An apparatus and method is described comprising: obtaining first measurement data relating to blood flow in a left vertebral artery of a subject from a first sensor of an apparatus applied to a neck of the subject； obtaining second measurement data relating to blood flow in a left carotid artery of the subject from a second sensor of the apparatus applied to the neck of the subject； obtaining third measurement data relating to blood flow in a right carotid artery of the subject from a third sensor applied to the neck of the subject； and obtaining fourth measurement data relating to blood flow in a right vertebral artery of the subject from a fourth sensor applied to the neck of the patient, wherein: the first to fourth measurement data are obtained in synchronism with each other； and each of the first to fourth measurement data includes one or more of pulse amplitude, blood flow velocity or blood flow quantity for the respective artery.
