Patent Application
20130147475
Embodiments of the disclosure relate generally to magnetic resonance systems, and more particularly relate to a magnetic resonance system integrated with hyperthermia and magnetic resonance imaging functions, and a method to switch between these functions.
Many clinical studies have shown the effectiveness of adjuvant hyperthermia when it is used in conjunction with radiotherapy and chemotherapy for cancer treatment. Increased tumor cell kill-rate is attained when the temperature in a tumor remains within 41° C. to 43° C. for a predefined period of time, while safety considerations require that the temperature of normal healthy tissue remains below some predetermined limit. In hyperthermia treatment, it is therefore necessary to control the temperature throughout the heated volume. Temperatures can be measured by invasive means, such as thermocouples, thermistors, or fiber-optic probes. However, only regions in close proximity to the probes can be monitored with these technologies, and thus, spatial sampling density of temperature is low. Furthermore, probe insertion may be painful and hazardous.
Magnetic resonance (MR) is a non-invasive and non-ionizing technique, which may produce anatomical images in any orientation. In addition, temperature measurements can be obtained by means of magnetic resonance imaging. However, conventional MR systems are not designed to accommodate hyperthermia systems. It is very challenging to combine hyperthermia and MR functions in a system by simply placing conventional RF hyperthermia apparatus inside a standard MR scanner. Significant changes are typically required for both systems to avoid crosstalk and degraded MR thermometry data, which may significantly affect the ability to track the thermal dose delivered.
It is desirable to provide a magnetic resonance system capable of combining hyperthermia and MR functions together, and a method for operating the magnetic resonance system with combined functions to address the above-mentioned problems.
In accordance with one embodiment disclosed herein, a coil assembly configured to operate in a first mode and a second mode is provided. The coil assembly includes a plurality of coil elements and a plurality of mode switches. Each mode switch is switchably coupled to at least two of the coil elements. In the first mode, at least one of the mode switches is switched off to uncouple at least two of the coil elements. The uncoupled coil elements transmit radio frequency signals in response to multiple first input signals supplied for heating. In the second mode, at least one of the mode switches is switched on to couple at least two of the coil elements. The coupled coil elements transmit or receive radio frequency signals in response to multiple second input signals supplied thereto for imaging.
In accordance with another embodiment disclosed herein, a magnetic resonance (MR) system is provided. The MR system includes a main magnet, a gradient coil, and a coil assembly. The main magnet is used for generating a main magnetic field. The gradient coil is used for applying gradient waveforms to the main magnetic field along selected gradient axes. The coil assembly includes a plurality of coil elements and a plurality of mode switches. Each mode switch is switchably coupled to at least two of the coil elements. When the plurality of mode switches is switched on, at least two of the coil elements are configured per channel to commonly receive an input RF signal with phase and magnitude for each channel. In this mode, the input RF signals enable magnetic resonance imaging for the monitoring of temperature in a region of interest in the subject. When the plurality of mode switches is switched off, each of the coil elements is configured to independently receive an input RF signal with phases and magnitudes that enable the targeting of a region of interest for heating.
In accordance with yet another embodiment disclosed herein, a method is provided for operating a magnetic resonance (MR) system. The MR system includes a plurality of coil elements, and a plurality of mode switches switchably coupled to the plurality of coil elements. The method for operating an MR-RF hyperthermia system includes at least the following actions: switching off the plurality of mode switches for uncoupling the plurality of coil elements; transmitting multi-channel radio frequency signals to a region of interest via the uncoupled coil elements; switching on the plurality of mode switches to constitute a plurality of coil groups, each coil group having at least two coupled coil elements; and transmitting multi-channel radio frequency signals to the region of interest or receiving multi-channel radio frequency signals from the region of interest through the plurality of coil groups.
In accordance with yet another embodiment disclosed herein, a computer-readable medium comprising non-transitory instructions stored thereon is provided. The non-transitory instructions may be executed by a magnetic resonance system to perform the following actions: switching off the plurality of mode switches for uncoupling the plurality of coil elements; transmitting multi-channel radio frequency signals to a region of interest via the uncoupled coil elements; switching on the plurality of mode switches to constitute a plurality of coil groups, each coil group having at least two coupled coil elements; and transmitting multi-channel radio frequency signals to the region of interest or receiving multi-channel radio frequency signals from the region of interest through the plurality of coil groups.
These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of “including”, “comprising”, or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect.
As discussed in detail below, embodiments of the present disclosure generally relates to a magnetic resonance (MR) system integrated with hyperthermia functions. More specifically, the MR system is provided with a particularly designed coil assembly. The coil assembly may be switched to operate at least in a first mode and a second mode. The first mode may be a hyperthermia mode, in which the coil assembly may be configured to enable a first function of hyperthermia treatment of a region of interest by irradiating radio frequency energies to the region of interest. The second mode may be a MR mode, in which the same coil assembly may be configured to enable a second function of temperature monitoring of the region of interest by radio frequency signals transmitting and receiving. Compared to conventional combination of a hyperthermia system and a MR system to get a hybrid system, using a single coil assembly with different operating modes may more effectively enable a MR system to provide hyperthermia functions. Because the coil assembly is switched to perform the hyperthermia functions and the MR thermometry functions, at least the problem of crosstalk between the hyperthermia system and the MR system is minimized or eliminated by the present disclosure. Moreover, the new designed coil assembly in some embodiments enables substantially contemporaneous heating and parallel imaging. The signal to noise ratio (SNR) is typically increased by placing the coil assembly closer to the body and the acquisition speed of MR thermometry can be increased by parallel imaging.
For better understanding the present disclosure, the detail description will be first made to an overall MR system.
Turning now to the figures,
The computer system 20 includes a number of modules that communicate with each other through electrical and/or data connections, for example, such as are provided by using a backplane 20a. Data connections may be wired links or wireless communication links or the like. The modules of the computer system 20 may include an image processor module 22, a CPU module 24, and a memory module 26. The memory module 26 may include a frame buffer for storing image data arrays. In an alternative embodiment, the image processor module 22 may be replaced by image processing functionality on the CPU module 24. The computer system 20 may be linked to archival media devices, permanent or back-up memory storage or a network. The computer system 20 may also communicate with a separate system control computer 32 through a link 34.
The system control computer 32 in one aspect includes a set of modules in communication with each other via electrical and/or data connections 32a. Data connections 32a may be wired links or wireless communication links or the like. In alternative embodiments, the modules of computer system 20 and system control computer 32 may be implemented on the same computer system or a plurality of computer systems. The modules of system control computer 32 may include a CPU module 36 and a pulse generator module 38 that connects to the operator console 12 through a communications link 40.
The pulse generator module 38 in one example is integrated into the scanner equipment (e.g., resonance assembly 52). It is through link 40 that the system control computer 32 receives commands from the operator to indicate the scan sequence that is to be performed. The pulse generator module 38 operates the system components that play out (i.e., perform) the desired pulse sequence by sending instructions, commands and/or requests describing the timing, strength and shape of the RF pulses and pulse sequences to be produced and the timing and length of the data acquisition window. The pulse generator module 38 connects to a gradient amplifier system 42 and produces data called gradient waveforms that control the timing and shape of the gradient pulses that are used during the scan. The pulse generator module 38 may also receive patient data from a physiological acquisition controller 44 that receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. The pulse generator module 38 connects to a scan room interface circuit 46 that receives signals from various sensors associated with the condition of the patient and the magnet system. It is also through the scan room interface circuit 46 that a patient positioning system 48 receives commands to move the patient table to the desired position for the scan.
The gradient waveforms produced by the pulse generator module 38 are applied to the gradient amplifier system 42 that is comprised of Gx, Gy, and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil in a gradient coil assembly generally designated 50 to produce the magnetic field gradient pulses used for spatially encoding acquired signals. The gradient coil assembly 50 forms part of a resonance assembly 52 that includes a polarizing superconducting magnet with superconducting main coils 54. Resonance assembly 52 may include a whole-body RF coil 56, surface or parallel imaging coils 76 or both. The coils 56, 76 of the RF coil assembly may be configured for both transmitting and receiving or for transmit-only or receive-only. A patient or imaging subject 70 may be positioned within a cylindrical patient imaging volume 72 of the resonance assembly 52. A transceiver module 58 in the system control computer 32 produces pulses that are amplified by an RF amplifier 60 and coupled to the RF coils 56, 76 by a transmit/receive switch 62. The resulting signals emitted by the excited nuclei in the patient may be sensed by the same RF coil 56 and coupled through the transmit/receive switch 62 to a preamplifier 64. Alternatively, the signals emitted by the excited nuclei may be sensed by separate receive coils such as parallel coils or surface coils 76. The amplified MR signals are demodulated, filtered and digitized in the receiver section of the transceiver 58. The transmit/receive switch 62 is controlled by a signal from the pulse generator module 38 to electrically connect the RF amplifier 60 to the RF coil 56 during the transmit mode and to connect the preamplifier 64 to the RF coil 56 during the receive mode. The transmit/receive switch 62 can also enable a separate RF coil (for example, a parallel or surface coil 76) to be used in either the transmit mode or receive mode.
The MR signals sensed by the RF coil 56 are digitized by the transceiver module 58 and transferred to a memory module 66 in the system control computer 32. Typically, frames of data corresponding to MR signals are stored temporarily in the memory module 66 until they are subsequently transformed to create images. An array processor 68 uses a known transformation method, most commonly a Fourier transform, to create images from the MR signals. These images are communicated through the link 34 to the computer system 20 where it is stored in memory. In response to commands received from the operator console 12, this image data may be archived in long-term storage or it may be further processed by the image processor 22 and conveyed to the operator console 12 and presented on the display 16. The system control computer 32 further includes a hyperthermia source for generating hyperthermia RF signals.
In one implementation, the coil assembly 100 may be implemented as a whole-body coil for used in the MR system 10. In other implementations, the coil assembly 100 may be implemented as a head coil, a torso coil, a neck-spine coil, a wrist coil, or a knee coil for used in the MR system 10.
Referring to
As further shown in
In one implementation, each of the plurality of coil groups 110a, 110b, and 110c may include three coil elements 112a, 112b, and 112c. In other implementations, fewer or more coil elements may be used for each coil group. The three coil elements 112a, 112b, and 112c in each coil group are substantially linearly stacked end to end along the same direction. It is understood that the three coil elements 112a, 112b, and 112c may be viewed as extending along the direction of the E-field polarization axis with the coil assembly 100 operating in the hyperthermia mode. It is also understood that the three coil elements 112a, 112b, and 112c may be viewed as extending along the direction of the main magnetic field B0 with the coil assembly 100 operating in the MR mode. In one implementation, the three coil elements 112a, 112b, and 112c may include dipole antennas. Although for purpose of description and not by way of limitation, dipole antennas are used throughout the description, the types of antenna may include patch, metal strips, metallic waveguide, dielectric waveguides, and resonant cavities. In one implementation, the dipole antennas 112a, 112b, and 112c may be made of metallic conductive strips, and each may include a first strip and a second strip.
Further referring to
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Δφ=360°/N (1),
where N is a number of the coil group, Δφ is a phase difference between any adjacent two coil groups. When the coil assembly 100 has sixteen coil groups, it can be determined that the phase difference Δφ is 22.5°. In one implementation, multiple radio frequency MR signals individually supplied to the plurality of coil groups may be adjusted to have identical magnitude. In another implementation, the degrees of individual amplitude and phase adjustment of each radio frequency MR signal may be determined according to RF shimming design technique. Each of the radio frequency MR signals is therefore appropriately scaled and phase shifted to produce a substantially homogeneous B1 field.
With continuing reference to
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As described with reference to
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In one implementation, the method 200 may begin at block 202. At block 202, an image of a region of interest that is planned with hyperthermia treatment is acquired. In one implementation, the MR system 10 as shown in
At block 204, the method 200 may continue to determine optimized signal parameters for the coil assembly 100 based on the acquired image information. More specifically, the image acquired at block 202 may be segmented to identify different tissue types as well as tumors. EM numerical simulations are then performed to obtain each dipole antenna's electric fields (E-fields). Given these E-fields and the subject's electrical conductivity distribution, optimized signal parameters including antenna phases and amplitudes can be determined
At block 206, upon the optimized signal parameters are determined, at least one mode switch of the coil assembly 100 may be switched for transforming the coil assembly 100 to operate in a hyperthermia mode. In one implementation, the mode switches 116a, 116b, as shown in
At block 208, the method 200 may continue to apply hyperthermia input RF signals to the coil assembly 100. Because the plurality of dipole antennas 112a, 112b, and 112c is disconnected from each other, each dipole antenna may be supplied with separate hyperthermia input RF signals. In one implementation, the plurality of first control switches 118a, 118b, and 118c in association with the plurality of dipole antennas 112a, 112b, and 112c may be turned on for supplying the hyperthermia input RF signals from the hyperthermia signal source 132 via multiple channels. The hyperthermia input RF signals may be split from the hyperthermia signal source 132 via the power splitter 134. Furthermore, the plurality of vector modulators 136a, 136b, and 136c may be used for adjusting the phase and amplitude of each of the hyperthermia input RF signals.
In other implementations, at block 208, when the coil assembly 100 operates in the hyperthermia mode, a bolus (not shown) containing high dielectric fluid or de-ionizing fluid may be positioned in the cylinder and around the human body. The bolus may be used to increase coupling of the RF energy to the human body and may be used to take away surface heat from the human body.
At block 212, the method 200 continues to determine whether a command is received for detecting a temperature of the target that is subject to a hyperthermia treatment. In one implementation, the MR system 10 may receive the command from the input device 13 or the control panel 14 shown in
At block 214, the method 200 continues to transform the coil assembly 100 to operate in a MR mode by switching the plurality of mode switches. As described herein with respect to
At block 216, the method 200 continues to apply radio frequency MR input signals to the plurality of coil groups 110a, 110b, and 110c, so as to transmit radio frequency signals to excite nuclei in the region of interest. In one implementation, each of the plurality of coil groups 110a, 110b, and 110c may be supplied with separate radio frequency MR signals. In one implementation, the plurality of second control switches 122a, 122b, and 122c in association with the plurality of coil groups 110a, 110b, and 110c may be turned on for supplying the radio frequency MR signals from the MR signal source 142 via multiple channels. The radio frequency MR signals may be split from the MR signal source 142 via the power splitter 144. Furthermore, the plurality of vector modulators 146a, 146b, and 146c may be used for adjusting the phase and amplitude of each of the radio frequency MR signals.
At block 216, the method 200 continues to receive radio frequency signals from the region of interest that is undergoing magnetic resonance imaging. As described above, the coil assembly 100 may include sixteen coil groups. When the coil assembly 100 receives radio frequency signals, in one implementation, all the sixteen coil groups are used for receiving the radio frequency signals. In other implementation, eight coil groups may be selected for receiving the radio frequency signals, while other eight coil groups are disabled. Then, a temperature of the subject can be detected by using the received radio frequency signals. In one implementation, a phase difference proton resonance frequency (PRF) shift thermometry method may be used for temperature mapping and distribution. The temperature change is estimated using the following relation:
where α is the thermal constant, γ is the gyromagnetic ratio, B0 is the main magnetic field strength, TE is the echo time, and Δφ is the phase difference between a baseline image acquired before heating and a measurement image acquired during heating. In other implementations, the temperature may be detected based on the relationship of the relaxation time with the temperature.
At block 218, the method 200 continues to determine whether the detected temperature distribution satisfies predetermined requirements. For example, in hyperthermia treatment, normal tissues surrounding the region of interest should not be over-heated. If the temperature distribution doesn't satisfy predetermined requirements, the method 200 may move to block 204 for modifying the optimized signal parameters for the coil assembly 100. If the temperature distribution satisfies predetermined requirements, the method 200 proceeds to block 222.
At block 222, the method 200 continues to determine whether the detected temperature reaches predetermined value. For example, in hyperthermia treatment, a region may be heated to above a predetermined value for several minutes. For example, the predetermined value is a value in the range of about 41° C. to about 43° C. In one implementation, the MR system 10 may determine whether a temperature of the target exceed a predetermined value. If the region of interest is not sufficiently heated, the method 200 moves to block 208 for continuing heating the region of interest. If the region of interest is sufficiently heated, the method 200 may end.
The operations described in the method 200 of
It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Furthermore, a person skilled in the art will recognize the interchangeability of various features from different embodiments. The various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure.
