Patent Application
20210007817
The present invention relates to the actuation of medical robots, and particularly surgical robots for magnetic resonance imaging (MRI)-guided interventions.
The following references are incorporated herein by reference in their entirety:
MRI superiority is well known over other imaging modalities, providing non-invasive and non-ionizing radiation, high-contrast imaging in particular for soft tissues, and also being capable of monitoring temperature changes during thermal therapy procedures, subtle morphological and pathological changes. These advantages have prompted MRI for the vibrant adoption in surgical interventions, ranging from neurosurgery, cardiac ablation, prostate biopsies to breast biopsies. However, MRI-compatible mechatronics is still challenged, in particular to maintain zero interference of its operation during the imaging.
The standard to quantify an MRI device safety was defined by the U.S. Food and Drug Administration (FDA), which followed the device's classification (ASTM F2503) by the American Society for Testing and Materials (ASTM) as “MR Safe”, “MR Conditional” and “MR Unsafe”. Physically, the electromagnetic (EM) field inside MRI scanner consists of 1) a homogeneous static field, 2) a pulsed gradient magnetic field, and 3) a pulsed radio frequency (RF) field. A device is considered MR safe if it poses no known hazards in any MRI environments.
The present invention provides a pair of cylinders connected via a long tube, which is sealed by a rolling diaphragm at the slave side and/or master side to produce low-friction transmission. Methods to integrate these components to generate bidirectional continuous rotation are also provided. These methods address challenges for MRI actuations including limited stroke and unidirectional actuation of a rolling diaphragm.
In the first aspect, an integrated fluid-powered (e.g. pneumatic, hydraulic) transmission system for MRI-guided interventions which can achieve infinite and continuous rotary motion with positional and torque control in an MR environment without interference by the magnetic resonance is provided. The system comprises at least a control unit (or interchangeably referred to “master unit”) with a plurality of cylinders where each of the cylinders is inserted on the bottom side with a piston and partially encloses the piston in the presence of a seal positioned within the cylinder between the piston and the top side of the cylinder; a slave unit with a plurality of cylinders where each of the cylinders is inserted on the bottom side with a piston and partially encloses the piston in the presence of a seal positioned within the cylinder between the piston and the top side of the cylinder; and a plurality of tubes where each of the tubes connects one master unit cylinder to a respective slave unit cylinder by inserting one end of the tube into an opening of the top side of the master unit cylinder and the other end of the tube into an opening of the top side of the slave unit cylinder in order to form a pair of master/slave cylinder pair, wherein each piston is spaced apart from a lateral surface of its respective cylinder. The tubes are preferably filled with pressurized fluid and said pressurized fluid is retained inside the tubes. To ensure an efficient transmission of pressure from the pressurized fluid to the piston head, a rolling diaphragm configured to seal the pressurized fluid inside the tubes is designed to have a shape matching the shape of the piston head and the cylinder interior wall such that a gap between the piston head and the cylinder interior wall can only accommodate a single folding of the rolling diaphragm. One or more piston rods of either or both of the master and slave units are configured to pass through a centre of an output axis of the rotary motion with a corresponding fixed joint at a periphery of a rotating plate situated at the centre of the output axis of the rotary motion such that output force from each of the corresponding piston rods does not transmit to the centre of the output axis of the rotary motion directly but acts on the rotation plate first before being transmitted to the centre of the output axis of the rotary motion in order to avoid singularity.
In one embodiment, the master unit is disposed in a control room while the slave unit is disposed in an MRI operating room. The master unit and slave unit are connected through a plurality of fluid-filled tubes which run through the penetration panel that contains RF-filters and waveguides and sits between the MRI operating room and the control room.
The actuation unit can comprise three or more piston-based cylinders. The cylinders can provide action-and-reaction transmission through a long hydraulic tube (about 10 meters) that passes through a waveguide in between the MRI and control room. By integrating three or more pairs of piston-based cylinders at a slave side, an actuation unit can be constructed. Different configurations are available for the cylinders' arrangements, e.g. parallel, axial, or radial. The displacement of each cylinder rod can be precisely adjusted by a remote-control method through hydraulic pipelines. Based on the kinematic and dynamic models of the integrated transmission, the positional or torque outputs can be controlled by adjusting the combination of output positions or torques of the cylinders.
The components of an actuation unit are made of MR-safe/compatible materials and the fluid can be transmitted via semi-rigid (for example, nylon) tubes. As it is also actuated by hydraulic/pneumatic power, the whole unit is MR-safe and minimizes imaging interference in an MR environment. Embodiments of the present invention provide an MR-safe actuation in all MRI-guided (robot-assisted) procedures, e.g. electrophysiology (EP) catheterization for heart rhythm disorders, stereotactic neurosurgery for movement disorders, and prostate biopsy. Serving as a basic unit, usually more than one actuator can be implemented in an autonomous device/robot. The actuators are low cost and can be designed for single-use and consumable for easy sterilization.
Embodiments of the present invention provide an MR-safe integrated fluid-powered transmission method and system, which is designed for the actuation of medical equipment or robots in an MR environment. The transmission method can provide continuous bilateral or bidirectional actuation with unlimited range via long hydraulic tubes (e.g., 10 m), with controllable output position and torque. Embodiments of the present invention can be installed in various MRI-guided obotic platforms for actuation, such as endovascular procedures, neurosurgery, prostate surgery, or breast biopsy.
The basic components of the integrated fluid transmission system are a pair of piston-based cylinders (101, 102) being situated in a control room and an MRI room, respectively, as seen in
Fluid can be filled in the pipelines of the long fluid tube 103 to transmit power in both directions toward the pair of piston-based cylinders (101, 102). The components, including piston rods 105, cylindrical housing 106, and bushings 107, are made of MR-safe or MR-conditional material(s). The cylinders (101, 102) contain rolling diaphragms 108 and/or other types of seals (e.g. sliding contact seals) to provide fluid sealing. For the actuators using sealed rolling diaphragms 108a, the static contact and sliding friction between the seal and cylinder can be inhibited. The rolling diaphragms 108 can seal a cylinder chamber 110 to retain pressurized fluid within the long fluid tube 103. To ensure symmetric rolling and constraining undesired ballooning/stretching of the diaphragm, the shapes of the piston head and cylinder wall are designed to tightly fit with the diaphragm hat, so that the gap in between can only accommodate a single folding of the diaphragm itself. As a result, the pressure reaction of the rolling diaphragm can be efficiently transmitted to the piston head.
By integrating three or more pairs of piston-based cylinders, an actuation unit can be constructed. Different configurations are available for the cylinders' arrangements, e.g. parallel, axial, or radial. The exemplary design is a radial configuration with 3 pairs of cylinders.
In an embodiment of the present invention, the integrated actuation unit comprises three or more cylinders with various arrangement methods. The actuation unit can provide an infinite range of bidirectional continuous rotation.
Three piston rods 301, 302, and 303 can be coupled with the output shaft 304 via a rotating plate 305 and a crankshaft 306, as shown in
More than three cylinders can be configured in the actuation unit and thereby increasing the output torque of the actuation unit. With the exception of being placed radially against the crank/eccentric shaft, the cylinders can also be arranged axially or in parallel, as shown in
An MR-safe continuous actuator unit can be configured to have three axially placed cylinders, as seen in
An MR-safe continuous actuator unit can be configured to have three cylinders placed in parallel, as seen in
The actuation unit can be made of MR-safe/conditional materials (e.g. plastics/polymers) and the power transmission can rely on fluid (hydraulics/pneumatics) inside of semi-rigid (e.g. nylon) tubes. Thus, the whole unit is MR-safe and minimizes imaging interference in an MR environment.
In an embodiment of the present invention, a master-slave system is adopted, in which the master unit can actuate a passive slave unit via two long hydraulic/pneumatic lines. The slave unit can be placed in the MRI room and is an actuation unit with three or more cylinders; the master part can be placed in the control room and comprises cylinders driven by DC motor(s). These master side cylinders can be incorporated into a similar structure as a slave unit, or separately controlled. By tuning the cross-sectional areas of the master and slave cylinders, a certain transmission ratio can be naturally formed without employing an additional gearbox.
To enhance transmission efficiency, the pair of pipelines can be pre-loaded with fluid at the same fluid pressure (>0.05 MPa). This increases the transmission stiffness by two means: 1) compressing any micro air bubbles that were inadvertently drawn into the pipelines during their connection; and 2) pre-stretching the seals (e.g. rolling diaphragms) that are naturally flexible in shape.
The transmission method can achieve positional and torque control in an MRI environment. The feed-forward continuous positional control can be realized by adjusting the combination of output positions of the pistons. By integrating rolling-diaphragm-sealed cylinders, the displacement of each cylinder rod can be precisely adjusted by a remote-control method through hydraulic pipelines that can be more than 10 meters. Then according to the kinematics, relations of the displacements can be found in order to generate a specific output angle with continuous motion. To achieve torque control and obtain more accurate positional control, MR-safe/conditional sensors can be integrated to provide feedback. Based on the feedback data and the kinematic/dynamic model of the fluid transmission, various functions can be achieved, including steady or controllable output velocity/torque and backlash compensation.
The kinematic model of the three-cylinder actuation unit can be derived as the following.
Key kinematics parameters of a single cylinder in
x
i(θ)=√{square root over ((s+R)2R2−2R(s+R)cos θ)}−s (1)
where R is the radius of the crankshaft and s is the distance from point P to the nearest point on crankshaft trajectory. As the three pistons are evenly placed in a circle, cylinder C2 and C3 have phase differences of 2π/3 and 4π/3 with cylinder C1. Therefore, the piston displacements of cylinder C2 and C3, the displacements, x2 and x3, can be derived by re-phasing the θ, respectively, with (θ−2π/3) and (θ−π/3) in equation (1). The misalignment is negligible for the installation of the rotating plate.
The dynamic model of the three-cylinder actuation unit is derived as follows. Each cylinder of the actuation unit can generate a unidirectional force, which comes from the positive pressure within the pipeline. Torques towards the output shaft, which are transferred from the forces of the cylinders, can then be described as τi=Fi·di, where Fi is the force provided by the ith cylinder and di is the distance between the center line of the ith piston rod and the rotation axis of the output shaft. di can be calculated as di=R·sin βi, where R is the rotational radius and βi can be further calculated by Sine Law as:
where θ is the angular position of the output shaft and φi is the phase for the ith cylinder, with values of 2π/3·(i−1) for i=1,2,3. The torques generated by the three cylinders are summed at the crankshaft as:
Σi=13 τi=I{umlaut over (θ)}+τ0 (3)
where Ir is the inertia of the rotational components, {umlaut over (θ)} is the angular acceleration of the output shaft.
Therefore, the correlation between the output torque and the forces provided by the cylinders, which are governed by fluid pressure, can be described by the dynamic model of the three-cylinder configuration. Torque control is then possible to be further implemented into the actuator.
A dynamic model for the fluid transmission can also be developed, with the consideration of fluid damping, inertia, and stiffness. The force, Fin, input piston is assumed to produce movement at constant velocity, with no load at the output piston (Fout=0). Analysis of damping in the hydraulic transmission lines begins with analyzing head loss, which is governed by the Bernoulli equation for steady and incompressible flow between any two points in a pipe. In this case, pipelines loss mainly contributes to head loss. Because the pipeline loss is proportional to the length, but inversely proportional to the diameters, the head loss in the cylinders is negligible when compared with that in the pipelines. The pipeline loss can be given as:
where λ is the flow coefficient, Lp and Dpi are, respectively, the length and inner diameter of pipelines, vf is the fluid velocity. For laminar pipe flow, the flow rate is given by λ=64/Re, where Re denotes the Reynolds number. By observing that F=P·A, the equivalent damping coefficient can be obtained as:
where μ is the dynamic viscosity of fluid, vin and Din are the velocity of piston and diameter of cylinder at master side, on which the force is applied.
For the fluid inertia, an equivalent mass as observed at the piston is considered, which can be determined by an energy calculation:
m
eq
v
in
2
=m
cyl
v
in
2
+m
p
v
f
2 (6)
where meg is the equivalent mass, mcyl is the fluid mass in cylinder, and mp is the fluid mass in the pipeline.
The transmission stiffness is determined by considering pipeline compliance at first. The following equations derive the hoop stress σθ and radial stress σr at the inner pipe wall in response to an applied pressure P according to Lamé Formula:
where Dpo is the outer diameter of the pipeline. If the pipe is assumed to be made of a linear isotropic material with a modulus of elasticity E and Poisson's ratio v, the hoop strain is equivalent to:
If the fluid volume variation inside the cylinder of input (Ain·Δxin) is equal to the variation in the pipe (ΔAp·L). Then the inner diameter variation of pipe can be determined as:
With Equations 7-9 and the assumption that the pressure comes from the input force Fin=P·Ain, the pipeline stiffness Kp observed at the piston can be derived as:
The fluid stiffness due to compression can be modeled as Kf=Ev·A2/V, where V is the total volume of fluid and Ev the fluid bulk modulus. Equivalent transmission stiffness, Kt, of the hydraulic transmission line is calculated as the series of pipeline compliance and fluid stiffness:
Components of the overall dynamic model of the passive fluid transmission system are shown in
In the Equation (12), q=[q1 q2 q3]T denotes the matrix containing displacements of input piston (q1), fluid (q2) and output piston (q3). c is the damping coefficient introduced by rolling diaphragm. Fin and Fout are the input and output force, respectively. The state space function can be given as following:
The present invention includes, but is not limited to, the following exemplified embodiments.
Embodiment 1. An integrated actuation system for a magnetic resonance environment comprising:
a master unit comprising:
a slave unit comprising:
a plurality of tubes, each tube connecting one master unit cylinder to a respective slave unit cylinder to form a master/slave cylinder pair, each end of the tube being inserted at the opening near the top surface of a respective cylinder of the master/slave cylinder pair.
Embodiment 2. The system of embodiment 1, wherein a body of the slave unit comprises non-ferromagnetic and MR-safe material.
Embodiment 3. The system of any of embodiments 1-2, wherein the master unit is disposed in a control room and the slave unit is disposed in an MRI operating room.
Embodiment 4. The system of any of embodiments 1-3, wherein the master unit or slave unit comprises three or more piston actuators.
Embodiment 5. The system of any of embodiments 1-4, wherein at least one of the seal comprises a rolling diaphragm or a sliding contact seal.
Embodiment 6. The system of any of embodiments 1-4, wherein the slave unit cylinders are configured radially, axially, or in parallel against an eccentric shaft.
Embodiment 7. The system of any of embodiments 1-4, wherein the slave unit cylinders are positioned radially, wherein each piston is attached to a rotating plate, and wherein all pistons are positioned in a single plane.
Embodiment 8. The system of any of embodiments 1-4, wherein the slave unit cylinders are attached radially or axially to an eccentric shaft, and wherein the slave unit cylinders are evenly spaced apart from each other around the eccentric shaft.
Embodiment 9. The system of any of embodiments 1-4, wherein the master unit cylinders and slave unit cylinders are positioned in parallel, wherein the pistons are connected to a crank shaft, and wherein the crank shaft is connected to an output shaft.
Embodiment 10. The system of any of embodiments 1-9, wherein the slave unit is connected with a second symmetric master unit at a master side by two or more tubes, wherein an electric motor at the master side drives the second symmetric master unit, and wherein the slave actuator replicates the motion simultaneously through hydraulic or pneumatic transmission.
Embodiment 11. The system of any of embodiments 1-10, wherein each piston in the slave unit is actuated by a corresponding piston in the master unit to form a master/slave piston pair, and wherein a plurality of electric motors are driving each master/slave piston pair, respectively.
Embodiment 12. The system of any of embodiments 1-11, wherein positional control of the slave unit is achieved through an inverse kinematic model of the integrated actuation system.
Embodiment 13. The system of any of embodiments 1-12, wherein torque control of the slave unit is achieved through a dynamic model of the integrated actuation system.
Embodiment 14. The system of any of embodiments 1-13, wherein the pipes are filled with fluid comprising liquid, gas, or a combination thereof.
Embodiment 15. The system according to any of embodiments 1-14, wherein the tubes comprise rigid or semi-rigid materials.
Embodiment 16. The system according to any of embodiments 1-15, wherein the tubes have sufficient length to extend from the master unit in an MRI control room to the slave unit in an MRI operating room.
A greater understanding of the present invention and of its many advantages may be had from the following examples, given by way of illustration. The following examples are illustrative of some of the methods, applications, embodiments and variants of the present invention. They are, of course, not to be considered as limiting the invention. Numerous changes and modifications can be made with respect to the invention.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
The experiment in Example 1 used a single-cylinder actuator. Experiments in examples 2, 3, and 4 used a three-cylinder actuator. In all tests, the master and slave parts of the transmission were connected by 10 meter semi-rigid nylon (PA 6) tubes, which had inner/outer diameters of 4/6 mm, respectively. Distilled water was employed as hydraulic fluid due to its availability and ease of implementation. The pre-loading levels of all fluid in all the pipelines were controlled by a pressurized air supply system, a pressure regulating valve and a fluid reservoir. The pre-pressurization was conducted before each operation to eliminate the backlash and ensure the symmetric folding/unfolding of the rolling diaphragms.
EXAMPLE 1
This experiment of the step response was conducted to evaluate the force transmission behavior between one pair of cylinders (see, for example,
The force transmission performance of the three-cylinder continuous motor was evaluated in a weight-lifting experiment. In this test, three master cylinders were independently actuated by electric motors with leadscrew drives. The output shaft was coupled to a winch of diameter Ø40 mm. The hydraulic fluid was pre-loaded at 0.1 MPa and the master-slave actuator lifted 2.5 kg at a constant velocity of 50.24 mm/s, corresponding to an output torque of 0.49 Nm and a net power of 1.23 W. The volumetric power density of the hydraulic transmission was 2.46 kW/m3. The torque/power outputs of this motor were mainly determined by the electric motor inputs at the master side. As such, the continuous motor can generate power as large as the electric motors can provide, up to the lower strength limit of the weakest component, e.g. tiny gear teeth and thin rolling diaphragms.
The dynamic performance of a three-cylinder continuous actuator was investigated with a frequency response method. No loading was added to the slave actuator. The three master cylinders were controlled using inverse kinematics. The slave actuator can thus follow the periodic sinusoidal input of the master actuator under an open-loop control, where the angular position θ=A sin(ω·t). The amplitude was 5° and the test frequency was from 0.1 to 7 Hz. The output angular position was measured by a differential encoder coupled with the output shaft.
EXAMPLE 4
To evaluate the accuracy of the 3-cylinder actuator with open-loop control, a positional tracking test was performed. The setup is the same as Example 3, but the periodic sinusoidal input at master side has a constant frequency of 0.05 Hz and a larger range of motion of 360°.
The results are illustrated in
Hydraulic transmissions were incorporated into a drive catheter robot capable of operating in an intraoperative MRI, as shown in
Three hydraulic actuation units are adopted in the robot. The bending and rotation degrees of freedom (DoF) employs the two-cylinder actuation units. The rotation range is amplified by placing the two cylinders at an acute angle of 27.5°. As a result, the robot can drive with a motion range of ±45° for catheter bending and ±360° for catheter rotation. As shown in
Two sets of experiments were designed and conducted to evaluate the performance of robotic catheterization. The experiments attempt to simulate long-range navigation of a catheter, from the femoral vein to the left atrium (LA), and also emulate a short-range navigation task for pulmonary vein isolation (PVI) inside an atrial phantom model.
For a long-range catheter navigation test, eleven rings 603 (inner diameter=Ø7 mm) were placed in sequence along a 310 mm distance with an average spacing of 31 mm, as shown in
The diagrams in
For the short-range catheter tip targeting test, an LA phantom model was designed and constructed based on a patient-specific imaging data, to simulate catheter tip targeting for PVI. It was 3D-printed with soft material (AgilusClear, Stratasys, USA), as shown in
This endoscopic view can be constructed in an MRI environment with accurate alignment between the MR-based tracking and the imaging, both of which are measured by MRI and in the same coordinate system. The MR-tracking devices can provide fast and accurate positional feedback of the catheter tip. Meanwhile, the fast MR images can be acquired in the region around the catheter tip by means of fast image registration, to register/realign the lesions on the pre-operative EP roadmap. In this way, all the components can be interleaved virtually but with an accurate alignment under MRI.
In the lab-based experiment, the real-time position and orientation of the endoscopic view was obtained from the tracking sensor near the catheter tip. A virtual LA phantom was registered to the actual phantom before the task. Six points were predefined on the LA phantom for the registration and transformation between tracking coordinates and virtual environment. The virtual view facilitates fine placement of the catheter tip while approaching the “lesion” targets, which were prescribed on the virtual LA phantom around the pulmonary vein ostium. During the task, a “lesion” was confirmed when the catheter tip collided with the virtual LA model in the virtual view.
A signal-to-noise ratio (SNR) test was conducted to evaluate the EM interference to the MR images during operation of the robot. Since the slave part of the robot shown in
All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
The present application claims priority from the U.S. Provisional Patent Application Ser. Number 62/640,302 filed Mar. 8, 2018, and the disclosure of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2019/051877 | 3/8/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62640302 | Mar 2018 | US |
