Rahel Heule1, Carl Ganter, Oliver Bieri. 1. Division of Radiological Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland.
Abstract
PURPOSE: In principle, double echo steady state (DESS) offers morphological and quantitative T2 imaging of cartilage within one single scan. However, accurate T2 estimation is hampered by its prominent T1 dependency in the limit of low flip angles, generally used to image cartilage morphology, as for the osteoarthritis initiative. A new postprocessing approach is introduced to overcome this T1-related bias for rapid DESS-based T2 quantification in the low flip angle regime. METHODS: Based on a rough global T1 estimator and a golden section search, T2 is extracted from the ratio of the two echoes acquired with DESS. The new relaxometry method is evaluated from simulations and in vivo 3D measurements of the knee joint at 3T. RESULTS: A pronounced reduction in the T1-related bias of DESS-T2 estimation and increased zonal variation in T2 between deep and superficial cartilage layers are observed. The improvement becomes particularly evident in the range of low flip angles (α < 45°), commonly used for morphological DESS imaging. CONCLUSION: Using a simple global T1 estimate, the reliability of DESS-T2 quantification can be considerably increased. The results emphasize the potential of DESS to fuse accurate quantitative T2 and morphological imaging of the musculoskeletal system within one single scan.
PURPOSE: In principle, double echo steady state (DESS) offers morphological and quantitative T2 imaging of cartilage within one single scan. However, accurate T2 estimation is hampered by its prominent T1 dependency in the limit of low flip angles, generally used to image cartilage morphology, as for the osteoarthritis initiative. A new postprocessing approach is introduced to overcome this T1-related bias for rapid DESS-based T2 quantification in the low flip angle regime. METHODS: Based on a rough global T1 estimator and a golden section search, T2 is extracted from the ratio of the two echoes acquired with DESS. The new relaxometry method is evaluated from simulations and in vivo 3D measurements of the knee joint at 3T. RESULTS: A pronounced reduction in the T1-related bias of DESS-T2 estimation and increased zonal variation in T2 between deep and superficial cartilage layers are observed. The improvement becomes particularly evident in the range of low flip angles (α < 45°), commonly used for morphological DESS imaging. CONCLUSION: Using a simple global T1 estimate, the reliability of DESS-T2 quantification can be considerably increased. The results emphasize the potential of DESS to fuse accurate quantitative T2 and morphological imaging of the musculoskeletal system within one single scan.
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