A Multiprocessing Scheme for PET Image Pre-Screening, Noise Reduction, Segmentation and Lesion Partitioning.

OBJECTIVE: Accurate segmentation and partitioning of lesions in PET images provide computer-aided procedures and doctors with parameters for tumour diagnosis, staging and prognosis. Currently, PET segmentation and lesion partitioning are manually measured by radiologists, which is time consuming and laborious, and tedious manual procedures might lead to inaccurate measurement results. Therefore, we designed a new automatic multiprocessing scheme for PET image pre-screening, noise reduction, segmentation and lesion partitioning in this study. PET image pre-screening can reduce the time cost of noise reduction, segmentation and lesion partitioning methods, and denoising can enhance both quantitative metrics and visual quality for better segmentation accuracy. For pre-screening, we propose a new differential activation filter (DAF) to screen the lesion images from whole-body scanning. For noise reduction, neural network inverse (NN inverse) as the inverse transformation of generalized Anscombe transformation (GAT), which does not depend on the distribution of residual noise, was presented to improve the SNR of images. For segmentation and lesion partitioning, definition density peak clustering (DDPC) was proposed to realize instance segmentation of lesion and normal tissue with unsupervised images, which helped reduce the cost of density calculation and completely deleted the cluster halo. The experimental results of clinical data demonstrate that our proposed methods have good results and better performance in noise reduction, segmentation and lesion partitioning compared with state-of-the-art methods.

Up/down conversion switching by adjusting the pulse width of red laser beams in LaF3:Tm³âº nanocrystals.

We demonstrate a versatile approach to fine-tuning the ratio of blue to near-infrared emission intensity from Tm3+ ions in LaF3 nanocrystals by adjusting the pulse widths and excitation wavelengths of red laser beams. The mechanism of color-tunable Tm3+ emission by pulse widths is explored, and a mechanism based on promoting the population of some luminescence levels and cutting off the population of others by suitably adjusting pulse duration is proposed. The underlying reason of excitation wavelength-modulated emission is ascribed to tuning absorption probability ratio of ground state absorption to excited state absorption by tuning the matching degree between the energies of excitation wavelength and ground (excited) state absorption of Tm3+. The ability of our LaF3:Tm3+ nanocrystals to emit variable emissions on demand in response to pulse width and excitation wavelength provides keen insights into controlling the population processes of luminescent levels and offers a versatile approach for tuning the spectral output.

[Direct determination of hyperfine structures and isotope shifts in the 6s5d 3D --> 6p5d 3F transitions of Ba I].

In the present experiments, a new method of atomic spectral measurement using states optical pre-selection was proposed and demonstrated, and the measurement of hyperfine-structures and isotope shifts in the 6s5d 3D --> 6p5d 3F transitions of Ba I was taken as an example. A 791 nm laser was used to excite the different hyperfine transitions 6s6s 1S0 --> 6s6p 3P1 for different isotopes of barium and different hyperfine energy-levels of 6s5d 3D2 for these isotopes were populated by the 6s6p 3P1 --> 6s5d 3D2 spontaneous radiations, then the corresponding fluorescence spectra of 6s5d 3D2 --> 6p5d 3F2 transitions excited by another 778 nm laser were recorded. Comparing of these spectra, 22 lines were recognized and the hyperfine-structure constants of 6s5d 3D2 and 6p5d 3F2 of 135Ba and 137Ba were evaluated consequently while the isotope shifts of these transitions were also determined.