Survival of itinerant excitations and quantum spin state transitions in YbMgGaO4 with chemical disorder

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO₄, a triangular lattice antiferromagnet with effective spin-1/2 Yb³⁺ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO₄ is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual κ₀/T term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO₄. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO₄.

It remains an open question as to whether the quantum spin liquid state survives material disorder, or is replaced by some spin-liquid like state. Here, Rao et al succeed in resolving a resolving a κ₀/T residual in the thermal conductivity of YbMgGaO₄ strongly suggesting the survival of the quantum spin liquid state.

1H MR Spectroscopy of Fine-Needle Aspiration Biopsy Specimens for the Discrimination of Breast Cancer

Purpose

To determine whether MR spectroscopic assessment of fine-needle aspiration (FNA) biopsy specimens from suspicious breast lesions could be used to improve the diagnostic utility of FNA biopsies for the characterization of breast lesions.

Materials and Methods

In this prospective study, a previously reported technique using high-spatial-resolution proton MR spectroscopy was modified and used to examine the utility of FNA biopsies in the evaluation of suspicious breast lesions. Tissue samples from 115 lesions (from 102 women; average age, 54 years) were excised by using FNA and core biopsies and were collected between September 7, 2012, and April 11, 2014. Histologic results from core biopsy specimens determined the lesions to be benign (n = 55), invasive ductal carcinoma (n = 51), invasive lobular carcinoma (n = 5), or ductal carcinoma in situ (n = 4). Measures of phosphocholine (PC), glycerophosphocholine, and choline relative to each other and to total creatine (tCr) were obtained from usable spectra. Planned comparisons among lesion groups were carried out using t test contrasts, and differences of each contrast level from zero were judged significant when the two-tailed P value was less than .05.

Results

Of the 115 samples, 69 (60%) yielded no usable MR spectra. Analysis of the 46 with usable spectra found that only the difference in PC/tCr between benign and cancer lesions was statistically significant (P = .028).

Conclusion

Given that 60% of FNA biopsy specimens yielded no usable spectra and that results were largely inconclusive when derived from usable spectra, the combined MR and FNA technique, as modified and implemented in this study, is of little value for detection and diagnosis of breast cancer.Keywords: Breast, MR-Spectroscopy, Neoplasms-Primary© RSNA, 2020.

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2BaCo(PO4)2

The most fascinating feature of certain two-dimensional (2D) gapless quantum spin liquid (QSL) is that their spinon excitations behave like the fermionic carriers of a paramagnetic metal. The spinon Fermi surface is then expected to produce a linear increase of the thermal conductivity with temperature that should manifest via a residual value (κ₀/T) in the zero-temperature limit. However, this linear in T behavior has been reported for very few QSL candidates. Here, we studied the ultralow-temperature thermal conductivity of an effective spin-1/2 triangular QSL candidate Na₂BaCo(PO₄)₂, which has an antiferromagnetic order at very low temperature (T_N ~ 148 mK), and observed a finite κ₀/T extrapolated from the data above T_N. Moreover, while approaching zero temperature, it exhibits series of quantum spin state transitions with applied field along the c axis. These observations indicate that Na₂BaCo(PO₄)₂ possibly behaves as a gapless QSL with itinerant spin excitations above T_N and its strong quantum spin fluctuations persist below T_N.

Neurophysiological effects of multiple mood episodes in bipolar disorder

OBJECTIVES

Bipolar disorder is marked by progressive symptomatic changes, which have been linked with episode-related structural findings-particularly in the prefrontal cortex. However, few studies have examined neurofunctional and neurochemical effects of disease burden. In this study, we compared first- and multi-episode bipolar individuals. We hypothesized that the latter would demonstrate evidence of neurophysiological differences consistent with a model of progressive functional degradation of these networks.

METHODS

First- and multi-episode manic bipolar subjects participated in functional magnetic resonance imaging (fMRI) including a continuous performance task with emotional distractors, and in single-voxel (¹ H) magnetic resonance spectroscopy (MRS). A priori fMRI regions-of-interest (ROI) included structures comprising prefrontal-striatal-amygdala networks; (¹ H)MRS voxels were placed within bilateral ventrolateral prefrontal (VLPFC) and anterior cingulate cortex (ACC). Both ROI and voxel-based brain activation in response to emotional stimuli, and neurochemical concentrations derived from (¹ H)MRS were compared across bipolar groups.

RESULTS

Multi-episode bipolar subjects showed relatively lower regional activation across prefrontal-striatal-amygdala networks, including bilateral VLPFC, orbitofrontal cortex, ACC, putamen, caudate, and amygdala. Exploratory whole-brain, voxel-based analysis suggested additional areas of lower activation extending into Brodmann area 22, posterior parietal regions, and right thalamus. Glutamate and N-acetylaspartate (NAA) concentrations were also relatively lower in the ACC of multi-episode subjects.

CONCLUSIONS

Disease burden, exemplified by multiple affective episodes is associated with evidence of widespread decrements in affective network activity. Lower ACC NAA concentration is similarly consistent with a model of progressive functional deficits. These findings support the functional significance of previously observed progressive structural changes throughout these regions.

Longitudinal proton spectroscopy study of the prefrontal cortex in youth at risk for bipolar disorder before and after their first mood episode

OBJECTIVES

To investigate neurochemical abnormalities in the left and right ventrolateral prefrontal cortex (VLPFC) and anterior cingulate cortex (ACC) of youth at risk for bipolar disorder using proton magnetic resonance spectroscopy before and after their first mood episode.

METHODS

Children and adolescents offspring of parents with bipolar I disorder (at-risk group, n = 117) and matched healthy controls (HC group, n = 61) were recruited at the University of Cincinnati. At-risk subjects had no lifetime major mood and psychotic disorders at baseline, and were followed up every 4 months to monitor for development of a major depressive, manic, hypomanic, or mixed mood episode. Levels of N-acetyl-aspartate (NAA), phosphocreatine plus creatine (PCr + Cr), choline-containing compounds, myo-inositol, and glutamate were determined using LCModel and corrected for partial volume effects.

RESULTS

There were no baseline differences in metabolite levels for any of the brain regions between at-risk and HC youth. Nineteen at-risk subjects developed a first mood episode during follow-up. Survival analyses showed that baseline PCr + Cr levels in the left VLPFC significantly predicted a mood episode during follow-up in the at-risk group (HR: 0.47, 95% CI: 0.27-0.82, P = 0.008). There were no longitudinal changes in metabolites levels in the VLPFC and ACC before and after a mood episode in at-risk subjects.

CONCLUSIONS

We found no evidence for abnormal proton spectroscopy metabolite levels in the VLPFC and ACC of at-risk youth, prior and after the development of their first mood episode. Preliminary findings of association between baseline PCr + Cr levels in the left VLPFC and risk to develop a mood episode warrant further investigation.

Prediction of lithium response in first-episode mania using the LITHium Intelligent Agent (LITHIA): Pilot data and proof-of-concept

OBJECTIVES

Individualized treatment for bipolar disorder based on neuroimaging treatment targets remains elusive. To address this shortcoming, we developed a linguistic machine learning system based on a cascading genetic fuzzy tree (GFT) design called the LITHium Intelligent Agent (LITHIA). Using multiple objectively defined functional magnetic resonance imaging (fMRI) and proton magnetic resonance spectroscopy (¹ H-MRS) inputs, we tested whether LITHIA could accurately predict the lithium response in participants with first-episode bipolar mania.

METHODS

We identified 20 subjects with first-episode bipolar mania who received an adequate trial of lithium over 8 weeks and both fMRI and ¹ H-MRS scans at baseline pre-treatment. We trained LITHIA using 18 ¹ H-MRS and 90 fMRI inputs over four training runs to classify treatment response and predict symptom reductions. Each training run contained a randomly selected 80% of the total sample and was followed by a 20% validation run. Over a different randomly selected distribution of the sample, we then compared LITHIA to eight common classification methods.

RESULTS

LITHIA demonstrated nearly perfect classification accuracy and was able to predict post-treatment symptom reductions at 8 weeks with at least 88% accuracy in training and 80% accuracy in validation. Moreover, LITHIA exceeded the predictive capacity of the eight comparator methods and showed little tendency towards overfitting.

CONCLUSIONS

The results provided proof-of-concept that a novel GFT is capable of providing control to a multidimensional bioinformatics problem-namely, prediction of the lithium response-in a pilot data set. Future work on this, and similar machine learning systems, could help assign psychiatric treatments more efficiently, thereby optimizing outcomes and limiting unnecessary treatment.

[Impact of carbon dioxide pneumoperitoneum in operating rooms on the health of medical staffs]

Objective: To evaluate the impact of CO(2) pneumoperitoneum in operating rooms on the health of medical staffs. Methods: In June 2016, the thirty-three medical staffs in operating rooms were chosen as the object of the research.Seventeen people who took part in the pneumoperitoneum operation were selected as a exposure group and sixteen people who took part in the laparotomy operation were selected as a control group.Vital signs and arterial blood gases of medical staffs in the two groups were both measured in pre-operation and post-operation. Occupational Health Questionnaires were conducted to collect information on age, weight and postoperative symptoms. The level of CO(2) in operating room was determined by a portable infrared CO(2) analyzer. Results: Compared with the control group, the concentration of CO(2) in the exposed group was higherat T(1), T(2) and T(3) (t=22.227, 13.583, 17.408, P<0.05) . Heart rates and PaCO(2) in the exposure group raised greatly (t=2.132, 2.129, P<0.05) , while pH decreased (t=-3.015, P<0.05) . The differences between the two groups were statistically significant. Conclusion: The increase of mild acidosis and thesense of job burnout in medical staffs could be caused by CO(2) pollution in the operating rooms.

fMRI brain activation changes following treatment of a first bipolar manic episode

OBJECTIVES

We tested the hypothesis that, with treatment, functional magnetic resonance imaging (fMRI) regional brain activation in first-episode mania would normalize - i.e., that differences from healthy subjects would diminish over time, and would be associated with clinical remission status, potentially identifying neuroanatomic treatment response markers.

METHODS

Forty-two participants with bipolar I disorder were recruited during their first manic episode, pseudo-randomized to open-label lithium or quetiapine, and followed for 8 weeks. fMRI scans were obtained at baseline and then after 1 and 8 weeks of treatment, while participants performed a continuous performance task with emotional distracters. Healthy participants received fMRI scans at these same intervals. Specific region-of-interest (ROI) activations within prefrontal emotional networks were assessed as potential measures of treatment response.

RESULTS

ROI data were reduced using exploratory factor analysis, which identified five factors that were organizationally consistent with functional anatomic models of human emotion modulation. Half of the participants with bipolar disorder achieved remission by Week 8 and were contrasted with the other half that did not. Analyses demonstrated that, in the bipolar disorder group in general, treatment led to decreases in activation across brain regions toward healthy subject values. However, differences in activation changes were observed between subjects with bipolar disorder who did or did not achieve remission in subcortical and amygdala factors.

CONCLUSIONS

These findings provide evidence for potential neuroanatomic treatment response markers in first-episode bipolar disorder.

Effects of fish oil supplementation on prefrontal metabolite concentrations in adolescents with major depressive disorder: a preliminary 1H MRS study

OBJECTIVE

To use proton magnetic resonance spectroscopy ((1)H MRS) to investigate the effects of fish oil (FO) supplementation on cortical metabolite concentrations in adolescents with major depressive disorder (MDD).

METHODS

Metabolite concentrations were determined by (1)H MRS in the anterior cingulate cortex and bilateral dorsolateral prefrontal cortex (DLPFC) of adolescents with MDD before and following 10-week open-label supplementation with low (2.4 g/day, n = 7) or high (16.2 g/day, n = 7) dose FO. Depressive symptom severity scores and erythrocyte fatty acid levels were also determined.

RESULTS

Baseline erythrocyte eicosapentaenoic acid (EPA) composition was positively correlated, and arachidonic acid (AA) and the AA/EPA ratio were inversely correlated, with choline (Cho) concentrations in the right DLPFC. Docosahexaenoic acid (DHA) composition was inversely correlated with myo-inositol (mI) concentrations in the left DLPFC. Erythrocyte EPA and DHA composition increased, and AA decreased, significantly following low-dose and high-dose FO supplementation. In the intent-to-treat sample, depressive symptom severity scores decreased significantly in the high-dose group (-40%, P < 0.0001) and there was a trend in the low-dose group (-20%, P = 0.06). There were no significant baseline-endpoint changes in metabolite levels in each voxel. In the low-dose group there were changes with large effect sizes, including a decrease in mI in the left DLPFC (-12%, P = 0.18, d = 0.8) and increases in glutamate + glutamine (Glx) (+12%, P = 0.19, d = 0.8) and Cho (+15%, P = 0.08, d = 1.2) in the right DLPFC. In the high-dose group, there was a trend for increases in Cho in the right DLPFC (+10%, P = 0.09, d = 1.2).

DISCUSSION

These preliminary data suggest that increasing the LCn-3 fatty acid status of adolescent MDD patients is associated with subtle changes in Glx, mI, and Cho concentrations in the DLPFC that warrant further evaluation in a larger controlled trial.

A pilot study of anterior cingulate cortex neurochemistry in adolescents with generalized anxiety disorder

BACKGROUND/AIMS

This study used proton magnetic resonance spectroscopy (¹H MRS) to evaluate the neurochemistry of the anterior cingulate cortex (ACC) in adolescents with generalized anxiety disorder (GAD).

METHODS

Adolescents with GAD (n = 10) and healthy subjects (n = 10) underwent a ¹H MRS scan at 4 T. Glutamate (Glu), N-acetyl aspartate, creatine (Cr) and myo-inositol concentrations were measured in the ACC and were compared between untreated adolescents with GAD and age- and sex-matched healthy subjects.

RESULTS

Glu/Cr ratios in the ACC correlated with the severity of both generalized anxiety symptoms on the Pediatric Anxiety Rating Scale and with total anxiety symptom severity as measured by the Hamilton Anxiety Rating Scale, but did not differ between adolescents with GAD and healthy subjects. In addition, no differences in N-acetyl aspartate, Cr, or myo-inositol were detected between groups.

CONCLUSION

These findings suggest that Glu/Cr in untreated adolescents with GAD may relate to the severity of anxiety symptoms and raise the possibility that dysregulation of Glu within the ACC may be linked to the pathophysiology of pediatric GAD.

N-acetyl aspartate levels in adolescents with bipolar and/or cannabis use disorders

OBJECTIVE

Bipolar and cannabis use disorders commonly co-occur during adolescence, and neurochemical studies may help clarify the pathophysiology underlying this co-occurrence. This study compared metabolite concentrations in the left ventral lateral prefrontal cortex among adolescents with bipolar disorder (bipolar group; n = 14), adolescents with a cannabis use disorder (cannabis use group; n = 13), adolescents with cannabis use and bipolar disorders (bipolar and cannabis group; n = 25), and healthy adolescents (healthy controls; n = 15). We hypothesized that adolescents with bipolar disorder (with or without cannabis use disorder) would have decreased N-acetyl aspartate levels in the ventral lateral prefrontal cortex compared to the other groups and that the bipolar and cannabis group would have the lowest N-acetyl aspartate levels of all groups.

METHODS

N-acetyl aspartate concentrations in the left ventral lateral prefrontal cortex were obtained using proton magnetic resonance spectroscopy.

RESULTS

Adolescents with bipolar disorder showed significantly lower left ventral lateral prefrontal cortex N-acetyl aspartate levels, but post hoc analyses indicated that this was primarily due to increased N-acetyl aspartate levels in the cannabis group. The cannabis use disorder group had significantly higher N-acetyl aspartate levels compared to the bipolar disorder and the bipolar and cannabis groups (p = .0002 and p = .0002, respectively). Pearson correlations revealed a significant positive correlation between amount of cannabis used and N-acetyl aspartate concentrations.

CONCLUSIONS

Adolescents with cannabis use disorder showed higher levels of N-acetyl aspartate concentrations that were significantly positively associated with the amount of cannabis used; however, this finding was not present in adolescents with comorbid bipolar disorder.

Low docosahexaenoic acid status is associated with reduced indices in cortical integrity in the anterior cingulate of healthy male children: a 1H MRS Study

Docosahexaenoic acid (DHA, 22:6n-3) is the principal omega-3 fatty acid in mammalian brain gray matter, and emerging preclinical evidence suggests that DHA has neurotrophic and neuroprotective properties. This study investigated relationships among DHA status, neurocognitive performance, and cortical metabolism measured with proton magnetic resonance spectroscopy (1H MRS) in healthy developing male children (aged 8-10 years, n = 38). Subjects were segregated into low-DHA (n = 19) and high-DHA (n = 19) status groups by a median split of erythrocyte DHA levels. Group differences in 1H MRS indices of cortical metabolism, including choline (Cho), creatine (Cr), glutamine + glutamate + γ-aminobutyric acid (Glx), myo-inositol (mI), and n-acetyl aspartate (NAA), were determined in the right and left dorsolateral prefrontal cortex (R/L-DLPFC, BA9) and bilateral anterior cingulate cortex (ACC, BA32/33). Group differences in neurocognitive performance were evaluated with the Kaufman Brief Intelligence Test and identical-pairs version of the continuous performance task (CPT-IP). Subjects in the low-DHA group consumed fish less frequently (P = 0.02), had slower reaction times on the CPT-IP (P = 0.007), and exhibited lower mI (P = 0.007), NAA (P = 0.007), Cho (P = 0.009), and Cr (P = 0.01) concentrations in the ACC compared with the high-DHA group. There were no group differences in ACC Glx or any metabolite in the L-DLPFC and R-DLPFC. These data indicate that low-DHA status is associated with reduced indices of metabolic function in the ACC and slower reaction time during sustained attention in developing male children.

Neuroanatomic abnormalities in adolescents with generalized anxiety disorder: a voxel-based morphometry study

BACKGROUND

Despite recent data implicating functional abnormalities in the neurocircuitry underlying emotional processing in pediatric anxiety disorders, little is known regarding neurostructural abnormalities within these systems.

METHODS

Using voxel-based morphometry, gray and white matter volumes were compared in 15 medication-free adolescents with generalized anxiety disorder (GAD; and no comorbid major depressive disorder) and 28 age- and sex-matched healthy comparison subjects.

RESULTS

Compared to healthy adolescents, youth with GAD had larger gray matter volumes in the right precuneus and right precentral gyrus and decreased gray matter volumes in the left orbital gyrus and posterior cingulate. White matter volumes were decreased in the left medial and superior frontal gyrus and were increased in the left inferior temporal gyrus in youth with GAD relative to healthy subjects.

CONCLUSIONS

Adolescents with GAD, who are early in the course of their illness, exhibit abnormalities in neural structures that subserve threat appraisal, modulation of fear responses, attachment, and mentalization.

Neurocircuitry of generalized anxiety disorder in adolescents: a pilot functional neuroimaging and functional connectivity study

BACKGROUND

Dysfunction of neural systems responsible for the processing of emotional stimuli is hypothesized to be involved in the pathophysiology of generalized anxiety disorder (GAD) in adolescents. We used standard fMRI and functional connectivity analyses to examine the functional neurocircuitry of GAD in adolescents.

METHODS

Ten adolescents with GAD and 10 healthy comparison subjects underwent fMRI while performing a continuous performance task with emotional and neutral distractors. Standard event-related voxel-wise fMRI and steady-state functional connectivity analyses were performed.

RESULTS

Increased activation was observed in the left medial prefrontal cortex and right ventrolateral prefrontal cortex (VLPFC) in response to emotional images compared to neutral imagines in youth with GAD. Connectivity analyses using the right VLPFC seed region suggested decreased connectivity between this region and the bilateral medial prefrontal cortex. Connectivity analyses using the right amygdala seed region revealed decreased correlation with the posterior cingulate cortex in adolescents with GAD. The left amygdala seed region demonstrated increased connectivity with the ipsilateral precuneus in youth with GAD compared to healthy subjects.

CONCLUSIONS

In addition to increased activation of the medial prefrontal cortex and right VLPFC, we observed altered connectivity between the amygdala or VLPFC and regions, which subserve mentalization (e.g. posterior cingulate cortex, precuneus, and medial prefrontal cortex). This suggests that structures that regulate emotion and affect interact abnormally with key structures that are involved in mentalization, a process known to be disrupted in GAD.

1H NMR analysis of choline metabolites in fine-needle-aspirate biopsies of breast cancer

OBJECT

The relative amounts of choline (Cho), phosphocholine (PC), and glycerophosphocholine (GPC) may be sensitive indicators of breast cancer and the degree of malignancy. Here we implement some simple modifications to a previously developed (1)H NMR analysis of fine-needle-aspirate (FNA) biopsies designed to yield sufficient spectral resolution of Cho, PC, and GPC for usable relative quantitation of these metabolites.

MATERIALS AND METHODS

FNA biopsies of eighteen breast lesions were examined using our modified procedure for direct (1)H NMR at 400 MHz. Resonances of choline metabolites and potential interferences were fit using the computer program NUTS.

RESULTS

Quantitation of PC, GPC, and Cho relative to each other and to (phospho)creatine was obtained for eleven confirmed cases of infiltrating ductal carcinoma. Reliable results could not be obtained for the remaining cases primarily due to interference from lidocaine anesthetic.

CONCLUSION

Some simple modifications of a previously developed (1)H NMR analysis of FNAs yielded sufficient spectral resolution of Cho, PC, and GPC to permit usable relative quantitation at 400 MHz. In 9 of the 11 quantified cases the sum of GPC and Cho exceeded 42 % of the total choline-metabolite peak area.

4-T 7Li 3D MR spectroscopy imaging in the brains of bipolar disorder subjects

This work demonstrates the first whole brain "high spatial resolution" (7)Li MR spectroscopy imaging in bipolar disorder subjects. The in vivo quantification is validated by a phantom containing 5 mM lithium salt using the identical radiofrequency sequence and imaging protocol. This study is the first demonstration of the (7)Li distribution in the brain of bipolar disorder patients on lithium therapy using a 3D MR spectroscopy imaging approach. The results show that brain lithium level is strongly correlated with serum lithium concentration. The brain-to-serum lithium ratios for the average brain and the local maximum were 0.39 ± 0.08 (r = 0.93) and 0.92 ± 0.16 (r = 0.90), respectively. The lithium distribution is found to be nonuniform throughout the brain for all patients, which is somewhat unexpected and highly intriguing. This uneven distribution is more evident in subjects at a higher therapeutic serum lithium level. This finding may suggest that lithium targets specific brain tissues and/or certain enzymatic and macromolecular sites that are associated with therapeutic effect. Further investigations of bipolar disorder patients on lithium therapy using 3D (7)Li MR spectroscopy imaging are warranted.

Neurometabolite effects of response to quetiapine and placebo in adolescents with bipolar depression

OBJECTIVE

Mood stabilizers have been reported to affect brain concentrations of myo-inositol (mI) and N-acetylaspartate (NAA). We examined the effects of quetiapine (QUET), an atypical antipsychotic, on these neurochemicals, and potential predictors of response to QUET in adolescents with bipolar depression.

METHODS

Twenty-six adolescents with bipolar depression participated in an 8-week placebo-controlled trial of QUET monotherapy. Subjects were scanned at baseline and after 8 weeks with proton magnetic resonance spectroscopy (1H-MRS) at 3T and 4T at two sites, with 8 cm(3) voxels placed in the right and left dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC). LCModel was used to calculate absolute concentrations of NAA and mI.

RESULTS

Twenty-six subjects had pre- and posttreatment scans (mean age=15.6 years, 9 boys). Of these subjects, 5 out of 16 subjects receiving QUET and 5 out of 10 receiving placebo (PBO) were responders (50% decrease in Children's Depression Rating Scale [CDRS] score). Although baseline ACC mI did not predict responder status, responders had significantly lower posttreatment ACC mI values than did nonresponders (3.27±.71 vs. 4.23±.70; p=0.004). There were no significant differences in the changes in ACC and DLPFC NAA levels in the QUET group compared with the PBO group (ACC: -0.55±1.3 vs.+0.25±1.5, p=0.23; right-DLPFC: -0.55±1.3 vs. 0.33±0.89, p=0.13; left-DLPFC: -0.04±0.91 vs.+0.29±0.61, p=0.41).

CONCLUSION

We found that posttreatment, not baseline, ACC mI levels were associated with response to QUET in adolescents with bipolar depression. There were no differences in NAA concentration changes between the QUET and PBO groups. Larger studies including different brain regions would help to clarify the effects of QUET on neurochemistry in patients with bipolar disorder.

Glutamatergic effects of divalproex in adolescents with mania: a proton magnetic resonance spectroscopy study

OBJECTIVES

This study used proton magnetic resonance spectroscopy ((1)H MRS) to evaluate the in vivo effects of extended-release divalproex sodium on the glutamatergic system in adolescents with bipolar disorder, and to identify baseline neurochemical predictors of clinical remission.

METHOD

Adolescents with bipolar disorder who were experiencing a manic or mixed episode (N = 25) were treated with open-label, extended-release divalproex (serum levels 85-125 μg/mL) and underwent (1)H MRS scanning at baseline (before treatment) and on days 7 and 28. Healthy comparison subjects (n = 15) also underwent (1)H MRS scanning at the same time points. Glutamate (Glu) and glutamate+glutamine (Glx) concentrations were measured in three voxels: anterior cingulate cortex (ACC), left ventrolateral prefrontal cortex (LVLPFC), and right ventrolateral prefrontal cortex (RVLPFC), and were compared between bipolar and healthy subjects. Within the bipolar subjects, Glu and Glx concentrations at baseline and each time point were also compared between remitters and nonremitters after divalproex treatment.

RESULTS

At baseline, no differences in Glu or Glx concentrations between bipolar and healthy subjects were observed. Group (HC vs. BP) by time effects revealed an interaction for Glu in the ACC, and change over time effects for Glx were noted in the ACC in patients with bipolar disorder (increase from day 0 to day 7 and then a decrease from day 7 to day 28) but not in HC. Remitters had significantly lower baseline Glx concentrations in LVLPFC, and in remitters the change in LVLPFC Glu correlated with the change in YMRS score.

CONCLUSIONS

Successful treatment of mania with divalproex may be predicted by lower baseline concentrations of Glx in the LVLPFC. In addition, in remitters, the degree of symptomatic improvement is related to the change in Glu concentrations in this region, suggesting that divalproex may work via modulation of the prefrontal glutamatergic system in youth with bipolar disorder.

Neurochemical alteration in the caudate: implications for the pathophysiology of bipolar disorder

Several lines of evidence suggest that the neuropathophysiology of bipolar disorder is marked by structural and functional abnormalities in the caudate. We used magnetic resonance spectroscopy imaging (MRSI) to examine potential neurochemical changes in the caudate of adult bipolar patients (BP). 2D-MRSI scans including the caudate were obtained from 25 BP and 9 healthy subjects (HS). BP patients were further divided into medicated (n=14) and unmedicated (n=11) groups; the majority of medicated patients received atypical antipsychotics (AAP). Ratios of Cr/Cho, Cho/NAA and Cr/NAA in the caudate were compared between groups, controlling for age, gender and gray/white ratio. BP and HS did not significantly differ on any ratios. The Cr/Cho ratio, however, was significantly greater in medicated BP compared to HS. Conversely, the Cho/NAA ratio was non-significantly lower in medicated BP vs. HS. Medicated BP also showed significantly greater Cr/Cho and significantly smaller Cho/NAA ratios than unmedicated BP. Although we did not observe significant overall differences between BP and HS, our findings suggest the presence of reduced choline levels in the caudate of medicated BP receiving AAP. While speculative, these results suggest that AAP do not cause oxidative injury to neuronal membranes.

Brain-mapping techniques for evaluating poststroke recovery and rehabilitation: a review

Brain-mapping techniques have proven to be vital in understanding the molecular, cellular, and functional mechanisms of recovery after stroke. This article briefly summarizes the current molecular and functional concepts of stroke recovery and addresses how various neuroimaging techniques can be used to observe these changes. The authors provide an overview of various techniques including diffusion-tensor imaging (DTI), magnetic resonance spectroscopy (MRS), ligand-based positron emission tomography (PET), single-photon emission computed tomography (SPECT), regional cerebral blood flow (rCBF) and regional metabolic rate of glucose (rCMRglc) PET and SPECT, functional magnetic resonance imaging (fMRI), near infrared spectroscopy (NIRS), electroencephalography (EEG), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS). Discussion in the context of poststroke recovery research informs about the applications and limitations of the techniques in the area of rehabilitation research. The authors also provide suggestions on using these techniques in tandem to more thoroughly address the outstanding questions in the field.

Robust fully automated shimming of the human brain for high-field 1H spectroscopic imaging

Although a variety of methods have been proposed to provide automated adjustment of shim homogeneity, these methods typically fail or require large numbers of iterations in vivo when applied to regions with poor homogeneity, such as the temporal lobe. These limitations are largely due to 1) the limited accuracy of single evolution time measurements when full B0 mapping studies are used, and 2) inaccuracies arising from projection-based methods when the projections pass through regions where the inhomogeneity exceeds the order of the fitted parameters. To overcome these limitations we developed a novel B0 mapping method using multiple evolution times with a novel unwrapping scheme in combination with a user-defined ROI selection tool. We used these methods at 4T on 10 control subjects to obtain high-resolution spectroscopic images of glutamate from the bilateral hippocampi.

Fast spectroscopic imaging using online optimal sparsek-space acquisition and projections onto convex sets reconstruction

Long acquisition times, low resolution, and voxel contamination are major difficulties in the application of magnetic resonance spectroscopic imaging (MRSI). To overcome these difficulties, an online-optimized acquisition of k-space, termed sequential forward array selection (SFAS), was developed to reduce acquisition time without sacrificing spatial resolution. A 2D proton MRSI region of interest (ROI) was defined from a scout image and used to create a region of support (ROS) image. The ROS was then used to optimize and obtain a subset of k-space (i.e., a subset of nonuniform phase encodings) and hence reduce the acquisition time for MRSI. Reconstruction and processing software was developed in-house to process and reconstruct MRSI using the projections onto convex sets method. Phantom and in vivo studies showed that good-quality MRS images are obtainable with an approximately 80% reduction of data acquisition time. The reduction of the acquisition time depends on the area ratio of ROS to FOV (i.e., the smaller the ratio, the greater the time reduction). It is also possible to obtain higher-resolution MRS images within a reasonable time using this approach. MRSI with a resolution of 64 x 64 is possible with the acquisition time of the same as 24 x 24 using the traditional full k-space method.

In vivo GABA detection with improved selectivity and sensitivity by localized double quantum filter technique at 4.1T

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter for the normal function of mammal and human brain. It is difficult to detect GABA signal with the conventional single quantum technique due to its relatively low concentration and overlapping with other signals from creatine (Cr), glutathione (GSH), as well as macromolecules. Using a high-selective read pulse, DANTE, and at the facility of increased sensitivity and chemical shift resolution at high-field 4.1T, GABA editing by double quantum filter (DQF) with robust suppression of Cr and GSH was achieved. Our editing efficiency of 40-50% was achievable on a GABA phantom (50 mM GABA and 61 mM choline). Furthermore, GABA editing spectra were acquired with echo time TE = 77 ms, and any possible macromolecular contamination to GABA editing spectra was found to be negligible. This high-field DQF setup was applied to 11 healthy volunteers, and the mean GABA level was measured to be 1.12 +/- 0.15 mM in the occipital lobe in reference to 7.1 mM Cr concentration.

Regional cerebral blood flow and magnetic resonance spectroscopic imaging findings in diaschisis from stroke

BACKGROUND AND PURPOSE

This study evaluated blood flow and metabolite changes in cerebral diaschisis from internal capsule region infarction using regional cerebral blood flow (rCBF) single-photon emission computed tomography (SPECT) and 1H magnetic resonance spectroscopic imaging (MRSI). We hypothesized that complementary measures of diaschisis effects in white matter (characterized by 1H MRSI) and gray matter (characterized by changes in rCBF) can be measured and exhibit parallel changes.

METHODS

Five stroke patients and 16 normal controls underwent Tc-99m hexamethylpropyleneamine-oxime brain SPECT and 1H MRSI at 4.1 T. The metabolites N-acetyl aspartate (NAA) and creatine (Cr) were measured using 1H MRSI. The tissue content was expressed as the percent of gray or white matter in each MRSI voxel to allow comparison of the differential effects of diaschisis in gray and white matter tissue types. The blood flow and metabolite changes were evaluated at superior cerebral regions distant from the stroke to allow a measure of diaschisis relatively unconfounded by their expected changes in the infarction region.

RESULTS

The rCBF SPECT data in stroke patients showed a perfusion defect, with size ranging from 1.23 cc to 10.23 cc, in the region of cortical diaschisis. 1H MRSI showed increased Cr/NAA ratios in regions of white matter diaschisis. There was a tendency for larger rCBF defect size to be associated with greater increases in Cr/NAA values in the same diaschitic cerebral hemisphere, ipsilateral to the infarction.

CONCLUSION

Diaschisis ipsilateral to stroke in white matter can be characterized by 1H MRSI, and diaschisis ipsilateral to stroke in cortical gray matter regions can be characterized by changes in rCBF. The tendency for greater reductions in cortical rCBF values to be associated with increased Cr/NAA values in the same diaschitic cerebral hemisphere implies that a relationship exists between rCBF reductions in gray matter and abnormal changes in white matter subservient to it.

Normal T-cell response and in vivo magnetic resonance imaging of T cells loaded with HIV transactivator-peptide-derived superparamagnetic nanoparticles

The present study analyzed the feasibility of using magnetic resonance imaging (MRI) to monitor T-cell homing in vivo after loading T cells with superparamagnetic iron oxide (CLIO) nanoparticles derivatized with a peptide sequence from the transactivator protein (Tat) of HIV-1. T cells were isolated from C57BL/6 (B6) mice and loaded with 0, 400, 800, 1600, or 8000 ng/ml of FITC conjugated CLIO-Tat (FITC-CLIO-Tat). There was a dose-dependent uptake of FITC-CLIO-Tat by T cells. Stimulation of FITC-CLIO-Tat loaded T cells with anti-CD3 (0.1 microg/ml) plus IL-2 (5 ng/ml) elicited normal activation and activation-induced cell death (AICD) responses, and normal upregulation of CD69, ICAM-1 (CD54), L-selectin (CD62L), and Fas. The FITC-CLIO-Tat loaded T cells (3 x 10(7)) were transferred intravenously (i.v.) into B6 mice and the in vivo MRI of mice was acquired using a spin-echo pulse sequence at 4.7 T with a Bruker Biospec system. Homing of T cells into the spleen was observed by a decrease in MRI signal intensity within 1 h after the transfer, which remained decreased for 2-24 h after transfer. These homing data were confirmed by FACS analysis and biodistribution analysis using 125I-CLIO-Tat. Thus, T cells can be efficiently loaded with FITC-CLIO-Tat without interfering with their normal activation and AICD, or homing to the spleen, and the biodistribution of FITC-CLIO-Tat loaded T cells can be monitored in vivo over time by MRI.

Alkaline pH changes in the cerebellum of asymptomatic HIV-infected individuals

Human immunodeficiency virus (HIV) infection of the brain causes a complex cascade of cellular events involving several different cell types that eventually leads to neuronal cell death and the manifestation of the AIDS-associated dementia complex (ADC). Upon autopsy HIV-infected individuals show lesions within subcortical regions of the brain, including the cerebellum. Previously we have demonstrated, in primary and cell culture models of rat and human astrocytes, a change in intracellular pH (pH(i)) due to increased Na(+)/H(+) exchange following exposure to inactivated virus or gp120, the major HIV envelope glycoprotein. To further investigate whether any such in vivo pH(i) changes occur in human brains subsequent to HIV infection, we measured the pH(i) of the cerebellum in eight HIV-positive individuals and nine healthy volunteers using (31)P magnetic resonance spectroscopy imaging (MRSI) at high field strength (4.1 T). The results showed a significant difference between the age-adjusted mean pH(i) in the cerebellum in control group and patient groups (7.11 +/- 0.03 vs 7.16 +/- 0.04), and further HIV-infected individuals displayed a significant increase in the number of cerebellar volume elements that were alkaline. We hypothesize that this propensity towards alterations in cerebellar pH(i) may portend later neurological involvement resulting from HIV infection.

Statistically driven identification of focal metabolic abnormalities in temporal lobe epilepsy with corrections for tissue heterogeneity using 1H spectroscopic imaging

1H spectroscopic imaging of N-acetyl-aspartate, creatine, and choline has proven to be a sensitive indicator for the lateralization of seizure foci in temporal lobe epilepsy. Previous studies have used right-left comparisons to identify the epileptogenic tissue assuming that alterations due to the disease process outweigh the effects of tissue heterogeneity. To evaluate the effectiveness of tissue heterogeneity corrected analyses, we evaluated three criteria for lateralization of the seizure focus: 1) a statistically driven method adjusted for tissue composition, 2) a single valued threshold, and 3) a single global index of the hippocampus. The statistically driven analysis lateralized all eight patients correctly, whereas the single threshold method incorrectly lateralized one case and the global index failed to identify a significant difference in two cases. These findings indicate that increased accuracy and sensitivity can be obtained by correcting for tissue heterogeneity when analyzing spectroscopy studies of temporal lobe epilepsy.

Measurement of the tricarboxylic acid cycle rate in human grey and white matter in vivo by 1H-[13C] magnetic resonance spectroscopy at 4.1T

13C isotopic labeling data were obtained by 1H-observed/13C-edited magnetic resonance spectroscopy in the human brain in vivo and analyzed using a mathematical model to determine metabolic rates in human grey matter and white matter. 22.5-cc and 56-cc voxels were examined for grey matter and white matter, respectively. When partial volume effects were ignored, the measured tricarboxylic acid cycle rate was 0.72+/-0.22 (mean +/- SD) and 0.29+/-0.09 micromol min(-1) g(-1) (mean +/- SD) in voxels of approximately 70% grey and approximately 70% white matter, respectively. After correction for partial volume effects using a model with two tissue compartments, the tricarboxylic acid cycle rate in pure grey matter was higher (0.80+/-0.10 mol min(-1) g(-1); mean +/- SD) and in white matter was significantly lower (0.17+/-0.01 micromol min(-1) g(-1); mean +/- SD). In 1H-observed/13C-edited magnetic resonance spectroscopy labeling studies, the larger concentrations of labeled metabolites and faster metabolic rates in grey matter biased the measurements heavily toward grey matter, with labeling time courses in 70% grey matter appearing nearly identical to labeling in pure grey matter.

Ketosis and epilepsy: 31P spectroscopic imaging at 4.1 T

PURPOSE

To determine whether changes in the high-energy phosphates occur with use of the ketogenic diet in patients with intractable epilepsy.

METHODS

31P magnetic resonance spectroscopic imaging studies were performed at 4.1 T in seven patients with intractable epilepsy (four Lennox-Gastaut syndrome, one absence, one primary generalized tonic-clonic, and one partial complex) before and after institution of the ketogenic diet. Coronal 1H anatomic imaging also was performed to provide correlation to the 31P data.

RESULTS

Taking the patients as a group, the ratio of phosphocreatine (PC)/gamma-adenosine triphosphate (ATP) measured at baseline (regular diet) compared with that measured after the ketogenic diet showed a small but significant increase from 0.61+/-0.08 to 0.69+/-0.08 (p < 0.05). Comparing the ratio of PCr inorganic phosphorus (Pi) measured at baseline with the postketogenic diet, there was a significant increase from 2.45+/-0.27 to 2.99+/-0.44 (p < 0.05).

CONCLUSIONS

As a group, improvement of energy metabolism occurs with use of the ketogenic diet. This is in agreement with the chronic ketosis studies performed earlier in rodents.

Lateralization of human temporal lobe epilepsy by 31P NMR spectroscopic imaging at 4.1 T

OBJECTIVE

To compare the phosphorous metabolite ratios in the mesial temporal lobe of healthy volunteers (n = 20) with the corresponding ratios in patients with temporal lobe epilepsy (n = 30) using 31P NMR spectroscopic imaging and to lateralize the seizure focus in temporal lobe epilepsy patients using various phosphorous metabolite ratios-phosphocreatine to inorganic phosphate (PCr/Pi), PCr to adenosine triphosphate (PCr/gamma-ATP), and (gamma-ATP/Pi)--and to compare with clinical lateralization results.

METHODS

All 31P NMR spectroscopic imaging studies were performed on a high-field, 4.1 T, whole-body NMR spectroscopic imaging system using a 31P/1H double-tuned volume coil.

RESULTS

We found an average reduction of 15% in the PCr/Pi and gamma-ATP/Pi ratios compared with the corresponding ratios in healthy volunteers in the entire mesial temporal lobe, and more than a 30% reduction in these two ratios in the anterior region of the epileptogenic mesial temporal lobe. These ratios were also reduced significantly in the ipsilateral lobe when compared with their corresponding values in the contralateral lobe. In patients we lateralized the seizure focus, based on these 31P NMR data, and compared the results with the clinical lateralization. The lateralization based on either the PCr/Pi or the gamma-ATP/Pi ratio yielded a correspondence of 70 to 73% with the final clinical lateralization. In the subgroup of patients (n = 9) that needed intracranial EEG for the presurgical lateralization because of inconclusive results from the noninvasive methods, a 78% correspondence was found with the 31P NMR-based lateralization, whereas MRI provided a correspondence of only 33%, and scalp EEG provided a correspondence of only 56%.

CONCLUSIONS

These results suggest the utility of adding the 31P NMR method to the group of noninvasive modalities used for presurgical decision making in temporal lobe epilepsy patients.

Evaluation of 31P metabolite differences in human cerebral gray and white matter

31P NMR is commonly used to study brain energetics in health and disease. Due to sensitivity constraints, the NMR measurements are typically made in volumes that do not contain pure gray or white matter. For accurate evaluation of abnormalities in brain metabolite levels, it is necessary to consider the differences in normal levels of 31P metabolites in gray and white matter. In this study, voxels from a three-dimensional spectroscopic image acquisition were analyzed for their dependence on tissue type to assess differences in metabolite levels between gray and white matter. Specifically, gray matter was found to have significantly higher ratios of phosphocreatine (PCr) to gamma-ATP and PCr to the total 31P metabolite signal, whereas pH and the ratio of PCr to inorganic phosphate (Pi) were found to differ insignificantly between gray and white matter. Thus, tissue type can be an important factor to consider for alterations in bioenergetics by 31P NMR spectroscopic studies of the brain.

Biological and clinical MRS at ultra-high field

The advantages of performing spectroscopic studies at higher field strengths include increased SNR, improved spectral resolution for J-coupled resonances, and improvements in the selectivity of spectral editing schemes. By using pulse sequences that minimize the required echo time, refocus J-evolution, employ low peak B1 requiring pulses and take advantage of spectroscopic imaging methods, these advantages can also be utilized in clinical applications of spectroscopy at high field. In addition to the static measurements measurements of N-acetyl aspartate (NAA), creatine (CR) and choline (CH) which can be performed at 1.5 T, high resolution measurements of glutamate, glutamine, GABA and the incorporation of 13C labeled glucose into glutamate are possible with improved spatial and spectral resolution. These methods have been utilized in patients with seizure disorders and multiple sclerosis to identify, characterize and map the metabolic changes associated with these diseases and their treatment.

A general approach to error estimation and optimized experiment design, applied to multislice imaging of T1 in human brain at 4.1 T

In this report, a procedure to optimize inversion-recovery times, in order to minimize the uncertainty in the measured T1 from 2-point multislice images of the human brain at 4.1 T, is discussed. The 2-point, 40-slice measurement employed inversion-recovery delays chosen based on the minimization of noise-based uncertainties. For comparison of the measured T1 values and uncertainties, 10-point, 3-slice measurements were also acquired. The measured T1 values using the 2-point method were 814, 1361, and 3386 ms for white matter, gray matter, and cerebral spinal fluid, respectively, in agreement with the respective T1 values of 817, 1329, and 3320 ms obtained using the 10-point measurement. The 2-point, 40-slice method was used to determine the T1 in the cortical gray matter, cerebellar gray matter, caudate nucleus, cerebral peduncle, globus pallidus, colliculus, lenticular nucleus, base of the pons, substantia nigra, thalamus, white matter, corpus callosum, and internal capsule.

In vivo characterization of Gd(BME-DTTA), a myocardial MRI contrast agent: tissue distribution of its MRI intensity enhancement, and its effect on heart function

We have determined an LD50 of 0.56 +/- 0.05 mmol/kg for liposomal Gd(BME-DTTA) in mice and also shown that liposomal Gd(BME-DTTA) has no deleterious effects on heart rate, blood pressure, left ventricular force and AV conductance in ferret hearts in vivo at the magnetic resonance imaging (MRI)-effective dose of 0.05 mmol/kg body weight. In MRI images, a 1H signal intensity enhancement is observed in the following organs in decreasing order of the effect: heart approximately spleen > kidney > liver. This enhancement is stable for over 3 h in all organs. The results of 1H MRI and electron micrographs indicate that the lipophilic fatty acyl groups in the ligand BME structure and the particle sizes of liposomal Gd(BME-DTTA) are two important factors for tissue specificity of liposomal Gd(BME-DTTA) in the intensity enhancement. In vitro relaxivity of a liposomal Gd(BME-DTTA) sample, stored at 4 degrees C, remained stable for over 4 months of observation, but a significant decrease in relaxivity was observed in a sample stored at room temperature, most likely reflecting some deterioration in liposome chemistry.

13C editing of glutamate in human brain using J-refocused coherence transfer spectroscopy at 4.1 T

The method of single quantum 13C editing is analyzed and implemented with water suppressed J-refocused coherence transfer spectroscopy. Analysis of the 13C inversion pulse demonstrates that it is optimally placed into the second echo of the J-refocused sequence. We have used this method to acquire 13C-edited spectra of glutamate from phantoms and in vivo. The turnover of 13C4-labeled glutamate in human brain in vivo was observed in parasagittal gray matter using a volume head coil at 4.1 T with a time resolution of 5.3 min.

Is the intracellular pH different from normal in the epileptic focus of patients with temporal lobe epilepsy? A 31P NMR study

We performed in vivo 31P NMR spectroscopic studies of human brain on a 4.1 T whole-body NMR system. Based on a control group of 20 healthy volunteers, the normal pHi was 7.05 (SD, 0.06; SEM, 0.01) in the left temporal lobe and 7.04 (SD, 0.04; SEM, 0.01) in the right temporal lobe. We also studied a patient group consisting of 13 individuals with unilateral temporal lobe epilepsy. The mean pHi was 7.02 (SD, 0.04; SEM, 0.01) in the ipsilateral lobe and 7.02 (SD, 0.05; SEM, 0.01) in the contralateral lobe. These results clearly show that no statistically significant difference in pHi is observed between the two lobes, either in normal controls or in patients. Also, no significant pHi difference exists between the control group and the patient group. Lateralization in each of the 13 patients with unilateral epilepsy, based on their individual pHi difference between the ipsilateral lobe and contralateral lobe (delta pHi), showed that three patients were nondiagnostic cases because their delta pHis were not significantly different from zero (< or = 0.02), five patients showed small delta pHis consistent with their clinical lateralization, whereas the remaining five patients showed delta pHi-based lateralization opposite to the clinical findings. These results seem to indicate an essentially random distribution around delta pHi = 0 within a very small experimental error of +/-0.02 pH units. pHi obtained from eight different areas in each of the 13 unilateral patients also did not show any significantly nonzero delta pHi values. These results led to the conclusion that even at the excellent spectral resolution and reproducibility of the 4.1 T machine (typical SD of 0.05 pH units), no significant pHi effect, induced by temporal lobe epilepsy, could be detected. Therefore, in this study, delta pHi does not appear to be a clinically useful tool for the lateralization of epileptic foci in patients with temporal lobe epilepsy.

In vivo MRI visualization of acute myocardial ischemia and reperfusion in ferrets by the persistent action of the contrast agent Gd (BME-DTTA)

BACKGROUND

Contrast agent-enhanced magnetic resonance imaging (MRI) has the potential to visualize myocardial ischemia. To date, however, no agent has been found that has a sustained effect that allows MRI detection for the entire duration of ischemia and reperfusion and thus is useful in conjunction with stress test MRI. In this article, we introduce the gadolinium complex of N3,N6-bis(2'-myrisotyloxyethyl)-1,8-dioxo-triethylene- tetraamine-N,N,N1,N1-tetraacetic acid [Gd(BME-DTTA)], an agent potentially useful for such a purpose.

METHODS AND RESULTS

Four protocols were carried out. ECG-triggered, partially T1-weighted, spin-echo MRI was used in protocols A through C. In protocol A, in nonischemic ferrets, 50 mumol/kg Gd(BME-DTTA) induced a 70 +/- 5% intensity enhancement lasting 3 hours. In protocol B, the left anterior descending coronary artery was occluded, and a 99mTc-sestamibi-induced autoradiographic contrast verified (r = .87, P < .01) a Gd(BME-DTTA)-induced (n = 5) or Gd(DTPA)-induced (n = 4) MRI contrast. In the Gd(BME-DTTA) group a sustained contrast and in the Gd(DTPA) group a short-lived contrast were observed. In protocol C (n = 11), during ischemia, a 31 +/- 3.3% (P < .02) contrast was evident between the ischemic and nonischemic myocardial regions. Upon reperfusion, a contrast of 19 +/- 3% (P < .05) and 13 +/- 4.5% (P < .05) persisted for 5 and 15 minutes, respectively. Beyond 15 minutes, the contrast continued to diminish gradually. Nonradioactive microspheres verified (r = .87, P < .05) ischemia and reperfusion in this model. In protocol D (n = 4), blood delta R1 data showed that the blood pool retained Gd(BME-DTTA) for the entire time frame of the experiment at high enough concentration to provide an appropriate wash-in effect during the initial contrast enhancement and during reperfusion.

CONCLUSIONS

This study demonstrates that Gd(BME-DTTA) induces a sustained MRI contrast between regions of normal versus ischemic myocardium, showing the potential of this agent for the diagnosis of ischemic heart disease in conjunction with stress tests.

Gadolinium and dysprosium chelates of DTPA-amide-dextran: synthesis, 1H NMR relaxivity, and induced 23Na NMR shift

In this study the conjugated macromolecular ligand, diethylenetriaminepentaacetic acid (DTPA)-amide-dextran, was synthesized by attaching DTPA to the dextran macromolecule (M(r) approximately 6000) by a covalent amide bond. Subsequently, DTPA-amide-dextran was complexed with either of the two lanthanide metal ions dysprosium (Dy) or gadolinium (Gd). The paramagnetic 23Na NMR shift induced by Dy(DTPA-amide-dextran) and the relaxivity (rho 1) induced by Gd(DTPA-amide-dextran) were characterized. Dy(DTPA-amide-dextran) induced a 25% larger 23Na NMR shift than that induced by Dy(DTPA). Neither the shift induced by Dy(DTPA-amide-dextran) nor the shift induced by Dy(DTPA) was affected by increasing levels of calcium ions in the solution. offDTPA-amide-dextran) exhibited an in vitro rho 1 of 8.4 (mM s)-1 at a 0.23 T magnetic field and 9.3 (mM s)-1 at a 0.47 T magnetic field, thus indicating a positive magnetic field dependence.

A selective inversion recovery method for the improvement of 23Na NMR spectral resolution in isolated perfused rat hearts

Shift-reagent-aided 23Na NMR spectroscopy allows differentiation of the intracellular (Na(i)) and extracellular sodium (Na(o)) signals. The goal of the present study has been to develop a 23Na NMR spectroscopic method to minimize the intensity of the shift-reagent-shifted Na(o) signal and thus increase Na(i) resolution. This is achieved by a selective inversion recovery (SIR) method which enhances the resolution between the Na(i) and Na(o) peaks in shift-reagent-aided 23Na NMR spectroscopy. The application of SIR with Dy(TTHA), Tm(DOTP), or with low concentrations of Dy(PPP)2 results in both good spectral resolution and physiologically acceptable contractile function in the isolated, perfused rat heart model.

Improvement of spectral resolution in shift-reagent-aided 23Na NMR spectroscopy in the isolated perfused rat heart system

The level of intracellular sodium (Nai) is maintained at approximately 14 mM in healthy myocytes. When myocytes are damaged, Nai increases and therefore the level of Nai may be a means of evaluating myocardial cell integrity. A particularly useful method to monitor Nai levels is 23Na NMR spectroscopy. However, because of the isochronous nature of the extracellular sodium (Nao) and Nai NMR signals, paramagnetic lanthanide shift reagents (LSR), such as dysprosium triphosphate, Dy(PPP)7-(2), have been used to shift the Nao signal. This reveals the unshifted Nai signal and allows the NMR monitoring of Nai in isolated perfused hearts and other systems. A major shortcoming of this method (the "shift-only" method) is in the need to minimize the Nao signal by not submerging the perfused hearts in Na(+)-containing buffer. An equally undesirable alternative is the utilization of relatively high concentrations of LSR to shift a large Nao signal sufficiently to enable reasonable resolution and quantitation of Nai. We present here a method, the "shift-relaxation" method, which is a combination of using a mixture of Dy(PPP)7-(2), a shift reagent, and gadolinium triphosphate, Gd(PPP)7-(2), a relaxation agent, with data acquisition using an inversion-recovery (IR) pulse sequence. This combination allows differentiation between Nao and Nai by the difference in their respective T1 values in addition to the shift between them. With this technique we can selectively minimize the extracellular signal and therefore minimize the need for a large Dy-induced shift, as well as allow data acquisition on a heart submerged in Na(+)-containing perfusate. The resulting improved discrimination between Nai and Nao at relatively low levels of LSR should be helpful for ultimate in vivo applications and potential clinical applications, where a lower dose of LSR also means a decreased possibility of physiologically deleterious effects. Also included in this paper is a method for the quick determination of an accurate 180 degrees pulse which is required for the optimization of the IR method.