Chemical Shift Magnetic Resonance Imaging Research Articles

MRI as an Alternative to CT-Guided Biopsy of Adrenal Masses in Patients With Lung Cancer

Background. This study was performed to assess chemical shift magnetic resonance imaging (CSMRI) for characterizing adrenal masses in patients with lung cancer, and to compare charges associated with two algorithms for assessing adrenal masses in these patients. Methods. Forty-two patients with lung cancer underwent both CSMRI (using in-phase and opposed-phase gradient echo images) and computed tomography-guided percutaneous biopsy of adrenal masses. Adrenal-to-spleen signal intensity ratios on the opposed-phase images were correlated with histopathologic results. The normalized charges for two algorithms were compared. In algorithm A, computed tomography-guided biopsy is used first to evaluate an adrenal mass; in algorithm B, CSMRI is used first, followed by computed tomography-guided biopsy only if CSMRI findings are not diagnostic of adenoma. Results. Biopsy showed 24 (57%) adrenal adenomas and 18 (43%) metastases. Chemical shift magnetic resonance imaging was 96% sensitive for adenoma and 100% specific. The average normalized charges associated with algorithm A were $1,905 per patient versus $1,890 with algorithm B. Conclusions. Initial use of CSMRI in evaluating an adrenal mass in lung cancer patients can obviate biopsy in 55% of patients, and its charges are similar to those for performing computed tomography-guided biopsy in all patients.

Temperature Measurement of Foods Using Chemical Shift Magnetic Resonance Imaging as Compared with T1‐weighted Temperature Mapping

ABSTRACTA method based on change in proton precession frequency with temperature was compared with temperature measurement by T1‐weighted imaging. Temperature maps of a gel, and of cooked and raw red potatoes were developed during heating from 20 to 60°C. To measure change in proton precession frequency, a steady state free precession sequence allowed 2‐dimensional acquisitions in 8 sec with spatial resolution of 0.88 mm2. Temperature resolution with chemical shift imaging, ranged from 0.3 to 3°C, decreasing with increasing temperature due to a decrease in signal to noise ratio. The difference by this method and thermocouples was < 5°C. T1‐weighted spin‐echo images showed artifacts due to an inhomogeneous T1 distribution within the potatoes, indicating chemical shift was more reliable for inhomogeneous foods.

Adrenal Incidentalomas: Diagnostic Workup of the Incidentally Discovered Adrenal Mass

The incidentally discovered adrenal mass is a diagnostic dilemma veterinarians are likely to face with increasing frequency in the coming years. Dogs and cats may be more prone to functional adrenal lesions than are humans. Most adrenal tumors are benign, but a significant number of adrenocortical carcinomas (approximately 12%) and metastatic lesions within the adrenal glands (3% to 34%) do occur. Evaluation for hypertension, hypokalemia, and loss of hypothalamic-pituitary-adrenal responsiveness to a low dose of dexamethasone is appropriate for all patients with adrenal incidentalomas. The value of clinical and historical signs of hormonal overexpression should not be underestimated. More invasive or expensive diagnostic testing should be predicted on suspicions raised by the history and clinical signs. New diagnostic clinicopathologic tests, including plasma CgA and serum DHEAS, should be investigated in veterinary patients. Advanced diagnostic imaging using nuclear scintigraphy and chemical-shift MRI may offer veterinarians sensitive and specific noninvasive tools to consider for the evaluation of these patients. Patients with large masses, tumors with signs of malignancy, or productive adrenal tumors (plus or minus cortisol-producing tumors in which chemical ablation with mitotane can be attempted) should be considered candidates for exploratory surgery.

Chemical shift imaging at 4.7 tesla of brown adipose tissue

In vivo distinction between small deposits of brown adipose tissue (BAT) and surrounding tissues may be difficult. In this article, we propose an experiment paradigm, based on techniques of chemical shift magnetic resonance imaging (CSI), which can improve the methods presently available for the study of BAT. Male rats were examined in an imager-spectrometer equipped with a 4.7 T magnet. Proton spectra of isolated BAT deposits showed that both fat and water protons contributed significantly to the genesis of the magnetic resonance signal. An equivocal definition of BAT deposits was obtained by three (respectively, spin-echo, water-selective, and fat-selective) images. The spin-echo (SE), T1-weighted image provided the best anatomical description of the structures. The images selective for fat-protons displayed the degree of lipid accumulation in each area. The images selective for water-protons provided an internal control of adipose tissue localization. The proposed paradigm allows an unequivocal definition of BAT deposits and appears particularly useful in studies where experimental manipulation (i.e., cold acclimation or drug treatment) produces changes in this issue.

Magnetic resonance imaging differentiation of adrenal masses at 1.5 t: t2-weighted images, chemical shift imaging, and gd-dtpa dynamic studies

The purpose of our study was to assess the potential role of spin-echo (SE), chemical shift, and gadolinium-enhanced magnetic resonance imaging (MRI) in the differentiation of adrenal masses. Seventy-two adrenal masses (26 nonhyperfunctioning adenomas, 16 aldosterone-secreting adenomas and 6 other different benign cortical masses, 18 pheochromocytomas, and 6 malignant masses) in 63 patients were evaluated with spin-echo sequences, chemical shift imaging (CSI) and gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA) dynamic studies. Ratios and indices of signal intensity for all examined MRI methods were calculated and examined for significance of difference between different types of adrenal masses. Quantitative magnetic resonance evaluation of adrenal masses showed significant differences (at least alpha < 0.01) between nonhyperfunctioning adenomas vs. pheochromocytomas or vs. malignant lesions or vs. aldosterone-secreting adenomas and between pheochromocytomas vs. malignant lesions. The most specific indicators of adrenal mass character proved to be the CSI ratio based on opposed-phase and in-phase two-dimensional fast low-angle shot (FLASH) images, reflecting lipid content in the lesion, and Gd-DTPA dynamic studies ratios reflecting contrast agent inflow and washout in the lesion: WoMAX/LAST and Dyn1.2-3.2. There was no overlap of CSI ratio between adenomas and pheochromocytomas. The overlap of ranges of CSI ratio between nonhyperfunctioning adenomas and aldosterone-secreting adenomas was only 18.5%. There was no overlap of WoMAX/LAST ratio between adenomas and pheochromocytomas, or adenomas and malignant lesions. The overlap of ranges of Dyn1.2-3.2 ratio between pheochromocytomas and malignant lesions was only 17.6%. MRI enables good visualization and specific characterization of adrenal masses. The optimal MRI protocol for the adrenal region is presented.

Non-invasive neurochemical analysis of focal excitotoxic lesions in models of neurodegenerative illness using spectroscopic imaging.

Water-suppressed chemical shift magnetic resonance imaging was used to detect neurochemical alterations in vivo in neurotoxin-induced rat models of Huntington's and Parkinson's disease. The toxins were: N-methyl-4-phenylpyridinium (MPP+), aminooxyacetic acid (AOAA), 3-nitropropionic acid (3-NP), malonate, and azide. Local or systemic injection of these compounds caused secondary excitotoxic lesions by selective inhibition of mitochondrial respiration that gave rise to elevated lactate concentrations in the striatum. In addition, decreased N-acetylaspartate (NAA) concentrations were noted at the lesion site over time. Measurements of lactate washout kinetics demonstrated that t1/2 followed the order: 3-NP approximately MPP+ >> AOAA approximately malonate, which parallels the expected lifetimes of the neurotoxins based on their mechanisms of action. Further increases in lactate were also caused by intravenous infusion of glucose. At least part of the excitotoxicity is mediated through indirect glutamate pathways because lactate production and lesion size were diminished using unilateral decortectomies (blockade of glutamatergic input) or glutamate antagonists (MK-801). Lesion size and lactate were also diminished by energy repletion with ubiquinone and nicotinamide. Lactate measurements determined by magnetic resonance agreed with biochemical measurements made using freeze clamp techniques. Lesion size as measured with MR, although larger by 30%, agreed well with lesion size determined histologically. These experiments provide evidence for impairment of intracellular energy metabolism leading to indirect excitotoxicity for all the compounds mentioned before and demonstrate the feasibility of small-volume metabolite imaging for in vivo neurochemical analysis.

Analysis of the lipids of normal and Gaucher bone marrow

Quantitative chemical shift magnetic resonance imaging (QCSI) is currently being utilized for measuring the extent of bone marrow involvement and its response to enzyme replacement therapy in patients with Gaucher's disease. Quantitation of the major lipid species in human bone marrow is required to accurately interpret QCSI data on bone marrow composition. The major lipid species in bone marrow specimens from normal individuals and from patients with type 1 Gaucher's disease were analyzed by thin-layer and high-pressure liquid chromatography. In normal marrow (N = 5), triglycerides were by far the most abundant lipid (278 ± 70 mg/gm wet wt), with other non-polar lipids and phospholipids totaling less than 20 mg/gm wet weight. The concentration of glucocerebroside in normal marrow was 0.061 ± 0.06 mg/gm wet weight. Gaucher marrow (N = 9) had dramatically lower triglyceride levels (51 ± 53 mg/gm wet wt), and as expected, it had markedly elevated levels of glucocerebroside (7.1 ± 3.4 mg/gm wet wt). The other major non-polar lipids and phospholipids were measured in selected specimens, but none were found that differed so profoundly between normal and Gaucher's disease. These data support a model of bone marrow alteration in Gaucher's disease in which triglyceride-rich adipocytes are progressively replaced by storage cells, leading to an overall reduction in total lipid content. This phenomenon provides an explanation for the changes in proton signal intensity observed in QCSI studies of Gaucher bone marrow.

NGF, BDNF and NT-5, but not NT-3 protect against MPP + toxicity and oxidative stress in neonatal animals

A growing body of evidence suggests that neurotrophic factors can protect neurons against neuronal death. In the present study we examined whether systemic administration of members of the neurotrophin family, nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3) and neurotrophin 5 (NT-5) and basic fibroblast growth factor (bFGF) could protect against 1-methyl-4-phenylpyridinium (MPP +) induced striatal damage in neonatal rats. Systemic administration of NGF, BDNF and NT-5 produced significant neuroprotective effects, whereas NT-3 was ineffective. Systemic administration of bFGF had significant neuroprotective effects as assessed by T 2-weighted magnetic resonance imaging and measurements of n-acetylaspartate and lactate using chemical shift magnetic resonance imaging. Systemic administration of NGF, BDNF and bFGF, but not NT-3 attenuated MPP + induced increases in hydroxyl radical generation as assessed by the conversion of salicylate to 2,3- or 2,5-dihydroxybenzoic acid (DHBA). These results show that systemic administration of several neurotrophins and bFGF can attenuate neuronal damage induced by chemical hypoxia in vivo by a mechanism which may involve attenuation of oxidative stress.

Imaging of the ovary and adnexa: clinical issues and applications of MR imaging.

Many if not most adnexal masses that are resected for suspicion of malignancy are benign, and the ratio of benign to malignant masses removed increases dramatically if asymptomatic women are screened. More specific diagnostic tests may reduce the rate of unnecessary surgery in these patients. Magnetic resonance (MR) imaging may play a role in evaluating women with problematic ultrasound diagnoses. Conventional and chemical shift MR imaging can allow specific diagnosis of dermoid cysts, pedunculated leiomyomas, ovarian fibromas, most endometriomas, and hydrosalpinx. Gadolinium-enhanced MR imaging allows identification of papillary projections and septa in ovarian neoplasms and differentiation of clot and debris from vascularized tissue. Results of available studies suggest that MR imaging of the female pelvis is cost-effective in selected patients and can be used to obviate surgery in some patients. MR imaging with the use of these techniques may allow more appropriate clinical decisions to be made in selected patients with complex adnexal disease.

3-Acetylpyridine produces age-dependent excitotoxic lesions in rat striatum.

The effects of 3-acetylpyridine (3-AP) were studied in rat striatum. Striatal injections of 3-AP produced dose-dependent lesions. The lesion size was significantly increased in 4- and 12-month-old rats compared to 1-month-old rats. Coinjection of the competitive N-methyl-D-aspartate (NMDA) antagonist 2-amino-5-phosphonovaleric acid (APV) or systemic administration of the noncompetitive NMDA antagonist MK-801, the competitive NMDA antagonist LY274614, or the glutamate release inhibitor lamotrigine partially but significantly attenuated striatal lesion volume. Consistent with an NMDA receptor-mediated excitotoxic effect, histologic studies showed that 3-AP lesions result in relative sparing of NADPH-diaphorase neurons. Using freeze clamp, 3-AP resulted in a marked depletion of ATP. Two-dimensional water-suppressed proton chemical shift magnetic resonance imaging showed a striatal depletion of the neuronal marker N-acetylaspartate but no focal increase in lactate during the first 3 h after intrastriatal 3-AP injections. Pretreatment with fructose-1,6-biphosphate attenuated the lesion volume significantly, which may be due to its ability to serve as a substrate for glycolytic metabolism, with resulting ATP production. The results of the present studies support the hypothesis that 3-AP produces an impairment of energy metabolism due to its substitution for niacinamide in the formation of NAD(P). Furthermore, 3-AP toxicity may involve a secondary excitotoxic mechanism mediated by NMDA receptors.

Quantitation of lipid in biological tissue by chemical shift magnetic resonance imaging

A method combining several previously used approaches is described for the rapid, accurate quantitation of the fat content of biological tissue based on chemical shift images (CSI) corrected for magnetic field inhomogeneity, and compensated for T1 and T2 effects. The gravimetrically determined lipid content of fatty tissues (pork fat, rabbit and human liver) that had been differentially depleted of lipid by chloroform extraction correlated well (r = 0.99) with the lipid image intensities of the respective tissues. This multi-point CSI method was used to quantitate lipid in fresh fatty human liver tissue (wet and dry) containing varying amounts of lipid. Plots of integrated lipid intensity versus tissue lipid content gave straight parallel lines for hydrated (r = 0.94) and dehydrated (r = 0.98) tissues, permitting determination of a proportionality constant for measuring absolute amounts of lipid present in a specific biological tissue. These results suggest the feasibility of using the method in vivo for absolute quantitation of lipid in tissues of agricultural (e.g. pork, beef) and medical (e.g. human liver) interest.

State-of-the-art MR imaging of the adrenal gland.

The authors discuss the appearances of adrenal diseases characterizable with magnetic resonance (MR) imaging (pheochromocytomas, hemorrhage, cysts, adenomas, myelolipomas, and metastases), new imaging techniques, and differentiation of benign from malignant lesions. Most pheochromocytomas appear markedly hyperintense relative to the liver on T2-weighted images. However, this appearance is not specific, since adrenal metastases and adenomas may have similar features. Occasionally, pheochromocytomas may be iso- or hypointense to the liver on T2-weighted images. One of the new techniques for MR imaging of the adrenal gland, fat suppression, reduces cardiac and respiratory motion-induced artifacts, accentuates small differences in tissue contrast, and eliminates chemical shift artifacts. These advantages far outweigh the disadvantages of inhomogeneity of fat suppression and the fewer sections obtained per acquisition. Differentiation of adrenal metastases from adrenal adenomas with MR imaging is problematic with the use of signal intensity ratios (33% overlap) or T2 calculations. The future of discriminating between adrenal metastases and adenomas may rest with chemical shift MR imaging, which uses in-phase and out-of-phase gradient-echo pulse sequences. This approach relies on the fact that adrenal adenomas contain fat whereas metastases do not. The reported accuracy of chemical shift imaging in differentiating adrenal adenomas from metastases is 96%-100%.

Enhanced tumor detection in the presence of fatty liver disease: cell-specific contrast agents.

It is assumed that hepatobiliary, cell-specific contrast agents will be adversely affected by the presence of diffuse liver disease. The diagnostic efficacy for tumor detection in the presence of fatty liver disease was experimentally studied at contrast-enhanced magnetic resonance (MR) imaging with manganese-DPDP (N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis[phosphate]) and gadobenate dimeglumine (Gd-BOPTA/dimeg) and compared with conventional and chemical shift imaging. Carcinosarcoma was implanted into the liver of rats, and fatty liver was induced with L-ethionine. Without contrast agents, the tumor-fatty liver contrast-to-noise ratio (C/N) was increased on T1-weighted and decreased on T2-weighted MR images relative to tumor-bearing control rats without fatty liver. Chemical shift imaging (phase-contrast method) increased the tumor-fatty liver C/N from 2.3 +/- 1.0 to 6.1 +/- 1.7 (P < .001). Mn-DPDP and Gd-BOPTA/dimeg increased the tumor-fatty liver C/N from -5.4 +/- 1.6 to -11.0 +/- 1.9 and -9.8 +/- 3.4, respectively (P < .001). The hepatobiliary, cell-specific contrast agents were equally effective in both fatty and non-fatty liver and outperformed both chemical shift and conventional MR imaging in detecting liver tumors.

Age‐Dependent Striatal Excitotoxic Lesions Produced by the Endogenous Mitochondrial Inhibitor Malonate

Intrastriatal injection of malonate, a reversible inhibitor of succinate dehydrogenase (SDH), produced age-dependent striatal lesions, which were significantly greater in 4- and 12-month-old animals than in 1-month-old animals. Both histologic and neurochemical studies showed that the lesions were significantly attenuated by administration of the noncompetitive NMDA receptor antagonist MK-801. Water-suppressed chemical shift magnetic resonance imaging showed that malonate produces increased striatal lactate concentrations and striatal lesions on T2-weighted scans that were attenuated by MK-801. Neurochemical characterization of the lesions showed significant decreases in markers of medium-sized spiny neurons (GABA and substance P), whereas a marker of medium-sized aspiny neurons (somatostatin) was not different from control values, consistent with an NMDA receptor-mediated mechanism. The effects of intrastriatal injections of malonate on ATP concentrations were compared with those of the irreversible SDH inhibitor 3-nitropropionic acid (3-NP). The ATP depletions following an equimolar injection of malonate were less marked and more transient than those of 3-NP. These results show that the competitive SDH inhibitor malonate produces more transient and milder bioenergetic defects than 3-NP, which are associated with selective activation of NMDA receptors. The results strengthen the possibility that a subtle impairment of energy metabolism may play a role in the pathogenesis of Huntington's disease.

Pelvic endometriosis: detection and diagnosis with chemical shift MR imaging.

Fat-saturation magnetic resonance (MR) imaging for detection and characterization of pelvic endometriosis was prospectively investigated in 35 women with a clinical diagnosis of the disease. Large endometrioma was diagnosed when the lesion was larger than 1 cm in diameter and hyperintense on T1- and T2-weighted images. Small endometrioma was diagnosed when a well-demarcated hyperintense lesion less than 1 cm in diameter was seen on T1-weighted or fat-saturated T1-weighted images. Surgery performed after MR imaging revealed a normal pelvis in six patients, endometriosis in 26 (33 large and 19 small endometriomas), and other cystic lesions in three. Conventional T1- and T2-weighted imaging accurately demonstrated 27 of 33 large endometriomas and two of 19 small endometriomas. Fat-saturation T1-weighted imaging in combination with conventional technique accurately demonstrated 30 of 33 large and nine of 19 small endometriomas. Diagnostic accuracy was improved with addition of fat-saturated images, so their use together with conventional images is recommended in assessment of endometriosis.

Age‐Dependent Vulnerability of the Striatum to the Mitochondrial Toxin 3‐Nitropropionic Acid

The mechanisms of delayed onset and cell death in Huntington's disease (HD) are unknown. One possibility is that a genetic defect in energy metabolism may result in slow excitotoxic neuronal death. Therefore, we examined the effects of age on striatal lesions produced by local administration of the mitochondrial toxin 3-nitropropionic acid in rats. In vivo chemical shift magnetic resonance imaging showed marked increases in striatal lactate concentrations that significantly correlated with increasing age. Histologic and neurochemical studies showed a striking age dependence of the lesions, with 4- and 12-month-old animals being much more susceptible than 1-month-old animals. Continuous systemic administration of low doses of 3-nitropropionic acid for 1 month resulted in striatal lesions showing growth-related changes in dendrites of striatal spiny neurons using the Golgi technique. These results show that a known mitochondrial toxin can produce selective axon-sparing striatal lesions showing both the age dependence and striatal spiny neuron dendritic changes that characterize HD.

Benign adrenocortical masses: diagnosis with chemical shift MR imaging.

Benign adrenocortical masses often contain lipid; metastases and pheochromocytomas do not. Standard and lipid-sensitive (chemical shift) magnetic resonance (MR) images of the adrenal glands in 31 patients with 45 adrenal masses were reviewed to determine if simple visual analysis of these images would increase diagnostic specificity. Lipid was considered present if signal intensity of the adrenal mass relative to other tissues decreased on chemical shift images relative to comparable standard images. Both myelolipomas and 26 of 27 benign cortical masses displayed a loss of signal intensity on at least one chemical shift image; all 12 metastases, the three hemorrhages, and a cyst did not. Opposed-phase images were slightly more sensitive than fat-suppressed images in depicting lipid within benign cortical masses. All masses had higher signal intensity than that of the liver on standard T2-weighted MR images. Chemical shift MR imaging can demonstrate lipid within benign adrenocortical masses and thus increase specificity, potentially obviating biopsy and aggressive follow-up.

Diagnosis of fatty liver with MR imaging.

The diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cells-specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet-induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L-ethionine-induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell-specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1-weighted images and chemical shift images showed good correlation (r = .83 and .80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.

1-Methyl-4-phenylpyridinium produces excitotoxic lesions in rat striatum as a result of impairment of oxidative metabolism.

The effects of 1-methyl-4-phenylpyridinium (MPP+) were studied in rat striatum. Using freeze-clamp, microwave, and water-suppressed proton chemical shift magnetic resonance imaging techniques, MPP+ resulted in marked increases in lactate and a depletion of ATP for up to 48 h after the injections. MPP+ produced dose-dependent depletions of dopamine, serotonin, gamma-aminobutyric acid, and substance P that were partially blocked at 1 week by prior decortication or completely blocked by MK-801 at 24 h. The lesions showed relative sparing of somatostatin-neuropeptide Y neurons, consistent with N-methyl-D-aspartate (NMDA) excitotoxicity. MPP+ produces impairment of oxidative phosphorylation in vivo, which may result in membrane depolarization with persistent activation of NMDA receptors and excitotoxic neuronal degeneration. An impairment of energy metabolism may therefore underlie slow excitotoxic neuronal death in neurodegenerative diseases.

Fatty Liver

In vitro animal and human models were used to evaluate the potential of chemical shift magnetic resonance imaging (MRI) for assessing fatty liver. Phantoms of varying fat content were created from mayonnaise-agar preparations. Fatty liver was induced in eight rats by feeding them ethanol for three to six weeks (36% of total calories), whereas eight control rats were fed a normal diet. T1-weighted in-phase and opposed-phase MR images were obtained of the phantoms animals, and 28 human subjects. Additional images obtained in animals included long TR images with in-phase and opposed-phase technique, and hybrid chemical shift water and fat suppression. The rats were killed and histologic status was graded blindly by a hepatopathologist as normal, mild, moderate, or severe fatty change, for correlation with MR grading. Quantitative analysis of MR images included fat signal fraction for animals, and relative signal decrease between in-phase and opposed-phase images for phantom and human data. Phantom in-phase signal increased linearly with respect to fat content, whereas opposed-phase signal decreased linearly. MRI and histologic grading of rat livers were highly correlated, especially when based on water suppression images (r = 0.91, P = .0001). Opposed-phase images were also highly correlated, while fat suppression images were less effective. There was no overlap between MR-derived fat fractions for control (2.6%-5.7%) versus ethanol-fed rats (7.7%-17.9%, P = .0002). Human liver considered to be fatty by visual inspection (n = 8) had higher relative signal decrease than nonfatty liver (n = 22) (P less than .001). Phantom, animal, and human data demonstrate that comparison of T1-weighted in-phase and opposed-phase images is both practical and sensitive in the detection and grading of fatty liver.