Feasibility of a UTE Stack‐of‐Spirals Sequence for T1ρ Mapping of Achilles Tendinopathy

ABSTRACT We analyzed the feasibility of using a UTE stack‐of‐spirals turbo FLASH (STFL) sequence to measure T 1ρ relaxation in the Achilles tendon. Six HS (25–31 years) and five AT patients (32–47 years) participated. The study evaluates the clinical utility of the STFL sequence to generate T 1ρ maps using mono‐exponential (ME) and bi‐exponential (BE) fitting models. In a phantom experiment, ME‐T 1ρ values and SNR estimated from the STFL sequence are compared with those of the Cartesian turbo FLASH (CTFL) sequence. In human subjects, we evaluate differences in estimated ME (ME‐T 1ρ ) and BE parameters (short T 1ρ , long T 1ρ , and short fraction) between AT and HS groups along with repeatability of STFL. The agarose phantom demonstrates biases of 2.89% (3% agarose), −1.88% (5%), and −0.92% (7%) between ME‐T 1ρ values from STFL and CTFL. In the bovine Achilles tendon, STFL shows a large bias of −58.6%, with a lower median ME‐T 1ρ (2.9 ms) than CTFL (4.6 ms). SNR is higher in STFL (77.05–80.72 for 3%–7% agarose; 24.43 for bovine tendon) than CTFL (66.73–58.97 for agarose; 3.21 for bovine tendon). ME and BE parameters were averaged over the entire Achilles tendon, and none showed significant group differences ( p > 0.05; effect size = 0.05–0.22). Subregional analysis showed that in the mid‐Achilles tendon, short and long BE‐T 1ρ components were 26% and 37% lower in AT than HS, though not statistically significant. The LDA‐combined BE parameter showed significant group separation in the midtendon region ( p = 0.016; effect size = 1.53). In HS, the long BE‐T 1ρ component showed subregional variation ( p = 0.006), increasing 58% from calcaneal to midtendon, and then decreasing 23% toward the intramuscular region. ME and BE fitting showed high repeatability with scan‐rescan variations of 2.64% (T 1ρ ), 3.38% (short T 1ρ ), 3.0% (long T 1ρ ), and 0.21% (short fraction). We demonstrated the feasibility of using STFL for T 1ρ quantification in the Achilles tendon.