Patent Application
20070276240
There are a number of imaging technologies available to visualize internal structures of a target medium using either electromagnetic or acoustic waves. These conventional imaging technologies are widely used for applications in many different fields, such as security, non-destructive testing, geological study and medicine. A particular application of interest for these imaging technologies is detection of breast cancer, which affects a significant percentage of the world population.
The most widely used imaging technology to detect breast cancer is mammography, which is the process of imaging a breast using low dose X-rays to detect tumors and cysts; x-ray imaging is sensitive to variations in density of the tissue. Mammography involves compressing a breast between two plastic plates to even out the tissue for better imaging and to hold the breast still for motion blur prevention. The actual detection of tumors and cysts requires the trained eyes of a radiologist to interpret the resulting X-ray images, also known as mammograms.
Although mammography is a powerful tool in early detection of breast cancer, there are several concerns with mammography. One of these concerns is that mammography produces a significant number of false negatives, which allows the breast cancer to progress. Another concern is that mammography produces a high rate of false positives, which can lead to unnecessary, invasive and costly biopsies.
Due to the high rate of false positives, mammography is commonly used as the first screening procedure for detection of breast cancer. For suspicious mammograms, one or more additional procedures are usually performed using different imaging technologies, such as acoustic imaging, magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET). The most common follow-up procedure for suspicious mammograms is ultrasound imaging, which is the most common technique among acoustic imaging techniques. Ultrasound imaging involves the use of high frequency acoustic pressure waves, which are usually transmitted into a subject using a handheld probe. When the high frequency acoustic waves encounter a boundary of different materials, such as fluid, soft tissue and bone, some of the acoustic waves are reflected back into the probe. The intensity and travel time of the reflected acoustic waves are used to produce an electronic image on a display. While ultrasound imaging works well to detect differences in mechanical properties, such as density and modulus, ultrasound imaging does not work well to detect differences in electrical properties, such as polarizability and conductivity.
Microwave imaging has also been proposed as a follow-up procedure to further assess suspicious mammograms, but is not currently in practice. Microwave imaging involves the use of non-ionizing electromagnetic waves in the frequency range from 10s of megahertz to 100s of gigahertz, i.e., microwaves, which are transmitted into a subject using an array of transceiving antennas or an array of receiving antennas and transmitting antennas. When the transmitted microwaves encounter a boundary of different materials, some of the transmitted microwaves are scattered back to the antenna array. The scattered microwaves are used to produce an electronic image on a display, which generally represents a two-dimensional (2D) slice of a three-dimensional (3D) image. In addition to medical applications, microwave imaging has been used in many other applications, such as security inspection for contraband, ground-penetrating radar for geology and mine detection, and, of course, commercial radar. In contrast to ultrasound imaging, microwave imaging works well to detect differences in electrical properties of materials, but does not work as well to detect differences in structural properties of materials.
In view of the above-described limitations in ultrasound and microwave imaging, there is a need for a system and method for imaging a target medium that can effectively detect differences in structural properties, as well as differences in electrical properties.
A system and method for imaging a target medium uses both acoustic energy, e.g., ultrasound energy, and electromagnetic energy, e.g., microwave energy. The acoustic and electromagnetic energies are transmitted into the target medium using a transducer array of acoustic and electromagnetic transducers, which may also be used to receive reflections or attenuated versions of the acoustic energy and scattering of the electromagnetic energy from the target medium. The combined use of acoustic and electromagnetic energies provides enhanced detection of different internal materials of the target medium, which improves the information content of the resulting images of the target medium.
An imaging system in accordance with an embodiment of the invention comprises a transducer array, an acoustic transceiving unit, an electromagnetic transceiving unit and a processing unit. The transducer array comprises an acoustic transducer operable to transmit acoustic energy into the target medium in response to a first stimulus, an acoustic transducer operable to receive from the target medium an echo of the acoustic energy and to generate a first electrical signal in response thereto, an electromagnetic transducer operable to transmit electromagnetic energy into the target medium in response to a second stimulus, and an electromagnetic transducer operable to receive from the target medium an echo of the electromagnetic energy and to generate a second electrical signal in response thereto. The acoustic transceiving unit is connected to the transducer array to provide the first stimulus thereto and to receive the first electric signal therefrom. The electromagnetic transceiving unit is connected to the transducer array to provide the second stimulus thereto and to receive the second electrical signal therefrom. The processing unit is connected to the acoustic and electromagnetic transceiving units and operable to produce an image of the target medium in response at least in part to the first and second electrical signals.
A method for imaging a target medium in accordance with an embodiment of the invention comprises transmitting acoustic energy and electromagnetic energy into the target medium, receiving echoes of the acoustic energy and echoes of the electromagnetic energy from the target medium, generating respective electrical signals in response to the echoes of the acoustic energy and the echoes of the electromagnetic energy received from the target medium, and processing the electrical signals to produce an image of the target medium.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.
With reference to
The imaging system 100 is described herein as being used for breast cancer detection. However, the imaging system 100 may be used for other medical imaging applications, as well as non-medical imaging applications, such as non-destructive testing and security inspection. Furthermore, although the imaging system 100 is described herein as using ultrasound and microwave energies, i.e., ultrasound waves and microwaves, the imaging system may use other acoustic and electromagnetic energies.
As shown in
Similarly, the microwave transceiving unit 106 is configured to provide driving signals to the microwave antennas 124 of the scanning unit 102. The driving signals control the transmission of microwave energy from the scanning unit 102 into the target medium. The microwave transceiving unit 106 is also configured to receive electrical signals from the microwave antennas 124 of the scanning unit 102. These electrical signals are generated by the microwave antennas in response to echoes of the transmitted microwave energy received from the target medium. The microwave transceiving unit 106 is further configured to produce summed electrical signals in response to the received electrical signals from the microwave antennas 124. Each summed electrical signal is derived from the electrical signals that represent a microwave echo from a focused point in the target medium, which is further described below.
The processing unit 108 processes the summed electrical signals from the ultrasound and microwave transceiving units 104 and 106 to generate one or more images of the target medium. The images are typically three-dimensional (3D) images. As the target medium is scanned by the scanning unit 102, the processing unit 108 stores the acquired information for each 2D slice of the target medium in the storage device 109. The storage device 109 may be any type of a data storage device, such as a computer hard drive. The images of the target medium generated by the processing unit 108 are electronically displayed on the display unit 110. The acoustic and microwave 3D images may be displayed to correspond exactly to provide an overlay of the information from the two modalities in each slice view. The images may be displayed together using several color channels, e.g. red for microwave boundaries, blue for acoustic boundaries, and purple for regions of both microwave and acoustic reflectance.
As illustrated in
In the array 120, the ultrasound transducer elements 122 and the microwave antennas 124 can be positioned in different arrangements. In one arrangement, as illustrated in
In an alternative embodiment, illustrated in
In another alternative embodiment, the ultrasound transducer elements 122 and the microwave antennas 124 are stacked, as illustrated in
Turning back to
Turning now to
The transmit beamformer 728 drives the individual ultrasound transducer elements 122 of the scanning unit 102 using stimuli in the form of electrical signals. The electrical signals cause the ultrasound transducer elements 122 to generate ultrasound energy, which is transmitted into the target medium. In an embodiment, the transmit beamformer 728 drives the individual ultrasound transducer elements 122 in a manner that causes the ultrasound transducer elements to generate ultrasound energy, which is focused at points within the target medium along a linear path to form a narrow ultrasound beam on a scanning 15 plane. The scanning plane is a plane that extends through the ultrasound transducer elements 122 and is orthogonal to the plane on which the scan head 114 is linearly displaced. The ultrasound beam is produced by the constructive interference of the ultrasound energy from the different transducer elements 122. The focusing of the ultrasound energy from the ultrasound transducer elements 122 is achieved by selectively activating the ultrasound transducer elements in a predefined timing sequence using activation electrical signals transmitted from the transmit beamformer 728 to the ultrasound transducer elements via the switching device 726. The activation electrical signals drive the individual ultrasound transducer elements 122 to generate ultrasound energy, which is transmitted into the target medium. The ultrasound beam can also be steered to different direction on the scanning plane so that the ultrasound energy can be focused at different points within the target medium throughout the scanning plane to acquire imaging information on a 2D slice of the target medium. The steering of the ultrasound beam can be achieved by selectively activating the ultrasound transducer elements 122 using different timing sequences so that the ultrasound energy is focused at points within the target medium along various linear directions.
Echoes of the transmitted ultrasound energy are received by the ultrasound transducer elements 122 from the target medium. In response to the echoes, the ultrasound transducer elements 122 generate respective “ultrasound” electrical signals that represent the received-echoes. The ultrasound electrical signals are transmitted to the receive beamformer 730 via the switching device 726. Since an ultrasound echo of the ultrasound beam from a particular focused point within the target medium arrives at the individual ultrasound transducer elements 122 at different times, the receive beamformer 730 provides delays so that the ultrasound electrical signals corresponding to the ultrasound echo from that particular point can be combined to produce a summed ultrasound electrical signal. Using different delays, summed ultrasound electrical signals for points throughout the scanning plane can be produced. The summed ultrasound electrical signals are transmitted to the processing unit 108 where the signals are processed to form a 2D slice image of the target medium.
The above process of transmitting ultrasound energy and receiving ultrasound echoes is repeated as the ultrasound beam is steered on a particular scanning plane to acquire imaging information for one 2D slice image of the target medium. The entire process is then repeated as the scan head 114 is displaced step-wise along the tracks 116 by the motor 118 to scan additional 2D slices of the target medium. This process of transmitting and receiving ultrasound energy is commonly known as a phased array technique. However, in other embodiments, different techniques may be employed to image the target medium using ultrasound energy.
The microwave transceiving unit 106 includes a bi-directional coupler 732, a microwave transmitter 734 and a microwave receiver 736. The bi-directional coupler 732 connects the microwave antennas 124 to the microwave transmitter 734 and the microwave receiver 736 to transmit and receive electrical signals to and from the microwave antennas. In other embodiments, the bi-directional coupler 732 may alternatively be a circulator.
The microwave transmitter 734 drives the individual microwave antennas 124 using stimuli in the form of electrical signals so that the microwave antennas generate microwave energy, which is transmitted into the target medium. The microwave transmitter 734 generates the electrical signals with a frequency in the microwave range. The electrical signals are transmitted to the microwave antennas 124 via the bi-directional coupler 732 to drive the individual microwave antennas. In response to these electrical signals, the microwave antennas 124 generate and transmit microwave energy. Similar to the transmit beamformer 728 of the ultrasound transceiving unit 104, in an embodiment, the microwave transmitter 734 transmits the electrical signals in different timing sequences to focus and steer the microwave energy generated by the individual microwave antennas 124.
Echoes of the transmitted microwave energy are received by the microwave antennas 124. In response to the echoes, the microwave antennas 124 generate “microwave” electrical signals that represent the received microwave echoes. The microwave electrical signals are transmitted to the microwave receiver 736 via the bi-directional coupler 732. Similar to the receive beamformer 730 of the ultrasound transceiving unit 104, in an embodiment, the microwave transmitter 734 provides delays so that the microwave electrical signals corresponding to each focused point in the target medium can be combined to produce a summed microwave electrical signal.
In other embodiments, the transmission and reception of microwave energy may alternatively be performed in accordance with a beam steering technique in which microwave energy is transmitted by all the microwave -antennas 124 to form a directional beam but only one of the microwave antennas is used to receive the microwave echoes. Alternatively, some of the microwave -antennas 124 may be sequentially activated to transmit microwave energy and some of the non-transmitting microwave antennas may be used to receive the microwave echoes. Similar to the process of transmitting ultrasound energy and receiving ultrasound echoes, the process of transmitting microwave energy and receiving microwave echoes is repeated as the microwave beam is steered on a particular scanning plane, and then the entire process is repeated as the scan head 114 is displaced step-wise along the tracks 116 by the motor 118 to scan the target medium.
At each position of the scan head 114 along the tracks 116, the process of transmitting ultrasound energy and receiving ultrasound echoes and the process of transmitting microwave energy and receiving microwave echoes may be performed simultaneously. Alternatively, the two processes may be performed sequentially. If performed sequentially, either of the two processes may be performed first.
Turning now to
Turning back to
The processing unit 108 also provides control signals to the motor 118, the ultrasound transceiving unit 104 and the microwave transceiving unit 106. The control signals to the motor 118 control the step-wise displacement of the scan head 114 along the tracks 116. The control signals to the ultrasound transceiving unit 104 control the transmitting of ultrasound energy and the processing of ultrasound electrical signals generated by the ultrasound transducer elements 122 in response to received ultrasound echoes. Similarly, the control signals to the microwave transceiving unit 106 controls the transmitting of microwave energy and the processing of microwave electrical signals generated by the ultrasound transducer elements 122 in response to received microwave echoes.
Turning now to
The dual-mode scanning unit 802 includes the scanning plate 112 and the 2D array 820 of ultrasound transducer elements 122 and microwave antennas 124 on the stationary scan head 814. The ultrasound transducer elements 122 and the microwave antennas 124 in the 2D array 820 may be positioned in different arrangements. In one arrangement, illustrated in
The ultrasound transceiving unit 804 is connected to the ultrasound transducer elements 122 of the 2D array 820, while the microwave transceiving unit 806 is connected to the microwave antennas 124 of the 2D array 820. The ultrasound transceiving unit 804 is configured to control the transmission of ultrasound energy from the ultrasound transducer elements 122 of the 2D array 820 and to receive “ultrasound” electrical signals that are generated by the ultrasound transducer elements in response to received reflections of the transmitted ultrasound energy. Similarly, the microwave transceiving unit 806 is configured to control the transmission of microwave energy from the microwave antennas 124 of the 2D array 820 and to receive “microwave” electrical signals that are generated by the microwave antennas in response to the received microwave echoes.
In operation, the ultrasound and microwave transceiving units 804 and 806 selectively transmit activation electrical signals to the ultrasound transducer elements 122 and the microwave antennas 124 of the 2D array 820 to transmit ultrasound and microwave energies into the target medium. Echoes of the transmitted ultrasound and microwave energies from the target medium are then received by the ultrasound transducer elements 122 and the microwave antennas 124 of the 2D array 820. The transmitting and receiving of the respective energy may be sequentially performed by the same ultrasound transducer elements 122, i.e., the transceiving ultrasound transducer elements, or the same microwave antennas 124, i.e., the transceiving microwave antennas. Alternatively, the transmitting of the respective energy is performed by the transmitting ultrasound transducer elements 122 and the transmitting microwave antennas 124, while the receiving of the respective energy is performed by the receiving ultrasound transducer elements 122 and the receiving microwave antennas 124. The ultrasound and microwave transceiving units 804 and 806 can sequentially select a group of ultrasound transducer elements 122 and microwave antennas 124 of the 2D array 820 to scan the target medium. As an example, the ultrasound and microwave transceiving units 804 and 806 may sequentially select one or more columns of the ultrasound transducer elements 122 and the microwave antennas 124 in the 2D array 820 for transmission and reception of ultrasound and microwave energies to scan the target medium in a manner similar to the imaging system 100.
The processing unit 808 of the imaging system 800 processes signals generated by the ultrasound and microwave transceiving units 804 and 806 that represent the received ultrasound and microwave echoes to generate one or more images of the target medium. The images are typically three-dimensional (3D) images. These images of the target medium may be displayed on the display unit 110 or stored in the storage device 109 for subsequent display.
A method for imaging a target medium in accordance with an embodiment of the invention is described with reference to a process flow diagram of
Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.
