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The influence of minimal misalignment on the repeatability of PET images examined by the repositioning of point sources
摘要： Objective: We aimed to evaluate the influence of the minimal misalignment of the hot spot on the repeatability of PET images using the repositioning of point sources. Methods: Point sources with an inner-diameter of 1 mm were made with 1μL of 18F solution. Seven point sources were placed on the x-axis in the field-of-view. For fixed position imaging, PET data were acquired for 10 min 5 times serially. For variable position imaging, PET data were acquired for 10 minutes each with the point sources placed at 0 mm, ±0.5 mm, and ±1.0 mm in the x-axis direction. The data were reconstructed using ordered-subsets expectation maximization (OSEM) and OSEM with point-spread function (OSEM+PSF) algorithms. The image matrix was 128×128, 200×200, 256×256, 400×400, and 512×512 pixels. The normalized maximum count (rMax), the variation of rMax (CVmax) and full width at half maximum (FWHM) were analyzed. Results: The hot spots on OSEM images far from the center became faint and broad, while those on the OSEM+PSF images became small and dense. Although the rMax was overestimated at the 5 cm position on OSEM image, those at other positions were overestimated on OSEM+PSF images with a matrix size of ≥256×256. The rMax showed a similar pattern in fixed and variable position images. The CVmax in fixed position OSEM images were <2%, irrespective of the matrix size. In contrast, the CVmax in variable position images were higher in comparison to fixed position images. The CVmax of the OSEM+PSF images were higher in comparison to OSEM images. The FWHM increased at positions far from the center on OSEM image, while that was stable at all positions on OSEM+PSF images. Conclusion: The repeatability of the small hot spot was affected by the minimal misalignment, especially on the OSEM+PSF images. Precise positioning is necessary if PET is to be used as a biomarker. Professions should recognize that the PSF correction deteriorates the repeatability of the small hot spot although it improves the spatial resolution of PET images.
关键词： repositioning,repeatability,point-spread function,PET/CT
更新于2025-09-19 17:15:36
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Lip Repositioning Surgery Using an Er,Cr:YSGG Laser: A Case Series
摘要： Excessive gingival display (EGD) is a common esthetic concern. Lip repositioning surgery (LRS) was introduced as one of the treatment options to manage EGD. LRS can be used for skeletally and/or muscularly induced EGD. The present case series applied LRS using an Er,Cr:YSGG laser to treat 24 patients with minor vertical maxillary overgrowth or a hypermobile lip. At 6 months, the gingival display had decreased by 3.79 ± 1.59 mm (mean ± standard deviation), and the visible lip body when smiling had increased by 1.23 ± 0.74 mm. A questionnaire revealed that the level of satisfaction with the smile increased among the patients and that they had a positive attitude toward Er,Cr:YSGG laser–assisted LRS.
关键词： Er,excessive gingival display,Lip repositioning surgery,Cr:YSGG laser,smile esthetics
更新于2025-09-19 17:13:59
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A Monolithic Gimbal Micro-Mirror Fabricated and Remotely Tuned with a Femtosecond Laser
摘要： With the advent of ultrafast lasers, new manufacturing techniques have come into existence. In micromachining, the use of femtosecond lasers not only offers the possibility for three-dimensional monolithic fabrication inside a single optically transparent material, but also a means for remotely, and arbitrarily, deforming substrates with nanometer resolution. Exploiting this principle and combining it with flexure design, we demonstrate a monolithic micro-mirror entirely made with a femtosecond laser and whose orientation is tuned in a non-contact manner by exposing some part of the device to low energy femtosecond pulses. Given the non-contact nature of the process, the alignment can be very precisely controlled with a resolution that is many orders of magnitude better than conventional techniques based on mechanical positioners.
关键词： femtosecond laser machining,tunable optics,repositioning,integrated optics,monolithic,micro-optics,non-contact,fused silica,flexures
更新于2025-09-12 10:27:22