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3D-T1? 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. T1? 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 (T1? ) prepared zero echo time (ZTE)-based pointwise encoding time reduction with radial acquisition (3D-T1? -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 T1? -weighted images tissues with semisolid short T2 / T2* relaxation times in the knee and ankle joints at 3?T. ASSESSMENT:Mono- and biexponential T1? 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 T1? relaxation mapping using the proposed 3D-T1? -PETRA sequence. The in vivo study demonstrated an averaged mono-T1? 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-T1? -PETRA sequence allows volumetric, isotropic (0.78?×?0.78?×?0.78?mm), biexponential T1? assessment with corresponding fractions of the tissues with semisolid short T2 / T2* . LEVEL OF EVIDENCE:2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:1207-1218.

SUBMITTER: Sharafi A

PROVIDER: S-EPMC6816051 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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3D-T<sub>1ρ</sub> prepared zero echo time-based PETRA sequence for in vivo biexponential relaxation mapping of semisolid short-T<sub>2</sub> tissues at 3 T.

Sharafi Azadeh A Baboli Rahman R Chang Gregory G Regatte Ravinder R RR

Journal of magnetic resonance imaging : JMRI 20190128 4

<h4>Background</h4>In addition to the articular cartilage, osteoarthritis (OA) affects several other tissues such as tendons, ligaments, and subchondral bone. T1<sub>ρ</sub> relaxation study of these short T<sub>2</sub> tissues may provide a more comprehensive evaluation of OA.<h4>Purpose</h4>To develop a 3D spin-lattice relaxation in the rotating frame (T<sub>1ρ</sub> ) prepared zero echo time (ZTE)-based pointwise encoding time reduction with radial acquisition (3D-T<sub>1ρ</sub> -PETRA) seque ...[more]

PMID: 30693600

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Project description:BackgroundR1ρ (or spin-lock) imaging is prone to artifacts arising from field inhomogeneities that may impact the R1ρ quantification. Previous research has proposed two types of method to manage the artifacts in continuous-wave constant amplitude spin-lock, one is based on the composite block pulses to compensate for the field imperfections, another category uses adiabatic pulses in the R1ρ pre-pulse to excite and reverse the magnetization (named adiabatic prepared approach). Although both methods have proved their efficiency in alleviating artifacts, we observed that the adiabatic pulse approach could produce much lower R1ρ dispersion in human knee cartilage than the block pulse method (characterized by the R1ρ difference ∆R1ρ =11.4 Hz (from spin-lock field 50 to 500 Hz) for the block pulse method vs. ∆R1ρ =4.5 Hz for the adiabatic pulse approach). Prompted by this observation, the purpose of this study was to investigate the underlying factors that may affect the R1ρ dispersion through numerical simulations based on the two-pool exchanging Bloch-McConnell equations.MethodsThe effects of free water pool size Pa (from 0.80 to 0.95), chemical exchange rate kb (from the bound to free water pool, ranged from 500 to 3,000 Hz), adiabatic pulse duration Tp (from 5.0 to 25 ms), and the chemical shift of the bound pool ppmb (from 1.0 to 5.0 ppm) were examined on the degree of the R1ρ dispersion for the two R1ρ imaging methods.ResultsIn general, the greater the ppmb, kb, Tp, and the smaller Pa, the more significant difference in R1ρ dispersion between the block and adiabatic approaches, with the dispersion curve of the adiabatic method becoming flatter.ConclusionsThe adiabatic prepared approach may compromise the R1ρ dispersion, the effect is determined by the combination of the tissue and radiofrequency (RF) pulse properties. It is suggested that care should be taken when using the adiabatically prepared approach to study R1ρ dispersion.

Project description:BackgroundFast and accurate T1ρ mapping in myocardium is still a major challenge, particularly in small animal models. The complex sequence design owing to electrocardiogram and respiratory gating leads to quantification errors in in vivo experiments, due to variations of the T1ρ relaxation pathway. In this study, we present an improved quantification method for T1ρ using a newly derived formalism of a T1ρ* relaxation pathway.MethodsThe new signal equation was derived by solving a recursion problem for spin-lock prepared fast gradient echo readouts. Based on Bloch simulations, we compared quantification errors using the common monoexponential model and our corrected model. The method was validated in phantom experiments and tested in vivo for myocardial T1ρ mapping in mice. Here, the impact of the breath dependent spin recovery time Trec on the quantification results was examined in detail.ResultsSimulations indicate that a correction is necessary, since systematically underestimated values are measured under in vivo conditions. In the phantom study, the mean quantification error could be reduced from - 7.4% to - 0.97%. In vivo, a correlation of uncorrected T1ρ with the respiratory cycle was observed. Using the newly derived correction method, this correlation was significantly reduced from r = 0.708 (p < 0.001) to r = 0.204 and the standard deviation of left ventricular T1ρ values in different animals was reduced by at least 39%.ConclusionThe suggested quantification formalism enables fast and precise myocardial T1ρ quantification for small animals during free breathing and can improve the comparability of study results. Our new technique offers a reasonable tool for assessing myocardial diseases, since pathologies that cause a change in heart or breathing rates do not lead to systematic misinterpretations. Besides, the derived signal equation can be used for sequence optimization or for subsequent correction of prior study results.

Dataset Information

3D-T1? prepared zero echo time-based PETRA sequence for in vivo biexponential relaxation mapping of semisolid short-T2 tissues at 3 T.

Publications

3D-T<sub>1ρ</sub> prepared zero echo time-based PETRA sequence for in vivo biexponential relaxation mapping of semisolid short-T<sub>2</sub> tissues at 3 T.

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