Microwave imaging apparatus

Abstract

A microwave imaging apparatus, including a plurality of microwave sensor assemblies for arranging around an object to be imaged; and a central control component digitally coupled to each of the microwave sensor assemblies; wherein each of the microwave sensor assemblies is operative to: selectively generate and transmit microwave signals at each of a plurality of different frequencies into the object; receive microwave signals scattered and / or reflected by the object; process the received microwave signals to generate corresponding digital signals representing the received microwave signals for each of the plurality of different frequencies; and transmit the digital signals to the central control component; wherein the central control component is configured to: control operation of the microwave sensor assemblies; process the digital signals received from the plurality of microwave sensor assemblies to generate corresponding image data representing an image representing a spatial arrangement of internal features of the object.

Description

[0001] MICROWAVE IMAGING APPARATUS

[0002] TECHNICAL FIELD

[0003] The present invention relates to microwave imaging, and in particular to a microwave imaging apparatus.

[0004] BACKGROUND

[0005] Stroke is a time-critical medical condition that requires timely diagnosis and intervention to improve patient outcomes. Delays in diagnosis can significantly impact the effectiveness of treatment, potentially leading to severe complications, or even death. In such situations, the ability to make an early accurate diagnosis is crucial for informed decision making and timely intervention.

[0006] Traditionally, magnetic resonance imaging (MRI) has been used to generate accurate images of a subject's brain in order to detect and diagnose anomalies such as stroke. However, although MRI is the gold standard in terms of imaging accuracy, MRI equipment is extremely large and heavy, and requires specialised infrastructure such as substantial magnetic shielding, superconducting magnets and liquid helium refrigeration for their operation. Due to these factors and the high costs of MRI systems, they are generally only available in large hospitals, and are typically not readily available for use in an emergency.

[0007] To address these difficulties, microwave imaging systems have been developed as a simpler and lower cost means of imaging brains and other biological tissues, albeit at the cost of reduced image quality compared to MRI images.

[0008] Microwave imaging is typically performed by introducing an object to be imaged (e.g., a patient’s head) into an imaging region surrounded by an inwardly directed elliptical array of antennas. The antennas are sequentially energised to generate electromagnetic (microwave) signals that are scattered by, transmitted through, and reflected from the object, and are received by each of the antennas of the array (including the transmitting antenna) to collect meaningful information representing the spatial distribution of features within the object, an arrangement referred to in the art as a "multi-static" arrangement or configuration. The information collected thus includes measurements of the reflected signals for each individual antenna, and signals transmitted between each pair of antennas.

[0009] These measurements are performed over a frequency range by sequentially transmitting signals over a sweep of frequencies from each antenna, and receiving the resulting signals at the other antennas, in addition to measuring (by the transmitting antenna) the reflected signals. A commercially available device known in the art as a “vector network analyser” (or “VNA”) generates the measurement data from the signals received from the array by storing the ratio of the transmitted and received antenna voltages at each of the VNA’s ports as a function of frequency. The resulting data is typically referred to in the art as “scattering parameters” or “S parameters”.

[0010] The measured scattering parameters are in the form of at least a corresponding two- dimensional array of measurements of electromagnetic wave scattering by the object of interest, predominantly its internal features. Each measurement represents scattering of electromagnetic waves of a corresponding energy emitted by a corresponding transmitting antenna of the array of antennas disposed about the object, as measured by a corresponding receiving antenna of the array of antennas.

[0011] The S-parameters can be processed to generate image data representing an image showing the spatial arrangement of the object’s internal features, indicating, in the case of a human brain, the sizes and spatial locations of any stroke regions within the brain.

[0012] Traditionally, the processing of generating the image data involves a form of tomography, which is computationally intensive, and consequently can take considerable time before the image is available. In emergency situations, such delays can have dire consequences for a patient with bleeding in the brain, and consequently much recent research has focussed on developing alternative and more rapid ways of processing the S-parameters that do not involve tomography.

[0013] Despite such advances, a problem remains that microwave imaging systems, although vastly smaller and cheaper than MRI systems, are nevertheless still not generally suitable for portable use in, say, ambulances. The consequence is that a subject who may be suffering from stroke or brain injury must still be transported to a hospital or other clinical setting in order to have their brain imaged, the resulting delay potentially causing disability or even death.

[0014] It is desired to overcome or alleviate one or more difficulties of the prior art, or to at least provide a useful alternative.

[0015] SUMMARY

[0016] In accordance with some embodiments of the present invention, there is provided a microwave imaging apparatus, including: a plurality of microwave sensor assemblies for arranging around an object to be imaged; and a central control component digitally coupled to each of the microwave sensor assemblies; wherein each of the microwave sensor assemblies is operative to:

[0017] (i) selectively generate and transmit microwave signals at each of a plurality of different frequencies into the object;

[0018] (ii) receive microwave signals scattered and / or reflected by the object;

[0019] (iii) process the received microwave signals to generate corresponding digital signals representing the received microwave signals for each of the plurality of different frequencies; and

[0020] (iv) transmit the digital signals to the central control component; wherein the central control component is configured to:

[0021] (i) control operation of the microwave sensor assemblies;

[0022] (ii) receive the digital signals from each of the microwave sensor assemblies; and

[0023] (iii) process the digital signals received from the plurality of microwave sensor assemblies to generate corresponding image data representing an image representing a spatial arrangement of internal features of the object. In some embodiments, each of the microwave sensor assemblies includes a corresponding transceiver assembly and a corresponding antenna assembly communicatively coupled to the corresponding transceiver assembly.

[0024] In some embodiments, each antenna assembly includes:

[0025] (i) a microwave signal port coupled to the corresponding transceiver assembly;

[0026] (ii) a microwave antenna to transmit microwave signals received from the microwave signal port into the object, and to transmit microwave signals received from the object to the microwave signal port;

[0027] (iii) a plurality of calibration components;

[0028] (iv) a control port to receive control signals from the corresponding transceiver assembly; and

[0029] (v) a microwave signal switching component configured to selectively couple the microwave signal port to the microwave antenna or a selected one of the calibration components in dependence on the control signals.

[0030] In some embodiments, each of the microwave transceiver assemblies includes:

[0031] (i) digital signal ports coupled to the central control component;

[0032] (ii) a microwave signal port coupled to the corresponding antenna assembly;

[0033] (iii) signal synthesisers configured to selectively generate signals at each of a plurality of microwave frequencies;

[0034] (iv) switching components configured to selectively route microwave signals within the microwave transceiver assembly;

[0035] (v) a frequency mixer to shift the microwave signals received from the microwave signal port to generate corresponding intermediate frequency signals;

[0036] (vi) an analogue to digital converter (ADC) configured to digitise the intermediate frequency signals; and (v) a processing component configured to control the signal synthesisers the switching components and the frequency mixer, and to process the digitised intermediate frequency signals to generate the corresponding digital signals representing the received microwave signals for each of the plurality of different frequencies.

[0037] In some embodiments, the processing component is or includes an FPGA.

[0038] In some embodiments, the central control component is configured to simultaneously transmit a synchronisation pulse to the microwave transceiver assemblies, and each of the microwave transceiver assemblies is configured to synchronise its signal synthesisers to the received synchronisation pulse such that the microwave signals transmitted by the microwave sensor assemblies to the central control component are mutually synchronised.

[0039] In some embodiments, the central control component includes:

[0040] (i) digital data ports coupled to respective ones of the microwave sensor assemblies;

[0041] (ii) at least one field-programmable gate array (FPGA) and / or application-specific integrated circuit (ASIC) configured to receive digital data from the microwave sensor assemblies and to process the received digital data to generate corresponding data structures;

[0042] (iii) a processor coupled to the at least one FPGA and / or ASIC, and configured to process the data structures to generate the image data.

[0043] In some embodiments, the central control component further includes a communications interface to transmit the image data to an external display device to display the image of internal features of the object to a user.

[0044] In some embodiments, the communications interface is a wireless communications interface to wirelessly transmit the image data to the display device. In some embodiments, the central control component further includes a wired communication interface to provide electronic access to the central control component.

[0045] In some embodiments, the microwave transceiver assemblies are configured to receive digital clock and synchronisation signals from the central control component, and to use the received digital clock and synchronisation signals to synchronise the generation of the transmit microwave signals and the processing of the received microwave signals.

[0046] In some embodiments, the corresponding digital signals generated by each of the microwave sensor assemblies represents the received microwave signals for each of the plurality of different frequencies as a corresponding pair of complex scalar values per measurement.

[0047] In some embodiments, the internal features of the object are stroke regions within a human brain.

[0048] In accordance with some embodiments of the present invention, there is provided a process for synchronising the microwave sensor assemblies of any one of the above microwave imaging apparatuses, the process including the steps of: receiving digital clock and synchronisation signals from the central control component; and using the received digital clock and synchronisation signals to synchronise the generation of the transmit microwave signals and the processing of the received microwave signals.

[0049] In some embodiments, the received digital clock and synchronisation signals are used to synchronise the phases of the signal synthesisers.

[0050] Also described herein is a microwave imaging apparatus, including: a plurality of microwave sensor assemblies arranged around an imaging region for receiving an object to be imaged therein; and a central control component digitally coupled to each of the microwave sensor assemblies; wherein each of the microwave sensor assemblies is operative to:

[0051] (i) selectively generate and transmit microwave signals at each of a plurality of different frequencies into the object in the imaging region;

[0052] (ii) receive microwave signals scattered or reflected by the object in the imaging region;

[0053] (iii) process the received microwave signals to generate corresponding digital signals representing the received microwave signals for each of the plurality of different frequencies as a corresponding pair of complex scalar values per measurement; and

[0054] (iv) transmit the digital signals to the central control component; wherein the central control component is configured to:

[0055] (i) control operation of the microwave sensor assemblies;

[0056] (ii) receive the digital signals from each of the microwave sensor assemblies; and

[0057] (iii) process the digital signals received from the plurality of microwave sensor assemblies to generate corresponding image data representing an image of internal features of the object in the imaging region.

[0058] BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Some embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, in which:

[0060] Figure 1 is a high level block diagram of a microwave imaging apparatus in accordance with an embodiment of the present invention, transmitting images to a portable wireless display device such as a tablet computing device;

[0061] Figure 2 is a block diagram of the microwave imaging apparatus, showing a plurality of microwave sensor assemblies controlled by a central control component;

[0062] Figure 3 is a block diagram of a transceiver assembly of the microwave imaging apparatus; and Figure 4 is a schematic diagram illustrating the synchronisation of synthesised signals via a digital clock and synchronisation pulse distributed to the transceiver assemblies from the central control component.

[0063] DETAILED DESCRIPTION

[0064] In view of the difficulties described above, the inventors have developed a new form of microwave imaging apparatus, as described below. The microwave imaging apparatus has a new architecture that allows embodiments of the microwave imaging apparatus to be low- cost, low power, and portable.

[0065] As shown in Figure 1, a microwave imaging apparatus 100 includes a central control component 102 communicatively coupled to an array of microwave sensor assemblies 104 arranged around an imaging region to receive an object whose internal features are to be imaged. The microwave imaging apparatus 100 generates image data 106 representing the spatial arrangement of those internal features within the object, and transmits that data to an imaging device 108 such as a tablet computing device for display to a user of the apparatus 100. Embodiments of the present invention are described herein in the context of medical imaging, wherein the object to be imaged is a body part: specifically, a human head 106 so that anomalies such as stroke regions within the brain can be visualised. However, it should be understood that the invention has broader application, and may also be applied to image other body parts, and / or other types of object.

[0066] In the described embodiments, where the microwave imaging apparatus 100 is applied to image internal features of the human brain, the array of microwave sensor assemblies 104 is attached to or embedded in a support in the form of a helmet 106 to be worn on the head of a human subject, as shown in the lower part of Figure 1. However, this need not be the case in other embodiments, in particular where a different type of object is to be imaged.

[0067] Each of the microwave sensor assemblies 104 includes a corresponding transceiver assembly 202 coupled to a corresponding antenna assembly 204. A major component of any microwave imaging system is the hardware used to generate and capture the microwave signals. The microwave imaging apparatus described herein effectively replaces the vector network analyser of prior art microwave imaging systems with the transceiver assemblies 202, each of which is tightly integrated and co-located with the corresponding antenna assembly 204, as shown in Figure 1. The microwave sensor assemblies 104 are controlled and mutually synchronized by the central controller 102.

[0068] As shown in Figures 2 and 3, each of the antenna assemblies 204 includes not only a corresponding antenna, but also a corresponding set of calibration standards that have been characterized over a range of temperatures. This characterization data is used to calibrate measurements when the transceiver assemblies 202 are in operation. Having each pair of antenna and transceiver assemblies 202, 204 tightly coupled as an integrated ‘imaging assembly’ 104 reduces the need for microwave frequency capable interconnects, which reduces the cost and weight of the apparatus, and makes it less sensitive to vibration. A further benefit of distributing the microwave signal ports over the microwave sensor assemblies 104 is their improved isolation in the microwave transmit and receive chains.

[0069] Figure 3 includes a block diagram of a transceiver assembly 202. Each transceiver assembly 202 can be selectively and dynamically configured by the central control component 102 as either a transmitter or a receiver. When configured as a transmitter (as shown), the components along the upper part of Figure 3 constitute a "transmit chain" under control of a dedicated hardware component 302, which in the described embodiments is a field- programmable gate array (FPGA), but in other embodiments could alternatively be an application-specific integrated circuit (ASIC) or some other form of dedicated hardware controller or processor, or any practical combination of such forms.

[0070] The components of the transmit chain include (from left to right) a transmit signal synthesiser 304, a set of low pass filters 306, a transmit signal amplifier 308, and another low pass filter 310. To transmit a microwave signal into the object to be imaged, the transmit signal synthesiser 304 selectively generates a transmission signal at a selected one of a plurality of microwave frequencies. The synthesised signal is fed to the corresponding antenna assembly 204 via, in sequence, a selected one of the set of low pass filters 306, the transmit signal amplifier 308, and the further low pass filter 310. The resulting amplified and filtered signal is then fed to the antenna assembly 204 via two couplers 312, 314. The couplers 312, 314 allow the receive chain (described below) to selectively sense either a reference of the transmitted signal (via the left coupler 312, as shown), or the antenna signal (via the right coupler 314). This selection is determined by the state of a set of three switches 316, and enables the calculation of the reflection coefficient as the ratio of the sensed transmitted and reflected signals. The FPGA 302 controls the selection of the transmit signal frequency, the corresponding low pass filter 304, and routing of the microwave signals by the switches 316.

[0071] When configured as a receiver (not shown), the components of the transceiver assembly 202 shown along the lower part of Figure 3 constitute a "receive chain" under control of the FPGA 302. The receive chain has a single-stage superheterodyne receiver architecture.

[0072] The receive chain components include (in sequence, and roughly from right to left) routing switches 316, a receive amplifier 318, a frequency mixer 320 fed by a receiver signal synthesiser or local oscillator 322 via a low pass filter 324, another amplifier 326 and low pass filter 328 and finally an Analog-to-Digital Converter (ADC) 330.

[0073] To receive and process microwave signals received by the corresponding antenna from the imaging region, the FPGA 302 configures the microwave signal switches 316 to sense the signals from the antenna assembly 204 rather than from the transmit chain, as described above. Microwave signals scattered, transmitted and / or reflected by the object and received by the antenna assembly 204 are routed to the frequency mixer 320 via the receive amplifier 318. The FPGA 302 controls the receiver signal synthesiser or local oscillator 322, causing it to generate a local oscillator signal at a selected frequency, being the frequency of the corresponding transmitted microwave signal. The frequency mixer 322 receives this signal (via the low pass filter 324) and mixes it with the microwave signal from the antenna to generate a heterodyned signal in which the transmitting frequency has effectively been subtracted. The heterodyned signal is passed to the ADC 330 via the low pass filter 328, and the resulting digitised signal is provided to the FPGA 302. The FPGA 302 processes the digitised signal generated by the ADC 330 to generate the corresponding S-parameter as a single complex number for each individual measurement, and transmits this complex value to the central control component 102 in the form of its two components; z.e., as two scalar values. This significantly reduces the computational load on the transceiver assembly 202 relative to, for example, sending the entire ADC stream to the central control component 102, and also reduces the bandwidth required by the digital interconnects, simplifying the apparatus architecture.

[0074] The trace noise and dynamic range of the apparatus are limited by the choice of the synthesisers 304, 322 and the signal receiver chain components, respectively. As most signals in a passive measurement system are quite low in amplitude, using an ADC 330 with a high bit (at least Mbit) resolution is important for achieving a high dynamic range (above 90 dB), which translates to an ability to detect smaller anomalies in the object (of the order of mm for length, width and height spatial dimensions). In the described embodiments, the ADC 330 is a 16-bit ADC, resulting in a dynamic range of 100 dB. However, the ADC is the most expensive component of the transceiver assemblies 202, and thus has a significant effect on the overall cost of the apparatus.

[0075] Error correction and calibration are important features of any network analysis system. In the described embodiments, the microwave imaging apparatus collects additional information through temperature sensors (not shown) coupled to the control signal connections of the antenna assemblies 204, and also within the synthesisers 304, 322, the calibration standards 204, and a calibration thru connection 212 to facilitate error correction between and within the imaging assemblies 104. The calibration thru’s connection 212 ensures that there is a detectable signal across the full frequency band of operation. This is in contrast to the prior art antenna measurements, which would be inferior due to the measured band being slightly larger than the operating band of the antennas. By integrating these calibration standards within the apparatus, the plane of measurement (from a network analysis point of view) is moved directly to the feed of the antennas.

[0076] In some prior art microwave imaging systems, multiple receive chains have been employed to measure the input voltage waveform and the Device-Under-Test (DUT) (z.e., the object to be imaged) impacted voltage waveform simultaneously. In contrast, each transceiver assembly 202 of the microwave imaging apparatus 100 has only a single receive chain, and assumes that the DUT / object is Linear Time-Invariant (LTI) during the measurements, thereby reducing the size and cost of the transceiver assembly 202 at the expense of increased data collection time. To measure the input voltage waveform, the FPGA 302 configures the routing switches 316 to connect the receive amplifier 318 to the output of the low pass filter 310 and isolate it from the antenna assembly 204.

[0077] The state of each transceiver assembly 202 is dictated by the central control component 102, which communicates with each transceiver assembly 202 via dedicated lightweight and inexpensive digital cabling. The central control component 102 orchestrates the overall process of measuring the signal from every port to every other port, and repeating this for each frequency in the sweep. For example, in one embodiment, the microwave imaging apparatus is configured with 28-ports (and thus 28 microwave sensor assemblies 104) and to scan over 51 frequency values to provide a total of 28x28x51 (~ 40,000) measurements. Because all the receivers operate simultaneously, the imaging apparatus can be configured to sequence the transmissions by either having each port transmit over all frequencies first before switching to the next port, or by transmitting each frequency over all ports first before switching to the next frequency. In the described embodiments, the central control component 102 is configured to orchestrate the measurements by successively transmitting over all ports for each frequency before stepping to the next frequency in the sweep, referred to herein as a 'port-first' sweep process. This configuration is advantageous because the time required for Tx / Rx switching is substantially less than the time required to change the frequency of each synthesiser 304, 322.

[0078] The central control component 102 synchronises the transmit signal and local oscillator synthesizers 304, 322 of all transceiver assemblies 202 immediately prior to each measurement by transmitting both a low-frequency input clock and a synchronisation pulse (the latter not shown) over digital cabling. The central control component 102 distributes the synchronisation pulse to all transceiver assemblies 202 at the commencement of every new frequency measurement, such that all of the synthesizers 304, 322 are repeatedly synchronised in phase relative to each other. This synchronisation pulse and clock signal distribution ensures that the digital data received by the central control component 102 from the transceivers 202 is phase aligned, and enables the simultaneous collection of S-parameter data from all ports.

[0079] Figure 4 is a schematic diagram illustrating the synchronisation process. For simplicity of illustration, only two ports (z.e., transceiver assemblies 202) are shown. The upper part of the Figure illustrates the distribution of the digital clock 402 and synchronisation 404 signals to the transmit signal and local oscillator synthesizers 304, 322 of two transceiver assemblies 202, and the lower part of the Figure illustrates the resulting waveform synchronisation. In contrast to prior art systems that achieve synchronisation by distributing high frequency (~ GHz) local oscillator signals, the synchronisation of the transmit signal and local oscillator synthesizers 304, 322 of all transceiver assemblies 202 by distribution of a relatively low frequency (some tens of MHz) digital clock 402 and associated digital phase synchronisation 404 pulses reduces the size, weight, complexity and cost of the microwave imaging apparatus by reducing the amount of high frequency (GHz) cabling required, and also makes it less sensitive to cable movement and vibration because such cable movements will be small (-millimetres), relative to the wavelength of the digital synchronisation signal frequency (which is tens of meters). Although optical signals could be used to address the vibration and movement concerns, doing so would substantially increase the complexity and cost of the apparatus.

[0080] As shown in Figure 2, the central control component 102 includes a central microcontroller or processor 206 to control the overall operation of the imaging apparatus, and a hardware component 208 dedicated to simultaneously receiving digital signals representing the complex values from all of the transceiver assemblies 202, and aggregating these into a single data structure representing a single sweep, effectively a three-dimensional array of S- parameters with dimensions (nTx x nRx x nAntennas). In the described embodiments, the hardware component (also referred to herein as the "data aggregation" component) 208 is a field-programmable gate array (FPGA), but in other embodiments could alternatively be an application-specific integrated circuit (ASIC) or some other form of dedicated hardware controller or processor, or any practical combination of such forms. The central microcontroller or processor 206 processes the aggregated data from the data aggregation component) 208 to generate corresponding image data representing an image of the spatial arrangement of internal features of the object. In the described embodiments, the imaging data is transmitted to an external display device for display to a user, although in other embodiments the imaging apparatus can include an integrated display screen. In the described embodiments, the central control component 102 includes a wireless communications component 210 so that the apparatus can wirelessly transmit the image data to a wireless display device such as a tablet computing device. Thus, in the described context of medical imaging, images of a patient's brain can be displayed to a paramedic in the back of an ambulance.

[0081] In general, a microwave imaging apparatus in accordance with the present invention can include any practical number of imaging assemblies 104. In one embodiment, the microwave imaging apparatus has 28 microwave sensor assemblies 104, and can sweep over all 28 ports and 101 frequencies from 0.5 to 1.5 GHz in under 0.5 seconds, while maintaining 100 dB of dynamic range. The microwave imaging apparatus has a low power consumption, and can be battery powered. In some embodiments, the microwave imaging apparatus is battery powered, weighs less than 12 kg, and is small enough to be carried by a paramedic in a backpack, allowing it to be carried to patients in emergency situations.

[0082] Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

CLAIMS:

1. A microwave imaging apparatus, including: a plurality of microwave sensor assemblies for arranging around an object to be imaged; and a central control component digitally coupled to each of the microwave sensor assemblies; wherein each of the microwave sensor assemblies is operative to:(i) selectively generate and transmit microwave signals at each of a plurality of different frequencies into the object;(ii) receive microwave signals scattered and / or reflected by the object;(iii) process the received microwave signals to generate corresponding digital signals representing the received microwave signals for each of the plurality of different frequencies; and(iv) transmit the digital signals to the central control component; wherein the central control component is configured to:(iv) control operation of the microwave sensor assemblies;(v) receive the digital signals from each of the microwave sensor assemblies; and(vi) process the digital signals received from the plurality of microwave sensor assemblies to generate corresponding image data representing an image representing a spatial arrangement of internal features of the object.

2. The microwave imaging apparatus of claim 1, wherein each of the microwave sensor assemblies includes a corresponding transceiver assembly and a corresponding antenna assembly communicatively coupled to the corresponding transceiver assembly.

3. The microwave imaging apparatus of claim 2, wherein each antenna assembly includes:(i) a microwave signal port coupled to the corresponding transceiver assembly;(ii) a microwave antenna to transmit microwave signals received from the microwave signal port into the object, and to transmit microwave signals received from the object to the microwave signal port;(iii) a plurality of calibration components;(iv) a control port to receive control signals from the corresponding transceiver assembly; and(v) a microwave signal switching component configured to selectively couple the microwave signal port to the microwave antenna or a selected one of the calibration components in dependence on the control signals.

4. The microwave imaging apparatus of claim 2 or 3, wherein each of the microwave transceiver assemblies includes:(i) digital signal ports coupled to the central control component;(ii) a microwave signal port coupled to the corresponding antenna assembly;(iii) signal synthesisers configured to selectively generate signals at each of a plurality of microwave frequencies;(iv) switching components configured to selectively route microwave signals within the microwave transceiver assembly;(v) a frequency mixer to shift the microwave signals received from the microwave signal port to generate corresponding intermediate frequency signals;(vi) an analogue to digital converter (ADC) configured to digitise the intermediate frequency signals; and(v) a processing component configured to control the signal synthesisers the switching components and the frequency mixer, and to process the digitised intermediate frequency signals to generate thecorresponding digital signals representing the received microwave signals for each of the plurality of different frequencies.

5. The microwave imaging apparatus of claim 4, wherein the processing component is an FPGA.

6. The microwave imaging apparatus of claim 4 or 5, wherein the central control component is configured to simultaneously transmit a synchronisation pulse to the microwave transceiver assemblies, and each of the microwave transceiver assemblies is configured to synchronise its signal synthesisers to the received synchronisation pulse such that the microwave signals transmitted by the microwave sensor assemblies to the central control component are mutually synchronised.

7. The microwave imaging apparatus of any one of claims 1 to 6, wherein the central control component includes:(i) digital data ports coupled to respective ones of the microwave sensor assemblies;(ii) at least one field-programmable gate array (FPGA) and / or application-specific integrated circuit (ASIC) configured to receive digital data from the microwave sensor assemblies and to process the received digital data to generate corresponding data structures;(iii) a processor coupled to the at least one FPGA and / or ASIC, and configured to process the data structures to generate the image data.

8. The microwave imaging apparatus of claim 7, wherein the central control component further includes a communications interface to transmit the image data to an external display device to display the image of internal features of the object to a user.

9. The microwave imaging apparatus of claim 8, wherein the communications interface is a wireless communications interface to wirelessly transmit the image data to the display device.

10. The microwave imaging apparatus of any one of claims 7 to 9, wherein the central control component further includes a wired communication interface to provide electronic access to the central control component.

11. The microwave imaging apparatus of any one of claims 1 to 10, wherein the microwave transceiver assemblies are configured to receive digital clock and synchronisation signals from the central control component, and to use the received digital clock and synchronisation signals to synchronise the generation of the transmit microwave signals and the processing of the received microwave signals.

12. The microwave imaging apparatus of any one of claims 1 to 11, wherein the corresponding digital signals generated by each of the microwave sensor assemblies represents the received microwave signals for each of the plurality of different frequencies as a corresponding pair of complex scalar values per measurement.

13. The microwave imaging apparatus of any one of claims 1 to 12, wherein the internal features of the object are stroke regions within a human brain.

14. A process for synchronising the microwave sensor assemblies of the microwave imaging apparatus of any one of claims 1 to 13, the process including the steps of: receiving digital clock and synchronisation signals from the central control component; and using the received digital clock and synchronisation signals to synchronise the generation of the transmit microwave signals and the processing of the received microwave signals.

15. The process of claim 14 when dependent upon claim 4, wherein the received digital clock and synchronisation signals are used to synchronise the phases of the signal synthesisers.

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