Preliminary Exploration of T1ρ and T2 Mapping in Porcine Articular Cartilage Using Very-Low-Field Magnetic Resonance Imaging

Objective:
The high prevalence of osteoarthritis emphasizes the need for a cost-effective and accessible method for its early diagnosis. Recently, the portability and affordability of very-low-field (VLF) magnetic resonance imaging (MRI, 10–100 mT) have caused it to gain popularity. Nevertheless, there is insufficient evidence to quantify early degenerative changes in cartilage using VLF MRI. This study assessed the potential of
T
_1ρ
and
T
₂
mapping for detecting degenerative changes in porcine cartilage specimens using a 50 mT MRI scanner.
Methods: T
₂
- and
T
_1ρ
-weighted images were acquired using a 50 mT MRI scanner with 2D spin-echo and triple-refocused
T
_1ρ
preparation sequences. MRI scans of porcine cartilage were also acquired using a 3 T MRI scanner for comparison. A mono-exponential algorithm was applied to fit a series of
T
₂
- and
T
_1ρ
-weighted images.
T
₂
values for CuSO
₄
·5H
₂
O solutions measured via Carr–Purcell–Meiboom–Gill (CPMG) and spin-echo sequences were compared to verify the algorithm's reliability. The nonparametric Kruskal-Wallis statistical test was used to compare
T
₂
and
T
_1ρ
values. Experimental repeatability was assessed using the root-mean-square of the coefficient of variation (rms
CV
).
Results: T
₂
values of the CuSO
₄
·5H
₂
O solutions obtained using the spin-echo sequence showed differences within 2.3% of those obtained using the CPMG sequence, indicating the algorithm's reliability. The
T
_1ρ
values for varying concentrations of agarose gel solutions were higher than the
T
₂
values. Furthermore, 50 mT and 3 T MRI results showed that both the
T
_1ρ
and
T
₂
values were significantly higher for porcine cartilage degraded for 6 h vs intact cartilage, with
p
-values of 0.006 and 0.01, respectively. Our experimental results showed good reproducibility (rms
CV
< 8%).
Conclusion:
We demonstrated the feasibility of quantitative cartilage imaging via
T
₂
and
T
_1ρ
mapping at 50 mT MRI for the first time.