Comparison of Fourier and Bayesian Analysis of NMR Signals. II. Examination of Truncated Free Induction Decay NMR Data

Kotyk, John J.; Hoffman, Norman G.; Hutton, William; Bretthorst, G. Larry; Ackerman, Joseph J. H.

doi:10.1006/jmra.1995.1183

Cited by 17 publications

(13 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Respiratory-gated LASER spectra were collected with echo time ϭ 39 ms; recycle time ϭ ϳ1 s (the exact value of recycle time depends on respiratory rate, and thus varies slightly from animal to animal); sweep width ϭ 7,812 Hz; acquisition time ϭ 262 ms; number of data points ϭ 4,096. Amplitudes of water and lipid signals were measured using Bayesian Probability Theory methods (38,39) and were corrected for differences in T1 and T2 values for water and lipid, as described previously (25).…”

Section: Methodsmentioning

confidence: 99%

Hepatic steatosis, inflammation, and ER stress in mice maintained long term on a very low-carbohydrate ketogenic diet

Garbow

Doherty

Schugar

et al. 2011

American Journal of Physiology-Gastrointestinal and Liver Physi

150

156

View full text Add to dashboard Cite

Garbow JR, Doherty JM, Schugar RC, Travers S, Weber ML, Wentz AE, Ezenwajiaku N, Cotter DG, Brunt EM, Crawford PA. Hepatic steatosis, inflammation, and ER stress in mice maintained long term on a very low-carbohydrate ketogenic diet. Am J Physiol Gastrointest Liver Physiol 300: G956 -G967, 2011. First published March 31, 2011 doi:10.1152/ajpgi.00539.2010.-Low-carbohydrate diets are used to manage obesity, seizure disorders, and malignancies of the central nervous system. These diets create a distinctive, but incompletely defined, cellular, molecular, and integrated metabolic state. Here, we determine the systemic and hepatic effects of longterm administration of a very low-carbohydrate, low-protein, and high-fat ketogenic diet, serially comparing these effects to a highsimple-carbohydrate, high-fat Western diet and a low-fat, polysaccharide-rich control chow diet in C57BL/6J mice. Longitudinal measurement of body composition, serum metabolites, and intrahepatic fat content, using in vivo magnetic resonance spectroscopy, reveals that mice fed the ketogenic diet over 12 wk remain lean, euglycemic, and hypoinsulinemic but accumulate hepatic lipid in a temporal pattern very distinct from animals fed the Western diet. Ketogenic diet-fed mice ultimately develop systemic glucose intolerance, hepatic endoplasmic reticulum stress, steatosis, cellular injury, and macrophage accumulation, but surprisingly insulin-induced hepatic Akt phosphorylation and whole-body insulin responsiveness are not impaired. Moreover, whereas hepatic Pparg mRNA abundance is augmented by both high-fat diets, each diet confers splice variant specificity. The distinctive nutrient milieu created by long-term administration of this low-carbohydrate, low-protein ketogenic diet in mice evokes unique signatures of nonalcoholic fatty liver disease and whole-body glucose homeostasis. nutrient state; magnetic resonance spectroscopy; peroxisome proliferator activated receptor-␥; insulin resistance; unfolded protein response; x-box-binding protein-1 splicing; high-fat diets; fatty liver disease THERAPEUTIC USE OF REDUCED-CARBOHYDRATE diets has been extensively studied for the amelioration of a multitude of clinical states, including obesity and its metabolic complications, seizure disorders, and malignancies of the central nervous system (21,23,26,36,41,54,55,59,64). Nonetheless, the full scope of metabolic effects incurred by low-, and very low (ketogenic)-carbohydrate diets (KD) has only been preliminarily characterized. In wild-type mice, KDs result in weight loss and increased hepatic and myocardial fatty acid oxidation, compared with mice maintained on standard chow diets rich in polysaccharides (5,35,62). Whereas leptin-deficient obese (ob/ob) animals maintained on KD for 7 wk exhibit persistent weight gain, glucose tolerance and insulin resistance improve compared with ob/ob mice maintained on standard chow diet (3, 57). Collectively, encouraging preclinical and clinical studies of low-carbohydrate KDs have favored their continued study for anticonv...

show abstract

Section: Methodsmentioning

confidence: 99%

Hepatic steatosis, inflammation, and ER stress in mice maintained long term on a very low-carbohydrate ketogenic diet

Garbow

Doherty

Schugar

et al. 2011

American Journal of Physiology-Gastrointestinal and Liver Physi

150

156

View full text Add to dashboard Cite

show abstract

“…Figure 2 (top) displays the resonances found in this expanded aliphatic proton region using BPT, demonstrating BPT's ability to accurately model these data. BPT can accurately quantitate low-level signals, even in the presence of baseline distortions (40)(41)(42). As a consequence, we confidently included all of the aliphatic proton signals, and not just the methylene peak, in determining the lipid content of the liver.…”

Section: Downloaded Frommentioning

confidence: 99%

“…Bayesian probability theory (BPT) methods have been described for the analysis of magnetic resonance data (40)(41)(42). For spectral analysis, BPT allows modeling of the experimental data and extraction of the relevant spectral parameters.…”

Section: Bayesian Probability Theory Analysismentioning

confidence: 99%

In vivo MRS measurement of liver lipid levels in mice

Garbow

Lin

Sakata

et al. 2004

Journal of Lipid Research

View full text Add to dashboard Cite

A magnetic resonance spectroscopy (MRS) procedure for in vivo measurement of lipid levels in mouse liver is described and validated. The method uses respiratory-gated, localized spectroscopy to collect proton spectra from voxels within the mouse liver. Bayesian probability theory analysis of these spectra allows the relative intensities of the lipid and water resonances within the liver to be accurately measured. All spectral data were corrected for measured spin-spin relaxation. A total of 48 mice were used in this study, including wild-type mice and two different transgenic mouse strains. Different groups of these mice were fed high-fat or low-fat diets or liquid diets with and without the addition of alcohol. Proton spectra were collected at baseline and, subsequently, Alcoholic (1, 2) and nonalcoholic fatty liver (NAFL) (3-7) are highly prevalent in human populations and may develop into steatohepatitis and in some cases into cirrhosis requiring liver transplantation. Animal models of both conditions have been developed. Mouse models are particularly useful because genetic manipulations are highly developed in inbred mice. However, longitudinal studies require the killing of animals because no noninvasive method for quantifying liver fat is available. Here, we describe a noninvasive, nondestructive method for quantifying the liver fat contents of the mouse using a NAFL mouse model. The overwhelming majority of NAFL cases are associated with obesity, dyslipidemia, hypertension, insulin-resistant type 2 diabetes mellitus, and atherosclerotic cardiovascular disease (8)(9)(10)(11)(12). This constellation defines the metabolic syndrome (13,14). One naturally occurring cause of fatty liver is familial hypobetalipoproteinemia (FHBL). FHBL is defined by less than fifth percentile plasma levels of LDL-cholesterol and/or total apolipoprotein B (apoB), segregating in families as an autosomal dominant trait (15-17). The mean liver triglyceride content in apoBimpaired FHBL subjects is 3-to 5-fold greater than that of controls (18,19).In an attempt to understand the cellular/molecular bases of hypobetalipoproteinemia, several recombinant mice mimicking human FHBL have been produced (19)(20)(21)(22)(23)(24)(25). The resulting mice closely resemble their human counterparts with respect to the fatty liver phenotype. Thus, these mice could serve as good models of one genetic form of fatty liver for studies of the progression of fatty liver and on the effects of metabolic, hormonal, and therapeutic perturbations over time.One current limitation of such studies is the absence of an accurate, quantifiable, noninvasive method for repeat assessments of liver fat in animals. In humans, the gold standard for quantifying liver fat is the liver biopsy, which is invasive and, at best, semiquantitative. The analogous procedure in animals is killing of the animal and direct analysis of liver fat by standard chemical methods after extraction. Obviously, direct sampling of livers for fat analysis is not ideal for longitudinal, fol...

show abstract

“…However, very short-lived, eddy-current-induced gradients (τ < 2 ms) are not detected by the six-point sample method. This limitation arises because accurate frequency estimation is compromised by severely truncated FID data [35]. In some circumstances, this limitation may be of very little or no consequence.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, there is an unavoidable tradeoff between accurate time-evolution registration and accurate frequency estimation. Fortunately, Bayesian estimation of resonance-frequency is quite accurate provided the data acquisition period (i.e., time-domain truncation) is not too short [35]. It was determined empirically that data collected in the absence of time-varying eddy currents with acquisition times less than 8 ms led to frequency estimates for the six resonances that deviated unacceptably from those determined by analysis of non-truncated FIDs.…”

Section: Methodsmentioning

confidence: 99%

Quantification and compensation of eddy-current-induced magnetic-field gradients

Spees

Buhl

Sun

et al. 2011

Journal of Magnetic Resonance

View full text Add to dashboard Cite

Two robust techniques for quantification and compensation of eddy-current-induced magnetic-field gradients and static magnetic-field shifts (ΔB0) in MRI systems are described. Purpose-built 1-D or 6-point phantoms are employed. Both procedures involve measuring the effects of a prior magnetic-field-gradient test pulse on the phantom’s free induction decay (FID). Phantom-specific analysis of the resulting FID data produces estimates of the time-dependent, eddy-current-induced magnetic field gradient(s) and ΔB0 shift. Using Bayesian methods, the time dependencies of the eddy-current-induced decays are modeled as sums of exponentially decaying components, each defined by an amplitude and time constant. These amplitudes and time constants are employed to adjust the scanner’s gradient pre-emphasis unit and eliminate undesirable eddy-current effects. Measurement with the six-point sample phantom allows for simultaneous, direct estimation of both on-axis and cross-term eddy-current-induced gradients. The two methods are demonstrated and validated on several MRI systems with actively-shielded gradient coil sets.

show abstract

Comparison of Fourier and Bayesian Analysis of NMR Signals. II. Examination of Truncated Free Induction Decay NMR Data

Cited by 17 publications

References 0 publications

Hepatic steatosis, inflammation, and ER stress in mice maintained long term on a very low-carbohydrate ketogenic diet

Hepatic steatosis, inflammation, and ER stress in mice maintained long term on a very low-carbohydrate ketogenic diet

In vivo MRS measurement of liver lipid levels in mice

Quantification and compensation of eddy-current-induced magnetic-field gradients

Contact Info

Product

Resources

About