Methods and apparatus for performing sonomammography and enhanced x-ray imaging

Claims

What is claimed is:

1. In apparatus for obtaining images of biological tissue by passing X-ray radiation through a biological tissue to form an image in a receptor, the apparatus comprising an X-ray source for emitting X-ray radiation, first and second compression surfaces adapted for immobilizing the biological tissue therebetween, and a receptor disposed adjacent the second compression surface, the X-ray source disposed adjacent the first compression surface so that X-ray radiation emitted from the source passes through the biological tissue and is received by the receptor, the improvement comprising:

a compression plate that is radiolucent and sonolucent, the compression plate having first and second surfaces, the second surface forming the first compression surface;

an ultrasonic transducer disposed adjacent to the first surface of the compression plate; and

drive means for moving the ultrasonic transducer across the first surface of the compression plate while the biological tissue remains immobilized between the first and second compression surfaces.

2. The apparatus as defined in claim 1 wherein the compression plate comprises a material selected from the group consisting of Kapton.RTM., a Surlyn.RTM. ionomer, and a polymethyl pentene.

3. The apparatus as defined in claim 2 wherein the polymethyl pentene is TPX.RTM..

4. The apparatus as defined in claim 2 wherein the material has a periphery and the material is coupled around the periphery to a rigid frame.

5. The apparatus as defined in claim 1 further comprising a gel pad for acoustically coupling a portion of the biological tissue to the ultrasonic transducer.

6. The apparatus as defined in claim 5 wherein the biological tissue has an X-ray attenuation characteristic, the gel pad is disposed between the first and second compression surfaces and in contact with the biological tissue, and the gel pad comprises a material that conforms to the shape of the biological tissue and has an X-ray attenuation characteristic near the X-ray attenuation characteristic of the biological tissue.

7. The apparatus as defined in claim 6 wherein the gel pad reduces scattering of the X-ray radiation relative to scattering of the X-ray radiation in air.

8. The apparatus as defined in claim 5 wherein the biological tissue comprises a portion of a patient and has a non-uniform shape and a surface area, the compression plate imposes a force on the biological tissue to compress the biological tissue to a uniform thickness, and the gel pad conforms to the non-uniform shape to distribute the force over the surface area and reduce discomfort in the patient.

9. The apparatus as defined in claim 8 wherein the gel pad comprises an adherent surface that assists in positioning the biological tissue between the upper compression surface and the lower compression surface.

10. The apparatus as defined in claim 1 further comprising lubricating means for providing a film of fluid between the ultrasonic transducer and the compression plate to lubricate and acoustically couple the ultrasonic transducer to the compression plate.

11. The apparatus as defined in claim 1 wherein the drive means further comprises:

a gantry support;

a gantry movably engaged with the gantry support for movement in the distal and proximal directions;

a carriage movably engaged with the gantry for lateral movement.

12. The apparatus as defined in claim 11 wherein the drive means further comprises:

a first motorized cable arrangement for driving the gantry along the gantry support;

a second motorized cable arrangement for driving the carriage along the gantry; and

circuitry for controlling operation of the first and second motorized cable arrangements.

13. The apparatus as defined in claim 1 further comprising:

a biopsy instrument support;

means for aligning the biopsy instrument support with the ultrasonic transducer so that a medical practitioner may perform a biopsy guided by the plurality of ultrasonic images.

14. In apparatus for obtaining images of biological tissue by passing X-ray radiation through a biological tissue to form an image in a receptor, the apparatus comprising an X-ray source for emitting X-ray radiation, first and second compression surfaces adapted for immobilizing the biological tissue therebetween, and a receptor disposed adjacent the second compression surface, the X-ray source disposed adjacent the first compression surface so that X-ray radiation emitted from the source passes through the biological tissue and is received by the receptor, the improvement comprising:

an ultrasonic transducer disposed adjacent the second compression surface, the ultrasonic transducer being radiolucent;

a coupling medium that acoustically couples the ultrasonic transducer to the second compression surface; and

control circuitry for activating the ultrasonic transducer to generate a plurality of ultrasound images of the biological tissue while the biological tissue remains immobilized between the upper and lower compression surfaces.

15. The apparatus as defined in claim 14 further comprising a gel pad for acoustically coupling a portion of the biological tissue to the ultrasonic transducer.

16. The apparatus as defined in claim 14 wherein the biological tissue has an X-ray attenuation characteristic, the gel pad is disposed between the first and second compression surfaces and in contact with the biological tissue, and the gel pad comprises a material that conforms to the shape of the biological tissue and has an X-ray attenuation characteristic near the X-ray attenuation characteristic of the biological tissue.

17. The apparatus as defined in claim 16 wherein the gel pad reduces scattering of the X-ray radiation relative to scattering of the X-ray radiation in air

18. The apparatus as defined in claim 14 wherein the biological tissue comprises a portion of a patient and has a non-uniform shape and a surface area, the first and second compression surfaces impose a force on the biological tissue to compress the biological tissue to a uniform thickness, and the gel pad conforms to the non-uniform shape to distribute the force over the surface area and reduce discomfort in the patient.

19. The apparatus as defined in claim 18 wherein the gel pad comprises an adherent surface that assists in positioning the biological tissue between the first and second compression surfaces.

20. The apparatus as defined in claim 14 wherein the ultrasonic transducer comprises a multiplicity of piezoelectric transducer elements.

21. The apparatus as defined in claim 20 wherein the control circuitry further comprises circuitry for activating predetermined ones of the multiplicity of piezoelectric transducer elements to provide beam forming and elevational focussing of the acoustic energy.

22. The apparatus as defined in claim 20 wherein the control circuitry comprises circuitry for activating a predetermined plurality of the multiplicity of piezoelectric elements to generate an ultrasonic image at a predetermined location, the apparatus further comprising:

a biopsy instrument support;

means for aligning the biopsy instrument support with the predetermined plurality of piezoelectric elements so that a medical practitioner may perform a biopsy guided by the ultrasonic image at the predetermined location.

23. In apparatus for obtaining images of a biological tissue having a shape by passing X-ray radiation through a biological tissue to form an image in a receptor, the biological tissue having an X-ray attenuation characteristic, the apparatus comprising an X-ray source for emitting X-ray radiation, first and second compression surfaces adapted for immobilizing the biological tissue therebetween so that the biological tissue has a portion of uniform thickness and a peripheral portion of non-uniform thickness, and a receptor disposed adjacent the second compression surface, the X-ray source disposed adjacent the first compression surface so that X-ray radiation emitted from the source passes through the biological tissue and is received by the receptor, the improvement comprising:

an ultrasonic transducer disposed between the first and second compression surfaces;

a gel pad disposed between the first and second compression surfaces and in contact with the biological tissue, the gel pad acoustically coupling a portion of the biological tissue to the ultrasonic transducer, comprising a material that conforms to the shape of the biological tissue and having an X-ray attenuation characteristic near the X-ray attenuation characteristic of the biological tissue, the gel pad enhancing the image of the peripheral portion formed in the receptor; and

gantry means for moving the ultrasonic transducer along a curved path between the first and second compression surfaces while the biological tissue remains immobilized therebetween.

24. The apparatus as defined in claim 23 wherein the gel pad reduces scattering of the X-ray radiation relative to scattering of the X-ray radiation in air.

25. The apparatus as defined in claim 23 wherein the biological tissue comprises a portion of a patient and has a non-uniform shape and a surface area, the first and second compression surfaces impose a force on the biological tissue, and the gel pad conforms to the non-uniform shape to distribute the force over the surface area and reduce discomfort in the patient.

26. The apparatus as defined in claim 25 wherein the gel pad comprises an adherent surface that assists in positioning the biological tissue between the first and second compression surfaces.

27. Apparatus for generating a plurality of ultrasound images of a biological tissue, the apparatus for use with an X-ray system that forms an image of the biological tissue in a receptor, the apparatus comprising:

a compression plate that is radiolucent and sonolucent, the compression plate having first and second surfaces, the first surface forming a compression surface against which the biological tissue is immobilized;

an ultrasonic transducer disposed adjacent the second surface; and

drive means for moving the ultrasonic transducer across the second surface while the biological tissue remains immobilized against the compression surface.

28. The apparatus as defined in claim 27 wherein the compression plate comprises a material selected for a group consisting of Kapton.RTM., a Surlyn.RTM. ionomer, and a polymethyl pentene.

29. The apparatus as defined in claim 28 wherein the polymethyl pentene is TPX.RTM..

30. The apparatus as defined in claim 28 wherein the material has a periphery and the material is coupled around the periphery to a rigid frame.

31. The apparatus as defined in claim 27 further comprising a gel pad for acoustically coupling a portion of the biological tissue to the ultrasonic transducer.

32. The apparatus as defined in claim 31 wherein the biological tissue has an X-ray attenuation characteristic, the gel pad is disposed against the compression surface and in contact with the biological tissue, and comprises a material that conforms to the shape of the biological tissue and has an X-ray attenuation characteristic near the X-ray attenuation characteristic of the biological tissue.

33. The apparatus as defined in claim 32 wherein the gel pad reduces scattering of the X-ray radiation relative to scattering of the X-ray radiation in air.

34. The apparatus as defined in claim 31 wherein the biological tissue comprises a portion of a patient and has a non-uniform shape and a surface area, the compression plate imposes a force on the biological tissue to compress the biological tissue to a uniform thickness, and the gel pad conforms to the non-uniform shape to distribute the force over the surface area and reduce discomfort in the patient.

35. The apparatus as defined in claim 34 wherein the gel pad comprises an adherent surface that assists in positioning the biological tissue relative to the compression surface.

36. The apparatus as defined in claim 27 further comprising lubricating means for providing a film of fluid between the ultrasonic transducer and the compression plate to lubricate and acoustically couple the ultrasonic transducer and the compression plate.

37. The apparatus as defined in claim 27 wherein the drive means further comprises:

a gantry support;

a gantry movably engaged with the gantry support for movement in the distal and proximal directions;

a carriage movably engaged with the gantry for lateral movement.

38. The apparatus as defined in claim 37 wherein the drive means further comprises:

a first motorized cable arrangement for driving the gantry along the gantry support;

a second motorized cable arrangement for driving the carriage along the gantry; and

circuitry for controlling operation of the first and second motorized cable arrangements.

39. The apparatus as defined in claim 37 further comprising:

a biopsy instrument support;

means for aligning the biopsy instrument support with the ultrasonic transducer so that a medical practitioner may perform a biopsy guided by the plurality of ultrasonic images.

40. Apparatus for generating a plurality of ultrasound images of a biological tissue, the apparatus for use with an X-ray system that forms an image of the biological tissue in a receptor, the receptor, the apparatus comprising:

a compression surface against which the biological tissue is immobilized, the compression surface being radiolucent;

an ultrasonic transducer disposed adjacent the compression surface;

a coupling medium interposed between the ultrasonic transducer and the compression surface; and

control circuitry for activating the ultrasonic transducer to generate a plurality of ultrasound images of the biological tissue while the biological tissue remains immobilized against the compression surface.

41. The apparatus as defined in claim 40 further comprising a gel pad for acoustically coupling a portion of the biological tissue to the ultrasonic transducer.

42. The apparatus as defined in claim 41 wherein the biological tissue has an X-ray attenuation characteristic, the gel pad is disposed against the compression surface and in contact with the biological tissue, and the gel pad comprises a material that conforms to the shape of the biological tissue and has an X-ray attenuation characteristic near the X-ray attenuation characteristic of the biological tissue.

43. The apparatus as defined in claim 42 wherein the gel pad reduces scattering of the X-ray radiation relative to scattering of the X-ray radiation in air.

44. The apparatus as defined in claim 41 wherein the biological tissue comprises a portion of a patient and has a non-uniform shape and a surface area, the compression surface imposes a force on the biological tissue to compress the biological tissue to a uniform thickness, and the gel pad conforms to the non-uniform shape to distribute the force over the surface area and reduce discomfort in the patient.

45. The apparatus as defined in claim 44 wherein the gel pad comprises an adherent surface that assists in positioning the biological tissue relative to the compression surface.

46. The apparatus as defined in claim 41 wherein the ultrasonic transducer comprises a multiplicity of piezoelectric transducer elements.

47. The apparatus as defined in claim 48 wherein the control circuitry further comprises circuitry for activating predetermined ones of the multiplicity of piezoelectric transducer elements to provide beam forming and elevational focussing of the acoustic energy.

48. The apparatus as defined in claim 46 wherein the control circuitry comprises circuitry for activating a predetermined plurality of the multiplicity of piezoelectric elements to generate an ultrasonic image at a predetermined location, the apparatus further comprising:

a biopsy instrument support;

means for aligning the biopsy instrument support with the predetermined plurality of piezoelectric elements so that a medical practitioner may perform a biopsy guided by the ultrasonic image at the predetermined location.

49. Apparatus for generating a plurality of ultrasound images of a biological tissue, including peripheral portions, the apparatus for use with an X-ray system that forms an image of the biological tissue in a receptor, so that when the apparatus is used with the X-ray system, the plurality of ultrasound images of the biological tissue may be correlated to the image formed in the receptor, the X-ray system including first and second compression surfaces adapted for immobilizing the biological tissue therebetween so that the biological tissue has a portion of uniform thickness and a peripheral portion of non-uniform thickness, the biological tissue having an X-ray attenuation characteristic the apparatus comprising:

an ultrasonic transducer disposed between the first and second compression surfaces;

a gel pad disposed between the first and second compression surfaces and in contact with the biological tissue, the gel pad acoustically coupling a portion of the biological tissue to the ultrasonic transducer, comprising a material that conforms to the shape of the biological tissue and having an X-ray attenuation characteristic near the X-ray attenuation characteristic of the biological tissue, the gel pad enhancing the image of the peripheral portion formed in the receptor; and

gantry means for moving the ultrasonic transducer along a curved path between the first and second compression surfaces while the biological tissue remains immobilized therebetween, so that the ultrasonic transducer generates a plurality of ultrasound images of the biological tissue that may be correlated to the image formed in the receptor.

50. The apparatus as defined in claim 49 wherein the gel pad reduces scattering of the X-ray radiation relative to scattering of the X-ray radiation in air.

51. The apparatus as defined in claim 49 wherein the biological tissue comprises a portion of a patient and has a non-uniform shape and a surface area, the first and second compression surfaces impose a force on the biological tissue, and the gel pad conforms to the non-uniform shape to distribute the force over the surface area and reduce discomfort in the patient.

52. The apparatus as defined in claim 51 wherein the gel pad comprises an adherent surface that assists in positioning the biological tissue between the first and second compression surfaces.

53. A method of obtaining an X-ray image of a biological tissue and an ultrasound image of the biological tissue that may be correlated to the X-ray image, comprising a series of steps of:

(a) immobilizing the biological tissue with respect to a reference point using a compression plate that is radiolucent and sonolucent;

(b) exposing the biological tissue to X-ray radiation to generate an X-ray image of the biological tissue in a receptor;

(c) acoustically coupling an ultrasound transducer to the compression plate to generate a plurality of ultrasound images of the biological tissue without intervening movement of the biological tissue with respect to the reference point; and

(d) displaying any one of the plurality of ultrasound images corresponding to a predetermined location on the X-ray image.

54. The method as defined in claim 53 wherein step (b) is performed after step (c).

55. The method as defined in claim 53 further comprising steps of:

(e) repeatedly generating and displaying a plurality of ultrasound images on a timewise basis;

(f) inserting a biopsy instrument into the biological tissue so that a portion of the biopsy instrument is visible in the plurality of ultrasound images; and

(g) maneuvering the biopsy instrument to a desired location within the biological tissue based on the X-ray image and the plurality of ultrasound images.

56. The method as defined in claim 53 further comprising steps of:

(e) storing the plurality of ultrasound images in a storage medium; and

(f) retrieving any one of the plurality of ultrasound images from the storage medium corresponding to a predetermined location on the X-ray image.

57. The method as defined in claim 53 further comprising a step of processing the plurality of ultrasound images to enhance the diagnostic capabilities of those images.

58. The method as defined in claim 53 further comprising steps of:

(e) repeatedly generating and displaying a plurality of ultrasound images on a timewise basis at a location within the biological tissue;

(f) processing the plurality of ultrasound images at the location to provide an indicator corresponding to blood flow at that location.

59. The method as defined in claim 53 further comprising steps of:

(e) generating a plurality of Doppler signals for the biological tissue by acoustically coupling an ultrasonic transducer to the biological tissue, without intervening movement of the biological tissue with respect to the reference point; and

(f) displaying an indicator corresponding to the plurality of Doppler signals for a predetermined location on the X-ray image.

60. The method as defined in claim 53 further comprising a series of steps of:

(e) storing the plurality of ultrasound images in a storage medium; and

(f) displaying selected ones of the plurality of ultrasound images to provide a holographic view of the interior features of the biological tissue.

61. The method as defined in claim 53 wherein the compression plate lies in an X-Y plane and each one of the ultrasound images comprises a multiplicity of digitally encoded data values obtained at a multiplicity of planes along a Z axis orthogonal to the X-Y plane, the method further comprising the steps of:

(e) summing the multiplicity of digitally encoded data values along the Z axis to generate a projection of the plurality of ultrasound images into the X-Y plane; and

(f) displaying the projection.

62. The method as defined in claim 61 further comprising a step of comparing the X-ray image to the projection to isolate selected ones of the interior features of the biological tissue.

63. The method as defined in claim 62 wherein the X-ray image and the projection are color coded.

64. The method as defined in claim 62 wherein step (a) is performed after step (c).

65. A method of screening a biological tissue for abnormalities, comprising a series of steps of:

(a) immobilizing the biological tissue with respect to a reference point using a compression plate that is radiolucent and sonolucent;

(b) exposing the biological tissue to X-ray radiation to generate an X-ray image of the biological tissue in a receptor;

(c) applying a first compressive load to the biological tissue;

(d) acoustically coupling an ultrasound transducer to the compression plate to generate a first plurality of digitally encoded ultrasound images of the biological tissue with respect to the reference point;

(e) storing the first plurality of digitally encoded ultrasound images;

(f) applying a second compressive load to the biological tissue, the second compressive load different than the first compressive load;

(g) operating the ultrasound transducer to generate a second plurality of digitally encoded ultrasound images of the biological tissue with respect to the reference point;

(h) digitally subtracting each one of the second plurality of digitally encoded ultrasound images from a corresponding one of the first plurality of digitally encoded ultrasound images with respect to the reference point;

(i) displaying the difference of first and second digitally encoded ultrasound images; and

(j) comparing the difference of the first and second digitally encoded ultrasound images at a predetermined location to a corresponding location on the X-ray image.

66. The method as defined in claim 65 wherein the first and second pluralities of digitally encoded ultrasound image are color coded.

BACKGROUND OF THE INVENTION

The use of X-ray technology for providing two-dimensional images of breast tissue for diagnosis of carcinoma or other abnormalities is well known. X-ray imaging has a number of limitations which are universally recognized by radiologists. In particular, X-ray imaging of breast tissue has the inherent limitation that a mammogram provides only a two-dimensional image of a three-dimensional object. Thus, although a potential area of concern may be indicated on a mammogram, the elevation of the subject area within the breast may be uncertain, leading to a biopsy of broader scope than would otherwise be necessary.

In addition to conventional mammograms, apparatus has been developed that employs ultrasound technology for breast tissue imaging. Ultrasound imaging devices display echoes received from a piezoelectric transducer as brightness levels proportional to the backscattered echo amplitude. The brightness levels are displayed at the appropriate echo range and transducer position or orientation, resulting in cross-sectional images of the object in a plane perpendicular to the transducer emitting face.

Previously known ultrasound equipment, in the form of dedicated ultrasound breast imaging apparatus, have met with limited acceptance by the medical community. For example, Brenden U.S. Pat. No. 3,765,403 describes the use of ultrasound technology to provide direct and holographic imaging of breast tissue. That device requires the patient to lie prone on a patient supporting surface while her breast is immersed in a water-filled tank. Taenzer U.S. Pat. No. 4,434,799 describes an alternative device wherein the patient's breast is immobilized between an ultrasonic transducer and ultrasonic receiving transducer. Both of the systems described in those patents are dedicated ultrasound systems.

In addition to dedicated apparatus, hand-held ultrasound devices have found application in performing free-hand examinations. Free-hand examination using a hand-held ultrasound transducer is described, for example, Mendelson, "Ultrasound Secures Place In Breast Ca Management" Diagnostic Imaging, Apr. 1991, pp 120-129. A drawback of such freehand examinations, when used to supplement mammography, is the inability to provide geometric registration between the mammogram and ultrasound images. This lack of registration may result in the freehand ultrasound examination being directed at a different portion of the breast tissue than would otherwise have been indicated were geometric registration possible.

For example, recent studies have shown that over 10% of the masses detected with free-hand ultrasound and initially believed to be the mammographically detected mass, were subsequently found to represent different areas of the breast. Because ultrasound can depict 2-3 times more cysts than mammography, the possibility of characterizing a malignant lesion as benign is real.

In addition, the three dimensional shape of the lesions, as reported in Homer, "Imaging Features And Management Of Characteristically Benign And Probably Benign Lesions, Rad. Clin. N. Am., 25:939-951 (1987) and the increased vascularity associated with carcinoma, as reported in Cosgrove et al.,"Color Doppler Signals From Breast Tumors", Radiology, 176:175-180 (1990), have been suggested to be added to the diagnostic criteria. Such volumetric spatial registration of the ultrasonic data with a mammogram cannot be accomplished with previously known ultrasound devices.

While there is recognition within the medical community of the advantages offered by ultrasound technology, the construction of conventional mammography and sonography equipment has prevented combination of these two technologies. In particular, polycarbonates such as Lexan.RTM., are typically used in mammography because of their tensile strength and transparency to X-ray. These materials are acoustically opaque.

On the other hand, the compression plates used in the conventional breast ultrasound devices, for example, Brenden U.S. Pat. No. 3,765,403, are composed of materials such as polystyrene or polyurethane, which have insufficient tensile strength for use in mammography equipment.

Because of their high densities, all of the materials potentially useful for the compression plates in mammography equipment have relatively high attenuation and reflection coefficients (table 1, below). These characteristics limit the use of ultrasound to low frequencies (3 MHz or below as described in Taenzer U.S. Pat. No. 4,434,799) and shallow depths. At 10 MHz and a 0.5 to 1 cm round trip path through a typical compression plate, the attenuation with most polymers would be 20-50 dB.

For any interface thicker than a quarter wavelength (several hundred microns, depending on the nominal frequency and acoustic velocity within the material) transmission loss must also be taken into account (which could exceed 50 dB). In addition, the impedance mismatch between the biological tissues, the compression plate and the transducer results in at least a 6 dB loss at each interface, or an additional total loss of 24 dB round trip. Since the total dynamic range is no greater than 100 dB for a typical ultrasound system, ultrasound imaging through previously known mammographic compression plates would be impossible.

In addition, since the acoustic propagation within the compression plate is substantially different than water or the coupling gel, refraction effects on each of the emitted waves from the elements of a phased array, would severely corrupt the beam forming process that assumes a constant velocity of 1540 m/sec.

TABLE 1 ______________________________________ Attenuation Coefficient Impedance Material (dB/MHz/cm) (Pa s/m) ______________________________________ Polyvinylchloride 11.1 3.4 Polybutane 6.1 3.2 Polyacetyl, 2.5-3.3 2.2 Polyethylene, Polypropylene Polyamid (Nylon) 1.1 2.9 Polystyrene 1 2.5 Water 0.02 1.5 ______________________________________

The lower frequencies used in the previously known ultrasonic devices would be inadequate for the diagnostic applications, which currently require 7-10 MHz transducers, yet this higher frequency requirement would increase the transmission loss by at least threefold (in dB). While it is possible to generate larger pulses in the transducer in the water bath approach, the low electro-mechanical efficiency results in heat generation. Placing the transducer directly upon the compression plate, and as a result in close proximity to the biological tissue, would require even higher energy pulses from each element. The resulting heat generation would cause damage and should be avoided.

Conway, "Occult Breast Masses: Use Of A Mammographic Localizing Grid For US Evaluation", Radiology, 181:143-146 (1991) and Brem and Gatewood,"Template Guided Breast Ultrasound", Radiology, 184:872-874 (1992), describe attempts to achieve spatial registration between a mammogram and an ultrasound image by cutting a hole in the compression plate of the mammography device to insert an ultrasound transducer. In Conway et al., a cut-open compression plate with a localization grid was used to allow acoustic transmission. Using the identical ultrasound device, the ultrasound study was performed in free-hand and through the localizing grid. Several additional X-ray exposures were needed to detect the lesion, replace the compression plate with the cut-out grid compression plate, then place the cut-out over the coordinates of the lesion. The grid positioned ultrasound detected 24% more lesions than free-hand. Ten percent were misidentified using free-hand ultrasound. None of the lesions were misidentified with the grid-guided compression.

The approach described in the foregoing articles has several practical drawbacks. For example, in Conway the patient'