| 摘要 |
A needle guiding apparatus transmits ultrasonic sound waves through a hollow hypodermic needle. The sound waves travel down the needle and a portion of the energy in the sound waves is reflected back up the needle by the tissues at which the needle is pointed. If the needle is pointed at a vessel in which blood is flowing, the frequency of the reflected sound waves is Doppler shifted by an amount proportional to the velocity of blood cell flow in the vessel. The needle guiding apparatus detects and amplifies the Doppler shifted signal and the resulting signal is used to drive a speaker and thereby generate an audible signal. As the needle is brought closer to the vessel, the Doppler sounds become stronger in amplitude and the angle of the needle with respect to the vessel affects the pitch of the Doppler shifted signal. These audible indications are used by the clinician, while varying the angle of the needle, to identify the proper direction to proceed in order to insert the needle in the vessel. |
