An Off-Axis Differential Method for Improvement of a Femtosecond Laser Differential Chromatic Confocal Probe

This paper presents an off-axis differential method for the improvement of a femtosecond laser differential chromatic confocal probe having a dual-detector configuration. In the proposed off-axis differential method employing a pair of single-mode fiber detectors, a major modification is made to the conventional differential setup in such a way that the fiber detector in the reference detector is located at the focal plane of a collecting lens but with a certain amount of off-axis detector shift, while the fiber detector in the measurement detector is located on the rear focal plane without the off-axis detector shift; this setup is different from the conventional one where the difference between the two confocal detectors is provided by giving a defocus to one of the fiber detectors. The newly proposed off-axis differential method enables the differential chromatic confocal setup to obtain the normalized chromatic confocal output with a better signal-to-noise ratio and approaches a Z-directional measurement range of approximately 46 μm, as well as a measurement resolution of 20 nm, while simplifying the optical alignments in the differential chromatic confocal setup, as well as the signal processing through eliminating the complicated arithmetic operations in the determination of the peak wavelength. Numerical calculations based on a theoretical equation and experiments are carried out to verify the feasibility of the proposed off-axis differential method for the differential chromatic confocal probe with a mode-locked femtosecond laser source.

Multiscale UAS Radiation Mapping Within the Chernobyl Exclusion Zone (CEZ).

<p>The accident occurring at the Chernobyl Nuclear Power Plant (ChNPP) in 1986 remains the most prolific in the history of civil nuclear power generation. In the decades since the incident, remote characterisation technologies have advanced significantly in their capabilities. Current knowledge of <sup>137</sup>Cs distribution within the CEZ is provided by extensive ground sampling investigations conducted at the turn of the millennium. Whilst this method has a high degree of accuracy, it does not allow for local-scale variation to be resolved. Furthermore, the physical collection of samples is labour intensive and suffers from inconsistent sampling densities throughout the extent of the surveyed area. Inconsistent data spacing occurs due to time and resource constraints, terrain difficulties and exposure risk from the physical radiation hazard, which all relate to using humans to collect the samples. Airborne monitoring using UASs is a solution to overcoming the drawbacks experienced from ground-based sampling, albeit coming at a loss of absolute measurement accuracy. This method allows for the creation of a consistent network of sampling points at a high resolution, independent from terrain conditions and without exposing the operators to potentially harmful doses of radiation.</p><p>This work presents a comprehensive UAS radiation mapping investigation aiming to evaluate the <sup>137</sup>Cs distribution within the CEZ using two distinct radiation mapping UASs to conduct surveys at different spatial resolutions. The first comprises of a lightweight (8 kg) fixed-wing UAS equipped with a dual detector payload (2 x 32.8 cm<sup>3</sup> CsI[Tl] detectors) to map over large areas at a relatively high forward velocity (14 – 18 m s<sup>-1</sup>) and a  medium-low spatial resolution (20 – 60 m pixel<sup>-1</sup>). A multi-rotor aerial vehicle is preferred for the second system, which was used to monitor smaller areas of interest (highlighted by the fixed-wing survey), at a higher spatial resolution (3 – 10 m pixel<sup>-1</sup>) and a much lower forward velocity of approximately 3 m s<sup>-1</sup>. This system was heavier than the fixed-wing variant, weighing approximately 11 kg.</p><p>In the seven days of active fieldwork in the CEZ, more than 650 km of combined flight distance was covered by the two systems, characterising a total area of approximately 15 km<sup>2</sup>. Through a series of carefully calibrated processing algorithms, both the <sup>137</sup>Cs activity (in kBq m<sup>-2</sup>) and the dose-rate (µSv hr<sup>-1</sup>) resulting from <sup>137</sup>Cs deposition at one metre above ground level are evaluated. Error propagation through this procedure indicates a base-rate error of 11.5-13.9% in the estimation of <sup>137</sup>Cs activity from the air, while the basal error for the dose-rate estimation is lower at approximately 5.5 – 6.2%. Minimum detectable activity (MDA) was calculated as 98.1 ± 0.4 kBq m<sup>-2 </sup>for the fixed-wing system operating at 40 - 60 m altitude and 33.5 ± 0.9 kBq m<sup>-2</sup> for the multi-rotor at 8 - 20 m altitude.</p>

Molecular Breast Imaging in Patients with Suspicious Calcifications

Objective We evaluated the accuracy of molecular breast imaging (MBI)—a nuclear medicine technique that employs dedicated dual-detector, cadmium zinc telluride gamma cameras to image the functional uptake of a radiopharmaceutical (typically Tc-99m sestamibi) in the breast—in patients with suspicious calcifications on mammography. Methods Women scheduled for stereotactic biopsy of calcifications detected on 2D digital mammography were prospectively enrolled to undergo MBI before biopsy. Molecular breast imaging was performed with injection of Tc-99m sestamibi and a dual-detector, cadmium zinc telluride gamma camera. Positive findings on either modality were biopsied. High-risk and malignant biopsy findings were excised. Results In 71 participants, 76 areas of calcifications were recommended for biopsy after mammography, and 24 (32%) were malignant, including 20 cases of ductal carcinoma in situ (DCIS) and 4 cases of invasive ductal cancer. Prebiopsy MBI was positive in 17 of the 76 (22%) calcifications, including 10 of 20 (50%) DCISs and 2 of 4 (50%) invasive cancers. The median pathologic size for MBI–positive cancers was 1.5 cm (range 0.5–3.2 cm) compared with 0.9 cm (range 0.1–2.0 cm) for MBI–negative cancers (P = 0.09). Non-mass uptake on MBI led to additional biopsies of 6 sites in 6 patients, and 2 of 6 (33%) MBI–detected incidental lesions showed malignancy; both DCIS contralateral to the mammographically detected calcifications. The overall per-lesion positive and negative predictive values of MBI in this prebiopsy setting were 61% (14 of 23) and 80% (47 of 59), respectively. Conclusion Molecular breast imaging has insufficient negative predictive value to identify calcifications in which biopsy could be avoided. However, among women presenting for biopsy of suspicious calcifications, MBI revealed additional sites of mammographically occult breast cancer. To avoid biopsy of suspicious calcifications on mammography, negative findings on MBI should not be used.

Effect of Pointing Error on BER Performance of a Multi-wavelength OCDMA FSO System with SIK Dual Detector Receiver

A novel analytical approach is presented to evaluate the bit error rate (BER) performance of a multi-wavelength optical code division multiple access (MW-OCDMA) free space optical (FSO) system using optical domain encoder and sequence inverse keying (SIK) balanced photodetector direct detection receiver taking the effect of pointing errors into considerations. The analysis is carried out to find the expression for the signal, multi-access interference (MAI) and crosstalk at the output of the SIK receiver in presence of pointing error. The BER performance results are evaluated for different values of standard deviation of pointing error, code length, number of simultaneous user and other system parameters. It is found that, MW-OCDMA system offers improved BER performance over single wavelength OCDMA FSO system. However, the performance of an MW-OCDMA system is degraded due to the effect of pointing error between the laser transmitter and optical receiver and the system suffers significant power penalty at a given BER of 10−9. The penalty is found to be 11.0 dB, 24.0 dB and 30 dB for jitter standard deviation of 1.3, 1.8 and 2.5 respectively when code length is 512 and number of user is 8 for number of wavelength 8. Further, the penalty can be greatly reduced by increasing the code length for a given number of user and number of wavelength.