Comparative Analysis of Blood T₂ Values Measured by T₂-TRIR and TRUST

Background: Venous blood oxygenation (Yv), which can be derived from venous blood T₂ (T₂b), combined with oxygen-extraction fraction (OEF) and cerebral metabolic rate of oxygen, is considered indicative for tissue viability and brain functioning and frequently assessed in patients with sickle cell disease. Recently, T₂-Prepared-Blood-Relaxation-Imaging-with-Inversion-Recovery (T₂-TRIR) was introduced allowing for simultaneous measurements of blood T₂ and T₁ (T₁b), potentially improving Yv estimation by overcoming the need to estimate hematocrit. Purpose: To optimize and compare T₂-TRIR with T₂-relaxation-under-spin-tagging (TRUST) sequence. Study Type: Prospective. Population: A total of 12 healthy volunteers (six female, 27 ± 3 years old) and 7 patients with sickle cell disease (five female, 32 ± 12 years old). Field Strength/Sequence: 3 T; turbo field echo planar imaging (TFEPI), echo planar imaging (EPI), and fast field echo (FFE). Assessment: T₂b, Yv, and OEF from TRUST and T₂-TRIR were compared and T₂-TRIR-derived T₁b was assessed. Within- and between-session repeatability was quantified in the controls, whereas sensitivity to hemodynamic changes after acetazolamide (ACZ) administration was assessed in the patients. Statistical Tests: Shapiro–Wilk, one-sample and paired-sample t-test, repeated measures ANOVA, mixed linear model, Bland–Altman analysis and correlation analysis. Sidak multiple-comparison correction was performed. Significance level was 0.05. Results: In controls, T₂b from T₂-TRIR (70 ± 11 msec) was higher compared to TRUST (60 ± 8 msec). In patients, T₂b values were lower pre- compared to post-ACZ administration (TRUST: 80 ± 15 msec and 106 ± 23 msec and T₂-TRIR: 95 ± 21 msec and 125 ± 36 msec). Consequently, Yv and OEF were lower and higher pre- compared to post-ACZ administration (TRUST Yv: 68% ± 7% and 77% ± 8%, T₂-TRIR Yv: 74% ± 8% and 80% ± 6%, TRUST OEF: 30% ± 7% and 21% ± 8%, and T₂-TRIR OEF: 25% ± 8% and 18% ± 6%). Data Conclusion: TRUST and T₂-TRIR are reproducible, but T₂-TRIR-derived T₂b values are significantly higher compared to TRUST, resulting in higher Yv and lower OEF estimates. This bias might be considered when evaluating cerebral oxygen homeostasis. Evidence Level: 2. Technical Efficacy: Stage 2.