T2 Accuracy on a whole-body imager

MR oximetry requires a T₂ measurement that is accurate within 5% in vivo. Simple methods are susceptible to signal loss and tend to underestimate T₂. Current methods utilize RF pulses or RF cycling patterns that prevent signal loss at each data acquisition. However, using these methods with imperfect pulses, T₂ tends to be overestimated due to temporary storage of the magnetization along the longitudinal axis where it decays more slowly with a time constant T₁T₂. To reduce the T₁ dependence while preventing signal loss, we utilize simple 90_x180_y90_x composite pulses and good RF cycling patterns. These trains are critical for T₂ accuracy over typical ranges of RF and static field inhomogeneities and refocusing intervals. T₁ signal decay during each 90_x180_y90_x pulse must be accounted for to yield accuracy within 5% when the pulse-width is 10% or more of the refocusing interval. A simple correction scheme compensates for this T₁-related error effectively.     

MRI as an alternative to serum ferritin for diagnosis of iron overload in children in the context of immune response after stem cell transplantation

Multiple blood cell transfusions may cause iron overload or even liver fibrosis, requiring early diagnosis and intervention. SF is the standard for estimating iron levels in the body, but it also increases with inflammation. We hypothesized that T₂* magnetic resonance (MR) relaxometry is a more accurate alternative for follow‐up in pediatric patients before and after allogenic SCT. Twenty‐three children (mean age 10.2 years, 10 female, 13 male) were evaluated prospectively before SCT as well as at least 1 year after SCT with T₂* relaxometry on a 1.5 T MR‐scanner to estimate liver iron concentrations from the T₂* values (“MR‐Fe”). The results were compared with SF, while also considering CRP, and correlated with the number of transfusions. Overall, 24.3 transfusions were administered in average, mainly within 100 days of SCT (mean 10.5 units). Both MR‐Fe and SF increased after SCT and decreased in the absence of new transfusions 1 year later without chelate therapy. This suggests regeneration of LP and iron loss, although the original states were not reached. Additionally, simultaneous peaks of CRP and SF were observed directly after SCT. MR‐Fe did neither reveal these peaks nor was it associated with CRP (P = .39). We postulate that these early CRP and SF peaks after SCT are probably related to inflammatory reactions and not to iron overload. Thus, SF is not reliable for iron overload diagnosis after SCT in every condition. Beside this interaction, SF and MR‐Fe revealed similar accuracy. MRI, however, has practical and economical disadvantages in routine estimation of iron.     

Multi‐parametric MRI characterization of healthy human thigh muscles at 3.0 T – relaxation,magnetization transfer,fat/water,and diffusion tensor imaging

Muscle diseases commonly have clinical presentations of inflammation, fat infiltration, fibrosis, and atrophy. However, the results of existing laboratory tests and clinical presentations are not well correlated. Advanced quantitative MRI techniques may allow the assessment of myo‐pathological changes in a sensitive and objective manner. To progress towards this goal, an array of quantitative MRI protocols was implemented for human thigh muscles; their reproducibility was assessed; and the statistical relationships among parameters were determined. These quantitative methods included fat/water imaging, multiple spin‐echo T₂ imaging (with and without fat signal suppression, FS), selective inversion recovery for T₁ and quantitative magnetization transfer (qMT) imaging (with and without FS), and diffusion tensor imaging. Data were acquired at 3.0 T from nine healthy subjects. To assess the repeatability of each method, the subjects were re‐imaged an average of 35 days later. Pre‐testing lifestyle restrictions were applied to standardize physiological conditions across scans. Strong between‐day intra‐class correlations were observed in all quantitative indices except for the macromolecular‐to‐free water pool size ratio (PSR) with FS, a metric derived from qMT data. Two‐way analysis of variance revealed no significant between‐day differences in the mean values for any parameter estimate. The repeatability was further assessed with Bland–Altman plots, and low repeatability coefficients were obtained for all parameters. Among‐muscle differences in the quantitative MRI indices and inter‐class correlations among the parameters were identified. There were inverse relationships between fractional anisotropy (FA) and the second eigenvalue, the third eigenvalue, and the standard deviation of the first eigenvector. The FA was positively related to the PSR, while the other diffusion indices were inversely related to the PSR. These findings support the use of these T₁, T₂, fat/water, and DTI protocols for characterizing skeletal muscle using MRI. Moreover, the data support the existence of a common biophysical mechanism, water content, as a source of variation in these parameters. Copyright © 2014 John Wiley & Sons, Ltd.     

Tissue‐ and column‐specific measurements from multi‐parameter mapping of the human cervical spinal cord at 3 T

The aim of this study was to quantify a range of MR parameters [apparent proton density, longitudinal relaxation time T₁, magnetisation transfer (MT) ratio, MT saturation (which represents the additional percentage MT saturation of the longitudinal magnetisation caused by a single MT pulse) and apparent transverse relaxation rate R₂*] in the white matter columns and grey matter of the healthy cervical spinal cord. The cervical cords of 13 healthy volunteers were scanned at 3 T using a protocol optimised for multi‐parameter mapping. Intra‐subject co‐registration was performed using linear registration, and tissue‐ and column‐specific parameter values were calculated. Cervical cord parameter values measured from levels C1–C5 in 13 subjects are: apparent proton density, 4822 ± 718 a.u.; MT ratio, 40.4 ± 1.53 p.u.; MT saturation, 1.40 ± 0.12 p.u.; T₁ = 1848 ± 143 ms; R₂* = 22.6 ± 1.53 s^–1. Inter‐subject coefficients of variation were low in both the cervical cord and tissue‐ and column‐specific measurements, illustrating the potential of this method for the investigation of changes in these parameters caused by pathology. In summary, an optimised cervical cord multi‐parameter mapping protocol was developed, enabling tissue‐ and column‐specific measurements to be made. This technique has the potential to provide insight into the pathological processes occurring in the cervical cord affected by neurological disorders. © 2013 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.     

Osmotic effects on the T2 relaxation decay of in vivo muscle.

Saline solutions are commonly employed as a vehicle for drugs administered intramuscularly. In this study, in vivo measurements of spin-spin relaxation (T2) processes by magnetic resonance imaging (MRI) were performed to investigate the distribution of water in rat masseter muscle tissue after intramuscular injection of saline solutions of varying tonicity. Prior to saline injection, image-based T2 relaxation decay of muscle was monoexponential. After injection of saline, the T2 relaxation decay became multiexponential. Non-negative least squares (NNLS) analysis of the decay curves revealed two relaxation components: a fast component (T2 = 20-40 ms) and a slow component (T2 = 150-400 ms), which are assigned to intra- and extracellular water protons, respectively. Injection of hypertonic saline solutions significantly increased the extracellular water component in muscle tissue compared to isotonic saline solutions, an effect which lasted for more than 60 min. These findings suggest that MRI techniques may be useful to investigate the effect of hyper- or hypotonic solutions on muscle tissue in vivo.     

Correlation of proton transverse relaxation rates (R2) with iron concentrations in postmortem brain tissue from alzheimer's disease patients

Iron accumulates in the Alzheimer's disease (AD) brain and is directly associated with β‐amyloid pathology. The proton transverse relaxation rate (R₂) has a strong linear relationship with iron concentrations in healthy brain tissue; however, an independent test of this relationship has not been extended to AD brain tissue. In this study in vitro single spin‐echo (SE) measurements were made on tissue samples from four human AD brains using a 4.7T MRI research scanner. R₂ values were calculated for 14 cortical and subcortical gray matter (GM) and white matter (WM) regions. Atomic absorption spectroscopy was used to measure iron concentrations in the corresponding excised brain regions. Significant positive linear correlations were observed between R₂ values and iron concentrations in GM regions assessed across individual tissue samples and data averaged by brain region. With the use of a predictive model for R₂, a threshold iron concentration of 55 μg Fe/g wet tissue was determined above which R₂ appears to be dominated by the affects of iron in AD brain tissue. High‐field MRI may therefore be a useful research tool for assessing brain iron changes associated with AD. Magn Reson Med 57:172–180, 2007. © 2006 Wiley‐Liss, Inc.     

New Composite Hydrogel Based on Whey and Gelatin Crosslinked with Copper Sulphate

By-products from the meat and dairy industries are important sources of high biological value proteins. This paper explores possibilities for improving the swelling and integrity of a cross-linked whey and gelatin hydrogel with different amounts of CuSO₄ × 5H₂O. Overall, swelling tests demonstrate that cross-linked samples show a better hydration capacity and stability in the hydration medium, but different copper concentrations lead to different swelling behavior. At concentrations smaller than 0.39%, the sample lasts for 75 h in a water environment before beginning to disintegrate. At a concentration of copper sulphate higher than 0.55%, the stability of the sample increased substantially. The swelling kinetics has been investigated. The diffusion constant values increased with the increase in copper concentration, but, at the highest concentration of copper (0.86%), its value has decreased. Spectroscopy analyses such as Fourier transform infrared (FT-IR), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-VIS), and nuclear magnetic resonance (NMR) relaxometry analyses revealed changes in the secondary and tertiary structure of proteins as a result of the interaction of Cu²⁺ ions with functional groups of protein chains. In addition to its cross-linking ability, CuSO₄ × 5H₂O has also shown excellent antibacterial properties over common bacterial strains responsible for food spoilage. The result of this research demonstrates the potential of this hydrogel system as a unique material for food packaging.