QtracW Threshold Tracking Software

QtracW Threshold Tracking Software


  • Stimulus response software for nerve, muscle or cortical excitabilty
  • Acquisition via National Instruments DAQ interfaces
  • Compatible with the Digitimer DS5 and DS4 isolated current stimulators
  • Software licences available for 3 or more years



Introduction to QtracW Threshold Tracking Software
QtracW Threshold Tracking Software is a flexible, stimulus-response data acquisition program with averaging, threshold-tracking and latency-tracking facilities, originally written for studies of human nerves in vivo, but also used for microneurography, muscle excitability testing and cortical excitability testing with transcranial magnetic stimulation. It is most appropriate for experiments in which the excitability or response of the preparation varies slowly with time, either due to programmed changes in the stimulus or to an externally initiated treatment, and the data of primary interest are the changes in selected parameters (threshold, amplitude, latency, etc.) of the response with time. All or selected raw response waveforms can also be recorded, enabling the time course of additional response parameters to be calculated after the recording is finished. QTrac (which became QtracW when adapted for Windows) comprises separate stimulation and plotting programs, QTracS and QTracP, both written in Visual Basic 6.0, which have the same mode of operation and share many of the same facilities.

The Digitimer DS5 Bipolar Constant Current Stimulator was specifically designed to work with QtracW software for human studies of nerve excitability. The major components of a human nerve excitability setup include a PC running QtracW software, a nerve stimulator (e.g. Digitimer DS5), an isolated EMG amplifier (e.g. Digitimer D440-2) and a compatible DAQ interface. We also strongly recommend the Quest Scientific Humbug Noise Eliminator to remove mains interference, as many QtracW systems are mobile and used in electrically noisy hospital environments.  For animal-based studies, our DS4 Biphasic Stimulator is compatible with QtracW.

For those unfamiliar with the application of QtracW software in studies of nerve excitabiltiy, we recommend the recent article by Prof. Matthew Kiernan and colleagues (Kiernan et al. 2020), which provides guidelines for the measurement of axonal excitability and provides a state of the art review of  axonal excitability research.

Compatible DAQ Hardware
National Instruments DAQ interfaces are recommended for use with QtracW software (see below). Please consult the QtracW users manual for the latest details on specific models.

Obtaining QtracW
The most recent version of QtracW software can be freely downloaded from the QtracW FTP site (login details available from Digitimer upon request). After 50 days evaluation QtracW will only function through use of a USB hardware dongle/key which is provided once a licence has been purchased from Digitimer. All new licences are activated for 3 years.

Installation Instructions
All the necessary files and installation instructions are available from the QtracW FTP site.

QtracW Training
A series of highly successful nerve excitability workshops have been held between 2009 and 2016. Further workshops may be organised in the future if there is adequate demand. Please contact us if you are interested in attending a workshop and we can put you in touch with the organisers if any are planned.

Purchasing QtracW
New QtracW users need to purchase a 3 year licence pack from Digitimer, with non-commercial academic and clinical users receiving a 50% discount from the full price. This initial pack consists of one QtracSP dongle (stimulation and analysis/plotting) and two QtracP (analysis/plotting only) dongles. Once a user becomes a registered QtracW licencee, further dongles can be purchased individually with variable lifetimes (one to five years) and capabilities (either QtracP or QtracSP). It is also possible to extend the lifetime of a dongle by paying the appropriate licence fee. Existing QtracW users can also transfer remaining licence time from a password on their computer to up to three USB dongles (only one QtracS) using “DongleExtend” software. Please contact Digitimer for further details.

Hardware & Software Requirements
QTrac can be used with PCs running Windows XP, Vista, 7, 8 or 10. (Qtrac may also be used on a Mac, if Parallels is used to install Windows and a Windows keyboard is added.)

QtracS currently supports the following data acquisition cards/units:

  • PCI: PCI-6221M (National Instruments) (All Qtrac functions)
  • PCMCIA: DAQCard-6062E (National Instruments) (Digital o/p not supported)
  • USB: USB-6221, USB-6251 (NI) (All Qtrac functions)
  • USB-6341 (National Instruments) (All Qtrac functions)
  • Micro-1401 (Cambridge Electronic Design) (Digital o/p not supported)
  • Power-1401 (Cambridge Electronic Design) (Digital o/p not supported)

Muscle Excitability (MScanFit)
MScanFit is a freeware program which is described in the paper ‘Estimating motor unit numbers from a CMAP scan’ (Bostock, 2015).  The program works by generating a motor unit model to account for a detailed stimulus-response curve or CMAP scan. Full details of the assumptions, the generation of a preliminary model, and the method of refining the model to improve the fit to the recorded CMAP scan can be found in that paper.

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Product Information

Typical Equipment Setup for DS5/QtracW Installation

QtracW Operator’s Manual

Publications which cite use of QtracW can be found on Google Scholar.




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