Transcranial Doppler penetrance of methyl methacrylate: technical note.

Methyl methacrylate is often used in cranioplasties and reconstructions of crainiectomies at sites through which transcranial Doppler (TCD) examinations are performed for assessment of cerebral hemodynamics. To assess the penetrance of methyl methacrylate by a transcranial Doppler ultrasound beam, methyl methacrylate discs of thickness from 4 to 10 mm were constructed and placed in the path of the ultrasound beam during routine-insonation of the middle cerebral artery and femoral artery in a healthy volunteer. The quality of ultrasound signals obtainable markedly deteriorated as thicker discs were used, and was almost completely absent at a thickness of 10 mm. The impairment of ultrasound transmission at frequencies used for transcranial Doppler ultrasound by methyl methacrylate is significant and represents a limitation in TCD studies that should be recognized by the clinician.