Frontal bone windows for transcranial color-coded duplex sonography

Background and Purpose-The use of the conventional temporal bone window for transcranial color-coded duplex sonography (TCCS) often results in difficu lties in obtaining angle-corrected flow Velocity measurements of the A2 seg ment of the anterior cerebral artery, the posterior communicating artery, a nd the midline venous vasculature because of the unfavorable insonation ang le. The same applies to B-mode imaging of the frontal parenchyma. However, transorbital TCCS raises problems with the insonation of the orbital lens. To overcome these drawbacks, we studied the feasibility of frontal bone win dows for TCCS examinations. Methods-In 75 healthy volunteers (mean age, 45.3+/-17.0 years; age range, 1 7 to 77 years), the circle of Willis and the venous midline vasculature wer e insonated through a lateral and paramedian frontal bone window. Insonatio n quality of parenchymal structures (B-mode) was graded on a 3-point scale depending on the visibility of typical parenchymal landmarks. In a similar manner, the quality of the color-/Doppper-mode imaging of the arteries of t he circle of Willis and the internal cerebral Veins was assessed. In 15 pat ients (mean age, 62.7+/-13.7 years; age range, 33 to 83 years), the color-/ Doppler-mode imaging quality of the intracranial vessels before and after a pplication of an ultrasound contrast-enhancing agent was compared. Results-B-mode insonation quality was optimal to fair in 73.3% of cases usi ng the lateral and in 52.0% of cases using the paramedian frontal bone wind ow, with defined parenchymal structures used as reference. Insonation quali ty decreased in those older than 60 years. In those younger than 60 years, angle-corrected flow velocity measurements of the A2 segment of the anterio r cerebral artery and the internal cerebral vein were possible in 73.6% and 60.0%, respectively. Contrast enhancement resulted in a highly significant improvement in the imaging quality of the intracranial vessels. Conclusions-The transfrontal bone windows offer new possibilities for TCCS examinations, although the insonation quality is inferior to the convention al temporal bone window in terms of failure of an acoustic window. This can be compensated for by application of an ultrasound contrast-enhancing agen t.