CLAIMS 1. A method of sterilizing a mammalian subject comprising the step of directing energy from outside of the subject's body, through the skin of the scrotum into the body and onto the tissue constituting a spermatic duct to thereby kill at least some of such tissue at a location along the length of the spermatic duct, whereby scar tissue will form and occlude the spermatic duct.

2. A method as claimed in claim 1 wherein said step of directing energy includes directing ultrasonic energy.

3. A method as claimed in claim 2 wherein said directing step includes pinching the scrotum of the subject and capturing the spermatic duct in the pinched region, and applying energy through the skin covering the pinched region.

4. A method as claimed in claim 3 wherein said step of applying energy on the exterior of the pinched region includes the step of applying a probe adapted to emit energy to the pinched region of the scrotum.

5. A method as claimed in claim 4 further comprising the step of maintaining said probe in a preselected position relative to the pinched region by means of one or more guide members connected to said probe and engaged with said pinched region.

6. A method as claimed in claim 5 wherein said one or more guide members include a pair of opposed guide members projecting from said probe and wherein said pinched region of the scrotum is engaged between said pair of opposed guide members.

7. A method as claimed in claim 6 wherein said pinched region of the scrotum projects generally in a Z direction relative to said guide members and said probe, and said pinched region and said spermatic duct extend generally in a Y direction transverse to said Z direction, and wherein said step of directing ultrasonic energy includes emitting the sonic energy from one or more transducers defining an emitting surface offset from the pinched region in said Z direction, the method further comprising the step of providing a sonic transmission element extending between the emitting surface and the skin of said engaged region.

8. A method as claimed in claim 7 wherein said emitting surface is substantially in the form of a sector of a cylindrical surface having an axis extending in said Y direction, the axis of the emitting surface being disposed within the pinched region of the scrotum.

9. A method as claimed in claim 8 wherein said transducer has an f- number of about 0.5 or less.

10. A method as claimed in claim 7 wherein a first one of said one or more guide members includes first and second elements spaced apart from one another in said Y direction and defining a first space therebetween, and wherein said sonic transmission element extends into said first space and engages the skin of the pinched region in said first space.

11. A method as claimed in claim 10 wherein a second one of said one or more guide members includes first and second elements spaced apart from one another in said Y direction and defining a second space therebetween, and wherein said sonic transmission element extends into said second space and engages the skin of the pinched region in said second space.

12. A method as claimed in claim 1 wherein said step of directing energy is performed so as to deliver a predetermined dose of energy to the tissue surrounding the spermatic duct, without feedback control of such dose during the directing step.

13. A method as claimed in claim 1 further comprising the steps of. monitoring one or more effects of the applied energy and controlling the dose of energy delivered to the tissue based upon said monitoring to thereby provide feedback control of the applied dose.

14. A method as claimed in claim 13 wherein said one or more effects include echogenicity of tissue surrounding the spermatic duct.

15. A method as claimed in claim 13 wherein said step of applying energy includes the step of actuating one or more transducers to apply heating pulses of ultrasonic energy and said monitoring step includes the step of monitoring signals generated by at least one of said one or more transducers responsive to ultrasonic energy impinging thereon.

16. A method as claimed in claim 15 further comprising the step of actuating at least one of said one or more transducers to emit one or more monitoring pulses of ultrasonic energy interspersed with said heating pulses, said monitoring step including the step of detecting signals generated by at least one of said one or more transducers responsive to echoes of said monitoring pulses impinging thereon.

17. A method as claimed in claim 16 wherein said one or more monitoring pulses includes an initial monitoring pulse prior to application of said heating pulses and one or more in-process monitoring pulses after application of at least one heating pulse, and wherein said monitoring step includes comparing signals produced by at least one of said transducers responsive to said in-process monitoring pulses with signals produced by the same one of said transducers responsive to the initial monitoring pulse.

18. A method as claimed in claim 2 wherein said spermatic duct is the vas deferens.

19. A method as claimed in claim 1 further comprising the step of reversing the occlusion of said spermatic duct by surgically removing said scar tissue and reconnecting regions of said spermatic duct on opposite sides of said scar tissue.

20. A method of occluding a tubular anatomical structure in the body of a mammalian subject comprising the step of directing ultrasonic energy from outside of the subject's body, into the body and onto the tissue constituting the tubular anatomical structure to thereby kill at least some of such tissue at a location along the length of the anatomical structure, whereby scar tissue will form and occlude the anatomical structure.

21. A method as claimed in claim 20 wherein said directing step includes maintaining a probe having one or more ultrasonic transducers associated therewith and adapted to emit ultrasonic energy so that said ultrasonic energy will be focused in a focal region at known disposition relative to the probe at a preselected disposition relative to a portion of the subject's body incorporating the anatomical structure so that the focal region encompasses the anatomical structure.

22. A method as claimed in claim 21 wherein said step of maintaining said probe in a preselected disposition relative to the portion of the subject's body is performed by engaging one or more guide members connected to said probe and with such portion of the subject's body.

23. A method as claimed in claim 22 wherein said one or more guide members include a pair of opposed guide members and wherein said portion of the subject's body is pinched between said pair of opposed guide members.

24. A method as claimed in claim 23 wherein said portion of the body generally in a Z direction relative to said guide members and said probe, and said pinched portion and said anatomical structure extend generally in a Y direction transverse to said Z direction, and wherein said step of directing ultrasonic energy includes emitting the sonic energy from one or more transducers defining an emitting surface offset from the pinched region in said Z direction, the method further comprising the step of providing a sonic transmission element extending between the emitting surface and the skin of said pinched portion.

25. A method as claimed in claim 24 wherein said emitting surface is substantially in the form of a sector of a cylindrical surface having an axis extending in said Y direction, the axis of the emitting surface being disposed within the pinched portion of the subject's body.

26. A method as claimed in claim 24 wherein a first one of said one or more guide members includes first and second elements spaced apart from one another in said Y direction and defining a first space therebetween, and wherein said sonic transmission element extends into said first space and engages the skin of the pinched region in said first space.

27. A method as claimed in claim 26 wherein a second one of said one or more guide members includes first and second elements spaced apart from one another in said Y direction and defining a second space therebetween, and wherein said sonic transmission element extends into said second space and engages the skin of the pinched portion in said second space.

28. A method as claimed in claim 20 wherein said step of directing energy is performed so as to deliver a predetermined dose of energy to the tissue surrounding. the anatomical structure, without feedback control of such dose during the directing step.

29. A method as claimed in claim 20 further comprising the steps of monitoring one or more effects of the applied energy and controlling the dose of energy delivered to the tissue based upon said monitoring to thereby provide feedback control of the applied dose.

30. A method as claimed in claim 29 wherein said one or more effects include echogenicity of tissue surrounding the anatomical structure.

31. A method as claimed in claim 29 wherein said step of applying energy includes the step of actuating one or more transducers to apply heating pulses of ultrasonic energy and said monitoring step includes the step of monitoring signals generated by at least one of said one or more transducers responsive to ultrasonic energy impinging thereon.

32. A method as claimed in claim 31 further comprising the step of actuating at least one of said one or more transducers to emit one or more monitoring pulses of ultrasonic energy interspersed with said heating pulses, said monitoring step including the step of detecting signals generated by at least one of said one or more transducers responsive to echoes of said monitoring pulses impinging thereon.

33. A method as ciaimed in claim 32 wherein said one or more monitoring pulses includes an initial monitoring pulse prior to application of said heating pulses and one or more in-process monitoring pulses after application of at least one heating pulse, and wherein said monitoring step includes comparing signals produced by at least one of said transducers responsive to said in-process monitoring pulses with signals produced by the same one of said transducers responsive to the initial monitoring pulse.

34. A method as claimed in claim 20 further comprising the step of reversing the occlusion of said tubular structure surgically by removing said scar tissue and reconnecting regions of said tubular structure on opposite sides of said scar tissue.

35. A method of performing hyperthermia within the body of a mammalian subject comprising the steps of: providing an exogenous ultrasonic contrast medium within the body of the subject, said contrast medium having sonic propagation properties different than the sonic propagation properties of the tissue surrounding the medium; and directing ultrasonic energy into the body and focusing the ultrasonic energy in a. focal region encompassing at least a portion of the ultrasonic contrast medium, said ultrasonic energy being dissipated preferentially in said medium or at an interface between said contrast medium and the tissue surrounding the medium so as to heat the tissue surrounding the medium.

36. A method as claimed in claim 35 wherein said ultrasonic energy heats the tissue surrounding the medium to a degree sufficient to kill at least some of such tissue.

37. A method as claimed in claim 36 wherein said ultrasonic contrast medium is disposed within a tubular anatomical structure and wherein said ultrasonic energy heats the tissue surrounding the tubular structure at one or more locations along such structure, whereby scar tissue will form in said tubular structure at said one or more locations.

38. A method as claimed in claim 35 wherein said exogenous ultrasonic contrast medium is a sonically dispersive medium including a fluid and a plurality of micro particles having acoustic impedance different from the acoustic impedance of the fluid.

39. A method as claimed in claim 38 wherein said micro particles include gas-filled micro spheres.

40. A method as claimed in claim 37 wherein said structure is selected from the group consisting of blood vessels, fallopian tubes, structures of the urinary tract and spermatic ducts.

41. A method as claimed in claim 37 further comprising imaging a region of the subject including at least a portion of said tubular structure by an ultrasonic imaging technique while said contrast medium is present in said tubular structure.

42. A method as claimed in claim 41 further comprising the step of aiming said ultrasonic energy at least in part based on the image derived from said ultrasonic imaging technique.

43. Apparatus for occluding a tubular anatomical structure including: (a) a probe including a housing having an operative region and one or more ultrasonic transducers operatively associated with said housing, said transducers being adapted to deliver ultrasonic energy at a focal region having a known disposition relative to said operative region of said housing; and (b) one or more guide members projecting from said housing for engaging a portion of a subject's body to hold that portion of the body in position relative to the operative region of the housing so that the focal region will lie at a known disposition to the body portion engaged by the guide members.

44. Apparatus as claimed in claim 43 wherein said one or more guide members are adapted to engage the skin of the subject's body covering the engaged portion of the body.

45. Apparatus as claimed in claim 43 wherein said one or more guide members include first and second opposed guide members adapted to receive a pinched portion of the body and maintain said operative region in preselected disposition relative to said pinched region.

46. Apparatus as claimed in claim 45 wherein one or both of said guide members is movable relative to the housing so that said guide members can be moved toward and away from one another so as to pinch a portion of the subject's body in a gap between said guide members.

47. Apparatus as claimed in claim 46 wherein guide members are adapted to pinch said portion of the body therebetween so that the pinched portion projects generally in a Z direction relative to said guide members and said probe, said one or more transducers defining an emitting surface offset in said Z direction from the gap between said guide members.

48. Apparatus as claimed in claim 47 wherein said emitting surface is substantially in the form of a sector of a cylindrical surface having an axis extending in a Y direction transverse to said Z direction, said guide members being movable towards and away from one another generally in an X direction transverse to said Y and Z directions, the axis of the emitting surface being disposed within the gap between said guide members.

49. Apparatus as claimed in claim 47 wherein said transducer has an f- number less than 1.

50. Apparatus as claimed in claim 47 wherein said first guide member includes first and second elements spaced apart from one another in said Y direction and defining a first space therebetween.

51. Apparatus as claimed in claim 50 wherein a second one of said one or more guide members includes first and second elements spaced apart from one another in said Y direction and defining a second space therebetween.

52. Apparatus as claimed in claim 51 further comprising a sonic transmission element extending between the emitting surface and the gap between. the guide members so that the flexible sonic transmission element will engage the skin of the pinched portion of the body held in said gap, said sonic transmission element extending into said spaces defined by said guide members.

53. Apparatus as claimed in claim 46 wherein said one or more transducers are adapted to deliver ultrasonic energy at a focal location, the apparatus further including means for moving said focal location relative to said housing as said guide members move towards and away from one another.

54. Apparatus as claimed in claim 46 wherein said one or more transducers include one or more transducers mounted to a carriage, said carriage being movable in carriage movement directions so that said carriage moves toward said guide members as said guide members move toward one another.