Observation Images Research Articles

Reliability of T2-weighted signal intensity-based quantitative measurements and visual grading of lumbar disc degeneration on MRI.

Decrease in signal intensity (SI) of the nucleus pulposus (NP) on T2-weighted (T2W) images, a sign of disc degeneration (DD), is usually graded based on an observer's image interpretation. No gold standard for quantitative assessment of NP SI exists to date. To compare different quantitative methods and visual gradings of lumbar DD and to evaluate the ability of the quantitative methods to differentiate DD grades. The mean SI of 95 lumbar discs was measured from sagittal T2W images using three regions of interest (ROI): the whole disc, ellipsoid ROI on the NP, and targeted ROI on the most homogenous, brightest area of the NP. SI values were adjusted with cerebrospinal fluid (CSF) SI and compared with vertebral bone SI-adjusted values. DD was evaluated with Pfirrmann grading and visual grading of NP SI. Intra- and inter-observer agreements and relationships between measurements and visual gradings were assessed. Repeatability of all measurements was excellent. All measurements had a strong correlation with Pfirrmann grading and visual NP SI grading, and the CSF SI-adjusted values had a stronger correlation than the vertebral bone SI-adjusted values. The SI values obtained with the targeted ROI had the most significant differences between visual DD grades. Quantitative measurement of the NP SI provides a reliable method for evaluating lumbar DD. Targeted selection of the NP structures included in the measurement offers the best differentiation of DD grades. A reliable quantitative method for DD evaluation is needed for the development of machine-learning-based DD classification.

Spinor-Based Attitude Determination with Star Sensor Considering Depth

A star sensor is a high-precision satellite attitude measurement device. Since its observation information has only two-dimensional direction vectors, when a star sensor is used for attitude determination the dimension of the observation information is less than the number of attitude angles determined, so mainstream algorithms usually only guarantee the accuracy of the pitch angle and the roll angle. In view of the lack of depth information in the observation's imaging geometric condition, this article proposes a spinor-based attitude determination model, which describes a straight line passing through two stars with the spinor and maps the depth information of the straight line with the pitch, to establish an imaging geometry model of the spinor coplanar condition. Experiments show that the yaw-angle attitude accuracy of the method is an order of magnitude better than that of mainstream algorithms, and the accuracy of the three attitude angles reaches the arc-second level.

Retardation magnification and the appearance of relativistic jets★

Thanks to the availability of high-resolution high-sensitivity telescopes such as the Very Large Array, the Hubble Space Telescope, and the Chandra X-ray Observatory, there is now a wealth of observational data on relativistic jets from active galactic nuclei (AGN) as well as galactic sources such as Black-Hole X-ray Binaries. Since the jet speeds cannot be constrained well from observations, but are generally believed to be relativistic, physical quantities inferred from observables are commonly expressed in terms of the unknown beaming parameters: the bulk Lorentz factor and the line-of-sight angle, usually in their combination as relativistic Doppler factor. This paper aims to resolve the discrepancies existing in the literature about such "de-beaming" of derived quantities, in particular regarding the minimum-energy magnetic field estimate. The discrepancies arise because the distinction is not normally made between the case of a fixed source observed with different beaming parameters and the case where the source projection on the sky is held fixed. The former is usually considered, but it is the latter that corresponds to interpreting actual jet observations. Furthermore, attention is drawn to the fact that apparent superluminal motion has a spatial corollary, here called "retardation magnification", which implies that most parts of a relativistic jet that are actually present in the observer's frame (a "world map" in relativity terminology) are in fact hidden on the observer's image (the "world picture" in general, or "supersnapshot" in the special case of astronomy).

A method of clustering observers with different visual characteristics

Evaluation of observer's image perception in medical images is important, and yet has not been performed because it is difficult to quantify visual characteristics. In the present study, we investigated the observer's image perception by clustering a group of 20 observers. Images of a contrast–detail (C–D) phantom, which had cylinders of 10 rows and 10 columns with different diameters and lengths, were acquired with an X-ray screen-film system with fixed exposure conditions. A group of 10 films were prepared for visual evaluations. Sixteen radiological technicians, three radiologists and one medical physicist participated in the observation test. All observers read the phantom radiographs on a transillumination image viewer with room lights off. The detectability was defined as the shortest length of the cylinders of which border the observers could recognize from the background, and was recorded using the number of columns. The detectability was calculated as the average of 10 readings for each observer, and plotted for different phantom diameter. The unweighted pair-group method using arithmetic averages (UPGMA) was adopted for clustering. The observers were clustered into two groups: one group selected objects with a demarcation from the vicinity, and the other group searched for the objects with their eyes constrained. This study showed a usefulness of the cluster method to select personnels with the similar perceptual predisposition when a C–D phantom was used in image quality control.