T2 Relaxation Time Measurements Research Articles

MRI‐based myelin water imaging: A technical review

Multiexponential T2 relaxation time measurement in the central nervous system shows a component that originates from water trapped between the lipid bilayers of myelin. This myelin water component is of significant interest as it provides a myelin-specific MRI signal of value in assessing myelin changes in cerebral white matter in vivo. In this article, the various acquisition and analysis strategies proposed to date for myelin water imaging are reviewed and research conducted into their validity and clinical applicability is presented. Comparisons between the imaging methods are made with a discussion regarding potential difficulties and model limitations.

Annular Repair Using High-Density Collagen Gel

Animal in vivo study. To test the capability of high-density collagen gel to repair annular defects. Annular defects are associated with spontaneous disc herniations and disc degeneration, which can lead to significant morbidity. Persistent annular defects after surgical discectomies can increase reherniation rates. Several synthetic and biological materials have been developed for annular repair. This is the first study to test an injectable biomaterial in vivo. We punctured caudal intervertebral discs in 42 athymic rats, using an 18-gauge needle to create an annular defect. High-density collagen (HDC), either alone or cross-linked with riboflavin (RF), was injected into the defect. There were 4 separate study groups: HDC, HDC cross-linked with either 0.25 mM RF or 0.50 mM RF, and a negative control that was punctured and not treated. The animals were followed for 5 weeks; radiographs were used to assess disc heights and magnetic resonance images were used to evaluate degenerative changes. We developed an algorithm on the basis of T2-relaxation time measurements to assess the size of the nucleus pulposus. Tails were collected for histological analysis to evaluate disc degeneration and measure the cross-sectional area of the nucleus pulposus. After 5 weeks, the control and the uncross-linked HDC groups both showed signs of progressive degenerative changes with minimal or no residual nucleus pulposus tissue in the disc space. Cross-linking significantly improved the ability of HDC gels to repair annular defects. The 0.50 mM RF cross-linked group showed only a slight decrease in nuclear tissue when compared with healthy discs, with no signs of intervertebral disc (IVD) degeneration. The annulus fibrosus was partially repaired by a fibrous cap that bridged the defect. Host fibroblasts infiltrated and remodeled the injected collagen. HDC is capable of repairing annular defects induced by needle puncture. The stiffness of HDC can be modified by riboflavin cross-linking and seems to positively affect the repair mechanism. These results need to be replicated in a larger animal model. N/A.

Usefulness of T1 mapping on Gd-EOB-DTPA-enhanced MR imaging in assessment of non-alcoholic fatty liver disease

This study evaluates the value of Gd-EOB-DTPA-enhanced MRI for diagnosis and staging of non-alcoholic fatty liver disease (NAFLD) in an animal model by T1 relaxation time measurement. Thirty-four rabbits were divided into the control group (n = 10) and NAFLD group, which was split into four groups (n = 6) with a high-fat diet for an interval of 3 weeks. A dual flip angle was performed before and at the hepatobiliary phase (HBP). T1 relaxation times of the liver parenchyma and the decrease rate (∆%) were calculated. Histological findings according to semi-quantitative scoring of steatosis, activity and fibrosis were the standard of reference. HBP and ∆%T1 relaxation time measurement showed significant differences between normal and NAFLD groups, between non-alcoholic steatohepatitis (NASH) and NAFLD without NASH (p = 0.000-0.049), between fibrosis groups (p = 0.000-0.019), but no difference between F1 and F2 (p = 0.834). The areas under the receiver operating characteristic curves (AUCs) of T1 relaxation time for HBP and ∆% were 0.86-0.93 for the selection of NASH and activity score ≥2, and 0.86-0.95 for the selection of F ≥ 1, 2, 3. No significant difference was found for diagnostic performance between HBP and ∆%T1 relaxation time. HBP T1 relaxation time measurement of Gd-EOB-DTPA-enhanced MRI was useful to evaluate NAFLD according to the SAF score. HBP T1 relaxation time measurement was as accurate as ∆%T1 relaxation time. • Gd-EOB-DTPA-enhanced MRI could give useful information on NAFLD. •HBP T 1 relaxation time measurement was useful for the evaluation of NAFLD. • HBP T 1 relaxation time measurement was as accurate as ∆%.

Gadolinium-free extracellular MR contrast agent for tumor imaging

To evaluate a new formulation of manganese porphyrin as a potential gadolinium (Gd)-free extracellular magnetic resonance imaging (MRI) contrast agent for dynamic contrast-enhanced (DCE) MRI of tumors. A previously reported new contrast agent, MnTCP, was evaluated in six female tumor-bearing nude rats. MRI was performed on a 3 T clinical scanner 3 to 4 weeks after inoculation of breast tumor cells in the mammary fat pads. Gd-DTPA was injected intravenously, followed by injection of MnTCP at least 2 hours later (both at 0.05 mmol/kg). T1 relaxation time measurements and DCE-MRI were performed. Enhancement and clearance patterns were visually similar between MnTCP and Gd-DTPA. However, relative R1 increases in all 11 tumors were larger for MnTCP over 60 minutes postcontrast, the difference being significant as late as 20 minutes (R1post /R1pre = 1.42 ± 0.15 for MnTCP vs. 1.20 ± 0.08 for Gd-DTPA, P < 0.05). R1 -related effects for MnTCP were largely reduced after 60 minutes (R1post /R1pre = 1.13 ± 0.07) and completely gone within 24 hours (R1post /R1pre = 0.97 ± 0.06). DCE-MRI revealed a consistently larger (1.5 to over 2-fold) peak enhancement and higher values of the steepest slope, time-to-peak, and AUC60 in all tumors with MnTCP (P < 0.01). MnTCP is an alternative to extracellular Gd agents for tumor imaging, offering sensitive detection and rapid renal clearance.

Improving the Understanding of the Properties and Retention Behavior of Chemically Bonded Stationary Phases Employing Suspended-state HR/MAS NMR Spectroscopy

Molecular recognition processes are predicted to become the basis of all advanced separation techniques. In solution and recently also in suspension ligand-receptor interactions can be studied using methods of high-resolution (HR) suspended-state NMR spectroscopy, for example by employing the saturation transfer difference (STD) NMR technique. In this approach molecular recognition processes of (R) and (S)-flurbiprofen on different derivatized polysaccharide-based silica chiral stationary phases (CSP) typically used in high performance liquid chromatography (HPLC) have been investigated. In addition to chromatographic investigations suspended-state high-resolution/ magic angle spinning (HR/MAS) NMR measurement were performed. A separation of racemic flurbiprofen was obtained on two out of three CSP column materials under identical chromatographic conditions. Hence, we expected significant different binding affinities resulting in spatial interactions stabilizing one transient diastereomeric complex relative to the other. Due to these differences we used for screening purposes T1 relaxation time measurements and the saturation transfer difference (STD) NMR methodology to study the interaction strength between (R) and (S) enantiomers and the three CSP materials used. Thus, saturation transfer difference (STD) NMR experiments can provide valuable information for the design and implementation of novel, task-specific or tailored stationary phases.

Phase-mixing and molecular dynamics in poly(urethane urea) elastomers by solid-state NMR

The dynamical heterogeneity in a series of 4,4′-dicyclohexylmethane diisocyanate-diethyltoluenediamine-poly(tetramethylene oxide) based poly(urethane urea) (PUU) elastomers was studied by solid-state nuclear magnetic resonance (NMR) methods. Extensive phase mixing was evidenced by the 1H wideline signal, which can be approximately fitted by a single exponential model. 13C T1 relaxation time measurements indicate that the hard segments (HS) exhibit some small-amplitude mobility, likely “activated” by neighboring soft segments (SS). Fitting of the time-domain wideline separation (TD-WISE) data was employed to characterize the extent of phase mixing, which revealed that a PUU elastomer contains four fractions: rigid-HS, mobile-HS, rigid-SS, and mobile-SS regions. For a variety of SS MWs, the dynamics and relative portions of rigid vs. mobile fractions among HS were substantially similar, while those for the SS exhibit large contrast. Furthermore, the dynamics in the rigid-SS fraction is at least an order of magnitude slower than that in mobile-SS for all PUUs. Greater phase-mixing substantially lowers the SS mobility, facilitating SS to undergo glass transition at high strain rates, thus can be key to enhancing dynamic mechanical strengthening.

Hydrogenation and Silylation of a Double-Cyclometalated Ruthenium Complex: Structures and Dynamic Behavior of Hydrido and Hydridosilicate Ruthenium Complexes

A double-cyclometalated ruthenium complex containing a chiral tripodal phospholane has been prepared by reaction with [Ru(η4-COD)(η3-methylallyl)2] via elimination of isobutene. The ruthenium–carbon bonds of this compound were reversibly cleaved by H2, resulting in an equilibrium between a tri- and a tetrahydride (4 and 5). T1 relaxation time measurements revealed the nonclassical nature of the fluctuating hydrides. Release of the gas led to complete re-formation of the cyclometalated compound. Reaction of 3 with D2 afforded D10-5, in which six ortho-phenyl protons and four hydrides were replaced by deuterium. Furthermore, diphenylsilane was found to readily insert into one Ru–C bond to form 6, containing a κ3-dihydridosilicate fragment. On the basis of deuterium labeling experiments, the fast exchange between the two hydrides was shown to include a reductive elimination/oxidative addition step involving the remaining metalated phenyl group. Again, pressurization of 6 with H2 resulted in reversible cleavage of the remaining Ru–C bond, yielding the corresponding trihydride 7.

Cardiac magnetic resonance T1 mapping of left atrial myocardium

Cardiac magnetic resonance (CMR) T1 mapping is an emerging tool for objective quantification of myocardial fibrosis. To (a) establish the feasibility of left atrial (LA) T1 measurements, (b) determine the range of LA T1 values in patients with atrial fibrillation (AF) vs healthy volunteers, and (c) validate T1 mapping vs LA intracardiac electrogram voltage amplitude measures. CMR imaging at 1.5 T was performed in 51 consecutive patients before AF ablation and in 16 healthy volunteers. T1 measurements were obtained from the posterior LA myocardium by using the modified Look-Locker inversion-recovery sequence. Given the established association of reduced electrogram amplitude with fibrosis, intracardiac point-by-point bipolar LA voltage measures were recorded for the validation of T1 measurements. The median LA T1 relaxation time was shorter in patients with AF (387 [interquartile range 364-428] ms) compared to healthy volunteers (459 [interquartile range 418-532] ms; P < .001) and was shorter in patients with AF with prior ablation compared to patients without prior ablation (P = .035). In a generalized estimating equations model, adjusting for data clusters per participant, age, rhythm during CMR, prior ablation, AF type, hypertension, and diabetes, each 100-ms increase in T1 relaxation time was associated with 0.1 mV increase in intracardiac bipolar LA voltage (P = .025). Measurement of the LA myocardium T1 relaxation time is feasible and strongly associated with invasive voltage measures. This methodology may improve the quantification of fibrotic changes in thin-walled myocardial tissues.

Longer T2relaxation time is a marker of hypothalamic gliosis in mice with diet-induced obesity

A hallmark of brain injury from infection, vascular, neurodegenerative, and other disorders is the development of gliosis, which can be detected by magnetic resonance imaging (MRI). In rodent models of diet-induced obesity (DIO), high-fat diet (HFD) consumption rapidly induces inflammation and gliosis in energy-regulating regions of the mediobasal hypothalamus (MBH), and recently we reported MRI findings suggestive of MBH gliosis in obese humans. Thus, noninvasive imaging may obviate the need to assess MBH gliosis using histopathological end points, an obvious limitation to human studies. To investigate whether quantitative MRI is a valid tool with which to measure MBH gliosis, we performed analyses, including measurement of T(2) relaxation time from high-field MR brain imaging of mice fed HFD and chow-fed controls. Mean bilateral T(2) relaxation time was prolonged significantly in the MBH, but not in the thalamus or cortex, of HFD-fed mice compared with chow-fed controls. Histological analysis confirmed evidence of increased astrocytosis and microglial accumulation in the MBH of HFD-fed mice compared with controls, and T(2) relaxation times in the right MBH correlated positively with mean intensity of glial fibrillary acidic protein staining (a marker of astrocytes) in HFD-fed animals. Our findings indicate that T(2) relaxation time obtained from high-field MRI is a useful noninvasive measurement of HFD-induced gliosis in the mouse hypothalamus with potential for translation to human studies.

Synthesis, Crystal Structure, and Solid-State NMR Investigations of Heteronuclear Zn/Co Coordination Networks — A Comparative Study

Synthesis and solid-state NMR characterization of two isomorphous series of zinc and cobalt coordination networks with 1,2,4-triazolyl benzoate ligands are reported. Both series consist of 3D diamondoid networks with four-fold interpenetration. Solid-state NMR identifies the metal coordination of the ligands, and assignment of all (1)H and (13)C shifts was enabled by the combination of (13)C editing, FSLG-HETCOR spectra, and 2D (1)H-(1)H back-to-back (BABA) spectra with results from NMR-CASTEP calculations. The incorporation of Co(2+) replacing Zn(2+) ions in the MOF over the full range of concentrations has significant influences on the NMR spectra. A uniform distribution of metal ions is documented based on the analysis of (1)H T1 relaxation time measurements.

Quantitative evaluation of MRI and histological characteristics of the 5xFAD Alzheimer mouse brain

Assessment of β-amyloid (Aβ) plaque load in Alzheimer's disease by MRI would provide an important biomarker to monitor disease progression or treatment response. Alterations in tissue structure caused by the presence of Aβ may cause localised changes that can be detected by quantitative T₁ and T₂ relaxation time measurements averaged over larger areas of tissue than that of individual plaques. We constructed depth profiles of the T₁ and T₂ relaxation times of the cerebral cortex with subjacent white matter and hippocampus in six 5xFAD transgenic and six control mice at 11 months of age. We registered these profiles with corresponding profiles of three immunohistochemical markers: β-amyloid; neuron-specific nuclear protein (NeuN), a marker of neuronal cell load; and myelin basic protein (MBP), a marker of myelin load. We found lower T₁ in the 5xFAD transgenic mice compared to wild type control mice at all depths, with maximum sensitivity for detection at specific layers. T₁ negatively correlated with Aβ staining intensity in the 5xFAD mice which had no changes in NeuN and MBP staining compared to wild type mice. We postulate that these relaxation time changes are due to the presence of β-amyloid in the transgenic mice. It may be clinically feasible to develop a similar layered analysis protocol as a biomarker for Alzheimer's disease in humans.

Functional MRI Measurements to Predict Early Adenoviral Gene Therapy Response in Ovarian Cancer Mouse Model

Anti-angiogenic and anti-lymphangiogenic gene therapy is a new potential method for the treatment of epithelial ovarian carcinoma. We studied the usefulness and feasibility of diffusion-weighted magnetic resonance imaging (DW-MRI) and relaxation measurements as surrogate markers of AdsVEGFR-2, AdsVEGFR-3, AdsNRP-1 and AdsNRP-2 gene therapy treatment responses in an intraperitoneal ovarian cancer mouse model (n= 45). Gene therapy was also combined with paclitaxel and carboplatin chemotherapy. Gene therapy was performed when visible tumors were noticed in MRI. Adenoviral gene transfer was dosed intravenously (2×109 pfu), while chemotherapy was dosed intraperitoneally. The study groups were: AdLacZ as controls (group I); AdsVEGFR-2 and AdsVEGFR-3 (group II); combination of AdsVEGFR-2, AdsVEGFR-3 and chemotherapy (group III) and AdsNRP-1 and AdsNRP-2 (group IV). Antitumor effectiveness was assessed by sequential MRI, immunohistochemistry, microvessel density, overall tumor growth, formation of ascites and survival time. Early responses in tumor tissue were evaluated with MRI measurements using relaxation times T2, T1ρ, TRAFF2, TRAFF4 and water apparent diffusion coefficient (ADC). The mean survival of mice (30 days) was significantly prolonged in group II as compared to controls (24 days) or other treatment groups (p= 0.003). The mean vascular density (MVD) and total vascular area (TVA) were significantly lower compared to controls in all groups: group II (p= 0.001), group III (p= 0.002), group IV (p= 0.026). T2 relaxation times were significantly increased at day 8 after the gene transfer in the combination gene therapy and chemotherapy group III compared to controls (p= 0.005). ADC values in the tumors were significantly increased in group IV at four days compared to controls (p= 0.044). Early changes in T2 relaxation times and ADC values after gene therapy suggest the potential of T2 relaxation time measurements and DW-MRI as early markers of treatment response after anti-angiogenic gene therapy and chemotherapy.

Metabolic Profiling and Outer Pericarp Water State in Zespri, CI.GI, and Hayward Kiwifruits

The metabolic profiling of aqueous extracts of Zespri Gold ( Actinidia chinensis ) and CI.GI (a controlled crossbreed from different species of Actinidia deliciosa ) kiwifruits and the water state of the outer pericarp of entire fruits were monitored over the season by means of high-field NMR spectroscopy and T(2) relaxation time measurements, respectively, and compared with the corresponding ones of Hayward kiwifruits previously investigated. A more complete assignment of the (1)H spectrum with respect to that obtained previously was reported: histidine, phenylalanine, quercetin 3-rhamnoside, and epicatechin were identified. Metabolic profiling confirmed Zespri's earlier maturation compared with the two other varieties. The water state of entire kiwifruits was measured nondestructively on fruits attached to the plants or detached from the plants. T(2) relaxation times were found to be sensitive to the kiwifruit developmental stage.

New Treatments and Imaging Strategies in Degenerative Disease of the Intervertebral Disks

Magnetic resonance (MR) imaging in patients with persistent low back pain and sciatica effectively demonstrates spine anatomy and the relationship of nerve roots and intervertebral disks. Except in cases with nerve root compression, disk extrusion, or central stenosis, conventional anatomic MR images do not help distinguish effectively between painful and nonpainful degenerating disks. Hypoxia, inflammation, innervation, accelerated catabolism, and reduced water and glycosaminoglycan content characterize degenerated disks, the extent of which may distinguish nonpainful from painful ones. Applied to the spine, "functional" imaging techniques such as MR spectroscopy, T1ρ calculation, T2 relaxation time measurement, diffusion quantitative imaging, and radio nucleotide imaging provide measurements of some of these degenerative features. Novel minimally invasive therapies, with injected growth factors or genetic materials, target these processes in the disk and effectively reverse degeneration in controlled laboratory conditions. Functional imaging has applications in clinical trials to evaluate the efficacy of these therapies and eventually to select patients for treatment. This report summarizes the biochemical processes in disk degeneration, the application of advanced disk imaging techniques, and the novel biologic therapies that presently have the most clinical promise.

OS044. Morphological differences in murine placenta detected by magneticresonance imaging measurements of T2 relaxation times in mouse models ofpreeclampsia

We have demonstrated that morphologically distinct regions of the murine placenta can be detected by magnetic resonance imaging (MRI), with image contrast arising from the variation in T2 relaxation times between regions and dependent upon blood flow. Previous studies of human placenta by other groups have shown a homogeneous tissue with correlation of relaxation times with gestational age and a trend for shorter relaxation times in pregnancies complicated by preeclampsia and fetal growth restriction. The ability to detect morphological changes and alterations in blood flow in experimental models of preeclampsia would be a significant boost in understanding the relationship between abnormal placental implantation, reduced placental perfusion, inflammatory cytokines, angiogenic molecules and other factors that may play a role in the syndrome. The aim of this study was to investigate whether morphological changes or abnormalities can be detected by T2 mapping in the placenta of mice subject to two experimental models of preeclampsia (reduced uterine perfusion pressure (RUPP) model and TNF-α induced model). Pregnant C57BL/6JArc mice were, on day 13.5 of gestation, either subject to a unilateral ligation of the right uterine artery (RUPP) (n=2) or given an infusion of TNF-α by subcutaneous insertion of a mini-osmotic pump primed to deliver 500ng/kg/day for 4days (n=2). Controls were normal pregnant (n=2), sham-operated (n=1) or saline infused animals(n=1). MRI images were acquired on anaesthetised mice on day 17.5 of gestation using a Bruker Avance 11.7 Tesla wide-bore spectrometer with micro-imaging probe capable of generating gradients of 0.45T/m. T2 measurements were acquired using an MSME sequence protocol (Bruker MSME-T2-map) with an in-plane resolution of 0.1-0.2mm. Matlab was used to generate R2 (i.e.,1/T2) maps from the acquired data with the T2 values being calculated from selected regions of interest from 2-6 individual placenta from each mouse. Differences in the pattern of the regions of T2 contrast in the placenta were observed between normal, TNF-α treated and RUPP mice. The ratio of T2 values from the inner two regions was also significantly altered in TNF-α treated 1.98±0.09 (p=0.007); RUPP 1.94±0.11 (p=0.006) compared to normal animals 2.5±0.1 . These results demonstrate that morphological differences or abnormalities can be detected by T2 mapping in the placenta of mice subject to experimental models of preeclampsia and may be used to analyse changes quantitatively. This technology has the potential to be used when studying the dynamic changes in the placenta of pregnancies complicated by preeclampsia.

PP084. Magnetic resonance imaging measurements of T2 relaxation times within contrasting regions of murine placenta is dependent upon blood flow

It has been postulated that reduced placental perfusion as a result of abnormal placental implantation is the initiating event that leads to the maternal symptoms of preeclampsia. To be able to directly measure blood flow and perfusion in the placenta in experimental models of preeclampsia would provide valuable insight into the structural abnormalities of this syndrome. Magnetic resonance imaging (MRI) offers visualization of anatomy and analysis of changes in tissue morphology and function including blood flow and perfusion. The major source of image contrast in MRI comes from the variation in relaxation times between tissues. Previously, human placenta has appeared as fairly homogeneous in studies of T1 and T2 relaxation times, with no internal morphology apparent. The aim of this study was to investigate, using much higher field strengths (11.7Tesla) and much higher resolution than have been used previously, whether structural inhomogeneities in the placenta can be discerned by T2 mapping and whether T2 mapping is capable of detecting structural abnormalities that may affect blood flow in a preeclamptic placenta. Magnetic resonance images were acquired on an anaesthetised C57BL/6JArc mouse placed in a vertical animal probe using a Bruker Avance 11.7Tesla wide-bore spectrometer with micro-imaging probe capable of generating gradients of 0.45T/m. T2 measurements were acquired using an MSME sequence protocol (Bruker MSME-T2-map) with an in-plane resolution of 0.1-0.2mm. Matlab was used to generate R2 (i.e., 1/T2) maps from the acquired data with the T2 values being calculated from selected regions of interest within 5 individual placenta. Additional T2 measurements were acquired on the same slices immediately after blood flow was reduced to zero. Three distinct regions of T2 contrast were discerned in the mouse placenta, likely correlating to the labrynthine, junctional and decidual zones. The contrast between the inner two regions was substantially abrogated when blood flow ceased upon euthanasia of the animal by anaesthetic overdose (p<0.005), whereas the decidual region remained unchanged (p=0.13). These results demonstrate that morphologically distinct regions of the mouse placenta can be detected through the mapping of T2 relaxation times. The contrast between regions is lost when blood flow ceases and the placenta becomes homogeneous in appearance, suggesting that differences in T2 relaxation times across regions of the placenta may be used to non-invasively examine structural abnormalities and blood flow in the placenta of experimental animal models of preeclampsia.

Effect of short-term unloading on T2 relaxation time in the lumbar intervertebral disc—in vivo magnetic resonance imaging study at 3.0 tesla

Background contextDiurnal changes in T2 values, indicative for changes in water content, have been reported in the lumbar intervertebral discs. However, data concerning short-term T2 changes are missing.PurposeThe purpose of this study was to investigate the short-term effects of unloading on T2 values in lumbar intervertebral discs in vivo.Study designExperimental study with repeated measurements of lumbar discs T2 relaxation time during a period of 38 minutes of supine posture.Patient sampleForty-one patients with acute or chronic low back pain (visual analog scale ≥3).Outcome measuresT2 relaxation time in the intervertebral disc, lumbar lordosis angle, and intervertebral disc height.MethodsForty-one patients (mean age, 41.6 years) were investigated in the supine position using a 3-tesla magnetic resonance system. Sagittal T2 mapping was performed immediately after unloading and after a mean delay of 38 minutes. No patient movement was allowed between the measurements. One region of interest (ROI) was manually placed in both the anterior and the posterior annulus fibrosus (AF) and three ROIs in the nucleus pulposus (NP).ResultsThere was a statistically significant decrease in the anterior NP (−2.7 ms; p<.05) and an increase in T2 values in the posterior AF (+3.5 ms; p<.001). Discs with initially low T2 values in the NP showed minor increase in the posterior AF (+1.6 ms; p<.05), whereas a major increase in the posterior AF was found in discs with initially high T2 values in the NP (+6.8 ms; p=.001). Patients examined in the morning showed no differences, but those investigated in the afternoon showed a decrease in the anterior NP (−5.3 ms; p<.05) and an increase in the posterior AF (+7.8 ms; p=.002). No significant differences were observed in other regions. Correlation analysis showed moderate correlations between the time of investigation and T2 changes in the posterior AF (r=0.46; p=.002).ConclusionsA shift of water from the anterior to the posterior disc regions seems to occur after unloading the lumbar spine in the supine position. The clinical relevance of these changes needs to be investigated.

MR relaxometry of the liver: significant elevation of T1 relaxation time in patients with liver cirrhosis

To evaluate hepatic relaxation times T1, T2 and T2* in healthy subjects and patients with liver cirrhosis stratified by the Child-Pugh classification (CPC). Sixty-one consecutive patients were stratified by CPC (class A026; B020; C015) and compared with age-matched controls (n = 31). Relaxometry measurements were performed at 1.5 T using six saturation recovery times (200-3,000 ms) to determine liver T1, six echo times (TE 14-113 ms) for T2 and eight TE (4.8-38 ms) for T2* assessment. Signal intensities in selected regions of interest in the liver parenchyma were fitted to theoretical models with least squares minimisation algorithms to determine T1, T2 and T2*. The most significant difference was the higher T1 values (852 ± 132 ms) in cirrhotic livers compared with controls (678 ± 45 ms, P < 0.0001). A less significant difference was seen for T2* (23 ± 5 vs. 26 ± 7 ms). Subdifferentiation showed a statistically significant difference between control group and individual CPC classes as well as between class C and classes A or B for T1 relaxation times. Measurement of T1 relaxation time can differentiate healthy subjects from patients with liver cirrhosis, and can distinguish between mild/moderate disease (CPC A/B) and advanced disease (CPC C). • Significantly elevated magnetic resonance T1 relaxation times are found in liver cirrhosis. • T1 relaxation times can distinguish healthy subjects from patients with liver cirrhosis. • T1 relaxation times can distinguish Child-Pugh classes Aand B from C.

Comparison of two ultrashort echo time sequences for the quantification of T1 within phantom and human Achilles tendon at 3 T

Ultrashort echo time (UTE) techniques enable direct imaging of musculoskeletal tissues with short T2 allowing measurement of T1 relaxation times. This article presents comparison of optimized 3D variable flip angle UTE (VFA-UTE) and 2D saturation recovery UTE (SR-UTE) sequences to quantify T1 in agar phantoms and human Achilles tendon. Achilles tendon T1 values for asymptomatic volunteers were compared to Achilles tendon T1 values calculated from patients with clinical diagnoses of spondyloarthritis (SpA) and Achilles tendinopathy using an optimized VFA-UTE sequence. T1 values from phantom data for VFA- and SR-UTE compare well against calculated T1 values from an assumed gold standard inversion recovery spin echo sequence. Mean T1 values in asymptomatic Achilles tendon were found to be 725±42 ms and 698±54 ms for SR- and VFA-UTE, respectively. The patient group mean T1 value for Achilles tendon was found to be 957±173 ms (P<0.05) using an optimized VFA-UTE sequence with pulse repetition time of 6 ms and flip angles 4, 19, and 24°, taking a total 9 min acquisition time. The VFA-UTE technique appears clinically feasible for quantifying T1 in Achilles tendon. T1 measurements offer potential for detecting changes in Achilles tendon due to SpA without need for intravenous contrast agents.

Peripheral Nerve Repair: Monitoring by Using Gadofluorine M–enhanced MR Imaging with Chitosan Nerve Conduits with Cultured Mesenchymal Stem Cells in Rat Model of Neurotmesis

To observe the longitudinal changes of nerve repair in rats after tissue-engineered construct implantation at magnetic resonance (MR) imaging and to determine whether the enhanced nerve regeneration with use of tissue-engineered constructs could be monitored with gadofluorine M-enhanced MR imaging or nerve T2 relaxation time measurement. All experimental protocols were approved by the institutional Animal Use and Care Committee. Tissue-engineered constructs were prepared by seeding mesenchymal stem cells (MSCs) into chitosan nerve tubes. Thirty-six rats with sciatic nerve transection injury underwent nerve tube implantation with (n = 18) or without (n = 18) MSC seeding. Sequential T2 measurement, gadofluorine M-enhanced MR imaging, and sciatic function index measurement were performed over an 8-week follow-up period, with histologic assessments performed at regular intervals. T2 relaxation times and signal intensity at gadofluorine M-enhanced T1-weighted imaging were measured and were compared by using repeated-measures analysis of variance followed by the Student-Neuman-Keuls post-hoc test for multiple pairwise comparisons. Nerve T2 relaxation times and gadofluorine M enhancement, as well as functional changes, showed a similar time course. Nerves implanted with MSC-seeded tubes achieved slightly better functional recovery and enhanced nerve regeneration while showing a slower return to baseline T2 relaxation time and a more rapid decline in gadofluorine M enhancement compared with nerves implanted with chitosan tubes alone. T2 values of the distal portion of transected nerves showed a more rapid return to baseline level than did gadofluorine M enhancement. Peripheral nerve repair with use of tissue-engineered constructs can be monitored by using gadofluorine M-enhanced MR imaging and T2 relaxation time measurements. T2 relaxation time seems more sensitive than gadofluorine M-enhanced MR imaging for detecting nerve regeneration.