Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a sensitive gas detection technique which requires frequent calibration and has a long response time. Here we report beat frequency (BF) QEPAS that can be used for ultra-sensitive calibration-free trace-gas detection and fast spectral scan applications. The resonance frequency and Q-factor of the quartz tuning fork (QTF) as well as the trace-gas concentration can be obtained simultaneously by detecting the beat frequency signal generated when the transient response signal of the QTF is demodulated at its non-resonance frequency. Hence, BF-QEPAS avoids a calibration process and permits continuous monitoring of a targeted trace gas. Three semiconductor lasers were selected as the excitation source to verify the performance of the BF-QEPAS technique. The BF-QEPAS method is capable of measuring lower trace-gas concentration levels with shorter averaging times as compared to conventional PAS and QEPAS techniques and determines the electrical QTF parameters precisely.

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Purpose In vivo range verification in proton therapy is a critical step to help minimize range and dose uncertainty. We propose to employ a time reversal (TR)‐based approach using proton‐induced acoustics (protoacoustics) to reconstruct pressure/dose distribution in heterogeneous tissues. Methods The dose distribution of mono‐energetic proton pencil beam in a CT‐based patient phantom was calculated by Monte Carlo simulation. K‐wave toolbox was used to investigate protoacoustic pressurization, propagation and reconstruction in 2D. To address the tissue heterogeneity effect, a number of physical parameters, including mass density (ρ), speed of sound (c), volumetric thermal expansion coefficient (αV), isobaric specific heat capacity (Cp) and attenuation power law prefactor (α0), were empirically converted from CT number. The performance was evaluated using two figures of merit: mean square error (MSE) of pressure profiles and Bragg peak localization error (ΔBP). The impact of six parameters of the TR inversion was examined, including number of sensors, sampling duration, sampling timestep, spill time, noise level and number of iterations. Results The quantitative accuracy of TR reconstruction and its dependency on the selected parameters is presented. Under optimum conditions, the positioning accuracy of the Bragg peak can be controlled below 1 mm. For instance, MSE is 0.0123 and ΔBP is 0.59 mm under the following conditions (32 sensors, sampling duration: 600 µs, sampling timestep: 40 ns, spill time: 1 µs, no noise). Conclusions The feasibility of TR‐based protoacoustic reconstruction in 2D for proton range verification was first demonstrated. The approach is not only applicable to pencil beam, but also has potential to be extended to passive scattering systems.

Two compact TDLAS sensor systems based on different structural optical cores were developed. The two optical cores combine two recent developments, gallium antimonide (GaSb)-based ICL and a compact multipass gas cell (MPGC) with the goal to create compact TDLAS based sensors for the mid-IR gas detection with high detection sensitivity and low power consumption. The sensors achieved minimum detection limits of ~5 ppbv and ~8 ppbv, respectively, for CH₄ and C₂H₆ concentration measurements with a 3.7-W power consumption.

Non-small cell lung cancer (NSCLC) is one of the most malignant cancers in the world. Early diagnosis of NSCLC has become especially important for patient treatment and prognosis. Increasing evidence suggest that long non-coding RNA GAS5 plays vital roles in cancer proliferation and differentiation in NSCLC. However, its clinical value in the diagnosis of NSCLC is unclear. The objective of this study was to evaluate the importance of circulating GAS5 as a biomarker for NSCLC diagnosis. In our study, quantitative real-time PCR (QRT-PCR) was applied to detect the GAS5 expression level in 80 pairs of cancer tissues and 57 pairs of plasma samples of NSCLC patients. Further analysis was performed to study the differential expression of circulating GAS5 in 111 NSCLC patients and 78 healthy controls in our study. The results showed that GAS5 decreased in NSCLC tissues compared to noncancerous tissues (P<0.001). Furthermore, the GAS5 expression level was statistically declined in early stage of NSCLC before surgery compared with healthy controls (P<0.05) and sharply increased in postoperative groups (P=0.026). ROC curve analysis for early stage of NSCLC with the combination of GAS5, CEA and CA199 showed that the area under the ROC curve (AUC) was 0.734 (95% CI, 0.628‑0.839; P<0.0005). In conclusion, circulating GAS5 could be functioned as a potential combined biomarker for screening NSCLC and patient monitoring after surgical treatment.