Abstract:
Systems and methods are provided for positioning a therapeutic device relative to a target displaced on a platform. A base member has a first track extending along a length of the platform for defining a first pathway for translating the therapeutic device relative to the target. A curved frame is slidably mounted on the base member through the first track. The curved frame has a second track along an interior wall of the curved frame for defining a second pathway for translating the therapeutic device relative to the target. A housing is disposed in the second track of the curved frame and configured to receive the therapeutic device. The housing is extendible at least along a radial direction of the curved frame for defining a third pathway for translating the therapeutic device relative to the target. Applications of the systems and methods may include image-guided thermal therapy.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/016,659, titled “MRI guided thermal therapy system,” filed Dec. 26, 2007, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     This application relates to positioning systems, for example, positioning systems for thermal therapy. 
     Thermal therapy makes use of heating techniques, for example, for treating cancers and tissue anomalies. One form of thermal therapy, for example, uses high intensity focused ultrasound (HIFU). By inducing local heating, HIFU can cause irreversible tissue necrosis rapidly, e.g., within a few seconds. 
     For a thermal therapy procedure to be both safe and effective, the amount of energy delivered to a patient, for example, through an energy transducer, is preferably controlled. The focus of energy application may also be controlled to direct energy only into intended regions while leaving surrounding healthy tissue undamaged. This can be done, for example, by adjusting the location of the energy transducer using a positioning system. 
     In some thermal therapy systems, imaging devices (e.g., magnetic resonance imaging systems (MRI) and computed tomography (CT) systems) are used in conjunction with the energy transducer to provide image guidance in real time. The duration, intensity, and location of energy application can be respectively determined, for example, by estimating the degree of tissue necrosis in a diseased region through MRI-based temperature measurements. 
     SUMMARY 
     In one aspect, in general, a system is provided for positioning a therapeutic device relative to a target displaced on a platform. A base member has a first track extending along a length of the platform for defining a first pathway for translating the therapeutic device relative to the target. A curved frame is slidably mounted on the base member through the first track. The curved frame has a second track along an interior wall of the curved frame for defining a second pathway for translating the therapeutic device relative to the target. A housing is disposed in the second track of the curved frame and configured to receive the therapeutic device. The housing is extendible at least along a radial direction of the curved frame for defining a third pathway for translating the therapeutic device relative to the target. 
     Embodiments of this system may have one or more of the following features. 
     The therapeutic device may include an ultrasound transducer, or alternatively, a biopsy needle. 
     The housing may include a means for pivoting the therapeutic device to enable rotation of the therapeutic device about one or more of three orthogonal axes. 
     An actuator may be coupled to the housing and configured to receive one or more control signals for actuating the housing. A second actuator may be coupled to the curved frame and configured to receive a control signal for actuating the housing. A third actuator may be coupled to the first track and configured to receive a control signal for actuating the curved frame. 
     The therapeutic device may include an energy transducer configured to direct a signal at a selected region of the target for inducing thermal effect. The signal directed at the selected region of the target may include a spatial energy field. 
     An imaging device may be provided for obtaining information characterizing a degree of the induced thermal effect at the selected region of the target. 
     In addition, a processor may be provided for receiving and processing the information obtained by the imaging device to generate the control signal(s) for actuating the housing and/or the curved frame. The processor may be further configured to generate the control signal by comparing the degree of the induced thermal effect with a desired thermal effect. 
     The processor may include a control module coupled to the energy transducer. The control module may be configured to generate a second control signal for controlling a characteristic of the signal of the energy transducer based on the information obtained by the imaging device. The characteristic of the signal may include a magnitude and/or duration of the signal. 
     In some examples, the energy transducer may include an array of energy-transducing elements, each element configured to generate a respective component of the signal of the energy transducer. The control module may be further configured to generate a third control signal for controlling a respective frequency of each of the respective components of the signal. Additionally, the control module may be configured to generate a fourth control signal for controlling a respective phase of each of the respective components of the signal. 
     The imaging device may be an MRI (magnetic resonance imaging), or alternatively, a CT (computed tomography) system. 
     The base member may be mechanically coupled, for example, fixed or movably coupled to the platform. It may include a first base member and a second base member substantially parallel to the first base member, each having a respective track extending along the length of the platform. 
     In some examples, the base member may further include a sheet (or mat) that can be translated relative to the platform. The sheet can be configured to receive MRI receiver coils. 
     In another aspect, in general, a method is provided for positioning a therapeutic device relative to a target displaced on a platform. The therapeutic device is configured to induce a therapeutic effect at a selected region of the target. The method includes detecting information characterizing a degree of the therapeutic effect at the selected region of the target; processing the detected information to determine a desired location of the therapeutic device relative to the target; and generating a signal for a positioner coupled to the therapeutic device for directing the therapeutic device to the desired location, including translating the therapeutic device in one or more of a predefined set of pathways. The predefined set of pathways includes a first pathway for translating the therapeutic device along a length of the platform; a second pathway for translating the therapeutic device along a curved path in a plane substantially perpendicular to the first pathway; and a third pathway for translating the therapeutic device along a radial axis of the curved path. 
     Embodiments of this method may have one or more of the following features. 
     Detecting information characterizing a degree of the therapeutic effect may include generating a medical image of the selected region of the target. The medical image may include an MR image or a CT image. 
     Processing the detected information may include comparing the degree of the therapeutic effect with a desired therapeutic effect. 
     The therapeutic device may include an ultrasound transducer, and the therapeutic effect may include a thermal effect. 
     The method may further include rotating the therapeutic device about one or more of three orthogonal axes. 
     In another aspect, in general, an apparatus is provided for image-guided therapy. An imaging system includes a platform for supporting a target and for translating the target to a desired location. The platform is movable relative to the imaging system. A positioning system is coupled to the platform and configured for positioning a therapeutic device relative to the target on the platform. The positioning system includes a base member mechanically coupled to the platform. The base member has a first track extending along a length of the platform. A curved frame is slidably mounted on the base member through the first track, the curved frame having a second track along an interior wall of the curved frame. A housing is disposed in the second track of the curved frame and configured to receive the therapeutic device, the housing being extendible at least along a radial direction of the curved frame. 
     Embodiments of this apparatus may have one or more of the following features. 
     A first control system may be coupled to the imaging system and configured to provide a first control signal for moving the platform relative to a stationary imaging system, e.g., a magnet. 
     A second control system may be coupled to the positioning system and configured to provide a second control signal for controlling the positioning system to move the therapeutic device relative to the target. 
     The second control system may include a processor for receiving an image of the patient generated by the imaging system and for processing the image to determine a degree of an effect of the therapy. The processor may be further configured to compare the degree of the effect of the therapy with a desired result and to generate the second control signal for controlling the positioning system based on a result of the comparison. 
     The therapeutic device includes an ultrasound transducer. 
     The imaging system may include an MRI device. 
     Various embodiments of the aspects described above may include one or more of the following advantages. 
     In some embodiments where the therapeutic device (e.g., ultrasound transducer) is to be used in conjunction with one or more imaging system, the system for positioning the therapeutic device is configured in a curved shape suitable to fit inside the main structure of the imaging system (such as a ring-shaped gantry of MRI or CT scanner). In some examples, because the based member of the system is mechanically coupled to the platform (rather than fixed to the scanner or other structures of the imaging system), the positioning of the therapeutic device relative to the patient body can be controlled without the need to compensate for platform travel, which may be needed, for example, when different segments of the patient body need to be imaged before or during the procedure. Further, the system for positioning the therapeutic device can be configured as a stand-alone system and conveniently integrated with various imaging modalities without having to modify the imaging machine to use. Additionally, the freedom of the platform to be moved relative to the first track (e.g., guide rails) or the base member will allow the patient to be sent to other imaging system such as CT or PET (Positron emission tomography) device for imaging. 
     Other features and advantages of the invention are apparent from the following description, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is an isometric view of one embodiment of a positioning system for use with an energy transducer. 
         FIGS. 2A-2C  are schematic representations of various modes of translation and rotations provided by the positioning system of  FIG. 1 . 
         FIG. 3  is a block diagram of one embodiment of an MRI-guided thermal therapy system. 
         FIG. 4  is a flow chart of a procedure for use with the MRI-guided thermal therapy system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     1 Positioning System 
     Referring to  FIG. 1 , one embodiment of a positioning system  100  is provided for positioning an energy transducer  120  (e.g., an ultrasound transducer) configured for performing a thermal procedure on a patient (not shown). The transducer  120  is configured to direct a spatial energy field  130  (e.g., in the form of ultrasound beams) toward a target tissue region within the patient. Each sonication of the beams may treat a defined portion of the target tissue, for example, a small focal area of the beams. The entire target tissue can be treated by moving the transducer  120  to successively apply sonication to each of a sequence of portions of the target tissue, for example, according to a protocol established by a computer program or a physician. 
     In some examples, a fluid-filled bag  140  may be coupled to (or otherwise positioned against) a surface of the transducer  120  so that, when the transducer  120  is pressed against the patient body, the contents of the bag  140  (e.g., acoustic gel, water, or other fluid) may facilitate acoustic coupling between the transducer  120  and the patient. 
     To position the transducer  120  at the desired locations for therapy, the positioning system  100  provides a set of mechanical and/or electrical components that may operate together to translate the transducer  120  in linear and/or rotational modes in multiple dimensions as described in detail below. 
     In this embodiment, the positioning system  100  includes a platform  102  for supporting the patient to be treated. Depending on the nature of the treatment, the patient may lie on the platform  102  either in a prone position (face down), or alternatively, in a supine position (face up). The platform  102  can be translated in a linear manner along its longitudinal axis (referred to herein as D 1  as shown in  FIG. 1 ) for moving the patient to a desired location. In some cases where the patient is to be monitored by MRI during the procedure, the platform  102  can be used to place the patient at various locations inside the MRI magnet for imaging. 
     The positioning system  100  also includes a base member  104  mechanically coupled to the platform  102 . In some examples, the base member  104  is secured to the platform  102  and thus follows the movement of the platform  102 . The base member  104  has a pair of linear guide rails  106   a  and  106   b  in parallel alignment. A curved frame  110  (e.g., an arc-shaped frame) is slidably mounted onto the guide rails  106   a  and  106   b  by engaging slide blocks  111   a  and  111   b  with guide rails  106   a  and  106   b , respectively. Thus, the curved frame  110  is movable along axis D 2  relative to the guide rails  106  and the platform  102 . 
     A housing  114  is mounted onto the curved frame  110  through a rail track  112  along an inner wall of the curved frame  110 . The housing  114  is configured to move the transducer  120  in both linear and rotational directions. For example, the housing  114  may include an extension arm  116  extendable along a radial direction of the curved frame  114 . The housing  114  may also include a pivoting member  118  (e.g., a swivel) configured for rotating the transducer  120  about one or more of three orthogonal axes. 
     In some examples, the housing  114  may be coupled to an actuator (not shown) capable of receiving external signals for actuating the housing  114 . One example of the actuator is an electric motor, which can be a piezoelectric vibrational motor that may operate within the field of an MRI without producing substantial magnetic interference. The actuator may include a set of position sensors, for example, configured to measure the linear/rotational position of the transducer  120  to provide feedback positioning control. 
     Using the positioning system  100 , the transducer  120  can be translated relative to the patient in various linear and rotational modes, as described in detail below. 
     A first mode of translation is to move the platform  102  (and therefore the patient) along direction D 1 . For example, prior to the treatment, the patient may first lie down on the platform  102  outside an MRI gantry and then be moved into the gantry for imaging. 
     A second mode is to slide the curved frame  110  relative to the guide rails  106  or base member  104  along direction D 2 . In cases where the guide rails  106  or base member  104  is fixed to the platform  102 , sliding the curved frame  110  provides adjustment of the transducer  120  along the longitude axis D 2  with respect the patient lying on the platform  102 . 
     Referring now to  FIG. 2A , a third mode of translation is to slide the housing  114  via the rail track  112  along the inner wall of the curved frame  110  (referred to as direction D 3 ). 
     Referring to  FIG. 2B , a fourth mode of translation is to extend and contract the extension arm  116  along a radial axis (referred to as direction D 4 ) of the rail track  112 . This can provide fine tuning for focusing the ultrasound beams to the desired depth of the treatment region. 
     Referring to  FIG. 2C , the transducer  120  can be further rotated about each of three orthogonal axes (referred to as D 5 , D 6 , and D 7 ) through the pivoting member  118 . This can provide roll and pitch control of the transducer  120  so that ultrasound beams can be directed at various angles to reach the desired treatment spot. 
     Referring again to  FIG. 1 , in an alternative embodiment of the positioning system  100 , the guide rails  106   a  and  106   b  are directly mounted to the platform  102  without being coupled to the base member  104 . The base member  104  can be used as a mechanically separated piece of mat that may, for example, house MRI receiver coils or registration markers. Moreover, an additional set of sensor and/or actuator may be coupled to one or both of the slide blocks  111   a  and  111   b  for receiving control signal for translation. 
     2 MRI-guided Thermal Therapy 
     In some examples, the positioning system  100  may be integrated with one or more imaging devices that are configured, for example, to obtain anatomic and physiological information and conditions about the tissue of the patient and/or about the degree of treatment effects. Examples of imaging devices suitable for use here include magnetic resonance imaging (MRI) system and computed tomography (CT) system. When MRI is used during the thermal procedure, for instance, a portion or the entirety of the positioning system  100  may be placed within a magnet (not shown) of an MRI system, which forms a static magnetic field for generating MR images. 
     Referring to  FIG. 3 , one embodiment of an MRI-guided thermal therapy system  300  is shown. Patients are received and treated in an operation room  330 . The operation room  330  contains magnet  302  of an MRI system for imaging, a HIFU transducer  308  for directing acoustic beams to the target tissues of a patient, and the positioning system  100  of  FIG. 1  for translating the transducer  308  in multiple degrees of freedom to desired locations. 
     In this embodiment, the positioning system  100  includes a mechanical holder  310  (similar to the housing  114  of  FIG. 1 ) in which the transducer  308  is mounted. The mechanical holder  310  is coupled to one or more motors  314  for actuating the transducer  308 . The motor  314  may be a piezoelectric motor operative in the presence of strong magnetic fields, or alternatively, a hydraulic drive system without creating substantial interference with the magnetic fields of the MRI system. A position detector  312  (e.g., linear and/or rotary encoder) is coupled to each of one or more of the motors  314  for converting linear and rotary positions of the transducer  308  into electrical signals for positioning control. 
     In some examples, the transducer  308  may be a piezoelectric transducer that can convert electrical signals into ultrasonic signals. The power level and the duration of the ultrasonic signals can be modulated by external control signals, for example, activation signals provided by an amplifier  322  through a matching box  316 . In other examples, an array transducer (e.g., a 1D or 2D phased array) may be used. In addition to the power level and duration of the ultrasonic signals, the respective frequency and phase of the signal components generated by individual elements of the array may also be controlled. 
     A water bag  306  is coupled to the transducer  308  for facilitating acoustic transmission when the transducer  308  is pressed against the patient body (e.g., anterior abdominal wall) during treatment. Preferably, the membrane of the water bag  306  is made of materials that are substantially transparent to ultrasound beams, such as mylar, polyvinyl chloride (PVC), polyurethane (PU), or other suitable plastic thin film materials. 
     In some examples, MRI images of the patient may be taken before or during the treatment for planning and monitoring purposes. For instance, a radio frequency (RF) field may be directed at a tissue to be imaged, inducing proton resonance of the tissue that generates a magnetic resonance (MR) response signal. A surface coil assembly  304  is provided to detect the magnetic resonance signal, which can be used to construct images of the target tissue for analysis. In some examples, the surface coil assembly  304  may be positioned between the water bag  306  and the patient body to improve detection efficiency over a selected region of interest. 
     In order to reduce electromagnetic interference to the MRI system, a group of control electronics of the therapy system  300  are preferably located away from the magnet  302 , for example, in a control room  340  separate from the operation room  330 . In some examples, the group of control electronics includes a control circuit  318 , a power meter  324 , a function generator  320 , and an amplifier  322 . The control circuit  318  is configured to receive position information of the transducer  308  detected by the position detector  312  and to generate a control signal for the motor  314 . The control circuit  318  is also configured to receive instructions from a processor  326 , which processes the MR images of the patient to determine, for example, the amount of sonication needed to achieve a desired effect and the position of the treatment spot. Upon receiving instructions from the processor  326 , the control circuit  318  sends a signal  319  to the function generator  320  to generate a drive signal  321  that, after amplification by the amplifier  322 , is transmitted to the matching box  316  for modulating the acoustic output of the transducer  308 . Upon determining that the desired thermal effect is achieved, the processor  326  sends position control signals via the control circuit  318  to the motor set to translate the transducer to the next treatment position. 
     In some implementations, MRI images of the target tissue region are obtained during the treatment and processed to estimate the degree of thermal effects in the target region and to determine the amount of treatment that remains to be performed. 
     Referring now to  FIG. 4 , an exemplary procedure  400  for use with the MRI-guided thermal therapy system  300  is described in detail below. 
     At step  401 , a patient lies down on the platform  102 , and a physician places the transducer  308  and the surface coil  304  over a target region of the patient body (e.g., using the positioning system  100  of  FIG. 1 ). 
     At step  402 , the patient and the transducer  308  is delivered into the magnet  302 , for example, by moving the platform  102  into the magnet. 
     At step  403 , the physician performs MR scans on the patient to obtain images of the target area. These images may provide information relating to the patient&#39;s anatomic and physiological conditions, such as the size, distribution, and location of the tumor to be ablated as well as physical information about the surrounding healthy tissues, blood vessels, and rib cage structures. 
     At step  404 , these images may be further enhanced using image processing techniques such as segmentation and rendering to highlight tumor tissue from healthy tissue in 2D or 3D visualization. 
     At step  405 , the enhanced MR images as well as other information of the patient are used for determining a treatment plan, for example, with the assistance of a computer program. The treatment plan may include a set of target spots identified for sonication and the detailed procedure for treating each one of the target spots. 
     At step  406 , the thermal therapy system  300  performs a calibration test. The test may determine the initial location of the transducer and the initial parameters for modulating the transducer (in some cases, for respectively modulating the individual elements of an array transducer). 
     At steps  407  and  408 , the system  300  delivers a test sonication at a pre-determined lower energy setting for a short time interval on the first target spot. In the meantime, the MRI system scans the treatment area to obtain MR images, and in some examples, further processes the MR images to estimate the degree of thermal effect induced by the sonication (for example, based on a temperature mapping of the treated spot). 
     At step  409 , the system  300  uses the acquired MR images to determine whether the heated spot coincides with the intended treatment spot. In cases where the heated spot resides outside or partially outside the intended spot, coarse adjustment and/or fine tuning of the transducer&#39;s position is performed using the positioning system  100  (at step  410 ). The test sonication is repeated until the ultrasound beams are accurately focused to the intended spot. The positioning parameters for treating the first target spot are then recorded. 
     Based on the calibration results, the system  300  performs actual treatment to each of the target spots in the following steps. 
     At steps  412  and  413 , the system applies sonication to the first target spot at a pre-determined power level. MR images of the target spot are acquired for evaluating the degree of thermal effect in real time. Once a desired effect is achieved (e.g., indicated by detection of a predetermined tissue condition such as internal temperature or protein denaturation), the thermal session on the first target spot concludes (at step  415 ). 
     At step  416 , the transducer is moved to the next position to repeat the thermal procedure. After the last target spot in the treatment plan has been ablated, the system proceeds to a post-treatment stage, at which time MR images of the post-treatment tissue are used for evaluation and assessment. 
     It is to be understood that the systems and methods described above are intended to illustrate and not to limit the scope of the invention. Various alternative embodiments may be available. Also, the positioning system  100  of  FIG. 1  can be used for positioning various therapeutic and/or diagnostic devices besides the energy transducer  120  illustrated in the figure. For example, the housing  114  may be modified to hold a different type of ablation device or a biopsy needle. 
     For purposes of illustration, in the example of  FIG. 1 , the actuator is described as being coupled to the housing  114  for actuating the housing  114 . In other examples, there may be one or more actuators coupled to the housing  114  and/or other components of the positioning system  100  to facilitate motion control of the therapeutic device. For instance, there may be a set of actuators coupled to the positioning system  100  (including individual modules respectively coupled to the platform  102 , the slide blocks  110 , the extension arm  116 , the pivoting member  118 , and possibly other components) such that motion of the therapeutic device in each one of the six degrees of freedom (D 1 -D 6 ) can be controlled independently. Further, each one of these individual modules may be configured to be electrically/mechanically controlled by external signals. 
     In some implementations, the mechanical components of the positioning system  100  are made primarily of plastic materials together with some metallic parts. When used in conjunction with MRI systems, the therapeutic devices and the positioning system are configured to be MRI-compatible. When used with other imaging systems (e.g., X-ray or CT devices), even in cases where the therapeutic device and/or the coupled control components (such as motor or actuator) may cause certain interference to the images, image-guided therapy can still be performed by moving the patient in and out of the imaging gantry using the platform. 
     Other embodiments are within the scope of the following claims.