Band 92, Heft 1-2

The radio-frequency (RF) transmit power deposition in tissue during magnetic resonance imaging (MRI) at ultra-high fields, i.e. B 0 ≥ 7 T, is a major challenge for pulse sequences requesting large flip angles. The absorbed RF energy can pose safety risk to patients as it is rising temperature in the tissue. The temperature can be accessed using MRI itself via the proton-resonance frequency (PRF) shift technique, which at low B 0 has been shown a valid MR thermometry method. In this paper, we explore the applicability of the PRF method to the assessment of local temperature in 7 T MRI procedures. To this end, we built a phantom filled with a material presenting electrical conductivity and permittivity close to muscle tissue. Tubes filled with oil were placed nearby the phantom to observe the time dependent B 0 drift. MRI phase images were acquired by gradient-echo (GRE) sequences at time points between spin-echo sequences with large flip angle allowing for a continuous assessment of the temperature during a 114 min RF-heating experiment. All acquired phase images were post-processed with attention to the time dependent instability of B 0 , and, in addition, to potential spatial and temporal phase discontinuities, known as wraps. In this paper, we present a strategy to analyze and to unfold these phase wraps for large measurement fields and long acquisition times. It is shown that the PRF shift method is beneficial for the assessment of temperature at 7 T MRI. The temperature maps for axial and coronal planes display a temperature increase of approximately 3.5 °C during the time of the RF-heating experiment. Overall it is shown that B 0 -drift correction and, importantly, the spatio-temporal unwrapping are an indispensable part of post-processing.

Drag is a key criterion in assessing the quality of thermally cut sheet metal edges, which is critical to the reliability of the final product. The evaluation of drag has been described qualitatively and quantitatively, but the scientific literature lacks a methodical description of algorithmic tracking of the drag lines themselves. This absence of a standardized approach has hindered the objective determination of drag. With recent advances in the field towards automated quality assessment aimed at autonomous adaptation of process parameters, the need for consistent, fast and reliable assessment of drag lines has become apparent. To address this gap, this study introduces an innovative drag line tracking algorithm, inspired by the behavior of fluid flowing towards the lowest points, to compute a generalized drag line for an edge with a homogeneous cutting pattern. The algorithm utilizes the height data of the measured cut edges as a data base for the assessment of the drag lines. The results indicate that the drag lines identified by the algorithm are not only subjectively accurate, but also show a strong correlation with human-annotated drag lines across several metrics. This work lays the foundation for the objective evaluation of drag by not only describing an algorithm for the consistent determination of drag lines, but also by presenting a tool for human annotation and suitable customized metrics. As a result, it contributes significantly to the comprehensive evaluation of edge quality and represents a step forward in the automatic optimization of process parameters and the improvement of cutting edge quality.

Zusammenfasung Richtige und zuverlässige Messungen sind eine wichtige Voraussetzung für eine qualitativ hochwertige Industrieproduktion. Ein wichtiges Qualitätsmerkmal einer Messung ist deren Messunsicherheit. Erst mit der Angabe der Messunsicherheit kann die Qualität eines Messwertes beurteilt werden, was eine wesentliche Voraussetzung bei vielen Entscheidungen im Produktionsprozess und in der Kunden – Lieferanten Beziehung ist. Die Ermittlung von prüfmerkmalbezogenen Messunsicherheiten ist sehr aufwendig und bedarf meist einer großen firmeninternen Expertise oder muss durch extern beauftragte Dienstleister durchgeführt werden. In diesem Beitrag wird eine neu entwickelte Methode vorgestellt, mit der Anwender von Koordinatenmessgeräten (KMG) ohne besondere Vorkenntnisse die Messunsicherheit der Prüfmerkmale ihrer Messprozesse ermitteln können. Nach einer kurzen Beschreibung der notwendigen Grundlagen wird ein Einblick in die neuartige Methode der Unsicherheitsermittlung in der Koordinatenmesstechnik gegeben, die jetzt automatisiert und damit praxisgerecht erfolgt. Sie basiert auf der Verwendung von Grenzwerten der Gerätespezifikation unter Nutzung von Expertenwissen aus zahlreichen durch ein Kalibrierlaboratorium, das von der Deutschen Akkreditierungsstelle (DAkkS) für die Berechnung der Messunsicherheit von Koordinatenmessungen akkreditiert ist, durchgeführten Kalibriermessungen an KMG. Hiermit ist die Grundlage dafür gelegt, dass die eigentlich notwendige Angabe von Messunsicherheiten auch bei komplexen Anwendungen mit Koordinatenmessungen Eingang in die industrielle Qualitätssicherung findet.

This paper presents a measurement method for characterizing the frequency response of an optical microphone system using a purely optical approach. The use of optical methods allows to precisely determine the frequency response of the device from infra-sound up to 100 kHz in a single measurement, without the need of a reference microphone. The presented method relies on the inherently flat frequency characteristics of an optical cavity, allowing the assignment of any frequency-dependent behavior to secondary sources, such as the signal conditioning and data acquisition unit. The frequency characteristic was found to be strongly dependent on the settings of the internal amplifiers and high-pass filters, indicating the necessity of a calibration procedure if a flat frequency response is required.

Optical instruments are used in a broad range of applications in different fields of research and industry like microscopy, material science, metrology and fabrication. There, the optical adjustment of laser beams, optical rays and optical axes to a certain position is crucial for the correct function of the overall system. Often, multiple axes have to be adjusted, which requires the monitoring of multiple rays, preferably simultaneously. In this paper, a method for the spatial localisation of multiple laser beams is presented and demonstrated for an application in precision dimensional metrology. There, the position of seven spatially distributed laser beams can be detected with an uncertainty of <10 μm, enhancing the accuracy of the overall system. The underlying method is flexible in its approach and can be adapted to other optical systems.