Metal reflector-enhanced thermoacoustic imaging as a guidance for puncture biopsy

Puncture biopsy is an important clinical technique to obtain diseased tissue for pathological diagnosis,where imaging guidance is critical.In this paper,we describe a metal reflector-enhanced microwave-induced thermoacoustic imaging(TAI)approach capable of guiding puncture biopsy for detection of breast cancer and joint diseases.Numerical experimentations simulating puncture guidance in breast cancer and knee gout models werefirst conducted using(CST STUDIO SUITE)(CST)software,and then ex-vivo experiments were performed followed by qualitative observations and semi-quantitative analysis.The results of both the simulations and ex-vivo experiments showed that our reflector-enhanced TAI could image the puncture needle in high resolution with a large depth of>12 cm.

Prospects of microwave-induced thermoacoustic imaging

Microwave-induced thermoacoustic imaging(MTAI)has advantages including the large imaging depth,high imaging resolution,high imaging contrast,and fast imaging speed.The thermoacoustic(TA)group of South China Normal University has dedicated to developing TA imaging for more than a decade and has made many breakthroughs.This review introduces these breakthroughs from two aspects including the improvement in techniques and the exploration of applications.On the technological level,there are ultrashort microwave pulse(USMP)-inducedTA imaging that can improve the imaging resolution,nonlinear thermoacoustic imaging(NTAI)that can improve the imaging contrast,polarized microwave-inducedthermoacoustic imaging(P-MTAI)that can obtain cellular-level alignment information,and more convenient and accurate handheld and multimodal probes.On the application side,the optimization and expansion have been carried out,mainly concentrating on breast and myocardial imaging.Finally,several current research directions are introduced,including the application of P-MTAI on joint imaging and research on whole-body imaging of small animals.

Microwave-induced thermoacoustic imaging with functional nanoparticles

As an emerging hybrid imaging modality,microwave-induced thermoacoustic imaging(MTAI),using microwaves as the excitation source and ultrasonic signals as the information carrier for combining the characteristics of high contrast of electromagnetic imaging and high resolution of ultrasound imaging,has shown broad prospects in biomedical and clinical applications.The imaging contrast depends on the microwave-absorption coe±cient of the endogenous imaged tissue and the injected MTAI contrast agents.With systemically introduced functional nanoparticles,MTAI contrast and sensitivity can be further improved,and enables visualization of biological processes in vivo.In recent years,functional nanoparticles for MTAI have been developed to improve the performance and application range of MTAI in biomedical applications.This paper reviews the recent progress of functional nanoparticles for MTAI and their biomedical applications.The challenges and future directions of microwave thermoacoustic imaging with functional nanoparticles in theeld of translational medicine are discussed.

Thermoacoustic imaging:From single-element scanning to portable and array-based imaging

The microwave-induced thermoacoustic imaging(TAI)technology has both the advantages of high contrast of microwave imaging and high resolution of ultrasound imaging(UI),so it has carried out exploratory application research in various areas,such as the early detection of breast tumors and cerebrovascular diseases.However,the microwave generator used in the traditional TAI technology is huge and expensive,and the temporal resolution is also too low due to the single-element scanning mechanism.Thus,it is difficult to meet the needs of clinical applications.In this paper,the iterative process and the analysis of related application scenarios from single-element scanning to portable and array-based TAI,such as the miniaturized microwave generator,handheld antenna,multi-channel data acquisition,and UI/TAIdual-modality imaging,are reviewed,and the future trends of this technology are discussed.This review helps researchers in the field of TAI learn the technological development process and future trends.It also deepens clinicians’understanding of TAI so as to put forward more application requirements.

Microwave-induced thermoacoustic imaging of joints

Due to the complexity of joint structures and the diversity of disorders in the joints,the diagnosis of joint diseases is challenging.Current clinical diagnostic techniques for evaluating joint diseases,such as arthritis,have strengths and weaknesses.New imaging techniques need to be developed for the diagnosis or auxiliary diagnosis of arthritis.As an emerging nonintrusive low-cost imaging method,microwave-induced thermoacoustic imaging(TAI)can present tissue morphology while providing the tissue microwave energy absorption density distribution related to dielectric properties.TAI is currently in development to potentially visualize joint anatomic structures and to detect arthritis.Here,we offer a mini review to summarize the status of research on TAI of joints and present an outlook to the future development of TAI in the detection of joint diseases.

Biomedical microwave-induced thermoacoustic imaging

Microwave induced thermoacoustic imaging(MTAI)has emerged as a potential biomedical imaging modality with over 20-year growth.MTAI typically employs pulsed microwave as the pumping source,and detects the microwave-induced ultrasound wave via acoustic transducers.Therefore,it features high acoustic resolution,rich elect romagnetic contrast,and large imaging depth.Benefiting from these unique advantages,MTAI has been extensively applied to various fields including pathology,biology,material and medicine.Till now,MTAI has been deployed for a wide range of biomedical applications,including cancer diagnosis,joint evaluation,brain in-vestigation and endoscopy.This paper provides a comprehensive review on(1)essential physics(endogenous/exogenous contrast mechanisms,penetration depth and resolution),(2)hardware configurations and software implementations(excit ation source,antenna,ultrasound detector and image recovery algorithm),(3)animal studies and clinical applications,and(4)future directions.

A review of microwave-induced thermoacoustic imaging:Excitation source,data acquisition system and biomedical applications

Microwave-induced thermoacoustic imaging(TAI)is a noninvasive modality based on the differences in microwave absorption of various biological tissues.TAI has been extensively researched in recent years,and several studies have revealed that TAI possesses advantages such as high resolution,high contrast,high imaging depth and fast imaging speed.In this paper,we reviewed the development of the TAI technique,its excitation source,data acquisition system and biomedical applications.It is believed that TAI has great potential applications in biomedical research and clinical study.

Investigation of artifacts by mapping SAR in thermoacoustic imaging

Microwave-induced thermoacoustic imaging(MI-TAI)remains one of the focus of attention among biomedical imaging modalities over the last decade.However,the transmission and dis-tribution of microwave inside bio-tissues are complicated,thus result in severe artifacts.In this study,to reveal the underlying mechanisms of artifacts,we deeply investigate the distribution of specific absorption rate(SAR)inside tissue-mimicking phantoms with varied morphological features using both mathematical simulations and corresponding experiments.Our simulated results,which are confirmed by the associated experimental results,show that the SAR distri-bution highly depends on the geometries of the imaging targets and the polarizing features of the microwave.In addition,we propose the potential mechanisms including Mie-scattering,Fabry-Perot-feature,small curvature effect to interpret the diffraction effect in different scenarios,which may provide basic guidance to predict and distinguish the artifacts for TAI in both fundamental and clinical studies.

Study on response of metal wire in thermoacoustic imaging

Thermoacoustic imaging(TAI)is an emerging high-resolution and high-contrast imaging technology.In recent years,metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems.However,there is still a lack of analysis of the response characteristics and principles of metal wires in TAI.Through theoretical and simulation analyses,this paper proposes that the response of metal(copper)wires during TAI is equivalent to the response of antennas.More critically,the response of the copper wire is equivalent to the response of a half-wave dipole antenna.When its length is close to half the wavelength of the incident electromagnetic wave,it obtains the best response.In simulation,when the microwave excitation frequencies are 1.3 GHz,3.0 GHz,and 5.3 GHz,and the lengths of copper wires are separately set to 11 cm,5 cm,and 2.5 cm,the maximum SAR distribution and energy coupling effciency are obtained.This result is connected with the best response of half-wave dipole antennas with lengths of 11 cm,4.77 cm,and 2.7 cm under the theoretical design,respectively.Regarding the further application,TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging.Thus,this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies.

Microwave-induced thermoacoustic elastic imaging:A simulation study

Microwave-induced thermoacoustic imaging(MTI)has the advantages of high resolution,high contrast,non-ionization,and non-invasive.Recently,MTI was used in the¯eld of breast cancer screening.In this paper,based on the¯nite element method(FEM)and COMSOL Multiphysics software,a three-dimensional breast cancer model suitable for exploring the MTI process is proposed to investigate the in°uence of Young's modulus(YM)of breast cancer tissue on MTI.It is found that the process of electromagnetic heating and initial pressure generation of the entire breast tissue is earlier in time than the thermal expansion process.Besides,compared with normal breast tissue,tumor tissue has a greater temperature rise,displacement,and pressure rise.In particular,YM of the tumor is related to the speed of thermal expansion.In particular,the larger the YM of the tumor is,the higher the heating and contraction frequency is,and the greater the maximum pressure is.Di®erent Young's moduli correspond to di®erent thermoacoustic signal spectra.In MTI,this study can be used to judge di®erent degrees of breast cancer based on elastic imaging.In addition,this study is helpful in exploring the possibility of microwave-induced thermoacoustic elastic imaging(MTAE).

Defect-rich titanium nitride nanoparticle with high microwaveacoustic conversion efficiency for thermoacoustic imaging-guided deep tumor therapy

Pulse microwave excite thermoacoustic(TA)shockwave to destroy tumor cells in situ.This has promising applications for precise tumor therapy in deep tissue.Nanoparticle(NP)with high microwave-acoustic conversion is the key to enhance the efficiency of therapy.In this study,we firstly developed defect-rich titanium nitride nanoparticles(TiN NPs)for pulse microwave excited thermoacoustic(MTA)therapy.Due to a large number of local structural defects and charge carriers,TiN NPs exhibit excellent electromagnetic absorption through the dual mechanisms of dielectric loss and resistive loss.With pulsed microwave irradiation,it efficiently converts the microwave energy into shockwave via thermocavitation effect,achieving localized mechanical damage of mitochondria in the tumor cell and yielding a precise antitumor effect.In addition to the therapeutic function,the NP-mediated TA process also generates images that provide valuable information,including tumor size,shape,and location for treatment planning and monitoring.The experimental results showed that the TiN NPs could be efficiently accumulated in the tumor via intravenous infusion.With the deep tissue penetration characteristics of microwave,the proposed TiN-mediated MTA therapy effectively and precisely cures tumors in deep tissue without any detectable side effects.The results indicated that defect-rich TiN NPs are promising candidates for tumor therapy.

Thermoacoustic tomography of in vivo rat brain

We present for the¯rst time in vivo imaging of rat brain using microwave-induced thermoacoustic tomography(TAT).The in vivo imaging of rat brain was realized through an unconventional delivery of microwave energy from the front of rat brain(while the transducer was scanned along coronal plane of the animal brain),which maximized the microwave penetration into the brain.In addition,we found that the imaging contrast was highly dependent on the direction of the electric¯eld polarization(EFP)and that more tissue structures/compositions could be revealed when both X-and Y-EFPs were used for TAT.The in vivo TAT images of rat brain obtained were compared with the 3.0 T MRI images and histological photographs,and numerous important brain anatomical structures were identi¯ed.An example of our TAT approach for imaging a foreign object embedded in a rat brain was also demonstrated.This study suggests that TAT has a great potential to be used in neuroscience studies and in noninvasive imaging of brain disorders.

Thermoacoustic assessment of hematocrit changes in human forearms

Abnormal hematocrit(Hct)is associated with an increased risk of pre-hypertension and all-cause death in general population,and people with a high Hct value are susceptible to arterial cardiovascular disease and venous thromboembolism.In this study,we report for the first time on the ability of thermoacoustic imaging(TAI)for in vivo evaluating Hct changes in human forearms.In vitro blood samples with different Hct values from healthy volunteers(n=3)were prepared after centrifugation.TAI was performed using these samples in comparison with the direct measurements of conductivity.In vivo TAI was conducted in the forearm of healthy volunteers(n=7)where Hct changes were produced through a vascular occlusion stimulation over a period of time.The results of in vitro blood samples obtained from the 3 healthy subjects show that the thermoacoustic(TA)signals changes due to the variation of blood conductivity are closely related to the changes in Hct.In addition,the in vivo TA signals obtained from the 7 healthy subjects consistently increase in the artery/muscle and decrease in the vein during venous or arterial occlusion because of the changed Hct value in their forearms.These findings suggest that TAI has the potential to become a new tool for monitoring Hct changes for a variety of pre-clinical and clinical applications.