The negative impact of fatty liver on maximum standard uptake value of liver on FDG PET

Impact of patient characteristic factors on the dynamics of liver glucose metabolism: Evaluation of multiparametric imaging with dynamic whole-body 18 F-fluorodeoxyglucose-positron emission tomography

AIMS

To assess the impact of various patient characteristics on the dynamics of liver glucose metabolism using automated multiparametric imaging with whole-body dynamic 18 F-fluorodeoxyglucose (FDG)-positron emission tomography (PET).

MATERIALS AND METHODS

We retrospectively enrolled 540 patients who underwent whole-body dynamic FDG-PET. Three quantitative indices representing hepatic glucose metabolism [mean standardized uptake value normalized by lean body mass (SULmean), metabolic glucose rate (kinetic index) and distribution volume (DV)] were measured from multiparametric PET images produced automatically based on the Patlak plot model. Patient characteristics including age, sex, body mass index, fasting time, blood glucose level, and the presence of diabetes mellitus (DM) or hepatic steatosis (HS) were collected. We examined the correlations between the characteristic factors and three quantitative indices using multiple regression analysis.

RESULTS

The success rate of kinetic analysis using multiparametric PET imaging was 93.3% (504/540). Hepatic SULmean was significantly correlated with age (p < .001), sex (p < .001) and blood glucose level (p = .002). DV was significantly correlated with age (p = .033), sex (p < .001), body mass index (p = .002), fasting time (p = .043) and the presence of HS (p = .002). The kinetic index was significantly correlated with age (p < .001) and sex (p = .004). In the comparison of the healthy, DM and HS groups, patients with DM had a significantly increased SULmean, whereas patients with HS had a significantly decreased DV.

CONCLUSIONS

Our results showed that liver glucose metabolism was influenced by various patient characteristic factors. Multiparametric FDG-PET imaging can be used to analyse the kinetics of liver glucose metabolism in routine clinical practice.

The effect of hepatic steatosis on 18F-FDG uptake in PET-CT examinations of cancer Egyptian patients

BACKGROUND

Hepatic steatosis is the most common chronic hepatic disease. Imaging diagnosis of hepatic steatosis has been evaluated as an alternative to invasive histological diagnosis.

STUDY AIMS

The study aimed to assess the effect of hepatic steatosis on Flourine-18 fluorodeoxyglucose (18F-FDG) uptakes in cancer patients.

PATIENTS AND METHODS

Blood samples were collected from 50 cancer patients and analyzed to calculate fatty liver index and Hepatic steatosis index (HIS). Hepatic steatosis examined using high-resolution ultrasound and positron emission tomography-computed tomography (PET-CT). Linear attenuation coefficient, standardized-uptake value (SUV) mean (SUV mean), and SUV maximum (SUVmax) were measured. Accordingly, patients were divided equally into non-fatty liver, and fatty liver groups.

RESULTS

A significant increase in SUVmax and SUV mean was observed in the fatty liver group more than in the non-fatty liver group. HSI significantly increased in the fatty liver group compared to the non-fatty liver group. Liver tissue uptake FDG was significantly correlated with HSI values. SUV max significantly correlated with body mass index (BMI) in the non-fatty group only.

CONCLUSION

Hepatic changes in cancer patients affect the liver metabolic activity and thus the 18 F-FDG uptake. Therefore, further corrections should be considered when the liver is used as a comparator for PET-CT scans of cancer patients.

Hepatic Positron Emission Tomography: Applications in Metabolism, Haemodynamics and Cancer

Evaluating in vivo the metabolic rates of the human liver has been a challenge due to its unique perfusion system. Positron emission tomography (PET) represents the current gold standard for assessing non-invasively tissue metabolic rates in vivo. Here, we review the existing literature on the assessment of hepatic metabolism, haemodynamics and cancer with PET. The tracer mainly used in metabolic studies has been [¹⁸F]2-fluoro-2-deoxy-D-glucose (¹⁸F-FDG). Its application not only enables the evaluation of hepatic glucose uptake in a variety of metabolic conditions and interventions, but based on the kinetics of ¹⁸F-FDG, endogenous glucose production can also be assessed. 14(R,S)-[¹⁸F]fluoro-6-thia-Heptadecanoic acid (¹⁸F-FTHA), ¹¹C-Palmitate and ¹¹C-Acetate have also been applied for the assessment of hepatic fatty acid uptake rates (¹⁸F-FTHA and ¹¹C-Palmitate) and blood flow and oxidation (¹¹C-Acetate). Oxygen-15 labelled water (¹⁵O-H₂O) has been used for the quantification of hepatic perfusion. ¹⁸F-FDG is also the most common tracer used for hepatic cancer diagnostics, whereas ¹¹C-Acetate has also shown some promising applications in imaging liver malignancies. The modelling approaches used to analyse PET data and also the challenges in utilizing PET in the assessment of hepatic metabolism are presented.

Role of Positron Emission Tomography with 2-Deoxy-2-[fluorine-18]fluoro-D-glucose Integrated with Computed Tomography in the Evaluation of Hepatic Metabolic Activity due to Steatosis in Lymphoma Patients and its Impact on Deauville Score

BACKGROUND: Liver uptake of 2-Deoxy-2-[fluorine-18]fluoro-D-glucose integrated (18F-FDG) is taken as the reference tissue in interpretation of Deauville score (DS), which is considered a response assessment. AIM: This study was conducted to evaluate the prevalence of hepatic steatosis in patients with lymphoma and the impact of hepatic metabolic activity due to steatosis on 18F-FDG liver uptake and its effect on DS. MATERIAL AND METHODS: This prospective study was conducted on 77 cases. Seventy-seven patients had baseline positron emission tomography/computed tomography (PET/CT), 69 patients had interim PET/CT, 31 patients had end of treatment (EOT) PET/CT, and 3 patients had follow-up (FU) PET/CT after EOT. The study included 49 female patients (63.6%) and 28 male patients (36.4%). The mean age = 39.5 + 13. Forty-one patients (53.2%) diagnosed as non-Hodgkin lymphoma [HL] while 36 patients (46.8%) diagnosed as HL. Steatosis was diagnosed on the unenhanced CT part of PET/CT examinations using a cutoff value of 42 Hounsfield units. Both maximum standardized uptake value (SUVmax) and SULmax were recorded on the liver and the tumor target lesion. DS was then computed. RESULTS: Among 77 cases, prevalence of steatosis in baseline (10/77, 12.9%), interim (13/69, 18.8%), and EOT/FU (4/31, 12.9%), there was no significant difference in hepatic steatosis during their time course of their treatment. There was correlation between Liver SUVmax with body mass index (BMI) in each of interim and EOT PET/CT. Regarding SULmax, there was no correlation with BMI. There was no change in interpretation of DS using either SUVmax or SULmax. CONCLUSION: Steatosis has no practical issue regarding liver metabolic activity (either SUVmax or SULmax) in interpretation of DS. Liver SUVmax is affected by body weight. Unlike, SULmax is not affected by body weight.

Leptin resistance before and after obesity: evidence that tissue glucose uptake underlies adipocyte enlargement and liver steatosis/steatohepatitis in Zucker rats from early-life stages

BACKGROUND

Leptin resistance occurs in obese patients, but its independent contribution to adiposity and the accompanying metabolic diseases, i.e., diabetes, liver steatosis, and steatohepatitis, remains to be established. This study was conducted in an extreme model of leptin resistance to investigate mechanisms initiating diabetes, fat expansion, liver steatosis, and inflammatory disease, focusing on the involvement of glucose intolerance and organ-specific glucose uptake in brown and subcutaneous adipose tissues (BAT, SAT) and in the liver.

METHODS

We studied preobese and adult Zucker rats (fa/fa, fa/+ ) during fasting or glucose loading to assess glucose tolerance. Relevant pancreatic and intestinal hormonal levels were measured by Milliplex. Imaging of ¹⁸F-fluorodeoxyglucose by positron emission tomography was used to quantify glucose uptake in SAT, BAT, and liver, and evaluate its relationship with adipocyte size and biopsy-proven nonalcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH).

RESULTS

Preobese fa/fa pups showed impaired glucose tolerance, adipocyte enlargement, hepatic microsteatosis, and lobular inflammation, with elevated hepatic post-glucose load glucose uptake and production. Adult fa/fa rats had more severe glucose intolerance, fasting hyperglycemia, hormonal abnormalities, elevated glucose uptake in SAT and BAT, and more markedly in the liver, together with macrosteatosis, and highly prevalent hepatic inflammation. Organ glucose uptake was proportional to the degree of fat accumulation and tissue inflammation and was able to dissect healthy from NAFLD and NAFLD/NASH livers. Most severe NASH livers showed a decline in glucose uptake and liver enzymes.

CONCLUSIONS

In fa/fa Zucker rats, leptin resistance leads to glucose intolerance, mainly due to hepatic glucose overproduction, preceding obesity, and explaining pancreatic and intestinal hormonal changes and fat accumulation in adipocytes and hepatocytes. Our data support the involvement of liver glucose uptake in the pathogenesis of liver inflammatory disease. Its potential as more generalized biomarker or diagnostic approach remains to be established outside of our leptin-receptor-deficient rat model.

Brain-gut-liver interactions across the spectrum of insulin resistance in metabolic fatty liver disease

Metabolic associated fatty liver disease (MAFLD), formerly named "nonalcoholic fatty liver disease" occurs in about one-third of the general population of developed countries worldwide and behaves as a major morbidity and mortality risk factor for major causes of death, such as cardiovascular, digestive, metabolic, neoplastic and neuro-degenerative diseases. However, progression of MAFLD and its associated systemic complications occur almost invariably in patients who experience the additional burden of intrahepatic and/or systemic inflammation, which acts as disease accelerator. Our review is focused on the new knowledge about the brain-gut-liver axis in the context of metabolic dysregulations associated with fatty liver, where insulin resistance has been assumed to play an important role. Special emphasis has been given to digital imaging studies and in particular to positron emission tomography, as it represents a unique opportunity for the noninvasive in vivo study of tissue metabolism. An exhaustive revision of targeted animal models is also provided in order to clarify what the available preclinical evidence suggests for the causal interactions between fatty liver, dysregulated endogenous glucose production and insulin resistance.

Pilot Study to Diagnose Nonalcoholic Steatohepatitis With Dynamic 18F-FDG PET

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are major causes of chronic liver disease characterized by steatosis, inflammation, and fibrosis. Diagnosis of inflammation is limited by the need for liver biopsy. Dynamic PET with the widely used radiotracer ¹⁸F-FDG provides a novel method for evaluating spatial and temporal changes in liver inflammation.

MATERIALS AND METHODS

Patients with NAFLD or NASH underwent dynamic FDG PET and MRI within 6 months of undergoing liver biopsy. Liver time-activity curves were extracted to estimate kinetic parameters representing various rate constants of FDG transport using tracer kinetic modeling. Liver biopsy specimens were scored on the basis of NASH Clinical Research Network criteria.

RESULTS

This pilot study included 22 patients, 14 of whom were women. Patient age ranged from 18 to 70 years, and the mean body mass index (weight in kilograms divided by the square of height in meters) was 33.2 (range, 24-43.1). The K₁ value, which represents the rate of FDG transport from blood to hepatic tissue, was significantly correlated with inflammation (r = -0.7284; p = 0.0001) and the overall NAFLD activity score (NAS; r = -0.6750; p = 0.0006). K₁ values were inversely related to the hepatic inflammation score and NAS. Although heterogeneity in K₁ values across eight liver segments was noted, distinct segregation existed among segmental K₁ values dependent on the histologic inflammation score (p = 0.022) or NAS (p = 0.0091). K₁ had a strong association with both inflammation (ROC AUC value, 0.88) and the NAS (ROC AUC value, 0.89), with K₁ = 1.02 (mL/min/mL) corresponding to a sensitivity and specificity of 93% and 88%, respectively, for the NAS.

CONCLUSION

Dynamic FDG PET with tracer kinetic modeling has the potential to determine liver inflammation in patients with NAFLD and NASH and can fill an essential gap in diagnosis.

Clinical utility of FDG uptake within reticuloendothelial system on F-18 FDG PET/CT for prediction of tumor recurrence in breast cancer

BACKGROUND

The aim of this study was to investigate the metabolism of the spleen, bone marrow (BM), and liver from preoperative F-18 FDG PET/CT scans for the prediction of recurrence in breast cancer.

METHODS

We retrospectively included 153 patients diagnosed with invasive ductal carcinoma (IDC) of the breast who underwent preoperative F-18 FDG PET/CT scan and a curative operation. The mean standardized uptake value (SUVmean) of the spleen, liver, and BM and maximum SUV (SUVmax) of primary tumors were measured. The relationships between spleen, BM, and liver metabolism and clinicopathologic parameters were evaluated, and possible prognostic parameters predicting recurrence were assessed using disease-free survival (DFS).

RESULTS

Spleen SUVmean was significantly correlated with primary tumor SUVmax, pathologic T (pT) stage, and histologic grade of primary tumor. BM SUVmean also showed a positive correlation with primary tumor SUVmax. Spleen SUVmean were significantly associated with recurrence from binary logistic regression analysis (P = 0.004). Spleen, BM, liver, and primary tumor SUVs were all significant prognostic factors for DFS in univariate Cox regression analysis (all P<0.024). Among all PET parameters analyzed, spleen SUVmean ≥ 2.21 (P = 0.032) was in the multivariable analysis the powerful poor prognostic factor predicting DFS that was independent of other clinicopathological features like T stage (pT >2; P = 0.009) and estrogen receptor (ER) status (ER negativity; P = 0.001).

CONCLUSION

Splenic metabolism together with pT stage and ER status was an independent prognostic factor for predicting recurrence in breast cancer. Metabolic activity of reticuloendothelial system such as spleen, liver or BM on preoperative F-18 FDG PET/CT can be a meritorious imaging factor for discriminating patients with IDC that require adjunctive therapy to prevent recurrence.

Dynamic PET of human liver inflammation: impact of kinetic modeling with optimization-derived dual-blood input function

The hallmark of nonalcoholic steatohepatitis is hepatocellular inflammation and injury in the setting of hepatic steatosis. Recent work has indicated that dynamic 18F-FDG PET with kinetic modeling has the potential to assess hepatic inflammation noninvasively, while static FDG-PET is less promising. Because the liver has dual blood supplies, kinetic modeling of dynamic liver PET data is challenging in human studies. This paper aims to identify the optimal dual-input kinetic modeling approach for dynamic FDG-PET of human liver inflammation. Fourteen patients with nonalcoholic fatty liver disease were included. Each patient underwent 1 h dynamic FDG-PET/CT scan and had liver biopsy within six weeks. Three models were tested for kinetic analysis: the traditional two-tissue compartmental model with an image-derived single-blood input function (SBIF), a model with population-based dual-blood input function (DBIF), and a new model with optimization-derived DBIF through a joint estimation framework. The three models were compared using Akaike information criterion (AIC), F test and histopathologic inflammation score. Results showed that the optimization-derived DBIF model improved liver time activity curve fitting and achieved lower AIC values and higher F values than the SBIF and population-based DBIF models in all patients. The optimization-derived model significantly increased FDG K1 estimates by 101% and 27% as compared with traditional SBIF and population-based DBIF. K1 by the optimization-derived model was significantly associated with histopathologic grades of liver inflammation while the other two models did not provide a statistical significance. In conclusion, modeling of DBIF is critical for dynamic liver FDG-PET kinetic analysis in human studies. The optimization-derived DBIF model is more appropriate than SBIF and population-based DBIF for dynamic FDG-PET of liver inflammation.

Digital liver biopsy: Bio-imaging of fatty liver for translational and clinical research

The rapidly growing field of functional, molecular and structural bio-imaging is providing an extraordinary new opportunity to overcome the limits of invasive liver biopsy and introduce a "digital biopsy" for in vivo study of liver pathophysiology. To foster the application of bio-imaging in clinical and translational research, there is a need to standardize the methods of both acquisition and the storage of the bio-images of the liver. It can be hoped that the combination of digital, liquid and histologic liver biopsies will provide an innovative synergistic tri-dimensional approach to identifying new aetiologies, diagnostic and prognostic biomarkers and therapeutic targets for the optimization of personalized therapy of liver diseases and liver cancer. A group of experts of different disciplines (Special Interest Group for Personalized Hepatology of the Italian Association for the Study of the Liver, Institute for Biostructures and Bio-imaging of the National Research Council and Bio-banking and Biomolecular Resources Research Infrastructure) discussed criteria, methods and guidelines for facilitating the requisite application of data collection. This manuscript provides a multi-Author review of the issue with special focus on fatty liver.

Assessment of alteration in liver 18F-FDG uptake due to steatosis in lymphoma patients and its impact on the Deauville score

AIM

Our aim was (1) to evaluate the prevalence of steatosis in lymphoma patients and its evolution during treatment; (2) to evaluate the impact of hepatic steatosis on ¹⁸F-FDG liver uptake; and (3) to study how hepatic steatosis affects the Deauville score (DS) for discriminating between responders and non-responders.

METHODS

Over a 1-year period, 358 PET scans from 227 patients [122 diffuse large B cell lymphoma (DLBCL), 57 Hodgkin lymphoma (HL) and 48 Follicular lymphoma (FL)] referred for baseline (n = 143), interim (n = 79) and end-of-treatment (EoT, n = 136) PET scans were reviewed. Steatosis was diagnosed on the unenhanced CT part of PET/CT examinations using a cut-off value of 42 Hounsfield units (HU). EARL-compliant SUL_max were recorded on the liver and the tumour target lesion. DS were then computed.

RESULTS

Prevalence of steatosis at baseline, interim and EoT PET was 15/143 (10.5%), 6/79 (7.6%) and 16/136 (11.8%), respectively (p = 0.62).Ten out of 27 steatotic patients (37.0%) displayed a steatotic liver on all examinations. Six patients (22.2%) had a disappearance of hepatic steatosis during their time-course of treatment. Only one patient developed steatosis during his course of treatment. Liver SUL_max values were significantly lower in the steatosis versus non-steatotic groups of patients for interim (1.66 ± 0.36 versus 2.15 ± 0.27) and EoT (1.67 ± 0.29 versus 2.17 ± 0.30) PET. CT density was found to be an independent factor that correlated with liver SUL_max, while BMI, blood glucose level and the type of chemotherapy regimen were not. Using a method based on this correlation to correct liver SUL_max, all DS4 steatotic patients on interim (n = 1) and EoT (n = 2) PET moved to DS3.

CONCLUSIONS

Steatosis is actually a theoretical but not practical issue in most patients but should be recognised and corrected in appropriate cases, namely, for those patients scored DS4 with a percentage difference between the target lesion and the liver background lower than 30%.

Imaging patterns and focal lesions in fatty liver: a pictorial review

Non-alcoholic fatty liver disease is the most common cause of chronic liver disease and affects nearly one-third of US population. With the increasing trend of obesity in the population, associated fatty change in the liver will be a common feature observed in imaging studies. Fatty liver causes changes in liver parenchyma appearance on imaging modalities including ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) and may affect the imaging characteristics of focal liver lesions (FLLs). The imaging characteristics of FLLs were classically described in a non-fatty liver. In addition, focal fatty change and focal fat sparing may also simulate FLLs. Knowledge of characteristic patterns of fatty change in the liver (diffuse, geographical, focal, subcapsular, and perivascular) and their impact on the detection and characterization of FLL is therefore important. In general, fatty change may improve detection of FLLs on MRI using fat suppression sequences, but may reduce sensitivity on a single-phase (portal venous) CT and conventional ultrasound. In patients with fatty liver, MRI is generally superior to ultrasound and CT for detection and characterization of FLL. In this pictorial essay, we describe the imaging patterns of fatty change in the liver and its effect on detection and characterization of FLLs on ultrasound, CT, MRI, and PET.

The extent to which standardized uptake values reflect FDG phosphorylation in the liver and spleen as functions of time after injection of 18F-fluorodeoxyglucose

Purpose

In FDG PET/CT, standardized uptake value (SUV) is used to measure metabolic activity but detects un-phosphorylated FDG as well as phosphorylated FDG (FDG6P). Our aim was to determine the proportions of intrahepatic and intrasplenic FDG that are phosphorylated after FDG injection and compare them with SUVs.

Methods

Sixty patients undergoing whole-body PET/CT 60 min post-injection of FDG first had dynamic PET imaging for 30 min with measurement of hepatic and splenic FDG clearances using Patlak-Rutland analysis. The gradient of the Patlak-Rutland plot, which is proportional to clearance (Ki), was normalized to the intercept, which is proportional to FDG distribution volume (V(0)) with the same proportionality constant. Using measured values of Ki/V(0), FDG6P/FDG ratios as functions of time in the two organs were measured for assumed FDG blood disappearance half-times of 40, 50 and 60 min. Hepatic and splenic SUVs were measured from whole-body PET/CT.

Results

The mean (SD) Ki/V(0) was 0.0036 (0.0021) and 0.0060 (0.0041) ml/min/ml for the liver and spleen, respectively, but the hepatic SUV was 1.36-fold higher than the splenic SUV. This discrepancy was explained by the hepatic V(0) being 1.6-fold higher than the splenic V(0). The percentages of FDG phosphorylated 60 min post-injection were 27, 25 and 23% for the liver and 39, 36 and 34% for the spleen, for blood clearance half-times of 40, 50 and 60 min, respectively. SUV indices correlated poorly with Ki/V(0) for both organs.

Conclusions

SUV is largely determined by un-phosphorylated FDG in dynamic exchange with blood FDG, explaining the poor correlations between SUV indices and Ki/V(0).

The predictive ability of liver function indexes on 18F-FDG uptake in the liver

AIM

The liver is an important reference organ for positron emission tomography/ computed tomography (PET-CT) examination using 18F-fluorodeoxyglucose (18F-FDG). However, 18F-FDG uptake by the liver is affected by many factors. We therefore investigated the effect of hepatic function on 18F-FDG uptake in the liver.

METHODS

A retrospective analysis of data on the hepatic function and the mean liver standardized up-take value (SUV) of 18F-FDG uptake in the liver during PET-CT examination of 500 (381 males, 119 females, aged 27-71) physical examinees.

RESULTS

The mean liver SUV was 1.88 ± 0.20. The correlation coefficient and partial correlation coefficient for age, the levels of conjugated bilirubin, globulin, AST and the mean liver SUV were statistically significant (r' = 0.119, -0.197, -0.089 and 0.151, all p < 0.05). Multiple linear regression analysis showed that age and the levels of conjugated bilirubin, globulin and aspartate amino-transferase (AST) were independent factors that influenced changes in the mean liver SUV (β = 0.008, -0.025, -0.151 and 0.005, all p < 0.05). The globulin level had the biggest predictive ability (β' = -0.151, p < 0.05).

CONCLUSIONS

The uptake of 18F-FDG in the liver was influenced by some liver function indexes. The levels of conjugated bilirubin, globulin and AST were independent factors for predicting changes in the uptake of 18F-FDG in the liver. Liver function test results should be combined with an evaluation of the metabolic activity of the liver.

Hepatic glucose utilization in hepatic steatosis and obesity

Hepatic steatosis is associated with obesity and insulin resistance. Whether hepatic glucose utilization rate (glucose phosphorylation rate; MRglu) is increased in steatosis and/or obesity is uncertain. Our aim was to determine the separate relationships of steatosis and obesity with MRglu. Sixty patients referred for routine PET/CT had dynamic PET imaging over the abdomen for 30 min post-injection of F-18-fluorodeoxyglucose (FDG), followed by Patlak-Rutland graphical analysis of the liver using abdominal aorta for arterial input signal. The plot gradient was divided by the intercept to give hepatic FDG clearance normalized to hepatic FDG distribution volume (ml/min per 100 ml) and multiplied by blood glucose to give hepatic MRglu (μmol/min per 100 ml). Hepatic steatosis was defined as CT density of ≤40 HU measured from the 60 min whole body routine PET/CT and obesity as body mass index of ≥30 kg/m² Hepatic MRglu was higher in patients with steatosis (3.3±1.3 μmol/min per 100 ml) than those without (1.7±1.2 μmol/min per 100 ml; P<0.001) but there was no significant difference between obese (2.5±1.6 μmol/min per 100 ml) and non-obese patients (2.1±1.3 μmol/min per 100 ml). MRglu was increased in obese patients only if they had steatosis. Non-obese patients with steatosis still had increased MRglu. There was no association between MRglu and chemotherapy history. We conclude that MRglu is increased in hepatic steatosis probably through insulin resistance, hyperinsulinaemia and up-regulation of hepatic hexokinase, irrespective of obesity.

Relationships of body habitus and SUV indices with signal-to-noise ratio of hepatic (18)F-FDG PET

OBJECTIVE

Tissue accumulation of (18)F-FDG is quantified as standardised uptake value (SUV), which may be expressed as the voxel maximum (SUVmax) or mean (SUVmean). SUVmax/SUVmean may be a marker of hepatic steatosis, while the coefficient of variation (CV) of SUV may be a marker of hepatic fat distribution heterogeneity (HFDH). Alternatively, they may reflect low signal-to-noise ratio ('noise') in obese persons in whom hepatic steatosis is common. The study aim was to compare the impact of body size on noise versus SUV and CT density (CTD).

METHODS

Dynamic PET was performed (30×1min frames) following FDG injection in 60 patients undergoing routine PET/CT. Hepatic FDG clearance was measured using Patlak-Rutland graphical analysis with abdominal aorta as input. Noise was quantified as the standard deviation (SD) of the plot residuals (ignoring the first 2 frames), normalised to the intercept (NRMSD). SUVmax, SUVmean and CTD were measured from 60min whole body PET/CT. CV of SUV and SD of CTD were quantified in 28/60 patients using texture analysis.

RESULTS

NRMSD correlated with weight (r=0.49; p<0.0001) and BMI (r=0.48; p=0.0001). SUVmax, SUVmean, SUVmax/SUVmean, CV of SUV, CTD, and SD of CTD all correlated strongly with weight and BMI (p<0.0001). However, they correlated weakly with NRMSD, the strongest being SUVmax (r=0.34; p=0.008) and SD of CTD (r=0.42; n=28; p=0.026).

CONCLUSIONS

Noise is increased in overweight/obese persons but has little effect on SUV indices, CTD and their variabilities. SUVmax/SUVmean and CV of SUV are therefore, to some extent, markers of hepatic steatosis and HFDH, respectively.

Variability of Hepatic 18F-FDG Uptake at Interim PET in Patients With Hodgkin Lymphoma

INTRODUCTION

When evaluating response of Hodgkin lymphoma (HL) to chemotherapy on interim (18)F-FDG-PET/CT, physiological liver uptake is used as reference. Hodgkin lymphoma sites with uptake greater than liver are interpreted as positive. We aimed at examining factors that might influence liver uptake as reference organ.

METHODS

Fifty patients with HL who received baseline (18)F-FDG-PET/CT (PET1) and interim PET (PET2), usually after 2 cycles of adriamycin bleomycin, vinblastine, and dacarbazine chemotherapy, were included retrospectively. SUVmean normalized for body weight (SUVmean) and for lean body mass (SULmean) were obtained from regions of interest in the right lobe of the liver.

RESULTS

On univariate analysis, liver SUVmean on interim PET increased with increasing body mass index (BMI) (P = 0.0453) and were higher in women (P = 0.0401). These factors remained significant on multivariate analysis (P = 0.009 and P = 0.008, respectively). No significant correlation was found with postinjection delay, blood glucose level, and age. Liver SULmean were not affected by the studied variables. Average liver SUVmean in the 50 patients were similar at baseline and interim PET. In 11 patients (22%), however, there was 30% or greater variation in liver SUVmean between PET1 and PET2. No factors explaining intrapatient variation in hepatic uptake between PET1 and PET2 were found on correlation analysis.

CONCLUSION

At interim PET in patients with HL, liver SUVmean depends on BMI and sex, but not liver SULmean. Furthermore, our study, conducted with standard clinical procedure, also confirmed the high range of liver uptake values from one patient to another. Caution is required when using liver SUV as reference in patients with high BMI. Intrapatient fluctuation in liver SUVmean should also be expected.

Impacts of biological and procedural factors on semiquantification uptake value of liver in fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography imaging

BACKGROUND

Increased metabolic activity of fluorodeoxyglucose (FDG) in tissue is not only resulting of pathological uptake, but due to physiological uptake as well. This study aimed to determine the impacts of biological and procedural factors on FDG uptake of liver in whole body positron emission tomography/computed tomography (PET/CT) imaging.

METHODS

Whole body fluorine-18 ((18)F) FDG PET/CT scans of 51 oncology patients have been reviewed. Maximum standardized uptake value (SUVmax) of lesion-free liver was quantified in each patient. Pearson correlation was performed to determine the association between the factors of age, body mass index (BMI), blood glucose level, FDG dose and incubation period and liver SUVmax. Multivariate regression analysis was established to determine the significant factors that best predicted the liver SUVmax. Then the subjects were dichotomised into four BMI groups. Analysis of variance (ANOVA) was established for mean difference of SUVmax of liver between those BMI groups.

RESULTS

BMI and incubation period were significantly associated with liver SUVmax. These factors were accounted for 29.6% of the liver SUVmax variance. Statistically significant differences were observed in the mean SUVmax of liver among those BMI groups (P<0.05).

CONCLUSIONS

BMI and incubation period are significant factors affecting physiological FDG uptake of liver. It would be recommended to employ different cut-off value for physiological liver SUVmax as a reference standard for different BMI of patients in PET/CT interpretation and use a standard protocol for incubation period of patient to reduce variation in physiological FDG uptake of liver in PET/CT study.

Quantification of tumour (18) F-FDG uptake: Normalise to blood glucose or scale to liver uptake?

PURPOSE

To compare normalisation to blood glucose (BG) with scaling to hepatic uptake for quantification of tumour (18) F-FDG uptake using the brain as a surrogate for tumours.

METHODS

Standardised uptake value (SUV) was measured over the liver, cerebellum, basal ganglia, and frontal cortex in 304 patients undergoing (18) F-FDG PET/CT. The relationship between brain FDG clearance and SUV was theoretically defined.

RESULTS

Brain SUV decreased exponentially with BG, with similar constants between cerebellum, basal ganglia, and frontal cortex (0.099-0.119 mmol/l(-1)) and similar to values for tumours estimated from the literature. Liver SUV, however, correlated positively with BG. Brain-to-liver SUV ratio therefore showed an inverse correlation with BG, well-fitted with a hyperbolic function (R = 0.83), as theoretically predicted. Brain SUV normalised to BG (nSUV) displayed a nonlinear correlation with BG (R = 0.55); however, as theoretically predicted, brain nSUV/liver SUV showed almost no correlation with BG. Correction of brain SUV using BG raised to an exponential power of 0.099 mmol/l(-1) also eliminated the correlation between brain SUV and BG.

CONCLUSION

Brain SUV continues to correlate with BG after normalisation to BG. Likewise, liver SUV is unsuitable as a reference for tumour FDG uptake. Brain SUV divided by liver SUV, however, shows minimal dependence on BG.

KEY POINTS

• FDG standard uptake value in tumours helps clinicians assess response to treatment. • SUV is influenced by blood glucose; normalisation to blood glucose is recommended. • An alternative approach is to scale tumour SUV to liver SUV. • The brain used as a tumour surrogate shows that neither approach is valid. • Applying both approaches, however, appropriately corrects for blood glucose.

The combined effects of serum lipids, BMI, and fatty liver on 18F-FDG uptake in the liver in a large population from China: an 18F-FDG-PET/CT study

OBJECTIVES

The aim of the study was to investigate the combined effects of serum lipids, BMI, and fatty liver on the liver uptake of fluorine-18 fluorodeoxyglucose ((18)F-FDG).

METHODS

A total of 676 individuals were retrospectively studied. The mean standardized uptake value (SUV) was used to quantify liver (18)F-FDG uptake. Univariate analyses and multivariate regression models identified variables that predicted the mean liver SUV before and after dichotomizing participants into low and high BMI groups.

RESULTS

The mean liver SUV (1.831 ± 0.417) differed significantly among nutritional categories (P = 0.005) and degrees of fatty liver (P < 0.001). An increase in mean liver SUV was noted in individuals with mild and moderate fatty liver compared with normal individuals and in overweight individuals compared with underweight individuals, whereas a downward trend was identified in both individuals with severe fatty liver and those who were obese. BMI had the strongest association with severity of fatty liver (r = 0.443, P < 0.001). Triglyceride, HDL, apolipoprotein-A, age, and BMI were independent variables predicting liver SUV mean in the whole population, whereas fatty liver severity presented as an independent variable only in the low BMI population (P = 0.031).

CONCLUSION

BMI, age, triglyceride, HDL, and apolipoprotein-A were independent variables predicting liver (18)F-FDG uptake. Mild and moderate degree of fatty liver had a positive effect on liver (18)F-FDG uptake, whereas a severe degree of fatty liver negatively affected (18)F-FDG uptake. Attention should be paid to liver metabolism in patients with fatty liver before using liver as the comparator in determining focal (18)F-FDG uptake elsewhere within the abdomen.

Hepatic glucose uptake is increased in association with elevated serum γ-glutamyl transpeptidase and triglyceride

BACKGROUND

Subjects with fatty liver disease (FLD) can show increased hepatic 2-deoxy-2-((18)F)fluoro-D-glucose (FDG) uptake, but the role of hepatic inflammation has not been explored.

AIMS

We investigated whether hepatic inflammatory response, as implicated by elevated serum markers, is associated with increased liver FDG uptake in FLD.

METHODS

Liver sonography and FDG positron emission tomography was performed in 331 asymptomatic men with nonalcoholic FLD (NAFLD), 122 with alcoholic FLD (AFLD), and 349 controls. Mean standard uptake value (SUV) of liver FDG uptake was compared to cardiac risk factors and serum markers of liver injury.

RESULTS

Hepatic FDG mean SUV was increased in NAFLD (2.40 ± 0.25) and AFLD groups (2.44 ± 0.25) compared to controls (2.28 ± 0.26; both P < 0.001). Both FLD groups also had higher serum γ-glutamylranspeptidase (GGT), triglyceride (TG), hepatic transaminases, and LDL. High GGT and TG levels were independent determinants of increased FDG uptake for both FLD groups. Hepatic mean SUV significantly increased with high compared to low GGT for NAFLD (2.48 ± 0.28 vs. 2.37 ± 0.24), AFLD (2.51 ± 0.27 vs. 2.39 ± 0.23), and control groups (2.39 ± 0.22 vs. 2.26 ± 0.26). High TG increased hepatic mean SUV in AFLD and control groups. Furthermore, serum GGT and TG levels significantly correlated to hepatic mean SUV in all three groups.

CONCLUSIONS

Hepatic FDG uptake is closely associated with elevated TG and GGT regardless of the presence of FLD. Thus, inflammation response may play a major role in increased hepatic glucose uptake.

Hepatic steatosis is associated with increased hepatic FDG uptake

OBJECTIVE

The use of liver as a reference tissue for semi-quantification of tumour FDG uptake may not be valid in hepatic steatosis (HS). Previous studies on the relation between liver FDG uptake and HS have been contradictory probably because they ignored blood glucose (BG). Because hepatocyte and blood FDG concentrations equalize, liver FDG uptake parallels BG, which must therefore be considered when studying hepatic FDG uptake. We therefore re-examined the relation between HS and liver uptake taking BG into account.

METHODS

This was a retrospective study of 304 patients undergoing routine PET/CT with imaging 60min post-FDG. Average standard uptake value (SUVave), maximum SUV (SUVmax) and CT density (index of HS) were measured in a liver ROI. Blood pool SUV was based on the left ventricular cavity (SUVLV). Correlations were assessed using least squares fitting of continuous data. Patients were also divided into BG subgroups (<4, 4-5, 5-6, 6-8, 8-10 and 10+mmol/l).

RESULTS

SUVave, SUVmax and SUVLV displayed similar relations with BG. SUVmax/SUVLV, but not SUVave/SUVLV, correlated significantly with BG. SUVmax, but not SUVave, correlated inversely with CT density before and after adjusting for BG. SUVmax/SUVave correlated more strongly with CT density than SUVmax. CT density correlated inversely with SUVmax/SUVLV but positively with SUVave/SUVLV.

CONCLUSIONS

Hepatic SUV is more influenced by BG than by HS. Its relation with BG renders it unsuitable as a reference tissue. Nevertheless, hepatic fat does correlate positively with liver SUV, although this is seen only with SUVmax because SUVave is 'diluted' by hepatic fat.

Hepatic FDG Uptake is not Associated with Hepatic Steatosis but with Visceral Fat Volume in Cancer Screening

PURPOSE

We aimed to evaluate the relation between visceral fat volume and fluorodeoxyglucose (FDG) uptake of the liver measured by maximum or mean standardized uptake value.

METHODS

We retrospectively analyzed 96 consecutive records of positron emission tomography/computed tomography (PET/CT) performed for cancer screening between May 2011 and December 2011. Subjects were divided into 2 groups according to Hounsfield unit (HU) of the liver comparing with that of the spleen. The control group (20 women, 56 men) demonstrating HU of the liver equal or greater than that of the spleen included 76 patients, while the fatty liver group (2 women, 18 men) showing HU of the liver less than that of the spleen included 20 patients. We compared FDG uptake of the liver and visceral fat volume between two groups. We evaluated correlation of hepatic FDG uptake measured by maximum or mean standardized uptake value (SUV) with visceral fat volume and attenuation.

RESULTS

The fatty liver disease group showed higher aspartate aminotransferase (AST)of (24.42 ± 7.22, p = 0.012), alanine aminotransferase (ALT) of (25.16 ± 11.68, p = 0.001), body mass index (BMI) of (24.58 ± 3.29, p = 0.021), and visceral fat volume (3063.53 ± 1561.43, p = 0.011) than the control group. There were no statistically significant differences of mean standardized uptake value of the liver (liver SUVmean) (2.73 ± 0.19, p = 0.723), maximum standardized uptake value of the liver (liver SUVmax) (3.39 ± 0.53, p = 0.8248) and liver SUVmean/spleen SUVmean (1.13 ± 0.10, p = 0.081) between the two groups. Strong correlations were shown between liver SUVmean and BMI (r = 0.609, p < 0.001) and between liver SUVmean and visceral fat volume (r = 0.457, p < 0.001). Liver SUVmax was also strongly correlated with BMI (r = 0.622, p = 0.001) and visceral fat volume (r = 0.547, p < 0.001). There was no significant association of mean attenuation value of the liver (liver HUmean) with liver SUVmean (r = -0.003, p = 0.979) or liver SUVmax (r = -0.120, p = 0.244).

CONCLUSION

Hepatic FDG uptake quantified as SUVmean or SUVmax is not correlated with hepatic steatosis but with visceral fat volume in cancer screening.

[Variations of the hepatic SUV in relation to the body mass index in whole body PET-CT studies]

OBJECTIVE

To evaluate SUV changes in the liver in relation to body mass index (BMI) of patients who undergo whole body PET-CT scans.

MATERIAL AND METHODS

A retrospective study was performed. The variables studied were injected dose of (18F)FDG (mCi), age (years), blood glucose level (mg/dL), height (cm) and weight (kg). BMI was calculated and the SUV mean value was expressed according to gender and BMI. A linear regression analysis was applied to identify the independent variables that best predict the SUV value.

RESULTS

Six hundred and three patients were studied (305 women, 298 men; mean age: 54.9±15.2 years old). Mean SUV measurement was significantly higher in males than females and increased significantly both in male and female patients who were overweight and even more in obese patients. The independent variables that best predicted the SUV value were gender, age, and BMI. In those patients having similar characteristics related to the analyzed variables, the SUV value increased by 0.002 for each increase in one year, and by 0.066 per unit increase in the BMI value.

CONCLUSIONS

Hepatic uptake of (18F)FDG increases according to the patient's BMI. The independent variables that best predict the hepatic SUV value are age and sex of patients. Our findings show that the practice of using the physiological hepatic metabolic activity level as a reference regarding questionable deposits elsewhere in the abdomen and pelvis is not useful, at least in male patients with overweightness and obesity.