In Vivo Quantitative T₁ and T₂ Mapping of Human Breast Tissues Using a Custom-Built 50-mT MRI Prototype

The renewed interest in ultra-low-field MRI (< 0.1 T), with its advantages of cost-effectiveness and portability, is expected to drive a paradigm shift from traditional MRI scanners to point-of-care imaging systems. Here, we characterized the in vivo T₁ and T₂ relaxation times of healthy breast tissues using quantitative MRI at 50 mT to advance the development of ultra-low-field breast MRI methodologies. First, the developed in vivo quantitative mapping protocols were tested and validated using CuSO₄-doped water phantom experiments on the custom-built 50-mT MRI prototype. Then, in vivo quantitative T₁ and T₂ mapping of human breast tissues was measured in healthy female subjects. The T₁ and T₂ values for fat tissue, fibrous tissue, and glandular tissue components were determined using an automatic segmentation method based on the relaxation times. The mean T₁ times were 121.21 ± 14.57, 182.26 ± 20.96, and 238.32 ± 10.71 ms for fat tissue, fibrous tissue, and glandular tissue, respectively. While the mean T₂ times were 111.36 ± 14.28 and 69.44 ± 15.26 ms for fat tissue and fibroglandular tissue, respectively. For healthy breast tissues, the significantly shorter T₁ times at 50 mT are favorable for improving the imaging speed. T₂ times are similar to those seen at conventional clinical field strengths. Additionally, the relatively small difference in T₂ times between fibrous tissue and glandular tissue made it difficult to segment these two tissues independently. This work can provide a valuable reference for future breast tissues diagnostic imaging in ultra-low-field MRI scenarios, thereby promoting the wider adoption of portable breast MRI in routine breast disease screening.