Preparing to Scan

Before you can usefully record 3D ultrasound data, you need to run the various calibration routines, and in particular the spatial calibration routine. This enables the system to work out the location of the ultrasound beam with respect to the position sensor's receiver. Once you have calibrated your system, you must be careful not to disturb the attachment between the position sensor and the probe. You can then reuse the calibration for future scanning sessions by loading the appropriate calibration and setup files.

You can calibrate Stradx by scanning the bottom of a water bath. However, calibration on a simple plane is not particularly accurate and this will affect the quality of your reconstructions. To greatly improve the accuracy of your calibration, you can buy a calibration phantom from us. If you are interested, please email Richard Prager.

Whether you are scanning a water bath or the Cambridge phantom, it is important that you record this data set with position information `required' (see the section on the setup menu). Full recording instructions can be found below.

The default temporal calibration parameters for the Polhemus Patriot, Polhemus Fastrak, Northern Digital Polaris and Ascension Bird sensors are probably adequate, so it is less critical that you perform temporal calibration unless you have a strange ultrasound machine that introduces a large delay into its signal.

If you want to have the most accurate acquisition system, then follow the suggested calibration order. This covers spatial, temporal and probe shape calibrations, and also indicates how you can change the ultrasound depth and zoom settings after you have calibrated.

All the above assumes that you have a position sensor. If not, you should select `positions not required' in the setup panel, record the sequence of B-scans as described below, then retrospectively estimate the B-scans' relative positions. This allows qualitative 3D visualisation and analysis of the data set.

Stradx main window

Recording

To make a recording you must first open a file to associate with the record buffer. This is required because if you record to disk then data will be placed in the file as the recording takes place. Then just press the `Record' button to start recording, and press it again to stop. When you have finished recording, save the data to its file using the file menu. Alternatively, if you do not want to keep what you recorded, you can erase the data by pressing the `Clear' button.

If the setup option relating to position information is set to specify that position information is required, then recording will be blocked unless communication has been established with an appropriate position sensor. If you have problems establishing contact with your position sensor, see the troubleshooting section.

When you are recording directly to disk, the speed at which the file can be written will determine your acquisition frame rate. This means that you will get faster performance using a local disk than would be possible using a remote disk NFS-mounted across a network. The location of the disk does not affect the acquisition rate when you are recording to memory.

You can use the `Pause' button just as you would on a tape recorder. When `Pause' is on you can start the record process without ever incrementing the buffer counters. This enables you to get an approximate indication of the acquisition frame rate you will get. Note that predicting frame rate using `Pause' is more accurate when you are recording to memory rather than direct to disk. It is often faster for a disk to write the same block over and over again than to write a large file.

It is difficult for one person to operate Stradx's `Pause', `Record' and `Clear' buttons while simultaneously performing the ultrasound scan. The `MouseRecord' window, accessible via the file menu, tranfers these controls to the three mouse buttons. Click here for further details.