The effect of orientation on quantification of muscle creatine by 1H MR spectroscopy

B0 shimming for in vivo magnetic resonance spectroscopy: Experts' consensus recommendations

Magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) allow the chemical analysis of physiological processes in vivo and provide powerful tools in the life sciences and for clinical diagnostics. Excellent homogeneity of the static B₀ magnetic field over the object of interest is essential for achieving high-quality spectral results and quantitative metabolic measurements. The experimental minimization of B₀ variation is performed in a process called B₀ shimming. In this article, we summarize the concepts of B₀ field shimming using spherical harmonic shimming techniques, specific strategies for B₀ homogenization and crucial factors to consider for implementation and use in both brain and body. In addition, experts' recommendations are provided for minimum requirements for B₀ shim hardware and evaluation criteria for the primary outcome of adequate B₀ shimming for MRS and MRSI, such as the water spectroscopic linewidth.

Influence of muscle fiber orientation on water and metabolite relaxation times, magnetization transfer, and visibility in human skeletal muscle

PURPOSE

To gain a deeper understanding of the influence of skeletal muscle fiber orientation on metabolite visibility, magnetization transfer from water, and water proton relaxation rates in (1)H MR spectra.

METHODS

Non-water-suppressed MR spectroscopy was performed in tibialis anterior muscle (TA) of 10 healthy adults, with the TA oriented either parallel or at the magic angle to the 3T field. Spectra were acquired with metabolite-cycled PRESS, and water inversion from 50 to 2510 ms before excitation. Water proton T2 relaxation was sampled with STEAM with echo times from 12 to 272 ms.

RESULTS

Apparent concentrations of total creatine (tCr), taurine, and trimethylammonium compounds were reduced by 29% to 67% when TA was parallel to B0. Both tCr peak areas were strongly correlated to the methylene peak splitting. Magnetization transfer rates from water to tCr CH3 were not significantly different between orientations. Water T1s were similar between orientations, but T2s were statistically significantly shorter by 1 ms in the parallel orientation (P = 0.002).

CONCLUSION

Muscle metabolite visibilities in MR spectroscopy and water T2 times depend substantially on muscle fiber orientation relative to B0 . In contrast, magnetization transfer rates appear to depend on muscle composition, rather than fiber orientation.

1H Magnetic resonance spectroscopy findings in idiopathic inflammatory myopathies at 3 T: feasibility and first results

OBJECTIVE

The aim of this study was to investigate the feasibility and potential use of quantitative proton magnetic resonance spectroscopy (MRS) for determining metabolite concentrations in patients with suspected inflammatory myopathies.

MATERIALS AND METHODS

In this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant prospective study, 35 patients with a suspected inflammatory myopathy and 6 age-matched healthy volunteers underwent magnetic resonance imaging (MRI) (T1-weighted and short tau inversion recovery [STIR] sequences) and single-voxel MRS (point-resolved spectroscopy; repetition time/echo time, 2000/135 milliseconds; voxel size, 2.0 × 2.0 × 4.0 cm) at 3 T. The voxel was placed in a thigh muscle and targeted to one with abnormal STIR signal when possible. Absolute trimethylamine, creatine (Cr), and bulk lipid concentrations in each voxel were determined using the phantom replacement method. The MRS results of patients and healthy subjects were compared using the Wilcoxon rank sum test.

RESULTS

Twenty-one patients were diagnosed with an active idiopathic inflammatory myopathy (IIM). In 20 of these patients, MRI showed increased intramuscular STIR signal; however, the muscle where the voxel was placed was normal in 9 patients. Patients with an IIM demonstrated higher mean intramuscular Cr concentration compared with controls (62.1 vs 35.3 IU; P = 0.01), but there were no differences in the mean trimethylamine or lipid concentrations. In IIM patients with no intravoxel signal abnormality (9/21), the mean Cr concentration was still higher than that in healthy subjects (63.2 vs 35.3 IU; P = 0.001).

CONCLUSIONS

Quantitative 3-T MRS is feasible and may supplement the role of conventional MRI in the evaluation of patients with inflammatory myopathies, especially where MRI shows no obvious muscle abnormalities.

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.

Muscle metabolism in Duchenne muscular dystrophy assessed by in vivo proton magnetic resonance spectroscopy

PURPOSE

To investigate the correlation between muscle function and metabolism in muscle tissue of Duchenne muscular dystrophy (DMD) patients by in vivo proton magnetic resonance spectroscopy.

MATERIALS AND METHODS

In this prospective study, we enrolled 8 boys with DMD and 8 healthy volunteers. In vivo proton magnetic resonance spectroscopy of the soleus muscles was performed using a whole-body 3.0-Tesla imaging unit and a knee coil. The levels of trimethyl ammonium (TMA) and total creatine (tCr) were measured. We compared TMA/water, tCr/water, and TMA/tCr ratios, and scores for muscle function in the legs by using a t test.

RESULTS

Fat infiltrated the leg muscles in all patients but no volunteers. All patients had elevated creatine kinase levels. Magnetic resonance spectra of patients and volunteers showed TMA and tCr peaks. Ratios of TMA/water (P = 0.0015), tCr/water (P = 0.0167), and TMA/tCr (P = 0.0017), and muscle function scores (P = 0.0028) were significantly lower in patients than in volunteers. All patients had impaired muscle function, whereas all volunteers had normal function. Muscle function in the legs was negatively correlated with the TMA/tCr ratio (r2 = 0.878).

CONCLUSIONS

Metabolite ratios and muscle function scores were significantly decreased in patients with DMD when compared with normal control subjects. A statistically significant decrease in TMA/tCr ratio in patients with DMD as compared with control subjects was found to correlate with decreased muscle function.

In vivo proton magnetic resonance spectroscopy assessment for muscle metabolism in neuromuscular diseases

Muscle metabolites were obtained by in vivo proton magnetic resonance spectroscopy of 3 patients with Duchenne muscular dystrophy (DMD), 6 patients with spinal muscular atrophy (SMA), and 10 normal volunteers. Patients with DMD and SMA had lower trimethyl amide (TMA)/water and TMA/total creatine (tCr) ratios but normal tCr/water ratios.

Orientational dependence of trimethyl ammonium signal in human muscles by 1H magnetic resonance spectroscopic imaging

(1)H magnetic resonance spectroscopic imaging (MRSI) was used to investigate the effect of orientation on spectral characteristics of trimethyl ammonium (TMA) in human muscle at rest. Four different muscles in the healthy calf were studied: soleus, gastrocnemius, tibial posterior and anterior. The data demonstrate that muscle orientation can profoundly change apparent spectral characteristics of proton metabolites. In particular, muscle orientation can cause concerted changes in the spectral pattern of TMA/methyl (tCr) and methylene (Cr2) protons of creatine for a given muscle, a switch of TMA/tCr spectral patterns among different muscles and changes in the T(2) of TMA. A significant correlation was detected between TMA/tCr peaks and the Cr2 peak splitting (r=.62, P<.001). In vivo (1)H MRSI has the potential to simultaneously evaluate the orientation of muscle fibers and biochemical changes induced by a disease process or physiological activity.

Significant differences in proton trimethyl ammonium signals between human gastrocnemius and soleus muscle

PURPOSE

To study the apparent heterogeneous characteristics of trimethyl ammonium (TMA) in healthy human muscles at rest, and to illustrate the importance of establishing the baseline characteristics of proton metabolites in muscles with a West Nile patient.

MATERIALS AND METHODS

Point-resolved spectroscopy (PRESS) magnetic resonance spectroscopy imaging (MRSI) with lipid suppression and optional outer-volume presaturation were used to acquire 1H spectra of human muscles at rest at 1.5 Tesla. A total of 28 subjects (27 normal volunteers and 1 patient with West Nile disease) between the ages of 22 and 76 participated in the study.

RESULTS

The apparent T2 values of TMA for soleus and gastrocnemius muscles in normal volunteers are 180 +/- 50 and 80 +/- 20 msec, respectively. This difference has profound effects on the apparent spectral pattern of 1H metabolites. The TMA/total creatine (tCr) spectral pattern of the soleus muscle of a West Nile patient resembles that of gastrocnemius muscle of healthy volunteers.

CONCLUSION

There are significant differences in the apparent T2 values of TMA between healthy soleus and gastrocnemius muscles at rest. It is important to establish the baseline characteristics of proton metabolites before clinical or physiological studies can be performed.