There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

비만아 부모의 돌봄 경험: q 방법론

A 32 times 32 retinal prosthesis is under development towards the goal of restoring vision in blind patients affected by retinitis pigmentosa and age-related macular degeneration. The system consists of three major functional components namely, microstimulator, wireless data telemetry, and wireless power telemetry. The system design and the circuit design of these blocks are governed by both biomedical and IC design constraints. This paper will provide a status update of the work and discuss the remaining challenges to be overcome to realize a fully integrated and miniaturized retinal prosthesis unit. Some of the challenges are integrating passive devices such as coils, diodes and capacitors, need for high voltage devices for stimulation, biocompatible and hermetic interface of the electronics

Challenges in System and Circuit Design for High Density Retinal Prosthesis

Purpose: To assess changes in retinal vascular oxygen concentration in a diabetic rat model using hyperspectral computed tomographic imaging spectroscopy (HCTIS). 
Methods: Nine brown Norway rats were anesthetized and dilated for retinal imaging. Six rats were injected with 65 mg/kg of Streptozotocin (STZ) to induce hyperglycemia, and 3 rats with 0.9% saline control. Blood glucose levels were measured after a 12 hour fast using Accu-Chek Aviva Plus glucometer (Roche Inc). Baseline oximetry measurements and fundus photographs were taken in both eyes of each rat. HCTIS oximetry measurements were taken every 2 weeks after STZ injection for up to 2 months. The same vessel areas were selected for analysis at each time point. Fundus photos and FA were repeated at 2 months. Comparison of retinal arterial (A_(ox)) and venous (V_(ox)) oxygen saturation levels were made at each time point using the Student T-test. 
Results: All experimental rats developed and maintained hyperglycemia (mean 410±41 mg/dl), and all control rats remained normoglycemic (mean 124±24 mg/dl) over the 2 months of the study. For control rats (n=3) mean A_(ox) was 95±1%, 100±4%, 97±6%, 102±5%, and 100±7% and mean V_(ox) was 90±4%, 88±3%, 86±3%, 87±2%, and 87±5% at baseline, 2, 4, 6, and 8 weeks. For experimental rats (n=6) mean A_(ox) was 91±2%, 94±4%, 91±4%, 94±3%, 94±5% and mean V_(ox) was 89±3%, 90±4%, 88±2%, 86±3%, 85±3% at baseline, 2, 4, 6, and 8 weeks. There were no significant differences between control and experimental A_(ox) and V_(ox) for each time point. The arteriovenous difference at each time point also showed no clear trends. V_(ox) measurements in the diabetic rats showed a decreasing V_(ox) trend over time when compared with baseline (p=0.76, 0.57, 0.17, 0.07). 
Conclusions: There was a trend towards decreasing V_(ox) over 2 months time in experimentally induced diabetic rats but this was not statistically significant. There were no significant differences in A_(ox) and V_(ox) in rats with experimentally induced diabetes versus controls. HCTIS is a useful method for measuring retinal vascular oxygen content in the rat model.

Retinal Vascular Oxygen Saturation in Diabetic Rats: A Study using Hyperspectral Computed Tomographic Imaging Spectroscopy

Restoration of vision of blind people has been successful by implanting electrode arrays into the eyes near the retina. However, this method is invasive and may have a chance to cause surgical complications. Recently, both in vitro and in vivo studies show that ultrasound can be used to stimulate cells on the retina and subsequently stimulate the corresponding parts of the neurons in the brain to produce a perception of vision for certain blind people. Unlike implant of electrodes, ultrasound is non-invasive. In this paper, we studied a concave two-dimensional (2D) ring array transducer to produce high-resolution ultrasound images of objects on the retina to stimulate the brain for a perception of vision. The advantages of using concave 2D ring array transducer (20-MHz frequency or 0.075-mm wavelength, 14-mm outer diameter, 9-mm inner diameter, 18-mm curvature, a pitch of 4 wavelengths, and about 1000 elements) are that the array can fit the eyeballs better in shape, can reduce the number of transducer elements needed due to its curvature, and can avoid the heating to the lens of the eye due to the high ultrasound attenuation of the lens tissues. The high ultrasound frequency used allows a high full-width-at-half-maximum (FWHM) resolution about 0.147 mm.

Mark S. Humayun

Papers

Challenges in System and Circuit Design for High Density Retinal Prosthesis

Retinal Vascular Oxygen Saturation in Diabetic Rats: A Study using Hyperspectral Computed Tomographic Imaging Spectroscopy

Concave 2D Ring Array Transducer for Ultrasound Visual Stimulation of the Brain

Retinal tissue discrimination in an animal model using hyperspectral computed tomographic imaging spectroscopy (HCTIS)

Evaluation of an inactive epiretinal poly–dimethylsiloxane electrode array implanted in dogs by optical coherence tomography