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BACKGROUND: In addition to the articular cartilage, osteoarthritis (OA) affects several other tissues such as tendons, ligaments, and subchondral bone. T(1ρ) relaxation study of these short T(2) tissues may provide a more comprehensive evaluation of OA. PURPOSE: To develop a 3D spin-lattice relaxation in the rotating frame (T(1ρ)) prepared zero echo time (ZTE)-based pointwise encoding time reduction with radial acquisition (3D-T(1ρ)-PETRA) sequence for relaxation mapping of semisolid short-T(2) 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 T(1ρ)-weighted images tissues with semisolid short [Formula: see text] relaxation times in the knee and ankle joints at 3 T. ASSESSMENT: Mono- and biexponential T(1ρ) 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 T(1ρ) relaxation mapping using the proposed 3D-T(1ρ)-PETRA sequence. The in vivo study demonstrated an averaged mono-T(1ρ) 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-T(1ρ)-PETRA sequence allows volumetric, isotropic (0.78 × 0.78 × 0.78 mm), biexponential T(1ρ) assessment with corresponding fractions of the tissues with semisolid short [Formula: see text].

BACKGROUND: Measuring T(1ρ) in the knee menisci can potentially be used as noninvasive biomarkers in detecting early-stage osteoarthritis (OA). PURPOSE: To demonstrate the feasibility of biexponential T(1ρ) relaxation mapping of human knee menisci. STUDY TYPE: Prospective. POPULATION: Eight healthy volunteers with no known inflammation, trauma, or pain in the knee and three symptomatic subjects with early knee OA. FIELD STRENGTH/SEQUENCE: Customized Turbo-FLASH sequence to acquire 3D-T(1ρ)-weighted images on a 3 T MRI scanner. ASSESSMENT: T(1ρ) relaxation values were assessed in 11 meniscal regions of interest (ROIs) using monoexponential and biexponential models. STATISTICAL TESTS: Nonparametric rank-sum tests, Kruskal–Wallis test, and coefficient of variation. RESULTS: The mean monoexponential T(1ρ) relaxation in the lateral menisci were 28.05 ± 4.2 msec and 37.06 ± 10.64 msec for healthy subjects and early knee OA patients, respectively, while the short and long components were 8.07 ± 0.5 msec and 72.35 ± 3.2 msec for healthy subjects and 2.63 ± 2.99 msec and 55.27 ± 24.76 msec for early knee OA patients, respectively. The mean monoexponential T(1ρ) relaxation in the medial menisci were 34.30 ± 3.8 msec and 37.26 ± 11.38 msec for healthy and OA patients, respectively, while the short and long components were 7.76 ± 0.7 msec and 72.19± 4.2 msec for healthy subjects and 3.06 ± 3.24 msec and 55.27 ± 24.59 msec for OA patients, respectively. Statistically significant (P≤ 0.05) differences were observed in the monoexponential relaxation between some of the ROIs. The T(1ρ,short) was significantly lower (P = 0.02) in the patients than controls. The rmsCV% ranges were 1.51–16.6%, 3.59–14.3%, and 4.91–15.6% for T(1ρ)-mono, T(1ρ)-short, and T(1ρ)-long, respectively. DATA CONCLUSION: Our results showed that in all ROIs, T(1ρ) relaxation times of outer zones (red zones) were less than inner zones (white zones). Monoexponential T(1ρ) was increased in medial, lateral, and body menisci of early OA while the biexponential numbers were decreased in early OA patients. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 1

BACKGROUND: The progressive loss of hyaline articular cartilage due to osteoarthritis (OA) changes the functional and biochemical properties of cartilage. Measuring the T1ρ along with the morphological assessment can potentially be used as noninvasive biomarkers in detecting early-stage OA. To correlate the biochemical and morphological data, submillimeter isotropic resolution for both studies is required. PURPOSE: To implement a high spatial resolution 3D-isotropic-MRI sequence for simultaneous assessment of morphological and biexponential T(1ρ) relaxometry of human knee cartilage in-vivo. STUDY TYPE: Prospective. POPULATION: Ten healthy volunteers with no known inflammation, trauma or pain in the knee. FIELD STRENGTH/SEQUENCE: Standard FLASH sequence and customized Turbo-FLASH sequence to acquire 3D-isotropic-T(1ρ)-weighted images on a 3T MRI scanner. ASSESSMENT: The mean volume and thickness along with mono and biexponential T1ρ relaxations were assessed in the articular cartilage of 10 healthy volunteers. STATISTICAL TESTS: Non-parametric rank-sum tests. Bland-Altman analysis and coefficient of variation RESULTS: The mean monoexponential T(1ρ) relaxation was 40.7±4.8ms while the long and short components were 58.2±3.9ms and 6.5±0.6ms, respectively. The mean fractions of long and short T(1ρ) relaxation components were 63.7±5.9% and 36.3±5.9%, respectively. Statistically significant (p ≤0.03) differences were observed in the monoexponential and long components between some of the ROIs. No gender differences between biexponential components were observed (p>0.05). Mean cartilage volume and thickness were 25.9±6.4cm(3) and 2.2±0.7mm, respectively. Cartilage volume (p=0.01) and thickness (p=0.03) were significantly higher in male than female participants across all ROIs. Bland-Altman analysis showed agreement between two morphological methods with limits of agreement between −1000mm(3) and +1100mm(3) for volume, and −0.78mm and +0.46mm for thickness, respectively. DATA CONCLUSION: Simultaneous assessment of morphological and multicomponent T1ρ relaxation of knee joint with 0.7mm×0.7mm×0.7mm isotropic spatial resolution is demonstrated in-vivo. Comparison with a standard method showed that the proposed technique is suitable for assessing the volume and thickness of articular cartilage