NON-CONTACT LASER ULTRASOUND SYSTEM

Abstract

Non-contact ultrasound imaging system. The system includes a pulsed near infrared scanning laser source for illuminating a surface of a structure to generate ultrasonic elastic waves that propagate into the structure. A laser Doppler vibrometer measures vibration of the surface caused by the propagating ultrasonic waves in the structure and a data acquisition module processes data from the vibrometer to construct an image of the structure.

Claims

1. Non-contact ultrasound imaging system comprising: a pulsed near infrared scanning laser source for illuminating a surface of a structure to generate ultrasonic elastic waves that propagate into the structure; a laser Doppler vibrometer to measure vibration of the surface from the propagating ultrasonic waves in the structure; and a data acquisition module for processing data from the vibrometer to construct an image of the structure.

2. The system of claim 1 further including a camera to record locations of illuminating and vibrometer beam locations.

3. The system of claim 1 wherein the pulsed near infrared scanning laser is a Q-switched laser.

4. The system of claim 3 wherein the Q-switched laser operates at a 1-10 kilohertz framerate.

5. The system of claim 1 wherein the structure is a biological entity and the surface is skin.

6. The system of claim 1 wherein the system components are supported by an x-y translation stage mounted on a stand that fits over the structure.

7. The system of claim 1 wherein the laser source operates at approximately a 1500 nm wavelength.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0009] FIG. 1 is a schematic illustration of an embodiment the ultrasound imaging system disclosed herein.

[0010] FIG. 2 is a schematic illustration showing the creation of ultrasonic waves and measuring vibrating skin surface.

[0011] FIG. 3 includes ultrasound images of a foreign body embedded in a muscle tissue.

[0012] FIG. 4 is a schematic illustration of the system of the invention showing it mounted on a frame that fits over a subject being probed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] A pulsed near IR source (Q-switched laser) converts optical energy to ultrasonic waves within the skin surface via photoacoustic (PA) mechanisms. Laser Doppler vibrometry (LDV) is then used to measure probing ultrasound signals that return to the skin surface. A short wavelength (SWIR) or visible spectrum camera is used to record the image of the excitation and LDV beam locations on the patient target. A frame rate of 1-10 kiloHertz is adequate to capture relevant patient motion and jitter during the ultrasonic data acquisition process. A lidar system or optical camera set can also be used to map the 3D patient surface topography and then used to correct for transmitter and receiver geometries when applied to data and image processing.

[0014] The disclosed system produces useful ultrasound images in tissue while operating within eye and skin safety limits. Additionally, PA mechanisms can produce the full compilation of ultrasonic waves including compressional, shear, Rayleigh, and Love wave components. Using information from these various wave types yields not only anatomical images in the body, but can also provide elastic property distributions, in-situ that are useful for several emerging fields in medicine.

[0015] The system disclosed herein induces a probing ultrasonic wave initiated with an optical short pulse that triggers photoacoustic phenomena. This short pulse converts optical energy into mechanical energy via thermal loading, causing the optical absorbing material—human skin or structure surface—to locally deform very rapidly (stress-strain yields a propagating elastic wave) and launch the probing ultrasonic wave that can travel several inches into the body and back. The probing wave reflects off varying internal anatomical features with depth and emerges containing the subject interior image signal. The return signal is then measured at the skin or structure surface with a highly-sensitive laser Doppler vibrometer (LDV). The disclosed system does not require coupling gel or any other substance at the skin or target surface to enhance signal transmission as is the case with contact ultrasonic transducers used in routine medical practice.

[0016] With reference to FIG. 1, apparatus 10 includes an optical excitation source 12, a laser sensing receiver portion 14 and a camera portion 16. In operation, the laser 12 which may be a Q-switched laser illuminates a surface region 18 on a human body 20. The skin is thermally deformed rapidly resulting in a propagating elastic wave into the body 20. The ultrasonic wave travels into the body and is reflected back to the skin where the laser sensing receiver 14 detects the vibration at the surface. The laser sensing receiver 14 is preferably a highly sensitive laser Doppler vibrometer (LDV). The apparatus 10 may also include a data acquisition module for receiving the vibrometer information to create an image.

[0017] FIG. 2 illustrates how the system works. A pulsed optical source generates ultrasound through photoacoustic (PA) mechanisms. The laser receiver measures the vibrating return on the skin surface.

[0018] With reference now to FIG. 3, the left side panel shows a one inch thick muscle sample supported on a metal tabletop. A metal sliver is embedded one half inch below the muscle surface without disturbing the muscle surface. Its image is shown in the middle panel of FIG. 3. The rightmost panel in FIG. 3 shows a wound reflection after the metal sliver has been removed. The measurement was made from approximately a one meter standoff from the muscle specimen.

[0019] FIG. 4 shows the apparatus 10 supported on an x-y stage which is supported by the frame or stand 22. The stand 22 is useful in military field operations. The components shown in FIG. 4

[0020] include an excitation laser to launch ultrasonic waves, a fast steering mirror that directs the excitation laser and a receiving laser vibrometer that measures the ultrasonic return on the patient 10 skin surface. The components also include a shortwave infrared (SWIR) camera 16 to image the skin surface and laser contact points. The apparatus 10 also includes an acquisition system that records, stores and processes the acquired ultrasonic data to form the ultrasonic images. An optical camera can also be used to provide a fixed reference frame when using a simple red or green eye-safe laser. Lidar can also be used to provide a topographical reference of the patient surface that can be updated at a rate of 1 kilohertz to aid in data processing and image processing.

[0021] In a preferred embodiment, the Q-switched laser generates short optical pulses of approximately 3 nsec at a 1550 nm optical wavelength. A suitable beam diameter at a skin surface is 1-2 mm. Optical fluence level is 21 mJ/cm.sup.2. The laser may be a Continuum Panther OPO or a Continuum Minilite YAG Q-switched laser, for example. A suitable Q-switched Doppler vibrometer is a Polytec OFV 5000 LDV or a custom built unit.

[0022] Modifications and variations of the invention disclosed herein will be readily apparent to those of skill in the art and it is intended that all such modifications and variations be included within the scope of the appended claims.