title: Evaluation of a 1 MHz transducer for transcranial Doppler ultrasound including embolic signal detection.
abstract: A 1 MHz transducer for use with transcranial Doppler ultrasound may improve the intensity and therefore the detection of embolic signals (ES) and may also reduce the number of absent acoustic windows. A series of studies was performed to investigate its potential benefits. Firstly, ES were detected using a 1 MHz and a 2 MHz transducer both in vitro and in vivo. Secondly, the time taken to identify 100 middle cerebral arteries (MCA) was recorded for both transducers and the best Doppler signal obtained was reviewed off-line and graded for quality. ES were more intense when detected with the 1 MHz compared with the 2 MHz transducer, both in vitro (p <.0001) and in vivo (p <.0001). Of the 100 MCAs studied, 81 had acoustic windows identified with both transducers. The number of acoustic windows detected with one transducer but not the other was the same for both transducers (n = 3). The time taken to identify the MCA was longer with the 1 MHz transducer (p <.0001) and the quality of the signal achieved was poorer (p <.0001). In conclusion, the 1 MHz transducer improved embolic signal intensity but the overall quality of the flow spectrum obtained was poorer with the 1 MHz than with the 2 MHz transducer. A lower frequency transducer of 1 MHz or possibly 1.5 MHz with transcranial Doppler ultrasound may improve the application of embolic signal detection but may not improve the signal for routine measurement of flow velocities.
authors.affiliation: Department of Clinical Neuroscience, St George's Hospital Medical School, London, UK. h.markus@sghms.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Cullinane
authors.forename: H S
authors.initials: HS
authors.lastname: Markus
mesh_terms: D016894:Endarterectomy, Carotid / Q000009:adverse effects; D005260:Female; D006350:Heart Valve Prosthesis / Q000009:adverse effects; D006801:Humans; D020766:Intracranial Embolism / Q000000981:diagnostic imaging* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging; D008955:Models, Cardiovascular; D019047:Phantoms, Imaging; D014159:Transducers; D017585:Ultrasonography, Doppler, Transcranial / Q000295:instrumentation* / Q000379:methods