The automated assessment of ultrasound scanner lateral and slice thickness resolution: use of the step response.

The imaging performance assessment of ultrasound scanners based on traditional phantoms is limited by repeatability, subjectivity and systematic errors giving low confidence in results. A new approach to the automated measurement of scanner resolution is described. The method utilises a step change in backscatter to derive resolution from the imaging system line spread function and has been used to calculate resolution in two dimensions as a continuous function of depth. Resolution data was used to calculate resolution integrals for both lateral and slice thickness independently. For resolution integral repeatability, analysis of variance showed no significant difference between operators (p=0.05) with intra and inter-operator repeatability (+/-1 standard deviation) of 1.5% and 1.5% for lateral resolution, respectively, and 2.6% and 3.3% for slice thickness, respectively. Low contrast penetration was also calculated automatically and the worst case operator repeatability was 1.3%. The acoustic properties of the phantom were validated. The possibility of extending the technique to axial resolution is discussed.