Repeatability of Quantitative Knee Cartilage T1, T2, and T1ρ Mapping With 3D-MRI Fingerprinting

Abstract

Background: Three-dimensional MR fingerprinting (3D-MRF) techniques have been recently described for simultaneous multiparametric mapping of knee cartilage. However, investigation of repeatability remains limited.

Purpose: To assess the intra-day and inter-day repeatabilities of knee cartilage T₁, T₂, and T_1ρ maps using a 3D-MRF sequence for simultaneous measurement.

Study type: Prospective.

Subjects: Fourteen healthy subjects (35.4 ± 9.3 years, eight males), scanned on Day 1 and Day 7.

Field strength/sequence: 3 T/3D-MRF, T₁, T₂, and T_1ρ maps.

Assessment: The acquisition of 3D-MRF cartilage (simultaneous acquisition of T₁, T₂, and T_1ρ maps) were acquired using a dictionary pattern-matching approach. Conventional cartilage T₁, T₂, and T_1ρ maps were acquired using variable flip angles and a modified 3D-Turbo-Flash sequence with different echo and spin-lock times, respectively, and were fitted using mono-exponential models. Each sequence was acquired on Day 1 and Day 7 with two scans on each day.

Statistical tests: The mean and SD for cartilage T₁, T₂, and T_1ρ were calculated in five manually segmented regions of interest (ROIs), including lateral femur, lateral tibia, medial femur, medial tibia, and patella cartilages. Intra-subject and inter-subject repeatabilities were assessed using coefficient of variation (CV) and intra-class correlation coefficient (ICC), respectively, on the same day and among different days. Regression and Bland-Altman analysis were performed to compare maps between the conventional and 3D-MRF sequences.

Results: The CV in all ROIs was lower than 7.4%, 8.4%, and 7.5% and the ICC was higher than 0.56, 0.51, and 0.52 for cartilage T₁, T₂, and T_1ρ, respectively. The MRF results had a good agreement with the conventional methods with a linear regression slope >0.61 and R² > 0.59.

Conclusion: The 3D-MRF sequence had high intra-subject and inter-subject repeatabilities for simultaneously measuring knee cartilage T₁, T₂, and T_1ρ with good agreement with conventional sequences.

Evidence level: 1 TECHNICAL EFFICACY: Stage 1.

Keywords: MRF; knee cartilage; quantitative mapping; repeatability.

Figure 1:

Representative manual segmented ROIs. LFC: lateral femur cartilage; LTC: lateral tibia cartilage; MFC: medial femur cartilage; MTC: medial tibia cartilage; PC: patella cartilage.

Figure 2:

Representative cartilage PD, T₁, T₂, T_1ρ, and B₁₊ maps for a subject with four repeated scans. All four scans were acquired on day one and day seven in the lateral knee. As shown in the figure, the maps display high agreement of the T₁, T₂, T_1ρ, and B₁₊ maps in the ROIs across the four scans acquired one week apart.

Figure 3:

Representative cartilage PD, T₁, T₂, T_1ρ and B₁₊ maps for a male subject (left) and female subject (right), both of whom are 35 years old, showcasing the knee joint.

Figure 4:

Representative cartilage PD, T₁, T₂, T_1ρ, and B₁₊ maps for a 30-year-old subject (left) and a 62-year-old subject (right), both males in the knee joint.

Figure 5:

Bland–Altman plots for intra-day comparison (top) and inter-day comparison (bottom) for the cartilage T₁ (left), T₂ (middle), and T_1ρ (right) measurements estimated from the 3D-MRF. The blue dashed line indicates the average of the difference values; the red dashed line indicates the upper and lower limit of agreement of the 95% confidence; the black solid line indicates the difference value at 0. In the intra-day comparison (top), each point represents difference between the two scans acquired on the same day. In the inter-day comparison (bottom), each point represents the difference between the averages on day one and day seven, and the average of each day was calculated from the two scans on the same day.

Figure 6:

Regression plots (upper row) and Bland–Altman plots (lower row) for the comparison between the cartilage T₁ (left), T₂ (middle), and T_1ρ (right) measurements estimated from the conventional sequences and 3D-MRF. In the Bland-Altman plot: the blue dashed line indicates the average of the difference values; the red dashed line indicates the upper and lower limit of agreement of the 95% confidence; the black solid line indicates the difference value at 0. Each data point on the plots represents an average of the measurements of the two scans on the same day.