In vivo 3.0‐tesla magnetic resonance T1ρ and T2 relaxation mapping in subjects with intervertebral disc degeneration and clinical symptoms

The purpose of this study is (1) to determine the correlation between T_1ρ and T₂ and degenerative grade in intervertebral discs using in vivo 3.0‐T MRI, and (2) to determine the association between T_1ρ and T₂ and clinical findings as quantified by the SF‐36 Questionnaire and Oswestry Disability Index. Sixteen subjects participated in this study, and each completed SF‐36 and Oswestry Disability Index questionnaires. MRI T_1ρ and T₂ mapping was performed to determine T_1ρ (77 discs) and T₂ (44 discs) in the nucleus of the intervertebral disc, and T₂‐weighted images were acquired for Pfirrmann grading of disc degeneration. Pfirrmann grade was correlated with both T_1ρ (r = ?0.84; P < 0.01) and T₂ (r = ?0.61; P < 0.01). Mixed‐effects models demonstrate that only T_1ρ was associated with clinical questionnaires (R²_SF‐36 = 0.55, R²_O.D.I. = 0.56; P < 0.05). Although the averaged values of T_1ρ and T₂ were significantly correlated, they presented differences in spatial distribution and dynamic range, thus suggesting different sensitivities to tissue composition. This study suggests that T_1ρ may be sensitive to early degenerative changes (corroborating previous studies) and clinical symptoms in intervertebral disc degeneration. Magn Reson Med 63:1193–1200, 2010. © 2010 Wiley‐Liss, Inc.     

Indirectly probing Ca2+ handling alterations following myocardial infarction in a murine model using T1‐mapping manganese‐enhanced magnetic resonance imaging

Prolonged ischemia causes cellular necrosis and myocardial infarction (MI) via intracellular calcium (Ca²⁺) overload. Manganese‐enhanced MRI indirectly assesses Ca²⁺ influx movement in vivo as manganese (Mn²⁺) is a Ca²⁺ analog. To characterize myocardial Mn²⁺ efflux properties, T₁‐mapping manganese‐enhanced MRI studies were performed on adult male C57Bl/6 mice in which Ca²⁺ efflux was altered using pharmacological intervention agents or MI‐inducing surgery. Results showed that ( 1 ) Mn²⁺ efflux rate increased exponentially with increasing Mn²⁺ doses; ( 2 ) SEA0400 (a sodium–calcium exchanger inhibitor) decreased the rate of Mn²⁺ efflux; and ( 3 ) dobutamine (a positive inotropic agent) increased the Mn²⁺ efflux rate. A novel analysis technique also delineated regional features in the MI mice, which showed an increased Mn²⁺ efflux rate in the necrosed and peri‐infarcted tissue zones. The T₁‐mapping manganese‐enhanced MRI technique characterized alterations in myocardial Mn²⁺ efflux rates following both pharmacologic intervention and an acute MI. The Mn²⁺ efflux results were consistent with those in ex vivo studies showing an increased Ca²⁺ concentration under similar conditions. Thus, T₁‐mapping manganese‐enhanced MRI has the potential to indirectly identify and quantify intracellular Ca²⁺ handling in the peri‐infarcted tissue zones, which may reveal salvageable tissue in the post‐MI myocardium. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Spatial distribution and relationship of T1ρ and T2 relaxation times in knee cartilage with osteoarthritis

T_1ρ and T₂ relaxation time constants have been proposed to probe biochemical changes in osteoarthritic cartilage. This study aimed to evaluate the spatial correlation and distribution of T_1ρ and T₂ values in osteoarthritic cartilage. Ten patients with osteoarthritis (OA) and 10 controls were studied at 3T. The spatial correlation of T_1ρ and T₂ values was investigated using Z‐scores. The spatial variation of T_1ρ and T₂ values in patellar cartilage was studied in different cartilage layers. The distribution of these relaxation time constants was measured using texture analysis parameters based on gray‐level co‐occurrence matrices (GLCM). The mean Z‐scores for T_1ρ and T₂ values were significantly higher in OA patients vs. controls (P < 0.05). Regional correlation coefficients of T_1ρ and T₂ Z‐scores showed a large range in both controls and OA patients (0.2–0.7). OA patients had significantly greater GLCM contrast and entropy of T_1ρ values than controls (P < 0.05). In summary, T_1ρ and T₂ values are not only increased but are also more heterogeneous in osteoarthritic cartilage. T_1ρ and T₂ values show different spatial distributions and may provide complementary information regarding cartilage degeneration in OA. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Value of precontrast T1 for dGEMRIC of native articular cartilage

Purpose

To evaluate if the difference between pre‐ and post‐Gd‐DTPA^2‐ relaxation rate (ΔR₁) provides better differentiation of osteoarthritic patients (OA) from healthy subjects (HS) with dGEMRIC, as compared to post‐Gd‐DTPA^2‐ spin‐lattice relaxation time (T_1Gd).

Materials and Methods

Seventeen OA and 14 HS underwent pre‐ and 90 minutes postcontrast (Gd‐DTPA^2‐) magnetic resonance imaging (MRI) of the knee, using inversion recovery fast spin‐echo and/or Lock–Locker sequences for T₁ mapping. Effect sizes for T_1pre, T_1Gd, and ΔR₁ were calculated, and receiver operating characteristic (ROC) curve and regression analysis were also performed to assess the effectiveness of each parameter in the separation of OA and HS.

Results

T_1Gd and ΔR₁ were almost identical in terms of areas under ROC curves (0.903 and 0.914, respectively), and effect sizes (1.34 and 1.31, respectively). These were significantly higher than T_1pre. In addition, a high inverse correlation was observed between ΔR₁ vs. T_1Gd (R = 0.96).

Conclusion

Either T_1Gd or ΔR₁ could be used as an index in the evaluation of native cartilage. However, considering the practical logistical cost involved in terms of time and effort to acquire precontrast T₁ measurements, our data further support the continued use of T_1Gd as the dGEMRIC index in the evaluation of native cartilage. J. Magn. Reson. Imaging 2009;29:494–497. © 2009 Wiley‐Liss, Inc.     

Gleaning multicomponent T1 and T2 information from steady‐state imaging data

The driven‐equilibrium single‐pulse observation of T₁ (DESPOT1) and T₂ (DESPOT2) are rapid, accurate, and precise methods for voxelwise determination of the longitudinal and transverse relaxation times. A limitation of the methods, however, is the inherent assumption of single‐component relaxation. In a variety of biological tissues, in particular human white matter (WM) and gray matter (GM), the relaxation has been shown to be more completely characterized by a summation of two or more relaxation components, or species, each believed to be associated with unique microanatomical domains or water pools. Unfortunately, characterization of these components on a voxelwise, whole‐brain basis has traditionally been hindered by impractical acquisition times. In this work we extend the conventional DESPOT1 and DESPOT2 approaches to include multicomponent relaxation analysis. Following numerical analysis of the new technique, renamed multicomponent driven equilibrium single pulse observation of T₁/T₂ (mcDESPOT), whole‐brain multicomponent T₁ and T₂ quantification is demonstrated in vivo with clinically realistic times of between 16 and 30 min. Results obtained from four healthy individuals and two primary progressive multiple sclerosis (MS) patients demonstrate the future potential of the approach for identifying and assessing tissue changes associated with several neurodegenerative conditions, in particular those associated with WM. Magn Reson Med 60:1372–1387, 2008. © 2008 Wiley‐Liss, Inc.     

Breathhold multiecho fast spin‐echo pulse sequence for accurate R2 measurement in the heart and liver

Measurement of proton transverse relaxation rates (R₂) is a generally useful means for quantitative characterization of pathological changes in tissue with a variety of clinical applications. The most widely used R₂ measurement method is the Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence but its relatively long scan time requires respiratory gating for chest or body MRI, rendering this approach impractical for comprehensive assessment within a clinically‐acceptable examination time. The purpose of our study was to develop a breathhold multiecho fast spin‐echo (FSE) sequence for accurate measurement of R₂ in the liver and heart. Phantom experiments and studies of subjects in vivo were performed to compare the FSE data with the corresponding even‐echo CPMG data. For pooled data, the R₂ measurements were strongly correlated (Pearson correlation coefficient = 0.99) and in excellent agreement (mean difference [CPMG – FSE] = 0.10 s^–1; 95% limits of agreement were 1.98 and –1.78 s^–1) between the two pulse sequences. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Concurrent MR blood volume and vessel size estimation in tumors by robust and simultaneous ΔR2 and ΔR2* quantification

This work presents a novel method for concurrent estimation of the fractional blood volume and the mean vessel size of tumors based on a multi‐gradient‐echo‐multi‐spin‐echo sequence and the injection of a super‐paramagnetic blood‐pool agent. The approach further comprises a post‐processing technique for simultaneous estimation of changes in the transverse relaxation rates R₂ and R, which is robust against global B₀ and B₁ field inhomogeneities and slice imperfections. The accuracy of the simultaneous ΔR₂ and ΔR quantification approach is evaluated in a phantom. The simultaneous blood volume and vessel size estimates, obtained with MR, compare well to the immunohistological findings in a preclinical experiment (HT1080 cells, implanted in nude mice). Clinical translation is achieved in a patient with a pleomorphic sarcoma in the left pubic bone. The latter demonstrates the robustness of the technique against changes in the contrast agent concentration in blood during washout. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Dynamic and simultaneous MR measurement of R1 and R2* changes during respiratory challenges for the assessment of blood and tissue oxygenation

This work presents a novel method for the rapid and simultaneous measurement of R₁ and R₂* relaxation rates. It is based on a dynamic short repetition time steady‐state spoiled multigradient‐echo sequence and baseline R₁ and B₁ measurements. The accuracy of the approach was evaluated in simulations and a phantom experiment. The sensitivity and specificity of the method were demonstrated in one volunteer and in four patients with intracranial tumors during carbogen inhalation. We utilized (ΔR₂*, ΔR₁) scatter plots to analyze the multiparametric response amplitude of each voxel within an area of interest. In normal tissue R₂* decreased and R₁ increased moderately in response to the elevated blood and tissue oxygenation. A strong negative ΔR₂* and ΔR₁ response was observed in veins and some tumor areas. Moderate positive ΔR₂* and ΔR₁ response amplitudes were found in fluid‐rich tissue as in cerebrospinal fluid, peritumoral edema, and necrotic areas. The multiparametric approach was shown to increase the specificity and sensitivity of oxygen‐enhanced MRI compared to measuring ΔR₂* or ΔR₁ alone. It is thus expected to provide an optimal tool for the identification of tissue areas with low oxygenation, e.g., in tumors with compromised oxygen supply. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Interleaved T1 and T2 relaxation time mapping for cardiac applications

Purpose

To diagnose acute myocardial infarction (MI) with MRI, T₁‐weighted and T₂‐weighted images are required to detect necrosis and edema. The calculation of both T₁ and T₂ maps can be relevant for quantitative diagnosis. In this work, we present a simultaneous quantification of T₁‐T₂ relaxation times of a short‐axis view of the heart in a single scan.

Materials and Methods

An electrocardiograph (ECG)‐triggered, navigator‐gated, interleaved T₁ and T₂ mapping sequence was implemented for the quantification of the T₁ and T₂ values of phantoms, healthy volunteers, and three patients with acute MI. The proposed acquisition scheme consisted of an interleaved two‐dimensional (2D) steady‐state free precession (SSFP) sequence with three different modules: an inversion‐recovery (IR) sequence with multiple time delays, followed by a delay of one cardiac cycle for magnetization recovery and a T₂‐preparation pulse with multiple echo‐times for T₂ quantification.

Results

Measurements of in vivo relaxation times were in good agreement with literature values. The interleaved sequence was able to measure T₁ and T₂ relaxation times of the myocardium.

Conclusion

The interleaved sequence acquires data for the calculation of T₁ and T₂ maps in only one scan without the need for registration. This technique has the potential to differentiate between acute and chronic MI by estimating the concentration of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) in the necrotic tissue and to assess the extent of edema from T₂ maps. J. Magn. Reson. Imaging 2009;29:480–487. © 2009 Wiley‐Liss, Inc.     

Characterization of T2* heterogeneity in human brain white matter

Recent in vivo MRI studies at 7.0 T have demonstrated extensive heterogeneity of T₂* relaxation in white matter of the human brain. In order to study the origin of this heterogeneity, we performed T₂* measurements at 1.5, 3.0, and 7.0 T in normal volunteers. Formalin‐fixed brain tissue specimens were also studied using T₂*‐weighted MRI, histologic staining, chemical analysis, and electron microscopy. We found that T₂* relaxation rate (R₂* = 1/T₂*) in white matter in living human brain is linearly dependent on the main magnetic field strength, and the T₂* heterogeneity in white matter observed at 7.0 T can also be detected, albeit more weakly, at 1.5 and 3.0 T. The T₂* heterogeneity exists also in white matter of the formalin‐fixed brain tissue specimens, with prominent differences between the major fiber bundles such as the cingulum (CG) and the superior corona radiata. The white matter specimen with substantial difference in T₂* has no significant difference in the total iron content, as determined by chemical analysis. On the other hand, evidence from histologic staining and electron microscopy demonstrates these tissue specimens have apparent difference in myelin content and microstructure. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Measurement of intervertebral disc pressure with T1ρ MRI

The aim of this study is to demonstrate T_1ρ MRI's capability for measuring intervertebral disc osmotic pressure. Self‐coregistered sodium and T_1ρ‐weighted MR images were acquired on ex vivo bovine intervertebral discs (N = 12) on a 3 T clinical MRI scanner. The sodium MR images were used to calculate effective nucleus pulposus fixed‐charge‐density (mean = 138.2 ± 27.6 mM) and subsequently osmotic pressure (mean = 0.53 ± 0.18 atm), whereas the T_1ρ‐weighted images were used to compute T_1ρ relaxation maps. A significant linear correlation (R = 0.56, P < 0.01) between nucleus pulposus fixed‐charge‐density and T_1ρ relaxation time constant was observed. More importantly, a significant power correlation (R = 0.72, P < 0.01) between nucleus pulposus osmotic pressure as predicted by sodium MRI and T_1ρ relaxation time constant was also observed. The current clinical method for assessing disc pressure is discography, which is an invasive procedure that has been shown to have negative effects on disc biomechanical and biochemical properties. In contrast, T_1ρ MRI is noninvasive and can be easily implemented in a clinical setting due to its superior signal‐to‐noise ratio compared with sodium MRI. Therefore, T_1ρ MRI may serve as a noninvasive clinical tool for the longitudinal evaluation of disc osmotic pressure. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Experimental protocol for activation‐induced manganese‐enhanced MRI (AIM‐MRI) based on quantitative determination of Mn content in rat brain by fast T1 mapping

In activation‐induced manganese‐enhanced MRI (AIM‐MRI) experiments, differential accumulation of Mn in activated and silent brain areas is generally assessed using T₁‐weighted images and quantified by the enhancement of signal intensity (SI), calculated with reference to SI before Mn administration or to SI of brain regions unaffected by the specific stimulus. However, SI enhancement can be unreliable when animals are removed from and reinserted into the magnet. We have developed an experimental protocol based on repeated intraperitoneal (i.p.) injections of Mn, quantitative determination of T₁, and coregistration of images to a rat brain atlas that allows absolute quantification of Mn concentration in selected brain areas. Results showed that interanimal variability of postcontrast T₁ values was very low (compared to the experimental error in T₁ determinations) allowing detection of differential regional Mn uptake in stimulated and unstimulated animals. In addition we have determined in vivo relaxivity of Mn in brain tissue and its frequency dependence. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

On using T2 to assess extrinsic magnetic field inhomogeneity effects on T2* measurements in myocardial siderosis in thalassemia

Magnetic resonance T₂* has been validated as a noninvasive means of assessing myocardial iron overload. However, the effect on myocardial T₂* of factors such as shimming, variations in capillary geometry, and susceptibility in relation to the effects of iron has not been fully clarified. Since T₂ is not affected by extrinsic magnetic field inhomogeneity and has different sensitivity to capillary geometry, investigation into the in vivo relationship between myocardial T₂* and T₂ measurements can shed light on this important issue. This study was performed in 136 thalassemia patients. The myocardial T₂ and T₂* thresholds for normality created identical no‐iron‐overload and iron‐overloaded patient groups. In the no‐iron group, there was no correlation between myocardial T₂ and T₂*. In the iron‐overloaded patients, there was a linear correlation (R² = 0.89) between myocardial T₂* and T₂ measurements, which indicates that the iron deposition is the dominant factor in determining these two relaxation values in this scenario. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.     

Dose dependence and temporal evolution of the T1 relaxation time and MRI contrast in the rat brain after subcutaneous injection of manganese chloride

Divalent manganese ion (Mn²⁺) is a widely used T₁ contrast agent in manganese‐enhanced MRI studies to visualize functional neural tracts and anatomy in the brain in vivo. In animal studies, Mn²⁺ is administered at a dose that will maximize the contrast, while minimizing its toxic effects. In rodents, systemic administration of Mn²⁺ via intravenous injection has been shown to create unique MRI contrast in the brain at a maximum dose of 175 mg kg^?1. However, intravenous administration of Mn²⁺ results in faster bioelimination of excess Mn²⁺ from the plasma due to a steep concentration gradient between plasma and bile. By contrast, following subcutaneous injection (LD₅₀ value = 320 mg kg^?1), Mn²⁺ is released slowly into the bloodstream, thus avoiding immediate hepatic elimination resulting in prolonged accumulation of Mn²⁺ in the brain via the choroid plexus than that obtained via intravenous administration. The goal of this study was to investigate MRI dose response of Mn²⁺ in rat brain following subcutaneous administration of Mn²⁺. Dose dependence and temporal dynamics of Mn²⁺ after subcutaneous injection can prove useful for longitudinal in vivo studies that require brain enhancement to persist for a long period of time to visualize neuroarchitecture like in neurodegenerative disease studies. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

T2‐weighted MRI of post‐infarct myocardial edema in mice

T₂‐weighted, cardiac magnetic resonance imaging (T₂w CMR) can be used to noninvasively detect and quantify the edematous region that corresponds to the area at risk (AAR) following myocardial infarction (MI). Previously, CMR has been used to examine structure and function in mice, expediting the study of genetic manipulations. To date, CMR has not been applied to imaging of post‐MI AAR in mice. We developed a whole‐heart, T₂w CMR sequence to quantify the AAR in mouse models of ischemia and infarction. The ΔB₀ and ΔB₁ environment around the mouse heart at 7 T were measured, and a T₂‐preparation sequence suitable for these conditions was developed. Both in vivo T₂w and late gadolinium enhanced CMR were performed in mice after 20‐min coronary occlusions, resulting in measurements of AAR size of 32.5 ± 3.1 (mean ± SEM)% left ventricular mass, and MI size of 50.1 ± 6.4% AAR size. Excellent interobserver agreement and agreement with histology were also found. This T₂w imaging method for mice may allow for future investigations of genetic manipulations and novel therapies affecting the AAR and salvaged myocardium following reperfused MI. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Mn‐bicine: A low affinity chelate for manganese ion enhanced MRI

The toxicity of free Mn²⁺ is a bottleneck for the in vivo application of manganese ion enhanced MRI. To reduce free Mn²⁺ concentration ([Mn²⁺]), a low affinity chelate reagent: N,N‐bis(2‐hydroxyethyl)glycine (bicine) was used. Considering the conditional association constant of Mn‐bicine at pH 7.4 (10^2.9 M^?1), (i) a 100 mM Mn‐bicine solution should contain about 10 mM of free manganese ion, but (ii) free manganese will make up 3/4 of the final plasma concentration (0.5 mM) with an intravenous infusion of 100 mM Mn‐bicine. The T₁ relaxivity of Mn‐bicine in a 5 mM Mn‐bicine solution was estimated as 5 mM^?1 sec^?1 at 24°C, 7 T in a pH range of 6.8–7.5. Mn‐bicine demonstrated a tendency for better contractility when employed with an isolated perfused frog heart, compared with MnCl₂. A venous infusion of 100 mM Mn‐bicine (8.3 μmol kg^?1 min^?1) showed a minimal decrease and maintained a constant heart rate level and arterial pressure in rats, while rats infused with 100 mM of MnCl₂ showed a significant suppression of the hemodynamic functions. Thus, Mn‐bicine appears to be a better choice for maintaining the vital conditions of experimental animals, and may improve the reproducibility of manganese ion enhanced MRI. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Postmortem MRI of human brain hemispheres: T2 relaxation times during formaldehyde fixation

Unlike in vivo imaging, postmortem MRI allows for invasive examination of the tissue specimen immediately after the MR scan. However, natural tissue decomposition and chemical fixation cause the postmortem tissue's MRI properties to be different from those found in vivo. Moreover, these properties change as postmortem fixation time elapses. The goal of this study was to characterize the T₂ relaxation changes that occur over time in cadaveric human brain hemispheres during fixation. Five hemispheres immersed in formaldehyde solution were scanned on a weekly basis for 3 months postmortem, and once again at 6 months postmortem. The T₂ relaxation times were measured throughout the hemispheres. Over time, T₂ values near the edges of the hemispheres decreased rapidly after death, while T₂ values of deep tissue decreased more slowly. This difference is likely due to the relatively large distance from the hemisphere surface, and other barriers limiting diffusion of formaldehyde molecules to deep tissues. In addition, T₂ values in deep tissue did not continuously decay to a plateau, but instead reached a minimum and then increased to a plateau. This final increase may be due to the effects of prolonged tissue decomposition, a hypothesis that is supported by numerical simulations of the fixation process. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Change in the proton T1 of fat and water in mixture

This work describes observed changes in the proton T₁ relaxation time of both water and lipid when they are in relatively homogeneous mixtures. Results obtained from vegetable oil–water emulsions, pork kidney and lard mixtures, and excised samples of white and brown adipose tissues are presented to demonstrate this change in T₁ as a function of mixture fat fraction. As an initial proof of concept, a simpler acetone‐water experiment was performed to take advantage of complete miscibility between acetone and water and both components' single chemical shift peaks. Single‐voxel MR spectroscopy was used to measure the T₁ of predominant methylene spins in fat and the T₁ of water spins in each setup. In the vegetable oil–water emulsions, the T₁ of fat varied by as much as 3‐fold when water was the dominant mixture component. The T₁ of pure lard increased by 170 msec (+37%) when it was blended with lean kidney tissue in a 16% fatty mixture. The fat T₁ of lipid‐rich white adipose tissue was 312 msec. In contrast, the fat T₁ of leaner brown adipose tissue (fat fraction 53%) was 460 msec. A change in the water T₁ from that of pure water was also observed in the experiments. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

Quantification techniques to minimize the effects of native T1 variation and B1 inhomogeneity in dynamic contrast‐enhanced MRI of the breast at 3 T

The variation of the native T₁ (T₁₀) of different tissues and B₁ transmission‐field inhomogeneity at 3 T are major contributors of errors in the quantification of breast dynamic contrast‐enhanced MRI. To address these issues, we have introduced new enhancement indices derived from saturation‐recovery snapshot‐FLASH (SRSF) images. The stability of the new indices, i.e., the SRSF enhancement factor (EF_SRSF) and its simplified version (EF′_SRSF) with respect to differences in T₁₀ and B₁ inhomogeneity was compared against a typical index used in breast dynamic contrast‐enhanced MRI, i.e., the enhancement ratio (ER), by using computer simulations. Imaging experiments with Gd‐DTPA‐doped gel phantoms and a female volunteer were also performed. A lower error was observed in the new indices compared to enhancement ratio in the presence of typical T₁₀ variation and B₁ inhomogeneity. At changes of relaxation rate (ΔR₁) of 8 s^?1, the differences between a T₁₀ of 1266 and 566 ms are <1, 12, and 58%, respectively, for EF_SRSF, EF′_SRSF, and ER, whereas differences of 20, 8, and 51%, respectively, result from a 50% B₁ field reduction at the same ΔR₁. These quantification techniques may be a solution to minimize the effect of T₁₀ variation and B₁ inhomogeneity on dynamic contrast‐enhanced MRI of the breast at 3 T. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Comparison of T1 relaxation times of the neurochemical profile in rat brain at 9.4 tesla and 14.1 tesla

Knowledge of T₁ relaxation times can be important for accurate relative and absolute quantification of brain metabolites, for sensitivity optimizations, for characterizing molecular dynamics, and for studying changes induced by various pathological conditions. ¹H T₁ relaxation times of a series of brain metabolites, including J‐coupled ones, were determined using a progressive saturation (PS) technique that was validated with an adiabatic inversion‐recovery (IR) method. The ¹H T₁ relaxation times of 16 functional groups of the neurochemical profile were measured at 14.1T and 9.4T. Overall, the T₁ relaxation times found at 14.1T were, within the experimental error, identical to those at 9.4T. The T₁s of some coupled spin resonances of the neurochemical profile were measured for the first time (e.g., those of γ‐aminobutyrate [GABA], aspartate [Asp], alanine [Ala], phosphoethanolamine [PE], glutathione [GSH], N‐acetylaspartylglutamate [NAAG], and glutamine [Gln]). Our results suggest that T₁ does not increase substantially beyond 9.4T. Furthermore, the similarity of T₁ among the metabolites (～1.5 s) suggests that T₁ relaxation time corrections for metabolite quantification are likely to be similar when using rapid pulsing conditions. We therefore conclude that the putative T₁ increase of metabolites has a minimal impact on sensitivity when increasing B₀ beyond 9.4T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.