Full-spectrum Mode Research Articles

Portable fizzy extraction ion-mobility spectrometry system

Fizzy extraction (FE) is a technique that utilizes effervescence phenomenon to extract volatile organic compounds (VOCs) from liquid matrices for subsequent analysis. To induce effervescence, a liquid sample is first pressurized (at ∼ 150 kPa) with an extractant gas (here, nitrogen), and then rapidly depressurized. In this work, we combine an in-house-built FE system with a commercial ion-mobility spectrometry (IMS) module in order to develop a portable analytical platform for in-situ analysis of VOCs in liquid samples. The size and shape of the FE-IMS platform are similar to those of a typical airline catering trolley. Its operation is enabled by several electronic and electromechanical components (a single-board computer, two microcontroller boards, a relay board, six DC-DC converters, a pressure regulator, a solenoid valve, and a pinch valve). The platform can carry out the extraction procedure as well as acquire, process, and transmit the data to a cloud-storage service. A custom-designed graphical user interface allows the user to select one of the available operation modes: full spectrum mode, ion current profile mode, and cleaning mode. The interface also allows one to follow the analysis progress, display the final result, and upload it to the Internet cloud. The platform has been characterized using three standards: ethyl acetate, ethyl propanoate, and butanone; and their limits of detection are 4.51 × 10−8 M, 2.74 × 10−8 M, and 1.26 × 10−7 M, respectively. Furthermore, its ability to analyze real samples (alcoholic and non-alcoholic beverages) has been demonstrated.

A neural network-based method for spectral distortion correction in photon counting x-ray CT

Spectral CT using a photon counting x-ray detector (PCXD) shows great potential for measuring material composition based on energy dependent x-ray attenuation. Spectral CT is especially suited for imaging with K-edge contrast agents to address the otherwise limited contrast in soft tissues. We have developed a micro-CT system based on a PCXD. This system enables both 4 energy bins acquisition, as well as full-spectrum mode in which the energy thresholds of the PCXD are swept to sample the full energy spectrum for each detector element and projection angle. Measurements provided by the PCXD, however, are distorted due to undesirable physical effects in the detector and can be very noisy due to photon starvation in narrow energy bins. To address spectral distortions, we propose and demonstrate a novel artificial neural network (ANN)-based spectral distortion correction mechanism, which learns to undo the distortion in spectral CT, resulting in improved material decomposition accuracy. To address noise, post-reconstruction denoising based on bilateral filtration, which jointly enforces intensity gradient sparsity between spectral samples, is used to further improve the robustness of ANN training and material decomposition accuracy.Our ANN-based distortion correction method is calibrated using 3D-printed phantoms and a model of our spectral CT system. To enable realistic simulations and validation of our method, we first modeled the spectral distortions using experimental data acquired from 109Cd and 133Ba radioactive sources measured with our PCXD. Next, we trained an ANN to learn the relationship between the distorted spectral CT projections and the ideal, distortion-free projections in a calibration step. This required knowledge of the ground truth, distortion-free spectral CT projections, which were obtained by simulating a spectral CT scan of the digital version of a 3D-printed phantom. Once the training was completed, the trained ANN was used to perform distortion correction on any subsequent scans of the same system with the same parameters. We used joint bilateral filtration to perform noise reduction by jointly enforcing intensity gradient sparsity between the reconstructed images for each energy bin. Following reconstruction and denoising, the CT data was spectrally decomposed using the photoelectric effect, Compton scattering, and a K-edge material (i.e. iodine). The ANN-based distortion correction approach was tested using both simulations and experimental data acquired in phantoms and a mouse with our PCXD-based micro-CT system for 4 bins and full-spectrum acquisition modes. The iodine detectability and decomposition accuracy were assessed using the contrast-to-noise ratio and relative error in iodine concentration estimation metrics in images with and without distortion correction.In simulation, the material decomposition accuracy in the reconstructed data was vastly improved following distortion correction and denoising, with 50% and 20% reductions in material concentration measurement error in full-spectrum and 4 energy bins cases, respectively. Overall, experimental data confirms that full-spectrum mode provides superior results to 4-energy mode when the distortion corrections are applied. The material decomposition accuracy in the reconstructed data was vastly improved following distortion correction and denoising, with as much as a 41% reduction in material concentration measurement error for full-spectrum mode, while also bringing the iodine detectability to 4–6 mg ml−1. Distortion correction also improved the 4 bins mode data, but to a lesser extent.The results demonstrate the experimental feasibility and potential advantages of ANN-based distortion correction and joint bilateral filtration-based denoising for accurate K-edge imaging with a PCXD. Given the computational efficiency with which the ANN can be applied to projection data, the proposed scheme can be readily integrated into existing CT reconstruction pipelines.

A Foveon Sensor/Green-Pass Filter Technique for Direct Exposure of Traditional False Color Images

A direct exposure technique to simulate the vegetation red-magenta hues associated with the traditional Kodak Ektachrome Professional Infrared EIR film is proposed. The method uses the Foveon sensor in full spectrum mode as found in Sigma cameras in combination with green-pass filters to reproduce the red-magenta hues of healthy vegetation without resorting to multi-exposures or channel swaps as is the current norm in single sensor cameras. An array of commercially available green-pass filters are analyzed via spectrophotmetric, densitometric and colorimetric measurements. A calibration technique using color-compensating filters is presented such that any green-pass filter will transmit green wavelengths to a set norm and ensure repeatability. A color model for the Foveon/green-pass filter is developed using quantum efficiencies to explain the color effects observed. Color similarities in near-infrared, blue and black and differences in red and green compared with Kodak Ektachrome Infrared film are discussed. Aerial photography examples are discussed, and the technique is proposed as a more direct means of obtaining traditional false color infrared imagery for pictorial and scientific applications when using Foveon type commercially available digital cameras.

Superimposition of a Magnetic Field around an Ion Guide for Electron Ionization Time-of-Flight Mass Spectrometry

A new electron ionization source was developed for orthogonal acceleration time-of-flight mass spectrometry (TOFMS) based on the superimposition of a magnetic field around a radio frequency-only (rf-only) ion guide. The cylindrically symmetric magnetic field compresses the electron beam from the electron source into a long narrow volume along the ion guide axis. The magnetic field also helps to maintain a narrow energy distribution of electrons that penetrate the full length of the ion guide despite the influence of the radial rf field. Ionization occurs inside the ion guide with improved efficiency resulting from efficient use of electrons, prolonged interaction time, and nontraditionally large ionization volume. At the same time, the rf field effectively focuses ions radially and confines them to the axis of the ion guide by collisional focusing, leading to high ion transmission efficiency. Furthermore, the source can also be operated in a trap-and-pulse mode to improve the ion sampling duty cycle of orthogonal acceleration TOFMS. To validate the design concept of this new ion source, a simple prototype using a single set of cylindrical rods was constructed and retrofitted to an orthogonal acceleration TOFMS. A significant increase in ion signal intensity was observed by operating the source in a pulsed ion extraction mode. Low detection limits (for example, 12 fg for toluene) were determined at 12.5 spectra s(-1) in the full spectrum mode.

Analysis of volatile organic compounds, using the purge and trap injector coupled to a gas chromatograph/ion-trap mass spectrometer: Review of the results in Dutch surface water of the Rhine, Meuse, Northern Delta Area and Westerscheldt, over the period 1992–1997

Volatile organic compounds are widely introduced into the Dutch aquatic environment. Liquid–liquid extraction and isolation by means of resins give poor recoveries for volatiles. In this study, a method has been developed to analyse these compounds with a purge and trap injection (PTI) coupled to a chromatograph/ion trap mass spectrometer. Volatile compounds are “purged” from the sample by carrier gas flow and transported through a condenser to a cooled trap. The bulk of liquid matrix is condensed in the condenser, while volatile compounds are left unaffected. The compounds of interest are trapped at a low temperature, by liquid nitrogen in the cooled trap of fused silica. Injection takes place by flash heating of the trap. The detection limits of the volatile compounds are in the range of 0.001–0.04 μg l −1, in full spectrum mode. In this paper a review of the results in Dutch surface water of the Rhine, Meuse, Northern Delta Area and Westerscheldt, over the period 1992–1997, is presented. For calamities causing high levels of volatiles, the method is very useful. The compounds can be monitored over a certain period. In the Meuse, high levels of volatile organic compounds are observed. Diisopropyl ether at a maximum of 592 μg l −1.