Longitudinal and multi-echo transverse relaxation times of normal breast tissue at 3 Tesla

Abstract

Purpose: To measure longitudinal (T(1)) and multi-echo transverse (T(2)) relaxation times of healthy breast tissue at 3 Tesla (T).

Materials and methods: High-resolution relaxation time measurements were made in six healthy female subjects. Inversion recovery images were acquired at 10 inversion times between 100 ms and 4000 ms, and multiple spin echo images were acquired at 16 echo times between 10 ms and 160 ms.

Results: Longitudinal relaxation times T(1) were measured as 423 ± 12 ms for adipose tissue and 1680 ± 180 ms for fibroglandular tissue. Multi-echo transverse relaxation times T(2) were measured as 154 ± 9 ms for adipose tissue and 71 ± 6 ms for fibroglandular tissue. Histograms of the voxel-wise relaxation times and quantitative relaxation time maps are also presented.

Conclusion: T(1) and multi-echo T(2) relaxation times in normal human breast tissue are reported. These values are useful for pulse sequence design and optimization for 3T breast MRI. Compared with the literature, T(1) values are significantly longer at 3T, suggesting that longer repetition time and inversion time values should be used for similar image contrast.

Figure 1

T₁ (left) and multi-echo T₂ (right) relaxation measurements of a single volunteer. Images show the quantitative relaxation time maps, and selected voxels from adipose and fibroglandular tissue are selected to display signal as a function of TI (left) and TE (right). To measure T₁, magnitude-exponential curves are fit to inversion-recovery data from single representative voxels in the adipose (above) and fibroglandular (below) tissue data. To measure multi-echo T₂, exponential decay curves are fit to multiple-echo data from the same voxels. It can be seen that these models fit the experimental data well.

Figure 2

T₁ (upper) and multi-echo T₂ (lower) maps of all six volunteers. Adipose and fibroglandular tissue are well differentiated in both sets of images. Colored spots are included to link the images to histogram envelopes plotted below. T₁ is longer in fibroglandular tissue than adipose, whereas T₂ is longer in adipose than fibroglandular tissue.

Figure 3

Voxelwise scatter plot (a) and two-dimensional histogram (b) of T₁ against multi-echo ₂ relaxation times across all subjects. Larger open circles mark the values in Table 1, identified from analysis of the individual histograms.

Figure 4

T₁ relaxation times as a function of field strength up to 3T. The continuous data shows the parametrized function proposed by Bottomley et al (as mean ± standard deviation) with dotted lines denoting extrapolation beyond the original range (20). Other individual studies (,–19) are represented by individual points with error bars denoting ± standard deviation (except *for which error bars represent ± range/3) and marked with reference numbers. Points at 1.5T and 3T are displaced slightly along the x-axis to differentiate overlapping error bars (which are displayed asymmetrically for the same reason).