Metabolic changes assessed by 1H MR spectroscopy in the corpus callosum of post-COVID patients.

OBJECTIVE: Many patients with long COVID experience neurological and psychological symptoms. Signal abnormalities on MR images in the corpus callosum have been reported. Knowledge about the metabolic profile in the splenium of the corpus callosum (CCS) may contribute to a better understanding of the pathophysiology of long COVID. MATERIALS AND METHODS: Eighty-one subjects underwent proton MR spectroscopy examination. The metabolic concentrations of total N-acetylaspartate (NAA), choline-containing compounds (Cho), total creatine (Cr), myo-inositol (mI), and NAA/Cho in the CCS were statistically compared in the group of patients containing 58 subjects with positive IgG COVID-19 antibodies or positive SARS-CoV-2 qPCR test at least two months before the MR and the group of healthy controls containing 23 subjects with negative IgG antibodies. RESULTS: An age-dependent effect of SARS-CoV-2 on Cho concentrations in the CCS has been observed. Considering the subjective threshold of age = 40 years, older patients showed significantly increased Cho concentrations in the CCS than older healthy controls (p = 0.02). NAA, Cr, and mI were unchanged. All metabolite concentrations in the CCS of younger post-COVID-19 patients remained unaffected by SARS-CoV-2. Cho did not show any difference between symptomatic and asymptomatic patients (p = 0.91). DISCUSSION: Our results suggest that SARS-CoV-2 disproportionately increases Cho concentration in the CCS among older post-COVID-19 patients compared to younger ones. The observed changes in Cho may be related to the microstructural reorganization in the CCS also reported in diffusion measurements rather than increased membrane turnover. These changes do not seem to be related to neuropsychological problems of the post-COVID-19 patients. Further metabolic studies are recommended to confirm these observations.

Associations of Brain Atrophy and Cerebral Iron Accumulation at MRI with Clinical Severity in Wilson Disease.

Background Abnormal findings at brain MRI in patients with neurologic Wilson disease (WD) are characterized by signal intensity changes and cerebral atrophy. T2 signal hypointensities and atrophy are largely irreversible with treatment; their relationship with permanent disability has not been systematically investigated. Purpose To investigate associations of regional brain atrophy and iron accumulation at MRI with clinical severity in participants with neurologic WD who are undergoing long-term anti-copper treatment. Materials and Methods Participants with WD and controls were compared in a prospective study performed from 2015 to 2019. MRI at 3.0 T included three-dimensional T1-weighted and six-echo multigradient-echo pulse sequences for morphometry and quantitative susceptibility mapping, respectively. Neurologic severity was assessed with the Unified WD Rating Scale (UWDRS). Automated multi-atlas segmentation pipeline with dual contrast (susceptibility and T1) was used for the calculation of volumes and mean susceptibilities in deep gray matter nuclei. Additionally, whole-brain analysis using deformation and surface-based morphometry was performed. Least absolute shrinkage and selection operator regression was used to assess the association of regional volumes and susceptibilities with the UWDRS score. Results Twenty-nine participants with WD (mean age, 47 years ± 9 [standard deviation]; 15 women) and 26 controls (mean age, 45 years ± 12; 14 women) were evaluated. Whole-brain analysis demonstrated atrophy of the deep gray matter nuclei, brainstem, internal capsule, motor cortex and corticospinal pathway, and visual cortex and optic radiation in participants with WD (P < .05 at voxel level, corrected for family-wise error). The UWDRS score was negatively correlated with volumes of putamen (r = -0.63, P < .001), red nucleus (r = -0.58, P = .001), globus pallidus (r = -0.53, P = .003), and substantia nigra (r = -0.50, P = .006) but not with susceptibilities. Only the putaminal volume was identified as a stable factor associated with the UWDRS score (R2 = 0.38, P < .001) using least absolute shrinkage and selection operator regression. Conclusion Individuals with Wilson disease (WD) had widespread brain atrophy most pronounced in the central structures. The putaminal volume was associated with the Unified WD Rating Scale score and can be used as a surrogate imaging marker of clinical severity. © RSNA, 2021 Supplemental material is available for this article. See also the editorial by Du and Bydder in this issue.

Magnetic resonance markers of bilateral neuronal metabolic dysfunction in patients with unilateral internal carotid artery occlusion.

OBJECTIVES: To evaluate cerebral hemodynamic, metabolic and anatomic changes occurring in patients with unilateral occlusion of the internal carotid artery (ICA). MATERIALS AND METHODS: Twenty-two patients with unilateral occlusion of ICA and twenty age and sex matched healthy subjects were included in the study. Single voxel proton magnetic resonance spectroscopy (1H-MRS) of the centrum semiovale, semi-automated hippocampal volumetry in T1-weighted scans and transcranial Doppler examination (TCD) with calculation of Breath Holding Index (BHI) were performed in both groups. Metabolic, anatomic, and hemodynamic features were compared between the two groups. RESULTS: The N-acetylaspartate (NAA)/choline (Cho) ratio was significantly lower in both hemispheres of enrolled patients compared to controls (p = 0.005 for the side with occlusion, p = 0.04 for the side without occlusion). The hippocampus volume was significantly reduced bilaterally in patients compared to healthy subjects (p = 0.049). A statistically significant difference in BHI values was observed between the side with occlusion and without occlusion (p = 0.037) of the patients, as well as between BHI values of the side with occlusion and healthy volunteers (p = 0.014). DISCUSSION: Patients with unilateral ICA occlusion have reduced NAA/Cho ratio in the white matter of both hemispheres and have bilateral atrophy of hippocampus. The alteration of hemodynamics alone cannot explain these changes.

In Vitro 31P MR Chemical Shifts of In Vivo-Detectable Metabolites at 3T as a Basis Set for a Pilot Evaluation of Skeletal Muscle and Liver 31P Spectra with LCModel Software.

Most in vivo 31P MR studies are realized on 3T MR systems that provide sufficient signal intensity for prominent phosphorus metabolites. The identification of these metabolites in the in vivo spectra is performed by comparing their chemical shifts with the chemical shifts measured in vitro on high-field NMR spectrometers. To approach in vivo conditions at 3T, a set of phantoms with defined metabolite solutions were measured in a 3T whole-body MR system at 7.0 and 7.5 pH, at 37 °C. A free induction decay (FID) sequence with and without 1H decoupling was used. Chemical shifts were obtained of phosphoenolpyruvate (PEP), phosphatidylcholine (PtdC), phosphocholine (PC), phosphoethanolamine (PE), glycerophosphocholine (GPC), glycerophosphoetanolamine (GPE), uridine diphosphoglucose (UDPG), glucose-6-phosphate (G6P), glucose-1-phosphate (G1P), 2,3-diphosphoglycerate (2,3-DPG), nicotinamide adenine dinucleotide (NADH and NAD+), phosphocreatine (PCr), adenosine triphosphate (ATP), adenosine diphosphate (ADP), and inorganic phosphate (Pi). The measured chemical shifts were used to construct a basis set of 31P MR spectra for the evaluation of 31P in vivo spectra of muscle and the liver using LCModel software (linear combination model). Prior knowledge was successfully employed in the analysis of previously acquired in vivo data.

Origin of the 31 P MR signal at 5.3 ppm in patients with critical limb ischemia.

An unknown intense signal (Pun ) with a mean chemical shift of 5.3 ppm was observed in 31 P MR spectra from the calf muscles of patients with the diabetic foot syndrome. The aim of the study was to identify the origin of this signal and its potential as a biomarker of muscle injury. Calf muscles of 68 diabetic patients (66.3 ± 8.6 years; body mass index = 28.2 ± 4.3 kg/m2 ) and 12 age-matched healthy controls were examined by (dynamic) 31 P MRS (3 T system, 31 P/1 H coil). Phantoms (glucose-1-phosphate, Pi and PCr) were measured at pH values of 7.05 and 7.51. At rest, Pun signals with intensities higher than 50% of the Pi intensity were observed in 10 of the 68 examined diabetic subjects. We tested two hypothetical origins of the Pun signal: (1) phosphorus from phosphoesters and (2) phosphorus from extra- and intracellular alkaline phosphate pools. 2,3-diphosphoglycerate and glucose-1-phosphate are the only phosphoesters with signals in the chemical shift region close to 5.3 ppm. Both compounds can be excluded: 2,3-diphosphoglycerate due to the missing second signal component at 6.31 ppm; glucose-1-phosphate because its chemical shifts are about 0.2 ppm downfield from the Pi signal (4.9 ppm). If the Pun signal is from phosphate, it represents a pH value of 7.54 ± 0.05. Therefore, it could correspond to signals of Pi in mitochondria. However, patients with critical limb ischemia have rather few mitochondria and so the Pun signal probably originates from interstitia. Our data suggest that the increased Pun signal observed in patients with the diabetic foot syndrome is a biomarker of severe muscular damage.

Multiparametric Quantitative Brain MRI in Neurological and Hepatic Forms of Wilson's Disease.

BACKGROUND: In Wilson's disease (WD), demyelination, rarefaction, gliosis, and iron accumulation in the deep gray matter cause opposing effects on T2 -weighted MR signal. However, the degree and interplay of these changes in chronically treated WD patients has not been quantitatively studied. PURPOSE: To compare differences in brain multiparametric mapping between controls and chronically treated WD patients with neurological (neuro-WD) and hepatic (hep-WD) forms to infer the nature of residual WD neuropathology. STUDY TYPE: Cross-sectional. POPULATION/SUBJECTS: Thirty-eight WD patients (28 neuro-WD, 10 hep-WD); 26 healthy controls. FIELD STRENGTH/SEQUENCE: 3.0T: susceptibility, T2 *, T2 , T1 relaxometry; 1.5T: T2 , T1 relaxometry. ASSESSMENT: The following 3D regions of interest (ROIs) were manually segmented: globus pallidus, putamen, caudate nucleus, and thalamus. Mean bulk magnetic susceptibility, T2 *, T2 , and T1 relaxation times were calculated for each ROI. STATISTICAL TESTS: The effect of group (neuro-WD, hep-WD, controls) and age was assessed using a generalized least squares model with different variance for each ROI and quantitative parameter. A general linear hypothesis test with Tukey adjustment was used for post-hoc between-group analysis; P < 0.05 was considered significant. RESULTS: Susceptibility values were higher in all ROIs in neuro-WD compared to controls and hep-WD (P < 0.001). In basal ganglia, lower T2 and T2 * were found in neuro-WD compared to controls (P < 0.01) and hep-WD (P < 0.05) at 3.0T. Much smaller intergroup differences for T2 in basal ganglia were observed at 1.5T compared to 3.0T. In the thalamus, increased susceptibility in neuro-WD was accompanied by increased T1 at both field strengths (P < 0.001 to both groups), and an increased T2 at 1.5T only (P < 0.001 to both groups). DATA CONCLUSION: We observed significant residual brain MRI abnormalities in neuro-WD but not in hep-WD patients on chronic anticopper treatment. Patterns of changes were suggestive of iron accumulation in the basal ganglia and demyelination in the thalamus; 3.0T was more sensitive for detection of the former and 1.5T of the latter abnormality. LEVEL OF EVIDENCE: 2 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:1829-1835.

Ultralong TE In Vivo 1 H MR Spectroscopy of Omega-3 Fatty Acids in Subcutaneous Adipose Tissue at 7 T.

BACKGROUND: Omega-3 (n-3) fatty acids (FA) play and important role in neural development and other metabolic diseases such as obesity and diabetes. The knowledge about the in vivo content and distribution of n-3 FA in human body tissues is not well established and the standard quantification of FA is invasive and costly. PURPOSE: To detect omega-3 (n-3 CH3 ) and non-omega-3 (CH3 ) methyl group resonance lines with echo times up to 1200 msec, in oils, for the assessment of n-3 FA content, and the n-3 FA fraction in adipose tissue in vivo. STUDY TYPE: Prospective technical development. POPULATION: Three oils with different n-3 FA content and 24 healthy subjects. FIELD STRENGTH/SEQUENCE: Single-voxel MR spectroscopy (SVS) with a point-resolved spectroscopy (PRESS) sequence with an echo time (TE) of 1000 msec at 7 T. ASSESSMENT: Knowledge about the J-coupling evolution of both CH3 resonances was used for the optimal detection of the n-3 CH3 resonance line at a TE of 1000 msec. The accuracy of the method in oils and in vivo was validated from a biopsy sample with gas chromatography analysis. STATISTICAL TESTS: SVS data were compared to gas chromatography with the Pearson correlation coefficient. RESULTS: T2 relaxation times in oils were assessed as follows: CH2 , 65 ± 22 msec; CH3 , 325 ± 7 msec; and n-3 CH3 , 628 ± 34 msec. The n-3 FA fractions from oil phantom experiments (n = 3) were in agreement with chromatography analysis and the comparison of in vivo obtained data with the results of chromatography analysis (n = 5) yielded a significant correlation (P = 0.029). DATA CONCLUSION: PRESS with ultralong-TE can detect and quantify the n-3 CH3 signal in vivo at 7 T. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:71-82.

Low-molecular-weight paramagnetic 19F contrast agents for fluorine magnetic resonance imaging.

OBJECTIVE: 19F MRI requires biocompatible and non-toxic soluble contrast agents with high fluorine content and with suitable 19F relaxation times. Probes based on a DOTP chelate with 12 magnetically equivalent fluorine atoms (DOTP-tfe) and a lanthanide(III) ion shortening the relaxation times were prepared and tested. METHODS: Complexes of DOTP-tfe with trivalent paramagnetic Ce, Dy, Ho, Tm, and Yb ions were synthetized and characterized. 19F relaxation times were determined and compared to those of the La complex and of the empty ligand. In vitro and in vivo 19F MRI was performed at 4.7 T. RESULTS: 19F relaxation times strongly depended on the chelated lanthanide(III) ion. T1 ranged from 6.5 to 287 ms, T2 from 3.9 to 124.4 ms, and T2* from 1.1 to 3.1 ms. All complexes in combination with optimized sequences provided sufficient signal in vitro under conditions mimicking experiments in vivo (concentrations 1.25 mM, 15-min scanning time). As a proof of concept, two contrast agents were injected into the rat muscle; 19F MRI in vivo confirmed the in vivo applicability of the probe. CONCLUSION: DOTP-based 19F probes showed suitable properties for in vitro and in vivo visualization and biological applications. The lanthanide(III) ions enabled us to shorten the relaxation times and to trim the probes according to the actual needs. Similar to the clinically approved Gd3+ chelates, this customized probe design ensures consistent biochemical properties and similar safety profiles.

MR compatible ergometers for dynamic 31P MRS.

Magnetic Resonance (MR) compatible ergometers are specialized ergometers used inside the MR scanners for the characterization of tissue metabolism changes during physical stress. They are most commonly used for dynamic phosphorous magnetic resonance spectroscopy (31P MRS), but can also be used for lactate production measurements, perfusion studies using arterial spin labelling or muscle oxygenation measurements by blood oxygen dependent contrast sequences. We will primarily discuss the importance of ergometers in the context of dynamic 31P MRS. Dynamic 31P MRS can monitor muscle fatigue and energy reserve during muscle contractions as well as the dynamics of recuperation of skeletal muscle tissue during the following recovery through signal changes of phosphocreatine (PCr), inorganic phosphate and adenosine triphosphate (ATP). Based on the measured data it is possible to calculate intracellular pH, metabolic flux of ATP through creatine-kinase reaction, anaerobic glycolysis and oxidative phosphorylation and other metabolic parameters as mitochondrial capacity. This review primarily focuses on describing various technical designs of MR compatible ergometers for dynamic 31P MRS that must be constructed with respect to the presence of magnetic field. It is also expected that the construction of ergometers will be easy for the handling and well accepted by examined subjects.

The aging effect on prostate metabolite concentrations measured by 1H MR spectroscopy.

OBJECTIVE: The effects of aging, magnetic field and the voxel localization on measured concentrations of citrate (Cit), creatine (Cr), cholines (Cho) and polyamines (PA) in a healthy prostate were evaluated. MATERIALS AND METHODS: 36 examinations at both 1.5T and 3T imagers of 52 healthy subjects aged 19-71 years were performed with PRESS 3D-CSI sequences (TE = 120 and 145 ms). Concentrations in laboratory units and their ratios to citrate were calculated using the LCModel technique. Absolute concentrations were also obtained after the application of correction coefficients. Statistical analysis was performed using a robust linear mixed effects model. RESULTS: Significant effects of aging, the magnetic field strength and the voxel position in central (CZ) or peripheral (PZ) zones on all measured metabolites were found. The concentrations (mmol/kg wet tissue) including prediction intervals in a range of 20-70 years were found: Cit: 7.9-17.2; Cho: 1.4-1.7; Cr: 2.8-2.5; PA (as spermine): 0.6-2.1 at 3T in CZ. In PZ, the concentrations were higher by about 10 % as compared to CZ. CONCLUSION: Increasing citrate and spermine concentrations with age are significant and correlate well with a recently described increase of zinc in the prostate. These findings should be considered in decision-making if the values obtained from a subject are in the range of control values.

[Diabetic foot syndrome: importance of calf muscles MR spectroscopy in the assessment of limb ischemia and effect of revascularization]. / Syndrom diabetické nohy: význam MR spektroskopie lýtkových svalu pro hodnocení koncetinové ischemie a efektu revaskularizace.

AIM: The standard method for assessment of effect of revascularization in patients with diabetic foot (DF) and critical limb ischemia (CLI) is transcutaneous oxygen pressure (TcPO2). Phosphorus magnetic resonance spectroscopy (31P MRS) enables to evaluate oxidative muscle metabolism that could be impaired in patients with diabetes and its complications. The aim of our study was to compare MRS of calf muscle between patients with DF and CLI and healthy controls and to evaluate the contribution of MRS in the assessment of the effect of revascularization. METHODS: Thirty-four diabetic patients with DF and CLI treated either by autologous cell therapy (ACT; 15 patients) or percutaneous transluminal angioplasty (PTA; 12 patients) in our foot clinic during 2013-2016 and 19 healthy controls were included into the study. TcPO2 measurement was used as a standard method of non-invasive evaluation of limb ischemia. MRS examinations were performed using the whole-body 3T MR system 1 day before and 3 months after the procedure. Subjects were examined in a supine position with the coil fixed under the m. gastrocnemius. MRS parameters were obtained at rest and during the exercise period. Rest MRS parameters of oxidative muscle metabolism such as phosphocreatine (PCr), inorganic phosphate (Pi), phosphodiesters (PDE), adenosine triphosphate (ATP), dynamic MRS parameters such as recovery constant PCr (τPCr) and mitochondrial capacity (Qmax), and pH were compared between patients and healthy controls, and also before and 3 months after revascularization. RESULTS: Patients with CLI had significantly lower PCr/Pi (p < 0.001), significantly higher Pi and pH (both p < 0.01), significantly lower Qmax and prolonged τPCr (both p < 0.001) in comparison with healthy controls. We observed a significant improvement in TcPO2 at 3 months after revascularization (from 26.4 ± 11.7 to 39.7 ± 17.7 mm Hg, p < 0.005). However, the rest MRS parameters did not change significantly after revascularization. In individual cases we observed improvement of dynamic MRS parameters. There was no correlation between MRS parameters and TcPO2 values. CONCLUSION: Results of our study show impaired oxidative metabolism of calf muscles in patients with CLI in comparison with healthy controls. We observed an improvement in dynamic MRS parameters in individual cases; this finding should be verified in a large number of patients during longer follow-up.Key words: autologous cell therapy - critical limb ischemia - diabetic foot - MR spectroscopy.

Reverse asymmetry and changes in brain structural volume of the basal ganglia in ADHD, developmental changes and the impact of stimulant medications.

We discussed the cross section studies and the meta-analysis of published data in children and adolescents with ADHD (both drug naive and receiving stimulant medications), in comparison with healthy children and adolescents of the same age. In children and adolescents with ADHD the deceleration of the maturation dynamics of discrete CNS structures is found, volume reduction and decreased grey matter in prefrontal and occipital regions, which is accompanied by reverse asymmetry of the basal ganglia volume (putamen, nucleus caudate). The above mentioned developmental characteristics are valid only for the ADHD children, who have not been treated by stimulant medications. The stimulant treatment eliminates the mentioned changes into various extend. These developmental changes of CNS structures volume are missing in girls.

Long term pharmacotherapy by methylfenidate or atomoxetine DAT 1 10/10 ADHD children in correlation with results of the imaging methods.

OBJECTIVES: ADHD is one of the most significant diagnostic units in child and adolescent psychiatry. The occurrence in children is 5-6% and 50-80% continued to adult age. The presence of individual genes (polymorphism) on particular symptoms and processes in ADHD are not known. It is estimated that ADHD symptoms are up to 80% to genetic. The higher density of resultant DAT 1 protein was observed in ADHD patients in comparison with controls. The question was if DAT 1 10/10 predicted bad prognoses in long term therapy. METHODS: We compared 30 ADHD DAT 1 10/10 adolescents treated for 5-6 years. Patients with 30 control adolescents. They were the same age of probands and controls. All these subjects were examined by child psychiatry scales (Conners, Achenbach…). Biological changes were tested by MRI specific CNS volumometry. RESULTS: We didn't confirm bad prognoses in long term therapy with methylphenidate or atomoxetine in ADHD children DAT 1 10/10 in long term therapy. In MRI specific CNS volumometry were not identify any differences in controls and ADHD probands. Gray matter thickness was significantly higher in prefrontal and occipital areas in patients compared to control in prefrontal and occipital areas with cluster-wise p-value<0.05. By this method were not identify any cerebrum damage in long term therapy by methylphenidate and atomoxetine.

Eating two larger meals a day (breakfast and lunch) is more effective than six smaller meals in a reduced-energy regimen for patients with type 2 diabetes: a randomised crossover study.

AIMS/HYPOTHESIS: The aim of the study was to compare the effect of six (A6 regimen) vs two meals a day, breakfast and lunch (B2 regimen), on body weight, hepatic fat content (HFC), insulin resistance and beta cell function. METHODS: In a randomised, open, crossover, single-centre study (conducted in Prague, Czech Republic), we assigned 54 patients with type 2 diabetes treated with oral hypoglycaemic agents, both men and women, age 30-70 years, BMI 27-50 kg/m(2) and HbA1c 6-11.8% (42-105 mmol/mol), to follow two regimens of a hypoenergetic diet, A6 and B2, each for 12 weeks. Randomisation and allocation to trial groups (n = 27 and n = 27) were carried out by a central computer system. Individual calculations of energy requirements for both regimens were based on the formula: (resting energy expenditure × 1.5) - 2,092 kJ. The diet in both regimens had the same macronutrient and energy content. HFC was measured by proton magnetic resonance spectroscopy. Insulin sensitivity was measured by isoglycaemic-hyperinsulinaemic clamp and calculated by mathematical modelling as oral glucose insulin sensitivity (OGIS). Beta cell function was assessed during standard meal tests by C-peptide deconvolution and was quantified with a mathematical model. For statistical analysis, 2 × 2 crossover ANOVA was used. RESULTS: The intention-to-treat analysis included all participants (n = 54). Body weight decreased in both regimens (p < 0.001), more for B2 (-2.3 kg; 95% CI -2.7, -2.0 kg for A6 vs -3.7 kg; 95% CI -4.1, -3.4 kg for B2; p < 0.001). HFC decreased in response to both regimens (p < 0.001), more for B2 (-0.03%; 95% CI -0.033%, -0.027% for A6 vs -0.04%; 95% CI -0.041%, -0.035% for B2; p = 0.009). Fasting plasma glucose and C-peptide levels decreased in both regimens (p < 0.001), more for B2 (p = 0.004 and p = 0.04, respectively). Fasting plasma glucagon decreased with the B2 regimen (p < 0.001), whereas it increased (p = 0.04) for the A6 regimen (p < 0.001). OGIS increased in both regimens (p < 0.01), more for B2 (p = 0.01). No adverse events were observed for either regimen. CONCLUSIONS/INTERPRETATION: Eating only breakfast and lunch reduced body weight, HFC, fasting plasma glucose, C-peptide and glucagon, and increased OGIS, more than the same caloric restriction split into six meals. These results suggest that, for type 2 diabetic patients on a hypoenergetic diet, eating larger breakfasts and lunches may be more beneficial than six smaller meals during the day. Trial registration ClinicalTrials.gov number, NCT01277471, completed. Funding Grant NT/11238-4 from Ministry of Health, Prague, Czech Republic and the Agency of Charles University - GAUK No 702312.

The in vivo J-difference editing MEGA-PRESS technique for the detection of n-3 fatty acids.

In this study, we present a method for the detection of n-3 fatty acid (n-3 FA) signals using MRS in adipose tissue in vivo. This method (called oMEGA-PRESS) is based on the selective detection of the CH3 signal of n-3 FA using the MEGA-PRESS (MEshcher-GArwood Point-RESolved Spectroscopy) J-difference editing technique. We optimized the envelope shape and frequency of spectral editing pulses to minimize the spurious co-editing and incomplete subtraction of the CH3 signal of other FAs, which normally obscure the n-3 FA CH3 signal in MR spectra acquired using standard PRESS techniques. The post-processing of the individual data scans with the phase and frequency correction before data subtraction and averaging was implemented to further improve the quality of in vivo spectra. The technique was optimized in vitro on lipid phantoms using various concentrations of n-3 FA and examined in vivo at 3 T on 15 healthy volunteers. The proportion of n-3 FA estimated by the oMEGA-PRESS method in phantoms showed a highly significant linear correlation with the n-3 FA content determined by gas chromatography. The signal attributed to n-3 FA was observed in all subjects. Comparisons with the standard PRESS technique revealed an enhanced identification of the n-3 FA signal using oMEGA-PRESS. The presented method may be useful for the non-invasive quantification of n-3 FA in adipose tissue, and could aid in obtaining a better understanding of various aspects of n-3 FA metabolism.

Flip-angle mapping of 31P coils by steady-state MR spectroscopic imaging.

PURPOSE: Phosphorus ((31)P) MR spectroscopic imaging (MRSI) is primarily applied with sensitive, surface radiofrequency (RF) coils that provide inhomogeneous excitation RF field (B1(+)) and rough localization due to their B1(+) and sensitivity (B1(-)) profiles. A careful and time-consuming pulse adjustment and an accurate knowledge of flip angle (FA) are mandatory for quantification corrections. MATERIALS AND METHODS: In this study, a simple, fast, and universal (31)P B1(+) mapping method is proposed, which requires fast steady-state MRSI (typically one sixth of normal measurement time) in addition to the typical MRSI acquired within the examination protocol. The FA maps are calculated from the ratio of the signal intensities acquired by these two measurements and were used to correct for the influence of B1(+) on the metabolite maps. RESULTS: In vitro tests were performed on two scanners (3 and 7 Tesla) using a surface and a volume coil. The calculated FA maps were in good agreement with adjusted nominal FAs and the theoretical calculation using the Biot-Savart law. The method was successfully tested in vivo in the calf muscle and the brain of healthy volunteers (n = 4). The corrected metabolite maps show higher homogeneity compared with their noncorrected versions. CONCLUSION: The calculated FA maps helped with B1(+) inhomogeneity corrections of acquired in vivo data, and should also be useful with optimization and testing of pulse performances, or with the construction quality tests of new dual-channel (1)H/(31)P coils.

In vivo visualization of cells labeled with superparamagnetic iron oxides by a sub-millisecond gradient echo sequence.

OBJECT: In vivo magnetic resonance imaging (MRI) of iron-labeled pancreatic islets (PIs) transplanted into the liver is still challenging in humans. The aim of this study was to develop and evaluate a double contrast method for the detection of PIs labeled with superparamagnetic iron oxide (SPIO) nanoparticles. MATERIALS AND METHODS: A double-echo three-dimensional (3D) spoiled gradient echo sequence was adapted to yield a sub-millisecond first echo time using variable echo times and highly asymmetric Cartesian readout. Positive contrast was achieved by conventional and relative image subtraction. Experiments for cell detection efficiency were performed in vitro on gelatin phantoms, in vivo on a Lewis rat and on a patient 6 months after PI transplantation. RESULTS: It was demonstrated that the proposed method can be used for the detection of transplanted PIs with positive contrast in vitro and in vivo. For all experiments, relative subtraction yielded comparable and in some cases better contrast than conventional subtraction. For the first time, positive contrast imaging of transplanted human PIs was performed in vivo in patients. CONCLUSION: The proposed method allows 3D data acquisition within a single breath-hold and yields enhanced contrast-to-noise ratios of transplanted SPIO labeled pancreatic islets relative to negative contrast images, therefore providing improved identification.

Technical note: MR-compatible pedal ergometer with electromechanical pedal resistance and exercise triggering enhanced by visual feedback via video display.

BACKGROUND: During and after exercise, dynamic 31 P MR parameters are typically measured using an MR-compatible ergometer. Self-built equipment for local condition can be constructed where possible. PURPOSE: To develop a pedal resistance ergometer with rocker arm based on a system that combines electric weight displacement, visual self-monitoring, and exercise triggering. The repeatability and reproducibility were tested. METHODS: The hardware and software for the ergometer were constructed from commercial components in a home laboratory. Twelve volunteers participated in the testing of the ergometer. RESULTS: A fully automated ergometer system was developed, allowing the pedal resistance to be adjusted during the examination. The system includes a self-monitoring and triggering mechanism that enables both the operator and subject to monitor pedal frequency and force. The operator can modify the pedal resistance as desired during the exercise. This self-monitoring solution is simple and cost-effective, requiring only a commercial potentiometer, an Arduino converter, and a conventional video projector with a personal computer (PC). Additionally, all system components are located outside the magnetic resonance (MR) room, avoiding interference with the MR system. Results of several test of the reproducibility/repeatability of power at three pedal resistance values (15%, 24%, 25% maximal voluntary force) were expressed both as a coefficient of variation ranging from 6% to 3.1% and as an intraclass correlation of coefficient ranging from 0.96 to 0.99. Similar values were also found for other dynamic parameters of 31 P MR spectroscopy. These findings are similar to published data obtained on different types of ergometers. CONCLUSIONS: Based on more than 1 year of usage, the ergometer proved successful in handling stationary and variable loads, and can be easily operated by a single user.

Changes in the brain during long-term follow-up after liver transplantation.

PURPOSE: To examine changes in the brain before liver transplantation caused by the accumulation of paramagnetic ion deposits and to investigate recovery after liver transplantation over a long-term horizon. MATERIALS AND METHODS: Fifteen patients indicated for liver transplantation, 26 patients up to 2 years after, and 40 patients 8-15 years after liver transplantation were subjected to MR relaxometry. T(1) and T(2) relaxation times in the basal ganglia, thalamus, and white matter were evaluated. RESULTS: Relaxometry revealed a shortening of the relaxation times due to the deposition of paramagnetic ions in the basal ganglia before liver transplantation (P < 0.05), complete normalization of the relaxation times shortly after transplantation in the globus pallidus and caudate nucleus, and partial recovery of T(2) in the putamen. Relaxation times remained stable even 15 years posttransplantation. Increased relaxation times posttransplantation were found in the white matter and thalamus. CONCLUSION: The shortening of the relaxation times observed in the basal ganglia before liver transplantation was caused by paramagnetic ion deposition. The recovery observable within 2 years after transplantation was permanent, and no recurrence of paramagnetic ion deposition was observed even 15 years posttransplantation. Changes in the white matter and thalamus after transplantation were attributed to damage caused by permanent exposure to immunosuppressants.