A. Field of Invention
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.
B. Description of the Prior Art
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'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.
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'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.
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.
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.
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.
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.
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.
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.
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.
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.