Internal structure holography

#The present invention relates to a method and apparatus for internal examination of cavities and passageways of various structural bodies, and includes a method and apparatus for examination of the internal features of organs and passageways of the human body and of various regions of mechanical structures. More particularly, this invention concerns the use of laser beam sources placed outside of structure for laser hologram recordation of the appearance of selected features of cavities and passageways of the structure.

#Previous methods and apparatus for examination of the internal features of selected cavities and passageways of structures have suffered from a number of deficiencies and limitations. Prior methods and apparatus include the use of motion picture recordation and various still photography techniques which only provide two dimensional visualization of the structure. The technique of passage of a small optical viewing fiber into the structure limits the examination to an extremely small field of view, typically on the order of several millimeters in diameter. Another method employs x-ray scanning from a variety of angles, but this has much lower resolution than holographic techniques. Furthermore, such equipment is expensive to purchase and maintain, and the radiation exposure may prove harmful to the subject structure in the case of living tissue examinations. Current laser holographic techniques for internal examination utilize external laser beam sources which are quite expensive to purchase and maintain. They also are impractical to use due to assembly and alignment difficulties. In addition, they provide, under the best circumstances, only marginal quality holograms of the desired structure.

#A general object of the present invention is to provide a method and apparatus for recordation of holograms of the internal features of selected cavities and passageways of various structural bodies.

#Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a cross-sectional view of a cavity and passageway of a structure and a holographic probe positioned within the passageway of the structure;

#FIG. 2 is a cross-sectional view of the holographic probe positioned in the cavity of the structure with a holocamera positioned to produce a single beam reflection hologram;

#Referring to FIGS. 1-5, each holographic probe 10 generally includes a placement means such as probe housing 12, which may be rigid or flexible as needed to enable the placement or positioning of the distal, or examining, end of the probe housing 12 within the selected cavity or passageway of the structure, for example, within a cavity 14 to enable laser holographic recordation of the appearance of cavity walls 16. The positioning of the holographic probe 10 may be aided by an optical viewing fiber 17 to permit the examiner to maneuver the distal end of the holographic probe 10 to the desired location within the structure. In a preferred configuration the probe housing 12 is a flexible cylindrical tube and provides probe passageway 18 for transfer to the cavity 14 of a holocamera, indicated generally at 19. The holocamera 19 includes the viewing fiber 17, a lasing means and a recordation means for formation of the desired hologram. The holocamera 19 must be coupled to the distal end of the probe 10 or to a separate placement means to enable the holocamera 19 to be moved through the probe passageway 18 and to be placed at the desired location. One method of assisting in the smooth transfer of the holocamera 19 through the passageway 18 is to use one or more center spacer rings 21 which are positioned around the various components of the holocamera 19 and which support these components near the center of the passageway 18 of the probe housing 12 (i.e. see the fragmentary vertical sectional view of FIG. 5). The smooth, outer circumferential surface of the spacer rings 21 has a slightly smaller diameter than the inside diameter of the probe housing 12 and rides against the smooth inner walls of the probe housing 12 and therefore enables the smooth transfer of the holocamera 19 through the passageway 18.

#The lasing means positioned within the cavity 14 includes at least one laser beam source, such as a conventional laser waveguide terminating within the cavity 14 to provide a laser beam from an external laser source, or alternatively from an internally positioned diode laser 22 as shown in FIGS. 1-4. The recordation means is preferably photographic film 20 sensitive to laser light and typically is a silver halide based film sensitive to laser light with a wavelength below 750 nm.

#Diode lasers provide an extremely compact form of lasing means since the diode dimensions are typically in the millimeter size range, and as shown in FIGS. 1-4 the only electrical connections are two small wire leads 23 to and from each diode to provide power from a power supply (not shown). Therefore, by using diode lasers, the size of the holocamera 19 can be drastically reduced. Reducing the size of the holocamera 19 thus simplifies the recordation of a hologram within the cavity 14 of a structure, particularly for hologram recordation in a small cavity or in a cavity which is accessible only through a very narrow passageway. Examples of diode lasers which emit in the range of sensitivity of the preferred silver halide based film include GaAlAs diodes with a wavelength of 748 nm (see Appl. Optics 19(13), 2096, (1980)) and AlGaAs double heterojunction diodes with a wavelength of 680 to 700 nm at room temperature (see Appl. Phys. Lettr. 41(9), 796 (1982)). These reference materials are incorporated by reference herein.