Evaluating T1, T2 Relaxation, and Proton Density in Normal Brain Using Synthetic MRI with Fast Imaging Protocol

Synthetic MRI is being increasingly used for the quantification of brain longitudinal relaxation time (T1), transverse relaxation time (T2), and proton density (PD) values. However, the effect of fast imaging protocols on these quantitative values has not been fully estimated. The purpose of this study was to investigate the effect of fast scan parameters on T1, T2, and PD measured with a multi-dynamic multi-echo (MDME) sequence of normal brain at 3.0T. Thirty-four volunteers were scanned using 3 MDME sequences with different scan times (named Fast, 2 min, 29 sec; Routine, 4 min, 07 sec; and Research, 7 min, 46 sec, respectively). The measured T1, T2, and PD in 18 volumes of interest (VOI) of brain were compared between the 3 sequences using rank sum test, t test, coefficients of variation (CVs) analysis, correlation analysis, and Bland-Altman analysis. We found that even though T1, T2, and PD were significantly different between the 3 sequences in most of the brain regions, the intersequence CVs were relatively low and linear correlation were high. Bland-Altman plots showed that most of the values fall within the 95% prediction limits. We concluded that fast imaging protocols of MDME sequence used in our study can potentially be used for quantitative evaluation of brain tissues. Since changing scan parameters can affect the measured T1, T2, and PD values, it is necessary to use consistent scan parameter for comparing or following up cases quantitatively.

Longitudinal Relaxation (T 1) of Methane/Hydrogen Mixtures for Operando Characterization of Gas-Phase Reactions

Catalytic hydrogenation reactions are important in a modern hydrogen-based society. To optimize these gas-phase reactions, a deep understanding of heat, mass, and momentum transfer inside chemical reactors is required. Nuclear magnetic resonance (NMR) measurements can be used to obtain spatially resolved values of temperature, gas composition, and velocity in the usually opaque catalytic macrostructures. For this, the desired values are calculated from measured NMR parameters like signal amplitude, T ₁, or T ₂. However, information on how to calculate target values from these NMR parameters in gases is scarce, especially for mixtures of gases. To enable detailed NMR studies of hydrogenation reactions, we investigated the T ₁ relaxation of methane and hydrogen, which are two gases commonly present in hydrogenation reactions. To achieve industrially relevant conditions, the temperatures are varied from 290 to 600 K and the pressure from 1 bara to 5 bara, using different mixtures of methane and hydrogen. The results show that hydrogen, which is usually considered to be nondetectable in standard MRI sequences, can be measured at high concentrations, starting at a pressure of 3 bara even at temperatures above 400 K. In the investigated parameter range, the absolute T ₁ values of hydrogen show only small dependence on temperature, pressure, and composition, while T ₁ of methane is highly dependent on all three parameters. At a pressure of 5 bara, the measured values of T ₁ for methane agree very well with theoretical predictions, so that they can also be used for temperature calculations. Further, it can be shown that the same measurement technique can be used to accurately calculate gas ratios inside each voxel. In conclusion, this study covers important aspects of spatially resolved operando NMR measurements of gas-phase properties during hydrogenation reactions at industrially relevant conditions to help improve chemical processes in the gas phase.

Non-Conventional Time Domain (TD)-NMR Approaches for Food Quality: Case of Gelatin-Based Candies as a Model Food

The TD-NMR technique mostly involves the use of T1 (spin-lattice) and T2 (spin-spin) relaxation times to explain the changes occurring in food systems. However, these relaxation times are affected by many factors and might not always be the best indicators to work with in food-related TD-NMR studies. In this study, the non-conventional TD-NMR approaches of Solid Echo (SE)/Magic Sandwich Echo (MSE) and Spin Diffusion in food systems were used for the first time. Soft confectionary gelatin gels were formulated and conventional (T1) and non-conventional (SE, MSE and Spin Diffusion) TD-NMR experiments were performed. Corn syrups with different glucose/fructose compositions were used to prepare the soft candies. Hardness, °Brix (°Bx), and water activity (aw) measurements were also conducted complementary to NMR experiments. Relaxation times changed (p < 0.05) with respect to syrup type with no obvious trend. SE/MSE experiments were performed to calculate the crystallinity of the samples. Samples prepared with fructose had the lowest crystallinity values (p < 0.05). Spin Diffusion experiments were performed by using Goldman−Shen pulse sequence and the interface thickness (d) was calculated. Interface thickness values showed a wide range of variation (p < 0.05). Results showed that non-conventional NMR approaches had high potential to be utilized in food systems for quality control purposes.

Synthetic magnetic resonance imaging for quantitative parameter evaluation of temporomandibular joint disorders

OBJECTIVE

This study investigated the usefulness of quantitative parameters [longitudinal relaxation (T1), transverse relaxation (T2), and proton density (PD)] obtained with synthetic magnetic resonance imaging (MRI) in assessing the progression of temporomandibular joint (TMJ) disorders.

METHODS

For individual TMJ disorder diagnoses, the presence of disc displacement in MRI and the osseous change in cone-beam CT were investigated. Joints were classified into three stages: (1) silent stage, no disc displacement or osseous change; (2) incipient stage, presence of disc displacement and absence of osseous change; and (3) progressed stage, both disc displacement and osseous change. In synthetic MRI, the T1, T2, and PD values of the condyle bone marrow were measured simultaneously. The median T1, T2, and PD values were analyzed according to disc displacement, osseous changes, and joint stage.

RESULTS

Significant differences were observed in the T1 and PD values of joints with disc displacement or condylar osseous change compared to normal joints. The T1 and PD values also differed between the silent and progressed stages. The PD value differed between the silent and incipient groups, while the T2 value did not differ significantly among the three groups.

CONCLUSION

The PD and T1 values of condylar bone marrow obtained from synthetic MRI can be used as sensitive indicators of TMJ disorder progression. The PD value of the bone marrow showed potential as a useful biomarker for recognizing the initial stages of TMJ disorders. Synthetic MRI is useful for the simultaneous acquisition of effective MRI parameters for evaluating TMJ disorders.

The utility of MRI for measuring hematocrit in fetal anemia

BACKGROUND

Doppler ultrasound measurements of the peak systolic velocity of the middle cerebral artery can be used to noninvasively diagnose fetal anemia but are less precise following fetal blood transfusion and in late gestation. We have previously demonstrated the feasibility of estimating fetal hematocrit in vitro using magnetic resonance imaging relaxation times. Here we report the use of magnetic resonance imaging as a noninvasive tool to accurately detect fetal anemia in vivo.

OBJECTIVES

This study has 2 objectives: (1) to determine the feasibility and accuracy of magnetic resonance imaging in estimating hematocrit in anemic fetuses and (2) to compare magnetic resonance imaging and middle cerebral artery Doppler in detecting moderate to severe fetal anemia.

STUDY DESIGN

Fetuses undergoing fetal blood sampling or transfusion underwent magnetic resonance imaging examinations prior to and following their procedures at 1.5 Tesla (Siemens Avanto). A modified Look-Locker inversion pulse sequence and T₂ preparation sequence were applied for T₁ and T₂ mapping of the intrahepatic umbilical vein. Estimated fetal hematocrit was calculated using a combination of T₁ and T₂ values and compared with conventional hematocrit obtained from fetal blood samples and middle cerebral artery Doppler measurements.

RESULTS

Twenty-three fetuses were assessed during 33 magnetic resonance imaging scans. The mean absolute difference between the laboratory and magnetic resonance imaging-estimated hematocrit was 0.06 ± 0.05 with a correlation of 0.77 (P < .001) determined by a multilevel, mixed-effects model adjusting for the repeated measurements from the same participants, multiple gestation pregnancies, and the scan type (ie, before or after transfusion scan). Bland-Altman analysis revealed a systematic bias of -0.03 between the magnetic resonance imaging and fetal blood sampling measurements. Magnetic resonance imaging and middle cerebral artery Doppler had similar sensitivities of approximately 90% to detect moderate to severe anemia. However, magnetic resonance imaging had a higher specificity (93% [13/14], 95% confidence interval, 66-100%) than Doppler (71% [10/14], 95% confidence interval, 42-92%).

CONCLUSION

Moderate to severe fetal anemia can be detected noninvasively by magnetic resonance imaging with high sensitivity and specificity. Our results suggest an adjunct role for magnetic resonance imaging in fetuses with suspected anemia, particularly following previous transfusion and in late gestation.

Variable flip angle 3D ultrashort echo time (UTE) T1 mapping of mouse lung: A repeatability assessment

BACKGROUND

Lung T1 is a potential translational biomarker of lung disease. The precision and repeatability of variable flip angle (VFA) T1 mapping using modern 3D ultrashort echo time (UTE) imaging of the whole lung needs to be established before it can be used to assess response to disease and therapy.

PURPOSE

To evaluate the feasibility of regional lung T1 quantification with VFA 3D-UTE and to investigate long- and short-term T1 repeatability in the lungs of naive mice.

STUDY TYPE

Prospective preclinical animal study.

POPULATION

Eight naive mice and phantoms.

FIELD STRENGTH/SEQUENCE

3D free-breathing radial UTE (8 μs) at 4.7T.

ASSESSMENT

VFA 3D-UTE T1 calculations were validated against T1 values measured with inversion recovery (IR) in phantoms. Lung T1 and proton density (S0 ) measurements of whole lung and muscle were repeated five times over 1 month in free-breathing naive mice. Two consecutive T1 measurements were performed during one of the imaging sessions.

STATISTICAL TESTS

Agreement in T1 between VFA 3D-UTE and IR in phantoms was assessed using Bland-Altman and Pearson 's correlation analysis. The T1 repeatability in mice was evaluated using coefficient of variation (CV), repeated-measures analysis of variance (ANOVA), and paired t-test.

RESULTS

Good T1 agreement between the VFA 3D-UTE and IR methods was found in phantoms. T1 in lung and muscle showed a 5% and 3% CV (1255 ± 63 msec and 1432 ± 42 msec, respectively, mean ± SD) with no changes in T1 or S0 over a month. Consecutive measurements resulted in an increase of 2% in both lung T1 and S0 .

DATA CONCLUSION

VFA 3D-UTE shows promise as a reliable T1 mapping method that enables full lung coverage, high signal-to-noise ratio (∼25), and spatial resolution (300 μm) in freely breathing animals. The precision of the VFA 3D-UTE method will enable better design and powering of studies.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

In vivo measurement of T1 and T2 relaxation times in awake pigeon and rat brains at 7T

PURPOSE

Establishment of regional longitudinal (T₁ ) and transverse (T₂ ) relaxation times in awake pigeons and rats at 7T field strength. Regional differences in relaxation times between species and between two different pigeon breeds (homing pigeons and Figurita pigeons) were investigated.

METHODS

T₁ and T₂ relaxation times were determined for nine functionally equivalent brain regions in awake pigeons and rats using a multiple spin-echo saturation recovery method with variable repetition time and a multi-slice/multi-echo sequence, respectively. Optimized head fixation and habituation protocols were applied to accustom animals to the scanning conditions and to minimize movement.

RESULTS

The habituation protocol successfully limited movement of the awake animals to a negligible minimum, allowing reliable measurement of T₁ and T₂ values within all regions of interest. Significant differences in relaxation times were found between rats and pigeons but not between different pigeon breeds.

CONCLUSION

The obtained T₁ and T₂ values for awake pigeons and rats and the optimized habituation protocol will augment future MRI studies with awake animals. The differences in relaxation times observed between species underline the importance of the acquisition of T₁ /T₂ values as reference points for specific experiments. Magn Reson Med 79:1090-1100, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Investigation of the Longitudinal Relaxation Time of Rat Tibial Cortical Bone Using SWIFT

Sweep imaging with Fourier transform (SWIFT) method has been developed to image tissues with very short T₂ values, such as cortical bone. The purpose of this study was to measure the T₁ value of the rat cortical bone. It was approximately 120 ms on 7.04T. This result could thus be useful for studying bony tissue according to the SWIFT method in the future.

A rapid inversion technique for the measurement of longitudinal relaxation times of brain metabolites: application to lactate in high-grade gliomas at 3 T

The aim of this study was to develop a time-efficient inversion technique to measure the T1 relaxation time of the methyl group of lactate (Lac) in the presence of contaminating lipids and to measure T1 at 3 T in a cohort of primary high-grade gliomas. Three numerically optimized inversion times (TIs) were chosen to minimize the expected error in T1 estimates for a given input total scan duration (set to be 30 min). A two-cycle spectral editing scheme was used to suppress contaminating lipids. The T1 values were then estimated from least-squares fitting of signal measurements versus TI. Lac T1 was estimated as 2000 ± 280 ms. After correcting for T1 (and T2 from literature values), the mean absolute Lac concentration was estimated as 4.3 ± 2.6 mm. The technique developed agrees with the results obtained by standard inversion recovery and can be used to provide rapid T1 estimates of other spectral components as required. Lac T1 exhibits similar variations to other major metabolites observable by MRS in high-grade gliomas. The T1 estimate provided here will be useful for future MRS studies wishing to report relaxation-corrected estimates of Lac concentration as an objective tumor biomarker. Copyright © 2016 John Wiley & Sons, Ltd.

Relaxation properties of human umbilical cord blood at 1.5 Tesla

PURPOSE

To characterize the MRI relaxation properties of human umbilical cord blood at 1.5 Tesla.

METHODS

Relaxometry measurements were performed on cord blood specimens (N = 88, derived from six caesarean deliveries) spanning a broad range of hematocrits (Hct = 0.19-0.76) and oxygen saturations (sO₂ = 4-100%), to characterize the dependence of T₁ and T₂ on these blood properties. Adult blood data (N = 31 specimens, derived from two volunteers) were similarly studied to validate our experimental methods by comparison with existing literature. Using biophysical models previously developed for adult blood, new model parameters were estimated, which relate Hct and sO₂ to the observed cord blood relaxation times.

RESULTS

Fitted biophysical models explained more than 90% of the variation in T₁ and T₂ . In general, T₂ relaxation times of cord blood were longer (by up to 35%) than those of adult blood, whereas T₁ relaxation times were slightly shorter (by up to 10%).

CONCLUSIONS

The models and fitted parameters presented here can be used for calibration of future MRI investigations of fetal and neonatal blood physiology. This study is an important step in facilitating accurate, noninvasive assessments of fetal blood oxygen content, a valuable diagnostic parameter in the identification and treatment of fetal hypoxia. Magn Reson Med 77:1678-1690, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Native myocardial longitudinal (T1 ) relaxation time: Regional, age, and sex associations in the healthy adult heart

Purpose

To use magnetic resonance imaging (MRI) at two field strengths to assess healthy adults' regional myocardial noncontrast (native) T₁ relaxation time distribution, and global myocardial native T₁ between sexes and across age groups.

Materials and Methods

In all, 84 healthy volunteers underwent MRI at 1.5T and 3.0T. T₁ maps were acquired in three left ventricular short axis slices using an optimized modified Look–Locker inversion recovery investigational prototype sequence. T₁ measurements in msec were calculated from 16 regions‐of‐interest, and a global T₁ value from all evaluable segments per subject. Associations were assessed with a multivariate linear regression model.

Results

In total, 1297 (96.5%) segments were evaluable at 1.5T and 1263 (94.0%) segments at 3.0T. Native T₁ was higher in septal than lateral myocardium (1.5T: 956.3 ± 44.4 vs. 939.2 ± 54.2 msec; P < 0.001; 3.0T: 1158.2 ± 45.9 vs. 1148.9 ± 56.9 msec; P = 0.012). Native T₁ decreased with increasing age in females but not in males. Among lowest age tertile (<33 years) global native T₁ was higher in females than in males at 1.5T (960.0 ± 20.3 vs. 931.5 ± 22.2 msec, respectively; P = 0.003) and 3.0T (1166.5 ± 19.7 vs. 1130.2 ± 20.6 msec; P < 0.001). No sex differences were observed in upper age tertile (≥55 years) at 1.5T (937.7 ± 25.4 vs. 934.7 ± 22.3 msec; P = 0.762) or 3.0T (1153.0 ± 30.0 vs. 1132.3 ± 23.5 msec; P = 0.056). Association of global native T₁ to age (P = 0.002) and sex (P < 0.001) was independent of field strength and body size.

Conclusion

In healthy adults, native T₁ values are highest in the ventricular septum. Global native T₁ was inversely associated with age in women, but not in men. J. Magn. Reson. Imaging 2016;44:541–548.

T1 and T2 values of human neonatal blood at 3 Tesla: Dependence on hematocrit, oxygenation, and temperature

PURPOSE

Knowledge of blood T1 and T2 is of major importance in many applications of MRI in neonates. However, to date, there has not been a systematic study to examine neonatal blood T1/T2 relaxometry. This present study aims to investigate this topic.

METHODS

Using freshly collected blood samples from human umbilical cord, we performed in vitro experiments under controlled physiological conditions to measure blood T1 and T2 at 3 Tesla (T) and their dependence on several factors, including hematocrit (Hct), oxygenation (Y) and temperature.

RESULTS

The arterial T1 in neonates was 1825 ± 184 ms (Hct = 0.42 ± 0.08), longer than that of adult blood. Neonatal blood T1 was strongly dependent on Hct (P < 0.001) and Y (P = 0.005), and the dependence of T1 on Y was more prominent at higher Hct. The arterial T2 of neonatal blood was 191 ms at an Hct of 0.42, which was also longer than adult blood. Neonatal blood T2 was positively associated with blood oxygenation and negatively associated with hematocrit level, and can be characterized by an exchange model. Neonatal blood T1 was also positively associated with temperature (P < 0.001).

CONCLUSION

The values provided in this report may provide important reference and calibration information for sequence optimization and quantification of in vivo neonatal MRI studies.

Hyperpolarized singlet lifetimes of pyruvate in human blood and in the mouse

Hyperpolarized NMR is a promising technique for non-invasive imaging of tissue metabolism in vivo. However, the pathways that can be studied are limited by the fast T1 decay of the nuclear spin order. In metabolites containing pairs of coupled nuclear spins-1/2, the spin order may be maintained by exploiting the non-magnetic singlet (spin-0) state of the pair. This may allow preservation of the hyperpolarization in vivo during transport to tissues of interest, such as tumors, or to detect slower metabolic reactions. We show here that in human blood and in a mouse in vivo at millitesla fields the (13)C singlet lifetime of [1,2-(13)C2]pyruvate was significantly longer than the (13)C T1, although it was shorter than the T1 at field strengths of several tesla. We also examine the singlet-derived NMR spectrum observed for hyperpolarized [1,2-(13)C2]lactate, originating from the metabolism of [1,2-(13)C2]pyruvate.