University of Twente Student Theses


Relaxivity assessment and T1 mapping of ex vivo lymph nodes

Valk, Nuhamin (2023) Relaxivity assessment and T1 mapping of ex vivo lymph nodes.

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Abstract:Background: Breast cancer is the most prevalent cancer in Dutch women. A strong prognostic determinant is spread to the axillary lymph nodes, which can be determined using a sentinel lymph node biopsy (SLNB). This procedure uses radioactive tracers, although alternative magnetic tracers have been proposed, which are shown to be non-inferior and solve some of the issues associated with the use of radioactive materials. However, the need remains to remove the lymph node in order to assess the presence on metastases. MR mapping and evaluation could possibly provide a method to do this in vivo. Goal: Determine the relaxivity of the magnetic tracer used in SLNBs and create T1 maps of ex vivo lymph nodes of breast cancer patients, which can be used to evaluate lymph nodes on the presence of metastases. Method: To determine the tracer relaxivity, MRI data from various samples containing different concentrations of the tracer diluted in water was used. The relaxivity was then determined by the slope of the fit through the differences in R1 between the sample and water against the sample concentration. To create the T1 map, MRI data from a breast cancer patient that underwent an SLNB using a magnetic tracer was used. T1 was determined for each voxel by fitting signal intensities against inversion times. The results were mapped and analyzed on the goodness of fit. Results: Measurements of the same sample resulted in deviations in the measured T1 and the final relaxivity was determined as 15.4 s-1mM-1. Mapping of the lymph node generally lead to a good goodness of fit. Discussion: The tracer samples were not held at a constant temperature, which could explain the deviations in T1. It was not possible to map every voxel on every slice on the lymph node; data initialization and regularization is needed to improve the applicability of the fit. Furthermore, a quantitative analysis of the tracer concentration in a lymph node is prevented by the absence of a T1 map done prior to tracer admission, which is needed to calculate the difference in R1 caused by the tracer. Conclusion: This research provides the relaxivity of a magnetic tracer used in SLNBs and a method to acquire a T1 map of a lymph node. Further research is needed to overcome the lack of native T1 map, to increase the applicability of the fit by data initialization and regularization, and to analyze differences in magnetic properties and tracer uptake between lymphatic and metastatic tissue, so that quantitative assessment of the tracer concentration and evaluation on the presence of metastases using MRI could one day be possible.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Programme:Biomedical Technology BSc (56226)
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