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Rapid Musculoskeletal MRI with Phase-Sensitive Steady-State Free Precession: Comparison with Routine Knee MRI

¹ Department of Radiology, Stanford University School of Medicine, 300 Pasteur Dr., Stanford, CA 94305-5105.
² Department of Electrical Engineering, Stanford University School of Medicine, Stanford, CA.

View larger version (19K): [in a new window]   Fig. 1A. —Spectrum of balanced steady-state free precession sequence when TE is one half TR. Signal magnitude (A) and phase (B) are shown as function of resonance frequency. Water and fat each fall in one high-magnitude region of spectrum but have phase difference of 180°. This phase difference is exploited in phase-sensitive SSFP.

View larger version (10K): [in a new window]   Fig. 1B. —Spectrum of balanced steady-state free precession sequence when TE is one half TR. Signal magnitude (A) and phase (B) are shown as function of resonance frequency. Water and fat each fall in one high-magnitude region of spectrum but have phase difference of 180°. This phase difference is exploited in phase-sensitive SSFP.

View larger version (18K): [in a new window]   Fig. 2A. —Images showing that water and fat signals are out of phase. Imag = imaginary. Scatterplot of complex image voxels, with real component along horizontal axis and imaginary component along vertical axis. Signal is primarily along a line, which can be determined by regression. Data may be rotated so that this line falls along vertical axis.

View larger version (33K): [in a new window]   Fig. 2B. —Images showing that water and fat signals are out of phase. Imag = imaginary. Rotation of data with voxels having positive imaginary component gives voxels dominated by water. Inset shows phase-sensitive steady-state free precession (SSFP) image produced by these voxels.

View larger version (42K): [in a new window]   Fig. 2C. —Images showing that water and fat signals are out of phase. Imag = imaginary. Rotation of data with voxels having negative imaginary component gives voxels dominated by fat. Inset shows phase-sensitive SSFP image produced by these voxels.

View larger version (160K): [in a new window]   Fig. 3A. —30-year-old patient with normal knees. Proton density (A), fat-suppressed T2-weighted fast spin-echo (B), and phase-sensitive steady-state free precession (SSFP) (C) images show normal anterior and posterior cruciate ligaments. Signal intensity of ligament on phase-sensitive SSFP images is higher than background level. Articular cartilage is clearly delineated.

View larger version (114K): [in a new window]   Fig. 3B. —30-year-old patient with normal knees. Proton density (A), fat-suppressed T2-weighted fast spin-echo (B), and phase-sensitive steady-state free precession (SSFP) (C) images show normal anterior and posterior cruciate ligaments. Signal intensity of ligament on phase-sensitive SSFP images is higher than background level. Articular cartilage is clearly delineated.

View larger version (90K): [in a new window]   Fig. 3C. —30-year-old patient with normal knees. Proton density (A), fat-suppressed T2-weighted fast spin-echo (B), and phase-sensitive steady-state free precession (SSFP) (C) images show normal anterior and posterior cruciate ligaments. Signal intensity of ligament on phase-sensitive SSFP images is higher than background level. Articular cartilage is clearly delineated.

View larger version (143K): [in a new window]   Fig. 4A. —46-year-old man with medial knee pain. Proton density (A), fat-suppressed T2-weighted fast spin-echo (B), and phase-sensitive steady-state free precession (SSFP) (C) images show normal anterior horn of meniscus. Signal intensity in anterior horn of meniscus on phase-sensitive SSFP images is higher than background level. However, despite this normal finding, meniscal tear (arrow) is seen clearly in posterior horn.

View larger version (96K): [in a new window]   Fig. 4B. —46-year-old man with medial knee pain. Proton density (A), fat-suppressed T2-weighted fast spin-echo (B), and phase-sensitive steady-state free precession (SSFP) (C) images show normal anterior horn of meniscus. Signal intensity in anterior horn of meniscus on phase-sensitive SSFP images is higher than background level. However, despite this normal finding, meniscal tear (arrow) is seen clearly in posterior horn.

View larger version (90K): [in a new window]   Fig. 4C. —46-year-old man with medial knee pain. Proton density (A), fat-suppressed T2-weighted fast spin-echo (B), and phase-sensitive steady-state free precession (SSFP) (C) images show normal anterior horn of meniscus. Signal intensity in anterior horn of meniscus on phase-sensitive SSFP images is higher than background level. However, despite this normal finding, meniscal tear (arrow) is seen clearly in posterior horn.

View larger version (166K): [in a new window]   Fig. 5A. —36-year-old man with prior repair to anterior cruciate ligament. Fat-suppressed T2-weighted fast spin-echo (A) and phase-sensitive steady-state free precession (SSFP) (B) images show normal cartilage. Cartilage is delineated sharply on phase-sensitive SSFP images. Repair of anterior cruciate ligament is seen on fat-suppressed fast spin-echo and phase-sensitive SSFP images (arrowhead), demonstrating robustness of phase-sensitive SSFP fat–water separation technique to field inhomogeneity.

View larger version (142K): [in a new window]   Fig. 5B. —36-year-old man with prior repair to anterior cruciate ligament. Fat-suppressed T2-weighted fast spin-echo (A) and phase-sensitive steady-state free precession (SSFP) (B) images show normal cartilage. Cartilage is delineated sharply on phase-sensitive SSFP images. Repair of anterior cruciate ligament is seen on fat-suppressed fast spin-echo and phase-sensitive SSFP images (arrowhead), demonstrating robustness of phase-sensitive SSFP fat–water separation technique to field inhomogeneity.

View larger version (107K): [in a new window]   Fig. 6A. —31-year-old woman after volleyball injury. Comparison of fat-suppressed T2-weighted fast spin-echo (A), phase-sensitive steady-state free precession (SSFP) binned water (B), and phase-sensitive SSFP extended dynamic range (C) images of knee injury. Binned image underestimates bone marrow edema relative to fat-suppressed fast spin-echo image, whereas extended dynamic range image displays cortical bone with same intensity as cartilage. Thus, the pair of images are complementary. Mild femoral cartilage thinning is delineated (arrow).

View larger version (124K): [in a new window]   Fig. 6B. —31-year-old woman after volleyball injury. Comparison of fat-suppressed T2-weighted fast spin-echo (A), phase-sensitive steady-state free precession (SSFP) binned water (B), and phase-sensitive SSFP extended dynamic range (C) images of knee injury. Binned image underestimates bone marrow edema relative to fat-suppressed fast spin-echo image, whereas extended dynamic range image displays cortical bone with same intensity as cartilage. Thus, the pair of images are complementary. Mild femoral cartilage thinning is delineated (arrow).

View larger version (172K): [in a new window]   Fig. 6C. —31-year-old woman after volleyball injury. Comparison of fat-suppressed T2-weighted fast spin-echo (A), phase-sensitive steady-state free precession (SSFP) binned water (B), and phase-sensitive SSFP extended dynamic range (C) images of knee injury. Binned image underestimates bone marrow edema relative to fat-suppressed fast spin-echo image, whereas extended dynamic range image displays cortical bone with same intensity as cartilage. Thus, the pair of images are complementary. Mild femoral cartilage thinning is delineated (arrow).

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