Reproducibility of 7-T brain spectroscopy using an ultrashort echo time STimulated Echo Acquisition Mode sequence and automated voxel repositioning.

Establishing the reproducibility of brain MRS is important for clinical studies so that researchers can evaluate changes in metabolites due to treatment or the course of a disease and better understand the brain in healthy and disordered states. Prior 7-T MRS reproducibility studies using the stimulated echo acquisition mode (STEAM) sequence have focused on the anterior cingulate cortex or posterior cingulate cortex and precuneus. The purpose of this study was to evaluate the reproducibility of metabolite measurements in the dorsolateral prefrontal cortex (DLPFC) using an ultrashort echo time (TE) STEAM sequence and automated voxel repositioning. Spectra were acquired during two scan sessions from nine subjects using the AutoAlign method for voxel repositioning. Reproducibility was evaluated with coefficients of variation (CVs) and percentage differences. The mean intrasubject CVs were less than 6% for the major metabolites glutamate, N-acetylaspartate, total creatine, total choline, and myo-inositol. The mean CVs were less than 20% for the smaller signals of GABA, glutamine, glutathione, and taurine. These results indicate that 7-T MRS using a STEAM sequence with ultrashort TE and automated voxel repositioning provides excellent reproducibility of metabolites in the DLPFC.

Repeatability of proton magnetic resonance spectroscopy of the brain at 7 T: effect of scan time on semi-localized by adiabatic selective refocusing and short-echo time stimulated echo acquisition mode scans and their comparison.

BACKGROUND: Proton magnetic resonance spectroscopy (MRS) provides a unique opportunity for in vivo measurements of the brain's metabolic profile. Two methods of mainstream data acquisition are compared at 7 T, which provides certain advantages as well as challenges. The two representative methods have seldom been compared in terms of measured metabolite concentrations and different scan times. The current study investigated proton MRS of the posterior cingulate cortex using a semi-localized by adiabatic selective refocusing (sLASER) sequence and a short echo time (TE) stimulated echo acquisition mode (sSTEAM) sequence, and it compared their reliability and repeatability at 7 T using a 32-channel head coil. METHODS: Sixteen healthy subjects were prospectively enrolled and scanned twice with an off-bed interval between scans. The scan parameters for sLASER were a TR/TE of 6.5 s/32 ms and 32 and 48 averages (sLASER×32 and sLASER×48, respectively). The scan parameters for sSTEAM were a TR/TE of 4 s/5 ms and 32, 48, and 64 averages (sSTEAM4×32, sSTEAM4×48, and sSTEAM4×64, respectively) in addition to that with a TR/TE of 8 s/5 ms and 32 averages (sSTEAM8×32). Data were analyzed using LCModel. Metabolites quantified with Cramér-Rao lower bounds (CRLBs) >50% were classified as not detected, and metabolites quantified with mean or median CRLBs ≤20% were included for further analysis. The SNR, CRLBs, coefficient of variation (CV), and metabolite concentrations were statistically compared using the Shapiro-Wilk test, one-way ANOVA, or the Friedman test. RESULTS: The sLASER spectra for N-acetylaspartate + N-acetylaspartylglutamate (tNAA) and glutamate (Glu) had a comparable or higher SNR than sSTEAM spectra. Ten metabolites had lower CRLBs than prefixed thresholds: aspartate (Asp), γ-aminobutyric acid (GABA), glutamine (Gln), Glu, glutathione (GSH), myo-inositol (Ins), taurine (Tau), the total amount of phosphocholine + glycerophosphocholine (tCho), creatine + phosphocreatine (tCr), and tNAA. Performance of the two sequences was satisfactory except for GABA, for which sLASER yielded higher CRLBs (≥18%) than sSTEAM. Some significant differences in CRLBs were noted, but they were ≤2% except for GABA and Gln. Signal averaging significantly lowered CRLBs for some metabolites but only by a small amount. Measurement repeatability as indicated by median CVs was ≤10% for Gln, Glu, Ins, tCho, tCr, and tNAA in all scans, and that for Asp, GABA, GSH, and Tau was ≥10% under some scanning conditions. The CV for GABA according to sLASER was significantly higher than that according to sSTEAM, whereas the CV for Ins was higher according to sSTEAM. An increase in signal averaging contribute little to lower CVs except for Ins. CONCLUSIONS: Both sequences quantified brain metabolites with a high degree of precision and repeatability. They are comparable except for GABA, for which sSTEAM would be a better choice.

7T MRI Predicts Amelioration of Neurodegeneration in the Brain after AAV Gene Therapy.

GM1 gangliosidosis (GM1) is a fatal neurodegenerative lysosomal storage disease that occurs most commonly in young children, with no effective treatment available. Long-term follow-up of GM1 cats treated by bilateral thalamic and deep cerebellar nuclei (DCN) injection of adeno-associated virus (AAV)-mediated gene therapy has increased lifespan to 8 years of age, compared with an untreated lifespan of ~8 months. Due to risks associated with cerebellar injection in humans, the lateral ventricle was tested as a replacement route to deliver an AAVrh8 vector expressing feline ß-galactosidase (ß-gal), the defective enzyme in GM1. Treatment via the thalamus and lateral ventricle corrected storage, myelination, astrogliosis, and neuronal morphology in areas where ß-gal was effectively delivered. Oligodendrocyte number increased, but only in areas where myelination was corrected. Reduced AAV and ß-gal distribution were noted in the cerebellum with subsequent increases in storage, demyelination, astrogliosis, and neuronal degeneration. These postmortem findings were correlated with endpoint MRI and magnetic resonance spectroscopy (MRS). Compared with the moderate dose with which most cats were treated, a higher AAV dose produced superior survival, currently 6.5 years. Thus, MRI and MRS can predict therapeutic efficacy of AAV gene therapy and non-invasively monitor cellular events within the GM1 brain.

Adeno-Associated Virus Gene Therapy in a Sheep Model of Tay-Sachs Disease.

Tay-Sachs disease (TSD) is a fatal neurodegenerative disorder caused by a deficiency of the enzyme hexosaminidase A (HexA). TSD also occurs in sheep, the only experimental model of TSD that has clinical signs of disease. The natural history of sheep TSD was characterized using serial neurological evaluations, 7 Tesla magnetic resonance imaging, echocardiograms, electrodiagnostics, and cerebrospinal fluid biomarkers. Intracranial gene therapy was also tested using AAVrh8 monocistronic vectors encoding the α-subunit of Hex (TSD α) or a mixture of two vectors encoding both the α and ß subunits separately (TSD α + ß) injected at high (1.3 × 1013 vector genomes) or low (4.2 × 1012 vector genomes) dose. Delay of symptom onset and/or reduction of acquired symptoms were noted in all adeno-associated virus-treated sheep. Postmortem evaluation showed superior HexA and vector genome distribution in the brain of TSD α + ß sheep compared to TSD α sheep, but spinal cord distribution was low in all groups. Isozyme analysis showed superior HexA formation after treatment with both vectors (TSD α + ß), and ganglioside clearance was most widespread in the TSD α + ß high-dose sheep. Microglial activation and proliferation in TSD sheep-most prominent in the cerebrum-were attenuated after gene therapy. This report demonstrates therapeutic efficacy for TSD in the sheep brain, which is on the same order of magnitude as a child's brain.

Novel Biomarkers of Human GM1 Gangliosidosis Reflect the Clinical Efficacy of Gene Therapy in a Feline Model.

GM1 gangliosidosis is a fatal neurodegenerative disease that affects individuals of all ages. Favorable outcomes using adeno-associated viral (AAV) gene therapy in GM1 mice and cats have prompted consideration of human clinical trials, yet there remains a paucity of objective biomarkers to track disease status. We developed a panel of biomarkers using blood, urine, cerebrospinal fluid (CSF), electrodiagnostics, 7 T MRI, and magnetic resonance spectroscopy in GM1 cats-either untreated or AAV treated for more than 5 years-and compared them to markers in human GM1 patients where possible. Significant alterations were noted in CSF and blood of GM1 humans and cats, with partial or full normalization after gene therapy in cats. Gene therapy improved the rhythmic slowing of electroencephalograms (EEGs) in GM1 cats, a phenomenon present also in GM1 patients, but nonetheless the epileptiform activity persisted. After gene therapy, MR-based analyses revealed remarkable preservation of brain architecture and correction of brain metabolites associated with microgliosis, neuroaxonal loss, and demyelination. Therapeutic benefit of AAV gene therapy in GM1 cats, many of which maintain near-normal function >5 years post-treatment, supports the strong consideration of human clinical trials, for which the biomarkers described herein will be essential for outcome assessment.

Mucopolysaccharidosis-like phenotype in feline Sandhoff disease and partial correction after AAV gene therapy.

Sandhoff disease (SD) is a fatal neurodegenerative disease caused by a mutation in the enzyme ß-N-acetylhexosaminidase. Children with infantile onset SD develop seizures, loss of motor tone and swallowing problems, eventually reaching a vegetative state with death typically by 4years of age. Other symptoms include vertebral gibbus and cardiac abnormalities strikingly similar to those of the mucopolysaccharidoses. Isolated fibroblasts from SD patients have impaired catabolism of glycosaminoglycans (GAGs). To evaluate mucopolysaccharidosis-like features of the feline SD model, we utilized radiography, MRI, echocardiography, histopathology and GAG quantification of both central nervous system and peripheral tissues/fluids. The feline SD model exhibits cardiac valvular and structural abnormalities, skeletal changes and spinal cord compression that are consistent with accumulation of GAGs, but are much less prominent than the severe neurologic disease that defines the humane endpoint (4.5±0.5months). Sixteen weeks after intracranial AAV gene therapy, GAG storage was cleared in the SD cat cerebral cortex and liver, but not in the heart, lung, skeletal muscle, kidney, spleen, pancreas, small intestine, skin, or urine. GAG storage worsens with time and therefore may become a significant source of pathology in humans whose lives are substantially lengthened by gene therapy or other novel treatments for the primary, neurologic disease.

Evaluation of subchondral bone marrow lipids of acute anterior cruciate ligament (ACL)-injured patients at 3 T.

RATIONALE AND OBJECTIVES: The objectives of this study were to investigate the changes in compartment-specific subchondral bone marrow lipids of femoral-tibial bone in acute anterior cruciate ligament (ACL)-injured patients compared to that of healthy volunteers and patients with osteoarthritis (OA) (Kellgren-Lawrence [KL] grade 2-3). MATERIALS AND METHODS: A total of 55 subjects were recruited in the study and subdivided into three subgroups: 17 healthy controls (4 females, 13 males; mean age = 41 ± 16, age range 24-78 years), 17 patients with acute ACL injury (3 females, 14 males; mean age = 30 ± 11, age range 18-61 years), and 21 patients with KL2-3 OA (12 females, 9 males; mean age = 65 ± 12, age range 44-89 years). Routine clinical proton density-weighted fast spin echo images in sagittal (without fat saturation), axial, and coronal (fat saturation) planes were acquired on a 3 T clinical scanner for cartilage morphology using Whole-Organ Magnetic Resonance Imaging Score grading. A voxel of 10 × 10 × 10 mm(3) was positioned in the medial and lateral compartments of the tibia and femur for proton magnetic resonance spectroscopy measurements using the single voxel stimulated echo acquisition mode pulse sequence. All proton magnetic resonance data were processed with Java-based magnetic resonance user interface. Wilcoxon rank sum test and mixed model two-way analysis of variance were performed to determine significant differences between different compartments and examine the effect of ACL injury, OA grade and compartment, and their interactions. RESULTS: The index of unsaturation in lateral tibial compartment in ACL-injured patients was significantly higher (P < .05) than all compartments except lateral femoral in patients with KL2-3 OA. Significantly lower values (P < .05) were also identified in saturated lipids at 2.03 ppm in all compartments in ACL-injured patients than those of all compartments in patients with KL2-3 OA. CONCLUSIONS: The preliminary results suggest that the indices of unsaturation in the lateral tibial compartment and the peaks of saturated lipids at 1.3 and 2.03 ppm in medial tibial compartment may be clinically useful to characterize subchondral bone marrow among healthy controls, acute ACL-injured patients, and patients with OA.

Sustained normalization of neurological disease after intracranial gene therapy in a feline model.

Progressive debilitating neurological defects characterize feline G(M1) gangliosidosis, a lysosomal storage disease caused by deficiency of lysosomal ß-galactosidase. No effective therapy exists for affected children, who often die before age 5 years. An adeno-associated viral vector carrying the therapeutic gene was injected bilaterally into two brain targets (thalamus and deep cerebellar nuclei) of a feline model of G(M1) gangliosidosis. Gene therapy normalized ß-galactosidase activity and storage throughout the brain and spinal cord. The mean survival of 12 treated G(M1) animals was >38 months, compared to 8 months for untreated animals. Seven of the eight treated animals remaining alive demonstrated normalization of disease, with abrogation of many symptoms including gait deficits and postural imbalance. Sustained correction of the G(M1) gangliosidosis disease phenotype after limited intracranial targeting by gene therapy in a large animal model suggests that this approach may be useful for treating the human version of this lysosomal storage disorder.

Assessment of subchondral bone marrow lipids in healthy controls and mild osteoarthritis patients at 3T.

The compartment-specific lipid changes in femoral-tibial bone of healthy controls and mild osteoarthritis (OA) patients were quantified at 3.0 T. Healthy volunteers [Kellgren-Lawrence (KL) grade = 0; n = 15, 4 females, 11 males, mean age 39 ± 16 years, age range = 24-78 years] and mild OA patients (KL = 1, 2; n = 26, 12 females, 14 males, mean age 61 ± 14 years, age range = 27-80 years) were scanned on a 3 T scanner. Clinical proton density (PD)-weighted fast spin echo (FSE) images in the sagittal (without fat-saturation), axial and coronal (fat-saturation) planes were acquired for cartilage Whole-Organ MR Imaging Score (WORMS) grading. A voxel of 10 × 10 × 10 mm(3) was positioned in the medial and lateral compartments of the tibia [medial tibial (MT) and lateral tibial (LT)] and femur [medial femoral (MF) and lateral femoral (LF)] for MRS measurements using the single voxel-stimulated echo acquisition mode (STEAM) pulse sequence. All MRS data were processed with Java-based Magnetic Resonance User Interface (JMRUI). Wilcoxon's rank sum test and mixed model two-way analysis of variance (ANOVA) were performed to determine significant differences between different compartments as well as examine the effect of OA grade and compartment, and their interactions. Generally, the MF compartment index of unsaturation was increased in healthy subjects compared with OA subjects (whether graded by KL or WORMS score). Differences between MF at KL0 and all other compartments at KL1 except LF approached statistical significance (p < 0.05). Differences in saturated lipids signals could be observed predominantly in the 2.03 p.p.m. frequency shift. Healthy controls in the MF compartment had the lowest saturated lipid signals, and mild OA patients with KL2 and WORMS5-6 in the MF compartment had the highest saturated lipid signals compared with other compartments at 2.03 p.p.m. (p < 0.05).

Quantitative proton MR spectroscopy as a biomarker of tumor necrosis in the rabbit VX2 liver tumor.

PURPOSE: To compare metabolic magnetic resonance (MR) imaging findings (ie, quantification of tumor choline concentration) with percentage of necrosis on pathologic examination in rabbits bearing VX2 liver tumors. MATERIALS AND METHODS: VX2 tumors were implanted in the livers of 16 rabbits. MR imaging was performed with a 1.5-T MR scanner and extremity coil, and a hydrogen-1 ((1)H) proton MR spectroscopy ((1)H MRS) imaging protocol was used. Rabbits were euthanized immediately after imaging, and the tumor was harvested and sliced at 4-mm intervals in the axial plane. Choline concentration was calculated and was compared with the percentage of tumor necrosis on pathologic examination. RESULTS: Mean tumor size at pathologic examination was 16 mm (range, 12-22 mm). Mean percentage of necrosis at pathologic examination was 22% (range, 4%-44%). Choline concentration showed a relatively high inverse correlation with percentage of necrosis on pathologic examination, with an r value of 0.78 (P < .002). CONCLUSIONS: Choline concentration showed a relatively high inverse correlation with tumor necrosis on pathologic examination. Therefore, (1)H MRS may be useful to assess tumor necrosis.

Early response of hepatic malignancies to locoregional therapy-value of diffusion-weighted magnetic resonance imaging and proton magnetic resonance spectroscopy.

PURPOSE: The objective of our study was to determine the usefulness of the diffusion-weighted magnetic resonance imaging and proton magnetic resonance spectroscopy (H-MRS) of hepatic malignancies for the assessment of response to locoregional treatment. METHODS: Forty-four patients (29 men; mean age, 58 years) with hepatic malignancies were treated locally. Magnetic resonance imaging examinations obtained before and at 1 and 6 months after transarterial chemoembolization were analyzed retrospectively. Imaging criteria included change in tumor size, percentage of enhancement in the arterial and portal venous phases, diffusion-weighted magnetic resonance imaging apparent diffusion coefficients, and choline concentration by quantitative H-MRS. Response to treatment was grouped according to RECIST (Response Evaluation Criteria in Solid Tumors) and European Association for the Study of the Liver (EASL) criteria based on magnetic resonance imaging at 6 months after treatment. Statistical analysis used paired t test, Fisher exact test, and univariate and multivariate Cox proportional hazards models. RESULTS: Before treatment, the median tumor diameter was 6 cm; at 6 months after treatment, median tumor diameter was 5.1 cm. According to RECIST and EASL, 66% of the patients achieved partial response, 31% had stable disease, and 3% of the patients showed progressive disease. One month after transarterial chemoembolization, apparent diffusion coefficient increased (P < 0.14), and mean choline concentration of the tumors decreased (P < 0.008). CONCLUSIONS: Diffusion-weighted imaging and hepatic choline levels by H-MRS could predict response to locoregional therapy.

A feasibility study of quantitative molecular characterization of musculoskeletal lesions by proton MR spectroscopy at 3 T.

OBJECTIVE: The purpose of this study is to establish the feasibility and potential value of measuring the concentration of choline-containing compounds by proton MR spectroscopy (MRS) in musculoskeletal lesions at 3 T. SUBJECTS AND METHODS: Thirty-three subjects with 34 musculoskeletal lesions (four histologically proven malignant, 13 histologically proven benign or proven benign by follow-up analysis, and 17 posttreatment fibrosis with documented stability for 6-36 months) underwent single-voxel 3-T MRS studies. In each case, both water-suppressed and water-unsuppressed scans were obtained. The quality of the scans was recorded as excellent, adequate, or nondiagnostic, and the choline concentration was measured using water as the internal reference. The choline concentrations of benign and malignant lesions were compared using the Mann-Whitney test. RESULTS: Spectral quality was excellent in 26 cases, adequate in four cases, and nondiagnostic in four cases. For malignant lesions (three sarcomas), the choline concentrations were 1.5, 2.9, and 3.8 mmol/kg, respectively. For five benign lesions (two neurofibromas, two schwannomas, and one enchondroma), the choline concentrations were 0.11, 0.28, 0.13, 0.8, and 1.2 mmol/kg, respectively. For seven benign lesions (two hematomas, two bone cysts, one lipoma, one giant cell tumor, and one pigmented villonodular synovitis), the spectra showed negligible choline content. For three posttreatment fibrosis cases, the choline concentration range was 0.2-0.4 mmol/kg. For the remaining 12 posttreatment fibrosis cases, the spectra showed negligible choline content. Average choline concentrations were different for malignant and benign lesions (2.7 vs 0.5 mmol/kg; p = 0.01). CONCLUSION: The measurement of choline concentration within musculoskeletal lesions by MRS is feasible using an internal water-referencing method at 3 T and has potential for characterizing lesions for malignancy.

Quantification of muscle choline concentrations by proton MR spectroscopy at 3 T: technical feasibility.

OBJECTIVE: The quantification of choline in musculoskeletal tissues has several potential uses, including characterizing malignancy, but has not been previously achievable. We present a method of measuring the absolute concentration of choline by proton MR spectroscopy (MRS) in skeletal muscle at 3 T. MATERIALS AND METHODS: At 3 T, choline measurements were performed in phantoms and healthy volunteers using proton MRS (point-resolved spectroscopy sequence [PRESS]; TR/TE, 2,000/135). In vitro choline concentrations were measured in three phantom solutions (10, 5, 1.25 mmol). Choline T1 and T2 relaxation times were measured in the muscles of five healthy subjects. In vivo choline concentrations were measured using water as an internal reference and average T1 and T2 relaxation times in 20 muscle locations (quadriceps, hamstring, adductor) of seven healthy subjects (four men, three women). Descriptive statistics are reported. RESULTS: In vitro, the average measured choline concentrations of the 10-, 5-, and 1.25-mmol solutions were 9.91, 5.03, and 1.22 mmol, respectively. In vivo, the average T1 and T2 relaxation times of choline were 1,372+/-57 (SD) and 134+/-11 milliseconds, respectively. The average choline concentrations in the quadriceps and hamstring muscles were 10.0+/-0.4 (SD) and 8.0+/-2.9 mmol/kg. Interindividual variation existed in the choline concentrations (quadriceps range, 6.7-13 mmol/kg), but there was little variation by patient sex. CONCLUSION: In the musculoskeletal system, the measurement of choline concentration by proton MRS at 3 T is feasible using water as an internal reference. These data provide a quantitative basis for future investigations of metabolite concentrations in normal and diseased musculoskeletal tissues.

Characterization of adrenal pheochromocytoma using respiratory-triggered proton MR spectroscopy: initial experience.

OBJECTIVE: The aim of our study was to evaluate the feasibility of respiratory-triggered proton single-voxel MR spectroscopy for the diagnosis of adrenal pheochromocytoma and to determine whether certain spectral resonances detected on single-voxel MR spectroscopy are specific for adrenal pheochromocytomas compared with adrenal adenomas. CONCLUSION: Adrenal pheochromocytomas have a unique MR spectral signature, showing 6.8 ppm resonance that is not seen in adenomas. This unique spectral signature may be attributed to the presence of catecholamines and catecholamine metabolites that are abundant in pheochromocytomas.

Evaluation of 1H-magnetic resonance spectroscopy of breast cancer pre- and postgadolinium administration.

OBJECTIVES: We sought to evaluate spectroscopic measurements in breast cancer and compare variability in choline peak parameters related to contrast administration versus that inherent to repeated measurements. MATERIALS AND METHODS: Single-voxel, proton spectroscopy measurements were obtained before and after the administration of gadolinium on 15 patients with > or = 1-cm breast cancers. The protocol was repeated on a separate day in 7 patients. RESULTS: Postcontrast spectra demonstrated a significant increase in choline peak linewidth (day 1: 15% +/- 21%, P = 0.03; day 2: 19% +/- 12%, P = 0.001) and decrease in choline peak area (day 1: 11% +/- 9% (P < 0.001); day 2: 18% +/- 21% (P = 0.03). A variance-components analysis indicated that day-to-day variation in linewidth accounted for 0.0% of the total variation in width measurements and was not significant (P = 0.85). Day-to-day variation in area was also not significant (0.0%, P = 0.95). CONCLUSIONS: Contrast administration caused significant increases in choline peak linewidth and decreases in choline peak area in spectroscopic measurements of breast cancer.