Medical ultrasound imaging system with velocity-dependent rejection filtering

• US 4,850,364 A
• Filed: 11/12/1987
• Issued: 07/25/1989
• Est. Priority Date: 11/12/1987
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Leavitt, Steven C.
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US07/119,754
• Time in Patent Office: 621 Days
• Field of Search: 128/663, 128/661.08-661.10, 73/851.25
• US Class Current: 600/455
• CPC Class Codes: G01S 15/8981 Discriminating between fixed and moving objects or between objects moving at different speeds, e.g. wall clutter filter

Abstract

A medical Doppler ultrasound imaging system with improved filtering to separate blood flow information from clutter due to heart wall and vessel motion. In combination with a clutter rejection filter and velocity determination system as in the prior art, a velocity sample rejection system implements a velocity-dependent (i.e., frequency-dependent) threshold for rejecting velocity values, or samples, based on too weak echoes. That is, the acceptance/rejection threshold is a function of frequency. Optimally, the shape of the velocity-dependent thresholding function closely matches that of the attenuation transfer function of the clutter rejection filter. Thuys, for low velocity samples (corresponding to low Doppler frequency shifts), the rejection threshold is substantially lower than it is for high velocity samples. The rejection level increases monotonically as the signal deviates from the I.F.

Claims

1. In a medical Doppler ultrasound system of the type employing a transducer, a scanner unit and means operatively connected thereto for processing Doppler echoes received by the transducer to extract from the echoes, for display, signals corresponding to blood flow within a patient'"'"'s body, the means for processing echoes including means for sampling echoes, means for rejecting clutter from such echoes, and means for calculating from time-displaced pairs of such samples corresponding blood flow velocity values at selected points within the patient, means for generating a velocity value reject signal for each velocity value not meeting predetermined acceptability criteria, and means responsive to said reject signal for calculating the average at each point of those velocity values for which a reject signal has not been generated, the improvement comprising:

the means for generating a velocity value reject signal being adapted to compare against predetermined velocity-dependent criteria the amplitude of the velocity value and the amplitudes of the associated pair of samples, and generating a reject signal associated with the velocity value whenever one of said amplitudes fails said velocity-dependent criteria.

2. The system of claim 1 wherein the predetermined velocity-dependent criteria establishes for low velocity samples (corresponding to low Doppler frequency shifts) a rejection threshold substantially lower than the rejection threshold for high velocity samples.

3. The system of claim 2 wherein the rejection threshold increases monotonically as the echo frequency deviates from the I.F.

4. The system of claim 1 wherein the velocity-dependent criteria is, for at least one of said amplitudes, a stepwise approximation to the frequency response of the means for rejecting clutter.

5. A medical Doppler ultrasound system comprising:

a. a transducer;

b. a scanner unit operatively connected to the transducer for controlling the operation thereof and receiving Doppler echo signals therefrom;

c. means operatively connected to the scanner unit for receiving therefrom and processing Doppler echoes to extract from the echoes, for display, signals corresponding to blood flow within a patient'"'"'s body;

d. the means for processing echoes including

1. means fopr sampling echoes;

2. means for rejecting clutter from such echoes,

3. means for calculating from time-displaced parts of such samples corresponding blood flow velocity values at selected points within the patient, and

4. means for generating a velocity value reject signal for each velocity value not meeting predetermined acceptability criteria;

f. means responsive to said reject signal for calculating the average at each point of those velocity values for which a reject signal has not been generated; and

g. the means for generating a velocity value reject signal comparing against predetermined velocity-dependent criteria the amplitude of the velocity value and the amplitudes of the associated pair of samples, and generating a reject signal associated with the velocity value whenever one of said amplitudes fails said velocity-dependent criteria.