Ultrasound transducer unit and planar ultrasound lens

Details Ultrasound transducer unit and planar ultrasound lens Ultrasound transducer unit and planar ultrasound lens

2001-11-21

2004-09-07

Budd, Mark (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

Reexamination Certificate

active

06787974

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an ultrasound focusing lens, a disposable ultrasound assembly, and a disposable ultrasound assembly employing an ultrasound focusing lens.
There are forms of therapy that can be applied within the body of a human or other mammalian subject by applying energy to the subject. In hyperthermia, ultrasonic or radio frequency energy is applied from outside of the subject's body to heat certain body tissues. The applied energy can be focused to a small spot within the body so as to heat a particular tissue or group of tissues to a temperature sufficient to create a desired therapeutic effect. This technique can be used to selectively destroy unwanted tissue within the body. For example, tumors or other unwanted tissues can be destroyed by applying heat to the tissue and raising the temperature thereof to a level (commonly temperatures of about 60° C. to 80° C.) sufficient to kill the tissue without destroying adjacent, normal tissues. Such a process is commonly referred to as “thermal ablation.” Other hyperthermia treatments include selectively heating tissues so as to selectively activate a drug or promote some other physiologic change in a selected portion of the subject's body. Additional details on the techniques employed in hyperthermia treatments for ablation are disclosed in, for example, copending, commonly assigned PCT International Publication No. WO98/52465, the entire disclosure of which is incorporated herein by reference. Other therapies use the applied energy to destroy foreign objects or deposits within the body as, for example, in ultrasonic lithotripsy.
Often, magnetic resonance imaging devices are utilized in conjunction with ultrasonic treatments so as to ensure that the proper tissues are being affected. Combined magnetic resonance and ultrasonic equipment suitable for these applications are described in greater detail in copending, commonly assigned PCT International Publication No. WO98/52465.
Existing ultrasonic energy emitting devices include piezoelectric resonance units to produce ultrasound waves. A plurality of separate ultrasound emitting sections may be disposed in an array. It has been proposed to orient the array of ultrasound emitting sections in a relatively curved shape such that a focal length of about 20 cm is obtained. Ultrasonic emitting sections of the curved variety are typically produced by forming a curved structure, and disposing the individual ultrasound emitting sections on the curved structure to produce a unit capable of emitting a focused beam. Unfortunately, this technique is relatively expensive, in part because it requires a substantial number of processing steps to produce and locate the individual ultrasound emitting sections on the curved structure.
It is desirable in ultrasound surgery to minimize the space occupied by the equipment utilized to produce ultrasound energy (e.g., the piezoelectric transducer). A curved piezoelectric transducer to obtain focused ultrasound energy may occupy excessive space in the depth direction. Thus, it has been proposed to use a relatively planar piezoelectric transducer in combination with a focusing lens that is also preferably substantially planar. One such focusing lens employs a plurality of concentric rings, where each ring has a substantially rectangular cross-section. Additional details of this lens may be found in the following documents: (i) Todd Fjield, Christina Silcox, and Kullervo Hynynen, Low-Profile Lenses For Ultrasound Surgery, IEEE Ultrasonics Ferroelectrics And Frequency Control Symposium, Sendai, Japan, October 1998; and (ii) Todd Fjield, Christina Silcox, and Kullervo Hynynen, Low-Profile Lenses For Ultrasound Surgery, Phys. Med. Biol. 44, pp. 1803-1813 (1999). The entire disclosures of these documents are hereby incorporated by reference. As opposed to utilizing refraction theory (i.e. Snell's Law), the lenses disclosed in the above documents operate to shift the phase of the ultrasound wave as it passes through the lens such that additive phase is achieved at a focal point located away from the lens. Such a lens employs a multi-step approach where each ring has a cross-section that resembles stair steps. The ultrasound wave propagates through the lens and exits from the lens at one or more perpendicular surfaces, such as the tops of the stair steps of the rings.
It would be desirable to produce a substantially planar focusing lens that may be easily and cost effectively produced, that does not occupy excessive space in the depth direction, and that may be easily received in base equipment.
SUMMARY OF THE INVENTION
In accordance with at least one aspect of the invention, a lens for focusing an ultrasound wave having a wave length includes: a plurality of substantially concentric rings disposed about a central point, at least one of the rings having a substantially triangular cross-section defined by first, second, and third sections, the first section extending from a proximal end radially away from the central point to a distal end, the second section extending from the distal end of, and substantially perpendicular to, the first section and terminating at a peak, and the third section smoothly sloping from the proximal end of the first section to the peak of the second section, and wherein the first, second and third sections have lengths with respect to the wavelength of the ultrasound wave such that (i) phases of the ultrasound wave are substantially additive at a focal point located on an axis perpendicular to the lens that passes through the central point, and (ii) aggregate focused ultrasound energy would not be predicted at the focal point by Snell's law refraction.
In accordance with one or more other aspects of the invention, a disposable ultrasound wave unit includes: an ultrasound planar member including an array of piezoelectric transducers disposed between spaced apart forward and rearward surfaces, and being operable to produce an ultrasound wave propagating from the forward surface in a direction substantially perpendicular thereto; and a lens sonically communicating with the forward surface of the ultrasound planar member for focusing the ultrasound wave, the lens including: a substantially planar base having spaced apart first and second surfaces, the second surface being directed toward the forward surface of the ultrasound planar member; and a plurality of substantially concentric rings disposed about a central point on the first surface of the base, wherein each ring has a substantially triangular cross-section defined by first, second, and third sections, the first section extending from a proximal end radially away from the central point to a distal end along the first surface of the base, the second section extending from the distal end of, and substantially perpendicular to, the first section and terminating at a peak, and the third section smoothly sloping from the proximal end of the first section to the peak of the second section, and the first, second, and third sections of each ring having respective lengths such that (i) phases of the ultrasound wave are substantially additive at a focal point located on an axis perpendicular to the lens that passes through the central point, and (ii) aggregate focused ultrasound energy would not be predicted at the focal point by Snell's law refraction.
In accordance with still other aspects of the present invention, a lens for focusing an ultrasound wave includes: a base having spaced apart first and second surfaces and a central axis extending between the first and second surfaces; and a plurality of substantially concentric rings disposed about the central axis and defining respective contours of the first and second surfaces of the base, the substantially concentric rings being sized and shaped such that, in cross-section, a plurality of concentric radially extending zones are defined from the central axis toward a periphery of the base, at least some of the rings having a substantially triangular cross-section such th

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