Role of MR-DWI and MR-PWI in the radiotherapy of implanted pulmonary VX-2 carcinoma in rabbits

Objective： To detect the activity of tumor cells and tumor blood flow before and after the radiotherapy of implanted pulmonary VX-2 carcinoma in rabbit models by using magnetic resonance diffusion-weighted imaging（MR-DWI） and magnetic resonance perfusion weighted imaging（MR-PWI）, and to evaluate the effectiveness and safety of the radiotherapy based on the changes in the MR-DWI and MR-PWI parameters at different treatment stages.Methods： A total of 56 rabbit models with implanted pulmonary VX-2 carcinoma were established, and then equally divided into treatment group and control group. MR-DWI and MR-PWI were separately performed using a Philips Acheiva 1.5T MRI machine（Philips, Netherland）. MRI image processing was performed using special perfusion software and the WORKSPACE advanced workstation for MRI. MRDWI was applied for the observation of tumor signals and the measurement of apparent diffusion coefficient（ADC） values; whereas MR-PWI was used for the measurement of wash in rate（WIR）, wash out rate（WOR）, and maximum enhancement rate（MER）. The radiation treatment was performed using Siemens PRIMUS linear accelerator. In the treatment group, the radiotherapy was performed 21 days later on a once weekly dosage of 1,000 c Gy to yield a total dosage of 5,000 c Gy.Results： The ADC parameters in the region of interest on DWI were as follows： on the treatment day for the implanted pulmonary VX-2 carcinoma, the t values at the center and the edge of the lesions were 1.352 and 1.461 in the treatment group and control group（P〉0.05）. During weeks 0-1 after treatment, the t values at the center and the edge of the lesions were 1.336 and 1.137（P〉0.05）. During weeks 1-2, the t values were 1.731 and 1.736（P〈0.05）. During weeks 2-3, the t values were 1.742 and 1.749（P〈0.05）. During weeks 3-4, the t values were 2.050 and 2.127（P〈0.05）. During weeks 4-5, the t values were 2.764 and 2.985（P〈0.05）. The ADC values in the treatment group were significantly higher than in the control group. After the radiotherapy（5,000 c Gy）, the tumors remarkably shrank, along with low signal on DWI, decreased signal on ADC map, and remarkably increased ADC values. As shown on PWI, on the treatment day for the implanted pulmonary VX-2 carcinoma, the t values of the WIR, WOR, and MER at the center of the lesions were 1.05, 1.31, and 1.33 in the treatment group and control group（P〉0.05）; in addition, the t values of the WIR, WOR, and MER at the edge of the lesions were 1.35, 1.07, and 1.51（P〉0.05）. During weeks 0-1 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 1.821, 1.856, and 1.931（P〈0.05）; in addition, the t values of the WIR, WOR, and MER at the edge of the lesions were 1.799, 2.016, and 2.137（P〈0.05）. During weeks 1-1 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.574, 2.156, and 2.059（P〈0.05） and the t values of the WIR, WOR, and MER at the edge of the lesions were 1.869, 2.058, and 2.057（P〈0.05）. During weeks 2-3 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.461, 2.098, and 2.739（P〈0.05） and the t values of the WIR, WOR, and MER at the edge of the lesions were 2.951, 2.625, and 2.154（P〈0.05）. During weeks 3-4 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.584, 2.107, and 2.869（P〈0.05） and the t values of the WIR, WOR, and MER at the edge of the lesions were 2.057, 2.637, and 2.951（P〈0.05）. During weeks 4-5 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.894, 2.827, and 3.285（P〈0.05） and the t values of the WIR, WOR, andMER at the edge of the lesions were 3.45, 3.246, and 3.614（P〈0.05）. After the radiotherapy（500 c Gy）, the tumors shrank on the T1 WI, WIR, WOR, and MER; meanwhile, the PWI parameter gradually decreased and reached its minimum value.Conclusions： MR-DWI and MR-PWI can accurately and directly reflect the inactivation of tumor cells and the tumor hemodynamics in rabbit models with implanted pulmonary VX-2 carcinoma, and thus provide theoretical evidences for judging the clinical effectiveness of radiotherapy for the squamous cell carcinoma of the lung.

Frequency-comb-linearized, widely tunable lasers for coherent ranging

Tunable lasers,with the ability to continuously vary their emission wavelengths,have found widespread applications across various fields such as biomedical imaging,coherent ranging,optical communications,and spectroscopy.In these applications,a wide chirp range is advantageous for large spectral coverage and high frequency resolution.Besides,the frequency accuracy and precision also depend critically on the chirp linearity of the laser.While extensive efforts have been made on the development of many kinds of frequency-agile,widely tunable,narrow-linewidth lasers,wideband yet precise methods to characterize and linearize laser chirp dynamics are also demanded.Here we present an approach to characterize laser chirp dynamics using an optical frequency comb.The instantaneous laser frequency is tracked over terahertz bandwidth at 1 MHz intervals.Using this approach we calibrate the chirp performance of 12 tunable lasers from Toptica,Santec,New Focus,EXFO,and NKT that are commonly used in fiber optics and integrated photonics.In addition,with acquired knowledge of laser chirp dynamics,we demonstrate a simple frequency-linearization scheme that enables coherent ranging without any optical or electronic linearization unit.Our approach not only presents novel wideband,highresolution laser spectroscopy,but is also critical for sensing applications with ever-increasing requirements on performance.

A wideband,high-resolution vector spectrum analyzer for integrated photonics

The analysis of optical spectra—emission or absorption—has been arguably the most powerful approach for discovering and understanding matter.The invention and development of many kinds of spectrometers have equipped us with versatile yet ultra-sensitive diagnostic tools for trace gas detection,isotope analysis,and resolving hyperfine structures of atoms and molecules.With proliferating data and information,urgent and demanding requirements have been placed today on spectrum analysis with ever-increasing spectral bandwidth and frequency resolution.These requirements are especially stringent for broadband laser sources that carry massive information and for dispersive devices used in information processing systems.In addition,spectrum analyzers are expected to probe the device’s phase response where extra information is encoded.Here we demonstrate a novel vector spectrum analyzer(VSA)that is capable of characterizing passive devices and active laser sources in one setup.Such a dual-mode VSA can measure loss,phase response,and dispersion properties of passive devices.It also can coherently map a broadband laser spectrum into the RF domain.The VSA features a bandwidth of 55.1 THz(1260–1640 nm),a frequency resolution of 471 kHz,and a dynamic range of 56 dB.Meanwhile,our fiber-based VSA is compact and robust.It requires neither high-speed modulators and photodetectors nor any active feedback control.Finally,we employ our VSA for applications including characterization of integrated dispersive waveguides,mapping frequency comb spectra,and coherent light detection and ranging(LiDAR).Our VSA presents an innovative approach for device analysis and laser spectroscopy,and can play a critical role in future photonic systems and applications for sensing,communication,imaging,and quantum information processing.

Foundry manufacturing of tight-confinement,dispersion-engineered,ultralow-loss silicon nitride photonic integrated circuits

The foundry development of integrated photonics has revolutionized today’s optical interconnect and datacenters.Over the last decade,we have witnessed the rising of silicon nitride(Si_(3)N_(4)) integrated photonics,which is currently transferring from laboratory research to foundry manufacturing.The development and transition are triggered by the ultimate need for low optical loss offered by Si_(3)N_(4),which is beyond the reach of silicon and III-V semiconductors.Combined with modest Kerr nonlinearity,tight optical confinement,and dispersion engineering,Si_(3)N_(4) has today become the leading platform for linear and Kerr nonlinear photonics,and it has enabled chip-scale lasers featuring ultralow noise on par with table-top fiber lasers.However,so far all the reported fabrication processes of tight-confinement,dispersion-engineered Si_(3)N_(4) photonic integrated circuits(PICs)with optical loss down to few dB/m have only been developed on 4-inch(100 mm diameter)or smaller wafers.Yet,to transfer these processes to established CMOS foundries that typically operate 6-inch or even larger wafers,challenges remain.In this work,we demonstrate the first foundry-standard fabrication process of Si_(3)N_(4) PICs with only 2.6 dB/m loss,thickness above 800 nm,and near 100%fabrication yield on 6-inch(150 mm diameter)wafers.Such thick and ultralow-loss Si_(3)N_(4) PIC enables low-threshold generation of soliton frequency combs.Merging with advanced heterogeneous integration,active ultralow-loss Si_(3)N_(4) integrated photonics could pave an avenue to addressing future demands in our increasingly information-driven society.