Brain Metabolic Alterations in Adolescents and Young Adults With Fetal Alcohol Spectrum Disorders

BACKGROUND

Prenatal alcohol exposure affects brain structure and function. This study examined brain metabolism using magnetic resonance spectroscopy (MRS) and searched for regions of specific vulnerability in adolescents and young adults prenatally exposed to alcohol.

METHODS

Ten adolescents and young adults with confirmed heavy prenatal alcohol exposure and a diagnosis within the fetal alcohol spectrum disorders (FASD) were included. Three of them had fetal alcohol syndrome (FAS), 3 had partial FAS (PFAS), and 4 had alcohol-related neurobehavioral disorder (ARND). The control group consisted of 10 adolescents matched for age, sex, head circumference, handedness, and body mass. Exclusionary criteria were learning disorders and prenatal alcohol exposure. Three-dimensional (1)H magnetic resonance spectroscopic imaging ((1)H MRSI) was performed in the cerebrum and cerebellum. Metabolite ratios N-acetylaspartate/choline (NAA/Cho), NAA/creatine (Cr) and Cho/Cr, and absolute metabolite intensities were calculated for several anatomic regions.

RESULTS

In patients with FASD, lower NAA/Cho and/or NAA/Cr compared with controls were found in parietal and frontal cortices, frontal white matter, corpus callosum, thalamus, and cerebellar dentate nucleus. There was an increase in the absolute intensity of the glial markers Cho and Cr but no change in the neuronal marker NAA.

CONCLUSIONS

Our results suggest that prenatal alcohol exposure alters brain metabolism in a long-standing or permanent manner in multiple brain areas. These changes are in accordance with previous findings from structural and functional studies. Metabolic alterations represent changes in the glial cell pool rather than in the neurons.

Preliminary findings of proton magnetic resonance spectroscopy in occipital cortex during sleep deprivation

Proton magnetic resonance spectroscopy ((1)H MRS) has revealed biochemical alterations in various psychiatric disorders. Changes in brain metabolites may be caused not only by the disease's progression or response to treatment, but also by physiological variability. The aim of this study was to use (1)H MRS to assess the effects of specific short-term physiological states on major metabolites. Eight healthy women underwent (1)H MRS at the beginning and end of a 40-h period of sleep deprivation. The ratios of N-acetyl-aspartate (NAA), total creatine (tCr), and choline-containing compounds (Cho) to water (H(2)O) were determined from the occipital cortex during both baseline and photic stimulation conditions. During sleep deprivation, NAA/H(2)O decreased by 7% and Cho/H(2)O by 12%. Photic stimulation had no effect on the measured metabolites in the alert state, but in the sleep-deprived state the level of Cho/H(2)O increased during neuronal activation. The results suggest that NAA/H(2)O and Cho/H(2)O may depend on the state of alertness.

1H MRS studies in the Finnish boron neutron capture therapy project: detection of 10B-carrier, L-p-boronophenylalanine-fructose

This article summarizes the current status of 1H MRS in detecting and quantifying a boron neutron capture therapy (BNCT) boron carrier, L-p-boronophenylalanine-fructose (BPA-F) in vivo in the Finnish BNCT project. The applicability of 1H MRS to detect BPA-F is evaluated and discussed in a typical situation with a blood containing resection cavity within the gross tumour volume (GTV). 1H MRS is not an ideal method to study BPA concentration in GTV with blood in recent resection cavity. For an optimal identification of BPA signals in the in vivo 1H MR spectrum, both pre- and post-infusion 1H MRS should be performed. The post-infusion spectroscopy studies should be scheduled either prior to or, less optimally, immediately after the BNCT. The pre-BNCT MRS is necessary in order to utilise the MRS results in the actual dose planning.

Independent component analysis to proton spectroscopic imaging data of human brain tumours

In proton magnetic resonance spectroscopic imaging (1H MRSI), the recorded spectra are often linear combinations of spectra from different cell and tissue types within the voxel. This produces problems for data analysis and interpretation. A sophisticated approach is proposed here to handle the complexity of tissue heterogeneity in MRSI data. The independent component analysis (ICA) method was applied without prior knowledge to decompose the proton spectral components that relate to the heterogeneous cell populations with different proliferation and metabolism that are present in gliomas. The ability to classify brain tumours based on IC decomposite spectra was studied by grouping the components with histopathology. To this end, 10 controls and 34 patients with primary brain tumours were studied. The results indicate that ICA may reveal useful information from metabolic profiling for clinical purposes using long echo time MRSI of gliomas.

Decreased cerebellar total creatine in episodic ataxia type 2: a 1H MRS study

Episodic ataxia type 2 (EA2) affects mainly the cerebellum via mutations in the CACNA1A gene. The authors used proton MR spectroscopy to examine cerebellar and thalamic metabolism of nine mostly nonataxic EA2 family members (all with proven CACNA1A mutation) and nine healthy control subjects. Cerebellar total creatine was lower in the patient group (p = 0.005) than in control subjects, possibly reflecting an early sign of calcium channel dysfunction in EA2.

Five new cases of a recently described leukoencephalopathy with high brain lactate

BACKGROUND

A new leukoencephalopathy with brainstem and spinal cord involvement and high brain lactate was recently defined. The authors describe five new patients with this entity.

METHODS

Brain MRI was performed in all patients and spinal MRI and proton magnetic resonance spectroscopy (1H-MRS) in four patients. Laboratory examinations ruled out classic leukodystrophies.

RESULTS

MRI showed signal abnormalities in the periventricular and deep white matter, in the pyramidal tracts, mesencephalic trigeminal tracts, in the cerebellar connections, and in dorsal columns of the spinal cord. MRS showed decreased N-acetylaspartate and increased lactate in the white matter of all patients. In one patient choline-containing compounds were elevated. A slowly progressive sensory ataxia and tremor manifested at the age of 3 to 16 years and distal spasticity in adolescence. One 13-year-old patient was asymptomatic.

CONCLUSIONS

A slowly progressive sensory ataxia is a typical feature in this new leukodystrophy. MRS favors a primary axonal degeneration.

Brain metabolic alterations in patients with type 1 diabetes-hyperglycemia-induced injury

Microangiopathic end-organ injury is common in type 1 diabetes. However, the pathophysiology of diabetic encephalopathy is poorly understood. The authors studied 10 normotensive patients with type 1 diabetes with retinopathy, autonomic neuropathy, but without nephropathy, and 10 healthy subjects. Proton magnetic resonance spectroscopy was performed at 1.5 T in the frontal cortex, thalamus, and posterior frontal white matter. There was no change in N-acetyl-containing compounds (NA), but choline-containing compounds (Cho) were increased in the white matter and in the thalamus; myo-inositol was increased in the white matter, glucose excess was found in all brain, and water intensity was increased in the cortical voxel in the patients. Calculated lifetime glycemic exposure correlated inversely with Cho and NA in white matter and with Cho in thalamus. Concentrations of soluble intercellular adhesion molecules and vascular cell adhesion molecules were increased in the patients. In conclusion, in patients with type 1 diabetes, the increase in adhesion molecules and an association between altered brain metabolites and glycemic exposure suggest the presence of a vascularly mediated, progressive metabolic disturbance in the brain.

Stimulus-induced brain lactate: effects of aging and prolonged wakefulness

Both aging and sleep deprivation disturb the functions of the frontal lobes. Deficits in brain energy metabolism have been reported in these conditions. Neurons use not only glucose but also lactate as their energy substrate. The physiological response to elevated neuronal activity is a transient increase in lactate concentrations in the stimulated area. We have previously shown that cognitive stimulation increases brain lactate. To study the effect of prolonged wakefulness on the lactate response we designed an experiment to assess brain lactate levels during a 40-h sleep deprivation period in young (19-24 years old; n = 13) and in aged (60-68 years old; n = 12) healthy female volunteers. Brain lactate levels were assessed with proton MR-spectroscopy ((1)H MRS) during the performance of a silent word generation task. The (1)H MRS voxel location was individually selected, using functional magnetic resonance imaging, to cover the activated area in the left frontal lobe. The degree of sleepiness was verified using vigilance tests and self-rating scales. In the young alert subjects, the silent word generation test induced a 40% increase in lactate, but during the prolonged wakefulness period this response disappeared. In the aged subjects, the lactate response could not be detected even in the alert state. We propose that the absence of the lactate response may be a sign of malfunctioning of normal brain energy metabolism. The behavioral effects of prolonged wakefulness and aging may arise from this dysfunction.

Stimulus-induced brain lactate: effects of aging and prolonged wakefulness

Both aging and sleep deprivation disturb the functions of the frontal lobes. Deficits in brain energy metabolism have been reported in these conditions. Neurons use not only glucose but also lactate as their energy substrate. The physiological response to elevated neuronal activity is a transient increase in lactate concentrations in the stimulated area. We have previously shown that cognitive stimulation increases brain lactate. To study the effect of prolonged wakefulness on the lactate response we designed an experiment to assess brain lactate levels during a 40-h sleep deprivation period in young (19-24 years old; n = 13) and in aged (60-68 years old; n = 12) healthy female volunteers. Brain lactate levels were assessed with proton MR-spectroscopy ((1)H MRS) during the performance of a silent word generation task. The (1)H MRS voxel location was individually selected, using functional magnetic resonance imaging, to cover the activated area in the left frontal lobe. The degree of sleepiness was verified using vigilance tests and self-rating scales. In the young alert subjects, the silent word generation test induced a 40% increase in lactate, but during the prolonged wakefulness period this response disappeared. In the aged subjects, the lactate response could not be detected even in the alert state. We propose that the absence of the lactate response may be a sign of malfunctioning of normal brain energy metabolism. The behavioral effects of prolonged wakefulness and aging may arise from this dysfunction.

Low-Grade Gliomas and Focal Cortical Developmental Malformations: Differentiation with Proton MR Spectroscopy

PURPOSE

To assess proton magnetic resonance (MR) spectroscopy in differentiating between low-grade gliomas and focal cortical developmental malformations (FCDMs).

MATERIALS AND METHODS

Eighteen patients with seizures and a cortical brain lesion on MR images were studied with proton MR spectroscopy. A metabolite ratio analysis was performed, and the metabolite signals in the lesion core were compared with those in the contralateral centrum semiovale and in the corresponding brain sites in 18 control subjects to separately obtain the changes in N-acetylaspartate (NAA), choline-containing compounds (Cho), and creatine-phosphocreatine (Cr). Ten patients had a low-grade glioma (three, oligodendrogliomas; three, oligoastrocytomas; three, astrocytomas; and one, pilocytic astrocytoma), and eight had FCDM (five, focal cortical dysplasias and three, dysembryoplastic neuroepithelial tumors). Linear discriminant analysis and Student t test were used for statistical comparisons.

RESULTS

Loss of NAA and increase of Cho were more pronounced in low-grade gliomas than in FCDMs (NAA, -72% +/- 15 [+/- SD] vs -29% +/- 22, P <.001; Cho, 117% +/- 56 vs 21% +/- 66, P <.01). Changes in NAA and Cho helped differentiate low-grade gliomas from FCDMs, and changes in Cho and Cr helped differentiate astrocytomas from oligodendrogliomas and oligoastrocytomas. Metabolite NAA/Cho and NAA/Cr ratios helped differentiate low-grade gliomas from FCDMs but did not differentiate glioma subtypes.

CONCLUSION

MR spectroscopy allows distinction between low-grade gliomas and FCDMs and between low-grade glioma subtypes. Metabolite changes are more informative than are metabolite ratios.

Metabolic imaging of human cognition: an fMRI/1H-MRS study of brain lactate response to silent word generation

Proton magnetic resonance spectroscopy (1H-MRS) allows in vivo assessment of the metabolism related to human brain functions. Visual, auditory, tactile, and motor stimuli induce a temporary increase in the brain lactate level, which may act as a rapid source of energy for the activated neurons. The authors studied the metabolism of the frontal lobes during cognitive stimulation and measured local lactate levels with standard 1H-MRS, after localizing the activated area by functional MRI. Lactate levels were monitored while the subjects either silently listed numbers (baseline) or performed a silent word-generation task (stimulus-activation). The cognitive stimulus-activation produced a 50% increase in the brain lactate level in the left inferior frontal gyrus. The results show that metabolic imaging of neuronal activity related to cognition is possible using 1H-MRS.

1H MRS of a boron neutron capture therapy 10B-carrier, L-p-boronophenylalanine-fructose complex, BPA-F: phantom studies at 1.5 and 3.0 T

The quantification of a BNCT 10B-carrier, L-p-boronophenylalanine-fructose complex (BPA-F), was evaluated using 1H magnetic resonance spectroscopy (1H MRS) with phantoms at 1.5 and 3.0 T. For proper quantification, relaxation times T1 and T2 are needed. While T1 is relatively easy to determine, the determination of T2 of a coupled spin system of aromatic protons of BPA is not straightforward with standard MRS sequences. In addition, an uncoupled concentration reference for aromatic protons of BPA must be used with caution. In order to determine T2, the response of an aromatic proton spin system to the MRS sequence PRESS with various echo times was calculated and the product of the response curve with exponential decay was fitted to the measured intensities. Furthermore, the response curve can be used to correct the intensities, when an uncoupled resonance is used as a concentration reference. BPA was quantified using both phantom replacement and internal water referencing methods with accuracies of +/- 5% and +/- 15%. Our phantom results suggest that in vivo studies on BPA concentration determination will be feasible.

Quantification of human brain metabolites from in vivo 1H NMR magnitude spectra using automated artificial neural network analysis

Long echo time (TE=270 ms) in vivo proton NMR spectra resembling human brain metabolite patterns were simulated for lineshape fitting (LF) and quantitative artificial neural network (ANN) analyses. A set of experimental in vivo 1H NMR spectra were first analyzed by the LF method to match the signal-to-noise ratios and linewidths of simulated spectra to those in the experimental data. The performance of constructed ANNs was compared for the peak area determinations of choline-containing compounds (Cho), total creatine (Cr), and N-acetyl aspartate (NAA) signals using both manually phase-corrected and magnitude spectra as inputs. The peak area data from ANN and LF analyses for simulated spectra yielded high correlation coefficients demonstrating that the peak areas quantified with ANN gave similar results as LF analysis. Thus, a fully automated ANN method based on magnitude spectra has demonstrated potential for quantification of in vivo metabolites from long echo time spectroscopic imaging.

Proton spectroscopic imaging shows abnormalities in glial and neuronal cell pools in frontal lobe epilepsy

PURPOSE

Proton magnetic resonance spectroscopic imaging (1H MRSI) can lateralize the epileptogenic frontal lobe by detecting metabolic ratio abnormalities in frontal lobe epilepsy (FLE). We used 1H MRS to lateralize and localize the epileptogenic focus, and we also sought to characterize further the metabolic abnormality in FLE.

METHODS

We measured signals from N-acetyl aspartate (NAA), choline-containing compounds (Cho), and creatine + phosphocreatine (Cr) in the supraventricular brain of 14 patients with frontal or frontoparietal epilepsy and their matched controls. The supratentorial brain also was segmented into gray matter, white matter, and cerebrospinal fluid classes. Regional metabolite alterations were compared with localizing and lateralizing results from other examination modalities and with histology from three patients.

RESULTS

Spectroscopy lateralized the epileptogenic focus in 10 patients in agreement with video-EEG and functional imaging. In four patients, spectroscopy showed bilateral, focal metabolic abnormality, whereas video-EEG suggested unilateral or midline abnormality. In the epileptogenic focus, Cho and Cr were increased by 23% and 14%, respectively, and NAA was decreased by 11%, suggesting metabolic disturbances both in the glial and in the neuronal cell pools. Two Taylor dysplasia lesions confirmed by histology and one with radiologic diagnosis showed high Cho and low or normal NAA, whereas two dysembryoplastic neurogenic tumors had normal Cho and low NAA. Contralateral hemisphere NAA/(Cho + Cr) was decreased in FLE, indicating diffusely altered brain metabolism. Segmentation of brain tissue did not reveal atrophic changes in FLE.

CONCLUSIONS

Spectroscopy is useful in lateralizing frontoparietal epilepsy and shows promise as a "noninvasive biopsy" in epileptogenic lesions.

Spectroscopic imaging of radiation-induced effects in the white matter of glioma patients

External radiation therapy of brain tumors may cause adverse effects on normal brain tissue, resulting in severe neuropsychological and cognitive impairment. We investigated the late delayed radiation effects in the white matter (WM) using (1)H magnetic resonance spectroscopic imaging ((1)HMRSI). Nine glioma patients with local radiation-induced signal abnormalities in the T(2)-weighted MR images were studied with nine age- and sex-matched controls. The metabolite ratios in the radiation-induced hyper intensity area (RIHA) and in the normal appearing white matter (NAWM) of the patients were compared with respective WM areas of the controls. In RIHA, choline/creatine (Cho/Cr) was 17% decreased (1.22 +/- 0.13 vs 1.47 +/- 0.16, p = 0.0027, significant (s), unpaired Student's t test with Bonferroni correction) in the patients compared to the controls, while there was no difference in N-acetyl aspartate/Cr (NAA/Cr) (2.49 +/- 0.57 vs 2.98 +/- 0.32, p = 0.039) or NAA/Cho (2. 03 +/- 0.40 vs 2.04 +/- 0.17, p = 0.95). In NAWM, Cho/Cr was 24% decreased (1.21 +/- 0.15 vs 1.59 +/- 0.13, p < 0.0001, s) and NAA/Cho was 20% increased (2.49 +/- 0.49 vs 1.98 +/- 0.15, p = 0. 0082, s) in the patients compared to the controls, while there was no difference in NAA/Cr (2.99 +/- 0.46 vs 3.16 +/- 0.32, p = 0.38). NAA(RIHA)/NAA(NAWM) was 25% decreased (0.75 +/- 0.20 vs 1.00 +/- 0. 12, p = 0.0043, s) and Cr(RIHA)/Cr(NAWM) was 16% decreased (0.89 +/- 0.15 vs 1.06 +/- 0.10, p = 0.013, s) in the patients compared to the controls, while there was no difference in Cho(RIHA)/Cho(NAWM) (0.92 +/- 0.23 vs 0.98 +/- 0.10, p = 0.47). (1)HMRSI reveals widespread chemical changes in the WM after radiation therapy. In RIHA, there is loss of NAA, Cho, and Cr implying axonal and membrane damage and in NAWM, there is loss of Cho, reflecting membrane damage.

Central nervous system involvement in gyrate atrophy of the choroid and retina with hyperornithinaemia

In gyrate atrophy of the choroid and retina with hyperornithinaemia (GA), a genetically determined deficiency of ornithine delta-aminotransferase activity leads to high ornithine concentrations in body fluids. GA is characterized by centripetally progressing retinal and choroidal destruction and selective atrophy with tubular aggregates in type II skeletal muscle fibres. These findings have been suggested to be mediated by hyperornithinaemia-induced deficiency of high-energy creatine phosphate. As abnormal brain magnetic resonance images and electroencephalograms are found in another disorder of creatine metabolism, guanidinoacetate methyltransferase deficiency, we investigated the central nervous system involvement in GA, which seems to be associated with a milder degree of phosphocreatine deficiency. We compared 23 untreated GA patients with age-matched healthy controls, and with 9 patients who had received creatine or creatine precursor supplementation daily for several years. The mean age of the patients (32 +/- 18 years) was similar to that of the controls (36 +/- 22 years). The MRI or EEG findings of the patients on creatine supplementation did not differ from those of the untreated group. Brain MRI revealed degenerative lesions in the white matter in 50% of the GA patients, and 70% of the patients had premature atrophic changes, with a striking increase in the number of Virchow's spaces. Of the patients whose EEG was recorded, 58% had abnormal slow background activity, focal lesions or high-amplitude beta rhythm (> 50 microV). The EEG findings were not associated with the MRI changes or with the age or the sex of the patients. Early degenerative and atrophic brain changes and abnormal EEG are thus features of GA, in addition to the well-characterized eye and muscle manifestations.

Reduced brain creatine in gyrate atrophy of the choroid and retina with hyperornithinemia

OBJECTIVE

To analyze in vivo brain creatine (Cr) content in gyrate atrophy of the choroid and retina with hyperornithinemia (GA).

BACKGROUND

GA is caused by inherited deficiency of ornithine-delta-aminotransferase activity. Patients lose their vision by middle age and develop selective atrophy of type II skeletal muscle fibers. As demonstrated by MRS, the patients' skeletal muscles have diminished stores of high-energy Cr phosphate. Minor structural and electrophysiologic abnormalities in the brain of these patients also imply that the CNS may be affected.

METHODS

The authors acquired proton MR spectra of the basal ganglia of 22 healthy control subjects and 20 GA patients. Nine patients received supplementary Cr or its precursors, and one child was on an arginine-restricted diet to normalize plasma ornithine concentration. The ratios of N-acetylaspartate (NAA) to Cr, NAA to choline (Cho), and Cho to Cr, and the ratios of NAA, Cho, and Cr to tissue water were calculated.

RESULTS

NAA/Cr (Cho/Cr) in the untreated and treated patients and control subjects were (mean +/- SD) 3.3+/-0.4, 2.0+/-0.4, and 1.5+/-0.7 (1.9+/-0.3, 1.3+/-0.4, and 0.9+/-0.2), indicating that Cr content in untreated GA patients was proportionally and markedly diminished, and partially corrected by therapy (p < 0.0001). NAA/Cho was similar in all three groups. Cr/water in the untreated patients was only 46%, and increased to 75% of the control ratios in the treated patients (p < 0.0001).

CONCLUSIONS

Hyperornithinemia-associated Cr deficiency in GA also affects the CNS, further supporting the possibility that Cr deficiency also has a pathogenetic role in the retina. The deficiency was partially corrected by Cr supplementation and an arginine-restricted diet.

A new metabolite contributing to N-acetyl signal in 1H MRS of the brain in Salla disease

OBJECTIVE

To determine whether N-acetylaspartate (NAA) is reduced in patients with Salla disease, a neurodegenerative disorder.

BACKGROUND

1H MRS allows the brain metabolism to be studied noninvasively in vivo. N-acetyl (NA) is composed primarily of NAA, which is regarded as a neuronal marker. The NA signal in 1H MRS is reduced in several neurodegenerative disorders. Increased NA signal has thus far only been found in Canavan's disease as a result of NAA accumulation in the brain tissue. In Salla disease, an autosomal recessive free sialic acid storage disorder, N-acetylneuraminic acid (NANA), accumulates in lysosomes of brain tissue.

METHODS

The authors studied eight patients with Salla disease (age range, 6 to 44 years) and eight age-matched healthy volunteers using quantitative 1H MRS. The spectra were obtained from two selected 8-cm3 volumes of interest localized in the basal ganglia and in the parietal white matter using conventional 1.5-T MRI equipment. The spectral resonance lines of NA groups, creatine and phosphocreatine (Cr), and choline-containing compounds (Cho) were analyzed quantitatively. All MR images were evaluated to verify the state of myelination.

RESULTS

1H MRS from parietal white matter revealed 34% higher NA and 47% higher Cr concentrations, and a 35% lower Cho concentration in the patients with Salla disease compared with the age-matched control subjects. The patients had a 22% higher water content in their parietal white matter, whereas in the basal ganglia the water concentrations did not differ significantly. In the patients' basal ganglia the Cr concentration was 53% higher.

CONCLUSIONS

NAA is considered to be a neuronal marker that, except for Canavan's disease, has been found or assumed to be either stable or reduced. However, in Salla disease the high NA signal may have a contribution from accumulated lysosomal NANA, which offsets the possible loss of NAA. The high Cr is in line with the increased glucose uptake found in our earlier 2-fluoro-2-deoxy-D-glucose-PET study, reflecting increased energy demand. It is worth noting that in a conventional 1H MRS ratio-based analysis these underlying abnormalities would have remained undetected. Our study thus emphasizes the importance of a quantitative assessment of metabolite concentrations in 1H MRS for detecting altered brain metabolism.

MR image segmentation and tissue metabolite contrast in 1H spectroscopic imaging of normal and aging brain

The impact of image segmentation on 0.84-ml nominal voxel volume proton spectroscopic imaging in normal brain and in age-related cortical atrophy was investigated. Segmentation improved the gray matter-white matter (GM-WM) contrast for N-acetyl aspartate (NAA)/creatine (Cr) and choline (Cho)/Cr in normal brain, and for NAA/Cho and NAA/Cr in atrophic brain. NAA(GM/WM) (approximately 0.7), Cho(GM/WM) (approximately 0.8), and Cr(GM/WM) (approximately 1.3) in normal brain obtained with segmentation agreed with values obtained with quantitative magnetic resonance spectroscopy. Age-related cortical atrophy led to decreased cortical GM NAA/Cho and NAA/Cr; no changes were evident in WM or in NAA(GM/WM), Cho(GM/WM), or Cr(GM/WM). GM/WM metabolite analysis may be of limited use in conditions in which parallel metabolite changes occur in WM and GM.

Low field T1rho imaging of myositis

The purpose of this study was to evaluate 1/T1rho in relation to 1/T1 and 1/T2 in characterizing normal and diseased muscle. We measured the muscle relaxation rates 1/T1 and 1/T2 at 0.1 T and 1/T1rho at on-resonance locking fields B1 between 10 and 160 microT in myositis patients and normal volunteers. 1/T2 and 1/T1rho of muscle were lower in the patients than in the volunteers, whereas there was no difference in the 1/T1 values. The lower relaxation rates 1/T2 and 1/T1rho in the diseased muscle may be due to fat and connective tissue infiltrations and edema. 1/T1rho contrast between muscle and subcutaneous fat was higher than 1/T2 and 1/T1 contrast. This may be explained by the different B1 dispersion behavior of these two tissue types. 1/T1rho of fat is B1 field independent, whereas 1/T1rho of muscle decreases clearly with increasing B1 field. In conclusion, 1/T1rho provides a useful tool in manipulating contrast in magnetic resonance imaging of diseased muscle.

T1 rho MR imaging characteristics of human anterior tibial and gastrocnemius muscles

RATIONALE AND OBJECTIVES

The authors evaluated the value of T1 rho in relation to T1 and T2 in the characterization of human muscles.

MATERIALS AND METHODS

The authors studied the effect of muscle type (anterior tibial [AT] and gastrocnemius [GC]), sex, and age on 1/T1 and 1/T2 at 0.1 T and on 1/ T1 rho at locking-field B1s (spin-locking radio-frequency magnetic induction field) of 10-160 microT in 38 healthy volunteers. The contrast-to-noise ratio (CNR) between muscle and fat was evaluated with different T1-, T2-, and T1 rho-weighted magnetic resonance (MR) sequences.

RESULTS

The 1/T1, 1/T2, and 1/T1 rho were slightly higher in AT than in GC muscles. The 1/T2 and 1/T1 rho of AT muscles showed a sex dependence, whereas no correlation with age was found. The CNR of the T1 rho-weighted images did not markedly differ from that of the T1- and T2-weighted images.

CONCLUSION

T1 rho is as sensitive as T2 to the composition of muscle, whereas T1 is less sensitive. In MR imaging of normal muscle, T1 rho and T2 provide a relatively similar tissue contrast.

Increased choline signal coinciding with malignant degeneration of cerebral gliomas: a serial proton magnetic resonance spectroscopy imaging study

The authors tested the hypothesis that proton magnetic resonance spectroscopic (1H-MRS) imaging can be used as a supportive diagnostic tool to differentiate clinically stable brain tumors from those progressing as a result of low- to high-grade malignant transformation or posttherapeutic recurrence. Twenty-seven patients with cerebral gliomas verified on histological examination were studied repeatedly with 1H-MRS imaging over a period of 3.5 years. At the time of each 1H-MRS imaging study, clinical examination, MR imaging, positron emission tomography with 18F-fluorodeoxyglucose, and biopsy findings (when available) were used to categorize each patient as having either stable or progressive disease. Measures of the percentage changes in the choline (Cho) 1H-MRS imaging signal intensity between studies, which were obtained without knowledge of the clinical categorization, allowed the investigators to segregate the groups with a high degree of statistical significance. All progressive cases showed a Cho signal increase between studies of more than 45%, whereas all stable cases showed an elevation of less than 35%, no change, or even a decreased signal. The authors conclude that increased Cho levels coincide with malignant degeneration of cerebral gliomas and therefore may possibly be used as a supportive indicator of progression of these neoplasms.

Increased choline signal coinciding with malignant degeneration of cerebral gliomas: a serial proton magnetic resonance spectroscopy imaging study

The authors tested the hypothesis that proton magnetic resonance spectroscopy (1H-MRS) imaging can be used as a supportive diagnostic tool to differentiate clinically stable brain tumors from those progressing as a result of low- to high-grade malignant transformation or posttherapeutic recurrence. Twenty-seven patients with cerebral gliomas verified on histological examination were studied repeatedly with 1H-MRS imaging over a period of 3.5 years. At the time of each 1H-MRS imaging study, clinical examination, MR imaging, positron emission tomography with 18F-fluorodeoxyglucose, and biopsy findings (when available) were used to categorize each patient as having either stable or progressive disease. Measures of the percentage changes in the choline (Cho) 1H-MRS imaging signal intensity between studies, which were obtained without knowledge of the clinical categorization, allowed the investigators to segregate the groups with a high degree of statistical significance. All progressive cases showed a Cho signal increase between studies of more than 45%, whereas all stable cases showed an elevation of less than 35%, no change, or even a decreased signal. The authors conclude that increased Cho levels coincide with malignant degeneration of cerebral gliomas and therefore may possibly be used as a supportive indicator of progression of these neoplasms.

Proton magnetic resonance spectroscopic imaging in progressive supranuclear palsy, Parkinson's disease and corticobasal degeneration

We used proton magnetic resonance spectroscopic imaging (1H-MRSI) to assess the in vivo cortical and subcortical neuronal involvement in progressive supranuclear palsy, Parkinson's disease and corticobasal degeneration. This technique permitted the simultaneous measurement of compounds containing N-acetylaspartate (NA), choline (Cho), creatine-phosphocreatine (Cre) and lactate, from four 15-mm slices divided into 0.84-ml single-volume elements. The study included 12 patients with progressive supranuclear palsy, 10 with Parkinson's disease, nine with corticobasal degeneration and 11 age-matched normal control subjects. Regions of interest were selected from the brainstem, caudate, thalamus, lentiform nucleus, centrum semiovale, and from frontal, parietal, precentral, temporal and occipital cortices. Progressive supranuclear palsy patients, compared with control subjects, had significantly reduced NA/Cre in the brainstem, centrum semiovale, frontal and precentral cortex, and significantly reduced NA/Cho in the lentiform nucleus. Corticobasal degeneration patients, compared with control subjects, had significantly reduced NA/Cre in the centrum semiovale, and significantly reduced NA/Cho in the lentiform nucleus and parietal cortex. There were no significant differences between Parkinson's disease patients and control subjects, or between patients groups in any individual region of interest. In the parietal cortex of corticobasal degeneration patients, NA/Cho was significantly reduced contralateral to the most affected side. There were statistically significant group differences in the regional pattern of NA/Cre and NA/Cho reduction, comparing normal control subjects with all patient groups, Parkinson's disease with corticobasal degeneration, and Parkinson's disease with progressive supranuclear palsy. Although the occurrence of significant groups differences does not imply that it is possible to differentiate between individual patients using 1H-MRSI in progressive supranuclear palsy and corticobasal degeneration, detection of specific cortical and subcortical patterns of neuronal involvement is possible with this technique. We suggest that this regional pattern of neuronal involvement found in progressive supranuclear palsy and corticobasal degeneration may help in the diagnostic evaluation of affected individuals.

Cortical and subcortical chemical pathology in Alzheimer's disease as assessed by multislice proton magnetic resonance spectroscopic imaging

BACKGROUND

Multislide proton magnetic resonance spectroscopic imaging (1H-MRSI) permits the simultaneous acquisition of N-acetylaspartate (NA), choline (Cho), creatine/phosphocreatine (Cre), and lactate (Lac) signal intensities from four 15-mm slices divided into 0.84-ml single-volume elements. NA is inferred to be a neuron-specific molecule, whereas Cho mainly reflects glycerophosphocholine and phosphocholine, compounds involved in phospholipid metabolism.

OBJECTIVE

To assess whether 1H-MRSI could detect a regional pattern of cortical and subcortical involvement in the brain of Alzheimer's disease (AD) patients.

METHODS

1H-MRSI was performed in 15 patients with probable AD and 15 age-matched healthy controls. Regions of interest (ROIs) were selected from frontal (FC), temporal (TC), parietal (PC), occipital, and insular cortices, subcortical white matter (WM), and thalamus.

RESULTS

In AD patients, we found a significant reduction of NA/Cre in the FC, TC, and PC and a significant reduction of Cho/Cre in the WM.

CONCLUSIONS

This 1H-MRSI study of AD patients shows a regional pattern of neuronal damage in the associative cortices, as revealed by significant reduction of NA/Cre in the FC, TC, and PC, and regional derangement of phospholipid metabolism, as revealed by significant reduction of Cho/Cre in the WM.

Tissue characterization of intracranial tumors by magnetization transfer and spin-lattice relaxation parameters in vivo

T1s and magnetization transfer (MT) parameters of 36 intracranial tumors were determined in vivo at 0.1 T to assess their use in tissue characterization. The mobile water relaxation times (T1w) did not differ between tumor groups, whereas the T1s, the apparent MT relaxation times (T1a), and the parameters MT contrast (MTC) differed significantly between several tumor types. The MT rates (Rwm) demonstrated the most significant differences; Rwm values could reliably separate high grade and low grade gliomas. T1ws of the tumors were commonly in the same range as that of normal gray matter, whereas other parameters differed from those of normal brain. The results indicate that MT rates are superior to other parameters in the characterization of intracranial tumors and may be also useful clinically in the grading of gliomas.

Tissue characterisation of intracranial tumours: the value of magnetisation transfer and conventional MRI

We performed MRI on 85 patients with intracranial tumours to evaluate quantitative analysis in tumour characterisation. Signal intensities were measured on standard T2- and T1-weighted images, Gd-enhanced T1-weighted images and magnetisation transfer (MT) images. Statistically significant differences between tumour types were observed, but overlapping reduces their value. T2-weighted imaging was superior to T1-weighted imaging for tumour characterisation. Quantification of Gd enhancement was useful in the diagnosis of pituitary adenomas and haemangioblastomas, but of minor importance in other tumours, because of large nonspecific variation. The contribution of MT contrast to tumour characterisation resembled that of T2 contrast. However, MT imaging was superior to other sequences in the classification of intra-axial tumours. Low-grade astrocytomas, haemangioblastomas and craniopharyngiomas could be differentiated from other tumours on the basis of MT contrast. Reliable discrimination between meningiomas, high-grade astrocytomas and metastases was not possible by any of the methods.

Magnetization transfer in protein solutions at 0.1 T: dependence on concentration, molecular weight, and structure

RATIONALE AND OBJECTIVES

We observed the magnetization transfer rates in a variety of protein solutions at 0.1-T magnetic field and compared our results with previous investigations at high magnetic fields (> 0.5 T). The effects of protein concentration, size, pH, denaturation, cross linking, and fiber formation were investigated.

METHODS

We used the saturation transfer technique to determine the transfer of magnetization in gamma globulin, fibronectin, collagen, fibrinogen, and albumin solutions.

RESULTS

The observed transfer rate increased with increasing concentration and size of the protein. Protein degradation decreased the transfer rate. Cross linking and fiber formation each increased the transfer rate, whereas buffer pH had no effect.

CONCLUSION

Protein denaturation, aggregation, and fiber formation are important determinants of magnetization transfer in vitro. The size, concentration, and cross linking of the proteins contribute strongly to the transfer of magnetization at low fields, and the effect seems to be at least as important as at the higher fields.

MR classification of brain gliomas: value of magnetization transfer and conventional imaging

We compared quantitative analysis of conventional MR and magnetization transfer (MT) images with visual morphologic assessment of standard images in the classification of gliomas. Thirty-two patients with gliomas were imaged preoperatively. Relative signal intensities on T2- and T1-weighted images, Gd-enhancement, signal heterogeneity on T2-weighted and Gd-enhanced T1-weighted images and MT ratios were measured. In 16 astrocytomas, the MT ratios were correlated with the volume fraction of tumor cell nuclei in histological sections. Among the conventional sequences T2-weighted images were most accurate for quantitative classification; signal heterogeneity was more accurate than relative signal intensity. MT ratios were superior to quantitative analysis of conventional images and equal to visual morphologic evaluation in discriminating between low-grade and high-grade gliomas and correlated with the volume fraction of nuclei in the tumor tissue (r = 0.71, p < .01). The results indicate that quantitative analysis is generally of minor value in the grading of gliomas. In spite of sensitivity to tissue changes associated with malignancy MT imaging cannot significantly improve MR classification of gliomas.

Determination of magnetization transfer contrast in tissue: an MR imaging study of brain tumors

OBJECTIVE

In this study, the magnetization transfer contrast (MTC) on MR images of several brain tumors and the correlation between MTC and tumors' histologic features were investigated. MTC depends on the extent of magnetization transfer, or cross-relaxation, from tissue water protons to macromolecular protons. On the basis of the known increase of the cross-relaxation rate with increasing molecular weight of protein in protein solutions, the hypothesis that changes in MTC correlate directly with the macromolecular composition of various tumors was tested.

SUBJECTS AND METHODS

Preoperative MR images were obtained with a 0.1-T MR system in 40 patients with brain tumors. MTC was correlated with the histologic features and the dry weight of the tumors. The tumors studied included astrocytomas (10), acoustic schwannomas (three), meningiomas (12), pituitary adenomas (10), craniopharyngiomas (two), and hemangioblastomas (three).

RESULTS

MTC was 0.43 in normal white matter and 0.42 in normal gray matter, and varied from 0.11 to 0.37 in the tumors. The mean MTC in astrocytomas (0.21 +/- 0.09) was smaller than the mean MTC in the gray matter (p = .0001) or in the other solid tumors (0.34 +/- 0.07 to 0.37 +/- 0.09, p < .002). MTC was larger in high-grade than in low-grade astrocytomas (0.28 +/- 0.05 vs 0.14 +/- 0.04, p = .0005). In meningiomas, MTC correlated with the collagen content of the tumor tissue (r = .95, p = .01). The differences in contents of solids between the solid tumor groups were not significant (p > or = .1, NS).

CONCLUSION

When the previously demonstrated correlations between solid content and 1/T1 of the types of tumors studied are taken into consideration, the present results suggest a larger relative contribution from hydrodynamic vs cross-relaxation effects in astrocytomas than in benign tumors or in gray matter. The twofold difference in MTC between low- and high-grade astrocytomas probably reflects the amount of nuclear material in the tumor cells. Collagen content determined the differences in MTC among meningiomas. These results indicate that the major determinant of differences in MTC within these tumor groups is the high-molecular-weight tissue macromolecules, suggesting higher specificity for MTC than for T1 in discriminating between tissues on MR images.

T1 in subacute and chronic brain infarctions. Time-dependent development

RATIONALE AND OBJECTIVES

Time-dependent behavior of T1 in brain infarcts and in brain tissue of the contralateral hemisphere was studied in the subacute and early chronic stages of stroke.

METHODS

T1 was measured from magnetic resonance images (MRIs) of 29 patients as a function of infarct location and age. Another group of 11 patients was studied with consecutive MRI studies during the first 5 weeks after the onset of infarct, and the distribution of T1 in the infarctions was analyzed from T1 maps using a histographic method.

RESULTS

During the first 2 months after a stroke, T1 was longer in the infarcted gray matter than in the infarcted white matter (P = .002), and prolonged linearly in both. The histographic analysis showed a component arising from tissue breakdown products that could be identified for up to 5 weeks. A transient lengthening in T1 of the contralateral hemisphere, reaching a maximum at 3 weeks, also was observed.

CONCLUSIONS

These characteristics of recent infarctions differentiate them from older, gliotic lesions. The lengthening of T1 in the contralateral hemisphere may reflect remote flow and metabolic effects of brain infarctions.

Gadolinium-enhanced magnetization transfer contrast imaging of intracranial tumors

The magnetization transfer contrast (MTC) technique was used in low-field-strength (0.1 T) magnetic resonance (MR) imaging of 28 patients with intracranial tumors. MTC images were generated with an off-resonance, low-power radio-frequency pulse applied during the interpulse delay period of a gradient-echo partial-saturation sequence (TR msec/TE msec = 200/20). Images in the presence and absence of the MTC pulse were concurrently acquired before and after injection of gadopentetate dimeglumine at a dose of 0.1 mmol/kg. The contrast agent enhanced 27 of 28 tumors. Application of the MTC pulse improved the contrast-to-noise ratio (C/N) between tumor and normal white matter in 26 of 28 cases on the preinjection images and in 25 of 28 cases on the postinjection images. On the gadolinium-enhanced images, the mean C/N was 2.6 +/- 1.7 without the MTC pulse and 3.2 +/- 1.9 with the MTC pulse. The greatest contrast improvement with the MTC technique was obtained in tumors showing the strongest paramagnetic enhancement. The results indicate that MTC can improve contrast between normal brain and some intracranial neoplasms. The use of gadopentetate dimeglumine generally intensified this effect.

Ultrasonic guidance of lumbar sympathetic and celiac plexus block: a new technique

BACKGROUND AND OBJECTIVES

Lumbar sympathetic and celiac plexus block are widely used to treat chronic pain of diverse etiologies. To avoid complications and confirm the correct position of the needle, fluoroscopy and computed tomography have been used to follow the procedure visually. Our objective was to examine whether ultrasonography could be used instead of these techniques.

METHODS

Forty-eight neurolytic sympathectomies were performed using ultrasonographic guidance. The results were evaluated clinically and by color-doppler technique as applicable.

RESULTS

This new technique was shown to provide excellent results in ensuring the safe passage of the needle and documenting the correct spread of neurolytic agent (phenol-glycerol). The correct position of the needle was achieved on the first attempt in all cases.

CONCLUSIONS

The benefits of this technique are that it is inexpensive, there is no radiation, and the anatomy involved can be thoroughly examined before and after the procedure. Phenolglycerol may be the best choice as the neurolytic agent because it provides excellent contrast.

Magnetic field dependence of 1/T1 of human brain tumors. Correlations with histology

The authors have measured the magnetic field dependence of 1/T1 (nuclear magnetic relaxation dispersion, or NMRD profiles) of water protons of histologically characterized samples of astrocytomas, meningiomas, and lymphomas. The goal was to elucidate the determinants of 1/T1 of brain tumors at the cellular level and, in particular, to search for a possible correlation of the profiles with neoplastic properties, including degree of malignancy. Because of the recently demonstrated contribution of myelin to 1/T1 of white matter, careful histologic analyses were performed to correct for its presence. The range of magnitude of the profiles of differing types and grades of tumors correlates with the range of water content of these tumors; the correlation of water content with cellularity (density of cell nuclei in a histologic preparation), in turn, produces correlations of 1/T1 with tumor type. For all the tumors studied, 1/T1 is proportional to solids content; the constant of proportionality is relatively insensitive to tumor type and, for astrocytomas, grade of malignancy; and is about the same as that of normal gray matter. For low- and intermediate-grade astrocytomas that contain myelin, the myelin-specific contribution to 1/T1 has to be considered to make manifest the underlying correlations, which are best demonstrated at low fields, where the background contribution of water and dissolved oxygen is minimal. At high fields, where most imaging is done, a change in oxygen partial pressure, as for example from ischemia in very malignant tumors, is sufficient to alter 1/T1 significantly, reducing the intrinsic correlation between histology and 1/T1.

Relaxometry of brain: why white matter appears bright in MRI

The remarkable success of magnetic resonance imaging of adult brain relates to the unusually large ratio of the longitudinal relaxation rates 1/T1 of white and gray matter, approximately 2:1 at physiological temperature and traditional imaging fields. Several investigators have conjectured that myelin is the source of the greater 1/T1 of white matter without, however, suggesting details of the molecular mechanisms responsible. From measurements of the magnetic field dependence of 1/T1 (NMRD profiles) of adult and neonatal gray and white matter at 5 and 35 degrees C, we find a thermally activated contribution to the NMRD profile of adult white matter that is not present in the profiles of either adult gray or neonatal gray and white matter. We attribute this contribution to myelin and develop a quantitative model that accounts for the unique relaxation behavior of myelinated white matter. We find that myelin water, 15% of the total, has a relatively short T1 that arises from an unexpectedly large interaction with myelin lipid; when cast in terms of an interaction over the entire myelin bilipid-water interface, it is sevenfold greater than the analogous protein-water interfacial interaction. Its magnitude remains to be accounted for, but cholesterol, known to alter the relaxation rates of lipid protons, may play an important role. The contribution of myelin to 1/T1 at physiological temperatures is attributed to thermally activated transmembrane diffusion of water and, hence, more rapid mixing of axonal and the rapidly relaxing myelin water molecules.