Suitability of infrared spectroscopy for drug checking in harm reduction centres.

Drug checking is a service for people who use drugs that includes product analysis and an individual interview including results feedback and harm reduction counselling. It uses different analytical methods but few studies demonstrate their value in current practice. The main objective of this work is to compare the analytical performance of IR spectroscopy to laboratory reference method in the context of drug checking in a harm reduction centre. The secondary objectives are to carry out a description of the people who use drugs requesting a product analysis, and to compare the assumed compositions of products purchased with their real compositions. During 2018, all requests for drug testing analysis were included for on-site analysis by IR spectrometry in a harm reduction center and verified by the reference method (UPLC-HRMS) at Bordeaux University Hospital Center. Socioeconomic and product data were also collected. One hundred and thirty-six samples were collected. The results obtained with IR and UPLC-HRMS were compared. IR spectrometry results did not match with reference method in 8 % (n=11) of cases, corresponding to blotters, cannabis and some psychoactive substances present in mixture or in small quantities. Among the products collected, only 5.1 % (n=7) did not correspond to the declared product, either alone or with adulterants. The IR spectrometer allows a simple and rapid detection of at least one molecule, most often the one of interest. However, it is limited to powder and tablet type matrices and is not suitable for blotters, cannabis, mixed or low content substances for which high resolution mass spectrometry remains the reference method.

Effect of voxel size on the accuracy of 3D reconstructions with cone beam CT.

OBJECTIVES: The various types of cone beam CT (CBCT) differ in several technical characteristics, notably their spatial resolution, which is defined by the acquisition voxel size. However, data are still lacking on the effects of voxel size on the metric accuracy of three-dimensional (3D) reconstructions. This study was designed to assess the effect of isotropic voxel size on the 3D reconstruction accuracy and reproducibility of CBCT data. METHODS: The study sample comprised 70 teeth (from the Institut d'Anatomie Normale, Strasbourg, France). The teeth were scanned with a KODAK 9500 3D® CBCT (Carestream Health, Inc., Marne-la-Vallée, France), which has two voxel sizes: 200 µm (CBCT 200 µm group) and 300 µm (CBCT 300 µm group). These teeth had also been scanned with the KODAK 9000 3D® CBCT (Carestream Health, Inc.) (CBCT 76 µm group) and the SCANCO Medical micro-CT XtremeCT (SCANCO Medical, Brüttisellen, Switzerland) (micro-CT 41 µm group) considered as references. After semi-automatic segmentation with AMIRA® software (Visualization Sciences Group, Burlington, MA), tooth volumetric measurements were obtained. RESULTS: The Bland-Altman method showed no difference in tooth volumes despite a slight underestimation for the CBCT 200 µm and 300 µm groups compared with the two reference groups. The underestimation was statistically significant for the volumetric measurements of the CBCT 300 µm group relative to the two reference groups (Passing-Bablok method). CONCLUSIONS: CBCT is not only a tool that helps in diagnosis and detection but it has the complementary advantage of being a measuring instrument, the accuracy of which appears connected to the size of the voxels. Future applications of such measurements with CBCT are discussed.

Transport parameters for an ultrasonic pulsed wave propagating in a multiple scattering medium

A set of ultrasonic experimental methods was developed to characterize a multiple scattering medium in terms of l(s), l*, l(a), respectively, the elastic, transport, and absorption mean free paths and D the diffusion constant. Actually, these quantities are the key parameters for a wave propagating in a disordered medium. Although they are widely used in optics, they are less common in acoustics. The underlying model is based on the expansion of the average solution for the heterogeneous Green's function equation. To validate this theoretical approach, a sample made of randomly located steel rods was used as a prototype. Through time-resolved measurements of the transmitted amplitude, the difference between the ballistic and the coherent wave is highlighted. In varying the sample thickness, l(s) is determined, the coherent and diffusive regime are distinguished, and the transition from one to the other is followed. Furthermore, as a limit to a description of the average intensity based on the diffusion approximation, the existence of a coherent backscattering effect is shown. This latter gives a method to estimate D and l*. These quantities being determined, it becomes possible to infer l(a) using average time-resolved intensity measurements. Finally, some applications to coarse-grain stainless steels are discussed.

Acoustical imaging through a multiple scattering medium using a time-reversal mirror.

Acoustical imaging is based on the ability to focus an acoustic beam inside the zone of interest. This remains an issue through a high-order multiple scattering medium because the electronic delay lines that enable one to focus through a multiple scattering medium are a priori unknown. Using time-reversal principles, we show that images can be obtained through a very disordered medium. Surprisingly, the images are better than those obtained in a homogeneous medium with a classical imaging device.