Abstract:
An ultrasonic probe is composed of a beam having a fixed end and a free end, with an ultrasonic transceiver mounted on the free end. A driving mechanism is used to move said ultrasonic transceiver to one or more predetermined positions by applying an electromagnetic force on the beam.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A. Field of Invention 
         [0002]    This application pertains to a diagnostic ultrasonic scanning probe having a cantilevered or a hinged beam supporting an ultrasonic generator/sensor, as well as an excitation and control circuit for controlling linearly the lateral movement of the beam. Optionally the control circuit is integrated with the controls for the transducer. 
         [0003]    B. Description of the Prior Art 
         [0004]    Diagnostic ophthalmic ultrasonic probes make use of well-known, safe diagnostic medical imaging techniques in which ultrasound waves are used to create images representative of a patient&#39;s eyes. Ultrasonic probes are advantageous in that they are noninvasive diagnostic tools that provide images virtually instantaneously and can be used for the evaluation of various ophthalmic disorders. 
         [0005]    Ophthalmic ultrasound probes use pulse-echo system. A series of emitted pulses at pre-determined ultrasound frequency are emitted by the probe that is in contact with a patient&#39;s lid or eye. At every acoustic interface, some of the echoes are reflected back to the transducer, indicating a change in tissue density. The echoes returned to the probe are converted back into an electrical signal and processed as ultrasound images. Typically, ophthalmic ultrasound machines may use frequencies in the range of 6 to 80 MHz, compared with 2 to 6 MHz typically used in other fields of diagnostic ultrasound. Each pulse is followed by a brief pause (microseconds) during which echoes of the pulses are received and processed and the resulting images are presented on the display screen. 
         [0006]    The A-scan, B-scan and ultrasound biomicroscopy are the most commonly used ophthalmic ultrasound techniques. The A-scan technique results in a one-dimensional display of echo strength over time (time delay). The vertical spikes are generated that correspond to the reflected echo intensity and are typically demonstrated as a function of time. The technique commonly uses a frequency range of about 6 to 12 MHz and is mainly used for documenting axial eye length measurements of the eye: to measure the distance between the anterior cornea and retina. This distance is used to calculate the appropriate power of an intraocular lens implant used at cataract surgery. 
         [0007]    The B-scan technique generates a two dimensional image of the echoes along both a horizontal and vertical axis. It is an important tool for the clinical assessment of various ocular and orbital diseases. In situations in which normal examinations are not possible, such as lid problems, corneal opacities dense cataracts, or vitreous opacities, diagnostic B-scan ultrasound can accurately image intraocular structures and give valuable information on the status of the lens, retina, and other areas of anatomy. 
         [0008]    Ultrasound biomicroscopy is an ultrasonic technique that uses frequencies from 35 to 80 MHz for the acoustic evaluation of anterior segment of the eye. Higher frequency use results in more detailed imaging of the anterior segment of the eye. 
         [0009]    Historically ultrasonic probes have been utilized with a water stand-off and the examiner manipulating a transducer free hand. This technique was found to be unwieldy and time consuming. 
         [0010]    Currently, most B-scan diagnostic ultrasonic probes are in a self-contained cylindrical package—with a small amount of water or other fluid stand-off built into the device around the transducer element. The self-contained device may be positioned directly on the eye or lid by the physician and moved about without injuring the eye. Using these devices the probe—typically, a single transducer—is moved mechanically in an arc scan across the eye, and at regular intervals, an ultrasound pulse is directed into the eye and the resulting echoes are received by the same transducer and analyzed. 
         [0011]    The present state the art utilizes several motorized mechanical parts to provide this mechanical movement. In this design the transducer is typically driven in a sector or arc scan (although other scan configurations are possible) inside the enclosed water bath. Water or some other fluid is required in these systems since air results in total internal reflection and the ultrasonic beam fails to exit the probe. Moreover, the cabling between the probe and the mechanical device requires a coaxial cable of some design, carrying signals to and from the transducer, as well as leads carrying the drive current to the electric motor and the signal from the position sensor. These cables often fail with continued use due to mechanical fatigue as well as exposure to elevated temperatures. The probe is made compact by having the necessary drive components built into and closely around the rocking transducer assembly. 
         [0012]    Mechanical scanning is currently the industry standard in ophthalmic systems (including systems using combined A and B-scan capabilities). Despite the disadvantages associated with moving parts, such as wear and tear, vibration, and resultant heat the level of acoustic noise associated with these scanners was considered tolerable using insulation and software filters. 
         [0013]    Co-pending patent application US 20120236358 describes an ultrasonic probe with resonant beam vibrating at its natural mechanical frequency of resonance in a manner similar to a tuning fork to move an ultrasonic transceiver. 
       SUMMARY OF THE INVENTION 
       [0014]    The present inventors have developed a low cost ultrasonic probe particularly suited for ophthalmic applications. The present device uses an electromagnetically actuated beam. It has been found that this configuration results in a probe that is low cost, provides accurate results, and requires relatively minimal electronic control and the capability of mounting both B-scan and UBM probes on the same actuator. 
         [0015]    In one embodiment, the beam is a cantilevered beam fixed to a support structure. In another embodiment, the beam is provided with a hinge supporting the beam within the housing. In another embodiment, the beam is configured to move along a linear path. 
         [0016]    At least a portion of the beam is made of a magnetic or magnetizable material and an electromagnetic control circuit is used to drive the beam, or at least its free end along a predetermined angular path. An ultrasonic transceiver is mounted on the end of the beam and is driven by the beam along said path to scan the eye of a patient. Preferably, in one embodiment, one or more stationary electromagnetic coils interact with one or more permanent magnets mounted on the beam to generate a magnetic force on the beam thereby moving the beam along a predetermined path. Alternatively, the one or more electromagnetic coils are attached to the beam and the permanent magnet(s) are stationary. 
         [0017]    In one embodiment, the beam is supported in a manner that allows the whole beam is allowed to move in a direction preferably perpendicularly to a longitudinal axis of the beam. Magnetic or other means are used to reciprocate the beam in a predetermined motion thereby enabling the ultrasonic transducer to scan a patient&#39;s eye. 
         [0018]    In one embodiment, the control circuit includes a variable current generator and one or more coils receiving current from the current generator and applying a predetermined force on the beam thereby reciprocating the beam along the angular path. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0019]      FIG. 1  shows somewhat diagrammatic side sectional view of an ultrasonic probe constructed in accordance with this invention; 
           [0020]      FIG. 1A  shows a block diagram of the components of probe of  FIG. 1  used to position its ultrasonic transceiver; 
           [0021]      FIG. 2  shows an alternate embodiment with one or more position sensors; 
           [0022]      FIG. 3A, 3B  show somewhat diagrammatic front and side views of a probe with several discrete ultrasonic transceivers; 
           [0023]      FIG. 3C  shows an enlarged side view of a multi-mode ultrasonic transceiver; 
           [0024]      FIG. 4  shows a block diagram of another embodiment with the invention with vibration compensation; 
           [0025]      FIG. 5  shows a block diagram of a unified control system with interactive components for both positioning and the transceivers and acquiring ultrasonic images; 
           [0026]      FIG. 6  shows an alternate embodiment showing a side sectional, somewhat diagrammatic view of a transducer with a hingedly supported beam biased by two springs; 
           [0027]      FIG. 7  shows an alternate embodiment with a side sectional, somewhat diagrammatic view of a transducer with a hinged beam biased by a single coil springs; 
           [0028]      FIG. 8  shows another alternate embodiment of the invention in which a single magnet is provided on the beam rather than dual magnets; 
           [0029]      FIG. 9  shows yet another embodiment of the invention in which the beam is reciprocated laterally in a linear rather than angular motion; and 
           [0030]      FIG. 10  shows another embodiment with the magnets being stationary and the electromagnetic coils being attached to the beam. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    The present inventors have developed and experimentally tested an electromagnetic positioning mechanism for ophthalmic B-scan probe. The probe can be easily adapted to perform A-scan and UBM probes, as well as many other ultrasonic probes as well. 
         [0032]    As shown in  FIG. 1 , a probe  100  constructed in accordance with this invention includes a housing  10  which includes all the elements of the probe. Preferably, the housing  10  is preferably sized and shaped so that it can fit into the hand of a user. The housing  10  includes a beam  12  having an end  12 A supported within the housing  10  by a pair of claims  14 . The other end  12 B of the beam supports an ultrasonic transceiver  16 . As discussed below, the transceiver typically includes an ultrasonic pulse generator and a sensor sensing echoes from a target, such as an eye  18 . In one embodiment, the beam  12  is made of steel and consists of two sections  121  and  122  solidly and collinearly attached to each other. Section  121  has generally rectangular cross section of about 1″ long by 0.5″ wide by 0.05″ thick. The rectangular beam section  121  is followed or attached to cylindrical section  122  (holding the ultrasonic sensor  16 ). Section  122  has of 0.25″ diameter and 2.5″ length. The beam  12  is somewhat flexible so that when a force is applied on it, it can flex by an angle in either directions A or B. In normal use, the beam is forced to flex angularly in a reciprocating motion and a predetermined driven frequency normal for ultrasonic probes. For example, this frequency may be about 10-20 Hz. The deflection of the beam is sufficient to move the transceiver  16  by ±5 cm. The beam  12  is constructed and arranged so that has a much higher natural resonant frequency (e.g., several orders of magnitude) than the driven frequency. For a cantilevered steel beam of 1 inch length and 0.05″ thickness, the resonant frequency is about 500 Hz. As a result, the movement of the beam is not affected by external forces as the probe is being handled by a physician, for example during a normal image gathering process. In the prototype built by the inventors, clamps  14  selectively open and close to allow the beam  12  to be removed and replaced by a different beam having different physical characteristics (such as its resonant frequency) or different transducer  16 . Alternatively, the beam  12  and transducer  16  can be configured so that the transducer can be mounted at will, dismounted from the beam  12  and replaced with another transducer, as desired. 
         [0033]    A sheath  18  may be provided between the beam  12  and the clamps (or other structure used to support the beam  12  within the housing  10  to isolate the beam  12  mechanically and to prevent or at least reduce the vibration of the beam  12  and transducer  16  from being transmitted to the housing  10 . 
         [0034]    Also mounted on the beam  12  are two permanent magnets  20 ,  22 . These magnets are preferably strong magnets, made, for example, of rare earths such as neodymium, so that they can generate strong magnetic fields. 
         [0035]    Mounted within the housing  10  there are also two electromagnets  24 ,  26 . The electromagnets typically include coils  24 A,  26 A disposed on hollow shafts  24 B,  26 B. The electromagnets are excited by power from a power supply and control circuit  30 . The magnets  20 ,  22  and electromagnets  24 ,  26  are constructed and arranged to apply a deflecting force on the beam alternately in directions A and B, as discussed in more detail below. 
         [0036]    A somewhat simplified circuit diagram of the power and control circuit  30  is shown in  FIG. 1A . The circuit  30  receives power either from a battery (not shown) or from an AC power source (not shown) and it includes a microprocessor  32 . The microprocessor  32  receives inputs from a manual on/off switch  34 . The circuit  30  further includes a digital-to-analog converter  35  that provides analog control signals to two programmable current generators  36 ,  38 . (The digital-to-analog converter  35  could be incorporated into the microprocessor  32 . Alternatively, the current generators  36 ,  38  may be configured to respond to digital control signals, in which case the D/A converter  35  is omitted). The current generators  36 ,  38  generate respective current for coils  24 A,  24 B of electromagnets  24 A,  26  respectively. 
         [0037]    The magnetic fields generated by the coils  24 A,  26 A are uniform and have an intensity given by equation (1) below: 
         [0000]        B=μ   0   ni   (1)
 
         [0038]    where μ 0  is the magnetic permeability of air, n is the number of turns per unit length and i is the current through the electromagnet coil. The force experienced by each of the respective permanent magnets  20 ,  22  in the magnetic field of the electromagnets is given by: 
         [0000]        F=kB   (2)
 
         [0039]    where k is a constant dependent on the strength and length of the permanent magnet and B is the magnetic field of the solenoid. Hence the force on the cantilever beam  12  is a linear function of current through the electromagnet coil. The device is very stable and does not need a PID control system. As a result, the probe is low cost and stable. If two permanent and two electromagnets are used, as shown in  FIG. 1 , the force on the cantilevered scanning beam is doubled. The angular deflection of the cantilever is given by equation (3) below: 
         [0000]      θ= kBL   2   /EI   (3)
 
         [0040]    Where L is the distance between the center of the electromagnets and the clamps supporting beam  12 , as shown in  FIG. 1  and I is the average moment of inertia of the beam  12 . Hence by just changing the coil current i, the angle of deflection of the cantilever can be varied. Importantly, this angle can be varied linearly, making the control system simple and straight forward. 
         [0041]    After the device  10  is assembled it can be calibrated (e.g., the parameters of the equations above can be determined) by generating a current through each of the coils and measuring the resulting deflection angle θ. Alternatively, sensors such as Hall effect sensors may be placed near the beam, a known current can be applied to the coils and the device can be calibrated using the outputs of the sensors. 
         [0042]    It is believed that for most devices, the control circuit shown in  FIG. 1A  is sufficient. Moreover, the device shown in  FIGS. 1 and 1A  does not require stepper motors or complicated mechanical drive trains. The device is able to provide the angular reciprocating motion necessary for various ophthalmic applications. 
         [0043]    The device  100  operates as follows. The microprocessor  32  is programmed to reciprocate transceiver  16  by about ±5 cm and a frequency of 10 Hz using a triangular, sinusoidal or other similar wave shapes. The physician positions the device as shown in  FIG. 1  with the transceiver  16  pointed at the eye, and he then activates an an/off manual switch  34  on housing  12 . The position of the switch  34  is sensed by the microprocessor  32  which then sends appropriate control signals to the programmable current generators  36 ,  38  to generate respective current wave shapes. As discussed above, since the circuit in  FIG. 1A  is linear, the microprocessor  34  and generators  36 ,  38  cooperate to generate to vary current i (which is a DC current) linearly to follow the desired waveshapes. In response, the beam  12  reciprocates angularly moving the transceiver  16  back and forth and allowing the transceiver  16  to scan the eye  18 . 
         [0044]    In some instances, it may be desirable to position the transducer  16  to a predetermined angle. For this situation, a manual switch  40 . When this switch is activated, the microprocessor generates a positioning signal to the current generators  36 ,  38  thereby causing the beam to move the transceiver  16  to a predetermined position or angle. 
         [0045]    For some applications, because of various internal effects, the movement of the transceiver  16  may not be precise enough. For these applications, a modified control circuit with feedback control loop may be used. For example, the device  100  can be provided with either a single sensor  42  or a pair of sensors  42 ,  44  disposed symmetrically on the two sides of the beam  12 . The modified control circuit  50  is shown in  FIG. 2 . The target signal t is sent from the microprocessor  32  to a summer  54 . The output of the summer c is fed to current generators  36 ,  38 . The generators generate a current i that is fed to the coils  24 A,  26 A. The coils deflect the beam and the actual position of the beam  12  is sensed by sensors  42 ,  44  and the sensed signals s are fed back to the summer  54 . The circuit  50  can be implemented with a single sensor, with two sensors, in which case, one of the sensors is used when the beam moves in direction A and the other sensor is used when the beam moves in direction B. 
         [0046]    Preferably, the beam  12  and the transceiver  16  are constructed so that the transceiver can be easily removed from the beam end  12 B and changed to a different transceiver. In one embodiment, the beam end  12 B is provided with two transceivers  16 A,  16 B arranged side by side, as seen in  FIGS. 3A and 3B , with two transceivers being separated by a distance of that can be 2-3 times the cross-sectional diameter of transceivers. The two transceivers  16 A,  16 B can be operating at different frequencies, for example, one being configured to perform A scans and the other being configured to perform B scans. Thus, the device  100  is ‘modular’ in nature as it allows for both high and low frequency ultrasound probes to be mounted on the same device. The low frequency ultrasound transceiver is used for a generic ophthalmic scan and the high frequency transceiver is used for ultrasonic bio microscopy or UBM. This is a major improvement over the present state-of-art probes which have either high frequency or low frequency transducers. 
         [0047]    Alternately, a transceiver  16 C can be provided which has two transceiver portions  16 D and  16 E, as shown in  FIG. 3C . One transceiver portion is operates at a high frequency and the other portion can be operating at a low frequency. 
         [0048]    As previously indicated, the inventors believe that the device  100  as discussed above is very robust and can operate in satisfactory manner even in the presence of external vibrations. However, if it is desired to eliminate any interference from such vibrations, an active control system can be used, instead of the control systems from  FIG. 1A or 2 . Such an active control system  70  is shown in  FIG. 4  and it includes a position controller  72 , a vibration sensor  74 , a vibration controller  76  and a summer  78 . 
         [0049]    The position controller  72  is used to determine the desired position of the transceiver  16  and/or beam  12  as a function of time. The position controller  72  may include, for example, microprocessor  32  and the manual control switch  34 . The position controller generates a current i 1 ( t ). 
         [0050]    The undesired vibration is detected by a vibration sensor  74 . This sensor may be positioned to sense a vibration in the angular position of the transceiver  16 , or beam  12 . Alternatively, the sensor  74  may sense a vibration of another element of the device  100 , such as its housing  10 , etc. The output of vibration sensor  74  is presented to a vibration controller  76 . The vibration controller determines how the beam  12  should change its angular position to cancel the vibration detected by the sensor  74 . The system  76  then generates a second time varying current i 2 ( t ). The two signals i 1 ( t ) and i 2 ( t ) are added algebraically by summer  78  and provided to the coils  24 A,  26 A. 
         [0051]    In other words the vibration control system can simply superimpose a time-dependent current to the electromagnets in addition to the actuation voltage. The vibration control system may also use piezoelectric or otherwise active elements mounted on the probe cantilever to sense vibrations at various locations within or outside the housing  10 . 
         [0052]    In the embodiments described so far, the control system used for positioning the ultrasonic transceiver(s) are separate from, and operate independently of the control system used to operate the transceivers themselves. However, there may be several advantages in unifying these two systems to make them less expensive, more energy efficient and obtain more accurate, higher resolution images. One such unified system is shown in  FIG. 5 . This unified system  200  can include two processing modules: a positioning module  202  for positioning an ultrasonic transceiver  204  and an image acquisition module  206  for activating the transceiver  204  as required, and to collect the resulting imaging data. 
         [0053]    The unified system  200  operates as follows. A scanning pattern memory  205  is used to store scanning patterns for different kinds of scanning techniques discussed above. For example, these patterns may define the scanning range required for the ultrasonic transducer  204 , the duration and/or intensity of ultrasonic pulses, the various positions of the transducer for each pulse, etc. When the image acquisition module  206  receives a request for an image, it first retrieves an appropriate scanning pattern from memory  208 . Then the module  206  sends one or more commands to positioning module  202 . The positioning module  202  is configured as described above and in  FIGS. 1-4  to position the transceiver  204  to a position dictated by the pattern from memory  208 . As discussed above, the position module  202  may be accurate enough to achieve this operation without any sensory feedback. Alternatively, one or more position sensors  210  may be used to determine that the transceiver  204  has reached the required position. 
         [0054]    Once the required position is reached, the image acquisition module  206  sends a command to the transceiver  204  to start the image acquisition process. As part of this process, the transceiver sends one or ultrasonic pulses toward the eye of patient. Echoes from these pulses are sensed within the transceiver and are transmitted as raw image data back to the image acquisition module  206 . The module  206  sends this raw data to an image processor  212 . The image processor either stores this data in an image memory  214 , or performs some processing on the raw data and the processed data is stored in memory  214 . The transceiver  204  is moved to the next position and a new set of raw data is collected until the whole eye is scanned, the raw data is processed and the desired image is obtained and stored in image memory  214 . 
         [0055]    In one embodiment, either during or after the image processing, the processor  212  checks the raw data to determine if the raw data is acceptable. Of the raw data or the resulting image is not acceptable, for example, because of some external causes such as vibrations, an error indication is activated by module  216  to indicate that this event. In this case, the whole process may be repeated. 
         [0056]    The system  200  shown as including several different modules, such as modules  202 ,  206   212  and  216  for the sake of clarity. However it should be understood that the invention could be implemented with all or some of these modules being incorporated into a single microprocessor. 
         [0057]    Moreover, the system may be configured to receive either one of several ultrasonic transceivers  204 , each transceiver being configured to perform a particular scanning technique. Alternatively, two transceivers may be mounted on the same beam and used as discussed above. 
         [0058]    In alternate embodiments of  FIGS. 6 and 7 , a probe is shown in which the cantilevered beam of the previous embodiments is replaced by a hinged beam. Referring to  FIG. 6 , probe  300  includes a housing or frame  310  including a post  302 . A beam  312  is supported on this post  302  by a hinge  304  that allows the beam  312  to pivot in an angular motion represented by arrow A around axis  306 . A pair of springs  308 A,  308 B bias the beam  312  toward a normal or neutral position which is preferably collinear with a longitudinal axis of the housing  310 . Magnets  322  are supported on beam  312  and cooperate with electromagnetic coils  324  to control the angular movement of the beam  312 . This movement is very similar to the movement of beam  12  but instead of bending along its length, beam  312  pivots about axis  306  and moves transceiver  316 . 
         [0059]    In another alternate embodiment shown in  FIG. 7 , beam  412  pivots about an axis  406  and is maintained in a neutral position by a coil-type spring  408 . Probe  400  operates essentially in the same manner as probe  300  of  FIG. 6 . 
         [0060]    In the embodiment of  FIG. 1  (and all subsequent embodiments described until now) two magnets  20 ,  22  are mounted on the beam  12 . The magnets are arranged and constructed so that one of their poles is disposed within one of the respective coils  24 A,  26 A of the electromagnets  24 ,  26 . In the embodiment of  FIG. 8 , an alternate arrangement of a probe  500  is shown. The system includes a beam  512  with electromagnets  524 ,  526 . However, instead of two permanent magnets, the beam carries a single permanent magnet  522  with a south pole and a north pole. The south pole extends into the coil of electromagnet  524  and the north pole extends into electromagnet  526  as shown. The operation of the device  500  is similar to the operation of the devices disclosed above. 
         [0061]    In the embodiments of  FIGS. 1 and 8  probes are shown having beams  12 ,  512  that are selectively deflected or pivoted, but in either case the respective ends of the beams are moved angularly along a predetermined path.  FIG. 9  shows yet another embodiment. In this embodiment, a probe  600  includes a beam  612  having one end  612 A mounted on a transversal rod or bearing shaft  613  by a linear bearing  615 . The linear bearing  615  is arranged and constructed to allow the beam to move laterally in either direction linearly on shaft  613 , perpendicularly to the longitudinal axis of the beam  612 . The bearing  615  insures that there is very little friction opposing the motion of the beam. The motion of the beam is indicated by arrows C, D. Shaft  613  is attached to the frame  610  and is stationary. 
         [0062]    Stiffening mechanisms  621 ,  623  are used to control the movement of the beam  612 . For example, the mechanisms may include spring  625 A,  625 B used to bias the beam  612  toward a predetermined neutral position. Damping devices  627 A,  6278  are used to dampen the movement of the beam to insure the beam  612  does not move too fast and overshoot a predetermined target or desired position. For the sake of simplicity, springs  625 A,  627 A are shown as coil springs but it should be understood that other kinds biasing devices may be used as well. Similarly, devices  625 B,  6273  are shown as dashpots, it being understood that other kinds of damping devices may be used as well. Moreover, the stiffening mechanisms  621 ,  623  may be used with the other embodiments to control the movement of a pivoting or flexing beam (shown in the other Figures) and not just the translating beam shown in  FIG. 9 . 
         [0063]      FIG. 10  shows yet another embodiment of the invention. In this embodiment, a probe  700  has two permanent magnets  720 ,  722  that are stationary and are supported by standard means on frame  710 . Electromagnets  724 ,  726  are mounted on the frame  712 . As before the magnets and electromagnets cooperate to generate magnetic forces for moving the beam  712  as described. 
         [0064]    Of course, the arrangement of permanent magnets  720 ,  722  and electromagnets  724 ,  726  can be used in all the other embodiments described above as well. 
         [0065]    Numerous modifications may be made to this invention without departing from its scope as defined in the appended claims.