901A HVSL
High-speed Video Sarcomere Length System
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Features

The 901A High-speed Video Sarcomere Length (HVSL) system will acquire images and calculate sarcomere length at up to 2,250 frames per second. The system includes the HVSL software, a control PC, a camera interface, all required cables and a high-speed CCD camera capable of providing full-frame images at 210 frames per second. With smaller regions of interest (ROI) the camera can provide images at up to 3,000 frames per second. In addition to real-time sarcomere length (SL) measurement, the software can also be used to stream images to disk and to calculate SL from captured image files.

The software includes a Scope function that provides a scrolling data display of sarcomere length with time. This display can record up to 2 hours of sarcomere length data. The Scope display can be frozen at any time and the user can then scroll through the sarcomere history. Scope can also log SL data to disk at rates of up to 1,000 samples per second.

The HVSL software and hardware operates on a dedicated Linux PC. For ease of calibrating the system the HVSL software provides two calibration methods, Field of View and Calibration Length. Image brightness and contrast are controllable through the software.

The High-speed Video Sarcomere Length program includes three length calculation methods: Fast Fourier Transform (FFT) with curve fit, autocorrelation function (ACF)/FFT/Curve Fit and ACF/Sine-fit. The FFT method calculates an FFT for each scan line in the Region of Interest (ROI). The average is computed, the peak identified and then a quadratic curve is fitted to the spectrum around this peak. The location of the maximum of this curve provides the sarcomere length. The ACF method calculates the autocorrelation of each scan line and then calculates the average over the ROI. For periodic images the result resembles a sine wave. The ACF/FFT/Curve Fit method performs an FFT on the average ACF and then fits a curve to the spectrum. The location of the maximum of the curve provides the sarcomere length. The ACF/Sine-fit method fits a sine function to the average ACF to determine sarcomere length.

Of these three methods the ACF/Sine-fit provides the most robust and accurate method of determining sarcomere length. With this technique the measurement resolution is not dependent on the size of the ROI or on the number of cycles in the ROI. Traditional FFT methods produce a coarse measurement of sarcomere length when the optical magnification and ROI result in a small number of sarcomeres present in the image. This is not the case with the ACF/Sine-fit method which maintains length resolution even with small sample size or small number of sarcomeres in the image.

Additionally, the ACF/Sine-fit algorithm also handles noisy or poor images better than the FFT method. This is due to our technique of calculating the FFT of the ACF function, removing peaks outside of the expected range of sarcomere lengths and then calculating the inverse FFT. The resultant series is a filtered version of the ACF and has most of the noise removed from it. The sine-fit is then performed on this series. The simple FFT calculation method does have the advantage that the processing time is faster and therefore provides a higher measurement rate.

Screen Shots (Click on Title for Larger Image)

HVSL Main Screen with Reduced Camera ROI

HVSL Scope Screen

HVSL Setup Screen

HVSL Analysis Screen