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Musculoskeletal MRI at 3.0 T: Relaxation Times and Image Contrast

¹ Department of Radiology, Stanford University, 300 Pasteur Dr., Grant Bldg. S0-68B, Stanford, CA 94305-5105.
² GE Applied Science Laboratory West, Menlo Park, CA.
³ Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada.

View larger version (13K): [in a new window]   Fig. 1A. —Accuracy and repeatability of measurements of T1 and T2 relaxation times at 1.5 T in a phantom (Eurospin). Solid lines indicate precision (± 3%) of relaxation times guaranteed by manufacturer. Diamonds are averages of five measurements of T1 (A) and T2 (B) relaxation times, and error bars are two times SD of those measurements. Note excellent accuracy and repeatability of T1 and T2 measurements at 1.5 T.

View larger version (12K): [in a new window]   Fig. 1B. —Accuracy and repeatability of measurements of T1 and T2 relaxation times at 1.5 T in a phantom (Eurospin). Solid lines indicate precision (± 3%) of relaxation times guaranteed by manufacturer. Diamonds are averages of five measurements of T1 (A) and T2 (B) relaxation times, and error bars are two times SD of those measurements. Note excellent accuracy and repeatability of T1 and T2 measurements at 1.5 T.

View larger version (14K): [in a new window]   Fig. 2A. —Accuracy and repeatability of measurements of T1 and T2 relaxation times at 3.0 T in a phantom (Eurospin). Solid lines indicate precision (± 3%) of relaxation times guaranteed by manufacturer. Diamonds are averages of five measurements of T1 (A) and T2 (B) relaxation times, and error bars are two times SD of those measurements. Note excellent accuracy and repeatability of T1 and T2 measurements at 3.0 T.

View larger version (12K): [in a new window]   Fig. 2B. —Accuracy and repeatability of measurements of T1 and T2 relaxation times at 3.0 T in a phantom (Eurospin). Solid lines indicate precision (± 3%) of relaxation times guaranteed by manufacturer. Diamonds are averages of five measurements of T1 (A) and T2 (B) relaxation times, and error bars are two times SD of those measurements. Note excellent accuracy and repeatability of T1 and T2 measurements at 3.0 T.

View larger version (10K): [in a new window]   Fig. 3A. —Calculated and measured signal levels at 1.5 T based on measured T1 relaxation times. Measured () and calculated (dotted lines) signal levels in muscle (A) and marrow fat (B) were normalized to 1 at TR of 6,000 msec. Note excellent agreement between predicted and calculated values, indicating measured relaxation times are accurate.

View larger version (9K): [in a new window]   Fig. 3B. —Calculated and measured signal levels at 1.5 T based on measured T1 relaxation times. Measured () and calculated (dotted lines) signal levels in muscle (A) and marrow fat (B) were normalized to 1 at TR of 6,000 msec. Note excellent agreement between predicted and calculated values, indicating measured relaxation times are accurate.

View larger version (10K): [in a new window]   Fig. 4A. —Calculated and measured signal levels at 3.0 T based on measured T1 relaxation times. Measured () and calculated (dotted lines) signal levels in muscle (A) and marrow fat (B) were normalized to 1 at TR of 6,000 msec. Note excellent agreement between predicted and calculated values, indicating measured relaxation times are accurate.

View larger version (9K): [in a new window]   Fig. 4B. —Calculated and measured signal levels at 3.0 T based on measured T1 relaxation times. Measured () and calculated (dotted lines) signal levels in muscle (A) and marrow fat (B) were normalized to 1 at TR of 6,000 msec. Note excellent agreement between predicted and calculated values, indicating measured relaxation times are accurate.

View larger version (15K): [in a new window]   Fig. 5A. —Calculated tissue signal levels at fixed TE (14 msec) for 1.5 and 3.0 T using measured relaxation times. Signal levels at 1.5 T (A) and 3.0 T (B) were divided by square root of TR and plotted versus TR with maximum signal level at 3.0 T normalized to 1.0. Difference between signal levels at any given TR determines contrast between tissues. Subcutaneous fat and bone marrow are plotted together as fat for simplicity. Note that at 3.0 T (B), because of increased T1 relaxation times, TR of 1,600 msec is required to achieve same signal level (zero contrast) of cartilage and fluid, which requires TR of only 1,200 msec at 1.5 T (A). At TR of 4,000 msec, fluid-to-cartilage contrast is greater at 3.0 T (0.12 vs 0.7) because of increase in magnetization.

View larger version (15K): [in a new window]   Fig. 5B. —Calculated tissue signal levels at fixed TE (14 msec) for 1.5 and 3.0 T using measured relaxation times. Signal levels at 1.5 T (A) and 3.0 T (B) were divided by square root of TR and plotted versus TR with maximum signal level at 3.0 T normalized to 1.0. Difference between signal levels at any given TR determines contrast between tissues. Subcutaneous fat and bone marrow are plotted together as fat for simplicity. Note that at 3.0 T (B), because of increased T1 relaxation times, TR of 1,600 msec is required to achieve same signal level (zero contrast) of cartilage and fluid, which requires TR of only 1,200 msec at 1.5 T (A). At TR of 4,000 msec, fluid-to-cartilage contrast is greater at 3.0 T (0.12 vs 0.7) because of increase in magnetization.

View larger version (174K): [in a new window]   Fig. 6A. —Images of knee of healthy volunteer obtained at 1.5 and 3.0 T. Sagittal proton density–weighted images at 1.5 T (A) and 3.0 T (B) with TR/TE of 4,000/14. Increase in signal-to-noise ratio at 3.0 T is evident. Visually, image contrast appears similar; quantification is shown in Figures 7A and 7B. Arrow in B indicates increased chemical shift at 3.0 T.

View larger version (170K): [in a new window]   Fig. 6B. —Images of knee of healthy volunteer obtained at 1.5 and 3.0 T. Sagittal proton density–weighted images at 1.5 T (A) and 3.0 T (B) with TR/TE of 4,000/14. Increase in signal-to-noise ratio at 3.0 T is evident. Visually, image contrast appears similar; quantification is shown in Figures 7A and 7B. Arrow in B indicates increased chemical shift at 3.0 T.

View larger version (139K): [in a new window]   Fig. 6C. —Images of knee of healthy volunteer obtained at 1.5 and 3.0 T. Coronal T1-weighted images at 1.5 T (C) and 3.0 T (D) with TR/TE of 800/14. Image contrast also appears similar in these images, with cartilage having higher signal than fluid at short TR. Note increase in chemical shift at 3.0 T (arrow, D).

View larger version (108K): [in a new window]   Fig. 6D. —Images of knee of healthy volunteer obtained at 1.5 and 3.0 T. Coronal T1-weighted images at 1.5 T (C) and 3.0 T (D) with TR/TE of 800/14. Image contrast also appears similar in these images, with cartilage having higher signal than fluid at short TR. Note increase in chemical shift at 3.0 T (arrow, D).

View larger version (12K): [in a new window]   Fig. 7A. —Measurements of signal-to-noise ratio (SNR) in one healthy volunteer at both 1.5 (black bars) and 3.0 T (white bars) with TE of 14 msec. SNR differences between 1.5 and 3.0 T were statistically significant (asterisk indicates p < 0.02). Difference of SNR values or contrast-to-noise ratio (CNR) for fluid and cartilage at TR of 4,000 msec is 16.2 at 1.5 T and 37.5 at 3.0 T.

View larger version (11K): [in a new window]   Fig. 7B. —Measurements of signal-to-noise ratio (SNR) in one healthy volunteer at both 1.5 (black bars) and 3.0 T (white bars) with TE of 14 msec. SNR differences between 1.5 and 3.0 T were statistically significant (asterisk indicates p < 0.02). CNR for cartilage and fluid at TR of 800 msec is 4.8 at 1.5 T and 11.9 at 3.0 T, also showing increase in contrast at 3.0 T.

View larger version (140K): [in a new window]   Fig. 8A. —T2-weighted images in 28-year-old healthy woman volunteer at 1.5 and 3.0 T using protocols based on measured relaxation times. Sagittal T2-weighted image at 1.5 T with section thickness of 3.5 mm (Table 2) shows cartilage signal-to-noise ratio (SNR) is 10.4 and muscle SNR is 5.8.

View larger version (145K): [in a new window]   Fig. 8B. —T2-weighted images in 28-year-old healthy woman volunteer at 1.5 and 3.0 T using protocols based on measured relaxation times. Sagittal T2-weighted image at 3.0 T using section thickness of 1.8 mm and parameters adjusted for relaxation times (Table 2) shows cartilage SNR is 11.5 and muscle SNR is 8.5.

View larger version (154K): [in a new window]   Fig. 8C. —T2-weighted images in 28-year-old healthy woman volunteer at 1.5 and 3.0 T using protocols based on measured relaxation times. Sagittal T2-weighted image at 1.5 T using section thickness of 1.8 mm shows much lower overall image SNR. Cartilage SNR is 3.8 and muscle SNR is 3.0. Muscle SNR at 1.5 T is slightly less than one-half SNR at 3.0 T using these parameters.

View larger version (142K): [in a new window]   Fig. 8D. —T2-weighted images in 28-year-old healthy woman volunteer at 1.5 and 3.0 T using protocols based on measured relaxation times. Sagittal T2-weighted image at 3.0 T with section thickness of 2.2 mm and parameters adjusted for relaxation times (Table 2) shows cartilage SNR is 15.7 and muscle SNR is 9.5.

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