Comparison of two region-of-interest placement methods for histogram analysis of apparent diffusion coefficient maps for glioma grading.

Objectives: We assessed the value of histogram analysis (HA) of apparent diffusion coefficient (ADC) maps for grading low-grade (LGG) and high-grade (HGG) gliomas. Methods: We compared the diagnostic performance of two region-of-interest (ROI) placement methods (ROI 1: the entire tumor; ROI 2: the tumor excluding cystic and necrotic portions). We retrospectively evaluated 54 patients with supratentorial gliomas (18 LGG and 36 HGG). All subjects underwent standard 3T contrast-enhanced magnetic resonance imaging. Histogram parameters of ADC maps calculated with the two segmentation methods comprised mean, median, maxi-mum, minimum, kurtosis, skewness, entropy, standard deviation (sd), mean of positive pixels (mpp), uniformity of positive pixels, and their ratios (r) between lesion and normal white matter. They were compared using the independent t-test, chi-square test, or Mann-Whitney U test. For statistically significant results, receiver operating characteristic curves were constructed, and the optimal cutoff value, sensitivity, and specificity were determined by maximizing Youden's index. Results: The ROI 1 method resulted in significantly higher rADC mean, rADC median, and rADC mpp for LGG than for HGG; these parameters had value for predicting the histological glioma grade with a cutoff (sensitivity, specificity) of 1.88 (77.8%, 61.1%), 2.25 (44.4%, 97.2%), and 1.88 (77.8%, 63.9%), respectively. The ROI 2 method resulted in significantly higher ADC mean, ADC median, ADC mpp, ADC sd, ADC max, rADC median, rADC mpp, rADC mean, rADC sd, and rADC max for LGG than for HGG, while skewness was lower for LGG than for HGG (0.27 [0.98] vs 0.91 [0.81], p = 0.014). In ROI 2, ADC median, ADC mpp, ADC mean, rADC median, rADC mpp, and rADC mean performed well in differentiating glioma grade with cutoffs (sensitivity, specificity) of 1.28 (77.8%, 88.9%), 1.28 (77.8%, 88.9%), 1.25 (77.8%, 91.7%), 1.81 (83.3%, 91.7%), 1.74 (83.3%, 91.7%), and 1.81 (83.3%, 91.7%), respectively. Conclusions: HA parameters had value for grading gliomas. Ex-cluding cystic and necrotic portions of the tumor for measuring HA parameters was preferable to using the entire tumor as the ROI. In this segmentation, rADC median showed the highest performance in predicting histological glioma grade, followed by rADC mpp, rADC mean, ADC median, ADC mpp, and ADC mean.

Single-composition Al3+-singly doped ZnO phosphors for UV-pumped warm white light-emitting diode applications.

The development of full-visible-spectrum phosphors is essential for next-generation light-emitting devices with better light quality. Herein, we report on a novel broad-band-emitting phosphor based on single-composition Al-doped ZnO phosphors. Under the UV excitation of 325 nm, the ZnO : Al phosphor exhibits a full spectrum emission in the visible wavelength range from 400 to 800 nm with a CIE chromaticity coordinate of (0.42, 0.48), a quantum efficiency of 43%, a color rendering index (CRI) of 74, a correlated color temperature (CCT) value of 3873 K and an activation energy of 0.22 eV. A prototype of a UV-pumped warm WLED with a high CRI of 87 and a CCT of 4067 K has been achieved by using only this broad-band-emitting Al3+-doped ZnO phosphor. The obtained results indicate that the single-composition Al3+-singly doped warm white emitting phosphor is a promising candidate for UV-pump warm white light-emitting diodes.

Generation of tunable subpicosecond pulses using low-Q dye cavities.

The design and operation characteristics of a low-Q cavity dye laser chain pumped by a single laser (seeded Q-switched Nd:YAG) for generating high-power tunable subpicosecond pulses are presented. Two low-Q short dye cavities in cascade pumped well above threshold followed by extracavity pulse shaping in a highly saturated absorber and amplifiers lead to stable generation of single 500-fs pulses, i.e., a pulse-shortening factor > 10(4) (from a smooth 6-ns pump pulse). Output pulse energies of 500 microJ (1-GW peak power) are produced from 40-mJ pump energy and used to generate high-power tunable subpicosecond pulses from 450 to 700 nm by supercontinuum generation, spectral selection, and amplification in dye amplifiers pumped by the same Nd:YAG laser. The spectral and time processes involved in these pulse-shortening methods are discussed with a rate-equation model.