3D Radial Knee Imaging at 0.55 T: Simultaneous T₁-T₂ Mapping and Synthetic Contrast Generation in Under 4 min

Area of Science:

• Magnetic Resonance Imaging
• Osteoarthritis Research
• Quantitative Medical Imaging

Background:

• Quantitative MRI (T1-T2) mapping is valuable for early osteoarthritis (OA) diagnosis in knees at higher field strengths (1.5T and 3T).
• Limited research exists on quantitative T1-T2 mapping at lower field strengths like 0.55T, hindering its application in diverse clinical settings.

Purpose of the Study:

• To develop and assess the feasibility of a novel 3D joint T1-T2 mapping and synthetic contrast radial MRI sequence for knee imaging at 0.55T.
• To enable quantitative and anatomical water-fat imaging at a lower magnetic field strength.

Main Methods:

• A 3D golden angle radial sequence with inversion recovery and T2-preparation was implemented for free-running data acquisition.
• Image reconstruction utilized parallel imaging and high-dimensional low-rank patch-based regularization.
• Water-fat separation and Bloch-equation dictionary matching were employed for T1-T2 map generation.

Main Results:

• Phantom validation showed good agreement with reference sequences (T1 bias: 1.78 ms, T2 bias: -0.23 ms).
• In vivo T1 and T2 values in articular cartilage were measured (T1=460±45 ms, T2=33±4 ms), comparable to reference values.
• Synthetic contrast images demonstrated comparable contrast-to-noise ratio (CNR) and relative contrast metrics to references.

Conclusions:

• The developed 3D T1-T2 mapping sequence is feasible for efficient knee imaging at 0.55T within approximately 3 minutes.
• This technique shows promise for quantitative assessment and potential early diagnosis of knee osteoarthritis at lower field strengths.
• Further studies with larger osteoarthritis cohorts at 0.55T are warranted to confirm clinical utility.