Limits...
Calibration of an orientation sensor for freehand 3D ultrasound and its use in a hybrid acquisition system.

Housden RJ, Treece GM, Gee AH, Prager RW - Biomed Eng Online (2008)

Bottom Line: In comparison, six degree-of-freedom drift correction was shown to produce excellent reconstructions.A hybrid system incorporating the MT9-B offers an attractive compromise between quality and ease of use.The position sensor is unobtrusive and the system is capable of faithful acquisition, with the one exception of linear drift in the elevational direction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK. rjh80@eng.cam.ac.uk

ABSTRACT

Background: Freehand 3D ultrasound is a powerful imaging modality with many potential applications. However, its reliance on add-on position sensors, which can be expensive, obtrusive and difficult to calibrate, is a major drawback. Alternatively, freehand 3D ultrasound can be acquired without a position sensor using image-based techniques. Sensorless reconstructions exhibit good fine scale detail but are prone to tracking drift, resulting in large scale geometrical distortions.

Method: We investigate an alternative position sensor, the Xsens MT9-B, which is relatively unobtrusive but measures orientation only. We describe a straightforward approach to calibrating the sensor, and we measure the calibration precision (by repeated calibrations) and the orientation accuracy (using independent orientation measurements). We introduce algorithms that allow the MT9-B potentially to correct both linear and angular drift in sensorless reconstructions.

Results: The MT9-B can be calibrated to a precision of around 1 degrees . Reconstruction accuracy is also around 1 degrees . The MT9-B was able to eliminate angular drift in sensorless reconstructions, though it had little impact on linear drift. In comparison, six degree-of-freedom drift correction was shown to produce excellent reconstructions.

Conclusion: Gold standard freehand 3D ultrasound acquisition requires the synthesis of image-based techniques, for good fine scale detail, and position sensors, for good large scale geometrical accuracy. A hybrid system incorporating the MT9-B offers an attractive compromise between quality and ease of use. The position sensor is unobtrusive and the system is capable of faithful acquisition, with the one exception of linear drift in the elevational direction.

Show MeSH

Related in: MedlinePlus

Reslice images of beef data set 1. The images show reslices through beef data set 1. The upper row of reslices are along the length of the data, showing the length and tilt. The lower row shows enlarged versions of the outlined region, highlighting the fine scale accuracy. (a) Position sensor only reconstruction. (b) Sensorless only. (c) Six degree-of-freedom correction. (d) Orientation-only correction.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2268692&req=5

Figure 7: Reslice images of beef data set 1. The images show reslices through beef data set 1. The upper row of reslices are along the length of the data, showing the length and tilt. The lower row shows enlarged versions of the outlined region, highlighting the fine scale accuracy. (a) Position sensor only reconstruction. (b) Sensorless only. (c) Six degree-of-freedom correction. (d) Orientation-only correction.

Mentions: Figures 7 and 8 show reslices though beef data set 1 and the phantom data set respectively, for the various reconstruction and drift correction methods. Although the sensorless reconstructions exhibit no qualitatively obvious length error, there is a significant tilt error which is particularly obvious in the longer phantom sequence. Also, the fine scale accuracy of the sensorless reconstruction is noticeably superior to that of the position sensor reconstruction, particularly in the beef data, which is more susceptible to probe pressure jitter. Both of the drift correction methods are able to significantly reduce the tilt error, without over-fitting to position sensor noise and thereby sacrificing the fine scale accuracy. It is evident from these reslices that tilt bias is a more significant problem than length bias. The limited orientation correction therefore provides a worthwhile improvement, despite the fact that it is unable to correct length bias.


Calibration of an orientation sensor for freehand 3D ultrasound and its use in a hybrid acquisition system.

Housden RJ, Treece GM, Gee AH, Prager RW - Biomed Eng Online (2008)

Reslice images of beef data set 1. The images show reslices through beef data set 1. The upper row of reslices are along the length of the data, showing the length and tilt. The lower row shows enlarged versions of the outlined region, highlighting the fine scale accuracy. (a) Position sensor only reconstruction. (b) Sensorless only. (c) Six degree-of-freedom correction. (d) Orientation-only correction.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2268692&req=5

Figure 7: Reslice images of beef data set 1. The images show reslices through beef data set 1. The upper row of reslices are along the length of the data, showing the length and tilt. The lower row shows enlarged versions of the outlined region, highlighting the fine scale accuracy. (a) Position sensor only reconstruction. (b) Sensorless only. (c) Six degree-of-freedom correction. (d) Orientation-only correction.
Mentions: Figures 7 and 8 show reslices though beef data set 1 and the phantom data set respectively, for the various reconstruction and drift correction methods. Although the sensorless reconstructions exhibit no qualitatively obvious length error, there is a significant tilt error which is particularly obvious in the longer phantom sequence. Also, the fine scale accuracy of the sensorless reconstruction is noticeably superior to that of the position sensor reconstruction, particularly in the beef data, which is more susceptible to probe pressure jitter. Both of the drift correction methods are able to significantly reduce the tilt error, without over-fitting to position sensor noise and thereby sacrificing the fine scale accuracy. It is evident from these reslices that tilt bias is a more significant problem than length bias. The limited orientation correction therefore provides a worthwhile improvement, despite the fact that it is unable to correct length bias.

Bottom Line: In comparison, six degree-of-freedom drift correction was shown to produce excellent reconstructions.A hybrid system incorporating the MT9-B offers an attractive compromise between quality and ease of use.The position sensor is unobtrusive and the system is capable of faithful acquisition, with the one exception of linear drift in the elevational direction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK. rjh80@eng.cam.ac.uk

ABSTRACT

Background: Freehand 3D ultrasound is a powerful imaging modality with many potential applications. However, its reliance on add-on position sensors, which can be expensive, obtrusive and difficult to calibrate, is a major drawback. Alternatively, freehand 3D ultrasound can be acquired without a position sensor using image-based techniques. Sensorless reconstructions exhibit good fine scale detail but are prone to tracking drift, resulting in large scale geometrical distortions.

Method: We investigate an alternative position sensor, the Xsens MT9-B, which is relatively unobtrusive but measures orientation only. We describe a straightforward approach to calibrating the sensor, and we measure the calibration precision (by repeated calibrations) and the orientation accuracy (using independent orientation measurements). We introduce algorithms that allow the MT9-B potentially to correct both linear and angular drift in sensorless reconstructions.

Results: The MT9-B can be calibrated to a precision of around 1 degrees . Reconstruction accuracy is also around 1 degrees . The MT9-B was able to eliminate angular drift in sensorless reconstructions, though it had little impact on linear drift. In comparison, six degree-of-freedom drift correction was shown to produce excellent reconstructions.

Conclusion: Gold standard freehand 3D ultrasound acquisition requires the synthesis of image-based techniques, for good fine scale detail, and position sensors, for good large scale geometrical accuracy. A hybrid system incorporating the MT9-B offers an attractive compromise between quality and ease of use. The position sensor is unobtrusive and the system is capable of faithful acquisition, with the one exception of linear drift in the elevational direction.

Show MeSH
Related in: MedlinePlus