Quantitative tests of liver function measure hepatic improvement after sustained virological response: results from the HALT-C trial.

BACKGROUND: The impact of virologic response on hepatic function has not been previously defined. AIM: To determine the relationships of quantitative liver function tests (QLFTs) with virological responses to peginterferon (PEG) +/- ribavirin (RBV) in patients with chronic hepatitis C and to use serial QLFTs to define the spectrum of hepatic improvement after sustained virological response (SVR). METHODS: Participants (n = 232) were enrolled in the Hepatitis C Antiviral Long-term Treatment against Cirrhosis (HALT-C) Trial, had failed prior therapy, had bridging fibrosis or cirrhosis and were retreated with PEG/RBV. All 232 patients had baseline QLFTs; 24 patients with SVR and 68 nonresponders had serial QLFTs. Lidocaine, [24-(13)C]cholate, galactose and (99m)Tc-sulfur colloid were administered intravenously; [2,2,4,2-(2)H]cholate, [1-(13)C]methionine, caffeine and antipyrine were administered orally. Clearances (Cl), breath (13)CO(2), monoethylglycylxylidide (MEGX), perfused hepatic mass (PHM) and liver volume were measured. RESULTS: Rates of SVR were 18-26% in patients with good function by QLFTs, but < or =6% in patients with poor function. Hepatic metabolism, measured by caffeine k(elim) (P = 0.02), antipyrine k(elim) (P = 0.05) and antipyrine Cl (P = 0.02) and the portal circulation, measured by cholate Cl(oral) (P = 0.0002) and cholate shunt (P = 0.0003) and PHM (P = 0.03) improved after SVR. CONCLUSION: Hepatic dysfunction impairs the virological response to PEG/RBV. SVR improves hepatic metabolism, the portal circulation and PHM.

The spectrum of hepatic functional impairment in compensated chronic hepatitis C: results from the Hepatitis C Anti-viral Long-term Treatment against Cirrhosis Trial.

BACKGROUND: The spectrum of functional impairment in patients with compensated chronic hepatitis C is incompletely defined. AIM: To define hepatic impairment by quantitative tests (quantitative liver function tests) and correlate results with disease severity in patients with chronic hepatitis C. METHODS: We studied 285 adult patients with chronic hepatitis C prior to treatment in the Hepatitis C Anti-viral Long-term Treatment against Cirrhosis Trial; 171 had Ishak fibrosis stages 2-4 (fibrosis) and 114 had stage 5 or 6 (cirrhosis). None had had clinical decompensation. A battery of 12 quantitative liver function test assessed the spectrum of hepatic microsomal, mitochondrial and cytosolic functions, and hepatic and portal blood flow. RESULTS: Twenty-six to 63% of patients with fibrosis and 45-89% with cirrhosis had hepatic impairment by quantitative liver function test; patients with cirrhosis had the greatest impairment (P-value ranging from 0.15 to <0.0001). Cholate Cl(oral), cholate shunt and perfused hepatic mass correlated with cirrhosis, stage of fibrosis (r = -0.51, +0.49, -0.51), varices and variceal size (r = -0.39, +0.36, -0.41). PHM < 95 and cholate shunt >35% identified 91% of patients with medium- or large-sized varices. CONCLUSIONS: Hepatic impairment is common in compensated patients with fibrosis or cirrhosis because of chronic hepatitis C. Cholate shunt, and cholate Cl(oral) and perfused hepatic mass, identify patients at risk for cirrhosis or varices.

Portal-systemic shunting in patients with fibrosis or cirrhosis due to chronic hepatitis C: the minimal model for measuring cholate clearances and shunt.

BACKGROUND: Measurement of portal inflow and portal-systemic shunt using cholate clearances could be useful in monitoring patients with liver disease. AIM: To examine relationships of cholate clearances and shunt to cirrhosis and varices and to define minimal sampling requirements. METHODS: Five hundred forty-eight studies were performed in 282 patients enrolled in the Hepatitis C Antiviral Long-term Treatment to prevent Cirrhosis (HALT-C) trial. Stable, non-radioactive isotopes of cholate were administered intravenously and orally, clearances (Cl(iv) and Cl(oral)) were calculated from [dose/area under curve (AUC)] and cholate shunt from [(AUC(oral):AUC(iv)) x (Dose(iv):Dose(oral)) x 100%]. RESULTS: Cholate Cl(oral) and cholate shunt correlated with prevalences of both cirrhosis and varices (P < 0.0001 for all). Peripheral venous sampling at 5, 20, 45, 60 and 90 min defined the minimal model. Linear regression of cholate shunt determined from five points within 90 min vs. the standard method of 14 points over 3 h yielded slope of 1.0 and intercept 0.5% (r(2) = 0.98, P < 0.0001). Results were identical in the 189 validation studies (slope 1.0, intercept 0.5%, r(2) = 0.99, P < 0.0001). CONCLUSIONS: Cholate Cl(oral) and cholate shunt may be useful in monitoring patients with liver disease. The 5-point model enhances application of cholate Cl(oral) and cholate shunt in the non-invasive assessment of the portal circulation.

A randomized, double-blind trial comparing pegylated interferon alfa-2b to interferon alfa-2b as initial treatment for chronic hepatitis C.

This international, randomized, active-controlled, parallel-group, double-blind dose-finding study compared peginterferon alfa-2b (PegIntron) to interferon alfa-2b for the initial treatment of compensated chronic hepatitis C. We randomly assigned 1,219 subjects to receive either the standard three-times-weekly (TIW) interferon alfa-2b dose (3 MIU) or the once-weekly (QW) peginterferon alfa-2b (0.5, 1.0, or 1.5 microg/kg). Subjects were treated for 48 weeks and then followed for an additional 24 weeks. All 3 peginterferon alfa-2b doses significantly (P < or =.042) improved virologic response rates (loss of detectable serum HCV RNA) after treatment and after follow-up, as compared with interferon alfa-2b. Unlike the end-of-treatment virologic response, the sustained virologic response rate was not dose-related above 1.0 microg/kg peginterferon alfa-2b because of a higher relapse rate among patients treated with 1.5 microg/kg peginterferon alfa-2b, particularly among patients infected with genotype 1. All 3 peginterferon alfa-2b doses decreased liver inflammation to a greater extent than did interferon alfa-2b, particularly in subjects with sustained responses. No new adverse events were reported, and the majority of adverse events and changes in laboratory values were mild or moderate. In conclusion, peginterferon alfa-2b maintained (0.5 microg/kg) or surpassed (1.0, 1.5 microg/kg) the clinical efficacy of interferon alfa-2b while preserving its safety profile. The higher rate of virologic response during treatment with 1.5 microg/kg peginterferon alfa-2b in patients infected with genotype 1 and high viral levels warrants further evaluation.

Biochemical and viral response to consensus interferon (CIFN) therapy in chronic hepatitis C patients: effect of baseline viral concentration. Consensus Interferon Study Group.

OBJECTIVE: The effect of baseline viral concentration on response was assessed as part of a multicenter phase 3 trial evaluating the safety and efficacy of CIFN therapy for chronic HCV infection. METHODS: Patients (n = 472) received either CIFN 9 microg or IFN alpha-2b 3 MU subcutaneously t.i.w. for 24 wk, followed by 24 wk of observation. RESULTS: Efficacy was assessed by the percentage of patients who achieved normal ALT values or undetectable HCV RNA values (using RT-PCR with a sensitivity of 100 copies/ml). There was a clear relationship between baseline viral concentration and either ALT or HCV RNA response; patients with lower titer HCV RNA had better response rates. End-of-treatment HCV RNA responses were better for patients with low viral concentrations treated with CIFN (51%) than for patients treated with IFN a-2b (31%) (p = 0.03). ALT responses in patients with low viral concentrations were 60% for CIFN-treated patients and 27% for IFN alpha-2b-treated patients (p < 0.01) at the end of treatment. Patients with high titer HCV RNA were more likely to have a sustained HCV RNA response after treatment with CIFN 9 microg, compared with those treated with IFN alpha-2b (7% vs 0%, p = 0.03). CONCLUSIONS: Both genotype and baseline viral concentration were independent factors that affected response to interferon.

A novel, simple method of functional spleen volume calculation by liver-spleen scan.

UNLABELLED: Spleen enlargement is commonly associated with portal hypertension from cirrhosis and may cause thrombocytopenia. Thus, accurate assessment of spleen size may be helpful in the clinical evaluation. Spleen length is not a precise estimate of spleen size because of the variation in spleen configuration, and spleen volumes measured by edging techniques can be tedious. We present a new method of measuring the functional spleen volume by liver-spleen scan (LSSs), validation experiments and some clinical data. METHODS: The method involves measurement of the total spleen counts by SPECT and dividing by a representative voxel concentration on a single frame to obtain the organ volume. Validation included phantom studies and clinical evaluation in 443 consecutive patients, including 216 with histologic assessments of chronic liver disease (CLD) and 11 healthy volunteers. RESULTS: A calibration factor determined from phantoms was used to convert the calculated volume (CV) to the "true" volume (V): V = CV (0.956) - 66.5 (r = 0.9991; P < 0.001). The volume calculations were validated in a second group of phantoms (r= 0.981; P < 0.0001). Spleen volumes were expressed as volume (cm3) and as volume per pound ideal body weight (IBW) (cm3/lb) (the conversion factor to convert cm3/lb IBW to cm3/kg IBW is 2.2). Clinical studies of reproducibility included demonstration of a significant (P < 0.0001) linear correlation between volumes calculated from repeat LSSs within 9 mo of the initial LSS in 11 healthy volunteers and 32 patients with CLD: y = 1.02x - 25; r = 0.968. The correlation with spleen volumes from autopsy or splenectomy was significant: y = 0.766x + 57; r = 0.845; P < 0.001. The normal spleen volume in 11 patients was 201 +/- 77 cm3 and 1.43 +/- 0.68 cm3/lb IBW (upper limits of normal: 335 cm3 or 2.5 cm3/lb IBW). In 443 consecutive LSSs over 15 mo, half of the patients had spleen volumes above the upper limits of healthy volunteers, and CLD was present in 90.9% of these patients. In 216 patients with histologically proven liver disease, a progressive increase in the percentage of spleen volumes above the upper limits of normal was noted from no fibrosis (10%) to mild to moderate fibrosis (36.7%) to early cirrhosis (52%) to advanced liver disease (75%). The correlation of spleen volume with platelet count was excellent (r = 0.7635; P < 0.005). CONCLUSION: This novel spleen volume measurement detects serious liver disease and correlates with splenic hyperfunction.

Functional measurement of nonfibrotic hepatic mass in cirrhotic patients.

OBJECTIVES: We have postulated that the perfused hepatic mass (PHM) can be estimated by quantitative (volumetric) liver spleen scan (QLSS) using single photon emission computed tomography assessment of sulfur colloid distribution between liver, spleen, and bone marrow. Thus, this parameter should correlate with the amount of functioning tissue in the liver. As a "gold standard" estimate of the nonfibrotic functioning hepatic mass, the weight of the liver at autopsy or transplant was corrected for the amount of scar tissue present. QLSS parameters were correlated with functional hepatic mass in 13 patients with advanced liver disease with liver available at transplant (8 patients) or autopsy (5 patients) who had prior QLSS. METHODS: Greater than 1000 mm2 of a liver tissue was assessed histologically in all patients and from more than 2 regions of the liver in 9 of 13 patients. The total fibrosis score (TFS) (range, 0-17.5) was calculated as a semiquantitative estimate of hepatic fibrosis. The ratio of functioning tissue was calculated as (1 - TFS/20) and the amount of functioning tissue as the nonfibrotic weight (NFW): NFW = liver weight x (1--TFS/20). QLSS parameters were measured postprandially and 30 min after injection of 5 mCi of technetium Tc 99m sulfur colloid. Pixel and total counts from the liver, spleen, and bone marrow as well as organ length were measured. Liver/bone marrow index and liver/spleen index were calculated. The perfused hepatic mass (PHM) was defined as the mean of the liver/bone marrow index and liver/spleen index. RESULTS: All patients had cirrhosis: alcoholic (1 patient), alcoholic with alcoholic hepatitis (1 patient), hepatitis B (3 patients), hepatitis C (6 patients), hepatitis C with hepatocellular carcinoma (1 patient), and primary sclerosing cholangitis (n = 1). The ratio of functioning tissue was 0.54 +/- 0.07; liver weight 1215 +/- 317 g; and NFW = 658 +/- 193 g. The PHM = 55 +/- 14. The PHM calculated from the QLSS correlated strongly with the NFW (functioning tissue) at autopsy/transplant: NFW = 13 PHM - 55; r = 0.9505; p < 0.0001). CONCLUSIONS: In cirrhotic patients (a) we have confirmed that the sulfur colloid distribution by QLSS is determined by the perfused hepatic mass, and (b) the amount of functioning tissue can be precisely estimated by QLSS parameters.

Treatment of chronic hepatitis C with consensus interferon: a multicenter, randomized, controlled trial. Consensus Interferon Study Group.

This multicenter, randomized, controlled, double-blind, phase III study in 704 patients with chronic hepatitis C infection compared treatment with consensus interferon (CIFN), a non-natural recombinant type-1 interferon, with a standard regimen of recombinant interferon alfa-2b (IFN-alpha2b). Patients were randomized to receive CIFN at doses of 3 microg or 9 microg, or 15 microg IFN-alpha2b (3 million units), subcutaneously three times weekly for 24 weeks, followed by 24 weeks of observation. Efficacy was assessed by normalization of serum alanine transaminase (ALT) concentration and decrease in serum hepatitis C virus (HCV) RNA concentration below the limit of detection by reverse-transcription polymerase chain reaction (RT-PCR) (100 copies/mL). The beneficial effect of CIFN was greater with the 9-microg dose than the 3-microg dose. The sustained ALT and HCV RNA response rates were 20.3% and 12.1%, respectively, in the 9-microg CIFN cohort and 19.6% and 11.3%, respectively, in the 15-microg IFN-alpha2b cohort. However, patients receiving 9 microg of CIFN had a greater reduction in serum HCV RNA concentrations compared with patients receiving 15 microg IFN-alpha2b over the course of treatment (P < .01). Similarly, analysis of patients infected with HCV genotype 1 showed a greater reduction in serum HCV RNA concentration over the course of treatment for the 9-microg CIFN group when compared with the 15-microg IFN-alpha2b group (P < .01). In addition, a greater percentage of patients infected with HCV genotype 1 treated with 9 microg CIFN had undetectable HCV RNA concentrations when compared with patients in the 15-microg IFN-alpha2b cohort at the end of treatment (24% vs. 15%; P = .04). Improvements in liver histology were noted in all three treatment groups; 52% to 55% of the patients in the three cohorts had at least a 2-unit improvement in the Knodell score at the end of the posttreatment period. The adverse-events profiles were characteristic of treatment with type-1 interferon, and the incidences of anti-interferon antibody formation did not significantly differ among the three treatment groups. These results show that administration of 9 microg CIFN three times weekly for 6 months is safe and is effective in reducing serum HCV RNA concentration.

The liver-spleen scan as a quantitative liver function test: correlation with liver severity at peritoneoscopy.

Sulfur colloid distribution on liver-spleen scan is determined by the perfused Kupffer cell mass. The perfused Kupffer cell mass is proportional to the perfused hepatocyte mass, but is less affected by acute changes in hepatocyte function. Thus, sulfur colloid distribution parameters (precisely measured by quantitative liver-spleen scan [QLSS]) may be an excellent test of the perfused hepatic mass. Although no gold standard exists for confirmation, a close correlation should exist between liver disease severity assessed at peritoneoscopy and sulfur colloid distribution. Peritoneoscopy severity (scored as total peritoneoscopy score [PS]; range, 0-5) was assessed in 76 patients who also had QLSS. Multivariate equation were generated to estimate liver disease severity from the QLSS. These were then applied prospectively in 20 consecutive patients to validate these equations. In 76 patients, 62 were evaluated because of chronic liver disease (CLD) and included those with micronodular (20) and macronodular (20) cirrhosis with various degrees of severity (Child's A, 16; B, 29; C, 17). Multivariate analysis yielded a number of combinations of QLSS parameters that correlated with peritoneoscopic severity. These equations were used to estimate liver disease severity. Estimates of liver disease severity (estimated PS [EPS]) correlated well with the PS in these 76 patients (r = .9064; r2 = .8216; P < .0001). Adding histological fibrosis to the QLSS parameters yields an equation for estimating PS that was even more effective (r = .9462; r2 = .8953; P < .001). However, validation of multivariate equations requires confirmation of their value in a second population.(ABSTRACT TRUNCATED AT 250 WORDS)

Raising the dose of interferon does not improve the response in chronic hepatitis C.

We report results of dose escalation to 5 or 6 million units (MU) three times weekly (t.i.w.) of interferon-alpha in 17 consecutive patients with chronic active hepatitis C who were not responding to 3 MU t.i.w. after > or = 12 weeks of therapy. The mean pretreatment alanine aminotransferase (ALT) level was 206 +/- 62 U/L and, at the time of dose escalation, 113 +/- 71 U/L. Two patients could not tolerate the dose escalation. The remaining 15 patients were treated for an additional 10 +/- 3.5 weeks. Three patients had a complete response 3-8 weeks after dose escalation. At the end of high-dose therapy, the mean ALT level was 105 +/- 76 U/L (n = 15). During the 6-month posttreatment follow-up time, the mean ALT level was 147 +/- 85 U/L. All three responders had a relapse. Increasing the dose of interferon-alpha to 5-6 MU t.i.w. in chronic hepatitis C patients who are not responding to interferon-alpha, 3 MU t.i.w., at the 12th week of therapy is unlikely to result in sustained normalization of ALT levels.

Globulin correction of the albumin gradient: correlation with measured serum to ascites colloid osmotic pressure gradients.

The albumin difference or gradient between serum ascites is presumed to be an effective estimate of the colloid osmotic pressure gradient, although this has never been directly demonstrated. The colloid osmotic pressure gradient is controlled by the degree of portal hypertension. Thus the albumin gradient is clinically useful in detecting patients with ascites caused by portal hypertension, although some overlap in such patients' albumin gradients exists compared with those of patients without portal hypertension. Part of this overlap is related to the inverse correlation of the albumin gradient with serum globulin; globulins also contribute to colloid osmotic pressure. The ability to calculate colloid osmotic pressure in serum and ascites with albumin and globulin concentration or to correct the albumin gradient for the impact of globulins might improve the clinical usefulness of the ascitic fluid analysis in determining the presence of portal hypertension in ascitic patients with borderline albumin gradients. Thus we developed equations to calculate colloid osmotic pressure from multivariate discriminate analyses of albumin and globulin concentrations in serial dilution samples of pooled serum and subsequently validated these equations, along with older methods of calculating colloid osmotic pressure. In an initial set of dilution experiments, globulin concentration was closely correlated with the colloid osmotic pressure to albumin concentration ratio (r = 0.956; p less than 0.001). Multivariate discriminate analysis yielded an equation for calculating colloid osmotic pressure from albumin (A) and globulin (G) concentration with a ratio of colloid osmotic pressure to albumin (calculated colloid osmotic pressure = A(1.058G + 0.163A + 3.11) and two other equations.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis and hemodynamic assessment of portal hypertension.

Rational treatment of portal hypertensive complications requires a knowledge of the cause of portal hypertension and an assessment of the severity of liver disease. In the United States, chronic liver disease, usually due to alcohol, is the most common underlying cause. The history, physical examination, and laboratory analysis are usually sufficient to confirm the presence of underlying liver disease. If there is any question as to the etiology of portal hypertension, however, a more complete evaluation is required, whether the presenting complication is ascites, variceal bleeding, or hypersplenism. Usually, such an evaluation will require a liver biopsy, portal pressure measurement, and angiography. Occasionally, a noninvasive evaluation will be sufficient, but the value of these noninvasive parameters is still under investigation. Surgical mortality generally depends on the severity of the liver disease. Therefore, surgical intervention must be carefully considered in comparison to other therapeutic modalities depending on the patient's hepatic functional reserve. Secondary bacterial peritonitis due to perforation requires surgery regardless of the severity of the underlying liver disease.

Diagnostic paracentesis. A potent clinical tool.

Diagnostic paracentesis is a potent diagnostic tool capable of rapidly detecting portal hypertension and peritonitis. Gram's stain and chemical analysis of ascitic fluid add additional information by determining the predisposition to SBP, the presence of organisms, and the severity of peritonitis. In patients with a narrow A-GRAD, the chemical analysis, cell count and differential, and cytology will add direction for the work-up if the etiology is not apparent and confirmation if it is. This information should be available within a few hours of admission if the paracentesis and blood are obtained immediately. The results should optimize patient care and minimize costs.

Measurement of portal shunting in dogs.

A new method for measuring the quantity of portal blood bypassing the liver (shunted) has been developed and tested in the dog. Shunts were mimicked by the simultaneous infusion of glycocholic acid into a small peripheral portal venule and a peripheral vein. The total infused amount was kept constant, but the ratio at the two infusion sites varied. Determination of the extraction efficiency of the liver by simultaneously measuring the hepatic vein and arterial blood for systemically infused [14C]glycocholic acid permitted the calculation of shunted blood from information provided by the concentration of glycocholic acid in the hepatic vein, artery, and portal vein blood. This method was tested for various proportion of shunting from none to complete. The total hepatic flow was determined with single injection of indocyanine green and the individual arterial and portal vein flows determined with flowmeters. The input ratios of shunting related quite closely to that calculated from the flowmeters or the hepatic extraction ratio.

Ascitic fluid analysis in malignancy-related ascites.

A prospective study identified 45 patients with malignancy-related ascites among 448 ascites patients (10% of the total). Patients were categorized into five subgroups based on the pathophysiology of ascites formation. Each subgroup had a distinctive ascitic fluid analysis. Patients with peritoneal carcinomatosis but without massive liver metastases (53.3% of the patients with malignancy-related ascites) had a uniformly positive ascitic fluid cytology, high ascitic fluid protein concentration and low serum-ascites albumin gradient. Patients with massive liver metastases and no other cause for ascites formation (13.3% of the series) had a negative cytology, low ascitic fluid protein concentration, high serum-ascites albumin gradient and markedly elevated serum alkaline phosphatase. Those with peritoneal carcinomatosis and massive liver metastases (13.3% of the series) had a nearly uniformly positive ascitic fluid cytology, variable protein concentration, high serum-ascites albumin gradient and markedly elevated serum alkaline phosphatase. Chylous ascites (6.7%) was characterized by a milky appearance, negative cytology and an elevated ascitic fluid triglyceride concentration. Patients with hepatocellular carcinoma superimposed on cirrhosis (13.3%) had negative ascitic fluid cytology, low ascitic fluid protein concentration, high serum-ascites albumin gradient and elevated serum and ascitic fluid alpha-fetoprotein concentration. Two-thirds of patients with malignancy-related ascites had peritoneal carcinomatosis; 96.7% of patients with peritoneal carcinomatosis had positive ascitic fluid cytology. Ascitic fluid analysis is helpful in identifying and distinguishing the subgroups of malignancy-related ascites.

Hepatofugal portal flow in cirrhosis: observations on hepatic hemodynamics and the nature of the arterioportal communications.

Six of 85 patients (7%) with alcoholic liver disease undergoing transhepatic portal pressure measurement had either stagnant (3 patients) or reversed (3 patients) portal blood flow documented by gentle hand injection of 1 to 2 ml of angiographic contrast. Portal blood flow was uniformly hepatopetal in 24 patients with nonalcoholic liver disease. Recurrent spontaneous hepatic encephalopathy and sodium retention occurred in 4 of 6 patients with stagnant or reversed portal flow; gastrointestinal bleeding was not seen. Standard laboratory tests of liver function were widely variable. Net portal pressure was lower in this group than in patients with alcoholic liver disease and forward portal flow (9.2 +/- 2.6 vs. 15.6 +/- 4.1 mm Hg, p less than 0.001). Wedged hepatic vein pressure was 1 to 7 mm Hg higher than portal vein pressure in patients with reversed portal flow. The arterioportal extraction of bile acid was calculated from the difference in concentration between artery and portal vein, and total functional hepatic blood flow was calculated from the hepatic extraction and systemic clearance of indocyanine green. Extraction was 0%, and hepatic blood flow was 0.469 liter per min in a patient with hepatofugal portal flow and recurrent encephalopathy. Extraction was 20%, and hepatic blood flow was 4.014 liters per min in a patient who had never had encephalopathy. These data indicate that arterioportal communications may be sinusoidal or presinusoidal in patients who lose forward portal flow and that the amount of flow in the arterioportal circuit, together with its efficiency, largely determine the clinical outcome.

Estimation of acoustic attenuation in liver using one megabyte of data and the zero-crossings technique.

Statistical fluctuations due to scatter-induced frequency variations in reflected acoustic pulses are a major problem when estimating acoustic attenuation. Disagreement exists in the ultrasound community as to how much data is sufficient to overcome these statistical fluctuations. The range of attenuation values for normal livers and a tissue equivalent phantom, using 1 megabyte of data per liver and the zero-crossings technique, was investigated. The significance of statistical fluctuations and their effects on attenuation are discussed.