Automatic Localization and Monitoring of Intracranial Arteries during Transcranial Doppler Sonography by means of a TCD-MRA-Navigational System

Magnetic resonance angiography (MRA) and transcranial Doppler ultrasound sonography (TCD) are well established imaging modalities routinely used in clinical practice. In a preceding project a system was developed combining the high spatial resolution of MRA with the excellent blood flow dynamics of TCD. Thereby, a specially adapted optoelectronic navigation system registers the spatial orientation and location of the ultrasound (US) beam, which is correlated to the 3D MRA data by means of a stereotactic mask. The examiner is provided with a 3D "map" of the blood-vessel structure of the person being insonated. Points of insonation are displayed on the computer screen and can be stored for follow-up examinations. The previously developed system was designed for a handheld TCD probe. Experimental measurements on volunteers demonstrate the usefulness of the system. However, the manual handling of the US probe still strongly depends on the skills of the operator. It is therefore the aim of the presented project to motorise the US probe enabling automatic TCD examinations. Target points of insonation will be predefined by the physician within the 3D MRA data. so that even untrained personal should be able to execute the automatic TCD investigation. Repeated monitoring of cerebral blood flow over a prolonged period of time can thus be executed easier and more accurate. To realise the aim of the presented project a motorised US probe will have to be developed and then combined with the existing system. The main goal in designing the motorised US probe thereby will be to ensure that the device can be applied together with any available TCD system. For the integration of the motorised US probe into the existing navigation system the existing software will have to be upgraded to include e.g. the possibility of target point pre-definition, corrections of US refractions at the skull bone and a modified internal data format to ensure high computational performance. After the successful realization of automatic stereotactic TCD guidance the system will be validated on volunteers.