Investigations on Microwave Imaging and Microwave Hyperthermia for Detection and Treatment of Skin Cancer

Abstract

Cancer is one of the most dangerous disease identified globally and a majority of the cancer affected population suffers from skin cancer. In order to detect and cure skin cancer, Microwave and Microwave Hyperthermia are the proposed non –invasive and non –ionizing techniques in the presented research work. Microwave imaging (MWI) utilizing ultra wideband (UWB) technology has garnered significant attention in recent years due to the inherent advantages of UWB technology like large bandwidth, low power consumption, high speed, and short-distance data transmission. For the proposed doctoral research, ultra wide band (UWB) microstrip patch antennas (MPAs) are designed, simulated, fabricated and tested for validation and use of these UWB antennas as sensors to record ‘S’ parameter data from the human forearm phantom. The recorded data is then used to plot a dielectric profile of the scanned forearm phantom using the monostatic radar-based microwave imaging technique. The reconstructed 2D images of the scanned skin area show a good correlation between the actual tumor placement and its identified position (typical Signal to Clutter Ratio and Signal to Mean Ratio of 12 dB and 18 dB respectively). Hyperthermia (HT) is a non-invasive technique where the cancer-affected body part is exposed to focussed electromagnetic (EM) radiations using an applicator, while ensuring that power levels in surrounding healthy tissues are kept at minimal values. The HT applicator is preferred to operate at the ISM band because biological tissues, particularly water molecules, exhibit significant absorption at these frequencies, enhancing the heating efficiency of tissues. The interaction between electromagnetic waves and water molecules results in dielectric heating, which is particularly advantageous for hyperthermia treatments targeting superficial skin cancers. At ISM frequencies, electromagnetic waves can penetrate biological tissues to an optimal depth while generating the thermal effects for effective hyperthermia treatment. Thus, the proposed doctoral research is focused design of ISM band Archimedean spiral antenna integrated with two different types of AMC as an HT applicator for treating skin cancer. The AMC based reflector helps in improvement of the antenna gain and penetration depth up to optimized values for the desired purpose. Therefore, the presented doctoral thesis work focuses on designing miniaturized antennas with high performance for MWI and HT applications. In the imaging context, stacked geometries and spiral-shaped and hybrid fractal design (combination of modified Pythagorean tree and Koch Snowflake) offer solutions by enabling miniaturization and achieving UWB frequency responses. Similarly, for microwave hyperthermia, the Archimedean spiral antenna provides superior results in terms of uniform heat distribution. The performance of the Archimedean spiral is further enhanced by incorporating a reflector at the back. FSS and AMC-based reflectors are used to improve the gain, penetration depth and bandwidth of the proposed antennas. Objective 1 presents the design, fabrication, and testing of three different microstrip patch antennas with UWB performance to be used as a sensor for MWI applications. The first design introduces a stacked Microstrip patch antenna (SAMPA) for MWI. This UWB SAMPA has a three-layer stacked aperture-coupled structure with a defective ground plane measuring 36 × 30 × 4.85 mm³. The simulated bandwidth achieved is 6.23 GHz (6.14 to 12.37 GHz), while the V measured bandwidth is 5.28 GHz (5.72 to 11 GHz). To validate its performance as a sensor for MWI, it is simulated with a designed four-layered phantom of a human forearm and reflection parameters data is collected (with and without tumor inside the phantom). The significant contrast between the reflection parameters for the case of with and without a tumor inside it validates the presence of a tumor inside the designed phantom. The antenna collected S-parameters from the phantom, are processed using the CF-DMAS beamforming algorithm in MATLAB to produce a 2D image of the scanned area. For experimental validation, an in vitro skin sample is prepared using gelatine (for skin), white soft paraffin (for fat), sodium chloride, gelatine, distilled water, and sugar (for muscles), flour, water, and vegetable oil (for bone), and a 40% glycerol solution (for cancerous cells). The fabricated SAMPA prototype is placed 10 mm from the phantom to record S-parameters at various time intervals. This data is processed using the CF-DMAS algorithm, generating a 2D image identifying the cancer-affected area's location and size. Additionally, the proposed UWB antenna is confirmed to be safe for human exposure, with a simulated SAR value below 1.6 W/kg for 1 g of human tissue on a forearm phantom, ensuring it meets safety standards. The second antenna design is an Archimedean Spiral microstrip-patch antenna (ASMA) for skin cancer detection using monostatic radar-based microwave imaging (MSRMI). The proposed work the presents the design, development, and testing of this low-profile UWB ASMA, which consists of a spiral resonator with a defected ground structure (DGS) and a slotted microstrip feed line with dimensions of 38×38×.87 mm3 . The proposed antenna shows an impedance bandwidth for the frequency range of 2.2 to 13.9 GHz (simulated) with an impedance bandwidth of 11.7 GHz and 2.3-13.34 GHz (measured) with an impedance BW of 11.04 GHz. In-silico analysis of the proposed ASMA for MI is carried out with the Gustav model using Computer Simulation Technology (CST) Microwave Studio. The validation and testing of the proposed UWB antenna is done using the same procedure of phantom fabrication and testing of S parameter data and reconstruction of the 2D image of scanned skin area as done for design 1. The reconstructed image has Signal to Clutter Ratio and Signal to Mean Ratio of 16 dB and 15.5 dB respectively. The third design introduces a microstrip patch antenna based on hybrid fractal designs, combining modified Pythagorean tree and Koch Snowflake structures into a hybrid fractal shape, serving as a sensor for the MWI technique. The proposed compact antenna has dimensions of 24 × 20 × 0.84 mm3 and operates over a frequency range of 5.7–16.94 GHz, with a bandwidth of 11.24 GHz. Experimental measurements of the fabricated HFMPA prototype align well with simulated results, confirming a frequency range of 5.71–16.36 GHz and a bandwidth of 10.65 GHz. This study includes a simulation setup where forearm phantoms, replicating the electrical properties of human tissues, are positioned parallel to the antenna. The antenna transmits UWB pulses toward the phantoms and captures the reflected signals as reflection parameters (S11) at various locations. The differences in the S11 measurements between phantoms with tumors and those without tumor, help in identifying cancerous cells in the forearm tissues. The validation and testing of the proposed UWB antenna is done using the same procedure of phantom fabrication and testing of S parameter data and reconstruction of the 2D image of scanned skin area as done for design 1. The reconstructed VI image has Signal to Clutter Ratio and Signal to Mean Ratio of 13.9 dB and 16.5 dB respectively. Objective 2 focuses on using three designed antennas of objective one as a sensor and utilizing different beam forming algorithms such as Delay and Sum (DAS) and Coherent Factor-Delay Multiply and Sum (CF-DMAS) to reconstruct the image of the scanned area of the forearm. Back-scattered signals are collected at different positions over the bio-phantom and pre processed, and different Synthetic focal points are created. Thus, using MATLAB, the above points are used to regenerate the dielectric profile of the scanned human forearm phantom with a highlighted tumor. For the first designed antenna of objective one, the CF-DMAS algorithm was used to reconstruct the image of the cancerous area with an error of 7.75%. For the second designed antenna of objective one, the DAS and CF-DMAS algorithm are used to reconstruct the image of the cancerous area with 5% and 1.25 % size error of the tumour. Similarly, for the third antenna design of objective one, the CF-DMAS algorithm is used to reconstruct the image of the cancerous area with a size error of 2.5%with respect to the actual one in the phantom. Objective 3 and objective 4 focus on designing, fabricating and testing two different miniaturized Archimedean spiral microstrip patch antennas backed with Epsilon negative (ENG) and Double Negative (DNG) metamaterial-based FSS and AMC sheets (reflectors) as Microwave Hyperthermia (MWHT) applicators for treatment of skin cancer The first design introduces an Archimedean Spiral Micro-Strip Patch Antenna (ASMPA) with dimensions of 40×40×3.245 mm³, backed by an epsilon-negative (ENG) metamaterial reflector (48×48×1.57 mm³) positioned 34 mm away from it, collectively known as the MWHT applicator. The MWHT applicator operates within a 2.4-2.53 GHz frequency range and provides a peak gain of 5.9 dB at 2.4 GHz. The MWHT applicator’s performance is also studied using a realistic human forearm model based on Penne’s Bio-Heat equations in CST MPHYSICS STUDIO, achieving a temperature rise of 41-45°C in the targeted areas. It offers a penetration depth of 32 mm and an effective field surface (EFS) of 32×32 mm² for treating deep-seated tumors, with a safe SAR value of 7.5 W/kg. The second design introduces an Archimedean Spiral Microstrip Patch Antenna (AMSPA) with dimensions of 38×38×1.64 mm³, backed by a meshed-shaped AMC reflector (48×48×3.27 mm³) placed at an optimized distance of 12 mm from the AMSPA. Together, they are known as the MWHT applicator. The applicator provides an impedance bandwidth of 470 MHz (2.21 to 2.68 GHz) at 2.5 GHz and a high gain of 6.8 dB. Thermal analysis of the bio phantom, using CST Multiphysics, based on Penne’s Bio-Heat equation, shows that exposure to EM waves radiated by the MWHT applicator, powered by a 2.5 W input, results in a temperature rise of 45 °C over superficial tumors (with an effective treatment area of 32×32 mm²) and 43 °C over deep-seated tumors (with an effective treatment area of 28×28 mm²) after 30 minutes. It offers a penetration depth of 30 mm and an effective field surface (EFS) of 36×36 mm² for deep seated tumor treatment, with a safe SAR value of 8 W/kg. Objective 5 presents the testing of the above antennas (objectives 1, 3, and 4) for Microwave Imaging and Hyperthermia of skin cancer. For experimental validation of antennas (objective 1), an in vitro skin sample is prepared using gelatine (for skin), white soft paraffin (for fat), sodium chloride, gelatine, distilled water, and sugar (for muscles), flour, water, and vegetable VII oil (for bone), and a 40% glycerol solution (for cancerous cells). The fabricated SAMPA prototype is placed at a distance of 10 mm from the phantom to record S-parameters at various intervals. This data was processed using the DAS and CF-DMAS algorithms to generate a 2D images that identify the cancer-affected area's location and size. Additionally, the design antennas were confirmed to be safe for human exposure, with a simulated SAR value below 1.6 W/kg for 1 g of human tissue on a forearm phantom, ensuring it meets safety standards.