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Automated ultrasound calibration solution for the Ultrasound Fracture Analysis Scanning System

Bakulina, Alena

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Ultrasound calibration is an essential element for morphometric three-dimensional (3D) ultrasound medical systems that are equipped with two-dimensional (2D) ultrasound probes (transducers). Such systems have a position sensor that measures the position of a transducer in space. These measurements are used to combine 2D ultrasound scans into a 3D volume for further object reconstruction and visualisation. However, spatial transformation between the scan coordinate system and the position sensor transmitter remains unknown. The calibration procedure provides this transformation, normally obtained by scanning a device with known geometrical properties called ultrasound phantom. The accuracy of the calibration transformation directly influences the 3D reconstruction quality, however the accuracy is not the only quality characteristic of a calibration device. Phantoms vary in construction providing different calibration procedures, speed, number and positions of scans, type of calibration landmarks, automatic or manual data acquisition and segmentation, and many other criteria. The calibration method should be chosen individually for every calibrated system and there is no "one for all" solution.

In this work we introduce a novel calibration phantom with a custom calibration procedure designed for the UFASS - the Ultrasound Fracture Analysis Scanning System - an automated scanner for orthopaedic diagnostics. Our method is designed to fulfil the calibration objectives of the UFASS which are not fully covered by any of the standard phantoms.

Our phantom is based on spherical landmarks chosen for their support of a number of calibration requirements such as automated data acquisition and segmentation, and a variety of scanning positions and orientations. It consists of 12 small balls that centre coordinates must be measured with the ultrasound probe during the calibration procedure. We suggest and successfully implement a novel method to obtain and process the input ultrasound data from the phantom without manual operations from a user. Our method uses the motion controller of the UFASS to sequentially move the ultrasound probe and obtain parallel sphere slices with a small step. The scan corresponding to the central section is found by matching a circle template of the sphere's radius to each image. The image with the highest cross-correlation with the template is the central sphere section and it's circle centre is the sphere's centre.

For the UFASS our method outperforms comparable calibration solutions providing the automated data acquisition and landmarks detection procedure, high calibration speed, low calibration error, and requiring no experience and no expert knowledge from the end user performing the calibration.

Item Type: Dissertation
Supervisor: Männer, Prof. Dr. Reinhard
Date of thesis defense: 22 June 2016
Date Deposited: 24 Aug 2016 12:41
Date: 2016
Faculties / Institutes: The Faculty of Mathematics and Computer Science > Department of Computer Science
Subjects: 004 Data processing Computer science
Controlled Keywords: Ultrasound calibration, Ultrasound phantom
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