequency of once every 2 seconds were recorded and evaluated off Line. Focal perfusion deficit was identified if no contrast enhancement was visualised in a circ umscribed region of interest and insufficient temporal bone window was excl uded. In cases of reappearance of contrast enhancement reperfusion was asse ssed. Results-Adequate cerebral contrast enhancement could be seen in 21 subjects . In seven, a large hemispheric deficit of contrast enhancement affecting t he entire middle cerebral artery (MCA) territory was detectable; the lentif orm nucleus was affected in three subjects. Assessment of cerebral contrast abnormalities was possible in two patients with superficial MCA infarction s but in none of the patients with lacunar ischaemias. None of the control persons had focal deficits of cerebral echo contrast enhancement. In all pa tients with complete MCA infarction and striatocapsular infarction , presum ed ischaemic areas in HI examinations correlated with final CT findings. Ov erall sensitivity and specifity of HI examinations for predicting size and localisation of the infarction were contrast 75 and 100%, respectively. Dur ing follow up, reappearance of contrast enhancement was determined in three patients, in two patients circulatory arrest due to malignant brain oedema with missing enhancement in the entire cerebral hemisphere could be seen. Extent of contrast enhancement deficits significantly correlated with the c linical status on admission and after 1 week (p<0.01). Conclusions-Second harmonic imaging is the first ultrasonic technique that enables visualisation of pathological cerebral echo contrast enhancement. B ecause this method identifies deficits of focal contrast enhancement in pat ients with acute stroke and allows estimation of the final infarct size and clinical prognosis, it may help to select and monitor patients for invasiv e therapies.