Patent Application
20160022246
The present invention generally relates to an apparatus for non-invasively measuring intracranial pressure and more specifically relates to a head frame with an integrated pressure chamber for non-invasively measuring intracranial pressure.
This invention is a new apparatus capable of being used in conjunction with our methods previously described in U.S. Pat. Nos. 5,951,477 and 8,394,025. This new head frame offers advantages over the apparatuses described in the '477 and '025 patents.
An apparatus for determining the pressure and flow inside the ophthalmic artery is described in U.S. Pat. No. 4,907,595 to Strauss. The apparatus uses a rigid chamber that can be affixed and sealed over the human eye so that it can be pressurized to apply an external pressure against the eyeball. An ultrasonic transducer is also mounted to the chamber and oriented to transmit ultrasonic pulses for a Doppler type measurement of the flow inside the ophthalmic artery (OA). The apparatus operates by enabling an operator to increase the pressure to such a level that the blood flow through the OA ceases. The pressure at which this occurs is then an indication of the pressure inside the OA. Typically, the pressure at which this event occurs is in the range of about 170 mmHg.
A problem associated with an apparatus as described in the '595 Patent is that the pressure necessary to obtain the desired measurement is so high that it generally exceeds maximum recommended pressures by a significant amount. When such device is then used for an extended time, tissue damage can arise and may result in an increase in the intracranial pressure, ICP, to unacceptable levels.
In our previously granted '477 and '025 patents we described an apparatus and method for determining the pressure inside the brain. An apparatus as described in the '477 and '025 patents requires annular inflatable pressure chamber with an ultrasonic transducer positioned in the open center of the annular chamber. Thus, the ultrasonic transducer would be positioned against the closed eye-lid of a patient, only separated by the thin, flexible layer of ultrasonically transparent material, sonogel or sonopad.
An apparatus in accordance with either the '477 or the '025 patents restricted the size of the ultrasonic transducer. The diameter of the ultrasonic transducer could only be equal to or less than the diameter of the opening in the annular pressure chamber. The ultrasonic transducer was further limited in size and movement by skull bones around the eye. Further, previously described apparatuses allowed for risk of injury to the patient's eye or facial tissues arround the eye upon movement and adjustment of the ultrasonic transducer's position either manually or robotically.
An apparatus in accordance with the invention is a head frame having a lens or shield with a smooth, hard surface and a pressure controlled ultrasonically transparent liquid-filled chamber formed by an elastic film fixed to one side of the lens or shield. Connectors positioned on the lens allow for inlet and outlet of liquid into the pressure chamber. When the head frame of the invention is mounted on the head of a patient and pressure in the chamber is increased, the elastic film expands and conforms to shape of the patient's closed eye imparting a pressure on the tissues around the eye and orbital tissues.
With an apparatus in accordance with the invention one can derive an indication of the pressure inside a skull in a non-invasive manner using previously known methods, such as that described in our '025 patent without risk of injury to the patient's eye. Such methods involve use of an ultrasonic Doppler device to measure blood flow velocities in intracranial and extracranial segments of the ophthalmic artery under varying amounts of pressure applied to the tissues around the eye.
An apparatus in accordance with the invention allows for measurement of the intracranial pressure of a patient without placing the ultrasonic transducer of Doppler device against the eye-lid of the patient. A further aspect of the invention enables the use of a wide range of ultrasonic transducers of different sizes. The diameter of the ultrasonic transducer of Doppler device is not limited, allowing for optimization of the ultrasonic beam and better Doppler signal to noise ratio. Because the ultrasonic transducer of Doppler device is not placed against the eye of the patient, the present invention enables measurement of intracranial pressure by manual operator or robotic driver without discomfort or risk of injury to patient.
An apparatus in accordance with the invention is compatible with all patients and can conform to any patent's eye independent of race and/or facial structure. An apparatus in accordance with the invention provides a surface area that allows for the ultrasonic transducer of Doppler device to be positioned away from the eye and allows for free movement across the entire area of the shield or lens.
It is therefore an object of the invention to allow for the fast and safe optimal positioning of the ultrasonic transducer in order to cross the intracranial and extracranial segments of an ophthalmic artery with the ultrasonic beam at the needed depths from the surface of the ultrasonic transducer and also for non-invasive measurement of intracranial pressure of any patient regardless of age, race, or facial structure.
a-3b are perspective views of the head frame with a collapsed chamber and an expanded chamber, respectively.
a-4c are front elevational view, top plan view and a side elevational view with the dotted line indicating an expanded chamber, respectively.
The exemplary embodiments of the present invention may be further understood with reference to the following description and the related appended drawings, wherein like elements are provided with the same reference numerals. The exemplary embodiments of the present invention are related to a head frame for use in non-invasively determining the absolute value of intracranial pressure (ICP) of a living body.
With an apparatus in accordance with the invention the ICP inside a person's head can be determined from an observation of the blood velocities inside the two segments of the ophthalmic artery (OA) by using an ultrasonic Doppler apparatus which senses the response of the blood flow to a pressure “challenge” applied to the tissues around the eye and orbital tissues. The pressure is applied to the eye at the necessary level for equilibrating parameters representative of the intracranial and extracranial blood flows in the OA leading to the eye. The possibility of this type of measurement has been demonstrated with the analysis presented in our previous U.S. Pat. Nos. 5,951,477 and 8,394,025.
The apparatus of the present invention is significantly improved over previous apparatuses used for noninvasive measurement of ICP for several reasons. The transducer surface of an apparatus in accordance with the present invention is not located against the closed eyelid of a patient, but is located on the shield of the apparatus, reducing risk of injury when an ultrasonic device is being used to take measurements.
Additionally, the shield provides an unrestricted surface to allow for easy movement and manipulation of ultrasonic transducer. Manipulation of the ultrasonic transducer of Doppler device is required to locate and steer the ultrasonic transducer toward the intracranial and extracranial segments of of the ophthalmic artery. The manipulation and steering of the ultrasonic transducer may be performed manually or by robotic steering. Because the transducer is not placed against the eyelid of the patient, robotic manipulation is much safer with the present invention.
With reference to
Strap 30 secures head frame 10 in place on the head of the patient. Elastic film 22 is fixed to the inner side of the shield 20. An expandable chamber 28 is formed by the elastic film 22 sealed with the shield 20. To inflate the chamber 28, pressurized liquid is sent into the chamber through a first connector 24. When the chamber 28 is pressurized the elastic film 22 conforms to the eye of a patient and imparts pressure on the eye and tissues around the eye of the patient. Connectors 24, 25 provide an inlet and outlet of liquid into the chamber 28 for adjusting the pressure of the chamber 28 and are in connection with a pressurized liquid. The location of the connectors 24, 25 may be anywhere on the shield that would not interfere with the manipulation of a transducer in measuring or monitoring the ICP of the patient. In the Figures, the connectors 24, 25 are located near the edge of the shield close to the nose of the patient, but could be positioned in other locations.
The connectors 24, 25 are in connection with a source of pressurized liquid. The pressurized liquid may be any ultrasonically transparent liquid. It is preferable that the liquid have low attenuation of ultrasound and provide optimal speed of ultrasound. In some embodiments the pressurized liquid is water. Pure water without gas is the preferred liquid. The pressurized liquid may also be an acoustic gel. Ultrasonically transparent liquid is liquid that does not contain solid particles or gas. It is further preferable that the pressurized liquid does not pose a hazard to the patient in the case of a leak or rupture.
In some embodiments connectors 24, 25 are connected via tubing 26 to a system for monitoring and adjusting the amount of liquid and therefore pressure in the chamber 28. For example, the tubing may be connected to an electromechanical pump, valves, microcontroller with pressure sensor, and other components to monitor and adjust the pressure in the chamber 28.
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The strap 30 of the head frame 10 may be elastic or inelastic. The strap 30 is adjustable so as to allow the head frame 10 to be used with any patient. The head frame 10 of this invention may be disposable.
As can be seen best in the series of
It is preferable that in combination, the materials of shield 20 and elastic film 22 must not distort or attenuate an ultrasonic beam in the frequency range 1.5 MHz to 3.0 MHz. It is further preferable that the materials be non-allergenic and transparent. The shield 20 of the current invention provides a suitable surface for making acoustic contact with an ultrasonic transducer 40. In some embodiments shield 20 is made of transparent polycarbonate. The elastic film 22, in some embodiments is made of synthetic polyisoprene latex having a thickness between 40 and 60 microns.
An advantage of head frame 10 is that the structure of the head frame 10, with corresponding lens 20 and chamber 28, provides protection for the patient's eye when an ultrasonic transducer of Doppler device or transducer 40 is in use. The apparatus of this invention further allows for safe manual or robotic positioning of ultrasonic transducer and for measurement of intracranial pressure without risk of injury to patient. Head frame 10 allows for accurate measurements by an ultrasonic Doppler device by providing a lens 20 surface that can accommodate a variety of ultrasonic transducer diameters. Ultrasonic transducers used in connection with the invention are preferably between 15 mm and 30 mm in diameter.
By accommodating a wide range of transducer sizes, the apparatus of this invention provides the user with the ability to optimize the diameter of the ultrasonic transducer 40 to achieve the most accurate Doppler signals. Larger diameter transducers provide a greater ability to focus the ultrasonic beam. A focused ultrasonic beam provides stronger signals and better signal to noise ratios.
For use with a patient, the operator or user would place the head frame 10 on the head of the patient with the elastic film 22 proximal the patient's eye area. The operator would adjust the strap 30 to secure the head frame 10 in place. The operator would then apply pressure to the eye of the patient by sending pressurized liquid through the first connector 24. The elastic film 22 would expand and conform to the eye of the patient.
Next, the operator would position the transducer in acoustic contact with the shield 20 for either manual or robotic manipulation. The positions and optimal depths of intracranial and extracranial segments of the ophthalmic artery are located by manipulation of the transducer 40 on the outer surface of the shield 20 away from the patient's eye. The transducer 40 connected to Doppler device can then measure the velocity of the blood flow in the intracranial and extracranial segments of the OA. The operator may adjust the pressure by sending fluid in through connector 24 or allowing fluid out of the chamber 28 through a second connector 25. The adjustment of pressure in the chamber 28 has little or no effect on the angle and position of the ultrasonic transducer 40. This allows the transducer 40 to continue measuring the appropriate blood flow velocities as the pressure is adjusted.
It should be understood that the foregoing is illustrative and not limiting, and that obvious modifications may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, reference should be made primarily to the accompanying claims to determine the scope of the invention.
