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The objective of the present study was to evaluate the application of dual-source CT perfusion imaging and MRI for the diagnosis of primary liver cancer. Sixty-three patients with primary liver cancer were selected between February 2015 and May 2016. All patients underwent examinations by dual-source CT perfusion imaging and MRI. The perfusion parameters of the focus center and normal liver parenchyma by CT examination and the hemodynamic parameters of the focus center and normal liver parenchyma by MRI examination were analyzed. The accuracy rates of the three detection methods (CT perfusion imaging, MRI, and combined examination) were analyzed and compared by ROC curves. Dual-source CT perfusion imaging revealed that blood flow and blood volume of the focus center were significantly higher than those of normal liver parenchyma (P<0.05). MRI examination showed that hepatic arterial perfusion and hepatic perfusion index of the focus center were significantly higher than those of normal liver parenchyma; portal venous perfusion of the focus center was significantly lower than that of normal liver parenchyma (P<0.05); the difference in total liver perfusion between the focus center and normal liver parenchyma was not significant (P>0.05); the accuracy rates of CT perfusion imaging, MRI, and combined examination were 76.19, 85.71, and 95.24% respectively; the area under the curve of CT perfusion imaging was 0.753 (P<0.05), the sensitivity was 79.2% and the specificity was 74.7%; the area under the curve of MRI was 0.846 (P<0.05), the sensitivity was 84.6%, and the specificity was 80.5%; the area under the curve of CT combined with MRI was 0.947 (P<0.05), the sensitivity was 94.6%, and the specificity was 86.5%. In conclusion, the effect of dual-source CT perfusion imaging combined with MRI for examination of primary liver cancer is superior to that of single use of CT or MRI, and has high clinical application and popularization value. [ABSTRACT FROM AUTHOR]

Background In a deforming anatomic environment, the motion of an instrument suffers from complex geometrical and dynamic constraints, robot assisted minimally invasive surgery therefore requires more sophisticated skills for surgeons. This paper proposes a novel dynamic virtual fixture (DVF) to enhance the surgical operation accuracy of admittance-type medical robotics in the deforming environment. Methods A framework for DVF on the Euclidean Group SE(3) is presented, which unites rotation and translation in a compact form. First, we constructed the holonomic/ non-holonomic constraints, and then searched for the corresponded reference to make a distinction between preferred and non-preferred directions. Second, different control strategies are employed to deal with the tasks along the distinguished directions. The desired spatial compliance matrix is synthesized from an allowable motion screw set to filter out the task unrelated components from manual input, the operator has complete control over the preferred directions; while the relative motion between the surgical instrument and the anatomy structures is actively tracked and cancelled, the deviation relative to the reference is compensated jointly by the operator and DVF controllers. The operator, haptic device, admittance-type proxy and virtual deforming environment are involved in a hardware-in-the-loop experiment, human-robot cooperation with the assistance of DVF controller is carried out on a deforming sphere to simulate beating heart surgery, performance of the proposed DVF on admittance-type proxy is evaluated, and both human factors and control parameters are analyzed. Results The DVF can improve the dynamic properties of human-robot cooperation in a low-frequency (0 ~ 40 rad/sec) deforming environment, and maintain synergy of orientation and translation during the operation. Statistical analysis reveals that the operator has intuitive control over the preferred directions, human and the DVF controller jointly control the motion along the non-preferred directions, the target deformation is tracked activly. Conclusions The proposed DVF for an admittance-type manipulator is capable of assisting the operator to deal with skilled operations in a deforming environment. [ABSTRACT FROM AUTHOR]

Argon atom ionizing in the ultrafast two-colour field has been used to investigate the physical mechanism of terahertz (THz) generation. We measured simultaneously pulse energies of THz and high-harmonics as the phase delay between the fundamental and its second harmonic was varied. The optimal phase delay of THz generation is determined according to the inherent attochirp of the emitted high-harmonics. The dynamic analysis of the tunnelling electron wave packet driven by the Coulomb-laser coupling shows that laser-assisted soft collisions of the electron wave packet with the atomic core play a key role. it is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. [ABSTRACT FROM AUTHOR]

Background: Robot-assisted needle steering facilitates the percutaneous renal access (PRA) for their accuracy and consistency over manual operation. However, inaccurate image-robot correspondence and uncertainties in robot parameters make the needle track deviate from the intrarenal target. This paper aims to simplify the image-tracker -robot registration procedure and improves the accuracy of needle alignment for robot assisted ultrasound-guided PRA. Methods: First, a semi-automatic rigid registration is used for the alignment of the preoperative MR volume and the intraoperative orthogonal US slices. Passive markers are mounted both on US probe and robot end-effector, the planned puncture path is transferred from the MR volume frame into optical tracker frame. Tracker-robot correspondence and robot calibration are performed iteratively using a simplified scheme, both position and orientation information are incorporated to estimate the transformation matrix, only several key structural robot parameters and joint zeropositions are calibrated for simplicity in solving the inverse kinematic. Furthermore, an optical tracker feedback control is designed for compensating inaccuracies in robot parameters and tracker-robot correspondence, and improving the accuracy of needle alignment. The intervention procedure was implemented by a telemanipulated 5R1P robot, two experiments were conducted to validate the efficiency of robot-tracker registration method and the optical tracker feedback control, robot assisted needle insertion experiment was conducted on kidney phantom to evaluate the system performance. Results: The relative positioning accuracy of needle alignment is 0.24±0.08 mm, the directional accuracy is 6.78±1.65 × 10-4rad; the needle-target distance of needle insertion is 2.15±0. 17 mm. The optical tracker feedback control method performs stable against wide range of angular disturbance over (0 ∼ 0.4) radians, and the length disturbance over (0 ∼ 100) mm. Conclusions: The proposed optical tracker based robot registration and servoing method is capable of accurate three dimension needle operation for PRA procedure with improved precision and shortened time. [ABSTRACT FROM AUTHOR]

We perform a joint measurement of terahertz waves and high-harmonics generated from argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase delay between the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics. [ABSTRACT FROM AUTHOR]

In this work, we characterize the transmission properties of the focusing-laser-induced filament by using terahertz (THz) time domain spectroscopy. Significant resonance absorption of the THz wave is identified, which is attributed to the dynamic screening of the ionized electrons. The polarization and intensity of the filament-generated pulse have been varied to study their influences on the resonance absorption. Our results suggest that the electron density of the filament can be determined by fitting the phase shifts and absorption properties around the absorption. This method provides not only an alternative to the plasma diagnostics with plasma frequency at the THz range, but also a supplement to the existing generation theory of THz waves from plasma. [ABSTRACT FROM AUTHOR]

Terahertz radiation from tunneling ionization of gaseous atoms and molecules in the two-color laser fields with various polarizations has been investigated. We experimentally demonstrate that the efficiency of terahertz emission in the circularly polarized laser fields with the same helicity is 5 times higher than that with linearly polarized two-color femtosecond pulses in high laser intensity. By solving time-dependent Schrödinger equation, this enhancement is well explained based on the analysis of electron tunneling ionization and subsequent dynamics. [ABSTRACT FROM AUTHOR]

We report the synchronized measurements of terahertz wave generation and high-harmonic generation from aligned nitrogen molecules in dual-color laser fields. Both yields are found to be alignment dependent, showing the importance of molecular structures in the generation processes. By calibrating the angular ionization rates with the terahertz yields, we present a new way of retrieving the angular differential photoionization cross section (PICS) from the harmonic signals which avoids specific model calculations or separate measurements of the alignment-dependent ionization rates. The measured PICS is found to be consistent with theoretical predications, although some discrepancies exist. This all-optical method provides a new alternative for investigating molecular structures. [ABSTRACT FROM AUTHOR]

Electro-optic effects of PbZr0.52Ti0.48O3 (PZT) and BaTiO3 (BTO) ferroelectric thin films in the terahertz frequency range are studied with high-sensitive terahertz time-domain spectroscopy. A linear response of PZT film with the linear electro-optic coefficient rc  = 6.73 × 10−11 m/V and a quadratic response of BTO film with the second-order electro-optic coefficient Rc  = 1.42 × 10−17 m2/V2 are observed at the frequency of 1 terahertz under the applied static electric field less than 80 kV/cm. The calculation of rc and Rc based on the Landau-Devonshire free energy theory explains the different electro-optic effects of PZT and BTO well. [ABSTRACT FROM AUTHOR]

Isolated attosecond pulses with a duration of 88 as are generated in the spectral range of 29–72 eV using double optical gating technique. The gate width is set to be shorter than half the optical cycle to avoid carrier envelop phase stabilization of the 4.2 fs driving laser pulses centered at 800 nm. The attosecond pulse duration is measured with the technique of frequency resolved optical gating for complete reconstruction of attosecond bursts. [ABSTRACT FROM AUTHOR]

We present the experimental and theoretical details of our recent published letter Huang et al (2015 Phys. Rev. Lett.115 123002) on synchronized high-harmonic and terahertz-wave spectroscopy (HATS) from nonadiabatically aligned nitrogen molecules in dual-color laser fields. By associating alignment-angle dependent terahertz wave generation (TWG) with high harmonic generation (HHG), the angular differential photoionization cross section (PICS) for molecules can be reconstructed. The angles at which the PICS’s minima are located show great convergence between the theoretical predictions and the experimentally deduced results when choosing a suitable internuclear distance. We also show the optimal relative phase between the dual-color laser fields for TWG does not change with the alignment angle at a precision of about 50 attoseconds. This all-optical method provides an alternative for investigating molecular structures and dynamics. [ABSTRACT FROM AUTHOR]