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MR Imaging Relaxation Times of Abdominal and Pelvic Tissues Measured in Vivo at 3.0 T: Preliminary Results¹

¹ From the Department of Radiology, Center for Advanced Imaging/West, CC090, Beth Israel Deaconess Medical Center, 1 Deaconess Rd, Boston, MA 02215. Received October 16, 2002; revision requested December 23; final revision received May 22, 2003; accepted July 1. Supported in part by the French Society of Radiology (SFR), the French Association for Research in Oncology (ARC), and the National Institute of Biomedical Imaging and Bioengineering grant R21EB00562. Address correspondence to C.M.J.d.B. (e-mail: cdebazel@caregroup.harvard.edu).

View larger version (133K): [in a new window]   Figure 1. MR images obtained at 3.0 T with a half-Fourier acquisition single-shot fast SE sequence combined with inversion recovery (repetition time [TR], 5,000 msec; inversion time [TI], 150 msec; field of view, 360 x 252 mm; section thickness, 5 mm; acquisition matrix, 256 x 160; effective TE, 60 msec). Transverse sections through A, the liver and the spleen and B, the level of the kidney. Sagittal sections through C, the uterus, and D, the prostate and vertebra were used to generate the regions of interest (ROIs), which are indicated by white circles and labels. The scale is in centimeters.

View larger version (40K): [in a new window]   Figure 2. A, Diagram of the single-shot fast SE sequence (SSFSE) combined with multiple inversion recovery for measurement of T1 relaxation time. B, SE preparation for the measurement of T2 relaxation time. In A, the T1 contrast was obtained by using an inversion-recovery preparation with a variable TI applied before the single-shot fast SE imaging sequence. In B, a variable delay between the 90° excitation pulse and the first refocusing pulse of the single-shot fast SE imaging sequence was used to vary the SE T2 contrast of the single-shot fast SE images. An equal delay between the following refocusing pulses was used in the single-shot fast SE imaging sequence. The T2 contrast imparted by the phase ordering of the single-shot fast SE sequence was constant.

View larger version (21K): [in a new window]   Figure 3. Simulation of the systematic error introduced by using magnitude images in the presence of noise. For a range of true signal intensities detected in one coil of a four-coil array (dashed line), the signal intensity that would be measured on a magnitude image in the presence of noise was calculated, in accordance with reference 8. A constant noise SD of 1 was assumed for each coil. This simulated magnitude signal (solid line) is much higher than the true signal intensity in the absence of noise. An approximate expression for measured signal that takes into account the noise level (Eq [1]) is also plotted as a dotted line; however, the agreement with the true curve is so good that the dotted line is mostly obscured by the solid line.

View larger version (17K): [in a new window]   Figure 4a. (a) T1 relaxation times in phantoms obtained with the single-shot fast SE sequence (solid line) and the standard inversion-recovery method (dashed line). We used eight phantoms with different concentrations of MnCl2 in water. The mean relative difference in T1 relaxation time for each phantom was less than 2%, with an SD between differences of 1%. (b) T2 relaxation times in the same phantoms obtained with the single-shot fast SE sequence (solid line) and the standard SE method (dashed line). The mean relative difference in T2 relaxation time for each phantom was found to be 3%, with an SD between differences of 3%.

View larger version (18K): [in a new window]   Figure 4b. (a) T1 relaxation times in phantoms obtained with the single-shot fast SE sequence (solid line) and the standard inversion-recovery method (dashed line). We used eight phantoms with different concentrations of MnCl2 in water. The mean relative difference in T1 relaxation time for each phantom was less than 2%, with an SD between differences of 1%. (b) T2 relaxation times in the same phantoms obtained with the single-shot fast SE sequence (solid line) and the standard SE method (dashed line). The mean relative difference in T2 relaxation time for each phantom was found to be 3%, with an SD between differences of 3%.

View larger version (83K): [in a new window]   Figure 5a. (a) Transverse MR images obtained through the level of the kidney at 3.0 T with a half-Fourier acquisition single-shot fast SE sequence combined with inversion recovery (field of view, 360 x 252; section thickness, 5 mm; acquisition matrix, 256 x 160; effective TE, 60). Six TIs (100, 150, 250, 500, 750, and 1,000 msec) were used to measure T1 relaxation time, with a constant TR of 5,000 msec. The imaging reconstruction produced magnitude images, so large positive and negative values appear as areas of high signal intensity. The scale is in centimeters. (b) Graph shows signal intensities in the ROIs as a function of inversion-recovery TI time, as measured in the images shown in a. Fitted curves are shown as continuous lines through the data points and were used to measure T1 relaxation time.

View larger version (32K): [in a new window]   Figure 5b. (a) Transverse MR images obtained through the level of the kidney at 3.0 T with a half-Fourier acquisition single-shot fast SE sequence combined with inversion recovery (field of view, 360 x 252; section thickness, 5 mm; acquisition matrix, 256 x 160; effective TE, 60). Six TIs (100, 150, 250, 500, 750, and 1,000 msec) were used to measure T1 relaxation time, with a constant TR of 5,000 msec. The imaging reconstruction produced magnitude images, so large positive and negative values appear as areas of high signal intensity. The scale is in centimeters. (b) Graph shows signal intensities in the ROIs as a function of inversion-recovery TI time, as measured in the images shown in a. Fitted curves are shown as continuous lines through the data points and were used to measure T1 relaxation time.

View larger version (72K): [in a new window]   Figure 6a. (a) Transverse MR images obtained through the level of the kidney at 3.0 T with a half-Fourier acquisition single-shot fast SE sequence combined with SE preparation (field of view, 360 x 252; section thickness, 5 mm; acquisition matrix, 256 x 160; effective TE, 60 msec). Six preparation TEs (15, 27, 42, 72, 122, and 202 msec) were used to measure the T2 relaxation time with a constant TR of 2,000 msec. With a short T2 relaxation time (37 msec), the signal decayed more rapidly in the liver than in fat, which exhibited a longer T2 relaxation time (66 msec). The scale is in centimeters. (b) Signal intensities in the ROIs as a function of SE preparation time and TI, as measured in the images in a. Fitted curves are shown as continuous lines through the data points and were used to measure T2 relaxation time.

View larger version (26K): [in a new window]   Figure 6b. (a) Transverse MR images obtained through the level of the kidney at 3.0 T with a half-Fourier acquisition single-shot fast SE sequence combined with SE preparation (field of view, 360 x 252; section thickness, 5 mm; acquisition matrix, 256 x 160; effective TE, 60 msec). Six preparation TEs (15, 27, 42, 72, 122, and 202 msec) were used to measure the T2 relaxation time with a constant TR of 2,000 msec. With a short T2 relaxation time (37 msec), the signal decayed more rapidly in the liver than in fat, which exhibited a longer T2 relaxation time (66 msec). The scale is in centimeters. (b) Signal intensities in the ROIs as a function of SE preparation time and TI, as measured in the images in a. Fitted curves are shown as continuous lines through the data points and were used to measure T2 relaxation time.