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MR Imaging of Human Brain at 3.0 T: Preliminary Report on Transverse Relaxation Rates and Relation to Estimated Iron Content

¹ Departments of Neurology (N.G., J.M.G., P.B.B., R.A.K.)
² Radiology (R.M.S., E.M.S., J.P.W.), Henry Ford Hospital and Health Sciences Center, K-11, 2799 W Grand Blvd, Detroit, MI 48202.

View larger version (72K): [in a new window]   Figure 1a. (a) Eight thin-section spin-echo MR images (repetition time msec/echo time msec, 1,500/98; field of view, 220 mm; matrix size, 128 x 128 [zero-filled to 256 x 256]; imaging bandwidth, 25 kHz) show most of the mesencephalon and lower portion of the globus pallidus. Images were reconstructed from the final echo of the GESFIDE sequence. Slight ghosting associated with inflowing blood can be observed on the most caudal section (top left). However, the artifacts are well separated from the substantia nigra. Images have been cropped to 80% of the full field of view. Top red box = enlarged region shown in b, bottom red box = enlarged region shown in c. (b, c) Enlarged images of the regions enclosed by the red boxes in a. Note the low-signal-intensity regions, which correspond to (b) the substantia nigra (SN) and the red nucleus (RN) and (c) the globus pallidus (GP), putamen (PUT), and caudate head (CA).

View larger version (177K): [in a new window]   Figure 1b. (a) Eight thin-section spin-echo MR images (repetition time msec/echo time msec, 1,500/98; field of view, 220 mm; matrix size, 128 x 128 [zero-filled to 256 x 256]; imaging bandwidth, 25 kHz) show most of the mesencephalon and lower portion of the globus pallidus. Images were reconstructed from the final echo of the GESFIDE sequence. Slight ghosting associated with inflowing blood can be observed on the most caudal section (top left). However, the artifacts are well separated from the substantia nigra. Images have been cropped to 80% of the full field of view. Top red box = enlarged region shown in b, bottom red box = enlarged region shown in c. (b, c) Enlarged images of the regions enclosed by the red boxes in a. Note the low-signal-intensity regions, which correspond to (b) the substantia nigra (SN) and the red nucleus (RN) and (c) the globus pallidus (GP), putamen (PUT), and caudate head (CA).

View larger version (175K): [in a new window]   Figure 1c. (a) Eight thin-section spin-echo MR images (repetition time msec/echo time msec, 1,500/98; field of view, 220 mm; matrix size, 128 x 128 [zero-filled to 256 x 256]; imaging bandwidth, 25 kHz) show most of the mesencephalon and lower portion of the globus pallidus. Images were reconstructed from the final echo of the GESFIDE sequence. Slight ghosting associated with inflowing blood can be observed on the most caudal section (top left). However, the artifacts are well separated from the substantia nigra. Images have been cropped to 80% of the full field of view. Top red box = enlarged region shown in b, bottom red box = enlarged region shown in c. (b, c) Enlarged images of the regions enclosed by the red boxes in a. Note the low-signal-intensity regions, which correspond to (b) the substantia nigra (SN) and the red nucleus (RN) and (c) the globus pallidus (GP), putamen (PUT), and caudate head (CA).

View larger version (156K): [in a new window]   Figure 2. Maps of the transverse relaxation rates R2*, R2, and R2'. The top row corresponds to the regions shown in Figure 1b, and the bottom row corresponds to the regions illustrated in Figure 1c. Representative ROIs (outlined in red) for the substantia nigra (SN), red nucleus (RN), globus pallidus (GP), putamen (PUT), and caudate head (CA) are shown on R2* maps. ROIs were constructed as described in the Materials and Methods. The intensities of the maps have been adjusted for the purpose of display, such that the brightness of the substantia nigra (top row) or globus pallidus (bottom row) is similar for all three maps.

View larger version (30K): [in a new window]   Figure 3. Plot of measured R2 and R2' values versus estimates of nonheme iron concentrations [Fe] in the substantia nigra (SN), red nucleus (RN), globus pallidus (GP), putamen (PUT), caudate head (CA), prefrontal cortex (PFC), and frontal WM (FWM). Values of [Fe] were obtained from the literature (4). Regression lines for the six GM regions, (ie, not including frontal WM), are illustrated by the dotted line (for R2) and the dashed line (for R2'). Slopes and vertical axis intercepts, as well as correlation coefficients, are given in Table 1.

View larger version (15K): [in a new window]   Figure 4. Plots of the log of the signal versus echo time for single-section regions within the substantia nigra (SN) and frontal WM (FWM) in one subject. The slopes of the dotted lines and dashed lines represent R2* and R2-, respectively. Dotted and dashed lines were obtained by using least-squares fits of the first five data points (acquired before the 180° pulse) and the remaining six points, respectively. Note that for the data presented in Figure 3, the relaxation rates were based on pixel-by-pixel fits, as explained in Materials and Methods. The difference in slope between each dotted line and its corresponding dashed line is due to the reversal of the R2' decay by means of the 180° pulse.

View larger version (14K): [in a new window]   Figure 5. Graph shows comparison of the iron-dependent part of R2 measured at 3.0 T with previous measurements obtained at 0.5 T and 1.5 T (7). These values represent the slopes (m in Eq [2]) of the linear relationship between R2 and the iron concentration. The lower field strength estimates (7) were obtained not by direct measurements of R2 but by measuring the ratio of the signal in several GM regions to that of WM. Error bars = error estimates.

View larger version (14K): [in a new window]   Figure 6a. Comparisons of R2 measured at 3.0 T with previously reported values (12,24,25) for other field strengths. (a) Graph depicts values obtained at 1.5 and 4.0 T (24) and at 3.0 T (see Table 2) for the substantia nigra (SN) and red nucleus (RN). Error bars = SEM. (b) Graph shows measurements obtained at 0.5 and 1.5 T (12), at 3.0 T (see Table 2), and at 4.0 T (25), for the globus pallidus (GP), putamen (PUT), caudate head (CA), and frontal WM (FWM). Error bars = SEM.

View larger version (15K): [in a new window]   Figure 6b. Comparisons of R2 measured at 3.0 T with previously reported values (12,24,25) for other field strengths. (a) Graph depicts values obtained at 1.5 and 4.0 T (24) and at 3.0 T (see Table 2) for the substantia nigra (SN) and red nucleus (RN). Error bars = SEM. (b) Graph shows measurements obtained at 0.5 and 1.5 T (12), at 3.0 T (see Table 2), and at 4.0 T (25), for the globus pallidus (GP), putamen (PUT), caudate head (CA), and frontal WM (FWM). Error bars = SEM.