Objectives The purposes of this study were to evaluate various physiological fluorodeoxyglucose (FDG) accumulations in the head and neck and to compare those with tumor (pathological) FDG accumulation. Methods One hundred and twelve patients with head and neck carcinomas were studied. PET/computed tomography examinations were performed 1 h after intravenous injection of fluorine-18-labeled FDG. The tumor and the physiological FDG accumulations were identified with PET/computed tomography images, and the maximum of the standardized uptake value (SUV_max) was calculated. Results Physiological FDG accumulation was observed in tonsil, extraocular muscle, masticatory muscle, vocal cord, and the major salivary glands: parotid, submandibular, and sublingual gland. The accumulation in tonsil, extraocular muscle, and sublingual gland showed relatively high SUV_max. The tumor FDG accumulation was significantly higher than any physiological FDG accumulation. The optimal cut-off values of SUV_max for differentiating physiological FDG accumulation from pathological FDG accumulation were 4.0 for parotid gland, 4.5 for submandibular gland, 5.5 for sublingual gland, 8.0 for tonsil, and 10.0 for extraocular muscle. The right-to-left ratio of SUV_max was less than 1.5 in any physiological accumulation. Conclusion Tonsil, extraocular muscle, and sublingual gland showed relatively high FDG accumulation, which was sometimes similar to tumor accumulation. The right-to-left ratio of SUV_max was considered useful in differentiating tumor from physiological accumulation, and the presence of tumor might be highly suspected in cases with a ratio of 1.5 or more.

Electric field measurement based on electric-field-induced second-harmonic generation (E-FISHG) of gas molecules is a promising method that enables noninvasive field measurement in gases. Although the probing laser beam is focused on the target area by a lens, the signal detected by the E-FISHG method is affected by the electric field along the probing laser path. The influencing path spans many tens of times the Rayleigh length of the front and rear of the focused spot. The E-FISHG signal has been frequently calibrated under uniform electric fields. However, this can yield a significantly incorrect calibrated value if the difference between the electric-field profiles in the measurement and calibration is not considered. In this paper, we propose a method to calibrate and furthermore restore the electric-field profile along a probing optical path by measuring a series of E-FISHG signals by changing the focusing spot position. The electric-field profile along the probing laser path is successfully restored from the measured E-FISHG signal sequence, which is verified by an experiment.

To quantitatively evaluate diffusion and perfusion status of lateral pterygoid muscle (LPM) in patients with temporomandibular joint disorder (TMD) by intravoxel incoherent motion (IVIM) imaging and to correlate with findings on temporomandibular joints (TMJs) by conventional MRI. 42 patients with TMD underwent MRI. To assess IVIM parameters, diffusion-weighted imaging was obtained by spin-echo-based single-shot echoplanar imaging. Regions of interest were created on all diffusion-weighted images of the superior belly of the lateral pterygoid (SLP) and inferior belly of the lateral pterygoid (ILP) at b-values 0–500 s mm⁻². Then, IVIM parameters, diffusion (D) and perfusion (f) were calculated using biexponential fittings. The correlation of these values with conventional MRI findings on TMJs was investigated. For SLP, the f parameter in TMJs with anterior disc displacement without reduction was significantly higher than that in normal ones (p = 0.015). It was also significantly higher in TMJs with joint effusion than in those without (p = 0.016). On the other hand, for both SLP and ILP, the D parameter significantly increased in TMJs with osteoarthritis compared with those without (p = 0.015 and p = 0.022, respectively). Pathological changes of LPM in patients with TMD may be quantitatively evaluated by IVIM parameters.

The electric field induced second harmonic generation (E-FISH) technique has been widely utilized for the electric field measurement of atmospheric-pressure nonthermal plasmas. However, the measurement accuracy has not been quantified. Further, the E-FISH signal generation that is necessary to the evaluation of the measurement accuracy has been formulated only for the probe laser beam focused by a spherical lens and not for the cylindrical lens. Here, the E-FISH method utilizing the focusing cylindrical lens was studied for accurate one-dimensional (1D) electric field measurement of the primary-to-secondary transition phase of a single-filament positive streamer discharge generated in atmospheric-pressure air. A combination of numerical analysis and the E-FISH signal measurement was used to establish the radial distribution of the electric field vectors and the accompanying measurement accuracy. The E-FISH methodology captured a distinct evolution in the 1D electric field varying over timescales of ∼ 1 ns and length scales of 100 µm. At the instant when the primary streamer arrived at the cathode, the electric field at 3 mm above the cathode surface was found to be as high as 225 Td, while the field at 10 mm above the cathode surface was as low as 5 Td. At the final stage of the primary-to-secondary transition phase completed in 3 ns from the primary streamer arrival at the cathode, the electric field at 3 mm above the cathode was found to be lower than that observed at 10 mm from the cathode; this finding is consistent with predictions made based on a previous model describing the initiation of the secondary streamer discharge and previously published electron density measurement.

We investigated the performance of electric-field-induced second-harmonic generation (E-FISHG) by spectroscopic measurement using high-intensity femtosecond laser pulses. The second-harmonic intensity increased quadratically versus the applied electric field, as expected from the theory, up to 15 kV/cm with the laser energy up to 2.5 mJ, which is times higher than the observable optical breakdown threshold. In addition, when the laser energy was 2.8 mJ, times signal intensity at 0.23 mJ was obtained. These results suggest that the electric-field measurement by E-FISHG with high-intensity second harmonics is expected by using high-intensity laser pulses above the observable optical breakdown threshold. Spectroscopic measurement shows no E-FISHG of white light generated by self-phase modulation in laser-induced filament.

Electric-field measurement based on the electric-field-induced second-harmonic generation (E-FISHG) method is a promising tool for a noncontact field measurement in plasmas and gases. For the E-FISHG method, a probing laser beam is focused at the measurement target by a lens, and the signals integrated along the laser path are acquired. Although the signal is frequently calibrated under uniform electric fields, the yielded value is erroneous if one does not consider the difference in the electric-field-profiles between the calibration and measurement. In this paper, we review the calibration and measurement targets of relevant studies, assess the error in the conventional method for the streamer discharge measurement, and give guidelines on which calibration approach to use depending on the electric field profile to be measured. Our approach uses cylindrical-to-cylindrical electrodes and multipoint measurement corresponding to the target length along the optical path, gas, and pressure.