Elsevier

Magnetic Resonance Imaging

Volume 25, Issue 7, September 2007, Pages 1105-1111
Magnetic Resonance Imaging

Original contribution
Intramyocellular lipid quantification: comparison between 3.0- and 1.5-T 1H-MRS

https://doi.org/10.1016/j.mri.2006.12.003Get rights and content

Abstract

Objective

This study aimed to prospectively compare measurement precision of calf intramyocellular lipid (IMCL) quantification at 3.0 and 1.5 T using 1H magnetic resonance spectroscopy (1H-MRS).

Materials and Methods

We examined the soleus and tibialis anterior (TA) muscles of 15 male adults [21–48 years of age, body mass index (BMI)=21.9–38.0 kg/m2]. Each subject underwent 3.0- and 1.5-T single-voxel, short-echo-time, point-resolved 1H-MRS both at baseline and at 31-day follow-up. The IMCL methylene peak (1.3 ppm) was scaled to unsuppressed water peak (4.7 ppm) using the LCModel routine. Full width at half maximum (FWHM) and signal-to-noise ratios (SNRs) of unsuppressed water peak were measured using jMRUI software. Measurement precision was tested by comparing interexamination coefficients of variation (CV) between different field strengths using Wilcoxon matched pairs signed rank test in all subjects. Overweight subjects (BMI>25 kg/m2) were analyzed separately to examine the benefits of 3.0-T acquisitions in subjects with increased adiposity.

Results

No significant difference between 3.0 and 1.5 T was noted in CVs for IMCL of soleus (P=.5). CVs of TA were significantly higher at 3.0 T (P=.02). SNR was significantly increased at 3.0 T for soleus (64%, P<.001) and TA (62%, P<.001) but was lower than the expected improvement of 100%. FWHM at 3.0 T was significantly increased for soleus (19%, P<.001) and TA (7%, P<.01). Separate analysis of overweight subjects showed no significant difference between 3.0- and 1.5-T CVs for IMCL of soleus (P=.8) and TA (P=.4).

Conclusion

Using current technology, 1H-MRS for IMCL at 3.0 T did not improve measurement precision, as compared with 1.5 T.

Introduction

Fat deposition in skeletal muscle plays a significant role in the regulation of insulin metabolism. Fat storage in muscle occurs in the form of cytoplasmic fat droplets within myocytes [intramyocellular lipids (IMCLs)] or in adipocytes between muscle cells and fascicles [extramyocellular lipids (EMCL)] [1], [2]. IMCL accumulation is strongly associated with insulin resistance [3], [4], [5], [6] and is currently a critical endpoint in studies that evaluate insulin homeostasis. To this effect, 1H magnetic resonance spectroscopy (1H-MRS) has become the key noninvasive technique for measuring IMCL in conditions with insulin resistance, such as type 2 diabetes mellitus [3], obesity [6] and HIV-lipodystrophy syndrome [7].

In vivo 1H-MRS IMCL quantification is performed with a high level of technical success on clinical 1.5-T scanners [1], [2], [8], with measurement variability in the range of 13% (intraday scans) and 14–21% (interexamination scans) [9]. With the widespread availability of 3.0-T MR scanners, there is growing interest in the performance of high-field muscle 1H-MRS with respect to 1.5 T. 1H-MRS performed at 3.0 T has theoretical advantages of higher signal-to-noise ratio (SNR) and improved chemical shift dispersion, potentially increasing measurement precision and sensitivity. However, these gains may be partially offset by changes in relaxation times and linewidth broadening due to susceptibility effects at higher magnetic field strengths [10], [11].

Prior measurements of relaxation times at 4.0 T demonstrated increases of 70–90% in T1 and decreases of 10–20% in T2 when compared with 1.5 T [12]. In a study that compares 3.0 T with 1.5 T, Gold et al. [13] showed that musculoskeletal tissues at 3.0 T had significantly higher T1 relaxation times (15–22%), while T2 relaxation times were significantly lower (10–37%). Changes in T2 relaxation times may have an effect on IMCL quantification, as they contribute to linewidth broadening that may decrease measurement precision. Increased susceptibility effects at 3.0 T may also represent a potential drawback: this may limit the advantages of better peak separation due to broadening of the EMCL linewidth. In addition, spectral distortions and SNR loss due to more severe eddy current artifacts and increased chemical shift artifact may represent additional factors that decrease measurement precision at 3.0 T [14].

A recent report on IMCL quantification using long-echo 1H-MRS examined separate subject groups at 3.0 and 1.5 T, measuring variability in a same-day session without repositioning [15]. To our knowledge, no prior studies have compared IMCL measurement variability in the same subject group performing 1H-MRS both at 3.0 and 1.5 T on baseline and follow-up visits. The purpose of our study was to prospectively examine, in a single cohort, temporal changes in IMCL measured by 3.0- and 1.5-T 1H-MRS and determine if variability indices were significantly different when both field strengths are compared.

Section snippets

Materials and methods

The recruitment procedures and study protocol were HIPAA compliant and performed with the approval of our institutional review board. Written informed consent was obtained from all subjects.

Results

A total of 15 male subjects were recruited. No subjects were excluded based on information provided during the screening interview. No subjects referred changes in dietary habits or physical activity during the study. Data from participating subjects are outlined in Table 1.

All subjects completed the entire scanning protocol, generating a total of 120 spectra, with 30 soleus and 30 tibialis anterior (TA) spectra acquired at 3.0 T and at 1.5 T. Soleus spectra with indistinct IMCL methylene peak

Discussion

The rationale for performing 1H-MRS for IMCL at higher magnetic fields comes from the expectation of improved measurement precision. Several factors affect the precision of IMCL quantification and are strongly related to variability introduced by field-strength-dependent changes, equipment performance, repositioning, biologic variation and fitting error. IMCL methylene (1.3 ppm) demonstrates consistent overlap with neighboring lipid peaks in the 0.9- to 1.5-ppm range, which may potentially

Acknowledgment

This study was funded in part by NIH Grant M01 RR01066 and MGH Musculoskeletal Imaging Research Core.

References (25)

  • A. Naressi et al.

    Java-based graphical user interface for the MRUI quantitation package

    MAGMA

    (2001)
  • R.J. Kuczmarski et al.

    Criteria for definition of overweight in transition: background and recommendations for the United States

    Am J Clin Nutr

    (2000)
  • F. Schick et al.

    Comparison of localized proton NMR signals of skeletal muscle and fat tissue in vivo: two lipid compartments in muscle tissue

    Magn Reson Med

    (1993)
  • C. Boesch et al.

    In vivo determination of intra-myocellular lipids in human muscle by means of localized 1H-MR-spectroscopy

    Magn Reson Med

    (1997)
  • S. Jacob et al.

    Association of increased intramyocellular lipid content with insulin resistance in lean nondiabetic offspring of type 2 diabetic subjects

    Diabetes

    (1999)
  • M. Krssak et al.

    Intramyocellular lipid concentrations are correlated with insulin sensitivity in humans: a 1H NMR spectroscopy study

    Diabetologia

    (1999)
  • K. Levin et al.

    Morphometric documentation of abnormal intramyocellular fat storage and reduced glycogen in obese patients with Type II diabetes

    Diabetologia

    (2001)
  • R. Sinha et al.

    Assessment of skeletal muscle triglyceride content by (1)H nuclear magnetic resonance spectroscopy in lean and obese adolescents: relationships to insulin sensitivity, total body fat, and central adiposity

    Diabetes

    (2002)
  • M. Torriani et al.

    Increased intramyocellular lipid accumulation in HIV-infected women with fat redistribution

    J Appl Physiol

    (2006)
  • L.S. Szczepaniak et al.

    Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo

    Am J Physiol

    (1999)
  • M. Torriani et al.

    Intramyocellular lipid quantification: repeatability with 1H MR spectroscopy

    Radiology

    (2005)
  • K. Kantarci et al.

    Proton MR spectroscopy in mild cognitive impairment and Alzheimer disease: comparison of 1.5 and 3 T

    AJNR Am J Neuroradiol

    (2003)

    • Cited by (10)

    View all citing articles on Scopus
    View full text
    Copyright © 2007 Elsevier Inc. All rights reserved.