Recovery Of Longitudinal Magnetization Research Articles

Estimation of Radiation Damping Rates Using 133Cs, 7Li and 31P Solution NMR Spectroscopy and a Theoretical NMR RASER Model

Radio amplification using stimulated emission of radiation (RASER) effects in the NMR can increase NMR signals over time due to a feedback loop between the sample magnetization and the probe coil coupled with radiation damping (RD). Previously, RD rates had been directly observed only for the 1H, 3He, 17O and 129Xe nuclei. We report that experimental direct measurements of an NMR RASER to determine RD time constants for the three heteronuclei (133Cs (I = 7/2), 7Li (I = 3/2) and 31P (I = 1/2)) in a highly concentrated solution from the NMR RASER emissions using a conventional NMR probe. Under conditions where the RD rate exceeds the transverse relaxation rate (i.e., the NMR RASER condition is fulfilled), we recorded both the transverse NMR RASER response to imperfect inversion and the recovery of longitudinal magnetization. The data were directly evaluated based on the well-known Bloom model as estimated RD rate constants of 8.0, 1.8 and 25 Hz for 133Cs, 7Li and 31P, respectively. The proposed method can be applied to observe RD rate constants for the other nuclei as well.

A novel myocardial T1 analysis method robust to fluctuations in longitudinal magnetization recovery due to heart rate variability in polarity-corrected inversion time preparation

Myocardial T1 mapping is useful for characterizing the myocardial tissues. Polarity-corrected inversion time preparation (PCTIP), one of the T1 mapping techniques, was expected to reduce measurement underestimation versus the MOLLI method. However, measurement accuracy is reportedly reduced, especially at high heart rates (HR), owing to the shorter time interval of inversion recovery (IR) pulses. This phantom-based experiment aimed to evaluate the dependence of T1 mapping with PCTIP on HR. Here we proposed and evaluated the effectiveness of a novel HR-independent analysis method for T1 mapping. A PCTIP scan using a 3-T magnetic resonance imaging scanner was performed on a T1 measurement phantom. The virtual HR were set at 50, 60, 75, and 100bpm. The T1 of the phantom was estimated by a least-squares fit of the PCTIP data for each obtained inversion time and a theoretical longitudinal relaxation formula. This analysis was performed for the conventional and proposed formulas. The proposed formula was derived for adapting to the transient state of longitudinal magnetization recovery caused by the trigger interval as a recurrence formula. The estimated T1 measurements using the conventional formula varied widely with HR and the accuracy decreased, especially at a high HR. However, the proposed analysis showed good accuracy versus the conventional method independent of HR. T1 mapping using the PCTIP method combined with the novel method proposed here showed good accuracy.

Conductor–Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH4/Al2O3

Synthesizing Li-ion-conducting solid electrolytes with application-relevant properties for new energy storage devices is a challenging task that relies on a few design principles to tune ionic conductivity. When starting with originally poor ionic compounds, in many cases, a combination of several strategies, such as doping or substitution, is needed to achieve sufficiently high ionic conductivities. For nanostructured materials, the introduction of conductor–insulator interfacial regions represents another important design strategy. Unfortunately, for most of the two-phase nanostructured ceramics studied so far, the lower limiting conductivity values needed for applications could not be reached. Here, we show that in nanoconfined LiBH4/Al2O3 prepared by melt infiltration, a percolating network of fast conductor–insulator Li+ diffusion pathways could be realized. These heterocontacts provide regions with extremely rapid 7Li NMR spin fluctuations giving direct evidence for very fast Li+ jump processes in both nanoconfined LiBH4/Al2O3 and LiBH4-LiI/Al2O3. Compared to the nanocrystalline, Al2O3-free reference system LiBH4-LiI, nanoconfinement leads to a strongly enhanced recovery of the 7Li NMR longitudinal magnetization. The fact that almost no difference is seen between LiBH4-LiI/Al2O3 and LiBH4/Al2O3 unequivocally reveals that the overall 7Li NMR spin-lattice relaxation rates are solely controlled by the spin fluctuations near or in the conductor–insulator interfacial regions. Thus, the conductor–insulator nanoeffect, which in the ideal case relies on a percolation network of space charge regions, is independent of the choice of the bulk crystal structure of LiBH4, either being orthorhombic (LiBH4/Al2O3) or hexagonal (LiBH4-LiI/Al2O3). 7Li (and 1H) NMR shows that rapid local interfacial Li-ion dynamics is corroborated by rather small activation energies on the order of only 0.1 eV. In addition, the LiI-stabilized layer-structured form of LiBH4 guarantees fast two-dimensional (2D) bulk ion dynamics and contributes to facilitating fast long-range ion transport.

NMR Investigation of the WTe2 Weyl Semimetal below the Topological Transition Temperature

NMR investigations are performed on 125Te nuclei of WTe2 Weyl topological semimetal at temperatures of 41 and 293 K. The measurements were carried out using a Bruker Avance 500 NMR pulse spectrometer. The 125Te NMR spectra for a WTe2 single crystal are obtained for the orientation of crystal axis c parallel and perpendicular to the quantizing field. A complicated form of the spectra was related to the presence of four nonequivalent positions of tellurium atoms in the crystalline structure of WTe2. The longitudinal magnetization recovery was studied after the pulse saturation for particular spectral lines. An exponential character of relaxation is revealed. The frequency shift and width of spectral lines were found to be insignificantly different at the two temperatures, while the times of nuclear spin-lattice relaxation at 41 K exceeded approximately by 30 times the corresponding times measured at room temperature. The strong temperature dependence of the relaxation is supposedly related to the contribution of the Weyl quasi-particles below the topological phase transition.

PENGARUH VARIASI TIME REPETITION (TR) TERHADAP KUALITAS CITRADAN INFORMASI CITRA PADA PEMERIKSAAN MRI LUMBALSEKUENS T2 FSE POTONGAN SAGITAL

Background : TR (Time Repetition) is an MRI parameter. TR controls the amount of longitudinal magnetization recovery before the next RF pulse. TR parameter is one of parameters that can affect image quality and image information. Long TR arrangements can increase SNR (Signal To Noise Ratio), CNR (Contrast To Noise Ratio) and provide better contrast, but increase the examination time. The purpose of this research is to know the effect of TR to image quality, difference of image information and TR optimal on MRI Lumbal sequence T2 FSE sagittal. Methods : The type of this research is quantitative research with experimental approach. The sample of research used is 6 probandus. TR variations used are TR 2000, 2500, 3000, 3500, 4000 with other parameters controlled. Aspects of image quality and image information values assessed in this study include Corpus Vertebrae, Discus Vertebrae, Cerebro Spinal Fluid (CSF), Medulla Spinalis, and Soft Tissue. Processing and analysis of image quality data is done by data normality test using shapiro-wilk, then test influence correlation pearson, linear regression and repeated anova. and for image information is done normality data test using shapiro-wilk, and friedman test. Result : The results of the test analysis showed that there was a TR effect on SNR image quality (p = 0.001) and CNR (p = 0.007) with (p <0.05) on all assessed organs. There is a difference in image information of MRI Lumbal T2 FSE sequence of sagittal pieces on Time Repetition variation with significance value (p <0.05). The optimal TR value on image quality is found on TR 4000 variation with mean of highest mean rank that is 42.82. While the optimal TR value on the image information is on the variation of TR 3000 with the highest mean mean rank is 3.25. TR 3000 is considered to produce better image information and is considered optimal on MRI Lumbal sequences of T2 FSE sagittal fragments compared to other TR variations with a duration of examination time of 2 minutes 30 seconds. Conclusion: Based on the results that good variation TR used on MRI Lumbal examination sequence T2 FSE sagital view is TR 3000 with best image qualit, informative image information and short scanning time.

Longer Repetition Time Proton MR Spectroscopy Shows Increasing Hippocampal and Parahippocampal Metabolite Concentrations with Aging.

Previous magnetic resonance spectroscopy (MRS) studies have concluded that hippocampal and parahippocampal metabolite concentrations remain stable during healthy adult aging. However, these studies used short repetition times (TR ≤ 2seconds), which lead to incomplete longitudinal magnetization recovery, and thus, heavily T1 -weighted measurements. It is important to accurately characterize brain metabolites changes with age to enable appropriate interpretations of MRS findings in the context of neurodegenerative diseases. Our goal was to assess hippocampal brain metabolite concentrations in a large cohort of diversely aged healthy volunteers using a longer TR of 4 seconds. Left hippocampal MR spectra were collected from 38 healthy volunteers at 3T. Absolute metabolite concentrations were determined for total N-acetyl-aspartate (tNAA), total creatine (tCr), total choline (tCho), glutamate and glutamine (Glx), and myoinositol (mI). Individual partial correlations between each metabolite with age were assessed using demographic information and voxel compartmentation as confounders. Hippocampal tNAA, tCr, tCho, and mI all increased with age (NAA: R2 = .17, P = .041; tCr: R2 = .45, P = .0002; tCho: R2 = .37, P = .001; mI: R2 = .44, P = .0003). There were no relationships between age and signal to noise ratio, linewidth, or scan date, indicating the correlations were not confounded by spectral quality. Furthermore, we did not observe a trend with age in the voxel tissue compartmentations. We observed increases in hippocampal/parahippocampal metabolite concentrations with age, a finding that is in contrast to previous literature. Our findings illustrate the importance of using a sufficiently long TR in MRS to avoid T1 -relaxation effects influencing the measurement of absolute metabolite concentrations.

Dynamical shift of NMR lines in nanostructured Ga–In–Sn melt

NMR spectrum and recovery of longitudinal nuclear magnetization after inverting pulses were measured for isotopes 69Ga and 71Ga in a liquid eutectic alloy Ga–In–Sn introduced in porous glasses having pores with the sizes of 25 and 7 nm. The measurements were conducted in the fields of 9.4, 11.7, and 17.6 T and compared with those for the bulk melt sample. Differences between the shape and position of the NMR lines in various fields and for different gallium isotopes were revealed in the melt introduced into the porous glass with the pores size of 7 nm. Data obtained for this sample were interpreted based on the theoretical model of dynamic quadrupolar shift, and correlation time of atomic motion was found within this model. Characteristics of the atomic motion calculated based on the dynamic shift model and from the spin relaxation data were shown to agree with each other.

Xenon-Water Interaction in Bacterial Suspensions as Studied by NMR

Xenon is a perspective gas for creation of oxygen free environment for different applications of biomaterials. To use xenon in suspensions and products properly it is necessary to know the molecular mechanisms of its interactions with water and cells. This work reports the study of bacterial suspensions of Escherichia coli in the presence of xenon using nuclear magnetic resonance (NMR). The work studied how the spin-lattice relaxation times of water protons in suspension change under xenon conditions. Xenon is able to form clathrate hydrates with water molecules at a temperature above the melting point of ice. The work studied NMR relaxation times which reflect the rotation freedom of water molecules in suspension. Lower relaxation times indicate reduced rotational freedom of water. Single exponential behavior of spin-lattice relaxation of protons in the suspensions of microorganisms has been registered. A recovery of longitudinal magnetization in cell suspensions with xenon clathrates has been characterized by two peaks in T1-distribution. Fast relaxing T1-component was related to the intracellular water and depended on the amount of xenon clathrates. The obtained results elucidate how the NMR method can monitor the process of clathrate formation and how the xenon atoms and hydrates interact with cells.

Mathematical optimization of contrast concentration for T1-weighted spoiled gradient echo imaging.

To develop and validate closed form mathematical expressions that predict the optimal contrast agent concentration for the maximum T1-weighted spoiled gradient echo (SGRE) signal. Gadolinium and iron-based contrast agents can have significant transverse relaxivity that leads to signal dropout with increasing contrast agent concentration. A mathematical expression for the "optimal" contrast agent concentration where recovery of longitudinal magnetization is offset by increasing transverse signal decay was derived. Expressions for the maximum possible SGRE signal were also derived. Three phantoms were constructed, each with varying concentrations of one of the following three agents: gadoteridol, gadobenate dimeglumine, and ferumoxytol. After measuring the longitudinal and transverse relaxivity of the three agents, the SGRE signal was measured in the phantoms over a wide range of flip angles and echo times. Excellent qualitative agreement between the SGRE signal behavior, optimal concentration, and optimal flip angle were observed between experimental measurements and theoretical predictions. This work provides validated mathematical expressions for contrast enhanced T1-weighted SGRE imaging and may provide guidance for contrast dosing and injection protocols, as well as for novel pulse sequence design.

Rapid volumetric T1 mapping of the abdomen using three-dimensional through-time spiral GRAPPA.

To develop an ultrafast T1 mapping method for high-resolution, volumetric T1 measurements in the abdomen. The Look-Locker method was combined with a stack-of-spirals acquisition accelerated using three-dimensional (3D) through-time spiral GRAPPA reconstruction for fast data acquisition. A segmented k-space acquisition scheme was proposed and the time delay between segments for the recovery of longitudinal magnetization was optimized using Bloch equation simulations. The accuracy of this method was validated in a phantom experiment and in vivo T1 measurements were performed with 35 asymptomatic subjects on both 1.5 Tesla (T) and 3T MRI systems. Phantom experiments yielded close agreement between the proposed method and gold standard measurements for a large range of T1 values (200 to 1600 ms). The in vivo results further demonstrate that high-resolution T1 maps (2 × 2 × 4 mm(3)) for 32 slices can be achieved in a single clinically feasible breath-hold of approximately 20 s. The T1 values for multiple organs and tissues in the abdomen are in agreement with the published literature. A high-resolution 3D abdominal T1 mapping technique was developed, which allows fast and accurate T1 mapping of multiple abdominal organs and tissues in a single breath-hold.

Myocardial T1 mapping in pediatric and congenital heart disease.

In addition to the depiction of anatomy and function, tissue characterization of the myocardium has emerged as an important asset of cardiac magnetic resonance (CMR). Among the tissue properties that are quantifiable by CMR is diffuse myocardial fibrosis. Diffuse fibrosis is regarded to be the common pathological pathway toward loss of myocardial function in many cardiac conditions, including congenital heart disease.1–4 As fibrosis seems to have a major role in myocardial failure and may be reversible,5–8 its assessment by CMR has the potential to transform the way we monitor and treat our patients.9 In this review, we describe the technical aspects of fibrosis quantification with CMR and outline past and potential applications in congenital and pediatric heart disease. Diffuse myocardial fibrosis, which is present to a varying degree in children with acquired and congenital heart disease, has been attributed to abnormal loading conditions, cyanosis, and genetic predisposition.1,7,10,11 Myocardial fibrosis manifests in the pressure-loaded left ventricle of infants and children with aortic stenosis and coarctation.1 In patients with tetralogy of Fallot right ventricular myofiber disorganization and interstitial fibrosis have been demonstrated histologically.2,12 Interestingly, right ventricular fibrosis not only occurs in late adult survivors, but is already present in infants with this condition.12 The changes in myocardial architecture observed with fibrotic remodeling can be detrimental to heart function: Fibrous endocardial thickening of the right ventricular infundibulum is a predictor of poor right ventricular function in patients after tetralogy of Fallot repair.3 In patients with tricuspid atresia myocardial fibrosis is associated with systolic ventricular dysfunction early in life.4,13 In addition to being a mediator of cardiac dysfunction, diffuse fibrosis is the substrate for electric instability and a risk factor for life-threatening ventricular arrhythmia.14 Antifibrotic drugs have …

Improve myocardial T1 measurement in rats with a new regression model: Application to myocardial infarction and beyond

To improve myocardial and blood T1 measurements with a multi-variable T1 fitting model specifically modified for a segmented multi-shot FLASH sequence. The proposed method was first evaluated in a series of phantoms simulating realistic tissues, and then in healthy rats (n = 8) and rats with acute myocardial infarction (MI) induced by coronary artery ligation (n = 8). By taking into account the saturation effect caused by sampling α-train pulses, and the longitudinal magnetization recovery between readouts, our model provided more accurate T1 estimate than the conventional three-parameter fit in phantoms under realistic gating procedures (error of -0.42 ± 1.73% versus -3.40 ± 1.46%, respectively, when using the measured inversion efficiency, β). The baseline myocardial T1 values in healthy rats was 1636.3 ± 23.4 ms at 7 Tesla. One day postligation, the T1 values in the remote and proximal myocardial areas were 1637.5 ± 62.6 ms and 1740.3 ± 70.5 ms, respectively. In rats with acute MI, regional differences in myocardial T1 values were observed both before and after the administration of gadolinium. The proposed method has improved T1 estimate as validated in phantoms and could advance applications in rodents using quantitative myocardial T1 mapping.

Effect of physiological Heart Rate variability on quantitative T2 measurement with ECG-gated Fast Spin Echo (FSE) sequence and its retrospective correction

ObjectQuantitative T2 measurement is applied in cardiac Magnetic Resonance Imaging (MRI) for the diagnosis and follow-up of myocardial pathologies. Standard Electrocardiogram (ECG)-gated fast spin echo pulse sequences can be used clinically for T2 assessment, with multiple breath-holds. However, heart rate is subject to physiological variability, which causes repetition time variations and affects the recovery of longitudinal magnetization between TR periods. Materials and methodsThe bias caused by heart rate variability on quantitative T2 measurements is evaluated for fast spin echo pulse sequence. Its retrospective correction based on an effective TR is proposed. Heart rate variations during breath-holds are provided by the ECG recordings from healthy volunteers. T2 measurements were performed on a phantom with known T2 values, by synchronizing the sequence with the recorded ECG. Cardiac T2 measurements were performed twice on six volunteers. The impact of T1 on T2 is also studied. ResultsMaximum error in T2 is 26% for phantoms and 18% for myocardial measurement. It is reduced by the proposed compensation method to 20% for phantoms and 10% for in vivo measurements. Only approximate knowledge of T1 is needed for T2 correction. ConclusionHeart rate variability may cause a bias in T2 measurement with ECG-gated FSE. It needs to be taken into account to avoid a misleading diagnosis from the measurements.

Étude de l’angiogenèse par TEMP/TDM au 99MTC-RGD sur un modèle de carcinome bronchique humain traité par bévacuzimab associé ou non a la radiothérapie

Quantitative T2 measurement is applied in cardiac Magnetic Resonance Imaging (MRI) for the diagnosis and follow-up of myocardial pathologies. Standard Electrocardiogram (ECG)-gated fast spin echo pulse sequences can be used clinically for T2 assessment, with multiple breath-holds. However, heart rate is subject to physiological variability, which causes repetition time variations and affects the recovery of longitudinal magnetization between TR periods.The bias caused by heart rate variability on quantitative T2 measurements is evaluated for fast spin echo pulse sequence. Its retrospective correction based on an effective TR is proposed. Heart rate variations during breath-holds are provided by the ECG recordings from healthy volunteers. T2 measurements were performed on a phantom with known T2 values, by synchronizing the sequence with the recorded ECG. Cardiac T2 measurements were performed twice on six volunteers. The impact of T1 on T2 is also studied.Maximum error in T2 is 26% for phantoms and 18% for myocardial measurement. It is reduced by the proposed compensation method to 20% for phantoms and 10% for in vivo measurements. Only approximate knowledge of T1 is needed for T2 correction.Heart rate variability may cause a bias in T2 measurement with ECG-gated FSE. It needs to be taken into account to avoid a misleading diagnosis from the measurements.

Can Quantitative Magnetic Resonance Imaging Predict Mechanical Behavior of Human Intervertebral Disks with Different Grades of Degeneration?

IntroductionThe dramatic changes in morphology, composition, and structure that occur in the intervertebral disk (IVD) with aging and degeneration are accompanied by specific changes in mechanical properties of the disk material.1,2 Evaluation of these changes in the IVD hinges on the ability to objectively and noninvasively assess the IVD matrix composition and integrity. Different studies on human IVDs have correlated IVD matrix composition and integrity to the longitudinal magnetization recovery T1, the transverse magnetization decay T2, the magnetization transfer ratio (MTR), and apparent diffusion coefficient (ADC).3,4 Correlations and multiple linear regressions have been also identified between quantitative magnetic resonance imaging (qMRI) parameters, biochemical, and mechanical parameters of targeted enzyme matrix denaturation and buffer-treated bovine IVDs. To this end, qMRI analysis can be used to correlate MRI signal to the mechanical properties of NP and AF tissue in order to predict structural changes in IVDs with degeneration. The aim of the present study was to determine how quantitative MRI parameters can predict biomechanical properties in human IVDs with different grades of degeneration.Materials and MethodsExperimental Groups Ten whole lumbar spine specimens, 5 disks per spine, were obtained through organ donations via Héma-Québec within 24 hours after death. Age of donors was from 32 to 77 years. The samples were vacuum sealed in plastic bags for MRI to maintain hydration.MRI Procedure The MRI examinations were carried out in a 1.5T whole-body Siemens’ Avanto system using the standard circularly polarized head coil. The samples were placed in a sagittal orientation and T1, T2, MTR, and ADC were measured as previously described.1 All disks (n = 50) were then graded from T2-weighted images according to the classification system described by Pfirrmann. Numerical analysis of quantitative MRI was performed using a custom code written in MATLAB (MathWorks, Natick, MA, USA) allowing the selection of the regions of interest (ROI) and the calculation of average signal intensities from all images. ROI were traced manually as polygonal shapes with no contact with the endplate tissues and were reproduced identically on all T1, T2, Ms/Mo ratio, and diffusion images.Mechanical Testing Procedure Confined compression tests were performed on 5-mm-diameter cylindrical plugs of tissue using a custom built axial testing machine. Material parameters (aggregate modulus HA and permeability k) were obtained from a linear biphasic fit. Dynamic shear testing was carried out using a rheometer (TA Instruments). Steady-state dynamic shear modulus and phase angle were calculated at each point of the frequency and strain sweeps and fitted with exponential functions.Statistical Methods Correlations between qMRI and mechanical parameters were investigated using Pearson test performed on GraphPad Prism software (GraphPad Software, La Jolla, CA, USA). Correlation between a mechanical parameter and an MR parameter in the same region of the disk was considered significant with p.ResultsSignificant correlations for the NP tissue were found between T2 and shear modulus |G*| (r = −0.465, p = 0.022), and between diffusion ADC and αδ (r = 0.4, p = 0.047) (Fig. 1). Significant correlations for the AF tissue were found between T1 and αδ (r = 0.372, p = 0.047) and between T1 and permeability k (r = −0.468, p = 0.043) (Fig. 2). No correlations were found between MTR and any mechanical parameters for both AF and NP tissues.ConclusionThe results of the present study are consistent with our previous studies in bovine model and indicate sensitivity to distinct changes at varying levels of degeneration. In the AF, permeability and phase angle were predicted by T1 while in the NP tissue, T2 was a stronger determinant of the tissue integrity (reflected by shear modulus). This may relate to the fact that T1 has been predominantly correlated to water content, while T2 is influenced by tissue anisotropy (orientation of collagen fibers), collagen concentration, and water content in tissues. These results prove that it is possible to develop correlations and multiple linear regressions in human IVDs which are essential for developing quantitative MRI as a diagnostic tool in determining the functional state of the disk.I confirm having declared any potential conflict of interest for all authors listed on this abstractYesDisclosure of InterestNone declaredMwale F, et al. Journal of Magnetic Resonance Imaging 2008; 27:563–573Iatridis J, et al. Journal of Biomechanics 1998; 31:535–544Antoniou, J. et al. Magnetic Resonance in Medicine1998; 40(6):900–907Antoniou, J. et al. Journal of Magnetic Resonance Imaging 2004; 22:963–972

Can Quantitative Magnetic Resonance Imaging Predict Mechanical Behavior of Human Intervertebral Disks with Different Grades of Degeneration?

Introduction The dramatic changes in morphology, composition, and structure that occur in the intervertebral disk (IVD) with aging and degeneration are accompanied by specific changes in mechanical properties of the disk material.1,2 Evaluation of these changes in the IVD hinges on the ability to objectively and noninvasively assess the IVD matrix composition and integrity. Different studies on human IVDs have correlated IVD matrix composition and integrity to the longitudinal magnetization recovery T1, the transverse magnetization decay T2, the magnetization transfer ratio (MTR), and apparent diffusion coefficient (ADC).3,4 Correlations and multiple linear regressions have been also identified between quantitative magnetic resonance imaging (qMRI) parameters, biochemical, and mechanical parameters of targeted enzyme matrix denaturation and buffer-treated bovine IVDs. To this end, qMRI analysis can be used to correlate MRI signal to the mechanical properties of NP and AF tissue in order to predict structural changes in IVDs with degeneration. The aim of the present study was to determine how quantitative MRI parameters can predict biomechanical properties in human IVDs with different grades of degeneration. Materials and Methods Experimental Groups Ten whole lumbar spine specimens, 5 disks per spine, were obtained through organ donations via Héma-Québec within 24 hours after death. Age of donors was from 32 to 77 years. The samples were vacuum sealed in plastic bags for MRI to maintain hydration. MRI Procedure The MRI examinations were carried out in a 1.5T whole-body Siemens’ Avanto system using the standard circularly polarized head coil. The samples were placed in a sagittal orientation and T1, T2, MTR, and ADC were measured as previously described.1 All disks ( n = 50) were then graded from T2-weighted images according to the classification system described by Pfirrmann. Numerical analysis of quantitative MRI was performed using a custom code written in MATLAB (MathWorks, Natick, MA, USA) allowing the selection of the regions of interest (ROI) and the calculation of average signal intensities from all images. ROI were traced manually as polygonal shapes with no contact with the endplate tissues and were reproduced identically on all T1, T2, Ms/Mo ratio, and diffusion images. Mechanical Testing Procedure Confined compression tests were performed on 5-mm-diameter cylindrical plugs of tissue using a custom built axial testing machine. Material parameters (aggregate modulus HA and permeability k) were obtained from a linear biphasic fit. Dynamic shear testing was carried out using a rheometer (TA Instruments). Steady-state dynamic shear modulus and phase angle were calculated at each point of the frequency and strain sweeps and fitted with exponential functions. Statistical Methods Correlations between qMRI and mechanical parameters were investigated using Pearson test performed on GraphPad Prism software (GraphPad Software, La Jolla, CA, USA). Correlation between a mechanical parameter and an MR parameter in the same region of the disk was considered significant with p. Results Significant correlations for the NP tissue were found between T2 and shear modulus |G*| ( r = −0.465, p = 0.022), and between diffusion ADC and αδ ( r = 0.4, p = 0.047) (Fig. 1). Significant correlations for the AF tissue were found between T1 and αδ ( r = 0.372, p = 0.047) and between T1 and permeability k ( r = −0.468, p = 0.043) (Fig. 2). No correlations were found between MTR and any mechanical parameters for both AF and NP tissues. Conclusion The results of the present study are consistent with our previous studies in bovine model and indicate sensitivity to distinct changes at varying levels of degeneration. In the AF, permeability and phase angle were predicted by T1 while in the NP tissue, T2 was a stronger determinant of the tissue integrity (reflected by shear modulus). This may relate to the fact that T1 has been predominantly correlated to water content, while T2 is influenced by tissue anisotropy (orientation of collagen fibers), collagen concentration, and water content in tissues. These results prove that it is possible to develop correlations and multiple linear regressions in human IVDs which are essential for developing quantitative MRI as a diagnostic tool in determining the functional state of the disk. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared Mwale F, et al. Journal of Magnetic Resonance Imaging 2008; 27:563–573 Iatridis J, et al. Journal of Biomechanics 1998; 31:535–544 Antoniou, J. et al. Magnetic Resonance in Medicine1998; 40(6):900–907 Antoniou, J. et al. Journal of Magnetic Resonance Imaging 2004; 22:963–972

Rapid T1 mapping of mouse myocardium with saturation recovery look‐locker method

Dynamic contrast-enhanced MRI using gadolinium or manganese provides unique characterization of myocardium and its pathology. In this study, an electrocardiography (ECG) triggered saturation recovery Look-Locker method was developed and validated for fast cardiac T(1) mapping in small animal models. By sampling the initial portion of the longitudinal magnetization recovery curve, high temporal resolution (∼ 3 min) can be achieved at a high spatial resolution (195 × 390 μm2) in mouse heart without the aid of parallel imaging or echo-planar imaging. Validation studies were performed both in vitro on a phantom and in vivo on C57BL/6 mice (n = 6). Our results showed a strong agreement between T(1) measured by saturation recovery Look-Locker and by the standard saturation recovery method in vitro or inversion recovery Look-Locker in vivo. The utility of saturation recovery Look-Locker in dynamic contrast-enhanced MRI studies was demonstrated in manganese-enhanced MRI experiments in mice. Our results suggest that saturation recovery Look-Locker can provide rapid and accurate cardiac T(1) mapping for studies using small animal models.

TH‐D‐201C‐02: Rapid T1 Mapping of Myocardium and Left Ventricle Blood for Small Animals Using Saturation Recovery Look‐Locker Method

Purpose: Dynamic contrast enhanced MRI (DCE‐MRI) has been increasingly used to delineate cardiac patho‐physiological conditions such as tumor and infarction. The time course of contrast agent in tissue and blood is required for quantitative analysis. However the sampling of contrast agent dynamics is challenging for small animal models because of the fast heart beat and blood circulation. Current study aims to develop and validate a rapid T1 mapping method for simultaneous quantification of myocardium and blood contrast agent concentrations in small animal DCE‐MRI studies. Method and Materials: An ECG‐triggered saturation recovery Look‐Locker (SRLL) method was developed for T1 estimation by sampling the initial portion of the longitudinal magnetization recovery curve. Monte‐Carlo simulations were conducted for error analysis and parameter optimization. Validation was performed on both phantom and mouse heart in vivo (n=7). SRLL and keyhole sampling scheme was also jointly applied in a manganese enhanced MRI experiment to show its practical utility. Results: Simulations showed that SRLL can provide accurate T1 estimation despite of heart rate fluctuation and field inhomogeneity. This was validated in both phantom and in vivo mouse heart by a strong agreement between T1 measured by SRLL and by the standard inversion recovery Look‐Locker method. The myocardium and blood T1 values were also consistent with the literature. No significant changes in SRLL measured T1 were found by the application of keyhole method. In the manganese enhanced MRI experiment T1 continuously decreased during MnCl2 injection and remained unchanged during the 15 min post infusion period. Conclusion: Our results indicate that SRLL can provide a robust measurement of myocardium and blood T1 in mice at high spatial (195×390 μm2) and temporal (3 min) resolutions. The application of keyhole can further reduce the imaging time to less than 2 min.

NMR of Liquid 3He in Pores of a Clay Sample

In the present work a new method for studying porous media by nuclear magnetic resonance of liquid 3He has been proposed. This method has been demonstrated by an example of a clay mineral sample. For the first time the integral porosity of the clay sample has been measured. For investigated samples the value of the integral porosity is in the range of 10–30%. The inverse Laplace transform of the 3He longitudinal magnetization recovery curve has been carried out and the distribution of the relaxation times T 1 has been obtained.

Modulated repetition time look‐locker (MORTLL): A method for rapid high resolution three‐dimensional T1 mapping

To demonstrate a modification of the Look-Locker (LL) technique that enables rapid high resolution T1 mapping over the physiologic range of intracranial T1 values, ranging from white matter to cerebrospinal fluid (CSF). This is achieved by use of a three-dimensional (3D) balanced steady-state free precession (b-SSFP) acquisition (for high signal-to-noise and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization. Two modifications to the Look-Locker technique were made to realize high resolution imaging in a clinically reasonable scan time. The 3D b-SSFP acquisition after an initial inversion pulse was followed by a variable repetition time. This technique makes it possible to image a volume of thin contiguous slices with high resolution and accuracy using a simple fitting procedure and is particularly useful for imaging long T1 species such as CSF. The total scan time is directly proportional to the number of slices to be acquired. The scan time was reduced by almost half when the repetition time was modified using a predesigned smooth function. Phantoms and volunteers were imaged at different resolutions on a 3 Tesla scanner. Results were compared with other accepted techniques. T1 values in the brain corresponded well with full repetition time imaging as well as inversion recovery spin echo imaging. T1 values for white matter, gray matter, and CSF were measured to be 755 +/- 10 ms, 1202 +/- 9 ms, and 4482 +/- 71 ms, respectively. Scan times were reduced by approximately half over full repetition time measurements. High resolution T1 maps can be obtained rapidly and with a relatively simple postprocessing method. The technique is particularly well suited for long T1 species. For example, changes in the composition of proteins in CSF are linked to various pathologies. The T1 values showed excellent agreement with values obtained from inversion recovery spin-echo imaging.