Transcranial Perfusion Sonography Using a Low Mechanical Index and Pulse Inversion Harmonic Imaging: Reliability, Inter-/Intraobserver Variability - Harrer, J. U.; Valaikiene, J.; Koch, H.; Knorr, R.; Horn, M.; Ickenstein, G.; Bogdahn, U.; Schlachetzki, F. (Ultraschall in der Medizin - European Journal of Ultrasound, 2011)