Effect of Sympathetic Blockade on Spontaneous Discharge and the H-Reflex at Myofascial Trigger Points in Rats.

Purpose: Myofascial trigger points (MTrPs) are the main cause of myofascial pain syndrome (MPS), and patients with MPS also have symptoms of sympathetic abnormalities. Consequently, this study aimed to investigate the potential relationship between MTrPs and sympathetic nerves. Materials and Methods: Twenty-four seven-week-old male rats were randomly divided into four groups (six rats every group). Groups I and II were kept in normal condition (n=12), and groups III and IV underwent MTrPs modelling (n=12). After successful MTrPs modelling, differences in sympathetic outcomes between the MTrPs groups (III and IV) and non-MTrPs groups (I and II) were observed. Sympathetic blockade was then applied to groups III and I (n=12). Data were collected on peak inversion spontaneous potentials (PISPs) and the H-reflex-evoked electromyography during spontaneous discharge at the MTrPs before and after sympathetic blockade. Results: Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and heart rate were significantly higher in the MTrPs group than in the non-MTrPs group (P<0.05). Compared with group I, group III had the PISPs potential lower wave amplitude, shorter duration and amplitude-to-duration ratio, and lower H latency and latency difference H-M (P<0.05). Compared with group IV, group III had the PISPs potential lower wave amplitude, duration, amplitude-to-duration ratio, M-wave latency, H maximum wave amplitude, and maximal wave amplitude ratio H/M (P<0.05). The changes before and after sympathetic blockade in the MTrPs group were significant, and the amplitude, duration, and amplitude-to-duration ratio of the PISPs potentials were lower after the blockade (P<0.05). Conclusion: MTrPs and sympathetic nerves interact with each other forming a specific relationship. MTrPs sensitize sympathetic nerves, and sympathetic nerve abnormalities affect local muscle myoelectric hyperactivity, leading to MTrPs. This finding is instructive for the clinical management of sympathetic disorders.

Ultrasound-switchable fluorescence thermometry with dual detection channels using temperature-sensitive liposomes.

Temperature measurements in biological tissues play a crucial role in studying metabolic activities. In this study, we introduce a noninvasive thermometry technique based on two-color ultrasound-switchable fluorescence (USF). This innovative method allows for a local temperature mapping within a microtube filled with temperature-sensitive liposomes as nano imaging agents. By measuring the temperature-dependent fluorescence emission of the liposomes using a spectrometer, we identify four characteristic temperatures. The local background temperature can be estimated by analyzing the corresponding appearance time of these four characteristic temperatures in the dynamic USF signals captured by a camera-based USF system with two detection channels. Simultaneous measurements with an infrared (IR) camera showed a 0.38°C ± 0.27°C difference between USF thermometry and IR thermography in a physiological temperature range of 36.48°C-40.14°C. This shows that the two-color USF thermometry technique is a reliable, noninvasive tool with excellent spatial and thermal resolution.

In vivo tumor ultrasound-switchable fluorescence imaging via intravenous injections of size-controlled thermosensitive nanoparticles.

Near-infrared fluorescence imaging has emerged as a noninvasive, inexpensive, and ionizing-radiation-free monitoring tool for assessing tumor growth and treatment efficacy. In particular, ultrasound switchable fluorescence (USF) imaging has been explored with improved imaging sensitivity and spatial resolution in centimeter-deep tissues. This study achieved size control of polymer-based and indocyanine green (ICG) encapsulated USF contrast agents, capable of accumulating at the tumor after intravenous injections. These nanoprobes varied in size from 58 nm to 321 nm. The bioimaging profiles demonstrated that the proposed nanoparticles can efficiently eliminate the background light from normal tissue and show a tumor-specific fluorescence enhancement in the BxPC-3 tumor-bearing mice models possibly via the enhanced permeability and retention effect. In vivo tumor USF imaging further proved that these nanoprobes can effectively be switched 'ON' with enhanced fluorescence in response to a focused ultrasound stimulation in the tumor microenvironment, contributing to the high-resolution USF images. Therefore, our findings suggest that ICG-encapsulated nanoparticles are good candidates for USF imaging of tumors in living animals, indicating their great potential in optical tumor imaging in deep tissue.

Noninvasive measurement of local temperature using ultrasound-switchable fluorescence.

Measuring the local background temperature in diseased and inflamed tissues is highly desirable, especially in a non-invasive way. In this work, ultrasound-switchable fluorescence (USF) technique was utilized to estimate the local background temperature for the first time by analyzing the temperature dependence of fluorescence emission from USF contrast agents induced by a focused ultrasound (FU) beam. First, temperature-sensitive USF agents with distinct temperature switching-on thresholds were synthesized, and their thermal switching characteristics were quantified using an independent spectrometer system. Second, the USF contrast agent suspension was injected into a microtube that was embedded into a phantom and the dynamic USF signal was acquired using a camera-based USF system. The differential profile of the measured dynamic USF signal was computed and compared with the thermal switching characteristics. This allowed for the calculation of the local background temperature of the sample in the FU focal volume based on the estimation of heating speed. An infrared (IR) camera was used to acquire the surface temperature of the sample and further compare it with the USF system. The results showed that the difference between the temperatures acquired from the USF thermometry and the IR thermography was 0.64 ± 0.43 °C when operating at the physiological temperature range from 35.27 to 39.31 °C. These results indicated the potential use of the USF system for measuring the local temperature in diseased tissues non-invasively. The designed USF-based thermometry shows a broad application prospect in high spatial resolution temperature imaging with a tunable measurement range in deep tissue.

Size effect of liposomes on centimeter-deep ultrasound-switchable fluorescence imaging and ultrasound-controlled release.

Liposomes have been widely used in both medical imaging and drug delivery fields due to their excellent biocompatibility and easy surface modification. Recently our lab reported for the first-time the implementation of temperature-sensitive and indocyanine green (ICG)-encapsulated liposome microparticles for in vivo ultrasound-switchable fluorescence (USF) imaging. A previous study showed that liposome microparticles achieved USF imaging in centimeter-deep tissue. This study aimed to control the size of liposomes at the nanoscale and study the size effect on the USF imaging depth. Also, we explored the feasibility of combining USF imaging with ultrasound-controlled release. Liposomes were synthesized via the hydration method and the size was controlled by an extruding process. Characterization parameters, including fluorescence profile, spectra, size, stability, encapsulation efficiency, and ultrasound-controlled release, were evaluated. USF imaging in blood serum was conducted successfully in a phantom model, and an imaging depth study was conducted at 1.0 cm and 2.5 cm and confirmed that nano-sized liposomes had a stronger USF signal than micron-sized liposomes. Additionally, releasing tests indicated that both ultrasound power and exposure time affected the release efficiency in that increasing the power and extending the exposure time led to higher release efficiency. Above all, this study shows the potential for using liposomes for USF imaging and ultrasound-controlled release.

Thermo- and pH-sensitive nanoparticles of poly (N-isopropylacrylamide-decenoic acid-1-vinylimidazole) for ultrasound switchable fluorescence imaging.

We herein report the synthesis of poly (9-decenoic acid-1-vinylimidazole-N-isopropylacrylamide) nanoparticles containing indocyanine green (ICG) in one pot and in water phase throughout the reaction. We have shown that copolymers of 9-decenoic acid and 1-vinylimidazole, or 9-decenoic acid alone, have an enhanced sensitivity to pH values between 7.4 and 6.8 and are superior to the widely used acrylic acid. We have also shown that incorporation of acidic comonomers leads to the favorable outcome of a higher fluorescence signal intensity in lower pH values, whereas the opposite is true of basic comonomers, where the fluorescence signal intensity is lower at low pH values. It was shown that to keep the pH response favorable the molar ratio of basic comonomers to acidic comonomers should roughly equal 1:4. We controlled the lower critical solution temperature (LCST) of the nanoparticles from around 30 to 38°C for different applications by adding acrylamide comonomers. Finally, the nanoparticles at varying pH values, when imaged by an ultrasound switchable fluorescence (USF) imaging system, showed pH sensitivity and thermosensitivity at physiological and tumor pH.

Improving sensitivity and imaging depth of ultrasound-switchable fluorescence via an EMCCD-gain-controlled system and a liposome-based contrast agent.

BACKGROUND: The ultrasound-switchable fluorescence (USF) technique was recently developed to achieve high-resolution fluorescence imaging in centimeters-deep tissue. This study introduced strategies to significantly improve imaging sensitivity and depth using an electron multiplying charge-coupled device (EMCCD) camera-based USF imaging system and a newly developed USF contrast agent of indocyanine green (ICG)-encapsulated liposomes. For a quantitative study, a phantom of a sub-millimeter silicone tube embedded in centimeter-thick chicken breast tissue was adopted in this study as a model. METHODS: The synthesized ICG-liposome was characterized and compared with the previously reported ICG-nanogel. The exposure of the EMCCD camera was controlled via the MATLAB (The MathWorks, Inc. USA), instead of an external hardware trigger. The stability of the electron multiplying (EM) gain of the EMCCD camera was compared between two trigger modes: the MATLAB trigger mode and the external hardware trigger mode. The signal-to-noise ratio (SNR) of the USF imaging with different EM gain in various thick tissue was studied. RESULTS: The hydrodynamic size of the ICG-liposome was ~181 nm. The ICG-liposome had a sharper temperature switching curve and a better USF performance than the previously reported ICG-nanogel. The EM gain was more stable in MATLAB trigger mode than the external hardware trigger mode. Although, as usual, the SNR decreased quickly with the increase of the tissue thickness, the proposed strategies improved the SNR and the imaging depth significantly by adopting the novel contrast agent and controlling the EM gain. CONCLUSIONS: We successfully imaged the sub-millimeter silicone tube with an inner diameter of 0.76 mm and an outer diameter of 1.65 mm in 5.5 cm-thick chicken breast tissue using 808 nm excitation light with a low intensity of 28.35 mW/cm2, the improved EMCCD camera-based USF imaging system and the novel ICG-liposomes.

Near-infrared temperature-switchable fluorescence nanoparticles.

BACKGROUND: Near infrared (NIR) environment-sensitive fluorophores are highly desired for many biomedical applications because of its non-invasive operation, high sensitivity and specificity, non-ionizing radiation and deep penetration in biological tissue. When the fluorophores are appropriately encapsulated in or conjugated with some thermal-sensitive polymers, they could work as excellent temperature-sensing probes. METHODS: In this study, we synthesized and characterized a series of NIR temperature-switchable nanoparticles based on two series of NIR fluorophores aza-BODIPY (ADP is used for abbreviation in this work) and Zinc phthalocyanine (ZnPc) and four pluronic polymers (F127, F98, F68 and F38). Encapsulating the fluorophores in the polymers by sonication, we synthesized the nanoparticles that showed switch-like functions of the fluorescence intensity (and/or lifetime) as the temperature, with high switch on-to-off ratio. We also investigated various factors that might change the temperature thresholds (Tth) of the switch functions, in order to control Tth during synthesis. RESULTS: These nanoparticles showed excellent temperature-switchable properties of fluorescence intensity and/or lifetime. Meanwhile, some factors (i.e., pluronic categories and nanoparticles' concentration) significantly affected the nanoparticles' Tths while other (i.e., fluorophore categories) that weakly affected Tths. CONCLUSIONS: By selecting appropriate pluronic categories and adjusting the nanoparticle's concentration, we can synthesize the nanoparticles with a wide range of Tths. These temperature-switchable fluorescence nanoparticles can be used for biomedical imaging and in vivo tissue temperature sensing/imaging.

In vivo ultrasound-switchable fluorescence imaging using a camera-based system.

Ultrasound-switchable fluorescence (USF) is a novel imaging technique that provides high spatial resolution fluorescence images in centimeter-deep biological tissue. Recently, we successfully demonstrated the feasibility of in vivo USF imaging using a frequency-domain photomultiplier tube-based system. In this work, for the first time we carried out in vivo USF imaging via a camera-based USF imaging system. The system acquires a USF signal on a two-dimensional (2D) plane, which facilitates the image acquisition because the USF scanning area can be planned based on the 2D image and provides high USF photon collection efficiency. We demonstrated in vivo USF imaging in the mouse's glioblastoma tumor with multiple targets via local injection. In addition, we designed the USF contrast agents with different particle sizes (70 nm and 330 nm) so that they could bio-distribute to various organs (spleen, liver, and kidney) via intravenous (IV) injections. The results showed that the contrast agents retained stable USF properties in tumors and some organs (spleen and liver). We successfully achieved in vivo USF imaging of the mouse's spleen and liver via IV injections. The USF imaging results were compared with the images acquired from a commercial X-ray micro computed tomography (micro-CT) system.

A Biocompatible and Near-Infrared Liposome for In Vivo Ultrasound-Switchable Fluorescence Imaging.

Fluorescence imaging is a remarkable tool for molecular targeting and multicolor imaging, but it suffers from low resolution in centimeter-deep tissues. The recently developed ultrasound-switchable fluorescence (USF) imaging has overcome this challenge and achieved in vivo imaging in a mouse with help from the indocyanine green (ICG) dye encapsulated poly(N-isopropylacrylamide) (ICG-PNIPAM) contrast agent. However, the ICG-PNIPAM has shortcomings, such as concerns about cytotoxicity and blueshifted excitation and emission spectra. This study introduces a newly developed ICG-encapsulated liposome to broaden the contrast agent selection for USF imaging and resolve the issues mentioned above. The emission peak of the ICG-liposome is 836 nm with excellent biostability and USF imaging capability. Furthermore, the cell viability test verifies the low cytotoxicity feature. Eventually, both ex vivo and in vivo USF imaging are successfully achieved and 3D USF images are acquired. The ex vivo result confirms that the ICG-liposome maintains the thermoresponsive characteristic at the right lobe of the liver and is able to conduct the USF imaging. The further in vivo USF imaging demonstrates that although the whole liver emitted fluorescence, only the right lobe of the liver contains the working ICG-liposome.

An ICCD camera-based time-domain ultrasound-switchable fluorescence imaging system.

Fluorescence imaging in centimeter-deep tissues with high resolution is highly desirable for many biomedical applications. Recently, we have developed a new imaging modality, ultrasound-switchable fluorescence (USF) imaging, for achieving this goal. In our previous work, we successfully achieved USF imaging with several types of USF contrast agents and imaging systems. In this study, we introduced a new USF imaging system: an intensified charge-coupled device (ICCD) camera-based, time-domain USF imaging system. We demonstrated the principle of time-domain USF imaging by using two USF contrast agents. With a series of USF imaging experiments, we demonstrated the tradeoffs among different experimental parameters (i.e., data acquisition time, including CCD camera recording time and intensifier gate delay; focused ultrasound (FU) power; and imaging depth) and the image qualities (i.e., signal-to-noise ratio, spatial resolution, and temporal resolution). In this study, we also discussed several imaging strategies for achieving a high-quality USF image via this time-domain system.

In vivo ultrasound-switchable fluorescence imaging.

The conventional fluorescence imaging has limited spatial resolution in centimeter-deep tissue because of the tissue's high scattering property. Ultrasound-switchable fluorescence (USF) imaging, a new imaging technique, was recently proposed to realize high-resolution fluorescence imaging in centimeter-deep tissue. However, in vivo USF imaging has not been achieved so far because of the lack of stable near-infrared contrast agents in a biological environment and the lack of data about their biodistributions. In this study, for the first time, we achieved in vivo USF imaging successfully in mice with high resolution. USF imaging in porcine heart tissue and mouse breast tumor via local injections were studied and demonstrated. In vivo and ex vivo USF imaging of the mouse spleen via intravenous injections was also successfully achieved. The results showed that the USF contrast agent adopted in this study was very stable in a biological environment, and it was mainly accumulated into the spleen of the mice. By comparing the results of CT imaging and the results of USF imaging, the accuracy of USF imaging was proved.

Modulation of ultrasound-switchable fluorescence for improving signal-to-noise ratio.

Simultaneously achieving high signal-to-noise ratio (SNR) (or sensitivity) and high resolution is desired in biomedical imaging. However, conventional imaging modality has a tradeoff between SNR (or sensitivity) and resolution. We developed a method to simultaneously achieve high SNR (or sensitivity) and high resolution for fluorescence imaging in deep tissue. We first introduce a recently developed deep-tissue high-resolution imaging technique termed as ultrasound-switchable fluorescence (USF). An approach of modulating ultrasound exposure time is adopted to increase the detectability of the USF signal. The control parameters of modulation of ultrasound­such as (1) frequency, (2) duty cycle, and (3) exposure duration­are varied to study their influence on the USF signal and SNR. We conclude that high SNR can be achieved by modulating ultrasound exposure without sacrificing the spatial resolution. This is important for future fluorescence molecular imaging of cancer in deep tissue.

New generation ICG-based contrast agents for ultrasound-switchable fluorescence imaging.

Recently, we developed a new technology, ultrasound-switchable fluorescence (USF), for high-resolution imaging in centimeter-deep tissues via fluorescence contrast. The success of USF imaging highly relies on excellent contrast agents. ICG-encapsulated poly(N-isopropylacrylamide) nanoparticles (ICG-NPs) are one of the families of the most successful near-infrared (NIR) USF contrast agents. However, the first-generation ICG-NPs have a short shelf life (<1 month). This work significantly increases the shelf life of the new-generation ICG-NPs (>6 months). In addition, we have conjugated hydroxyl or carboxyl function groups on the ICG-NPs for future molecular targeting. Finally, we have demonstrated the effect of temperature-switching threshold (Tth) and the background temperature (TBG) on the quality of USF images. We estimated that the Tth of the ICG-NPs should be controlled at ~38-40 °C (slightly above the body temperature of 37 °C) for future in vivo USF imaging. Addressing these challenges further reduces the application barriers of USF imaging.

Distributed MIMO chaotic radar based on wavelength-division multiplexing technology.

A distributed multiple-input multiple-output chaotic radar based on wavelength-division multiplexing technology (WDM) is proposed and demonstrated. The wideband quasi-orthogonal chaotic signals generated by different optoelectronic oscillators (OEOs) are emitted by separated antennas to gain spatial diversity against the fluctuation of a target's radar cross section and enhance the detection capability. The received signals collected by the receive antennas and the reference signals from the OEOs are delivered to the central station for joint processing by exploiting WDM technology. The centralized signal processing avoids precise time synchronization of the distributed system and greatly simplifies the remote units, which improves the localization accuracy of the entire system. A proof-of-concept experiment for two-dimensional localization of a metal target is demonstrated. The maximum position error is less than 6.5 cm.