Quantitative P-31 MR spectroscopy of the liver in alcoholic cirrhosis

Reproducibility of absolute quantification of adenosine triphosphate and inorganic phosphate in the liver with localized 31 P-magnetic resonance spectroscopy at 3-T using different coils

Concentrations of the key metabolites of hepatic energy metabolism, adenosine triphosphate (ATP) and inorganic phosphate (Pi ), can be altered in metabolic disorders such as diabetes mellitus. 31 Phosphorus (31 P)-magnetic resonance spectroscopy (MRS) is used to noninvasively measure hepatic metabolites, but measuring their absolute molar concentrations remains challenging. This study employed a 31 P-MRS method based on the phantom replacement technique for quantifying hepatic 31 P-metabolites on a 3-T clinical scanner. Two surface coils with different size and geometry were used to check for consistency in terms of repeatability and reproducibility and absolute concentrations of metabolites. Day-to-day (n = 8) and intra-day (n = 6) reproducibility was tested in healthy volunteers. In the day-to-day study, mean absolute concentrations of γ-ATP and Pi were 2.32 ± 0.24 and 1.73 ± 0.26 mM (coefficient of variation [CV]: 7.3% and 8.8%) for the single loop, and 2.32 ± 0.42 and 1.73 ± 0.27 mM (CVs 6.7% and 10.6%) for the quadrature coil, respectively. The intra-day study reproducibility using the quadrature coil yielded CVs of 4.7% and 6.8% for γ-ATP and Pi without repositioning, and 6.3% and 7.1% with full repositioning of the volunteer. The results of the day-to-day data did not differ between coils and visits. Both coils robustly yielded similar results for absolute concentrations of hepatic 31 P-metabolites. The current method, applied with two different surface coils, can be readily utilized in long-term and interventional studies. In comparison with the single loop coil, the quadrature coil also allows measurements at a greater distance between the coil and liver, which is relevant for studying people with obesity.

Feasibility of absolute quantification for 31 P MRS at 7 T

Purpose

Phosphorus spectroscopy can differentiate among liver disease stages and types. To quantify absolute concentrations of phosphorus metabolites, sensitivity calibration and transmit field (B1+) correction are required. The trend toward ultrahigh fields (7 T) and the use of multichannel RF coils makes this ever more challenging. We investigated the constraints on reference phantoms, and implemented techniques for the absolute quantification of human liver phosphorus spectra acquired using a 10‐cm loop and a 16‐channel array at 7 T.

Methods

The effect of phantom conductivity was assessed at 25.8 MHz (1.5 T), 49.9 MHz (3 T), and 120.3 MHz (7 T) by electromagnetic modeling. Radiofrequency field maps (B1±) were measured in phosphate phantoms (18 mM and 40 mM) at 7 T. These maps were used to assess the correction of 4 phantom 3D‐CSI data sets using 3 techniques: phantom replacement, explicit normalization, and simplified normalization. In vivo liver spectra acquired with a 10‐cm loop were corrected with all 3 methods. Simplified normalization was applied to in vivo 16‐channel array data sets.

Results

Simulations show that quantification errors of less than 3% are achievable using a uniform electrolyte phantom with a conductivity of 0.23‐0.86 S.m⁻¹ at 1.5 T, 0.39‐0.58 S.m⁻¹ at 3 T, and 0.34‐0.42 S.m⁻¹ (16‐19 mM KH₂PO_4(aq)) at 7 T. The mean γ‐ATP concentration quantified in vivo at 7 T was 1.39 ± 0.30 mmol.L⁻¹ to 1.71 ± 0.35 mmol.L⁻¹ wet tissue for the 10‐cm loop and 1.88 ± 0.25 mmol.L⁻¹ wet tissue for the array.

Conclusion

It is essential to select a calibration phantom with appropriate conductivity for quantitative phosphorus spectroscopy at 7 T. Using an 18‐mM phosphate phantom and simplified normalization, human liver phosphate metabolite concentrations were successfully quantified at 7 T.

In-vivo31P-MRS of skeletal muscle and liver: A way for non-invasive assessment of their metabolism

In addition to direct assessment of high energy phosphorus containing metabolite content within tissues, phosphorus magnetic resonance spectroscopy (³¹P-MRS) provides options to measure phospholipid metabolites and cellular pH, as well as the kinetics of chemical reactions of energy metabolism in vivo. Even though the great potential of ³¹P-MR was recognized over 30 years ago, modern MR systems, as well as new, dedicated hardware and measurement techniques provide further opportunities for research of human biochemistry. This paper presents a methodological overview of the ³¹P-MR techniques that can be used for basic, physiological, or clinical research of human skeletal muscle and liver in vivo. Practical issues of ³¹P-MRS experiments and examples of potential applications are also provided. As signal localization is essential for liver ³¹P-MRS and is important for dynamic muscle examinations as well, typical localization strategies for ³¹P-MR are also described.

Mr Spectroscopy in Clinical Research

MR spectroscopy (MRS) offers unique possibilities for non-invasive evaluation of biochemistry in vivo. During recent years there has been a growing body of evidence from clinical research studies on human beings using 31P and 1H MRS. The results indicate that it is possible to evaluate phosphorous energy metabolism, loss of neurones, and lactate production in a large number of brain diseases. Furthermore, 31P and 1H MRS may be particularly clinically useful in evaluation of various disorders in skeletal muscle. In the heart 31P MRS seems at the moment the most suitable for evaluation of global affections of the myocardium. In the liver 31P MRS appears to be rather insensitive and non-specific, but absolute quantification of metabolite concentrations and using metabolic “stress models” may prove useful in the future. The clinical role of MRS in oncology is still unclear, but it may be useful for noninvasive follow-up of treatment.

Taken together, the evidence obtained so far certainly shows some trends for clinical applications of MRS. Methods are now available for the clinical research necessary for establishing routine clinical MRS examinations.

Measuring short-term liver metabolism non-invasively: postprandial and post-exercise ¹H and ³¹P MR spectroscopy

OBJECT

The objective of this study was to determine the effects of a standardized fat rich meal and subsequent exercise on liver fat content by ¹H MRS and on liver adenosine triphosphate (ATP) content by ³¹P MRS in healthy subjects.

MATERIALS AND METHODS

Hepatic ¹H and proton decoupled ³¹P MRS were performed on nine healthy subjects on a clinical 3.0 T MR imager three times during a day: after (1) an overnight fast, (2) a following standardized fat rich meal and (3) a subsequent exercise session. Blood parameters were followed during the day to serve as a reference to MRS.

RESULTS

Liver fat content increased gradually over the day (p = 0.0001) with an overall increase of 30 %. Also γ-NTP changed significantly over the day (p = 0.005). γ-NTP/tP decreased by 9 % (p = 0.019, post hoc) from the postprandial to the post-exercise state.

CONCLUSION

Our study shows that in vivo MRS can depict short lived physiological changes; entering of fat into liver cells and consumption of ATP during exercise can be measured non-invasively in healthy subjects. The physiological state may have an impact on fat and energy metabolite levels. Hepatic ¹H and ³¹P MRS studies should be performed under standardized conditions.

Higher dietary fructose is associated with impaired hepatic adenosine triphosphate homeostasis in obese individuals with type 2 diabetes

Fructose consumption predicts increased hepatic fibrosis in those with nonalcoholic fatty liver disease (NAFLD). Because of its ability to lower hepatic adenosine triphosphate (ATP) levels, habitual fructose consumption could result in more hepatic ATP depletion and impaired ATP recovery. The degree of ATP depletion after an intravenous (IV) fructose challenge test in low- versus high-fructose consumers was assessed. We evaluated diabetic adults enrolled in the Action for Health in Diabetes Fatty Liver Ancillary Study (n = 244) for whom dietary fructose consumption estimated by a 130-item food frequency questionnaire and hepatic ATP measured by phosphorus magnetic resonance spectroscopy and uric acid (UA) levels were performed (n = 105). In a subset of participants (n = 25), an IV fructose challenge was utilized to assess change in hepatic ATP content. The relationships between dietary fructose, UA, and hepatic ATP depletion at baseline and after IV fructose challenge were evaluated in low- (<15 g/day) versus high-fructose (≥ 15 g/day) consumers. High dietary fructose consumers had slightly lower baseline hepatic ATP levels and a greater absolute change in hepatic α-ATP/ inorganic phosphate (Pi) ratio (0.08 versus 0.03; P = 0.05) and γ-ATP /Pi ratio after an IV fructose challenge (0.03 versus 0.06; P = 0.06). Patients with high UA (≥ 5.5 mg/dL) showed a lower minimum liver ATP/Pi ratio postfructose challenge (4.5 versus 7.0; P = 0.04).

CONCLUSIONS

High-fructose consumption depletes hepatic ATP and impairs recovery from ATP depletion after an IV fructose challenge. Subjects with high UA show a greater nadir in hepatic ATP in response to fructose. Both high dietary fructose intake and elevated UA level may predict more severe hepatic ATP depletion in response to fructose and hence may be risk factors for the development and progression of NAFLD.

Abnormal hepatic energy homeostasis in type 2 diabetes

Increased hepatocellular lipids relate to insulin resistance and are typical for individuals with type 2 diabetes mellitus (T2DM). Steatosis and T2DM have been further associated with impaired muscular adenosine triphosphate (ATP) turnover indicating reduced mitochondrial fitness. Thus, we tested the hypothesis that hepatic energy metabolism could be impaired even in metabolically well-controlled T2DM. We measured hepatic lipid volume fraction (HLVF) and absolute concentrations of gammaATP, inorganic phosphate (Pi), phosphomonoesters and phosphodiesters using noninvasive (1)H/ (31)P magnetic resonance spectroscopy in individuals with T2DM (58 +/- 6 years, 27 +/- 3 kg/m (2)), and age-matched and body mass index-matched (mCON; 61 +/- 4 years, 26 +/- 4 kg/m (2)) and young lean humans (yCON; 25 +/- 3 years, 22 +/- 2 kg/m (2), P < 0.005, P < 0.05 versus T2DM and mCON). Insulin-mediated whole-body glucose disposal (M) and endogenous glucose production (iEGP) were assessed during euglycemic-hyperinsulinemic clamps. Individuals with T2DM had 26% and 23% lower gammaATP (1.68 +/- 0.11; 2.26 +/- 0.20; 2.20 +/- 0.09 mmol/L; P < 0.05) than mCON and yCON individuals, respectively. Further, they had 28% and 31% lower Pi than did individuals from the mCON and yCON groups (0.96 +/- 0.06; 1.33 +/- 0.13; 1.41 +/- 0.07 mmol/L; P < 0.05). Phosphomonoesters, phosphodiesters, and liver aminotransferases did not differ between groups. HLVF was not different between those from the T2DM and mCON groups, but higher (P = 0.002) than in those from the yCON group. T2DM had 13-fold higher iEGP than mCON (P < 0.05). Even after adjustment for HLVF, hepatic ATP and Pi related negatively to hepatic insulin sensitivity (iEGP) (r =-0.665, P = 0.010, r =-0.680, P = 0.007) but not to whole-body insulin sensitivity.

CONCLUSION

These data suggest that impaired hepatic energy metabolism and insulin resistance could precede the development of steatosis in individuals with T2DM.

In vivo, high-field, 3-Tesla 1H MR spectroscopic assessment of liver fibrosis in HCV-correlated chronic liver disease

PURPOSE

Histology is the gold standard by which to diagnose and score hepatic fibrosis. Recently, it has been proposed that hepatic magnetic resonance spectroscopy (MRS) could provide an accurate representation of the disease process. The aim of this study was to correlate the in vivo high-field (3-Tesla) (1)H MRS features of noncirrhotic chronic hepatitis C patients stratified according to the histopathological stages of fibrosis.

MATERIALS AND METHOD

Six healthy controls and 23 patients with biopsy-proven precirrhotic hepatitic C virus (HCV)-related liver disease were included. The subdivision of patients into the histopathological stages of fibrosis was based on the Ishak fibrosis (F) scoring system: mild hepatitis (0< or =F< or =1), moderate (2< or =F< or =3) and severe hepatitis (4< or =F< or =5). For correlation analysis, the Spearman nonparametric test was used. Differences between groups were calculated with the nonparametric Mann-Whitney U test. A p value <0.05 was considered significant. The particular metabolite content was evaluated in relative units (RU), according to the pattern metabolite/H(2)O=area of the metabolite x1,000/area of nonsuppressed water.

RESULT

A significant statistical difference was observed between control vs. mild and moderate vs. severe disease severity in choline-containing compounds (CCC)/H(2)O ratios (p=0.0379 and p=0.0003) and in glutamine/glutamate (Glx)/H(2)O ratios (p=0.004 and p<0.0001), whereas a statistically significant difference in the lipid/H(2)O ratios was achieved only between control vs. moderate and between moderate vs. severe stages of disease (p=0.011 and p=0.0030).

CONCLUSION

High-field (1)H MRS successfully differentiates between mild/moderate vs. severe stages of chronic hepatitis and can be considered a complement to most standard imaging protocols in the liver.

Separation of advanced from mild fibrosis in diffuse liver disease using 31P magnetic resonance spectroscopy

31P-MRS using DRESS was used to compare absolute liver metabolite concentrations (PME, Pi, PDE, gammaATP, alphaATP, betaATP) in two distinct groups of patients with chronic diffuse liver disorders, one group with steatosis (NAFLD) and none to moderate inflammation (n=13), and one group with severe fibrosis or cirrhosis (n=16). All patients underwent liver biopsy and extensive biochemical evaluation. A control group (n=13) was also included. Absolute concentrations and the anabolic charge, AC=[PME]/([PME]+[PDE]), were calculated. Comparing the control and cirrhosis groups, lower concentrations of PDE (p=0.025) and a higher AC (p<0.001) were found in the cirrhosis group. Also compared to the NAFLD group, the cirrhosis group had lower concentrations of PDE (p=0.01) and a higher AC (p=0.009). No significant differences were found between the control and NAFLD group. When the MRS findings were related to the fibrosis stage obtained at biopsy, there were significant differences in PDE between stage F0-1 and stage F4 and in AC between stage F0-1 and stage F2-3. Using a PDE concentration of 10.5mM as a cut-off value to discriminate between mild, F0-2, and advanced, F3-4, fibrosis the sensitivity and specificity were 81% and 69%, respectively. An AC cut-off value of 0.27 showed a sensitivity of 93% and a specificity of 54%. In conclusion, the results suggest that PDE is a marker of liver fibrosis, and that AC is a potentially clinically useful parameter in discriminating mild fibrosis from advanced.

The influence of tissue blood flow volume on energy metabolism in masseter muscles

This study investigated the energy metabolism of masseter muscles by 31P-Magnetic Resonance Spectroscopy (MRS) during increased blood flow induced by hot pack application to clarify the influence of changes in blood flow on muscle fatigue. Twelve healthy subjects with no history of muscle pain in the masticatory system participated in this study. The 31P-MRS measurements were performed before and after hot pack application and the ratio of phosphocreatine (PCr) acting as the energy source to reproduce ATP to beta-ATP, the PCr/beta-ATP ratio, was analyzed. Results showed that PCr/beta-ATP ratios increased significantly by an average of 22.4% after the hot pack application. The results suggest that changes in blood flow volume influence the energy metabolism in masseter muscles and that blood flow increases due to the hot pack cause higher energy levels in masseter muscles and offer an advantageous condition for preventing and relieving muscle fatigue.

Monitoring fluoropyrimidine metabolism in solid tumors with in vivo (19)F magnetic resonance spectroscopy

(19)Fluorine magnetic resonance spectroscopy ((19)F MRS) offers unique possibilities for monitoring the pharmacokinetics of fluoropyrimidines in vivo in tumors and normal tissue in a non-invasive way, both in animals and in patients. This method may therefore be useful for predicting response to fluoropyrimidine-based therapy with or without the effects of modulating agents, and this may be of value for the individualization of anticancer therapy and the strategic development of new anticancer drugs. (19)F MRS has been very valuable in elucidating the basic aspects of fluoropyrimidine metabolism, especially in animal studies. Studies in humans have indicated its clinical potential, but widespread application has been hampered by the relatively low detection sensitivity of the method. The recent introduction of clinical MR scanners with magnetic fields above 1.5 T may stimulate increased clinical use of (19)F MRS.

Hepatic phospholipids in alcoholic liver disease assessed by proton-decoupled 31P magnetic resonance spectroscopy

BACKGROUND/AIMS

Alteration of the phospholipid composition of hepatic biomembranes may be one mechanism of alcoholic liver disease (ALD). We applied proton-decoupled (31)P magnetic resonance spectroscopic imaging ({(1)H}-(31)P MRSI) to 40 patients with ALD and to 13 healthy controls to confirm that metabolic alterations in hepatic phospholipid intermediates could be detected non-invasively.

METHODS

All patients underwent liver biopsy. Specimens were scored in non-cirrhosis [fatty liver (n=3), alcoholic hepatitis (n=2), fibrosis (n=4), alcoholic hepatitis plus fibrosis (n=16)], and cirrhosis (n=15). {(1)H}-(31)P spectra were collected on a clinical 1.5-Tesla MR system and were evaluated by calculating signal intensity ratios of hepatic phosphomonoester (PME), phosphodiester (PDE), phosphoethanolamine (PE), phosphocholine (PC), glycerophosphorylethanolamine (GPE), and glycerophosphorylcholine (GPC) resonances.

RESULTS

The signal intensity ratio GPE/GPC was significantly elevated in cirrhotic (1.19+/-0.22; P=0.002) and non-cirrhotic ALD patients (1.01+/-0.13; P=0.006) compared to healthy controls (0.68+/-0.04), while PE/PC and PME/PDE were significantly elevated in cirrhotic ALD patients compared to controls (1.68+/-0.60 vs. 0.97+/-0.31; P=0.02, and 0.38+/-0.02 vs. 0.25+/-0.01; P=0.002, respectively) and non-cirrhotic patients.

CONCLUSIONS

The data support that {(1)H}-(31)P MRSI appears to distinguish cirrhotic from non-cirrhotic ALD patients and confirms changes in hepatic phospholipid metabolism observed in an animal model.

Phosphorus-31 MR Spectroscopy in Pediatric Liver Transplant Recipients: A Noninvasive Assessment of Graft Status with Correlation with Liver Function Tests and Liver Biopsy

OBJECTIVE

Noninvasive in vivo hepatic phosphorus-31 MR spectroscopy has recently been shown to provide information about hepatic functional status. We sought to show the correlation of phosphorus-31 MR spectroscopy with blood biochemistry and liver biopsy results in pediatric patients after liver transplantation.

MATERIALS AND METHODS

Eleven pediatric transplant recipients (eight with good graft function, two with chronic hepatitis, and one with acute rejection) and four healthy control subjects were studied with in vivo 31P MR spectroscopy. Ratios of phosphomonoesters (PME) to total phosphorus (TP), phosphodiester (PDE) to TP, nucleotide triphosphates (NTP), inorganic phosphate (Pi), and intracellular acid-base status (pH) were measured. Liver function test (n = 11) and biopsy (n = 3) results were obtained for correlation with spectroscopic findings.

RESULTS

The eight patients with good graft function displayed spectral profiles similar to those of the healthy subjects, and no significant difference in the metabolic ratios of these patients compared with the control subjects was detected. Three patients with abnormal liver function and biopsy-proven hepatic complications showed elevated PME/TP ratios when compared with those of both the control subjects and the group with good graft function.

CONCLUSION

Phosphorus-31 MR spectroscopy is a feasible technique for the noninvasive assessment of host-related complications in pediatric patients after liver transplantation. Our preliminary data suggest that the technique may be integrated with MRI for the investigation of impaired liver function in transplant recipients when neither a biliary complication nor a vascular complication is identified.

Absolute quantification of human liver metabolite concentrations by localized in vivo 31P NMR spectroscopy in diffuse liver disease

Phosphorus-31 NMR spectroscopy using slice selection (DRESS) was used to investigate the absolute concentrations of metabolites in the human liver. Absolute concentrations provide more specific biochemical information compared to spectrum integral ratios. Nine patients with histopathologically proven diffuse liver disease and 12 healthy individuals were examined in a 1.5-T MR scanner (GE Signa LX Echospeed plus). The metabolite concentration quantification procedures included: (1) determination of optimal depth for the in vivo measurements, (2) mapping the detection coil characteristics, (3) calculation of selected slice and liver volume ratios using simple segmentation procedures and (4) spectral analysis in the time domain. The patients had significantly lower concentrations of phosphodiesters (PDE), 6.3+/-3.9 mM, and ATP-beta, 3.6+/-1.1 mM, (P<0.05) compared with the control group (10.0+/-4.2 mM and 4.2+/-0.3 mM, respectively). The concentrations of phosphomonoesters (PME) were higher in the patient group, although this was not significant. Constructing an anabolic charge (AC) based on absolute concentrations, [PME]/([PME] + [PDE]), the patients had a significantly larger AC than the control subjects, 0.29 vs. 0.16 (P<0.005). Absolute concentration measurements of phosphorus metabolites in the liver are feasible using a slice selective sequence, and the technique demonstrates significant differences between patients and healthy subjects.

Quantitative hepatic phosphorus-31 magnetic resonance spectroscopy in compensated and decompensated cirrhosis

Few studies have examined the physiological/biochemical status of hepatocytes in patients with compensated and decompensated cirrhosis in situ. Phosphorus-31 magnetic resonance spectroscopy ((31)P MRS) is a noninvasive technique that permits direct assessments of tissue bioenergetics and phospholipid metabolism. Quantitative (31)P MRS was employed to document differences in the hepatic metabolite concentrations among patients with compensated and decompensated cirrhosis as well as healthy controls. All MRS examinations were performed on a 1.5-T General Electric Signa whole body scanner. The concentration of hepatic phosphorylated metabolites among patients with compensated cirrhosis (n = 7) was similar to that among healthy controls (n = 8). However, patients with decompensated cirrhosis (n = 6) had significantly lower levels of hepatic ATP compared with patients with compensated cirrhosis and healthy controls (P < 0.02 and P < 0.009, respectively) and a higher phosphomonoester/phosphodiester ratio than controls (P < 0.003). The results of this study indicate that metabolic disturbances in hepatic energy and phospholipid metabolism exist in patients with decompensated cirrhosis that are not present in patients with compensated cirrhosis or healthy controls. These findings provide new insights into the pathophysiology of hepatic decompensation.

The relationship of in vivo 31P MR spectroscopy to histology in chronic hepatitis C

Liver biopsy remains the gold standard for characterizing diffuse liver disease and is associated with significant morbidity and, rarely, mortality. Our aim was to investigate whether a noninvasive technique, in vivo phosphorus 31 ((31)P)-magnetic resonance spectroscopy (MRS), could be used to assess the severity of hepatitis C virus (HCV)-related liver disease. Fifteen healthy controls and 48 patients with biopsy-proven HCV-related liver disease were studied prospectively. Based on their histologic fibrosis (F) and necroinflammatory (NI) scores, patients were divided into mild hepatitis (F <or= 2/6, NI <or= 3/18), moderate/severe hepatitis (3 <or= F < 6 or NI >or= 4/18), and cirrhosis (F = 6/6). Hepatic (31)P MR spectra were obtained using a 1.5-T spectroscopy system. Quantitation of the (31)P signals was performed in the time domain using the Advanced MAgnetic RESonance algorithm. There was a monotonic increase in the mean +/- 1 standard error phosphomonoester (PME) to phosphodiester (PDE) ratios for the control, mild disease, moderate disease, and cirrhosis groups: 0.15 +/- 0.01, 0.18 +/- 0.02, 0.25 +/- 0.02, 0.38 +/- 0.04, respectively (ANOVA, P <.001). An 80% sensitivity and specificity was achieved when using a PME/PDE ratio less than or equal to 0.2 to denote mild hepatitis and a corresponding ratio greater than or equal to 0.3 to denote cirrhosis. No other significant spectral changes were observed. In conclusion, (31)P MRS can separate mild from moderate disease and these 2 groups from cirrhosis. The ability to differentiate these populations of patients has therapeutic implications and (31)P MRS, in some situations, would not only complement a liver biopsy but could replace it and be of particular value in assessing disease progression.

Application of two-dimensional CSI for absolute quantification of phosphorus metabolites in the human liver

There have recently been a number of studies dealing with the absolute quantification of concentrations of MR-visible phosphorus compounds in different tissues. The use of absolute values rather than intensity ratios may furnish additional information about metabolic changes associated with different diseases. The purpose of this study was to develop a general procedure for measuring molar metabolite concentrations and to apply it with respect to the evaluation of human liver 31P-MRS data measured using a standard slice-selective two-dimensional CSI sequence and commercial 1H/31P surface coil. The experimental determination of all surface coil-related factors influencing signal intensity was undertaken using a gradient echo imaging technique that can be adapted to commercial systems. The resulting values for healthy volunteers (N = 9) showed concentrations of PME = 2.8 +/- 1.3 mM, PDE = 9.9 +/- 2.7 mM, P(i) = 1.7+/-0.7 mM, and ATP = 3.6 +/- 0.9 mM in the human liver. The data are quite consistent with published findings.

Abnormal liver metabolism in cancer patients detected by (31)P MR spectroscopy

There is accumulating evidence indicating that the presence of malignant disease is accompanied by profound changes of liver metabolism in the cancer-bearing host. We previously reported [P. C. Dagnelie, J. D. Bell, -S. C. R. Williams, T. E. Bates, P. D. Abel and C. S. Foster, Br. J. Cancer 67, 1303-1309 (1993)] marked (31)P MRS-detected alterations in phosphorylation status as well as in phospholipid and glucose metabolism in the liver of rats bearing Dunning prostate tumours. The aim of the present study was first to define abnormalities in liver metabolism in patients with a distant malignancy using (31)P MRS, and second to explore the value of including long-TR sequences in clinical (31)P MRS studies of the liver. Liver metabolite levels were expressed relative to total MR-detectable phosphate. In weight-losing (WL, n = 10), but not in weight-stable (WS, n = 13) cancer patients, liver phosphomonoester (PME) levels were significantly elevated, whereas phosphodiester (PDE) levels were reduced when compared with age-matched healthy subjects (n = 12). The TR 20:1 s ratio of PDE was increased in WS and WL cancer patients, suggesting longer T(1). At TR 20 s, but not at TR 1 s, ATP levels were significantly reduced in in WS and WL cancer patients compared with healthy subjects; similarly, P(i) levels were reduced in WL patients at TR 20 and 5s, but not at TR 1 s. ATP:P(i) ratios were unchanged regardless of TR. pH values increased in the order: healthy < cancer-WS < cancer-WL. The PME chemical shift had significantly moved downfield in cancer patients, reflecting increased contributions from glycolytic/gluconeogenic intermediates. The observed changes in PME are consistent with previous reports suggesting increased gluconeogenesis in the liver of patients with a distant malignant tumour. Furthermore, our data support the use of including long-TR sequences in clinical (31)P MRS liver studies.

Understanding the discrepancies between 31P MR spectroscopy assessed liver metabolite concentrations from different institutions

The high divergence between the liver metabolite concentrations and pH values reported in previous quantitative 31P magnetic resonance studies, for instance phosphomonoester (0.7-3.8 mM) and phosphodiester (3.5-9.7 mM), has not been addressed in the literature. To assess what level of discrepancy can be caused by processing and metabolite integration, in this study chemical shift imaging localized 31P magnetic resonance spectra of human liver were quantitated by three methods currently applied in clinical practice: peak areas defined manually by placement of two cursors vs. frequency domain curve fitting with the assumption of either Gaussian or Lorentzian line shapes. Large reproducible differences were found in liver metabolite peak areas but not in pH, indicating that processing and peak integration methods can only explain part of the discrepancies between the results from different institutions.

Effect of ethanol and fructose on liver metabolism: a dynamic 31Phosphorus magnetic resonance spectroscopy study in normal volunteers

In vivo 31Phosphorus magnetic resonance spectroscopy (31P-MRS) permits evaluation of dynamic changes of individual phosphorus-containing metabolites in the liver parenchyma, such as phosphomonoester (PME), adenosine triphosphate, and inorganic phosphate (Pi). Intravenous fructose load alters phosphorus metabolites and allows assessment of liver function by 31P-MRS. 31P-MRS data obtained in alcoholic liver disease are however inconclusive. To study the hypothesis that fructose load can be used to investigate metabolic effects of ethanol ingestion, the interaction of different metabolites--i.e., fructose and ethanol--were followed in vivo. Using a 1.5 Tesla magnetic resonance system, six healthy volunteers were examined in three sessions each: a session after administration of (a) fructose only (250 mg/kg) was compared with (b) fructose load after ethanol ingestion (0.8 g/kg). A control experiment (c) was done after ethanol only. Spectra were acquired using one-dimensional chemical shift imaging with a temporal resolution of 5 min. Following a fructose load, the concomitant uptake of ethanol showed drastic changes of individual metabolic steps of the hepatic metabolism (averages +/- standard deviation). While the velocity of the net formation of PME (relative increase 0.46 +/- 0.11 without ethanol vs. 0.61 +/- 0.25 with ethanol) and the use of adenosine triphosphate (-0.13 +/- 0.03 vs. -0.16 +/- 0.03) and Pi (-0.022 +/- 0.009 vs. -0.021 +/- 0.004) were not significantly affected by ethanol uptake, a significant (p < 0.01) reduction of PME degradation (31.3 +/- 9.4 vs. 61.9 +/- 16.9 relative total area) and absence of an overshoot for Pi (10.5 +/- 4.9 vs. -7.1 +/- 5.3 relative area 13 min to 43 min) was observed after ethanol administration. Dynamic 31P-MRS allows the observation of individual steps of hepatic metabolism in situ; fructose metabolism in the human liver is slowed down by concomitant ethanol ingestion after the phosphorylation step of fructose. This could be explained by inhibition of aldolase rather than ethanol-induced changes of the hepatic redox state. Fructose load can be used to study effects of alcohol ingestion and might therefore be useful in patients with alcoholic liver disease.

Constrained reconstruction applied to 2-D chemical shift imaging

The method of constrained reconstruction, previously applied to magnetic resonance imaging (MRI), is extended to magnetic resonance spectroscopy. This method assumes a model for the MR signal. The model parameters are estimated directly from the phase encoded data. This process obviates the need for the fast Fourier transform (FFT) (which often exhibits limited resolution and ringing artifact). The technique is tested on simulated data, phantom data, and data acquired from human liver in vivo. In each case, constrained reconstruction offers spatial resolution superior to that obtained with the FFT.

In vivo and in vitro hepatic 31P magnetic resonance spectroscopy and electron microscopy of the cirrhotic liver

In vivo 31P magnetic resonance spectroscopy (MRS) provides direct biochemical information on hepatic metabolic processes. To assess in vivo changes in hepatic 31P MRS in liver transplant candidates, we studied 31 patients with cirrhosis of varying aetiology; 14 with compensated cirrhosis (Pugh's score < or = 7) and 17 with decompensated cirrhosis (Pugh's score > or = 8). Underlying cellular abnormalities were characterised using in vitro 31P MRS and electron microscopy. In vitro spectra were obtained from liver extracts, freeze-clamped at recipient hepatectomy, from all subjects. Electron microscopy of liver tissue was also performed in 17 cases. Relative to nucleotide triphosphates, elevations in phosphomonoesters and reductions in phosphodiesters were observed in vivo with worsening liver function. In vitro spectra showed elevated phosphoethanolamine and phosphocholine, and reduced glycerophosphorylethanolamine and glycerophosphorylcholine, mirroring the in vivo changes, but no distinction was noted between compensated and decompensated cirrhosis. With electron microscopy, functional decompensation was associated with reduced endoplasmic reticulum in parenchymal liver disease, but elevated levels in biliary cirrhosis. We conclude that in vivo spectral abnormalities in cirrhosis are consistent with alterations in phospholipid metabolism and quantity of endoplasmic reticulum. However, in individual patients the biopsy results do not always mirror in vivo findings.

The total entropy for evaluating 31P-magnetic resonance spectra of the liver in healthy volunteers and patients with metastases

RATIONALE AND OBJECTIVES

The authors describe the clinical status of liver tissue with only a single numerical quantity (total entropy) derived from spectroscopic data of 31P-magnetic resonance (MR) spectra.

METHODS

Twenty-four patients with liver metastases and 20 volunteers were investigated with image-guided volume selective 31P-MR spectroscopy on a 1.5-T whole body scanner. From each in vivo 31P-MR spectrum, the ratios of phosphomonoester (PME)/beta-adenosine triphosphate (ATP), inorganic phosphate (Pi)/beta-ATP and phosphodiester (PDE)/ beta-ATP and the total entropy (H*) were calculated. Mean values and standard deviations were determined and significance of the differences were tested with Student's t test.

RESULTS

For patients, the H* = 4.7 +/- 4.3, PME/beta-ATP 0.72 +/- 0.28, Pi/beta-ATP = 1.00 +/- 0.39, PDE/beta-ATP = 1.68 +/- 0.59. For the volunteers, H* = 7.6 +/- 2.5, PME/beta-ATP = 0.39 +/- 0.15, Pi/beta-ATP = 0.90 +/- 0.19, PDE/beta-ATP = 1.25 +/- 0.28. The total entropy of patients' spectra showed significantly lower values compared with those of volunteers. PME/beta-ATP and PDE/beta-ATP of the patients increased and differed significantly from volunteer data.

CONCLUSIONS

It was demonstrated that the results of in vivo 31P-MR spectroscopy may be described with a single criterion by means of the total entropy.

Molar quantitation of hepatic metabolites in vivo in proton-decoupled, nuclear Overhauser effect enhanced 31P NMR spectra localized by three-dimensional chemical shift imaging

Proton decoupling and nuclear Overhauser effect (NOE) enhancement significantly improve the signal-to-noise ratio and enhance resolution of metabolites in in vivo 31P MRS. We obtained proton-decoupled, NOE-enhanced, phospholipid-saturated 31P spectra localized to defined regions within the normal liver using three-dimensional chemical shift imaging. Proton-decoupling resulted in the resolution of two major peaks in the phosphomonoester (PME) region, three peaks in the phosphodiester (PDE) region and a diphosphodiester peak. In order to obtain molar quantitation, we measured the NOE of all hepatic phosphorus resonances, and we corrected for saturation effects by measuring hepatic metabolite T1 using the variable nutation angle method with phase-cycled, B1-independent rotation, adiabatic pulses. After corrections for saturation effects, NOE enhancement, B1 variations and point spread effects, the following mean concentrations (mmol/l of liver) (+/-SD) were obtained: [PME1] = 1.2 +/- 0.4, [PME2 + 2,3-DPG] = 1.1 +/- 0.1, [Pi + 2,3-DPG] = 2.8 +/- 0.5, [GPEth] = 2.8 +/- 0.7, [GPChol] = 3.5 +/- 0.6 and [beta-NTP] = 3.8 +/- 0.3. T1 and NOE enhancement were strongly correlated (r = 90), and indicated that the fractional contribution of 1H-31P dipolar relaxation to total 31P relaxation is minimal for NTPs, moderate for PMEs and high for PDEs in liver. Proton-decoupling and NOE enhancement permit one to obtain more information about in vivo metabolism of liver than previously available and should enhance the utility of 31P MRS for the study of hepatic disorders.

Cirrhosis of the human liver: an in vitro 31P nuclear magnetic resonance study

Human livers with histologically proven cirrhosis were assessed using in vitro 31P NMR spectroscopy. Spectra were compared with those from histologically normal livers and showed significant elevations in phosphoethanolamine (PE) and phosphocholine (PC) and significant reductions in glycerophosphorylethanolamine (GPE) and glycerophosphorylcholine (GPC). There were no significant differences in spectra from livers with compensated and decompensated cirrhosis. These results help to characterise the alterations in membrane metabolism in cirrhosis of the liver.

In vivo hepatic 31P magnetic resonance spectroscopy in chronic alcohol abusers

BACKGROUND/AIMS

In vivo hepatic 31P magnetic resonance spectroscopy (MRS) can provide information on hepatic energy metabolism, phospholipid substrates, and hepatocyte lipid bilayers. The aim of this study was to ascertain the effects of alcohol ingestion on hepatic 31P spectral variables.

METHODS

Twenty-six chronic alcohol abusers underwent hepatic 31P MRS 6-12 hours after their last alcoholic drink; studies were repeated in 17 individuals following abstinence from alcohol. The reference population comprised 16 healthy volunteers. Ratios of phosphomonoesters (PME), inorganic phosphate, and phosphodiesters (PDE) relative to beta-adenosine triphosphate (ATP) were measured.

RESULTS

In patients with minimal liver injury, recent drinking was associated with a significant elevation in the mean PDE/ATP ratio (P < 0.0001) and an increase in mean PME/ATP, which was not significant; abstinence was associated with reductions in both metabolite ratios. In patients with alcoholic cirrhosis, recent drinking was associated with an elevation in mean PME/ATP (P < 0.05) and an increase in mean PDE/ATP, which was not significant; abstinence was associated with no significant change in PME/ATP but with a reduction in PDE/ATP.

CONCLUSIONS

In the absence of significant liver injury, chronic alcohol abuse is associated with the elevation of PME/ATP, possibly reflecting changes in hepatic redox potential, and of PDE/ATP, most likely reflecting the induction of hepatocyte endoplasmic reticulum. In the presence of cirrhosis, these changes are attenuated and modified.

Non-T1-weighted 31P chemical shift imaging of the human liver

A 31P chemical shift imaging (CSI) protocol was developed for human liver studies. It is shown that at the commonly used repetition time (TR) of 1 s T1-weighting reduces the integrated intensities of liver phosphate metabolite signals by 18 +/- 15% (inorganic phosphate, Pi) to 46 +/- 10% (phosphodiester, PDE), that is for an RF pulse angle of 60 degrees (weighted average) in liver. The loss in signal-to-noise ratio (S/N) at TR = 20 s, sufficient to eliminate spectral distortions caused by saturation, compared with TR = 1 s (47-65%) can be overcome by using one-dimensional (1D)-phase encoding with a small number of phase-encode steps. The liver spectra obtained by 1D-CSI with 4-step phase-encoding (spatial resolution 10 cm) have the highest S/N and, after multiplication of the PDE signal by a factor of 1.4, closely reflect the liver metabolite levels. It is concluded that clinical 31P MR studies of liver function can be performed without T1-weighting and that the current practice to compromise the MRS quantification of lever metabolites with uncertainties caused by (differential changes in) T1-weighting is not warranted.

Detection of liver fibrosis with magnetic cross-relaxation

The utility of MRI using magnetization transfer (MT) enhanced pulse sequences to diagnose hepatic cirrhosis in a rat model was investigated. Hepatic T1 was measured with and without MT off-resonance RF pulses in 17 treated and six control rats. The livers were evaluated histologically, and the hydroxyproline content quantitatively measured. We did not find a statistically significant linear correlation between the MR relaxation times and the degree of tissue injury. However, the MR measurements performed with MT were superior to those without differentiating the treated and control groups. Specifically, the T1 times were 695 +/- 76 ms for the treated group, versus 748 +/- 61 ms in the controls; P = 0.095. The T1sat times were also lower in the treated group, with statistical significance: 367 +/- 51 ms versus 421 +/- 38 ms, P = 0.016. Finally, the change in the relaxation rates (the inverse of the relaxation times) with and without saturation were 1.31 +/- 0.22 s-1 (treated group) versus 1.05 +/- 0.12 s-1 (controls), which differed significantly, P = 0.001.

Use of computer simulations for quantitation of 31P ISIS MRS results

The difficulties in quantitation of in vivo 31P spectra are exacerbated by the fact that, in general, coils with inhomogeneous B1 fields are used with in vivo samples. A general method for quantitation of in vivo 31P MRS results obtained with the ISIS localization method was developed using computer simulations. The simulation calculates the preparation of the sample magnetization throughout the sample by the ISIS pulse sequence, as well as the sensitivity of signal reception. The calculation accounts for both the B1 field and the B0 gradients applied to the sample. The sensitivity of the experiment is expressed by integration of the simulated signal over the sample, assuming a homogeneous sample. The primary advantage of this approach is that a separate localization experiment on a phantom of known concentration is not required each time parameters of the localization experiment, such as dimensions or location of the localized volume, are altered. In addition, the simulations indicate the degree of contamination (signal from outside of the localized volume) that occurs, and provide a means of comparing different executions of the ISIS experiment. Experiments were performed on phantoms to verify the simulations, and experimental results on human brain and liver are reproduced to show that this approach provides reasonable estimates of metabolite levels in terms of molar concentrations.