In vivo port wine stain, burn and melanin depth determination using a photoacoustic probe

• US 20040039379A1
• Filed: 02/07/2003
• Published: 02/26/2004
• Est. Priority Date: 04/10/2002
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Viator, John A., Jacques, Steven L., Nelson, J. Stuart, Paltauf, Guenther
• Granted Patent: US 7,322,972 B2
• Time in Patent Office: Days
• US Class Current: 606/9
• CPC Class Codes: A61B 18/203 applying laser energy to the outside of the body
• CPC Class Codes: A61B 2017/0011 piezoelectric
• CPC Class Codes: A61B 2018/00452 Skin
• CPC Class Codes: A61B 2018/00458 Deeper parts of the skin, e.g. treatment of vascular disorders or port wine stains
• CPC Class Codes: A61B 5/0095 by applying light and detecting acoustic waves, i.e. photoacoustic measurements
• CPC Class Codes: A61B 5/443 Evaluating skin constituents, e.g. elastin, melanin, water
• CPC Class Codes: A61B 5/444 Evaluating skin marks, e.g. mole, nevi, tumour, scar
• CPC Class Codes: A61B 5/445 Evaluating skin irritation or skin trauma, e.g. rash, eczema, wound, bed sore

Abstract

A photoacoustic probe for port wine stain (PWS), burn and melanin depth measurements is comprised of optical fibers for laser light delivery and a piezoelectric element for acoustic detection. The probe induced and measured photoacoustic waves in acryl amide tissue phantoms and PWS skin in vivo. Acoustic waves were denoised using spline wavelet transforms, then deconvolved with the impulse response of the probe to yield initial subsurface pressure distributions in phantoms and skin. The waves were then analyzed for epidermal melanin concentration, using a photoacoustic melanin index (PAMI) related to the amount of laser energy absorbed by melanin. Propagation time of the photoacoustic wave was used to determine the depth of blood perfusion underlying necrotic, burned tissue. Thus, the photoacoustic probe can be used for determining PWS, burn and melanin depth for most patients receiving laser therapy.

Claims

1. An apparatus for depth profiling subsurface skin structures comprising:

a handpiece for placement against the skin;

at least one optic fiber for delivering a light pulse to the skin;

an acoustic detector disposed in the handpiece for receiving photoacoustic waves from the skin; and

a circuit coupled to the acoustic detector for processing electrical signals generated by the acoustic detector.

2. The apparatus of claim 1 further comprising a source of light coupled to the optic fiber for generating the light pulse.

3. The apparatus of claim 2 where the source of light comprises a laser.

4. The apparatus of claim 2 where the source of light comprises a flash lamp.

5. The apparatus of claim 1 where handpiece defines a chamber which is liquid filled.

6. The apparatus of claim 1 further comprising means for micropositioning the optic fiber with respect to the skin.

7. The apparatus of claim 1 where the light pulse emerging from the optic fiber generates a photoacoustic impulse in the skin and where the acoustic detector is spaced apart from the skin to create an acoustic delay in response relative to the photoacoustic impulse.

8. The apparatus of claim 1 further comprising a plurality of optic fibers, each for delivering a light pulse to the skin.

9. The apparatus of claim 8 where the plurality of optic fibers each simultaneously deliver a light pulse to the skin at a single spot.

10. The apparatus of claim 8 where the plurality of optic fibers deliver a light pulse to the skin at a plurality of wavelengths.

11. The apparatus of claim 1 where the acoustic detector comprises a piezoelectric acoustic pressure transducer.

12. The apparatus of claim 1 where the skin structure is a skin burn and where the electrical signals generated by the acoustic detector are interpretable as depth profiles of the skin burn.

13. The apparatus of claim 1 where the skin structure is a port wine stain and where the electrical signals generated by the acoustic detector are interpretable as depth profiles of the port wine stain.

14. The apparatus of claim 1 where the skin structure is melanin and where the electrical signals generated by the acoustic detector are interpretable as depth profiles or concentration of the melanin.

15. A method for depth profiling subsurface skin structures comprising:

generating a light pulse;

delivering the light pulse to the skin;

sensing acoustic waves generated in the skin in response to the delivered light pulse; and

processing the sensed acoustic waves from the skin to derive measured data corresponding to the subsurface skin structures.

16. The method of claim 15 where processing the sensed acoustic waves from the skin to derive measured data corresponding to the subsurfacesubsurface skin structures comprises deriving measured data corresponding to depth profiles of port wine stains.

17. The method of claim 15 where processing the sensed acoustic waves from the skin to derive measured data corresponding to the subsurfacesubsurface skin structures comprises deriving measured data corresponding to depth profiles of port wine stains.

18. The method of claim 15 where processing the sensed acoustic waves from the skin to derive measured data corresponding to the subsurfacesubsurface skin structures comprises deriving measured data corresponding to depth profiles of burns in the skin.

19. The method of claim 15 where processing the sensed acoustic waves from the skin to derive measured data corresponding to the subsurfacesubsurface skin structures comprises deriving measured data corresponding to depth profiles of melanin in the skin.

20. The method of claim 15 where generating a light pulse comprises generating a laser pulse with a pulse duration short enough such that the resulting acoustic energy consequently generated in the skin through thermoelastic expansion of the skin does not propagate outside of the volume of light absorption during the laser pulse.