T1-mapping characterization of two tumor types

Abstract

T₁ mapping is a quantitative method to characterize tissues with magnetic resonance imaging in a quick and efficient manner. It utilizes the relaxation rate of protons to depict the underlying structures within the imaging frame. While T₁-mapping techniques are used with some frequency in areas such as cardiac imaging, their application for understanding malignancies and identifying tumor structures has yet to be thoroughly investigated. Utilizing a saturation recovery method to acquire T₁ maps for two different tumor models has revealed that longitudinal relaxation mapping is sensitive enough to distinguish between normal and malignant tissue. This is seen even with decreased signal/noise ratios using small voxel sizes to obtain high-resolution images. In both tumor models, it was revealed that relaxation mapping recorded significantly different relaxation values between regions encapsulating the tumor, muscle, kidney, or spleen, as well as between the cell lines themselves. This indicates a potential future application of relaxation mapping as a method to fingerprint various stages of tumor development and may prove a useful measure to identify micro-metastases.

Figure 1

Anatomical MR images of mouse 3 14 days post-tumor injection in the axial, sagittal, and coronal views. Images have been brightened to enhance visibility.

Figure 2

Average relaxation time of mouse 3 from day 16 to day 23 of the KPC tumor, spleen, and kidney. Image data from day 19 exclude the spleen due to animal positioning and slice selections. To adequately cover the full tumor volume in three slices, the spleen was excluded from the imaging plane during relaxation mapping. Days 16 and 19 are average values across three slices. Day 23 represents the average value across five slices.

Figure 3

Anatomical images of nu/nu mouse 1 in the axial, sagittal, and coronal views with the locations of the heating antenna, tumor, and kidney denoted with white arrows. Images have been brightened to enhance visibility.

Figure 4

Differences in relaxation values between tumor and muscle regions in HAC15 model. Mouse 12 demonstrates the general trend seen upon ablation, where after treatment the differences between the muscle and tumor tissue relaxation times decrease. In mouse 22, only 22% of the periphery of the tumor was ablated, and rather than having a decrease in the difference in relaxation time between the tumor and muscle tissue, there was a greater divergence between the longitudinal relaxation times.

Figure 5

Distribution of the longitudinal relaxation time across tissue and tumor types. The wide distribution of data may be due to the application of saturation recovery methods for T₁ mapping or the tissue heterogeneity often seen with the samples selected.

Figure 6

Axial anatomical image denoting the location of kidney, tumor, and ascites (left) and corresponding T₁ map (right) across three slices demonstrating the differentiation in relaxation time between tumor center, regions of desmoplasia, and ascites formation of PDAC tumors (implanted KPC cells). For a Figure360 author presentation of this figure, see https://doi.org/10.1016/j.bpr.2024.100157.