Bone disease is a growing epidemic in the world today that will lead to billions of dollars of medical bills. While a range of lifestyle and genetic factors play a role in the progression of disease, in overarching symptom of increased bone porosity leads to decreased mobility, pain, fracture, and even death. Therefore, it is important to monitor trabecular bone for better care of affected individuals. Photoacoustic microscopy (PAM) is a hybrid modality that combines high optical absorption qualities of biological tissue with high spatial resolution of ultrasound. Our study aims to further assess the ability to image bone microarchitecture with photoacoustic imaging. A picosecond-pulsed laser with a wavelength of 532 nm was used to excite the bone while ultrasonic transients were captured by a 20 MHz transducer. We first preformed studies to characterize our lateral resolution and optimize our system using phantoms mimicking different bone porosity. We then imaged pig bone ex-vivo. Our results show that this photoacoustic (PA) imaging has the potential to identify normal and osteoporosis diseased bone. The capability to noninvasively quantify bone tissue composition suggests a possible use of PAM as an optical biopsy for the diagnosis of bone pathologies such as osteoporosis, which are characterized by a progressive reduction and transformation of mineral in the bone matrix.
The new technique for the imaging guidance to real-time monitoring of electroporation-based medical interventions could be based on the electroacoustic tomography (EAT), where the electric field applied for the electroporation process leads to induced acoustic signals based on the flow of electrical current inside the target conductive tissue. A microsecond to nanosecond electric-pulse (𝜇𝑠 − 𝑛𝑠𝐸𝑃) excitation source is an essential part of this new imaging guided to real-time monitoring electroporation process. This paper presents the design, configuration, and measurement of a compact, low-cost high voltage MOSFET-based pulsed excitation source and the simple structure of the EAT system with the single channel ultrasonic transducer to acquire acoustic signals and complemented by experimentation of its function based on agar-conductive phantom studies. The high-voltage pulsed excitation source has variable pulse widths ranging from 100 𝑛𝑠 𝑡𝑜 10 𝜇𝑠 electric pulse with a variable pulse potential magnitude of up to 1200 Volts (V). The high-voltage 𝜇𝑠 − 𝑛𝑠𝐸𝑃 is powered from a variable input source of 11.3 to 16 V in direct current (DC) and a power controller using a 0 V to 5 V in DC power line so that it is able to provide 0 to full output in potential magnitude. The high-intensity, ultra-short pulsed electric field is then connected to two electrodes separated by a distance (d) where 𝑑 = 1500𝜇𝑚 𝑡𝑜 3400 𝜇 mounted into the conductive media. An unfocused ultrasound transducer with central frequency of 500 kHz is used to acquire real-time acoustic signals. Various conductive media, including two agar-based phantoms with conductivity of 1 𝜇𝑆/𝑐𝑚 , 34 𝑚𝑆/𝑐𝑚 were studied using this pulsed excitation source to induce corresponding acoustic signals. Results indicate feasibility of the enhancing the EAT system that used up to 8 kV/cm, 𝜇𝑠 𝑡𝑜 𝑛𝑠 pulsed excitation source used in the electroporation-based clinical processes enhancing the EAT system as an imaging guidance to real-time, in-situ monitoring for the electroporation-based techniques.
In our experiments, a technique has been developed to simultaneously acquire Electroacoustic (EA) signal captured by a single channel ultrasonic traducer in a linear array structure. The system utilizes micro- to nano-second pulsed electric field applied by an excitation source that can be used for clinical purposes (i.e. electroporation applications), and a conventional ultrasound transducer to acquire pulse electric field-induced acoustic signals. In this research, for the first time, we present a new real-time imaging-based technique when applying different electric field distributions that disturb electrically charged particles in the media that leads to a change of temperature which increases on the order of mK per a single high intensive, μ𝑠 −𝑛𝑠 short-pulse. We demonstrated this new technique by acquiring real-time acoustic signals induce by electric field distribution inside an agar-conductive based phantom. We used low-noise-amplifiers with a maximum gain of 60dB at 500 kHz with a linear scanning structure within less than 20sec, in 500 steps, and delay time of 500 ms to stabilize the transducer, and establish a linear scanning with a single element transducer. The corresponding EA images are reconstructed with a multi-step line back-projection algorithm. The approach can effectively reduce the artifacts associated with a conventional filter back projection algorithm used in other ultrasonic imaging by linear scanning structure because it is able to take information at multiple points to deliver the best possible image. This EAT technique provides a new and unique imaging approach for realtime, in-situ electrotherapy-based clinical practical applications.