Boyett M R, Moore M, Jewell B R, Montgomery R A, Kirby M S, Orchard C H
Department of Physiology, University of Leeds, Great Britain.
Pflugers Arch. 1988 Dec;413(2):197-205. doi: 10.1007/BF00582531.
An optical system for measuring changes in cell length during unloaded contractions of cardiac myocytes is described. A one-dimensional video "image" of a cell is obtained every 4 ms with a linear photodiode array, which is aligned with the longitudinal axis of the cell. The circuit used to process the image from the photodiode array has a variety of features to aid in the accurate determination of the distance between the ends of the cell, i.e. the cell length. First, the video image of the cell is divided into two "windows", one encompassing the "front" edge of the cell, the other encompassing the "rear" edge. Other cells or debris beyond the cell edges are excluded. Changes in the general light level, for example as a result of debris floating above the cell, have little effect because within the windows the "background light level" is subtracted from the signals before they are processed further. To detect the cell edges, the system determines when the signals within the windows exceed (front edge) or drop below (rear edge) chosen thresholds, which are different for the front and rear edges. The system has "memory" and it identifies the rear edge of the cell as the last time the signal falls below the threshold; because of this "bright spots" within the cell are not mistaken for the end of the cell. The system has "hysteresis", which enables it to ignore small fluctuations in brightness around the threshold. The system is easy to use, accurate, readily calibrated, and it has good spatial and time resolution (about 0.25 micron and 4 ms respectively).
本文描述了一种用于测量心肌细胞无负荷收缩过程中细胞长度变化的光学系统。利用线性光电二极管阵列，每隔4毫秒获取一次细胞的一维视频“图像”，该阵列与细胞的纵轴对齐。用于处理来自光电二极管阵列图像的电路具有多种特性，有助于精确测定细胞两端之间的距离，即细胞长度。首先，细胞的视频图像被分为两个“窗口”，一个围绕细胞的“前端”边缘，另一个围绕“后端”边缘。细胞边缘之外的其他细胞或碎片被排除。一般光水平的变化，例如由于细胞上方漂浮的碎片导致的变化，影响很小，因为在窗口内，信号在进一步处理之前会减去“背景光水平”。为了检测细胞边缘，系统确定窗口内的信号何时超过（前端边缘）或降至（后端边缘）选定的阈值，前端和后端边缘的阈值不同。该系统具有“记忆”功能，它将细胞的后端边缘识别为信号最后一次降至阈值以下的时刻；因此，细胞内的“亮点”不会被误认为是细胞的末端。该系统具有“滞后”特性，使其能够忽略阈值附近亮度的小波动。该系统易于使用、准确、易于校准，并且具有良好的空间和时间分辨率（分别约为0.25微米和4毫秒）。
