Abstract:
Embodiments of the present invention are directed to various aspects of imaging systems, including permeable and impermeable barriers separating liquid compartments, one of which contains the object to be imaged and the other an ultrasonic transducer, a fluidic bearing between a transducer carriage and guide supporting the carriage, a linear motor for the carriage, and a location sensing device for the carriage. A method and apparatus are disclosed for performing an ultrasound scan on a body part and specifically an instrument which directly attaches to the surface of the body. This apparatus provides high resolution images and increased depth of imaging for high resolution ultrasound of targeted subsurface body tissues. Targeted tissues may include joints, ocular structures, and internal organs. The method and apparatus stabilize and provide accurate determination of the position of the body part relative to the ultrasound probe.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation-in-part of U.S. application Ser. No. 14/278,960, filed May 15, 2014, entitled “Innovative Components for an Ultrasonic Arc Scanning Apparatus”, which is a divisional of U.S. application Ser. No. 12/347,674, filed Dec. 31, 2008, entitled “Innovative Components for an Ultrasonic Arc Scanning Apparatus”, which claims the benefits, under 35 U.S.C. §119(e), of U.S. Provisional Application Ser. Nos. 61/018,606 entitled “Innovative Components for an Ultrasonic Arc Scanning Apparatus”, filed Jan. 2, 2008; 61/022,449 entitled “Innovative Components for an Ultrasonic Arc Scanning Apparatus”, filed Jan. 21, 2008; 61/042,141 entitled “Innovative Components for an Ultrasonic Arc Scanning Apparatus”, filed Apr. 3, 2008; and 61/045,447 entitled “Innovative Components for an Ultrasonic Arc Scanning Apparatus”, filed Apr. 16, 2008, all of which are incorporated herein by these references. 
         [0002]    The present application is also a continuation-in-part of U.S. application Ser. No. 13/796,931, filed Mar. 12, 2013, entitled “Precision Ultrasonic Scanner for Body Parts with Extended Imaging Depth”, which claims the benefits, under 35 U.S.C. §119(e), of U.S. Provisional Application Ser. No. 61/609,626 entitled “Ultrasonic Scanner for Body Parts” filed Mar. 12, 2012 and U.S. Provisional Application Ser. No. 61/611,903 entitled “Extension of Imaging Depth for Ultrasonic Scanner” filed Mar. 16, 2012, all of which are incorporated herein by these references. 
     
    
     FIELD 
       [0003]    The present invention relates in general to a method and apparatus for performing an ultrasound scan on a body part and specifically to an instrument which directly attaches to the surface of the body yet provides very high resolution images. The present invention includes ultrasonic imaging of biological materials such as the joints, internal organs and ocular structures such as the cornea and natural lens of the eye. 
       BACKGROUND 
       [0004]    Ultrasonic imaging has found use in accurate measurement of structures of the eye, such as, for example, the cornea. Such measurements provide an ophthalmic surgeon valuable information that he can use to guide various surgical procedures performed on the cornea, one of the principal ones being the LASIK procedure for correcting refractive errors. They also provide diagnostic information after surgery has been performed to assess the geometrical location of corneal features such as the LASIK scar. This allows the surgeon to assess post surgical changes in the cornea as the cornea heals and to take steps to correct problems that can develop. 
         [0005]    Ultrasonic imaging of the cornea presents a problem not generally encountered in other types of tissue. The corneal surfaces are necessarily smooth and spherically shaped to perform the optical function of focusing light rays. Because the corneal structures are smooth and regular, ultrasonic energy is reflected only in specific directions. In particular, an ultrasound beam from a transducer will only be reflected directly back to that transducer when the beam is aligned perpendicular to the corneal surface. This kind of reflective property is called specular reflection. 
         [0006]    Because of the specular property of corneal surfaces, it will be appreciated that special care must be taken to align the transducer with the cornea at each position from which a partial image is to be formed. Ultrasonic imaging of large portions of the cornea can be accomplished by scanning the transducer along the cornea surface while continually adjusting the alignment of the transducer to provide a beam that is always directed toward the cornea&#39;s center of curvature. 
         [0007]    Corneal imaging and measuring of corneal dimensions require that the scanning motion of the transducer be smooth and precisely aligned. Departures, even as small as 5 microns, of the transducer position from a circular path or of the beam&#39;s direction from the center of curvature can significantly degrade the resulting image. Mechanisms for performing the requisite scan alignment are described in U.S. Pat. No. 6,491,637 and U.S. Pat. No. 5,331,962 which are incorporated herein by reference. The reference “Ultrasonography of the Eye and Orbit”, Second Edition, Coleman et al., published by Lippincott Williams &amp; Wilkins, 2006 contains an excellent historical and technical summary of ultrasonic imaging of the eye and is incorporated herein by this reference. 
         [0008]    While ultrasonic imaging may be used by ophthalmologists for quantitative analysis of laser refractive surgery, it may also be used for implantation of corneal and phakic lenses, implantation of intraocular lenses and specialty procedures such as glaucoma and cataract treatment. 
         [0009]    Except for on-axis measurements, dimensions of eye components behind the iris cannot be determined by optical means. New procedures such as implantation of accommodative lenses may provide nearly perfect vision without spectacles or contact lenses. Implantation of accommodative lenses requires precision measurements of, for example, the lens width for successful lens implantation. Ultrasonic imaging can be used to provide the required accurate images of the lens especially where it attaches to the ciliary muscle which is well off-axis and behind the iris and therefore not accessible to optical imaging. 
         [0010]    It must be appreciated that ultrasonic imaging requires a liquid medium to be interposed between the object being imaged and the transducer, which requires in turn that the eye, the transducer, and the path between them be at all times be immersed in a liquid medium. Concern for safety of the cornea introduces the practical requirement that the liquid medium be either pure water or normal saline water solution. In either case, the entire mechanism or major portions of it must be submerged in water for long periods. 
         [0011]    Conventional mechanical components for guiding and controlling the motion of the transducer, such as journal, ball or roller bearings, are ill-suited for underwater operation. Films inevitably form on the bearing components, interfering with their smooth operation. Anti-fouling solutions cannot be added to the water because they introduce an unacceptable risk of injury to the patient&#39;s eye even if the eye is separated from the main body of the liquid by a thin, ultrasonically transparent barrier. Leaks through the barrier film or accidental perforation of the barrier film are an ever present possibility in a practical clinical device. 
         [0012]    There remains, therefore, a need for a versatile scan head and transducer positioning apparatus; a water-proof arc scanning motor; an accurate transducer locator method; a fluid bearing method that can provide smooth scanning motion; and a disposable eyepiece, all of which are necessary for an improved ultrasonic arc scanning apparatus that can provide precision imaging for ophthalmology and optometry applications. 
         [0013]    Another challenge for any medical imaging system is to provide the highest possible image resolution while also attaining a high depth of image at a reasonable cost. Optical systems such as optical coherence tomography are compact and cost effective and provide excellent resolution. However, they are only capable of imaging a few millimeters into any opaque tissue surface as the light is rapidly absorbed. Current ultrasound systems are very compact and cost effective and have high tissue penetration depths of 100 mm or more. However, they offer relatively low resolution due to their low range of operating frequencies from about 5 MHz to about 10 MHz. MM systems are well-known imaging systems that provide both high depth of image and high resolution. However, they are characterized by high cost, large size and a costly dedicated infrastructure. High frequency ultrasound systems (from about 20 MHz to about 80 MHz) can provide high resolution but only with a limited image depth. 
         [0014]    There remains a further need for a low cost, portable ultrasound imaging system that has substantially higher resolution than currently available devices and yet provides a depth of image of that is of high utility for medical diagnosticians. 
       SUMMARY 
       [0015]    These and other needs are addressed by the present invention. The various embodiments and configurations of the present invention are directed generally to ultrasonic imaging of biological materials such as the cornea and lens of the eye and in particular directed to components for an ultrasonic arc scanning apparatus such as a scan head positioning apparatus, a water-proof arc scanning motor, a fluidic bearing and an eyepiece, all of which can be used to, improve the accuracy, precision and ease of use of an ultrasonic arc scanning apparatus. 
         [0016]    In one embodiment, a compact scan head positioning apparatus is disclosed. The function of this apparatus is to position the arc scanning assembly and ultrasonic transducer so that the transducer head is continuously following an arc guide centrated at a desired location. The arc guide has a radius of curvature that is approximately that of the eye component to be scanned. A successful scan often requires that the center of curvature of the arc assembly approximately match the center of curvature of the eye component of interest and that the scan head positioning apparatus be well-positioned to take advantage of the precision of a high-frequency ultrasonic pulse. A portion of the scan head positioning apparatus is installed in ambient air while a second portion of the scan head positioning apparatus containing the arc scanning head is installed in a chamber that is filled with water when operational. Thus, the scan head positioning apparatus should have both translating and rotating seals that function over distances and angles required to achieve the desired positioning of the arc scanning head relative to the component of the patient&#39;s eye to be scanned. 
         [0017]    In another embodiment, a fluidic bearing mechanism is disclosed. The function of the bearing is to allow smooth motion of the transducer carriage assembly along the arc guide which has been positioned by a scan head positioning apparatus such as described above. A successful scan normally requires that the transducer assembly move smoothly along the arc guide to take advantage of the precision of a high frequency ultrasonic pulse. 
         [0018]    In one configuration, the fluidic bearing mechanism is defined by a number of liquid flow passages in one or more of the arcuate guide. The liquid is pressurized to flow through the liquid passages and forms a liquid film along a selected interface between the guide assembly and carriage. A distance between the guide and carriage at the selected interface is greater than in the absence of the pressurized liquid. 
         [0019]    In yet another embodiment, a motor capable of being operated safely under water is disclosed. The function of the motor is to move a transducer carriage assembly rapidly back and forth along a normally fixed arc guide so as to allow an ultrasonic scan of an eye component to be made. 
         [0020]    In one configuration, the motor includes one or more magnets in one of the carriage and guide, and an iron-containing core surrounded by one or more electric coils in the other of the carriage and guide. In a preferred implementation, first and second magnets are in the carriage, and the electric coil and iron-containing core are in a guide track. The first and second magnets are positioned side-by-side, with the north-south polarities being opposed to one another. A long dimension of the electric coil(s) is adjacent to a face of the magnets to substantially maximize a propelling force. In a particularly preferred implementation, a mass of the carriage ranges from about 0.1 kg to about 0.3 kg. The electric coil is formed by a number of coil segments, with each of a number of subsets of the coil segments being powered selectively and independently by an electric circuit. A force caused by an electric current in a subset of the coil segments and local B-fields of the first and second magnets are in a common direction. 
         [0021]    In another embodiment, a carriage location sensing device is provided to determine a location of the carriage relative to the guide assembly. The sensing device can have numerous configurations. In one configuration, the location sensing device includes a position encoder mounted on the carriage. The encoder senses a position of the carriage by reading a magnetic strip positioned along a length of the guide track. In another configuration, the location sensing device includes an optical encoder mounted on the carriage. The optical encoder senses a position of the carriage by illuminating a length of the guide track with light and sensing one or more of a refractive, diffractive, diffusive, and reflective distribution of light. For example, the encoder can illuminate a bar code positioned along a length of the arc guide. The bar code will produce a unique distribution of reflected light at any position along the length of guide. In another configuration, the locating sensing device includes a magnetic field sensor. The sensed magnetic field is related to a position along the guide. In yet another configuration, the location sensing device includes a mechanical counter. The mechanical counter produces a count, which is related to dimensional units and to a position along the guide. 
         [0022]    Knowing the position of the carriage as a function of time can provide benefits. In a carriage motor having one or more magnets and an iron-containing core surrounded by electric coil segments, a controller, for example, can, at a selected point in time, selectively energize an electric coil segment in proximity to a sensed position of the carriage. The controller can, additionally or alternatively and at a selected point in time, selectively energize the transducer in response to a sensed position of the carriage to produce a non-uniform, desired physical spacing of ultrasound pulses. Position tracking is particularly beneficial where the carriage has a non-uniform velocity and/or acceleration along the guide. Simply put, the sensing device can provide precise position of the transducer carriage along the arc guide assembly which, in turn, allows for a precise and accurate ultrasonic scan to be made. 
         [0023]    In yet another embodiment, three configurations of an eyepiece are disclosed. These all provide an acoustic path for ultrasonic scanning and separate the water in which the patient&#39;s eye is immersed, from the water in the chamber in which the positioning and arc guide assembly are contained. These configurations are relatively free from annoying leakage problems, are comfortable to the patient and can be manufactured for a low cost as the eyepiece should be replaced for every new patient. The different configurations incorporate different attachment and sealing mechanisms. 
         [0024]    By way of example, a first configuration of an imaging device includes:
   (a) an eyepiece for receiving an eye of a patient;   (b) a first liquid chamber in contact with an ultrasonic transducer;   (c) a second liquid chamber in contact with the patient&#39;s eye to be imaged by the ultrasonic transducer; and
       (d) a barrier separating the first and second liquid chambers, wherein at least one of the following is true:
           (D1) the second liquid chamber comprises a drain port to drain liquid from the first liquid chamber; and   (D2) the barrier is permeable to the liquid but impermeable to selected biological microbes, the microbes being selected from the group consisting of bacterium, virus, and fungus.   
           
       
 
         [0031]    In another embodiment, a second configuration of an imaging device includes an eyepiece that includes a separate face seal ring. The face seal ring is filled with a liquid to better conform to a patient&#39;s face. 
         [0032]    The present disclosure is also directed towards providing an ultrasound imaging system that is portable. Such a system may be directly attached to the surface of the body and provide high resolution images of targeted subsurface body tissues with image resolution far superior to that of known state of the art ultrasound instruments without the need for a large, fixed and cumbersome instrument as required by other imaging technologies such as X-ray or Mill. Targeted tissues may include but not be limited to joints, ocular structures, and internal organs. 
         [0033]    The present disclosure is also directed towards providing an ultrasound imaging system that can produce high image resolution (down to about 100 μm) at depths in the range of about 50 mm to about 60 mm. A number of known techniques are combined in a novel fashion and facilitated by an ultrasound system such as described above that stabilize the body part (or eye in some specific cases) relative to the ultrasound probe. Where the highest precision is required, a means of further elimination of movement due to breathing or heart beat is also disclosed. 
         [0034]    An ultrasound scanner system is also disclosed, comprising (1) an instrument body; (2) a linear positioner assembly interconnected to the instrument body; (3) an ultrasound probe which emits and receives an ultrasound pulse, the ultrasound probe interconnected to the linear positioner assembly wherein the ultrasound probe may operate in at least one dimension; (4) an instrument chamber disposed within the body and engaged with a membrane; and (5) a sealing chamber engaged with the membrane and a scanned object, wherein a transducer in the ultrasound probe emits and receives the ultrasound pulse through the instrument chamber, the membrane and the sealing chamber, wherein the ultrasound pulse contacts the scanned object. 
         [0035]    A method is disclosed, comprising (1) sealing an ultrasound scanner to a scanned object; (2) filling a sealing chamber in a body of the ultrasound scanner with a sealing chamber fluid to provide a low acoustic impedance interface between the ultrasound scanner and a scanned object surface; (3) emitting and receiving an ultrasound pulse from a transducer contained in an ultrasound probe to generate an ultrasound image of a target matter within the scanned object. 
         [0036]    The following definitions are used herein: 
         [0037]    An A-scan is representation of the reflected amplitudes of ultrasonic pulses emitted by an ultrasonic transducer as a function of time. 
         [0038]    An accommodative lens, also known as a presbyopic lens or presby lens, is an intraocular lens implant that changes its focal distance in response to contraction of the ciliary muscle. When successfully implanted, an accommodative lens reverses presbyopia, the inability of the eye to change its focal distance from far to near. 
         [0039]    Aligning means positioning the transducer and transducer carriage guide preferably accurately and reproducibly in space with respect to a feature of the eye component of interest (such as the center of curvature or boundary of the cornea, lens, retina, etcetera). 
         [0040]    The anterior chamber comprises the region of the eye from the front of the eye to the iris. 
         [0041]    The anterior segment comprises the region of the eye from the front of the eye to just beyond the back of the lens. 
         [0042]    An arc scanner is a scanning device where the sensor moves in a substantially precise arc about the center of the area to be scanned with its beam constantly directed through a central point. 
         [0043]    Arc scanning transducer center of curvature is the same as the center of curvature of the arc scanning guide. 
         [0044]    Auto-centering means automatically, typically under computer control, causing centration of the arc scanning transducer with the eye component of interest. 
         [0045]    A B-scan is representation of data as a by converting A-scan data using acoustic velocities to an image of the eye using grayscales which correspond to A-scan amplitudes. 
         [0046]    A canthus is the angular junction of the eyelids at either corner of the eye where the upper and lower eyelids meet. 
         [0047]    Centration means substantially aligning the center of curvature of the arc scanning transducer in space with the center of curvature of the eye component of interest (such as the cornea, lens, retina, etcetera) such that rays from the transducer pass through both centers of curvature. A special case is when both centers of curvature are coincident. 
         [0048]    The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes. There are three sets of ciliary muscles in the eye, the longitudinal, radial, and circular muscles. They are near the front of the eye, above and below the lens. They are attached to the lens by connective tissue called the zonule of Zinn, and are responsible for shaping the lens to focus light on the retina. When the ciliary muscle relaxes, it flattens the lens, generally improving the focus for farther objects. When it contracts, the lens becomes more convex, generally improving the focus for closer objects. 
         [0049]    Depth of focus is the distance over which the image plane can be displaced while a single object plane remains in acceptably sharp focus. The depth of focus is substantially symmetrical about the image plane when the image plane is at the focal distance. 
         [0050]    Fixation means having the patient focus an eye on an optical target such that the eye&#39;s optical axis is in a known spatial relationship with the optical target. In fixation, the light source is axially aligned in the arc plane with the light source in the center of the arc so as to obtain maximum signal strength such that moving away from the center of the arc in either direction results in signal strength diminishing equally in either direction away from the center. 
         [0051]    The focal length or focal distance of a focused ultrasound system is the distance between the transducer element (which emits an ultrasound pulse from a finite diameter element) and the point where the ultrasound beam diameter is a minimum and generally of maximum amplitude. The beam at this minimum diameter is said to be in focus. 
         [0052]    A guide is an apparatus for directing the motion of another apparatus. 
         [0053]    Haptics are little curved hair-like protrusions extending from the outer diameter of some types of artificial lenses. These haptics attach these lens to the ciliary muscle by protruding into the ciliary sulcus and allow the lens to accommodate in response to the action of the ciliary muscle. 
         [0054]    An intraocular lens is an artificial lens that is implanted in the eye to take the place of the natural lens. 
         [0055]    LASIK is a procedure performed on the cornea for correcting refractive errors, such as myopia, hyperopia, and astigmatism. Commonly, an excimer laser selectively removes tissue from the inside of the cornea, after exposing it by cutting a thin flap, so as to reshape the external shape of the cornea. 
         [0056]    A meridian is a plane that cuts through a portion of a three-dimensional component such as the cornea or natural lens of the eye and its angle is expressed relative to a horizon defined by the canthi. 
         [0057]    MRI is magnetic resonance imaging. 
         [0058]    The natural lens (also known as the aquula or crystalline lens) is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation. The lens is located in the anterior segment of the eye behind the iris. The lens is suspended in place by the zonular fibers, which attach to the lens near its equatorial line and connect the lens to the ciliary body. The lens has an ellipsoid, biconvex shape whose size and shape can change due to accommodation and due to growth during aging. The lens is comprised of three main parts: namely the lens capsule, the lens epithelium, and the lens fibers. The lens capsule forms the outermost layer of the lens and the lens fibers form the bulk of the interior of the lens. The cells of the lens epithelium, located between the lens capsule and the outermost layer of lens fibers, are generally found only on the anterior side of the lens. 
         [0059]    Ocular means having to do with the eye or eyeball. 
         [0060]    Ophthalmology means the branch of medicine that deals with the eye. 
         [0061]    Optical as used herein refers to processes that use light rays. 
         [0062]    The optical axis of the eye is the line of best fit joining the centers of curvature of the refracting surfaces (the anterior and posterior surfaces of the cornea and lens). 
         [0063]    Pachymetery or corneal pachymetery is technically referred to as Time Domain Reflectometry ultrasound. A pulse of ultrasonic energy is sent toward the cornea and the time spacing of the returning echoes are used to arrive at corneal thickness. 
         [0064]    Phakic intraocular lenses, or phakic lenses, are lenses made of plastic or silicone that are implanted into the eye permanently to reduce a person&#39;s need for glasses or contact lenses. Phakic refers to the fact that the lens is implanted into the eye without removing the eye&#39;s natural lens. During phakic lens implantation surgery, a small incision is normally made in the front of the eye. The phakic lens is inserted through the incision and placed just in front of or just behind the iris. 
         [0065]    The posterior chamber comprises the region of the eye from the back of the iris to the front of the lens. 
         [0066]    The posterior segment comprises the region of the eye from the back of the lens to the rear of the eye comprising the retina and optical nerve. 
         [0067]    Presbyiopia is typically caused by a loss of elasticity of the natural lens inside the eye. This occurs as part of the ageing process and, although it cannot be ‘cured’, it can be corrected by wearing glasses or implanting an artificial lens. 
         [0068]    Purkinje images are reflections of objects from structure of the eye. There are at least four Purkinje images that are visible on looking at an eye. The first Purkinje image (P 1 ) is the reflection from the outer surface of the cornea. The second Purkinje image (P 2 ) is the reflection from the inner surface of the cornea. The third Purkinje image (P 3 ) is the reflection from the outer (anterior) surface of the lens. The fourth Purkinje image (P 4 ) is the reflection from the inner (posterior) surface of the lens. Unlike the others, P 4  is an inverted image. The first and fourth Purkinje images are used by some eye trackers, devices to measure the position of an eye. Purkinje images are named after Czech anatomist Jan Evangelista Purkyn{hacek over (e)} (1787-1869). 
         [0069]    Refractive means anything pertaining to the focusing of light rays by the various components of the eye. 
         [0070]    Registration means aligning. 
         [0071]    Sector scanner is an ultrasonic scanner that sweeps out a sector like a radar. The swept area is pie-shaped with its central point typically located near the face of the ultrasound transducer. 
         [0072]    A specular surface means a mirror-like surface that reflects either optical or acoustic waves. For example, an ultrasound beam emanating from a transducer will only be reflected directly back to that transducer when the beam is aligned perpendicular to a specular surface. 
         [0073]    The ciliary sulcus is the groove between the iris and ciliary body. The scleral sulcus is a slight groove at the junction of the sclera and cornea. 
         [0074]    A track is an apparatus along which another apparatus moves. 
         [0075]    Ultrasonic means sound that is above the human ear&#39;s upper frequency limit. When used for imaging an object like the eye, the sound passes through a liquid medium, and its frequency is many orders of magnitude greater than can be detected by the human ear. For high-resolution acoustic imaging in the eye, the frequency is typically in the approximate range of about 5 to about 80 MHz. 
         [0076]    Ultrasound probe means an assembly comprising a transducer element (typically a piezoelectric material), a probe body and electrical conduits that carry transmitted and received signals from the element to an analog-to-digital (A/D) converter external to the probe. 
         [0077]    Ultrasound pulse means a group of ultrasound waves centered around a center frequency where the pulse comprises at least one and up to about ten wave cycles. The ultrasound pulse is therefore a short burst of one to about ten wavelengths truncated at both ends of the wave train. An ultrasound pulse is further described in “Ultrasonography of the Eye and Orbit”, Second Edition, Coleman et al., published by Lippincott Williams &amp; Wilkins, 2006, which is incorporated herein by reference. 
         [0078]    The visual axis of the eye is the line joining the object of interest and the fovea and which passes through the nodal points. 
         [0079]    Zonules are tension-able ligaments extending from near the outer diameter of the crystalline lens. The zonules attach the lens to the ciliary body which allows the lens to accommodate in response to the action of the ciliary muscle. 
         [0080]    As used herein, “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0081]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating some embodiments and are not to be construed as limiting the invention. 
           [0082]      FIG. 1  is a schematic of the main elements of a human eye. 
           [0083]      FIG. 2 a    illustrates an arc scanning principle for ultrasonic scanners. 
           [0084]      FIG. 2 b    illustrates a sector scanning principle for ultrasonic scanners. 
           [0085]      FIG. 3  is a schematic of an arc scanning device. 
           [0086]      FIG. 4  illustrates an isometric view of a compact arc scanning head positioning mechanism. 
           [0087]      FIG. 5  further illustrates a compact arc scanning head positioning mechanism. 
           [0088]      FIG. 6  illustrates a magnetic positioning system. 
           [0089]      FIG. 7  illustrates a fluidic bearing operative between a fixed arc assembly and a moving transducer assembly. 
           [0090]      FIG. 8  is an isometric schematic of a linear induction motor to move a transducer assembly along a fixed arc assembly. 
           [0091]      FIG. 9  shows a schematic of the currents and magnetic forces that propel a transducer carriage along an arc guide track. 
           [0092]      FIG. 10  illustrates an embodiment of an eyepiece for an arc scanner. 
           [0093]      FIG. 11  illustrates an alternate embodiment of an eyepiece for an arc scanner. 
           [0094]      FIG. 12  illustrates another alternate embodiment of an eyepiece for an arc scanner. 
           [0095]      FIG. 13 a    illustrates the sealing method for the eyepiece of  FIG. 12 . 
           [0096]      FIG. 13 b    illustrates a detailed portion of  FIG. 13   a.    
           [0097]      FIG. 14  is a side view of an ultrasound scanner system with a single element ultrasound transducer. 
           [0098]      FIG. 15  is a top view of an ultrasound scanner system. 
           [0099]      FIG. 16  is a side view of an ultrasound scanner system with an annular array ultrasound transducer. 
           [0100]      FIG. 17  is a side view of an ultrasound scanner system with a linear array of ultrasound transducers. 
       
    
    
       [0101]    It should be understood that the drawings are not necessarily to scale. In certain instances, details that are not necessary for an understanding of the invention may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
     Precision Ultrasound Scanning for the Eye 
       [0102]    The embodiments described herein provide a superior design to prior art arc scanners. The embodiments disclose a scanning mechanism that is normally more tolerant of the underwater environment than prior art arc scanners. According to certain of the embodiments, an ultrasonic transducer is mounted to a transducer carriage that moves along a circularly curved guide. The carriage is typically guided by a guide, which is preferably configured as a track, so that the transducer beam axis is continuously directed towards a fixed center point regardless of the carriage&#39;s position along the guide. The guide assembly and the carriage have one or more smooth and precisely conforming surfaces that face one another and support a liquid film between them as described below. 
         [0103]    The embodiments described herein are illustrated by an arc scanner in which the guide assembly is formed in the fixed shape of an arc that approximates the curvature of the eye&#39;s cornea or anterior lens surface. The guide may also have a variable shape such, as for example, two or more arcs or any continuously curved shape including a linear guide. The guide may also be flexible such that it can be controlled to conform to a desired shape. This latter embodiment would be useful for positioning a transducer carriage such that the transducer is aimed in a desired direction so as to better image any specular or non-specular component in an eye. Such flexing and aiming can be made in response to the changing shape of an eye component being imaged. 
       Ultrasonic Scanning Principles 
       [0104]      FIG. 1  is a schematic of the main elements of a human eye. The principal refracting components are the cornea, iris and lens. The cornea, which is optically transparent, is located at the front of the eye enclosing front of the anterior chamber. The iris separates the anterior chamber from the posterior chamber. The front of the lens encloses the back side of the posterior chamber. The natural lens sits directly behind the iris. Only the central part of the lens, which is behind the pupil, can be seen optically. The anterior and posterior chambers comprise the anterior segment of the eye. The main volume or posterior segment of the eye lies behind the lens, with the retina and optical nerve at the rear of the posterior segment of the eye. The composition of the eye&#39;s aqueous and vitreous humour are very close to that of water with a density of about 1,000 kg/m 3 , and this allows the eye to be a very good medium for the transmission of acoustic energy. 
         [0105]    Optical means are suitable for viewing the anterior chamber and for viewing along the entire central axis of the eye. However, optical means cannot be used to view the portions of the posterior chamber lying immediately behind the iris, which includes the suspensory ligaments (called zonules), ciliary sulci and ciliary body. However, the eye components that cannot be viewed optically, can be viewed with high-frequency acoustic energy. As is well-known, acoustic frequencies in the ultrasonic range of about 10 MHz to about 60 MHz can be used to provide very high resolution images of, for example, the cornea and the lens. 
         [0106]      FIG. 2  illustrates two different types of scanning strategies for ultrasonic scanners capable of imaging most regions of the interior of an eye.  FIG. 2 a    illustrates the arc scanning principle for producing an ultrasonic scan of a component of an eye  201 . In this type of scanner, which is described, for example, in U.S. Pat. No. 6,315,727, U.S. Pat. No. 6,491,637, U.S. Pat. No. 6,887,203 and U.S. Pat. No. 7,048,690, a transducer is moved in an arc whose center is set at a location of interest in the eye. In  FIG. 2   a,  an ultrasonic transducer  203  is shown in a sequence of positions with the center of curvature of the arc guide  206  at approximately the center of curvature  202  of the cornea. The transducer  203  is moved in an arc as shown to produce many acoustic echoes (represented as rays  205 ) as it moves  204  along the arc guide which can then be combined to form a cross-sectional image of the eye features of interest. 
         [0107]      FIG. 2 b    illustrates the sector scanning principle for producing an ultrasonic image of a particular location with an eye  211 . In this type of hand-held scanner, which is described, for example, in U.S. Pat. No. 6,198, 956, an ultrasonic transducer  213  is shown being oscillated  216  about a fixed position  212  so as to produce  214  many acoustic echoes (represented as rays  215 ). These echoes can then be combined to form of a localized region of interest within the eye. The scanning principle illustrated in this figure is called sector scanning. 
         [0108]    In both the arc and sector ultrasonic scanners, the transducer acts as both the transmitter and receiver of acoustic signals. The transducer emits a short acoustic pulse and then receives the reflected acoustic signal. This technique is described, for example, in U.S. Pat. No. 5,293,871 and in “Ultrasonography of the Eye and Orbit”, Second Edition, Coleman et al., published by Lippincott Williams &amp; Wilkins, 2006. 
         [0109]    A sector scanner can be used to measure the thickness of an eye component such as, for example, the thickness of the cornea or the thickness of the lens along the optical axis. A sector scanner cannot be used to measure the length of specular features that extend laterally, such as, for example, the length of a LASIK scar, because only that small portion of the cornea that is perpendicular to the acoustic beam and reflects acoustic energy back to the transducer is visible to a sector scanner. With a sector scanner, the patient is typically required to be supine. 
         [0110]    An arc scanner, on the other hand, can be used to measure the thickness of an eye component such as, for example, the thickness of the cornea or the thickness of a lens as well as to measure the length of specular features that extend laterally, such as, for example, the length of a LASIK scar or the lateral length of a natural or implanted lens. In an arc scanner, the patient is typically looking downward at approximately 45 degrees from horizontal. This is a preferred position and has relevance to the design of an eyepiece described in  FIGS. 10 through 12 . 
         [0111]    Both arc and sector scanners are discussed on page  35  of “Ultrasonography of the Eye and Orbit”, Second Edition, Coleman et al., published by Lippincott Williams &amp; Wilkins, 2006. 
         [0112]      FIG. 3  shows the main elements of an arc scanning device illustrating positioning of a transducer along an arc guide whose center of curvature is centered approximately on the center of curvature of an eye component of interest.  FIG. 3  shows fixation lights  321  and  322  that allow the patient to fixate his or her eye to maintain it in a steady position during scanning.  FIG. 3  also shows an optical video camera  323  which may be used by the operator of the arc scanner to monitor the position of the patient&#39;s eye along an optical path  324  and to determine whether the patient&#39;s eye is open before a scan is initiated. The transducer and its arc guide assembly are immersed in a chamber of water  302  to provide a transmission path  314  for the acoustic signals. The patient&#39;s eye must also be immersed in water to provide continuity of the transmission path  314  for the acoustic signal.  FIG. 3  also shows a hygienic barrier  306  which separates the water chamber  301 ,  315  in which the transducer  305  and arc guide assembly  304  are contained from the water  310  in which the patient&#39;s eye is immersed. This barrier  306  provides the separation of water  302  in which the transducer  305  and arc track assembly  304  are contained from the water  310  in which the patient&#39;s eye is immersed. The arc guide assembly and associated components may be contaminated, for example, by particles from wearing mechanical components. The water  310  in which the patient&#39;s eye is immersed may be contaminated by bacteria or virus particles from the patient. As can be appreciated, the water  310  in which the patient&#39;s eye is immersed should be changed for every patient to prevent possible disease transmission. As can be further appreciated, the hygienic membrane  306  must be substantially transparent to ultrasound so as to maintain a clear acoustic transmission path between the patient&#39;s eye and the ultrasonic transducer. The hygienic membrane  306  is typically formed as part of a disposable eyepiece such as described in  FIGS. 10 through 12 . 
         [0113]    References are made herein to a medium suitable for conducting acoustic energy in the form of ultrasound. There are reasons to prefer that the medium be pure water or physiologic saline (also known as normal saline) but the embodiments do not exclude other media suitable for conducting acoustic energy in the form of ultrasound. Most other media present an increased danger to the patient&#39;s eye, even with a barrier interposed between the eye and the ultrasonic transducer. Barriers can leak or be breached, allowing the liquids on either side to mix, thus bringing a potentially harmful material into contact with the eye. 
         [0114]    It should be appreciated, however, that non-harmful, less-corrosive media and leakproof, impenetrable barriers might be developed or discovered. This might allow different media than pure water or physiologic saline to be used in this invention. Nothing about embodiments herein other than the hazards just described requires pure water or physiologic saline to be present in the chamber containing the transducer. All references to water in the following should accordingly be understood as referring to any suitable liquid. 
         [0115]      FIG. 3  illustrates the continuity of an acoustic transmission path through water. A chamber  301 ,  315  of water  302  is shown with a positioning arm  303  and arc guide assembly  304  on which an ultrasonic transducer  305  is mounted. An ultrasonically transparent barrier  306  separates chamber  301 ,  315  from the interior of an eyepiece. The eyepiece contains a separate volume of water  310  which fills the interior of the eyepiece and contacts a patient&#39;s eye surface  311 . The eyepiece is connected and sealed to the main chamber  301 ,  315  of the arc scanning device, and is also sealed against the patient&#39;s face  312 . As can be seen, there is a continuous path through water from the transducer  305  to the patient&#39;s eye surface  311  for the efficient passage of acoustic energy. The barrier  306  readily passes acoustic energy without alteration, thus forming a portion of the continuous path between the transducer  305  and the patient&#39;s eye surface  311 . Since the acoustic impedance of the patient&#39;s eye is approximately that of water, the acoustic energy from the transducer can be efficiently transmitted into the eye and reflected back from an eye component, such as for example, the surface of the cornea, to the transducer. Also shown in  FIG. 3  are a water fill tube  307  from a reservoir  317  to the main chamber  301 ,  315  and a separate water fill tube  309  from a reservoir  319  to the eyepiece. As can be appreciated, the water used in the eyepiece can be distilled or slightly saline to match the salinity of the eye, and the water used in the eyepiece can be introduced at a temperature that is comfortable for the patient. 
       Components of the Present Invention 
     Scan Head Positioning Apparatus 
       [0116]    The function of a scan head positioning apparatus is to position the arc scanning head assembly and ultrasonic transducer so that the transducer head is continuously on an arc guide that is positioned such that its center of curvature is at the approximate center of curvature of the eye component to be scanned. A successful scan often requires that the radius of curvature of the arc assembly approximately match the radius of curvature of the eye component of interest and that the scan head positioning apparatus be accurately positioned to take advantage of the precision of a high frequency ultrasonic pulse. 
         [0117]      FIG. 4  illustrates an isometric view of a compact scan head positioning mechanism. An axial carrier frame  402  and mounting plate  403  are fixed to the main arc scanner assembly. The scanner head mount arm  401  can move axially back and forth as shown by arrow  413 . The scanner head mount arm  401  can rotate about its axis as shown by arrows  414 . The scanner head mount arm  401  can move up and down as shown by arrows  411  and back and forth as shown by arrows  412 . The scan head, which is mounted on the scanner head mount arm  401 , is not shown in this figure. 
         [0118]      FIG. 5  further illustrates a compact scan head positioning mechanism.  FIG. 5  shows an arc scanner head  509  with ultrasonic transducer  508  mounted on the end of a scanner head mount arm  510 . These components (scanner head mount arm  510 , scanner head  509  and ultrasonic transducer  508 ) are operative under water and are sealed  511  from the rear portion of the positioning mechanism by a translational seal  506  and a rotational seal  507 . The translational seal  506  is preferably formed by a large rubber membrane that can flex with the small x and y motions required by the scanning head positioner, though any sealing mechanism may be employed. The z-axis seal and rotational seal  507  are attached to a stationary plate  501  which is affixed to the main arc scanner assembly. The z-axis and rotational seal  507  is typically formed by a circumferential groove type sealing mechanism with the groove facing into the water, though any sealing mechanism may be employed. The seal is preferably a commercially available seal from SealScience, model 810V. It allows both rotation and axial translation of the center tube while maintaining a water tight seal. The cross section of the seal is such that increased water pressure acts on the seal in a way that increases radial sealing force. The sealing surfaces are preferably anodized aluminum. Stationary plate  502  is also affixed to the main arc scanner assembly. The scanning head can be moved back and forth axially (the z-direction) by axial piston  503  or another suitable mechanism. The scanning head can be rotated (the beta-direction) about the z-axis by a rotary stepping motor (not shown) or another suitable device. The scanning head can be moved up and down (the y-direction) by piston  505  or another suitable mechanism. The scanning head can be moved from side to side (the x-direction) by piston  504  or another suitable mechanism. The components to the left or rear of stationary plate  501  remain in ambient air while the components to the right or font of stationary plate  501  are in immersed in water when the arc scanner is operational. 
       Magnetic Sensing System 
       [0119]    The carriage can be moved along the arc guide using any of a number of motive methods. In the preferred embodiment, the guide track contains windings arranged so that they together with the magnets in the carriage form a linear motor (described below in  FIGS. 8 and 9 ). Also in the preferred embodiment, there is a position encoder, preferably incremental and magnetic, borne by the guide track and the carriage, that allows external circuitry to sense the position of the carriage along the track. The positional information is used to control which windings are energized as the carriage moves along the track. It is also used to trigger the sending of ultrasonic pulses so as to provide, for example, a uniform physical spacing of the pulse-echo tracks in an ultrasound B-scan image. As can be appreciated, the positional information can be used to trigger the sending of ultrasonic pulses so as to provide a non-uniform but desired physical spacing of the pulse-echo tracks in an ultrasound B-scan image. 
         [0120]      FIG. 6  illustrates a magnetic positioning system. This positioning system provides precise position information for the transducer carriage along the arc guide assembly which, in turn, allows for a precise and accurate ultrasonic scan to be made.  FIG. 6  shows a scan head mounted on a scan head positioning assembly described previously. The scan head comprises an arc guide assembly  602  and a transducer carriage assembly  601 . Transducer  603  has been described previously. An OTS magnetic encoder (such as for example a Siko MSK5000) is contained in a housing  604  mounted on the side of the transducer carriage assembly  602 . The magnetic encoder senses its position by reading a magnetic strip  605  (shown as a black strip underneath the housing  604 ) which is attached to the arc guide track. The magnetic strip  605  is a flexible magnetic material with alternating north/south poles and with a distance between poles known to the encoder. The encoder then outputs standard quadrature encoder pulses as it moves along the magnetic strip. This model of encoder with the recommended magnetic strip delivers a 1 micron resolution or about 0.0005 degrees at the radius of the arc scanner. 
         [0121]    The magnetic positioning system is based on a home position on the arc guide track for the arc carriage and a series of magnetic combs installed along the arc guide track and whose spacings are accurately known. A coil in the arc carriage then counts current pulses as the carriage passes over the magnetic combs to determine a precise position of the carriage along the arc guide track. Other position sensing systems are possible. These include optical systems (optical bars replace the magnetic combs), mechanical systems and electrical systems (such as a potentiometer). The magnetic sensing system is preferred over the optical system which requires periodic cleaning and the mechanical system which is subject to buildup of mineral and other deposits. 
       Fluidic Bearing 
       [0122]    A bearing mechanism is another component of an arc scanner. The function of the bearing is to allow smooth motion of the transducer assembly along the arc guide assembly which has been positioned by a scan head positioning apparatus such as described above in  FIGS. 4 and 5 . A successful scan normally requires that the transducer assembly move smoothly and without jitter or jerk along the curved arc guide assembly to take advantage of the precision of a high frequency ultrasonic pulse (in physics, jerk is the rate of change of acceleration; more precisely, the derivative of acceleration with respect to time, the second derivative of velocity, or the third derivative of displacement). 
         [0123]    The carriage has a set of liquid passages that communicate with a source of liquid under pressure. The liquid passages also communicate with ports located on the smoothly conforming aspect of the carriage that meets a matching surface on the arc guide track to form a fluidic bearing. The liquid flows from the source through the passages to and through the ports, forming a liquid film between the carriage and the arc guide track. The pressure from the ports and in the liquid film urges or forces the carriage and the arc guide track apart, causing them to separate, reaching an equilibrium position with a thin film of liquid flowing out from between them. Following known practice in fluidic bearings, the size of the passages is chosen to make the pressure at each port largely independent of the flow through the other ports to provide stability to the fluidic bearing. It is preferred that the passages and exit ports are in the transducer carriage rather than in the arc guide track so that the ports are always covered, an arrangement that reduces the liquid mass flow requirement. 
         [0124]    As will be described below, a linear motor is used to propel the transducer carriage along the arc guide. The permanent magnets in the transducer carriage attract the carriage to the arc guide with considerable force. This makes it possible to use a fluidic bearing system as the fluid pressure generated force can be made to approximately balance the magnetic attraction force. This minimizes any mechanical drag of the transducer carriage on the arc guide and allows the system to move smoothly and without jitter. 
         [0125]      FIG. 7  illustrates a fluidic bearing operative between a fixed arc guide assembly  704  and a moving transducer carriage assembly  702 . It is understood that once the arc guide assembly  704  has been moved into position and secured by the positioning mechanism described in  FIGS. 4 and 5 , the motion of the transducer carriage assembly  702  is constrained to be along the arc guide assembly  704  for subsequent scanning operations. The view shown in  FIG. 7  is a normal section through the arc guide assembly  704  and a moving transducer carriage assembly  702 , with the rest  701  of the arc guide assembly  704  curving upward in the background. The arc guide assembly  704  contains linear motor coil elements  706  and their iron cores  720  which will be described further in  FIGS. 8 and 9 . The moving transducer carriage assembly  702  includes an ultrasonic transducer  703 , a transducer mount  709  and a magnetic sensor housing  705 . A water hose (not shown) is connected via fluid coupling  708 . An electrical conduit that transmits electronic signals to and from the transducer and transmits electronic signals to and from a position sensing means is not shown but is also attached to the transducer carriage assembly  702 . The position sensing means for determining the relative position between the moving transducer carriage assembly  702  and the arc guide assembly  704  may be, for example, a magnetically coded strip along the arc guide assembly  704  and a magnetic sensing element on the moving transducer carriage assembly  702 , such as described in  FIG. 6 . 
         [0126]    The ability to accurately detect the relative position between the moving transducer carriage assembly  702  and the arc guide assembly  704  can be important because it can accommodate non-uniform motion of the moving transducer carriage assembly  702 . For example, the transducer carriage assembly  702  may accelerate from rest at one end of the arc guide, reach a maximum velocity which may be maintained briefly near the center of the arc guide and then decelerate to rest at the opposite end of the arc guide. As a result of knowing the transducer carriage assembly  702  position along the arc guide, the pulsing and receiving periods of the transducer  703  can be programmed to correlate with the motion the transducer  703  along the arc guide so that a coherent image may be formed. The ability to operate with a non-uniform transducer carriage assembly  702  motion is enabled by the smooth acceleration and deceleration allowed by the fluidic bearing.  FIG. 7  shows the bearing surfaces  711 ,  712 ,  713  and  714  between the arc guide assembly  704  and the moving transducer carriage assembly  702 . 
         [0127]    Since the entire arc scan head assembly is under water, it is natural to use a fluid bearing where the fluid is also water. The fluid is pressurized by a small pump mounted on the transducer carriage assembly  702  and water is pumped through small holes located at regular intervals along the bearing surfaces  713  and  714  of the transducer carriage assembly  702 . The water in the main arc scan head chamber is commonly at approximately 1 bar or ambient pressure. The pump delivers fluid at pressures typically in the range of ½ to 2 bars above ambient pressure. The pressurized fluid then lifts the transducer carriage assembly  702  about 5 to about 10 microns off the surface of the arc guide assembly  704  and maintains this separation while fluid is continuously pumped through the small holes located along the bearing surfaces  713  and  714  of the transducer carriage assembly  702 . 
         [0128]    As has been shown experimentally, the linear motor cannot move the transducer carriage assembly  702  until the fluid bearing is activated because of the strong attractive force between magnets  707  and iron cores  720 . Once the fluid is being pumped through the small holes located along the bearing surfaces  713  and  714  of the transducer carriage assembly  702 , the transducer carriage assembly  702  rises to achieve a separation of a few microns and moves freely and without jerk along the arc guide track. 
       Linear Motor 
       [0129]    The function of the motor is to move a transducer carriage assembly along an arc guide assembly so as to allow an ultrasonic scan of an eye component to be made. The linear motor must be able to be operated safely under water since the entire arc scanning head is immersed in water. 
         [0130]    The following descriptions assume that the linear motor has magnets in the carriage and windings in the circular track. It should be noted that this could have been reversed, with the magnets in the circular track and the windings in the carriage, without changing the fundamental operation of the scanning system. Placing the magnets in the carriage represents the preferred embodiment and the best mode known to the inventors. 
         [0131]    The transducer carriage has one or more magnets affixed to it, and the track is made of or contains magnetic material such as iron. The magnets are arranged in the carriage so that the resulting magnetic field urges or attracts the carriage toward the track. Because the entire track and the carriage must be submerged in water during normal operation, the magnetic components are protected from corrosion by either choosing the exposed iron material to be a magnetic stainless steel or by sealing the iron in a material such as epoxy to protect it from water exposure. 
         [0132]    The transducer carriage assembly typically weighs in the range of about 0.1 kg to about 0.3 kg. This range of carriage assembly mass is light enough to allow rapid acceleration and deceleration yet heavy enough to provide sufficient inertia to filter out extraneous mechanical jitter in the motion of the transducer carriage along the arc guide track. The location of the center of mass of the transducer carriage is also important as it is desired that the carriage be reasonably balanced on the guide track. 
         [0133]      FIG. 8  is an isometric schematic of an apparatus containing a linear induction motor to move a transducer carriage assembly  803  along an arc guide assembly  801 .  FIG. 8  shows a transducer assembly  803  with an ultrasonic transducer  804 . The ultrasonic transducer  804  is mounted such that it always points at the center of curvature of the arc defined by the radius of curvature of arc guide assembly  801 . The transducer carriage assembly  803  moves along an arc guide assembly  801 , propelled by a linear induction motor arrangement. The motion of the transducer carriage assembly  803  may be non-uniform. For example, the transducer assembly  803  may accelerate from rest at one end  810  of the arc guide assembly  801 , reach a maximum velocity which may be maintained briefly near the center  811  of the arc guide assembly  801  and then decelerate to rest at the opposite end  812  of the arc guide assembly  801 . In a preferred embodiment, permanent magnets are installed in the transducer carriage assembly  803  and electrically powered field coils are installed down a central groove formed in the in the fixed arc assembly  801 . An example of such a groove and field coils can be seen in  FIG. 7  with field coils  706  positioned in a groove in the arc guide assembly  704 . 
         [0134]      FIG. 9  shows a schematic of the currents and magnetic forces that propel a transducer carriage along an arc guide assembly  903 . A transducer carriage  902  is shown with two permanent magnets  904  mounted side-by-side but with their north-south polarities on opposite faces. The two permanent magnets  904  are preferably of equal size. A carriage track  903  which forms an arc is shown with several wound conductive coils  905 , wound around an iron core  906  which is also formed as an arc in this side view. The coils  905  are approximately rectangular in cross section as shown, for example, in  FIG. 7  by callout  706 . The long side of the rectangular coil windings is preferably adjacent to the face of the magnets to maximize propelling force (this force is described below). The coils  905  may be made of any conductor material such, as for example, copper, aluminum and the like. The coils  905  are preferably sized and spaced such that three adjacent coils are approximately the same width as either one of the permanent magnets  904 . Starting at either end  901  of the arc guide, each set of three adjacent coils is powered by a 3 phase electrical circuit. The 3 phase circuit voltages are controlled by a Pulse Width Modulated (PWM) system that is in turn controlled by the position of the transducer carriage  902 . The position of the transducer carriage  902  relative to the arc guide  903  is determined, for example, by a magnetic strip sensor system such as described in  FIG. 6 . The combination of PWM; an accurate location sensing system; a fluid bearing between the arc guide and the transducer carriage (described in  FIG. 7 ); and the mass of the transducer carriage provides a very smooth motion of the transducer carriage  902  which is essential to making sharp, precision high-frequency acoustic measurements (approximately 3 MHz to approximately 60 MHz). 
         [0135]    In this application, it is preferable to embed the permanent magnets  904  in the moving transducer carriage  902  and to embed the coils  905  in the arc guide assembly  903 . Embedding the permanent magnets  904  in the moving transducer carriage  902  adds mass to the transducer carriage assembly  902  which helps to keep its motion along the arc guide track smooth. Embedding the coils  905  in the arc guide assembly  903  reduces the motion in the water of the electrical wires connecting the power source with the coils since the motion from positioning the scan head is far less than the motion of the transducer carriage back and forth along the arc guide track. This is a slightly less energy efficient design for a linear motor since all the coils are energized by the 3 phase power supply. However, motor efficiency is not a major concern in this application. 
         [0136]    With the transducer carriage position shown in the example of  FIG. 9 , the gap between the permanent magnets  904  is lined up with the gap between two adjacent coils  905  such that three coils  905  are centered beneath each permanent magnet  904 . The current is at a maximum in the two coils centered beneath each permanent magnet but in opposing directions as indicated by the current arrows represented by an end view of an arrow feather and an end view of an arrow head. The current is low but in the same direction in the coils adjacent to the coils carrying the maximum current, as indicated by the smaller current arrows. In this position, there is a force exerted on each of the magnets  904  along the same direction of the arc  903 . Since the magnets  904  are embedded and attached to the transducer carriage  902 , the transducer carriage  902  is propelled along the arc guide assembly. 
         [0137]    In this example, the coils  905  are wound around an iron core which is approximately rectangular in shape (although with rounded corners so as not to cut the coil wire as shown for example in  FIG. 7  by callout  706 ). The propelling force arises from the current in the coil elements adjacent to the permanent magnets interacting with the local magnetic field of the permanent magnets according to the well-known equation: 
         [0000]    
       
      
       dF=I dl×B  
      
     
         [0000]    where dF is the differential force
       I is the total current (number of windings times current in each winding)   dl is a differential length of coil winding   X represents the cross-product between dl and B   and B is the local magnetic field of the permanent magnet       
 
         [0142]    As can be seen, the force is orthogonal to both the direction of the current and the direction of the local B-field and so the force on the permanent magnets is along the arc guide assembly. It is noted that the force is caused by the current in the coil winding elements adjacent to the permanent magnet. The force caused by the current in the coil winding elements distant from the permanent magnet is in the opposite direction but is very weak as it is effectively shielded by the iron core  906 . The force caused by the current in the coil winding elements normal to the arc track are largely parallel to the magnetic field of the permanent magnets and so do not contribute to the propulsive force on the transducer carriage  902 . 
         [0143]    The permanent magnets  904  are held in place with a back iron component whose face is flush with the pole faces of the permanent magnets. The back iron with the two permanent magnets  904  thus form, in essence, a horseshoe magnet and can in fact be replaced by an appropriately shaped horseshoe magnet. A magnetic circuit is thus formed by the back iron, the permanent magnets  904  and the iron core  906 . 
       Eyepiece 
       [0144]    An eyepiece serves to complete a continuous acoustic path for ultrasonic scanning, that path extending from the transducer to the surface of the patient&#39;s eye. The eyepiece also separates the water in which the patient&#39;s eye is immersed from the water in the chamber in which the arc track assembly are contained. Finally, the eyepiece provides a steady rest for the patient and helps the patient to remain steady during a scan. To be practical, the eyepiece should be free from frequent leakage problems, should be comfortable to the patient and its manufacturing cost should be low since it should be replaced for every new patient. 
         [0145]      FIG. 10  illustrates an embodiment of an eyepiece that satisfies these requirements. The eyepiece comprises a mounting ring  1001  and an eye seal ring  1002 . The mounting ring  1001  is attached to and is typically a permanent part of the main arc scanner assembly. As shown here the mounting ring  1001  has several attachment grooves  1006  which can accept attaching mechanisms  1007  on an edge  1005  of the eye seal ring  1002 . In this embodiment, the attaching mechanisms  1007  are pushed down  1012  into the attachment grooves  1006  and then rotated  1011  into position to form a mechanical connection that seals the eye seal ring  1002  against the mounting ring  1001  to prevent water leakage. This is also known as a bayonet type connection. There may be a sealing ring  1005  which is compressed as the attaching mechanisms  1007  are rotated  1011  into position. The eye seal ring  1002  has a soft rubber or foam contoured face seal  1003  which is designed to seal against a typical human face around the eye that is to be scanned. The eye seal ring  1002  is also shown with its water fill tube  1004  on the top and a water drain tube  1014  on the bottom. A sealed hygienic barrier (not shown) is formed as part of the eye seal ring  1002  during manufacture and is typically located where the contoured face seal  1003  is connected at location  1008  to the main body of the eye seal ring  1002 . 
         [0146]    The hygienic barrier or membrane may be permeable or semi-permeable to water as long as it is impermeable to bacteria, viruses, fungi, and other potentially harmful biological and chemical impurities. The membrane is preferably impermeable to water to provide superior isolation from biological and non-biological impurities that may be dissolved or carried in water. The membrane is preferably optically clear to allow a video camera to view the eye (see  FIG. 3 ) through the membrane. The membrane preferably passes acoustic pulses without significant energy absorption or reflection. These conditions can be substantially met by a membrane that is thinner than an acoustic pulse wavelength. Eyepiece membranes have been made from materials such as, for example, polyethylene, mylar, polypropylene; vinylidene chloride; polyvinylidene chloride; or DuraSeal (made by Diversified Biotech) which is polyethylene based and free of and adhesives. A preferred material is medical grade polyethylene which has an acoustic impedance only somewhat higher than that of water (about 2.33 million kg/m 2 -s compared to 1.54 million kg/m 2 -s for water). The thickness of the membrane is preferably in the range of about 10 to about 30 microns. This thickness is a small part of an acoustic wavelength in water which is about 150 microns at 10 MHz and about 20 microns at 80 MHz. 
         [0147]      FIG. 11  illustrates an alternate embodiment of an eyepiece that also satisfies the practical requirements described above. The eyepiece comprises a mounting ring  1101  and an eye seal ring  1102 . The mounting ring  1101  is attached to and is typically a permanent part of the main arc scanner assembly. As shown here the mounting ring  1101  it has several attachment grooves  1106  which can accept attaching mechanisms  1107  on an edge  1108  of the eye seal ring  1102 . In this embodiment, the attaching mechanisms  1107  are pushed down  1111  into the attachment grooves  1106  and then snapped into position to form a mechanical connection that seals the eye seal ring  1102  against the mounting ring  1101  to prevent water leakage. This is also known as a snap-on type connection. There may be a sealing surface  1105  on the mounting ring  1101  and a matching sealing surface (not shown) on the eye seal ring  1102  which is compressed when the attaching mechanisms  1107  are snapped into position. The eye seal ring  1102  has a soft rubber or foam contoured face seal  1103  which is designed to seal against a typical human face around the eye that is to be scanned. The eye seal ring  1102  is also shown with its water fill tube  1104  on the top and a water drain tube  1114  on the bottom. A sealed hygienic barrier (not shown) is formed as part of the eye seal ring  1102  during manufacture and is typically located where the contoured face seal  1103  is connected at location  1108  to the main body of the eye seal ring  1102 . 
         [0148]      FIG. 12  illustrates yet another an embodiment of an eyepiece for an arc scanner. The eyepiece comprises a mounting ring  1202  and an eye seal ring  1201 . The mounting ring  1202  is attached to and is typically a permanent part of the main arc scanner assembly. As shown here the mounting ring  1202  has several attachment grooves, such as described in  FIG. 10 , which can accept attaching mechanisms on the eye seal ring  1201 . In this embodiment, the attaching mechanisms are pushed down into the attachment grooves and then rotated into position, such as described in  FIG. 10 , to form a mechanical connection that seals the eye seal ring against the mounting ring to prevent water leakage. This is also known as a bayonet type connection. In the embodiment disclosed in  FIG. 12 , there is an additional sealing feature comprises a groove  1203  molded as part of the eye seal ring  1201  and a matching tongue  1204  molded as part of the mounting ring  1202 . When the eye seal ring  1201  is rotated into position with the mounting ring  1202 , the tongue and groove form a threaded connection as described in  FIG. 13  which compress as the parts are rotated into position. This is similar in sealing action to a plastic bottle with a threaded top. Since both the eye seal ring  1201  and the mounting ring  1202  are typically made from a plastic, the compliance of the plastic further helps in forming a water tight seal. The eye seal ring  1201  has a soft rubber or foam face seal (not shown here) which is designed to seal against a typical human face around the eye that is to be scanned. A sealed hygienic barrier (not shown) is formed as part of the eye seal ring  1201  and is typically located where the contoured face seal is connected to the main body of the eye seal ring  1201 . 
         [0149]      FIG. 13  shows a section side view illustrating the tongue and groove portion of the sealing method for the eyepiece of  FIG. 12 .  FIG. 13 a    shows an eyepiece comprising a mounting ring  1302  and an eye seal ring  1301  is shown in sectional view with its tongue and groove sealing system indicated by callout  1303 . 
         [0150]      FIG. 13 b    illustrates a close up view of tongue and groove portion of the sealing method for the eyepiece of  FIG. 13   a.  The eyepiece mounting ring  1312  has a tongue  1314  molded into the eyepiece mounting ring  1312 . The eye seal ring  1311  has a matching groove  1313  molded into the eye seal ring  1311 . When the eye seal ring  1311  is rotated into position with the mounting ring  1312 , the tongue  1314  and groove  1313  compress, deform as necessary and form a tight seal as the parts are rotated into position. 
         [0151]    As described previously, the eye seal ring typically includes a soft rubber or foam contoured face seal which is designed to seal against a typical human face around the eye that is to be scanned. The contoured face seal may also be made from a foam material impregnated with, for example, mineral oil, to provide a superior sealing action against a typical human face around the eye. An alternative face sealing mechanism can also be provided by a hollow soft rubber or soft plastic ring molded into the removable eye seal ring that can be filled with water after the patient has placed their face against the eyepiece. This would be a third separate water-filled component of an arc scanner and would serve to better seal against the face around the eye for patients with irregular facial features around the eye. 
       Precision Ultrasound Scanning for Other Body Parts 
       [0152]    The current disclosure is also directed towards an imaging system that provides the convenience and lower cost of ultrasound imaging systems but with both high penetration depths and excellent resolution. This is achieved through a combination of ultrasound technologies and methods for holding and stabilizing the ultrasound probe relative to the body surface and the body part to be imaged. 
         [0153]    A conforming body seal and portable instrument body are disclosed, that together provide for a compact yet stable fixation of the probe relative to the body surface as compared to currently available handheld ultrasound systems. This enables longer scan times to be achieved because of the elimination of probe movement relative to the body part during a scan. Ultrasound imaging techniques such as coded excitation (chirp excitation in its simplest form), over-sampling/averaging and dynamic focal plane imaging can be utilized allowing much higher operating frequencies (frequencies in a range of about 20 MHz to about 80 MHz) with their higher resolution and yet approaching penetration depths of traditional low frequency (about 5 MHz to about 10 MHz) ultrasound handheld systems. 
         [0154]    This arrangement includes computer controlled movement of the ultrasound probe providing multiple image cross-sections for 3D imaging of targeted tissue or selection of a particular cross-section from a set that best isolates the tissue of interest without having to reposition the system by hand multiple times. This arrangement provides much higher repeatability of image biometry due to repeatable fixation of the probe relative to the body surface. 
       Portable Ultrasound Scanner 
       [0155]      FIG. 14  is a side view illustrating the basic components of an ultrasound scanner system with an ultrasound probe comprised of a single element ultrasound transducer. The device is comprised of a housing assembly  141  which is pressed to the surface layer  1414  of the patient overlaying the body part of interest  1415  and sealed by a conforming seal  142  to minimize leakage of saline solution  1412 . A membrane  145  separates the saline solution  1412  from the water  1411  used to immerse the ultrasound probe  143 . This membrane prevents water used in the probe section of the housing from mixing with the saline solution used in the section of the housing in contact with the patient. 
         [0156]    Assembly  1416  which holds membrane  145  in place is comprised of a clamp, sealing system and a conforming seal  142 . Conforming seal  142  may also be comprised of a layer of adhesive to facilitate the seal adhering to the patient&#39;s skin  1414 . Assembly  1416  corresponds in function to the disposable eyepiece used in an ultrasound eye scanner such as described in a previous section of this disclosure. The entire assembly  1416  is may be a disposable item that can be readily changed for each new patient. 
         [0157]    As can be appreciated, the saline solution may or may not be a sterile saline solution depending on the body part to be scanned. If the body part to be scanned is covered by intact skin then the saline solution need not be sterile and may be replaced with distilled water. In some cases, only the conforming seal may be replaced for scanning other body parts. In general, the entire assembly  1416  is replaced for each new patient. When the body part is an eye or when the body part is covered by injured or damaged skin, then a sterile saline solution should be used and the entire assembly should be replaced for each new patient. 
         [0158]    Both the saline solution  1412  and water bath  1411  are at ambient pressure, typically 1 atmosphere. In operation, the assembly is first placed over the body part of interest. Then the instrument chamber in the upper part of the housing is filled with water (typically distilled water) via fill tube  148 , fully immersing the ultrasound probe  143 . Then the saline solution  1412  is introduced via fill tube  147  into the sealing chamber that connects a disposable saline fill bag  146 . The operator can view the region around surface layer  1414  overlaying the body part of interest  1415  through positioning eyepiece  144 . The motion of the ultrasound probe  143  is controlled in three orthogonal directions x, y and z by motors Mx, My and Mz. The computerized operating instructions for these motors and the ultrasound probe  145  are communicated through cable bundle  149 . Motors Mx, My and Mz are operated under computer control to move the probe up and down in the z-direction or back and forth in the x- and y-directions on linear positioning assembly  1410 . The nominal focal distance of the ultrasound transducer  1421  is typically set as the distance from the pulse emitting element located at the tip of ultrasound probe  143  to approximately the centerline  1422  of the body part of interest  1415 . The ultrasound probe may be comprised of a single pulse emitting and receiving element or a more complex probe embodiment such as described in  FIGS. 16 and 17 . If an ultrasound probe comprised of a single pulse emitting and receiving element is used, the center pulse frequency is typically in the range of about 5 MHz to about 80 MHz. The depth of field of a single frequency focused probe is typically about 1 to 2 millimeters at about 40 MHz and a focal distance of about 12 millimeters. 
         [0159]      FIG. 15  is a top view of an ultrasound scanner system. This view shows the “footprint” of the conforming seal  152 . Ultrasound probe tip  153  can move in the x-direction  1552  and/or in the y-direction  1551  by using the linear positioning assembly  1410  described in  FIG. 14 . 
         [0160]    An example of a linear positioning assembly is disclosed in U.S. Pat. No. 8,317,702, entitled ““Alignment and Imaging of An Eye with an Ultrasonic Scanner” which is incorporated herein by reference. 
       Description of Components 
     Disposable Conforming Body Seal 
       [0161]    Referring again to  FIG. 14 , the disposable body seal  1416  is a component that may come in different shapes and forms to allow for optimal fit to a variety of body surfaces. It may have a shape to fit around the eye socket, be more curved to fit around a particular joint, or be more gently curved to fit on a more planar body surface such as an abdomen or back. All the sub-components described below are attached to one another into a single assembly  1416 . 
         [0162]    A first sub-component is a conforming seal  142  of a low durometer plastic or foam which easily conforms to the body surface and outlines the entire area to be scanned. This seal is designed to adhere on the body side to the skin surface to provide a stable fixation of the system to the body and provide a seal of the sterile saline solution  1412 . 
         [0163]    A second sub-component is a lower ring which provides for a rigid backing for the conforming seal and fill and drain lines  147  for the saline fill. 
         [0164]    A third sub-component is a membrane  145  that separates the disposable saline fill from the instrument system fluid (which is typically distilled water and is filtered and may be reuseable). This membrane  145  must be acoustically transparent (that is, it must have an acoustic impedance similar to that of water) to the ultrasound beam and optically transparent to allow manual positioning of the system to the healthcare provider&#39;s mark on the body surface. This membrane is bonded to both the upper and lower rings and provides a fluid seal for both the handheld fluid on one side and the sterile saline solution on the other. 
         [0165]    A fourth sub-component is an upper ring which provides for mechanical coupling of the body seal to the portable body and sealing of the fluid by O-ring or other suitable sealing method. 
         [0166]    A fifth sub-component is a saline fill bag  146  and lines  147  which provide the single use sterile saline fill fluid. Fill control can be, for example, by squeezing the fill bag  146  by hand to force saline fluid into the volume between the membrane and body surface and out again through an overfill line. 
       Instrument Main Body 
       [0167]    The portable instrument main body  141  is a component that serves as the main frame of the system and serves as the mounting of several system components including the disposable body seal on the bottom of the instrument. The system components housed in the instrument main body include the positioner carriage (described below). 
         [0168]    The portable instrument main body is comprised of a sealed chamber to contain the fluid (called the instrument chamber), typically distilled water, around the ultrasound probe. The system also includes fluid management system (not shown) which provides for filling and draining of the fluid  1411  to/from the instrument chamber and for the fluids storage and maintenance. The system instrument main body also includes a feed-through to provide for a means to get the electrical signals to and from the ultrasound probe and the positioner motors and sensors, which are inside the instrument chamber, to an external pulser, motion control, signal/image processing and display system (described below). If the device is an eye scanner, then a fixation target is included which provides a means for aligning the visual axis of the eye to the ultrasound axis as disclosed in U.S. Pat. No. 8,496,588, entitled “Procedures for an Ultrasonic Arc Scanning Apparatus” which is incorporated herein by reference. 
         [0169]    The system also includes a positioning eyepiece (described below) and a means for strapping the handheld instrument (not shown) around the limb or torso or head as a backup to the body seal disposable to assist in the stabilization of the handheld instrument to the body surface. 
       Positioner Carriage 
       [0170]    The positioner assembly  1410  is a subsystem that provides for fixating the ultrasound probe to a single or multi-axis movement system (including its actuators such as stepper motors) which is in turn are mounted inside the sealed chamber of the instrument main body. 
         [0171]    The movement system can be a single axis in its simplest form providing an image with only a single cross-section of the object to scan. The movement system could provide 2 or 3 axes of movement. In the system shown in  FIG. 14 , two linear axes of movement are shown in the x- and y-directions. This would provide for a multitude of cross-sections of an object with the possibility of providing 3D images. A third linear z-axis movement is shown for additional control of the depth of the optimal image for relatively deeper or shallower objects. 
         [0172]    A movement axis could also be arcuate to better conform to the tissue to be imaged such as the cornea (as in the case of an eye scanner) or for a bending joint such as a knee or elbow. 
       Positioning Eyepiece 
       [0173]    The positioning eyepiece  144  is a simple, low power optical microscope allowing the operator to center the position of the instrument on a mark on the body surface placed prior to mounting of the instrument by the healthcare professional or in the case of the eye scanner centering on the iris of the eye. This insures the image will capture the selected body part. In the case of two or more positioning axes, this positioning need only be approximate as the scan area will be sufficient to allow complete capture of the object body part even if not perfectly centered on the object body part. In the case of the eye scanner, additionally a reflection of a fixation target will be centered through the eyepiece for precision alignment of the positioner carriage. 
       Ultrasound Probe 
       [0174]    An ultrasound probe  143  is a device that provides for delivering ultrasound pulse trains to the targeted object and receiving of the returning ultrasound echoes, as is common practice in current ultrasound imaging systems. In  FIG. 14 , the probe is a cylindrical device and can either be a single or multiple element probe. Principal frequency is designed to be sufficiently high to allow much higher resolution than currently available handheld ultrasound imaging systems which are typically in the range of about 5 MHz to about 10 MHz. It is envisioned in this embodiment that the operating frequency of the probe be in the range of about 20 MHz to about 80 MHz. The focal plane of the probe is positioned at the approximate center plane of the targeted object. Advanced techniques for multiple-element annular elements are potentially used to allow for dynamic adjustment of the focal plane providing for multiple images with varying focal planes, then blended together for optimum full depth images across the entire thickness of the targeted object. Further, advanced coded excitation of the probe is used (such as chirp excitation and/or over-sampling) to further improve signal-to-noise ratio of the images particularly in the deepest parts of the scan where signal attenuation is at its highest. These advanced techniques will be important to achieving deeper imaging capability using a high frequency probe as the attenuation of the ultrasound signals in tissue are generally a function of frequency squared. It is highly desirable to use the higher operating frequency as the image resolution will increase linearly with operating frequency and thus providing much higher diagnostic value. This probe could also be a linear array and/or combined with a pivot mechanism at the probe&#39;s distal end to allow for pointing of the ultrasound beam from the end of the probe for more flexibility in optimizing scan geometry for best interface detection as disclosed in U.S. Pat. No. 9,039,623 entitled “Compound Scanning Head for an Ultrasonic Scanning Apparatus” which is incorporated herein by reference. 
       Control, Processing and Display System 
       [0175]    The external pulser, motion control, signal/image processing and display system (not shown) is a system may be configured as a standalone unit on a cart or nearby table or in a more compact form attached to the portable unit itself. This system provides the means for the following functions. 
         [0176]    A first function is to produce the excitation signals to the ultrasound probe (the pulser). These excitation signals may be for a single element or for multiple elements discussed in  FIG. 16  for an annular array probe embodiment or in discussed in  FIG. 17  for a linear array embodiment. Also coded excitation may be utilized for improvements in signal to noise (along with their companion compression filters in the signal processing). 
         [0177]    A second function is to carry out all signal processing of the returning ultrasound echoes including but not limited to such things as basics amplification and filtering of raw incoming signals, A/D conversion, all digital signal processing techniques, such as Fourier conversion and filtering, compression filtering and dynamic focusing. 
         [0178]    A third function is to carry out imaging processing to convert the processed signals into images for viewing by the healthcare professional. 
         [0179]    A fourth function is to provide the motioning control signals to the positioner actuators. 
         [0180]    A fifth function is to provide for storage of processed ultrasound signals and their companion images for later retrieval. 
         [0181]    A sixth function is to provide for the storage, filtering, delivery and evacuation of the instrument fluid that surrounds the ultrasound probe during scanning. 
       Operation 
       [0182]    The following is a brief description of instrument operation. A new disposable body seal is attached to the bottom of the portable instrument main body. The center of the scanning area is marked by the healthcare professional on the patient&#39;s body. The adhesive on the bottom surface of the conforming seal is exposed and the portable instrument and body seal disposable assembly are carefully positioned on the patient&#39;s skin. The positioning eyepiece is used to center the instrument on the mark on the patient&#39;s skin provided by the healthcare professional while the body seal is pressed against the body surface. In the case of the eye scanner the instrument center is aligned to the iris of the eye. Optionally a handheld stabilizing strap may be used to wrap around the torso, head or limb of choice to further stabilize the portable unit. The cable between the portable instrument and external pulser, motion control, signal/image processing and display system is then attached. Thereupon, the handheld fluid filling operation is performed by turning on the fill pump on the unit thereby transporting the instrument fluid from the reservoir to the instrument chamber. The saline fill bag attached to the disposable sealing assembly is squeezed until fluid flows from the overfill tube to the sealing chamber. 
         [0183]    The scanning parameters on the external pulser, motion control, signal/image processing and display system are then selected. In the case of the eye scanner, a second alignment will be required by centering the Purkinje reflection of the fixation target on cornea to the center of the instrument using the eyepiece and the positioner, thereby aligning the ultrasound axis to the visual axis of the eye as disclosed in previously referenced U.S. Pat. No. 8,496,588. The patient is instructed to stay focused on the fixation target throughout the scan. When the aforementioned steps are completed, the scan sequence is initiated. The scan sequence time is typically about a second to about several seconds. The images are reviewed to determine whether a re-scan is necessary. If the scans are acceptable, the procedure is terminated by draining and discarding the saline fluid from the sealing chamber. The instrument fluid is then pumped from the instrument chamber back to the reservoir. The body seal and stabilizing strap, if used, are removed from the patient. Finally, the disposable body seal is removed from portable unit and discarded. 
       Annular Array Embodiment 
       [0184]    The current disclosure is also directed towards an imaging system that provides the convenience and lower cost of ultrasound imaging systems but also with high penetration depths and resolution. This is achieved through a combination of existing ultrasound technologies and new methods for holding and stabilizing the ultrasound probe relative to the body surface. 
         [0185]    One of the existing ultrasound technologies, annular array transducers, is described, for example, in the following two references. The first is entitled “Design and Fabrication of a 40-MHz Annular Array Transducer” by Jeffrey A. Ketterling, Orlando Aristiz&#39;abal, Daniel H. Turnbull and Frederic L. Lizzi and is taken from IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 52, No. 4, April 2005. The second is entitled “Operational Verification of a 40-MHz Annular Array Transducer” by Jeffrey A. Ketterling, Sarayu Ramachandran and Orlando Aristiz&#39;abal and is taken from IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 53, No. 3, March 2006. 
         [0186]      FIG. 16  is a side view of an ultrasound scanner system with an annular array ultrasound transducer and illustrates the movement of an ultrasound annular array probe relative to body parts for extending the depth of high resolution imaging.  FIG. 16  is comprised of the same components as those of  FIG. 14  except that single transducer element ultrasound probe  143  is now a multi transducer element annular array probe  163 . In addition, a solid state motion sensor  1617  is shown attached to the outer housing. Such sensors can measure one or more of 3 axes of acceleration, 3 axes of gyroscopic (rotational) motion, 3 axes of gravitational variation and ambient pressure. The motion sensor may be used to compensate for the effects of breathing and/or heartbeat on the relative motion between the device housing and the body part being imaged. When ultrasound probe  163  is in a position with tip distance to the membrane  1624 , its focal center length is shown as length  1621  and its depth of field is two times distance  1628 . For an annular array probe, the total depth of field may be approximately 5 to 6 millimeters at a center frequency of about 40 MHz. When ultrasound probe  163  is in a position with tip distance to the membrane  1625 , its focal center length is shown as length  1623  and its depth of field is the same as before but centered at the new focal plane. Typically, focal length  1621  and focal length  1623  are the same. 
         [0187]    As described below, the total high resolution image zone available by moving the ultrasound probe from tip distance to the membrane  1624  (“D 1 ”) to tip distance to the membrane  1625  (“D 2 ”), Z-total is then computed by the formula 
         [0000]      Z-total−(D1−D2)+2Δz
 
         [0000]    where Δz (distance  1628 ) is equal to half of the depth of field. 
         [0188]    As noted previously, an conforming body seal and portable instrument body are disclosed that together provide for a compact yet stable fixation of the probe relative to the body surface and body part to be imaged as compared to prior art handheld ultrasound systems. 
         [0189]      FIG. 16  illustrates the movement of an ultrasound annular array probe relative to body parts for extending the range of high resolution imaging. The elements of  FIG. 16  include the following components. 
         [0190]    The first is a z-axis positioner that allows rapid and precise setting of the distance of the ultrasound probe or array (single element, annular array or linear array) from the body surface. The z-axis actuator, Mz, is mounted on the positioner carriage. In this figure, the ultrasound probe is moved between positions D 1  and D 2  relative to the fluid separation membrane. The probe would be prevented from further z-axis motion past the membrane by a stop mechanism on the z-axis actuator. 
         [0191]    The second is a y-axis positioner that allows for rapid and precise movement of the probe in the y-axis that allows for the creation of a B-Scan image. 
         [0192]    A third is an ultrasound probe. In the case of an annular array, the depth of focus is increased through synthetic focusing to provide a much larger high resolution image zone of 2Δz. This high resolution zone is a multiple of the high resolution zone of a non-synthetically focused probe as is well known to those versed in the art of ultrasound imaging. 
         [0193]    In operation, multiple sweeps of the probe in the y-axis are taken, each with a different probe z-position. Positions D 1  and D 2  are auspiciously chosen so there is some overlap of the high resolution zone. These zones can be combined with known windowing techniques. 
         [0194]    The total high resolution image zone, Z-total is then computed by the formula 
         [0000]        Z -total=( D 1 −D 2)+2Δ z  
 
         [0195]    It is clear that z-total can be further extended by y-axis subsequent sweeps of the ultrasound probe. However, ultimately signal to noise will degrade as the high resolution zone goes deeper into the tissue due to absorption of the ultrasound signals as it passes through a longer path length in tissue. To overcome this, well-known techniques such as coded excitation (chirp excitation as a common example) and over-sampling will be required to image tissue at ever lower signal levels in the deepest tissue. 
         [0196]    It must be noted that above disclosed techniques all require additional scanning time. In a prior art handheld device, this becomes problematic as hand motion interferes with proper imaging. However, probe stabilization as described above provides the stabilization of the probe and time needed to optimize the combination of techniques disclosed without the limits of scanning time imposed by other handheld devices. 
         [0197]    In the case where the best possible image quality is needed and that even breathing or heart beating produces movement that would blur the image, a solid state gyroscope and/or accelerometer could be attached to the body of the handheld device to detect these biorhythms and then make subsequent scan sweeps during the same time of each rhythm thereby eliminating this source of motion noise. Alternately, these data can be used to compensate for these biorhythms in the signal processing step. 
       Linear Array Embodiment 
       [0198]      FIG. 17  is a side view of an ultrasound scanner system with a linear array ultrasound transducer and illustrates the movement of an ultrasound linear array relative to body parts  1726 ,  1727  for extending the depth of high resolution imaging.  FIG. 17  is comprised of the same components as those of  FIG. 14  except that the single transducer element probe or annular array probe is replaced by a 1D, 1½D or 2D linear array  1718 . In addition, a solid state motion sensor such as described in  FIG. 16  may be included. The linear array may be used to change focal plane location and provide beam steering capability as described below. In the simplest embodiment, the linear array may be fixed in position. In other embodiments, the linear array assembly may be moved vertically in the z-direction and/or tilted about its center point and/or moved back and forth in the x-direction and y-direction for enhanced coverage. 
         [0199]      FIG. 17  illustrates how a linear array can be used for enhancing Z-total by the ability to be moved in the z-direction. This method could be used for eye scanning as well as scanning body parts where only a z-axis motion is necessary for enhancing high resolution image depth. Further, a phased array could also be used to synthetically angle the beam to allow best signal to noise of reflections off of key biologic interfaces that are not normal to the straight on beam or to place the effective focal plane a various depths. 
         [0200]    By using a linear phased array in the device shown in  FIG. 17 , it is possible to eliminate the positioner for scanning as it would only be required for the positioning step of centering on the Purkinje reflection in case of the eye or the technician&#39;s reference mark on the body surface. The linear sweep could be duplicated with a linear array. In addition, by utilizing synthetic focusing, the outgoing beam could be tilted (using only the extreme 4-8 elements in the array as is commonly done) to obtain the effect of the pivoting head on the compound probe. Thus, we can make the desired measurements just using planar sweeps and beam tilting. 
       Computer Control of the Positioning and Scanning Operations 
       [0201]    In the above-described embodiments, some components of the scanner system may utilize computer controls, processing, or storage. The first actuator Mx, second actuator My, and third actuator Mz may require controls imputing for moving or articulating ultrasound probe  143  or linear array  1718 . Further, the probe  143  or linear array  1718  may require control inputs as well as processing and storage from a computer system. 
         [0202]    In yet another embodiment, the disclosed systems and methods may be partially implemented in software that can be stored on a storage medium to include a computer-readable medium, executed on programmed general-purpose computer with the cooperation of a controller and memory, a special purpose computer, a microprocessor, or the like. In these instances, the systems and methods of this disclosure can be implemented as program embedded on personal computer such as an applet, JAVA® or CGI script, as a resource residing on a server or computer workstation, as a routine embedded in a dedicated measurement system, system component, or the like. The system can also be implemented by physically incorporating the system and/or method into a software and/or hardware system. 
         [0203]    In one embodiment, one or more computers are used to control, among other things, the rate or volume of dry product through one or more meters. In one embodiment, a user selectively inputs a volume or rate of one or more dry products through or into one or more meters. In one embodiment, the user interacts with the computer through any means known to those skilled in the art, to include a keyboard and/or display to include a touch-screen display. The term “computer-readable medium” as used herein refers to any tangible storage and/or transmission medium that participate in providing instructions to a processor for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, NVRAM, or magnetic or optical disks. Volatile media includes dynamic memory, such as main memory. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, magneto-optical medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, a solid state medium like a memory card, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. A digital file attachment to e-mail or other self-contained information archive or set of archives is considered a distribution medium equivalent to a tangible storage medium. When the computer-readable media is configured as a database, it is to be understood that the database may be any type of database, such as relational, hierarchical, object-oriented, and/or the like. Accordingly, the disclosure is considered to include a tangible storage medium or distribution medium and prior art-recognized equivalents and successor media, in which the software implementations of the present disclosure are stored. 
         [0204]    A number of variations and modifications of the inventions can be used. As will be appreciated, it would be possible to provide for some features of the inventions without providing others. For example, though the embodiments are discussed with reference to an arc scanning device, it is to be understood that the various embodiments may be used with other types of scanning devices, such as sector scanning devices. 
         [0205]    The present invention, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, sub-combinations, and subsets thereof. Those of skill in the art will understand how to make and use the present invention after understanding the present disclosure. The present invention, in various embodiments, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments hereof, including in the absence of such items as may have been used in previous devices or processes, for example for improving performance, achieving ease and\or reducing cost of implementation. 
         [0206]    The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention. 
         [0207]    Moreover though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.