Ophthalmological ultrasonography scanning apparatus

#The invention is in the field of medical ultrasound apparatus, particularly apparatus for use in ultrasonography of the eye.

#Ultrasound may be used in a variety of medical applications, including diagnostic ultrasonography of the eye. Diagnostic information is typically provided by an ultrasound pulse from a piezoelectric transducer, which is directed into a tissue. Reflected acoustic energy is detected (as ‘echoes’), so that the amplitude of the received energy may be correlated with the time delay in receipt of the echo. The amplitude of the echo signal is proportional to the scattering strength of the refractors in the tissue, and the time delay is proportional to the range of the refractors from the transducer. A variety of hand-held ultrasound instruments for measuring corneal thickness (called pachymeters) have been developed (for example see U.S. Pat. Nos. 4,564,018; 4,817,432; 4,930,512). Many prior art ultrasonic pachymeters provide A-scan output, in the form of waveforms displayed on a cathode ray tube, representing acoustic reflections in a single dimensional ‘column’ of tissue.

#In B-scan ultrasonography, a two-dimensional image is formed, in which pixel brightness reflects the amplitude of the reflected acoustic signal. A B-scan image therefore represents a cross-sectional slice of the imaged tissue. The cross-sectional information is typically provided by correlating information from a series of adjoining columnar scans (each of which may be used to produce A-scan output). For the purpose of producing B-scans, adjoining columnar scans may be produced by a number of methods: rectilinear translocation of a transducer over the tissue of interest; pivoting angular displacement of a single transducer over a fan-shaped area; or through the use of a linear array of transducers.

#FIG. 1A is a side elevational view of an ultrasound transducer support of the invention, showing a cam-actuated radius adjust mechanism.

#FIG. 1B is an isometric view of an alternative embodiment of the ultrasound transducer support of the invention, showing shaped arm linkages, as are also shown in FIG. 4.

#FIG. 1C is a schematic diagram showing a linking element connecting the front and rear swinging linkages which may form part of the transducer part of the invention.

#In one aspect, the invention provides an ultrasound transducer support comprising a transducer mount adapted to accommodate an ultrasound transducer, and a virtual centre mechanism. FIG. 1A illustrates an embodiment of a virtual center mechanism. First and second arm linkages 65A and 65B are each connected via three pivots to moving parts of the mechanism. Rear swinging pivots 96 connect first and second arm linkages 65A and 65B to rear radius adjust slider 71, and rear radius adjust slider 71 is attached to rear swinging linkage 81. Similarly, front swinging pivots 95 connect arm linkages 65A, 65B to front radius adjust slider 70, and front radius adjust slider 70 is attached to front swinging linkage 80. The front ends of the arm linkages 65A, 65B are connected by transducer pivots 60 to transducer mount 55, and transducer mount 55 is adapted to accommodate ultrasonic transducer 50. Front pivot 85 and rear pivot 86 are stationary relative to the swinging motion of front swinging linkage 80 and rear swinging linkage 81.

#The virtual centre mechanism is attached to transducer mount 55 for moving the ultrasound transducer 50 along an arcuate translation path 56 offset from a virtual centre of translocation 52 by a radius of transducer translocation, so that the focal point 51 of the ultrasound transducer 50 traverses an arcuate focal path 59 about virtual centre of translocation 52. As shown in FIG. 2, when rear swinging linkage 81 rotates about rear pivot 86, rear swinging pivots 96 describe arcuate paths about rear pivot 86. Arm linkages 65A, 65B move front swinging pivots 95, so that front swinging pivots 95 describe identical paths about front pivot 85. Similar triangles 53 show that this swinging motion causes ultrasonic transducer 50 to move in an arc such that its axis pivots about virtual center 52. In addition, transducer focus point 51 traverses an arc 59 about virtual center 52 at image radius 54. The pivoting motion of the apparatus may be driven by scanning driver 82, which may for example be a servo motor. It will be seen that focal point 51 may also lie behind virtual center 52, for example to scan the back of the eye.

#The mounting of transducer 50 in transducer mount 55 may be adapted so that the position of transducer 50 is adjustable relative to transducer mount 55. Such an adjustment may be difficult to accomplish during operation, due to the configuration of the assembled apparatus, as shown in FIG. 4. A radius adjust mechanism for adjusting the radius of transducer translocation may be provided, for example by radius adjust sliders 70, 71 which are movable relative to the respective pivot points 85, 86. In operation, the effect of movement of radius adjust sliders 70, 71 is to elongate similar triangles 53. The elongation of triangles 53 reflects simultaneous changes to three radii: a ‘first’ radius of rotation of front swinging pivots 95; a ‘second’ radius of rotation of rear swinging pivots 96, and the radius of transducer translocation circumscribed by transducer pivots 60. In addition, image radius 54 is changed (the distance between virtual centre 52 and the arcuate focal path 59 traversed by the focal point 51 of transducer 50). The radius adjustment may be driven by rotating radius adjust cams 75, 76 relative to swinging linkages 80, 81. Radius adjust cams 75, 76 may be linked by a rotation linking mechanism, such as anti-backlash belt 90, which operates so that adjusting one cam automatically adjusts the other cam by the same amount. Alternatively, a single cam 75 or 76 could be used on either slider 70 or 71, in which case the other slider would follow. Mechanisms other than cams, such as motors, gears, or other mechanical linkages may be used to actuate sliding movement of radius adjust sliders 70, 71.