User-defined Region Research Articles

Control of mobile manipulators for power assist systems

In this article, we present a control method for mobile power assist systems. Most mobile power assist systems have a heavy mobile base for preventing easy tumbling, so the continual movement of the base during operations causes high energy consumption and gives a high risk of human injury. Furthermore, the slow dynamics of the base limits the frequency bandwidth of the whole system. We propose a cooperation control method of the mobile base and manipulator, which removes the unnecessary movement of the base. In our scheme, the mobile base does not move until the tip position of the manipulator deviates from a user-defined preferred operating region. When the tip position reaches the boundary of the preferred operating region, the operator can feel reflecting force caused by the virtual impedance, which pushes the manipulator's tip into the preferred operating region. And if the operator applies larger force than a threshold value of reflecting force, the base starts moving to recover the manipulator's initial configuration. Our scheme is implemented by assigning a virtual mass–damper–spring impedance to the manipulator's tip. The experimental results show the efficacy of the proposed control methods. © 2000 John Wiley & Sons, Inc.

Spatial extent of pigment epithelial detachments in age-related macular degeneration

Objective To quantify the spatial extent of pigment epithelial detachment (PED) associated with age-related macular degeneration (AMD) using a rapid, noninvasive method. Design Prospective, cross-sectional study. Participants The authors tested 32 eyes of 21 patients (13 women and 8 men) with AMD 56 to 91 years of age (mean = 72.8 years). The authors retested seven eyes of six patients. Intervention Three-dimensional imaging and quantification of PED were performed in each subject using confocal infrared imaging (790 nm) with a Topographic Scanning System (TopSS). The data consisted of a series of 32 images within a 3-mm-depth range requiring 0.9 second. Three-dimensional calculations were made from the series. Main outcome measure Height, diameter, area, volume, and slope of each PED were obtained with two calculation methods. The Ellipse Method used a graphics tool to draw elliptical borders circumscribing the region of interest in the image. The software automatically calculated the values for all parameters for the region inside the ellipse, with the retinal reference plane adjusted to match the height of the surrounding retina. The User-Defined Region Method differed in that the region of interest was drawn manually. Results PEDs were easily detected in all patients using the TopSS. Maximum height of all PEDs above the reference plane ranged from 0.204 to 1.818 mm (mean = 0.57 mm). The diameter was 0.501 to 5.151 mm (mean = 2.711 mm), area was 0.179 to 20.402 mm 2 (mean = 6.585 mm 2), and volume was 0.012 to 13.981 mm 3 (mean = 2.173 mm 3). Intraobserver variability was low, with correlations between first and second measurements for the first visit ranging from r = 0.906 to 0.997 for slope and diameter, respectively. Conclusions Three-dimensional analysis with the TopSS provides objective outcome measures not obtainable with typical clinical methods such as fundus photography and angiography. Height and volume are crucial in determining whether neovascularization is worsening or persistent after photocoagulation. More longitudinal data are needed to determine whether tomographic data reduce the need for angiography. Unique to scanning laser tomography, exudative features were imaged at different depths.

Studies of porphyrin‐containing specimens using an optical spectrometer connected to a confocal scanning laser microscope

A spectrometer has been developed for use with a confocal scanning laser microscope. With this unit, spectral information from a single point or a user-defined region within the microscope specimen can be recorded. A glass prism is used to disperse the spectral components of the recorded light over a linear CCD photodiode array with 256 elements. A regulated cooling unit keeps the detector at 277 K, thereby allowing integration times of up to 60 s. The spectral resolving power, lambda/delta lambda, ranges from 350 at lambda = 400 nm to 100 at lambda = 700 nm. Since the entrance aperture of the spectrometer has the same size as the detector pinhole used during normal confocal scanning, the three-dimensional spatial resolution is equivalent to that of normal confocal scanning. Light from the specimen is deflected to the spectrometer by a solenoid controlled mirror, allowing fast and easy switching between normal confocal scanning and spectrometer readings. With this equipment, studies of rodent liver specimens containing porphyrins have been made. The subcellular localization is of interest for the mechanisms of photodynamic therapy (PDT) of malignant tumours. Spectroscopic detection is necessary to distinguish the porphyrin signal from other fluorescent components in the specimen. Two different substances were administered to the tissue, Photofrin, a haematoporphyrin derivative (HPD) and delta-amino levulinic acid (ALA), a precursor to protoporphyrin IX and haem in the haem cycle. Both are substances under clinical trials for PDT of malignant tumours. Following administration of these compounds to the tissue, the potent photosensitizer and fluorescent compound Photofrin, or protoporphyrin IX, respectively, is accumulated.(ABSTRACT TRUNCATED AT 250 WORDS)