Medical ultrasound imaging system with composite delay profile

Details Medical ultrasound imaging system with composite delay profile Medical ultrasound imaging system with composite delay profile

1999-02-19

2001-11-06

Jaworski, Francis J. (Department: 3737)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

Reexamination Certificate

active

06312386

ABSTRACT:

BACKGROUND
This invention relates to medical ultrasound diagnostic imaging, and in particular to systems and methods for providing more effective focusing of ultrasound waveforms.
In current ultrasound imaging systems, transducer probes which include many individual transducer elements are operated as phased arrays.
Delay profiles are applied either to transmit waveforms or to receive waveforms associated with individual transducer elements in order to achieve desired focusing characteristics. One prior-art approach is to use a simple delay profile in which all of the transducer elements of the transducer probe are focused at a single focal point. Another prior-art approach is to use a delay profile that provides a distributed focus, as for example the well-known Axicon profile that provides a line focus.
A third prior-art approach is to transmit two or more transmit focal zones simultaneously. This is typically done by superimposing two separate delay profiles such that each transducer element generates ultrasonic energy that focuses at each of the two or more focal zones. This approach is known as the multi-focus approach, and is described in U.S. Pat. Nos. 5,696,737, 5,675,554, 5,608,690, 5,740,128, as well as in U.S. patent application Ser. No. 09/089,463.
The Axicon focus is typically associated with large side lobe levels that can represent a substantial disadvantage in many clinical applications. The simultaneous transmission of multiple focal zones generally requires dedicated beamformer hardware. Also, if the probe is limited by regulatory power or thermal limits, then the use of the multi-focus approach may require reduced power which in turn is generally associated with a reduction in the signal to noise ratio.
Another approach for increasing depth to field includes the use of multiple sequential transmit events focused at respective ranges along with the same ultrasound line. This approach reduces the frame rate, though it can substantially increase the depth of field.
Thus, a need presently exists for an improved approach that increases depth of field while avoiding some or all of the disadvantages discussed above.
BRIEF SUMMARY
The preferred embodiments described below use several different types of composite delay profiles that have the advantage of extending depth of field while maintaining a high frame rate and reducing side lobe problems.
Some of the embodiments described below use a composite delay profile having at least a first, substantially point-focus delay profile for a first set of the transducer elements and a second, substantially point-focus delay profile for a second set of the transducer elements. The first and second delay profiles cause ultrasonic energy from the respective first and second sets of the transducer elements to constructively add at first and second respective spaced focal zones. This composite delay profile can be used either in the transmitter or the receiver of an ultrasound imaging system.
Other embodiments described below use a delay profile that includes first and second portions corresponding to respective parts of a point-focus delay profile, a third portion intermediate the point-focus delay profile and a first tangent to the point-focus delay profile, and a fourth portion intermediate the point-focus delay profile and a second tangent to the point-focus delay profile.
The foregoing discussion of the preferred embodiments has been provided only by way of introduction, and nothing in the section should be taken as a limitation on the following claims.


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U.S. application No. 09/089,463.

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