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

Phosphorus liver MRSI at 3 T using a novel dual-tuned eight-channel ³¹P/¹H H coil

Although phosphorus-31 (³¹P) magnetic resonance spectroscopy holds potential as noninvasive tool to monitor treatment response of liver malignancies, the lack of appropriate coils has so far restricted its use to liver lesions close to the surface. A novel eight-channel phased-array dual-tuned ³¹P/¹H coil that can assess ³¹P metabolism in deeper liver tissue as well is presented in this article. Analysis of its performance demonstrates that this coil can provide good sensitivity across a width of 20 cm, thereby enabling magnetic resonance spectroscopic imaging (MRSI) scans that can fully cover axial views of the abdomen in lean subjects. In vivo results and reproducibility of ³¹P MRSI at 3 T of axial slices covering the full depth of the liver are shown in healthy volunteers. To minimize intrasubject and intersubject data variability, spectra are corrected for coil sensitivities. Methods to maximize the reproducibility of coil placement and spectroscopic planning are discussed. The phosphomonoesters/phosphodiesters ratio calculated in healthy volunteers has an average intrasubject variation of 23% averaged over voxels selected from the entire liver. Finally, the feasibility of using the coil in the clinic is shown by preliminary ³¹P liver MRSI data obtained from a patient with hepatocellular carcinoma.

Magnetic resonance spectroscopy to study hepatic metabolism in diffuse liver diseases, diabetes and cancer

This review provides an overview of the current state of the art of magnetic resonance spectroscopy (MRS) in in vivo investigations of diffuse liver disease. So far, MRS of the human liver in vivo has mainly been used as a research tool rather than a clinical tool. The liver is particularly suitable for static and dynamic metabolic studies due to its high metabolic activity. Furthermore, its relatively superficial position allows excellent MRS localization, while its large volume allows detection of signals with relatively low intensity. This review describes the application of MRS to study the metabolic consequences of different conditions including diffuse and chronic liver diseases, congenital diseases, diabetes, and the presence of a distant malignancy on hepatic metabolism. In addition, future prospects of MRS are discussed. It is anticipated that future technical developments such as clinical MRS magnets with higher field strength (3 T) and improved delineation of multi-component signals such as phosphomonoester and phosphodiester using proton decoupling, especially if combined with price reductions for stable isotope tracers, will lead to intensified research into metabolic syndrome, cardiovascular disease, hepato-biliary diseases, as well as non-metastatic liver metabolism in patients with a distant malignant tumor.

Parametric exploration of the liver by magnetic resonance methods

MRI, as a completely noninvasive technique, can provide quantitative assessment of perfusion, diffusion, viscoelasticity and metabolism, yielding diverse information about liver function. Furthermore, pathological accumulations of iron and lipids can be quantified. Perfusion MRI with various contrast agents is commonly used for the detection and characterization of focal liver disease and the quantification of blood flow parameters. An extended new application is the evaluation of the therapeutic effect of antiangiogenic drugs on liver tumours. Novel, but already widespread, is a histologically validated relaxometry method using five gradient echo sequences for quantifying liver iron content elevation, a measure of inflammation, liver disease and cancer. Because of the high perfusion fraction in the liver, the apparent diffusion coefficients strongly depend on the gradient factors used in diffusion-weighted MRI. While complicating analysis, this offers the opportunity to study perfusion without contrast injection. Another novel method, MR elastography, has already been established as the only technique able to stage fibrosis or diagnose mild disease. Liver fat content is accurately determined with multivoxel MR spectroscopy (MRS) or by faster MRI methods that are, despite their widespread use, prone to systematic error. Focal liver disease characterisation will be of great benefit once multivoxel methods with fat suppression are implemented in proton MRS, in particular on high-field MR systems providing gains in signal-to-noise ratio and spectral resolution.

Multiple voxel 1H MR spectroscopy of phosphorylase-b kinase deficient patients (GSD IXa) showing an accumulation of fat in the liver that resolves with aging

BACKGROUND/AIMS

Phosphorylase-b deficient patients suffer from glycogen storage disease (GSD IXa) leading to liver enlargement which usually resolves during puberty and adolescence. This pathology has not yet been documented by (1)H MR spectroscopy (MRS) investigation.

METHODS

MRS of eight GSD IXa patients was performed in this study to assess whether or not liver fat content is elevated in GSD IXa and decreases with aging. An improvement in our MRS method compared with previous liver fat MRS studies is that we measured a plane of liver voxels at once rather than a single MRS voxel, yielding a reliable determination of liver fat content.

RESULTS

Fat contents of 3.4-10% were observed in young GSD IXa patients, as compared with 0.5-0.9% in controls, these dropped to control levels in patients past age 40 (r = -0.82; P < 0.01).

CONCLUSIONS

Liver fat content is increased in glycogen storage disease (GSD IXa) and normalizes with ageing. Assessing liver fat levels in this population is a novel and interesting concept. This could potentially enhance the understanding of liver function in that 20% of the population who has increased liver fat.

Hepatic 31P magnetic resonance spectroscopy: a hepatologist's user guide

Hepatic phosphorus magnetic resonance spectroscopy (31P MRS) offers the exciting potential of studying metabolic processes in the human liver in vivo. Many investigators have utilized 31P MRS to research a broad range of metabolic questions, and there is outstanding potential for this imaging modality in the future. However, at times it is difficult to appreciate this potential because most published series have been small, and comparisons between studies are difficult. Indeed, the published literature contains significant variation in data acquisition and data analysis techniques and, perhaps most importantly, the interpretation of the data itself. As MR technology continues to evolve and more studies are being performed, perhaps a greater consensus of study techniques and endpoints will emerge. This review summarizes the present literature on human hepatic 31P MRS.

Adenosine triphosphate infusion increases liver energy status in advanced lung cancer patients: an in vivo 31P magnetic resonance spectroscopy study

We recently observed inhibition of weight loss in patients with advanced nonsmall-cell lung cancer after intravenous infusion of ATP. Because liver ATP levels were found to be decreased in lung cancer patients with weight loss, the present 31P magnetic resonance spectroscopy (MRS) study was aimed at investigating whether ATP infusion restores liver energy status in these patients. Nine patients with advanced nonsmall-cell lung cancer (stage IIIB/IV) were studied 1 week before (baseline) and at 22 to 24 hours of continuous ATP infusion (37-75 microg/kg/min). Localized hepatic 31P MR spectra (repetition time 15 seconds), obtained in the overnight-fasted state, were analyzed for ATP and P(i) content. Ten healthy subjects (without ATP infusion) served as control. Liver ATP levels in lung cancer patients increased from 8.8 +/- 0.7% (relative to total MR-detectable phosphate; mean +/- SE) at baseline to 12.2 +/- 0.9% during ATP infusion (P <.05), i.e., a level similar to that in healthy subjects (11.9 +/- 0.9%). The increase in ATP level during ATP infusion was most prominent in patients with > or = 5% weight loss (baseline: 7.9 +/- 0.7%, during ATP infusion: 12.8 +/- 1.0%, P < 0.01). In conclusion, ATP infusion restores hepatic energy levels in patients with advanced lung cancer, especially in weight-losing patients. These changes may contribute to the previously reported beneficial effects of ATP infusion on the nutritional status of lung cancer patients.

Decreased energy and phosphorylation status in the liver of lung cancer patients with weight loss

BACKGROUND/AIMS

Altered energy status has been reported in the liver of tumour-bearing animals, but data on energy status in humans are scarce. Therefore, bioenergetics in tumour-free liver of lung cancer patients were monitored using 31P magnetic resonance spectroscopy (MRS) with infusion of L-alanine as a gluconeogenic challenge.

METHODS

Twenty-one overnight-fasted lung cancer patients without liver metastases, with (CaWL) or without weight loss (CaWS), and 12 healthy control subjects (C) were studied. Hepatic energy status was monitored before and during an i.v. L-alanine infusion of 1.4-2.8 mmol/kg + 2.8 mmol x kg(-1) x h(-1) for 90 min by 31p MR spectroscopy.

RESULTS

Baseline levels of ATP in WL lung cancer patients, expressed relative to total MR-detectable phosphate, were reduced (CaWL, 9.5+/-0.9% vs. CaWS, 12.6+/-0.8% and C, 12.4+/-0.8%; p<0.05) and inversely correlated with the degree of weight loss in lung cancer patients (r=-0.46, p=0.03). Pi/ATP ratios were increased (p<0.05), indicating reduced liver phosphorylation status. During L-alanine infusion, ATP levels decreased in all groups (p<0.05); in CaWL, ATP levels were lower at all time-points between 0-90 min as compared to both CaWS and C (p<0.05). Pi/ATP ratios were significantly higher after 70-90 min of L-alanine infusion in CaWL compared to CaWS and C (p<0.05).

CONCLUSIONS

Hepatic ATP and phosphorylation status are reduced in WL lung cancer patients, in contrast to WS patients and healthy subjects, and continue to decrease during infusion of a gluconeogenic substrate, suggesting impaired energy regenerating capacity in these patients.

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.

Navigated single-voxel proton spectroscopy of the human liver

The addition of a navigator echo acquisition to a 1H spectroscopy sequence allows retrospective motion correction using acceptance criteria based on measured displacement of the diaphragm. This technique has been applied to the acquisition of short echo-time 1H spectroscopy of the liver in seven normal subjects. Navigation correction significantly improved overall spectral quality as measured by the phase variance, linewidth and suppression ratio of the water resonance. The hepatic choline resonance was consistently observed in all navigated spectra. Retrospective navigation makes close to optimal use of data acquisition time and, unlike external respiratory transducers, allows direct measurement of diaphragm displacement. The reconstruction of multiple voxel spectra from a single data set was also demonstrated.

Phosphorus-31 chemical shift imaging of metastatic tumors located in the spine region

RATIONALE AND OBJECTIVES

Phosphorus-31 magnetic resonance spectroscopy was used in 14 cases to examine metastases of known malignant tumors located in the spine region. The purpose was to test the hypothesis that tumor phosphomonoester (PME) is elevated.

METHODS

Two-dimensional chemical shift imaging was used in combination with a slice-select gradient in the third dimension to obtain true three-dimensional localization.

RESULTS

The spectral maps revealed PME signals increased up to 10 times in voxels containing contrast-enhancing metastatic spine lesions compared with adjacent areas and peripheral muscle voxels. Phosphomonoester increase was significant for all tumors combined (8.6 +/- 5.3 arbitrary units versus 2.4 +/- 0.5 and 2.2 +/- 0.8 arbitrary units in unaffected myelum and corpora; P < 0.001), though smaller than 2 standard deviations in 5 of 14 cases. The latter shared high proportions of phosphocreatine, phosphocreatine > 30% of total phosphate, indicating substantial amounts of muscle tissue included in the tumor voxels (partial volume effect).

CONCLUSIONS

Phosphorus-31 MR spectroscopy can be of value in the recognition of malignant vertebral column abnormalities. Malignant tumor is marked by drastic PME increases-fourfold to tenfold, provided that partial volume effects are small.

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.