Impact of age on FDG uptake in the liver on PET scan

Influence of Covariates on 18F-FDG PET/CT Diagnostic Accuracy for Liver Metastasis

(1) Background: 18F-FDG PET/CT diagnostic accuracy for liver metastasis (LM) could be influenced by technical parameters, lesion size, and the patient's covariates. This retrospective study aimed to evaluate these covariates' impact on PET/CT sensitivity. (2) Methods: Consecutive patients with suspected LMs who underwent 18F-FDG PET/CT scans were included. PET/CT scans were interpreted visually. The reference standard integrated histopathological and imaging follow-up. Logistic regression modeling and average marginal predictions were used to calculate per-lesion diagnostic performance measures with cluster robust 95% confidence intervals and to assess the covariates' impact on PET/CT sensitivity. (3) Results: We included 192 patients with 330 lesions. 18F-FDG PET/CT exhibited a per-lesion sensitivity, specificity, positive predictive value, and negative predictive value of 86%, 79%, 91%, and 69%, respectively. In multivariate analysis, TOF PET/CT exhibited a higher sensitivity than non-TOF PET/CT (91% vs. 78%, p = 0.02). Sensitivity was reduced for lesions < 10 mm compared to larger lesions (56% vs. 93%, p < 0.001). A 5 kg/m2 increase in BMI led to an average 5% sensitivity reduction (p < 0.001). Age, sex, blood glucose level below 11 mmol/L, and liver density did not significantly impact sensitivity (p > 0.05). (4) Conclusions: 18F-FDG PET/CT sensitivity might be reduced with non-TOF PET, lesions < 10 mm, and higher BMI.

Relating Macroscopic PET Radiomics Features to Microscopic Tumor Phenotypes Using a Stochastic Mathematical Model of Cellular Metabolism and Proliferation

Cancers can manifest large variations in tumor phenotypes due to genetic and microenvironmental factors, which has motivated the development of quantitative radiomics-based image analysis with the aim to robustly classify tumor phenotypes in vivo. Positron emission tomography (PET) imaging can be particularly helpful in elucidating the metabolic profiles of tumors. However, the relatively low resolution, high noise, and limited PET data availability make it difficult to study the relationship between the microenvironment properties and metabolic tumor phenotype as seen on the images. Most of previously proposed digital PET phantoms of tumors are static, have an over-simplified morphology, and lack the link to cellular biology that ultimately governs the tumor evolution. In this work, we propose a novel method to investigate the relationship between microscopic tumor parameters and PET image characteristics based on the computational simulation of tumor growth. We use a hybrid, multiscale, stochastic mathematical model of cellular metabolism and proliferation to generate simulated cross-sections of tumors in vascularized normal tissue on a microscopic level. The generated longitudinal tumor growth sequences are converted to PET images with realistic resolution and noise. By changing the biological parameters of the model, such as the blood vessel density and conditions for necrosis, distinct tumor phenotypes can be obtained. The simulated cellular maps were compared to real histology slides of SiHa and WiDr xenografts imaged with Hoechst 33342 and pimonidazole. As an example application of the proposed method, we simulated six tumor phenotypes that contain various amounts of hypoxic and necrotic regions induced by a lack of oxygen and glucose, including phenotypes that are distinct on the microscopic level but visually similar in PET images. We computed 22 standardized Haralick texture features for each phenotype, and identified the features that could best discriminate the phenotypes with varying image noise levels. We demonstrated that "cluster shade" and "difference entropy" are the most effective and noise-resilient features for microscopic phenotype discrimination. Longitudinal analysis of the simulated tumor growth showed that radiomics analysis can be beneficial even in small lesions with a diameter of 3.5-4 resolution units, corresponding to 8.7-10.0 mm in modern PET scanners. Certain radiomics features were shown to change non-monotonically with tumor growth, which has implications for feature selection for tracking disease progression and therapy response.

Potential of Liver Serum Enzymes and SUVmax in Primary Tumors as Predictive Biomarkers With Correlational Evidence

Introduction Cancer exerts a substantial influence on the body's metabolism through varied mechanisms, instigating a metabolic reprogramming that maintains the unchecked growth and survival of cancer cells, consequently perturbing diverse metabolic parameters. The introduction of positron emission tomography-computed tomography (PET/CT), delivering detailed insights into both metabolic and morphological aspects, has brought about a revolutionary shift in modern cancer detection. Exploring the potential connection between PET-CT metabolic features and the metabolic parameters of liver enzymes in an individual can unveil novel avenues for cancer diagnosis and prognosis. Materials and methods This study conducted a retrospective analysis of patient records from our institution, covering the period from January 2021 to September 2023, focusing on individuals with various malignancies. The data included information on gender, age, clinical history, and liver serum parameters, which were compiled into tables. Additionally, inflammatory indicators such as ALT (alanine transaminase), ALP (alkaline phosphatase), total protein (TP), ALT/AST ratio, and SUVmax were collected and plotted. The study used Pearson correlation analysis to assess the relationship between each inflammatory variable and SUV (max) as determined by PET-CT. Results In breast cancer, there was a statistically significant positive correlation (R2=0.0651) between serum ALP levels and SUVmax as determined by regression analysis. Hodgkin lymphoma, on the other hand, showed a statistically significant negative correlation between the ALT-to-AST ratio (ALT/AST) and SUVmax (r = -0.45, R2 = 0.204). In non-Hodgkin lymphoma patients, total protein (TP) was negatively correlated with SUVmax (R2=-0.081, r= -0.28), while in lung cancer patients, there was a significant positive correlation with regression correlation coefficients (R2 = 0.026, 0.024, 0.024, and 0.018 for ALT/AST, TP, ALP, albumin, and ALT, respectively). Conclusion Aligning with these results, it can be a recent addition to acknowledge that both the tumor metabolic parameter (SUVmax) and the levels of liver serum enzymes exhibit a potential for predicting patient prognosis in various cancers.

Patient factors affecting 18F FDG uptake in children

PURPOSE

To characterize physiologic uptake of 18F FDG in children undergoing PET/CT as a step to informing efforts to optimize FDG PET image quality in children.

METHODS

This retrospective study included 193 clinically indicated 18F FDG PET/CT examinations from 139 patients. 3D spherical regions of interest (ROIs) in the liver and in the thigh muscle (an area of uniform low-level uptake) were used to measure counts and mean standardized uptake value by body weight (SUVmean-bw). Counts, SUVs, and liver signal to noise ratio (SNR) were assessed for associations with patient-specific predictor variables using Pearson correlation and multivariable linear regression.

RESULTS

Mean patient age was 11.0 ± 5.4 (SD) years, mean liver SUVmean-bw was 1.77 ± 0.60 and mean liver counts was 5387 ± 1875 Bq/mL. On univariable analysis liver SUVmean-bw and liver counts were strongly correlated with weight (r = 0.87, p < 0.0001), age (r = 0.75, p < 0.0001) and total injected activity (r = 0.85, p < 0.0001). Mean thigh counts were significantly associated only with injected activity/kilogram (r = 0.37, p < 0.0001). On multivariable analysis, body weight and age (which is collinear with body weight) were the only significant independent predictors (p < 0.0001). Liver SNR was moderately associated with all predictors apart from injected activity per kilogram (r = 0.09, p = 0.23).

CONCLUSION

Liver counts on 18F FDG PET/CT have a significant positive association with age and body weight. However, liver SNR has no significant association with injected activity per kilogram suggesting that increasing dose per kilogram may not improve image quality in young children.

Analysis of redox status and HDL subclasses in patients with lymphoma and the associations with FDG-PET/CT findings

Newer research points to alterations in the plasma redox status and the HDL subclass distributions in cancer. We aimed to assess the redox status and the HDL subclass distributions, lipids, and inflammatory markers in lymphoma patients in order to determine whether they were correlated with changes in FDG-PET/CT scans. At the beginning of this study, redox status, HDL subclasses, lipids, and inflammation biomarkers were determined in 58 patients with lymphoma (Hodgkin lymphoma, n=11 and non-Hodgkin lymphoma, n=47), and these same measurements were reassessed during their ensuing treatment (in 25 patients). Initially, the total oxidation status (TOS), the prooxidant-antioxidant balance (PAB), the OS index (OSI), the total protein sulfhydryl groups (SH-groups), and the advanced oxidation protein products (AOPP) were significantly higher in lymphoma patients as compared to healthy subjects, but the total antioxidant status (TAS) was significantly reduced. The PAB had a strong correlation with the CRP and interleukin-6 (rho=0.726, p<0.001; rho=0.386, p=0.003). The correlations between these parameters and the maximum standardized uptake values (SUVmax) were: PAB, rho=0.335 and p=0.010; SH-groups, rho=0.265 and p=0.044; CRP, rho=0.391 and p=0.002; HDL3b, rho=0.283 and p=0.031; HDL2b, rho= -0.294 and p=0.025; and HDL size, rho= -0.295 and p=0.024. The reductions in SUVmax between two follow-up points were associated with increases in the OSI, TOS, and SH-groups, as well as a reduction in the PAB and TAS. In conclusion, the redox parameters in patients with lymphoma were consistent with FDG-PET/CT findings. Targeting the redox status parameters and the HDL subclasses could be potential strategies in the molecular fight against lymphoma.

Reproducibility of [18F]FDG PET/CT liver SUV as reference or normalisation factor

INTRODUCTION

Although visual and quantitative assessments of [18F]FDG PET/CT studies typically rely on liver uptake value as a reference or normalisation factor, consensus or consistency in measuring [18F]FDG uptake is lacking. Therefore, we evaluate the variation of several liver standardised uptake value (SUV) measurements in lymphoma [18F]FDG PET/CT studies using different uptake metrics.

METHODS

PET/CT scans from 34 lymphoma patients were used to calculate SUVmaxliver, SUVpeakliver and SUVmeanliver as a function of (1) volume-of-interest (VOI) size, (2) location, (3) imaging time point and (4) as a function of total metabolic tumour volume (MTV). The impact of reconstruction protocol on liver uptake is studied on 15 baseline lymphoma patient scans. The effect of noise on liver SUV was assessed using full and 25% count images of 15 lymphoma scans.

RESULTS

Generally, SUVmaxliver and SUVpeakliver were 38% and 16% higher compared to SUVmeanliver. SUVmaxliver and SUVpeakliver increased up to 31% and 15% with VOI size while SUVmeanliver remained unchanged with the lowest variability for the largest VOI size. Liver uptake metrics were not affected by VOI location. Compared to baseline, liver uptake metrics were 15-18% and 9-18% higher at interim and EoT PET, respectively. SUVliver decreased with larger total MTVs. SUVmaxliver and SUVpeakliver were affected by reconstruction protocol up to 62%. SUVmax and SUVpeak moved 22% and 11% upward between full and 25% count images.

CONCLUSION

SUVmeanliver was most robust against VOI size, location, reconstruction protocol and image noise level, and is thus the most reproducible metric for liver uptake. The commonly recommended 3 cm diameter spherical VOI-based SUVmeanliver values were only slightly more variable than those seen with larger VOI sizes and are sufficient for SUVmeanliver measurements in future studies.

TRIAL REGISTRATION

EudraCT: 2006-005,174-42, 01-08-2008.

Improvement of liver metabolic activity in people with advanced HIV after antiretroviral therapy initiation

OBJECTIVE

Evaluating hepatic metabolic changes in people with HIV (PWH) with advanced disease, before and after antiretroviral therapy (ART) initiation, using [ 18 F]-fluorodeoxyglucose (FDG) PET-computed tomography (PET/CT). FDG PET/CT noninvasively quantifies glucose metabolism in organs.

DESIGN/METHODS

Forty-eight viremic PWH (CD4 + cell counts <100 cells/μl) underwent FDG PET/CT at baseline and approximately 6 weeks after ART initiation (short-term). Twenty-seven PWH participants underwent follow-up scans 2 years after treatment (long-term). FDG PET/CT scans from 20 healthy controls were used for comparison. Liver FDG uptake was quantified from the PET/CT scans. Imaging findings as well as clinical, laboratory, and immune markers were compared longitudinally and cross-sectionally to healthy controls.

RESULTS

Liver FDG uptake was lower at baseline and short-term in PWH compared with controls ( P  < 0.0001). At the long-term scan, liver FDG uptake of PWH increased relative to baseline and short-term ( P  = 0.0083 and 0.0052) but remained lower than controls' values ( P  = 0.004). Changes in FDG uptake correlated negatively with levels of glucagon, myeloperoxidase, sCD14, and MCP-1 and positively with markers of recovery (BMI, albumin, and CD4 + cell counts) ( P  < 0.01). In multivariable analyses of PWH values across timepoints, BMI and glucagon were the best set of predictors for liver FDG uptake ( P  < 0.0001).

CONCLUSION

Using FDG PET/CT, we found decreased liver glucose metabolism in PWH that could reflect hepatocytes/lymphocytes/myeloid cell loss and metabolic dysfunction because of inflammation. Although long-term ART seems to reverse many hepatic abnormalities, residual liver injury may still exist within 2 years of treatment initiation, especially in PWH who present with low nadir CD4 + cell counts.

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.

Gender-specific liver aging and magnetic resonance imaging

The number of imaging studies performed on elderly individuals will increase in the next several decades. It is important to understand normal age-related changes in the structural and functional imaging appearance of the liver. This article highlights a number of liver aging aspects which are particularly relevant to magnetic resonance imaging (MRI). Physiology of aging liver is associated with a reduction in size, in perfusion, and in function. Pulsed echo-Doppler showed substantial reduction of portal flow in elderly subjects, particularly those after the age of 75 years old. An MRI biomarker diffusion derived vessel density (DDVD) demonstrated that liver microperfusion volume in healthy females starts to decrease even before menopause age. Liver fat content and iron content increase with aging, and the change is more substantial in women after menopause. Adult men have higher liver fat and iron contents than women from the start and change less during aging. Nonalcoholic fatty liver disease (NAFLD) is very common among assumed healthy subjects. There is a male predominance of NAFLD from the paediatric population up to fifth decade of life in adults. After the age of 60 years, women overtake their male counterparts in prevalence of NAFLD. Higher liver fat leads to decreased apparent diffusion coefficient (ADC) and intravoxel incoherent motion (IVIM)-D_slow measures. Higher liver iron content shortens T2* measure, lower ADC and IVIM-D_slow measures, increases imaging noises and decreases liver visibility. Young women have high liver T1rho value and then decrease substantially, while liver T1rho in men remains relatively unchanged with aging. In positron emission tomography (PET) studies, aging is associated with an increase of both liver fluorine-18-fluorodeoxyglucose maximum standard uptake and mean standard uptake values.

PET/CT Variants and Pitfalls in Liver, Biliary Tract, Gallbladder and Pancreas

A wide variety of pathological anomalies may occur in the liver, biliary system, and pancreas. It is a necessity to use many different imaging techniques in order to distinguish such varied pathologies, especially those from malignant processes. Positron Emission Tomography/Computed Tomography (PET/CT) is an imaging method that has proven its diagnostic value in oncology and can be used for different clinical purposes. Fluoro-18 fluoro-2-deoxy-D-glucose has a wide range of uses as a dominant radiopharmaceutical in routine molecular imaging, however, molecular imaging has started to play a more important role in personalized cancer treatment in recent years with new Fluoro-18 and Gallium-68 labeled tracers. Although molecular imaging has a strong diagnostic effect, the surprises and pitfalls of molecular imaging can lead us to unexpected and misleading results. Prior to PET/CT analysis and reporting, information about possible technical and physiological pitfalls, normal histological features of tissues, inflammatory pathologies, specific clinical features of the case, treatment-related complications and past treatments should be evaluated in advance to avoid misinterpretation. In this review, the physiological and pathophysiological variants as well as pitfalls encountered in PET/CT imaging of the liver, biliary tract, gallbladder, and pancreas will be examined. Other benign and malignant pathologies that have been reported to date and that have led to incorrect evaluation will be listed. It is expected that the devices, software, and artificial intelligence applications that will be developed in the near future will enable much more effective and faster imaging that will reduce the potential causes of error. However, as a result of the dynamic and evolving structure of the information obtained by molecular imaging, the inclusion of the newly developed radiopharmaceuticals in routine practice will continue to carry new potentials as well as new troubles. Although molecular imaging will be the flagship of diagnostic oncology in the 21st century, the correct analysis and interpretation by the physician will continue to form the basis of achieving optimal performance.

A reduced physiological 18F-fluorodeoxyglucose uptake in the brain and liver caused by malignant lymphoma being deprived of the tracer

Purpose : To investigate whether or not the physiological brain and liver FDG uptake are decreased in patients with highly accelerated glycolysis lesions. Methods : We retrospectively analyzed 51 patients with malignant lymphoma. We compared the FDG uptake in the brain and liver of the patients with that in a control group. In 24 patients with a complete response (CR) or partial response (PR) to treatment, we compared the brain and liver uptake before and after treatment. Results : The maximum standardized uptake value (SUVmax) and total glycolytic volume (TGV) of the brain as well as the SUVmax and mean standardized uptake value (SUVmean) of the liver in malignant lymphoma patients were 13.1 ± 2.3, 7386.3 ± 1918.4, 3.2 ± 0.5, and 2.3 ± 0.4, respectively ; in the control group, these values were 14.9 ± 2.4, 8566.2 ± 1659.5, 3.4 ± 0.4, and 2.5 ± 0.3, respectively. The SUVmax and TGV of the brain and the SUVmean of the liver in malignant lymphoma patients were significantly lower than the control group. The SUVmax and TGV of the brain after treatment were significantly higher than before treatment. Both the SUVmax and SUVmean of liver after treatment were higher than before treatment, but not significant. Conclusion : A decreased physiological brain and liver FDG uptake is caused by highly accelerated lesion glycolysis. J. Med. Invest. 68 : 181-185, February, 2021.

Age-related changes of standardized uptake values in the blood pool and liver: a decade-long retrospective study of the outcomes of 2,526 subjects

Background

Background activity on fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is often used as a reference to assess a patient's response to tumor treatment. To produce a suitable background activity reference, we examined the variations in standardized uptake values (SUVs) in the blood pool and liver of a large multi-aged population.

Methods

A total of 2,526 subjects underwent ¹⁸F-FDG PET/CT examinations and were divided into 12 age groups. Pearson's partial correlation and multivariate regression analyses were performed to assess the associations between individual factors and SUVs of the blood pool and liver and to identify the factor that most influenced the SUVs. The mean SUVs across the age groups were also determined.

Results

Positive correlations were found between individual factors and SUVs. Age appeared to be the most important predictor of SUVs and was significantly associated with the blood pool SUV_max (ß=0.466, P=0.000), blood pool SUV_mean (ß=0.393, P=0.000), liver SUV_max (ß=0.347, P=0.000), and liver SUV_mean (ß=0.354, P=0.000). Blood pool and liver SUVs rose rapidly until the age of 20 and then showed a slow upward trend without reaching a plateau.

Conclusions

Age is an important factor that influences variations in the blood pool and liver SUVs. Our study clarified this understanding of age-related variations in SUVs and provided a normal range of blood pool and liver SUVs that may aid clinicians in evaluating tumors with greater accuracy.

Diffusely Decreased Liver Uptake on FDG PET and Cancer-Associated Cachexia With Reduced Survival

OBJECTIVES

We investigated clinical characteristics of patients with extremely increased or decreased physiologic F-FDG uptake of the liver and their prognosis.

METHODS

One thousand four hundred eighty-seven PET/CT scans of patients with known or suspected malignancy were retrospectively analyzed. A spherical volume of interest (3 cm in diameter) was set on the right lobe of the liver to calculate the SUVmean. Scans with extremely high (SUVmean >97.5th percentile) and low (SUVmean <2.5th percentile) FDG uptake in the liver were evaluated. Physical and laboratory data among a control group (n = 30), the extremely high liver uptake group (HG, n = 36), and the extremely low liver uptake group (LG, n = 36) were compared. Overall survival (OS) of the 3 groups was also compared.

RESULTS

Body weight and body mass index in the HG (SUVmean ≥3.04) were significantly higher than those in the control group. The LG cases (SUVmean ≤1.78) had anemia, impaired liver function, and systemic inflammation. They were also in a poor nutritional state. The characteristics of LG cases had many things in common with those of cachectic patients. Indeed, 36.1% of LG cases met the diagnostic criteria for cachexia. Moreover, in LG cases with viable and/or recurrent malignant lesions on FDG PET, the proportion of cachexia increased by 52.6%. The OS of LG cases (median, 33 months) was significantly worse than that of controls and HG cases.

CONCLUSIONS

Our data indicate that cancer patients with extremely decreased liver FDG uptake were likely to have cancer cachexia and a lower OS.

18F-FDG uptake in the normal appendix in adults: PET/CT evaluation

OBJECTIVE

This study aimed to determine the level of ¹⁸F fluorodeoxyglucose (¹⁸F-FDG) activity in the normal adult appendix using positron emission tomography/computed tomography (PET/CT).

MATERIALS AND METHODS

We performed a retrospective review of PET/CT images using ¹⁸F-FDG in 563 consecutive asymptomatic adult patients without appendiceal pathology. We excluded 257 patients for an undetected or obscured appendix and three patients for appendicitis found on CT imaging. FDG uptake in the appendix was qualitatively and quantitatively assessed. The maximum standardized uptake value (SUV_max) was calculated for quantitative analysis with SUV_max of the normal liver for comparison. A total of 303 patients (200 males, 103 females, mean age of 66 years) were included in this study. Medical charts and histories were evaluated for patients who showed positive FDG accumulation. Pearson's correlations between appendiceal SUV_max and age, body mass index, and blood glucose levels were analyzed.

RESULTS

The mean appendiceal SUV_max was 1.14 (range 0.52-5.12) with an appendix-to-liver SUV_max ratio of 0.34 (range 0.06-1.28). Three patients qualitatively showed a positive FDG accumulation with appendiceal SUV_max greater than 3.00. There were no correlations between appendiceal SUV_max and age, body mass index, or blood glucose levels.

CONCLUSIONS

FDG in the normal adult appendix shows a low activity level and is lower compared with normal liver. However, the normal appendix can rarely show high FDG accumulation. In such cases, differentiation from appendiceal pathology solely by PET/CT images would be difficult.

In vivo confirmation of altered hepatic glucose metabolism in patients with liver fibrosis/cirrhosis by 18F-FDG PET/CT

OBJECTIVE

The aim of this study was to assess the value of ¹⁸F-FDG PET/CT for quantitative assessment of hepatic metabolism in patients with different stages of liver fibrosis/cirrhosis.

MATERIALS AND METHODS

¹⁸F-FDG PET/CT scans of 37 patients either with or without liver fibrosis/cirrhosis, classified according to the METAVIR score (F0-F4) obtained from histopathological analysis of liver specimen, were analyzed retrospectively and classified as follows: no liver fibrosis (F0, n = 6), mild liver fibrosis (F1, n = 11), advanced liver fibrosis (F2, n = 6), severe liver fibrosis (F3, n = 5), and liver cirrhosis (F4, n = 11). The liver-to-blood ratio (LBR, scan time corrected for a reference time of 75 min) was compared between patient groups.

RESULTS

Patients with liver fibrosis or cirrhosis (≥ F1; LBR 1.53 ± 0.35) showed a significant higher LBR than patients with normal liver parenchyma (F0, 1.08 ± 0.23; P = 0.004). In direct comparison, LBR increased up to the advanced stage of liver fibrosis (F2; 2.00 ± 0.40) and decreased until liver cirrhosis is reached (F4, 1.32 ± 0.14).

CONCLUSION

Functional changes in liver parenchyma during liver fibrosis/cirrhosis affect hepatic glucose metabolism and significantly differ between stages of liver fibrosis/cirrhosis, classified according to the METAVIR scoring system, as demonstrated by LBR quantification by ¹⁸F-FDG PET/CT.

Therapeutic response to prednisone in relation to age in polymyalgia rheumatica: a comparison study

The aim of this study was to evaluate the impact of age on the therapeutic response to prednisone. This was a retrospective, monocentric study. We included patients diagnosed with PMR, according to ACR 2012 criteria. Patients were classified into two groups according to age (above or below 60 years old). We registered demographic, clinical, biological, imaging data, and therapeutic response profile. Local inflammation was evaluated at baseline with PET/CT imaging score. The treatment was standardised. The main endpoint was a corticosteroid dependence defined by the recurrence of PMR symptoms and/or the increase of CRP at two times. We included 14 patients younger than 60 years old (mean age 54 ± 0.8) and 28 patients older than 60 (mean age 75.8 ± 1.5). The "young PMR" group was mainly male (60 vs 27%; p < 0.05). Both groups were similar regarding morning stiffness, disease duration, WBC count, and CRP. The intensity of FDG uptake was lower (score of 16.9 ± 1.7 vs 26.5 ± 3.0; p < 0.05), there were more dependence on corticosteroids (60 vs 20%; p < 0.05) and methotrexate was more necessary (35 vs 6.5%; p < 0.05) in "young PMR" group. Young patients diagnosed with PMR are mostly men, are more dependent on corticosteroids, and have a lower PET-CT score at baseline in comparison to elderly patients diagnosed with PMR.

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%.

Concurrent Low Brain and High Liver Uptake on FDG PET Are Associated with Cardiovascular Risk Factors

Objective

Concurrent low brain and high liver uptake are sometimes observed on fluorine-18-labeled fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). We investigated the potential clinical significance of this uptake pattern related to metabolic syndrome (MS).

Materials and Methods

We retrospectively reviewed data from 264 consecutive males who had undergone general health check-ups, including FDG PET/CT scans. After an overnight fast, the men had their peripheral blood drawn and the levels of various laboratory parameters measured; an FDG PET/CT scan was performed on the same day. We measured the maximum standardized uptake values of the brain and liver from regions of interest manually placed over the frontal cortex at the level of the centrum semiovale and the right lobe of the liver parenchyma, respectively.

Results

Fasting blood glucose (FBG; odds ratio [OR] = 1.063, p < 0.001) and glycated hemoglobin (HbA1c; OR = 3.634, p = 0.010) were the strongest predictive factors for low brain FDG uptake, whereas waist circumference (OR = 1.200, p < 0.001) and γ-glutamyl transpeptidase (OR = 1.012, p = 0.001) were the strongest predictive factors for high liver uptake. Eleven subjects (4.2%) showed concurrent low brain and high liver FDG uptake, and all but one of these subjects (90.9%) had MS. Systolic blood pressure, waist circumference, FBG, triglyceride, alanine aminotransferase, insulin resistance (measured by homeostasis model assessment), insulin, HbA1c, and body mass index were higher in subjects with this FDG uptake pattern than in those without (all, p < 0.001).

Conclusion

Concurrent low brain and high liver FDG uptake were closely associated with MS. Moreover, subjects with this pattern had higher values for various cardiovascular risk factors than did those without.

Optimizing 18F-FDG Uptake Time Before Imaging Improves the Accuracy of PET/CT in Liver Lesions

(18)F-FDG PET/CT has emerged as one of the fastest-growing imaging modalities. A shorter protocol results in a lower target-to-background ratio, which can increase the challenge of identifying mildly (18)F-FDG-avid lesions and differentiating inflammatory or physiologic activity from malignant activity. The purpose of this study was to determine the delay between radiotracer injection and imaging that optimizes target-to-background ratio while maintaining counts high enough to ensure scan sensitivity.

METHODS

The study included 140 patients (66 male and 74 female; age range, 42-95 y) with suspected hepatic lesions as seen on an (18)F-FDG PET scan. SUV was determined as region-of-interest activity/(dose/total body weight).

RESULTS

The mean injected dose was 610 ± 66.6 MBq (16.5 ±1.8 mCi), with a mean glucose level of 107 ± 26.6 mg/dL (standardized to 90 mg/dL). The uptake time before imaging ranged from 61 to 158 min, with a mean of 108.8 ± 24.8 min. The P values for the correlation of SUV to time were 0.004, 0.003, and 0.0001 for malignant lesions, benign lesions, and background hepatic tissue, respectively.

CONCLUSION

An approximately 90-min time window from (18)F-FDG injection to PET imaging would significantly improve target-to-background ratio and, thus, quantitation and visual interpretation. This benefit outweighs the minimal loss in patient throughput.

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.

Liver metabolic activity changes over time with neoadjuvant therapy in locally advanced rectal cancer

OBJECTIVE

The aim of this study was to evaluate, using PET/computed tomography (CT), changes in liver metabolic activity in patients with locally advanced rectal cancer (LARC) after neoadjuvant chemoradiotherapy (CRT).

PATIENTS AND METHODS

A total of 29 biopsy-proven LARC patients between 2009 and 2012 were studied. Liver standardized uptake values (SUVs) and SUVs adjusted for lean body mass (SULs) were obtained from PET/CT images obtained at 1 h (early) and 2 h (late) after (18)F-fluorodeoxyglucose ((18)F-FDG) administration both before and after neoadjuvant CRT. Age, sex, BMI, lean body mass, blood glucose level, and (18)F-FDG dose, which can influence liver SUVs and SULs, were also analyzed.

RESULTS

Fourteen (48%) men and 15 (52%) women with a mean age of 62±11 years (range 34-80 years) were included in the study. The mean SUVs and SULs were significantly decreased in the late scans. Sex was significantly correlated with the mean liver SUV in early and late scans. The mean SUV differed significantly between male and female patients in early and late images (P<0.05). In a multivariate stepwise regression analysis, only liver SUVs (maximum and mean) were significantly associated with BMI before and after therapy. SUVs were significantly higher in the high (≥25) BMI group after but not before therapy. Mean SUL was not influenced by BMI.

CONCLUSION

Liver (18)F-FDG uptake is consistent before and after neoadjuvant CRT therapy in patients with LARC. When assessing response to therapy and using liver metabolic activity to indicate background activity, BMI should be considered as it can influence liver metabolic activity.

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.

Differentiation between Malignant and Benign Solitary Lesions in the Liver with (18)FDG PET/CT: Accuracy of Age-related Diagnostic Standard

OBJECTIVE

This study was to determine the reliability of age-stratified diagnostic index in differential diagnosis of malignant and benign solitary lesions in the liver using fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography ((18)FDG PET/CT).

METHODS

The enrolled 272 patients with solitary lesions in the liver were divided into three age groups, younger group (under 50 years), middle-aged group (50-69 years), and elderly group (70 years and above). Patients' ages were compared, and the optimal cut-offs of the standard uptake value (SUV) ratio (tumor-to-non-tumor ratio of the SUV), as well as areas under the curves (AUC), were evaluated in terms of malignant and benign lesions in each age group by using receiver operating characteristic (ROC) analysis. Based on optimal cut-offs, the sensitivity, specificity, accuracy were calculated, and the diagnostic accordance rate was compared between each age group and all patients, supported by (18)FDG PET/CT imaging data.

RESULTS

There was a significant age difference between the malignant and benign groups (t=3.905 p=0.0001). ROC analysis showed that the optimal cut-off value in all patients, younger group, middle-aged group and elderly group was 1.25, 1.17, 1.45 and 1.25 for SUVratio, and 0.856, 0.962, 0.650, 0.973 for AUC. The chi-square test proved that diagnostic accordance rate of (18)FDG PET/CT in younger group and elderly group were superior to that in all patients (χ(2)=13.352, P=0.0003) and (χ(2)=8.494, P=0.0036). Conversely, overall diagnostic accordance rate in all patient group was higher than that in middle-aged group (χ(2)=9.057, P=0.0026). Representative (18)FDG PET/CT imaging findings are demonstrated.

CONCLUSION

This study indicates that diagnostic optimal cut-offs of SUVratio of liver solitary lesions of (18)FDG PET/CT were different in each age group. In addition, the diagnostic performance of SUVratio was better in younger and elderly groups than that in all patients, and was poorer in middle-aged group than that in all patients. Therefore, age difference appears to be one of the important factors for discriminating malignant liver lesions from benign ones using (18) FDG PET/CT.

PET/CT mediastinal and liver FDG uptake: effects of biological and procedural factors

INTRODUCTION

To establish the effects of biological and procedural factors on mediastinal and liver [(18) F]-fluorodeoxyglucose (FDG) uptake in oncological FDG positron emission tomography/computed tomography (PET/CT).

METHODS

This retrospective study included 557 patients who had a baseline FDG PET/CT scan in 2008 and 2009. Mediastinal and liver standardised uptake values mean normalised to lean body mass (SUVlbm mean) were measured in each patient. Univariate and multivariate regression models were established. Study population was then dichotomised into low and high body mass index (BMI) groups, and linear regression models were established for the effects of age, incubation period and blood glucose levels.

RESULTS

BMI had the highest adjusted effect (standardised beta coefficient, b = 0.43) (P < 0.001) and partial correlation, adjusting for covariates included in the final model (r = 0.45; P < 0.001) on mediastinal FDG uptake. Partial correlations (r) were 0.22 for age, -0.17 for male gender, -0.25 for incubation period and 0.14 for blood glucose (P < 0.001). The linear regression models showed significant differences in mediastinal FDG uptake between the low and high BMI groups and the effects of age, incubation period and basal blood glucose levels (P < 0.001). Similar results were observed for liver FDG uptake except the partial correlation for incubation period was r = -0.09 (P = 0.02).

CONCLUSION

BMI has the highest effect and correlation on mediastinal and liver FDG uptake. FDG uptake time has a greater effect on mediastinal than liver SUVlbm mean.

Fluorodeoxyglucose positron emission tomography response and normal tissue regeneration after stereotactic body radiotherapy to liver metastases

PURPOSE

To characterize changes in standardized uptake value (SUV) in positron emission tomography (PET) scans and determine the pace of normal tissue regeneration after stereotactic body radiation therapy (SBRT) for solid tumor liver metastases.

METHODS AND MATERIALS

We reviewed records of patients with liver metastases treated with SBRT to ≥40 Gy in 3-5 fractions. Evaluable patients had pretreatment PET and ≥1 post-treatment PET. Each PET/CT scan was fused to the planning computed tomography (CT) scan. The maximum SUV (SUV(max)) for each lesion and the total liver volume were measured on each PET/CT scan. Maximum SUV levels before and after SBRT were recorded.

RESULTS

Twenty-seven patients with 35 treated liver lesions were studied. The median follow-up was 15.7 months (range, 1.5-38.4 mo), with 5 PET scans per patient (range, 2-14). Exponential decay curve fitting (r=0.97) showed that SUV(max) declined to a plateau of 3.1 for controlled lesions at 5 months after SBRT. The estimated SUV(max) decay half-time was 2.0 months. The SUV(max) in controlled lesions fluctuated up to 4.2 during follow-up and later declined; this level is close to 2 standard deviations above the mean normal liver SUV(max) (4.01). A failure cutoff of SUV(max) ≥6 is twice the calculated plateau SUV(max) of controlled lesions. Parenchymal liver volume decreased by 20% at 3-6 months and regenerated to a new baseline level approximately 10% below the pretreatment level at 12 months.

CONCLUSIONS

Maximum SUV decreases over the first months after SBRT to plateau at 3.1, similar to the median SUV(max) of normal livers. Transient moderate increases in SUV(max) may be observed after SBRT. We propose a cutoff SUV(max) ≥6, twice the baseline normal liver SUV(max), to score local failure by PET criteria. Post-SBRT values between 4 and 6 would be suspicious for local tumor persistence or recurrence. The volume of normal liver reached nadir 3-6 months after SBRT and regenerated within the next 6 months.

[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.

Measuring diffuse metabolic activity on FDG-PET/CT: new method for evaluating Langerhans cell histiocytosis activity in pulmonary parenchyma

INTRODUCTION

Pulmonary Langerhans cell histiocytosis (PLCH) is a rare cause of interstitial lung disease characterized by formation of nodules in the active phase of the disease that evolve into nonactive cystic lesions later on. To evaluate PLCH activity in patients, we developed a new method for measuring diffuse metabolic activity on fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) using a lung-to-liver activity ratio.

MATERIAL AND METHODS

We retrospectively studied a series of 4 FDG-PET and 23 FDG-PET/CT scans from 7 patients with PLCH and analyzed a sample of 100 randomly chosen FDG-PET/CT studies free from any known lung or hepatic diseases. Maximum standardized uptake value (SUVmax) in a spherical volume (6-8 cm in diameter) in the right lung was put into relation with SUVmax in a spherical volume (9-10 cm in diameter) in the reference liver parenchyma to set up the SUVmaxPULMO/SUVmaxHEPAR index. The index values were compared to the disease course in each patient.

RESULTS

In patients with PLCH, a close correlation between the index value and the disease course was found in all seven subjects, where the increasing index values indicated disease activity, while decreasing index values were observed after therapy administration. In the group of 100 healthy control subjects, we found index values lower than 0.3 in 80% and lower than 0.4 in 96% [range: 0.14-0.43; 0.24±0.07 (100)].

CONCLUSION

Measuring SUVmaxPULMO/SUVmaxHEPAR values and their time-trend monitoring represent simple, noninvasive screening tools allowing an early diagnosis and treatment response follow-up assessment in patients with PLCH.

Post-traumatic diaphragmatic herniation of the liver, examined by positron emission tomography: case report

We present a case of post-traumatic diaphragmatic herniation of the liver, which mimicked an intrathoracic tumor. After an automobile accident, the patient underwent thoracotomies for hemothorax and lung cancer in the right chest. Seven months later, computed tomography (CT) demonstrated a round tumor in the thorax adjacent to the right diaphragm with a higher density than the liver parenchyma. An intrathoracic tumor including a primary or metastatic lung cancer was suspected. However, positron emission tomography (PET) showed that the uptake of fluorine-18-fluorodeoxyglucose (FDG) was identical to that in the liver, and the tumor appeared to be contiguous with the liver. Thus, we suspected liver herniation. Core needle biopsy revealed liver cells without neoplastic tissue. Upon surgical exploration, herniation of the liver was found and repaired. PET was helpful in providing morphological and functional information leading to accurate diagnosis of liver herniation in this unusual case.