University of Twente Student Theses


Design of a temperature-controlled breast phantom for investigations into the temperature stability in a photoacoustic tomographic breast imager

Tijburg, Alette J. (2022) Design of a temperature-controlled breast phantom for investigations into the temperature stability in a photoacoustic tomographic breast imager.

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Abstract:Photoacoustic (PA) tomographic imaging is a promising technique to evaluate the response of breast cancer to neoadjuvant chemotherapy treatment. To bring this closer to regular application in clinical practice, high repeata- bility of image results is required. The objective of this study is to design and develop a temperature-controlled breast phantom that is suitable as a test object for investigations into the temperature fluctuations in the water in the imaging bowl of the PAMMOTH photoacoustic tomographic breast imager. Based on considerations regarding the temperature stability of the test object, needed for repeated measure- ments, and the suitability for being used in a PA tomographic breast imaging system, a set of twelve requirements was made. Fabrication of the prototype and final design included vacuum shaping techniques and 3D printing. Characterization of the temperature stability and homogeneity of the phantom was done using thermocouples and an infrared camera. The test object was subsequently used in the PAMMOTH system to obtain PA reconstructions of the created temperature-controlled breast phantom. The developed phantom consists of two main parts: a breast tissue-mimicking part and a temperature regulating system. The temperature system, being the innovative part of the phantom, consists of a heated water flow circuit that encapsulates the tissue-mimicking part. The encapsulating part of the flow circuit is composed of two vertically stacked, breast-shaped PVC cups, separated by a water supply ring. The ring is connected to a closed-loop pumping system that includes a water reservoir that is heated by a hot plate. The tissue-mimicking part was placed inside the inner PVC cup and consists of gel wax in which subresolution PA targets are embedded. The encapsulating flowing water layer was shown to have a homogeneous temperature distribution, which re- mained stable over the duration of a PAMMOTH measurement. However, due to the shortcomings of the hot plate, there was limited control over the exact temperature at which it stabilized. The temperature of the gel wax was shown to cool down but at a very slow rate such that it could be considered stable over the duration of a PAMMOTH measurement. This conclusion applied only if the gel wax was homogeneously pre-heated to the same temperature as the water flowing through the water layer. Spatial temperature inhomogeneity in the gel wax will result in spatial inhomogeneity in the speed of sound inside the phantom, which may complicate the use of the phantom as a test object for PA reconstruction. These findings imply that the developed phantom in its current state is not yet ready to be used as a test object in a repeatability study, as the temperature of the test object cannot be ensured to have exactly the same temperature in each repeated measurement. However, it is expected that improvements of the heating source for heating the water and better insulation of the gel wax on the top side of the phantom can improve the temperature stability of the phantom, thereby making it suitable for repeated measurements.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:44 medicine, 50 technical science in general
Programme:Biomedical Technology BSc (56226)
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