Blood vessel imaging using radiofrequency-induced second harmonic acoustic response

A one-step method for quantitative microwave-induced thermoacoustic tomography

BACKGROUND

Electrical conductivity directly correlates with tissue functional information such as blood and water contents, and quantitative extraction of tissue conductivity is of significant importance for disease detection and diagnosis using microwave-induced thermoacoustic tomography (TAT).

OBJECTIVE

The existing quantitative TAT (qTAT) approaches capable of extracting tissue conductivity require two steps for the recovery of conductivity. Such two steps approaches depend on an accurate knowledge of the microwave energy loss distribution in tissue and offer a slow computational convergence rate. The purpose of this study is to develop a new algorithm to reconstruct tissue conductivity with higher reconstruction accuracy and greater computational efficiency.

METHODS

We propose an improved qTAT method for direct recovery of tissue conductivity from thermoacoustic data measured along the boundary with only one step without the dependence of microwave energy loss information. The feasibility of our one-step qTAT method is validated in both simulated and tissue-mimicking phantom experiments with single-target and multi-target configurations with different contrast levels.

RESULTS

Compared with the previous two-step methods, our one-step qTAT method improves the accuracy of conductivity recovery with approximately one-fold reduction in the mean absolute error (MAE) and root mean square error (RMSE) with p-values greater than 0.05. In addition, the convergence rate is improved by more than two folds for the one-step method.

CONCLUSIONS

The study demonstrates that new method can quantitatively reconstruct conductivity of tissue more accurately and efficiently over the existing qTAT methods, leading to potentially enhanced accuracy for disease detection and diagnosis.

First assessment of thermoacoustic tomography for in vivo detection of rheumatoid arthritis in the finger joints detection of rheumatoid arthritis in the finger joints

BACKGROUND

The diagnosis of rheumatoid arthritis (RA) is complicated because of the complexity of symptoms and joint structures. Current clinical imaging techniques for the diagnosis of RA have strengths and weaknesses. Emerging imaging techniques need to be developed for the diagnosis or auxiliary diagnosis of RA.

PURPOSE

This study aimed to demonstrate the potential of thermoacoustic tomography (TAT) for in vivo detection of RA in the finger joints.

METHODS

Finger joints were imaged by a TAT system using three different microwave illumination methods including pyramidal horn antenna, and parallel in-phase and anti-phase microwave illuminations. Both diseased and healthy joints were imaged and compared when the three microwave illumination methods were used. Magnetic resonance imaging (MRI) of all the joints was performed to validate the TAT findings. In addition, two diseased joints were imaged at two time points by the pyramidal horn antenna-based TAT to track/monitor the progression of RA during a time period of 16 months. Three-dimensional (3-D) TAT images of the joints were also obtained.

RESULTS

The TAT images of the diseased joints displayed abnormalities in bone and soft tissues compared to the healthy ones. The TAT images by pyramidal horn antenna and in-phase microwave illumination showed high similarity in image appearance, while the anti-phase-based TAT images provided different information about the disease. We found that the TAT findings matched well with the MRI images. The 3-D TAT images effectively displayed the stereoscopic effect of joint lesions. Finally, it was evident that TAT could detect the development of the lesions in 16 months.

CONCLUSION

TAT can noninvasively visualize bone lesions and soft tissue abnormalities in the joints with RA. This first in vivo assessment of TAT provides a foundation for its clinical application to the diagnosis and monitoring of RA in the finger joints.

Noninvasive visualization of electrical conductivity in tissues at the micrometer scale

Despite its importance in regulating cellular or tissue function, electrical conductivity can only be visualized in tissue indirectly as voltage potentials using fluorescent techniques, or directly with radio waves. These either requires invasive procedures like genetic modification or suffers from limited resolution. Here, we introduce radio-frequency thermoacoustic mesoscopy (RThAM) for the noninvasive imaging of conductivity by exploiting the direct absorption of near-field ultrashort radio-frequency pulses to stimulate the emission of broadband ultrasound waves. Detection of ultrasound rather than radio waves enables micrometer-scale resolutions, over several millimeters of tissue depth. We confirm an imaging resolution of <30 μm in phantoms and demonstrate microscopic imaging of conductivity correlating to physical structures in 1- and 512-cell zebrafish embryos, as well as larvae. These results support RThAM as a promising method for high-resolution, label-free assessment of conductivity in tissues.

Numerical study of microwave induced thermoacoustic imaging for initial detection of cancer of breast on anatomically realistic breast phantom

BACKGROUND AND OBJECTIVE

Microwave-induced thermoacoustic imaging (MITAI) represents an innovative imaging approach for detection of breast cancer at initial phases by integrating the benefits provided by procedures of microwave and ultrasound imaging. The present investigation examines an innovative three-dimensional numerical modeling of MITAI as a problem with multi-physics nature.

METHODS

Simulations are performed by the use of COMSOL software. An anatomically realistic breast phantom representing various parts of a real breast, such as three different types of tissue, fibro-connective/glandular, transitional; and fatty, is taken into consideration along with a tumor. This breast phantom with a tumor is irradiated by a 2.45 GHz pulsed rectangular waveguide. The temperature increase and its consequent pressure caused by electromagnetic absorption are analyzed.

RESULTS

More temperature increase occurs in the tumor area than in the other parts of the breast, the fact which results in further increase in the pressure in the tumor area than other parts. This makes the tumor distinguishable. The ability of the MITAI process regarding the tumor size, shape (both geometrical shape and spatial orientation), location, the irradiation power level, and the pulse width is also investigated. It is demonstrated that tumor size does not have a significant impact on the efficiency of detection. In fact, very small tumors in the early stages of cancer development (with a radius of 0.25 cm) are also detectable by employing the MITAI technique. The geometrical shape of the tumor does not considerably affect the detecting performance just by itself. The spatial orientation of the tumor actually has a great impact on it. The location of the tumor is an essential factor involved in detection efficiency of MITAI. Tumors located in the fatty tissues would be much easier to be detected than those in the glandular tissues. Moreover, results denote that with augmentation of the irradiation power level or increasing the pulse width, stronger acoustic waves would be produced to make tumor detection easier.

CONCLUSION

These modeling and techniques may be applied aiming for determination of the amount of the generated pressure differences and acoustic pressure magnitude, and can be utilized as an effective prognosticator in practical tests.

An improved method for quantitative recovery of conductivity using tomographically measured thermoacoustic data

Noninvasive extraction of tissue conductivity distribution is important in brain imaging and cancer detection. Here we present an improved method that can accurately image tissue conductivity using tomographically measured microwave-induced thermoacoustic data. Our reconstruction algorithm is first tested using simulations, and then validated using tissue phantom experiments where saline-containing tubes are used as target(s) with various target sizes, positions and conductivities. The average error of reconstruction for the simulations is reduced from 4.87% to 1.38% compared with the previous algorithm. The experimental results obtained suggest that accurate quantitative thermoacoustic imaging would provide a potential tool for precision medicine.

Thermoacoustic tomography of germinal matrix hemorrhage in neonatal mouse cerebrum

BACKGROUND

Microwave-induced thermoacoustic tomography (TAT) has potential for detecting germinal matrix hemorrhage (GMH). However, it has not been demonstrated in vivo.

OBJECTIVE

To demonstrate the feasibility of TAT for in vivo detecting GMH by using neonatal mouse.

METHODS

A cylindrical-scanning TAT system was developed with optimized microwave irradiation and ultrasound detection for neonatal mouse imaging. Neonatal mice were used to develop GMH model by injection of autologous blood into the periventricular region. After TAT experiments, the animals were sacrificed, frozen and excised to validate the TAT findings. The detailed comparative analyses of the TAT images and corresponding photographs of the excised brain tissues were conducted.

RESULTS

Satisfactory matches are identified between the TAT images and corresponding histological sections, in terms of the shape and size of the brain tissues. Some organs and tissues were also identified. Particularly, comparing to the corresponding histological sections, using TAT enables to more accurately detect the hematoma region at different depths in the neonatal mouse brain.

CONCLUSIONS

This study demonstrates for the first time that TAT can detect GMH in neonatal mouse cerebrum in vivo. This represents the first important step towards the in vivo diagnosis and grading of hemorrhage in the infant human brain.

Radiofrequency Hyperthermia of Cancer Cells Enhanced by Silicic Acid Ions Released During the Biodegradation of Porous Silicon Nanowires

The radiofrequency (RF) mild hyperthermia effect sensitized by biodegradable nanoparticles is a promising approach for therapy and diagnostics of numerous human diseases including cancer. Herein, we report the significant enhancement of local destruction of cancer cells induced by RF hyperthermia in the presence of degraded low-toxic porous silicon (PSi) nanowires (NWs). Proper selection of RF irradiation time (10 min), intensity, concentration of PSi NWs, and incubation time (24 h) decreased cell viability to 10%, which can be potentially used for cancer treatment. The incubation for 24 h is critical for degradation of PSi NWs and the formation of silicic acid ions H⁺ and H₃SiO₄ ^- in abundance. The ions drastically change the solution conductivity in the vicinity of PSi NWs, which enhances the absorption of RF radiation and increases the hyperthermia effect. The high biodegradability and efficient photoluminescence of PSi NWs were governed by their mesoporous structure. The average size of pores was 10 nm, and the sizes of silicon nanocrystals (quantum dots) were 3-5 nm. Degradation of PSi NWs was observed as a significant decrease of optical absorbance, photoluminescence, and Raman signals of PSi NW suspensions after 24 h of incubation. Localization of PSi NWs at cell membranes revealed by confocal microscopy suggested that thermal poration of membranes could cause cell death. Thus, efficient photoluminescence in combination with RF-induced cell membrane breakdown indicates promising opportunities for theranostic applications of PSi NWs.

Technical Note: Anti-phase microwave illumination-based thermoacoustic tomography of in vivo human finger joints

PURPOSE

Thermoacoustic tomography (TAT) has been studied to image joints. While several joint tissues could be thermoacoustically imaged, tendons and bone could not be recovered completely or clearly. The purpose of this study was to overcome this limitation.

METHODS

We developed a novel TAT system based on anti-phase microwave illumination method to image the proximal interphalangeal joint and middle phalanx of a right middle finger from a healthy volunteer. The performance of this new system for imaging joints and tendons was compared with that by in-phase microwave illumination and a conventional pyramidal horn antenna.

RESULTS

Anti-phase microwave illumination can produce relatively homogeneous electric (E)-Field distributions inside the joint tissues. The homogeneous E-Field distributions can enhance the detectability of flexor tendon and extensor tendon. Anti-phase microwave illumination could image the flexor tendon, and extensor tendon and bone, which were not clearly imaged by the in-phase microwave illumination or by the horn antenna. The images generated by the in-phase microwave illumination and pyramidal horn antenna were almost identical in terms of the tissue types they imaged.

CONCLUSIONS

Anti-phase illumination can overcome the limitation associated with the conventional TAT by adding the ability of completely delineating tendons and bone in the joints. This study paves the way for us to continue the study and to validate its utility in detection of joint diseases.