Phantom assessment of three-dimensional geometric distortion of a dedicated wide-bore MR-simulator for radiotherapy

This study evaluated the machine-dependent three-dimensional geometric distortion images acquired from a 1.5T 700mm-wide bore MR-simulator based on a large geometric accuracy phantom. With the consideration of radiation therapy (RT) application requirements, every sequence was examined in various combinations of acquisition-orientations and receiver-bandwidths with console-integrated distortion correction enabled. Distortion was repeatedly measured over a six-month period. The distortion measured from the images acquired at the beginning of this period was employed to retrospectively correct the distortion in the subsequent acquisitions. Geometric distortion was analyzed within the largest field-of-view allowed. Six sequences were examined for comprehensive distortion analysis – VIBE, SPACE, TSE, FLASH, BLADE and PETRA. Based on optimal acquisition parameters, their diameter-sphere-volumes (DSVs) of CT-comparable geometric fidelity (where 1mm distortion was allowed) were 333.6mm, 315.1mm, 316.0mm, 318.9mm, 306.2mm and 314.5mm respectively. This was a significant increase from 254.0mm, 245.5mm, 228.9mm, 256.6mm, 230.8mm and 254.2mm DSVs respectively, when images were acquired using un-optimized parameters. The longitudinal stability of geometric distortion and the efficacy of retrospective correction of console-corrected images, based on prior distortion measurements, were inspected using VIBE and SPACE. The retrospectively corrected images achieved over 500mm DSVs with 1mm distortion allowed. The median distortion was below 1mm after retrospective correction, proving that obtaining prior distortion map for subsequent retrospective distortion correction is beneficial. The systematic evaluation of distortion using various combinations of sequence-type, acquisition-orientation and receiver-bandwidth in a six-month time span would be a valuable guideline for optimizing sequence for various RT applications.

Advanced Distortion Analysis of Heat Treated Rings*

The basic approach to interpret distortion as a system property is accepted in science and industry. The determination of significant factors and interactions on distortion in the overall production process of selected components represents a central point to identify relevant distortion mechanisms. In this context, a component specific distortion description is a major step to answer distortion problems. In the field of ball bearing engineering, roundness deviation of raceways is an important characteristic. But this parameter is not useful for distortion engineering because no information concerning ring shape is given. But in literature, roundness deviation can be separated in its respective forms like oval and triangle shape with harmonic analysis. In addition, this analysis can be used to specify an amplitude and a direction in the different shapes to describe distortion. In this article, harmonic analysis is used for advanced distortion analysis of tapered roller bearing. An analysis in graphical form is introduced, which illustrates both the amount and the direction of distortion.

Long-Term Efficacy, Visual Performance and Patient Reported Outcomes with a Trifocal Intraocular Lens: A Six-Year Follow-up

(1) Background: To evaluate the efficacy at 6 years postoperative after the implantation of a trifocal intraocular lens (IOL) AT Lisa Tri 839MP. The secondary objective was to evaluate the contrast sensitivity defocus curve (CSDC), light distortion analysis (LDA), and patient reported outcomes (PROs). (2) Methods: Sixty-two subjects participated in phone call interviews to collect data regarding a visual function questionnaire (VF-14), a patient reported spectacle independence questionnaire (PRSIQ), and questions related to satisfaction and decision to be implanted with the same IOL. Thirty-seven of these subjects were consecutively invited to a study visit for measurement of their visual acuity (VA), CSDC, and LDA. (3) Results: The mean monocular distance corrected VA was −0.05, 0.08, and 0.05 logMAR at far and distances of 67 cm and 40 cm, respectively. These VAs were significantly superior to those reported in previous literature (p < 0.05). The total area under the CSDC was 2.29 logCS/m−1 and the light distortion index 18.82%. The mean VF-14 score was 94.73, with 19.4% of subjects requiring spectacles occasionally for near distances, and 88.9% considering the decision of being operated again; (4) Conclusions: Long-term AT LISA Tri 839MP IOL efficacy results were equal or better than those reported 12 months postoperatively in previous studies. The spectacle independence and satisfaction rates were comparable to those reported in short-term studies.

Radiation Power Pattern Distortion Analysis Using MATLAB for MST Radar System

Most often, in MST radar system, a few number of transmitters are non-operational due to various factors, making the liner sub-arrays corresponding to these transmitters in effective. This results in the thinning of the aperture and deviation of the excitation from the specified Taylor distribution. The array pattern will be distorted due to this deviation, when compared to the reference pattern. This chapter gives a complete analysis to quantify the distortion in the radiation pattern due to Aperture thinning. MATLAB was extensively used to analyze the results. The results of the radiation pattern in both principal planed and for different azimuth angles with and without thinning/tilt are presented. Radiation pattern is viewed in both polar and rectangular (2-D and 3-D) forms. Conclusions on the results obtained are presented.