3D‐T_1ρ prepared zero echo time‐based PETRA sequence for in vivo biexponential relaxation mapping of semisolid short‐T₂ tissues at 3 T

Abstract

Background: In addition to the articular cartilage, osteoarthritis (OA) affects several other tissues such as tendons, ligaments, and subchondral bone. T1ρ relaxation study of these short T2 tissues may provide a more comprehensive evaluation of OA. Purpose: To develop a 3D spin-lattice relaxation in the rotating frame (T1ρ) prepared zero echo time (ZTE)-based pointwise encoding time reduction with radial acquisition (3D-T1ρ-PETRA) sequence for relaxation mapping of semisolid short-T2 tissues on a clinical 3 T scanner. Study Type: Prospective. Population: Phantom, two bovine whole knee joint and Achilles tendon specimens, 10 healthy volunteers with no known inflammation, trauma or pain in the knee or ankle. Field Strength/Sequence: A customized PETRA sequence to acquire fat-suppressed 3D T1ρ-weighted images tissues with semisolid short T2/T2* relaxation times in the knee and ankle joints at 3 T. Assessment: Mono- and biexponential T1ρ relaxation components were assessed in the patellar tendon (PT), anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and Achilles tendon (AT). Statistical Tests: Kruskal–Wallis with post-hoc Dunn’s test for multiple pairwise comparisons. Results: Phantom and ex vivo studies showed the feasibility of T1ρ relaxation mapping using the proposed 3D-T1ρ-PETRA sequence. The in vivo study demonstrated an averaged mono-T1ρ relaxation of (median [IQR]) 15.9 [14.5] msec, 23.6 [9.4] msec, 17.4 [7.4] msec, and 5.8 [10.2] msec in the PT, ACL, PCL, and AT, respectively. The bicomponent analysis showed the short and long components (with their relative fractions) of 0.65 [1.0] msec (46.9 [15.3]%) and 37.3 [18.4] msec (53.1 [15.3]%) for PT, 1.7 [2.1] msec (42.5 [12.5]%) and 43.7 [17.8] msec (57.5 [12.5]%) for ACL, and 1.2 [1.9] msec (42.6 [14.0]%) and 27.7 [14.7] msec (57.3 [14.0]%) for PCL and 0.4 [0.02] msec (58.8 [13.3]%/) and 31.3 [10.8] msec (41.2 [13.3]%) for AT. Statistically significant (P≤ 0.05) differences were observed in the mono- and biexponential relaxation between several regions. Data Conclusion: The 3D-T1ρ-PETRA sequence allows volumetric, isotropic (0.78 × 0.78 × 0.78 mm), biexponential T1ρ assessment with corresponding fractions of the tissues with semisolid short T2/T2*.

Bi-Exponential 3D UTE-T1ρ Relaxation Mapping of Ex Vivo Human Knee Patellar Tendon at 3T

“…Similarly, Liu et al [25], Jang et al [39], and Liu et al [38] employed UTE T2* quantification to show that the patellar tendon had a short T2* fraction of 75-85%. Our study showed different values than Sharafi et al, who found a T1ρ short fraction of ~47% [32]. Possible reasons for this could be differences in the acquisition techniques (e.g., PETRA versus UTE), different vendor platforms, different TSLs, differences between living and postmortem tissues, and subject variability.…”

“…For example, a 3D cartesian turbo flash sequence has been used for data acquisition with a T1ρ preparation module consisting of a spin-lock pulse divided into four segments with an alternating phase [19][20][21]. However, there appears to be only one study on the bicomponent analysis of T1ρ in the tendon, which used a pointwise encoding time reduction with radial acquisition (PETRA) sequence [32].…”

Bio‐SCOPE: fast biexponential T1ρ mapping of the brain using signal‐compensated low‐rank plus sparse matrix decomposition

“…Even though the minimum TE of the sequence, that is, 5.8 ms (limited by the device hardware and sequence implementation), was used in this study, the TE may not be short enough to preserve the signals from all short T 1 ρ components. An ultra‐short TE sequence may improve performance in biexponential T 1 ρ mapping, especially for short T 1 ρ components . In addition, the Hankel matrix has been proposed to enhance the low rankness of the image matrix in accelerated MRI.…”

“…An ultra-short TE sequence may improve performance in biexponential T 1ρ mapping, especially for short T 1ρ components. 49 In addition, the Hankel matrix [50][51][52] has been proposed to enhance the low rankness of the image matrix in accelerated MRI. It can also be used as an additional constraint to further improve the reconstruction performance of Bio-SCOPE and will be investigated in our future work.…”

Tendon evaluation with ultrashort echo time (UTE) MRI: a systematic review

“…Sharafi et al developed a 3D-T1ρ zero echo time (ZTE) based sequence with pointwise encoding time reduction with radial acquisition (PETRA) for biexponential relaxation mapping of knee tissues including patellar tendon and Achilles tendon. They were able to successfully demonstrate the feasibility of the sequence for bicomponent T1ρ assessment of these tissues (67). In this study, we reviewed various studies utilizing UTE sequences for tendon imaging, examining their results, advantages, and drawbacks.…”