Signal polarity restoration in a 3D inversion recovery sequence used with delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC).

PURPOSE: To develop an image reconstruction algorithm that restores the signal polarity in a three-dimensional inversion-recovery (3D-IR) sequence used in delayed gadolinium-enhanced MRI of cartilage (dGEMRIC). This approach effectively doubles the dynamic range of data used for T1 curve fitting. MATERIALS AND METHODS: We applied this reconstruction algorithm to a 3D-IR TFE sequence used for T1 mapping, validated the technique in a phantom study, and performed T1-map calculations in postosteochondral allograft transplant (OAT) patients. In addition, we performed a signal simulation study to assess the algorithm's capability to reduce the number of inversion times used in the 3D-IR TFE sequence. RESULTS: In comparison to a standard T1-mapping algorithm that uses the magnitude of the MRI signal, the proposed algorithm improves the reliability of T1 relaxation fits to the inversion-recovery three-parameter function. The signal simulation study shows that the number of TI inversion times can be reduced to as few as four, without compromising the accuracy of T1 calculations. CONCLUSION: This algorithm can be applied to any 2D- or 3D-IR acquisition sequence used in conjunction with dGEMRIC. Application of the algorithm improves the reliability of T1 calculations and allows the number of TIs to be reduced, leading to shorter scan times in dGEMRIC.

Measurement of brain iron distribution in Hallevorden-Spatz syndrome.

PURPOSE: To investigate spatial distribution of iron accumulation in the globus pallidus (GP) in patients with Hallevorden-Spatz syndrome (HSS) using phase imaging. We compared sensitivity of a phase imaging technique to relaxation rate measurement methods (R1,R2,R2*) for iron quantification. MATERIALS AND METHODS: R1, R2, and R2* were measured in GP structure of the brain of eight pantothenate kinase-associated neurodegeneration (PKAN) patients and a healthy volunteer using a 3T magnetic resonance imaging (MRI) scanner. The phase of gradient-echo images was preprocessed to eliminate phase 2pi wrapping and filtered to remove phase background variations. Phase gap across GP structure was used as a metric for iron effects quantification. RESULTS: Among the relaxation rates the most sensitive to iron accumulation was the R2* rate. The R1 and R2 rates demonstrated only small variations in this group of subjects. Up to an order of magnitude phase gap changes were measured between one PKAN patient and an age-matched healthy volunteer. Assuming that phase gap differences scale linearly with iron concentration we estimate that up to 2 mg Fe/g ww accumulates in GP of these patients. CONCLUSION: Our results demonstrate significantly higher sensitivity of the phase measurements for quantitative assessment of iron concentration compared to the relaxation rate measurements. Phase measurements could potentially be used for monitoring a progression and a response to therapy in PKAN.