NI LabVIEW Assists Creation of Cell Culture Mapping System

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- Andrew Madry, Madry Technologies Pty Ltd.

The Challenge:
Measuring the electrical signals from a grid of electrodes in contact with a single layer of beating heart cells in a culture.

The Solution:
Using LabVIEW, PXI, and DAQ to help configure a complete data acquisition, processing, and display system.

Andrew Madry - Madry Technologies Pty Ltd.

Initial System Considerations
Madry Technologies Pty. Ltd. is a scientific and engineering consultancy business based in Sydney, Australia. One of our specialty areas includes working closely with biomedical researchers to develop data acquisition and analysis systems.

In one of our recent projects, electrophysiology researchers at Westmead Hospital in Sydney required a system to acquire and analyze signals measured using a microelectrode array. During this study, researchers grow a single layer of heart cells in a culture on the electrode array. As the living cells beat, the researchers obtain valuable information related to heart rhythm disorders from the electrical signals measured in the cell culture.

Apart from the fact that off-the-shelf software lacked the specialized analysis functions the researchers required, the system hardware requirements posed several technology challenges given the available budget. The basic hardware requirements for the system included:

  • Simultaneous sampling of 64 channels at high data rates of up to 70 kHz with possibility of future channel expansion
  • Data storage to a hard disk at the same time as display, at a minimum of 10 MB/s
  • High quality graphics for data visualization

PXI Platform Selection
Considering the need for high-speed disk storage and advanced graphics for data visualization, we selected a Dell dual Xeon processor system with fast SCSI Ultra160 hard disks as the computer platform.

For ideal data acquisition needs, we chose the NI PXI platform. Most modern PCs only provide a small number of internal slots for plug in cards, but PXI forms an extension of the PC’s internal PCI bus and supports a large number of slots for instrument hardware. The ability to upgrade to more channels in the future, using either a larger chassis with up to 18 slots or multiple chassis, is another benefit of the PXI platform.

Four NI PXI-6070 1.25 MS/s E series multifunction DAQ cards assisted the sampling of 64 channels at up to 70 kHz per channel. The E series multichannel analog input cards successively sample input channels to each card using a multiplexer and a single high quality instrumentation amplifier and analog-to-digital converter. The software controls the time between the samples. For bandwidth limited signals, the relative channel timing can be recovered accurately. In this project, the ability to lock the timing signals of the individual cards together also became necessary so that researchers could obtain the relative timing between all channels in the system to the required accuracy.

Incorporation of LabVIEW into Development
We used a software architecture that set one of the boards as a master and the others as subordinates with acquisition timing signals locked to the master. The PXI backplane provided advanced timing and triggering functions for this purpose, and NI LabVIEW routed the timing signals. We tested the synchronization of the cards by feeding a sine wave of known frequency into all channels. By measuring the phase between the sampled channels using an application developed with LabVIEW, we were able to check the sampling time delay between any two channels in the system. This showed our ability to synchronize cards together within the accuracy specified for the hardware. By using the NI MXI-3 PCI-to-PCI bridge technology with an optical fiber link immune to electrical interference from the desktop PC to the PXI chassis, we could place the analysis computer some distance away from the electrode array and data acquisition system.

We developed a software application using LabVIEW to provide the display and data capture facilities the researchers required. We used a dual monitor graphics card to provide simultaneous display of live data and analysis of snap shot data. Using the Windows Operating System, LabVIEW also helped our project development by being an ActiveX container, which incorporated specialized visualization functions into the application. The electrophysiology researchers call this "cardiac mapping" a process that displays the relative timing of the electrical signals measured by the array.

Future System Use
The system is now in use, and researchers envision the same hardware system will be reconfigured for other research applications. One reason the system may be used in other applications is the ability of the PXI hardware platform to simply perform reconfiguration tasks. For example, researchers foresee future use of an IMAQ camera image acquisition system incorporated into the system.

As biomedical researchers strive to obtain ground breaking results, they require new analysis tools. In this application, LabVIEW saved considerable software development time in the creation of a new tool. The hardware provided a platform for researchers to expand upon in the future thus making the best use of sought-after research funding.

For more information, contact:
Andrew Madry
Madry Technologies Pty Ltd
Suite 8/80, Cecil Ave.
Castle Hill, Australia 2154
Tel: +61 2 88507240
Fax: +61 2 88507241

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