Spiral scanner with electronic control

Details Spiral scanner with electronic control Spiral scanner with electronic control

2001-01-25

2003-09-30

Van, Quang T. (Department: 3742)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

C244S003160

Reexamination Certificate

active

06626834

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to scanning devices whereby a target within a conical scanning field may be scanned so as to obtain a three dimensional scanned image. The target is spirally scanned. The invention also provides for volumetric scanning of a target within the conical scanning field. The invention is particularly directed towards ultrasonic scanners, but optical scanners are also contemplated.
BRIEF DISCUSSION OF THE INVENTION
Typically, the present invention is directed to an ultrasonic scanning apparatus wherein an ultrasonic transducer is mounted for continuous rotation about a pivot point, with motive force provided by electromagnetic means under digital electronic control. Preferably, a scanning apparatus in keeping with the present invention employs a transducer assembly which is disposed within a hand-held probe.
Briefly, such an ultrasonic scanner has a housing, and an ultrasonic transducer disposed within the housing and mounted therein for two-way tilt motion about a pivot point by means of a gimbal or similar mechanism. A permanent magnet is affixed to the rear of the transducer, and electromagnetic means are provided to effect movement of the transducer/magnet assembly. The electromagnetic means comprises at least two electromagnet coils which jointly form a hemispheric electromagnet coil assembly. The electromagnetic coils are driven by polyphase sinusoidal electric currents, causing rotation of the transducer about an axis. Periodic amplitude variation of the polyphase electric currents will effect periodic change of the angle between the axis and a fixed central axis, thereby causing the ultrasonic beam to sweep out a conical volume—and thereby resulting in volumetric scanning.
Electrical means are provided for energizing the transducer and receiving signals therefrom which are indicative of reflected scanning energy which is reflected back from a target in the conical scanning field. Digitizing means are provided to convert the received signals to digital form for storage and/or display.
Sequential control means are provided to energize the electromagnet coils with precise phasing, and further more to synchronize transducer motion, periodic energization of the transducer, and digitization of signals received from the transducer. Of course, suitable storage and/or display means are provided to store and/or to present the signals received by the transducer to an operator, in any one of several time-varying graphical representations.
In an extension of the present invention, the transducer may be replaced by a mirror, with an external light source being arranged to direct light onto the mirror from whence it will be re-directed and transmitted linearly outwardly therefrom.
PRIOR ART CONSIDERED HEREIN
The following is a list of issued United States patents and Published Canadian Patent Applications which are referred to hereafter:
U.S. Pat. No. 4,092,867
issued Jun. 6, 1978
MATZUK
U.S. Pat. No. 4,732,156
issued Mar. 22, 1988
NAKAMURA
U.S. Pat. No. 5,159,931
issued Nov. 3, 1992
PINI
U.S. Pat. No. 5,357,963
issued Oct. 25, 1994
MAYOL et al
U.S. Pat. No. 5,454,371
issued Oct. 3, 1995
FENSTER et al
U.S. Pat. No. 5,562,095
issued Oct. 8, 1996
DOWNEY et al
U.S. Pat. No. 5,647,367
issued Jul. 15, 1997
LUM et al
U.S. Pat. No. 5,701,901
issued Dec. 30, 1997
LUM et al
U.S. Pat. No. 5,842,473
issued Dec. 1, 1998
FENSTER et al
U.S. Pat. No. 5,964,707
issued Oct. 12, 1999
FENSTER et al
U.S. Pat. No. “unknown”
to issue from Ser. No.
DUNNE
09/409,095-now allowed
CAPTA 2,261,227
filed Jun. 25, 1998-
FENSTER et al
laid open Jan. 7, 1999
CAPTA 2,254,939
filed Mar. 20, 1998-
FENSTER et al
laid open Oct. 1, 1998
BACKGROUND OF THE INVENTION
Ultrasonic imaging, also called echography or B-mode (“brightness mode”) ultrasound, involves an ultrasonic transducer which repeatedly emits pulses of high-frequency sound and receives the resulting echo signals. A focused beam of sound is normally used, and various means are employed to sweep this beam repeatedly through a range of directions. Electronic processing of the received echo signals, synchronized to the movement of the beam, results in formation of a video image (normally cross-sectional) of structures (such as human tissues) in the beam's path.
For purposes of clarity, the following discussion refers specifically to the medical diagnostic imaging situation in which the target of the ultrasonic imaging system is tissue in a living human patient. It should be realized that ultrasonic scanning is also used in other applications including non-human (veterinary or in vitro tissue sample) biological imaging and also non-biological imaging applications (non-destructive materials testing), and that the present invention applies without limitation to all of such ultrasonic imaging applications.
In ultrasonic scanners for medical diagnostic imaging, the transducer and beam-sweeping components are normally assembled in the form of a hand-held probe connected to the rest of the imaging system by means of a cable. In the following discussion, the term “probe” will be used generically to refer to the transducer and beam-scanning assembly, though it should be realized that not all ultrasonic scanning systems will have or need a physically distinct probe component.
Historically, B-mode ultrasound imaging has been a two-dimensional process. The sweep motion of the sound beam emitted and received by the transducer is confined to a single plane intersecting the target to be imaged, and a cross-sectional image results. U.S. Pat. Nos. 5,159,931, 5,454,371, 5,562,095, 5,842,473, and 5,964,707 describe methods by which three-dimensional images may be assembled from multiple planar echographic images. However, it is also possible to reconstruct three-dimensional images directly, by causing the transducer to move with two degrees of freedom, with the result that the sound beam sweeps throughout the target volume in some predetermined (programmed) path. The present invention relates to this latter approach, and is referred to as volumetric scanning.
Many techniques for sweeping the sound beam are known; U.S. Pat. No. 4,092,867 presents a good summary. Today, two main approaches are in common use. In the mechanical sector-scan approach, a transducer is mechanically oscillated about a pivot axis, causing the sound beam to sweep through a sector. In the electronic transducer array approach, a fixed array of multiple transducer elements is used, and the sound beam is formed, focused, and swept entirely electronically.
Attempts to use the electronic array approach for volumetric scanning, using a two-dimensional array of transducer elements, have not yet proved practical, and in any event the cost and complexity of the electronics to process the hundreds of individual element signals which would be required are formidable. In contrast, the simple mechanical sector-scan approach can in principle be adapted for volumetric scanning by permitting the transducer to oscillate about a pivot point rather than a pivot axis, e.g. using a gimbal or similar mechanism.
Any number of sweep paths may be envisaged, and if the electronic array approach is used almost any path might reasonably be used to effectively scan a target volume at high speed. With mechanical scanning, however, the only practical sweep path is a circular spiral. Non-spiral paths require rapid changes of the acceleration vector, which in practice will greatly limit the operating speed. Rapid scanning is desirable because it permits dynamic imaging in the presence of motion, e.g. of the living fetus in utero, of the tissues in the eye, or in the course of interventional medical procedures such as catheterization or laparoscopic surgery. The present invention relates to mechanical, spiral scanning of a single transducer mounted for motion with two degrees of freedom in e.g. a gimbal.
Because the sound frequencies used in ultrasonic imaging are effectively blocked by air, it is necessary to acoustically couple the transducer to the target under investigation via one or more acoust

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