The appropriate whole body metric for calculating standardised uptake value and the influence of sex

SUV normalisation and reference tissue selection for [1⁸F]mFBG PET-CT in paediatric and adult patients

PURPOSE

Meta-[1⁸F]fluorobenzylguanidine ([1⁸F]mFBG) PET-CT is a novel imaging modality for norepinephrine transporter-expressing tumours, such as neuroblastoma and phaeochromocytoma, enabling quantitative assessment and improved diagnostic accuracy compared to meta-[123I]iodobenzylguanidine ([123I]mIBG) scintigraphy. This study aims to: 1) Identify the optimal standardised uptake value (SUV) normalisation method: body weight (BW) or lean body mass (LBM); 2) Determine the most stable reference tissue with SUV uptake below pathological levels.

METHODS

We analysed 63 [1⁸F]mFBG PET-CTs from 35 patients (20 paediatric neuroblastoma, 15 adult phaeochromocytoma). SUVmean was measured in the liver, blood pool, bone marrow, and muscle, normalised using BW (SUVBW), LBM via James (SUVLBMJames), and LBM via Janmahasatian (SUVLBMJanma). Variability of SUVs and their correlation with weight were assessed.

RESULTS

LBM-based normalisation reduced SUV variability compared to BW-based normalisation. Bone marrow demonstrated the lowest variability and least weight dependency (r2 0.45 for SUVBW versus 0.31 for SUVLBMJanma). The liver had the highest SUVs, increasing the risk of false negatives if used as reference tissue, while the blood pool had the lowest SUVs, raising the risk of false positives. Muscle showed relatively stable SUVs with increasing weight but higher variability than bone marrow.

CONCLUSION

LBM-based SUV normalisation reduces weight dependency for [1⁸F]mFBG PET-CT. Bone marrow is the most reliable reference tissue due to its low variability and balanced SUVs, while muscle may serve as an alternative if diffuse bone marrow uptake is present. These findings support standardising LBM-adjusted SUV methods and using bone marrow as the primary reference tissue to enhance diagnostic accuracy.

CLINICAL TRIAL REGISTRATION

 EudraCT Number: 2019-003713-33; EU Clinical Trials Number: 2024-513622-35-00.

Improving accuracy of SUV estimates in paediatric oncology: Recommending against the use of body weight corrected SUV in [18F]FDG PET

PURPOSE

Few studies have assessed body weight dependency of Standardised Uptake Value (SUV) formulations in paediatric patients. This study aims to compare different SUV formulations measured in reference tissues in paediatric patients and determine which correction method shows the least dependency on body weight.

METHODS

A single-centre, retrospective analysis of [18F]FDG PET/CT scans was performed. SUV measurements were taken from liver and blood pool using EARL1 reconstructions. SUV measurements were corrected for body weight (SUVBW), lean body mass (LBM) according to James (SUVLBMJames) and Janmahasatian (SUVLBMJanma), and body surface area (BSA) according to DuBois (SUVBSADuBois) and Haycock (SUVBSAHaycock). The coefficient of determination (r2) was used to assess the correlation between SUV and body weight.

RESULTS

In total, 461 scans were analysed, including 185 (40%) from female patients. The median age of patients was 12 years (IQR 8-15.5 years). SUVBW exhibited the strongest correlation with body weight, with r2 = 0.65 for the liver and r2 = 0.50 for the blood pool. In contrast, SUVBSADuBois and SUVBSAHaycock had the weakest correlation, with r2 = 0.09 for the liver and r2 = 0.06 for the blood pool. SUVLBMJames and SUVLBMJanma had moderate correlations, with r2 = 0.51 and r2 = 0.44 for the liver and blood pool, respectively, and r2 = 0.47 and r2 = 0.42, respectively.

CONCLUSION

In paediatric [18F]FDG PET/CT scans, SUVBW should be avoided due to elevating values in heavier patients. SUVBSA presents the least dependency on body weight and provides the most consistent assessments of metabolic activity.

Validation of quantitative [18F]NaF PET uptake parameters in bone diseases: a systematic review

PURPOSE

[18F]NaF PET has become an increasingly important tool in clinical practice toward understanding and evaluating diseases and conditions in which bone metabolism is disrupted. Full kinetic analysis using nonlinear regression (NLR) with a two-tissue compartment model to determine the net rate of influx (Ki) of [18F]NaF is considered the gold standard for quantification of [18F]NaF uptake. However, dynamic scanning often is impractical in a clinical setting, leading to the development of simplified semi-quantitative parameters. This systematic review investigated which uptake parameters have been used to evaluate bone disorders and how they have been validated to measure disease activity.

METHODS

A literature search (in PubMed, Embase.com, and Clarivate Analytics/Web of Science Core Collection) was performed up to 28th November 2023, in collaboration with an information specialist. Each database was searched for relevant literature regarding the use of [18F]NAF PET/CT to measure disease activity in bone-related disorders. The main aim was to explore whether the reported semi-quantitative uptake values were validated against full kinetic analysis. A second aim was to investigate whether the chosen uptake parameter correlated with a disease-specific outcome or marker, validating its use as a clinical outcome or disease marker.

RESULTS

The initial search included 1636 articles leading to 92 studies spanning 29 different bone-related conditions in which [18F]NaF PET was used to quantify [18F]NaF uptake. In 12 bone-related disorders, kinetic analysis was performed and compared with simplified uptake parameters. SUVmean (standardized uptake value) and SUVmax were used most frequently, though normalization of these values varied greatly between studies. In some disorders, various studies were performed evaluating [18F]NaF uptake as a marker of bone metabolism, but unfortunately, not all studies used this same approach, making it difficult to compare results between those studies.

CONCLUSION

When using [18F]NaF PET to evaluate disease activity or treatment response in various bone-related disorders, it is essential to detail scanning protocols and analytical procedures. The most accurate outcome parameter can only be obtained through kinetic analysis and is better suited for research. Simplified uptake parameters are better suited for routine clinical practice and repeated measurements.

Comprehensive literature review of oral and intravenous contrast-enhanced PET/CT: a step forward?

The integration of diagnostic CT scans into PET/CT facilitates a comprehensive single examination, presenting potential advantages for patients seeking a thorough one-shot check-up. The introduction of iodinated contrast media during PET scanning raises theoretical concerns about potential interference with uptake quantification, due to the modification of tissue density on CT. Nevertheless, this impact appears generally insignificant for clinical use, compared to the intrinsic variability of standardized uptake values. On the other hand, with the growing indications of PET, especially 18F-FDG PET, contrast enhancement increases the diagnostic performances of the exam, and provides additional information. This improvement in performance achieved through contrast-enhanced PET/CT must be carefully evaluated considering the associated risks and side-effects stemming from the administration of iodinated contrast media. Within this article, we present a comprehensive literature review of contrast enhanced PET/CT, examining the potential impact of iodinated contrast media on quantification, additional side-effects and the pivotal clinically demonstrated benefits of an all-encompassing examination for patients. In conclusion, the clinical benefits of iodinated contrast media are mainly validated by the large diffusion in PET protocols. Contrary to positive oral contrast, which does not appear to offer any major advantage in patient management, intravenous iodine contrast media provides clinical benefits without significant artifact on images or quantification. However, studies on the benefit-risk balance for patients are still lacking.

Different hydration protocols for the quantification of healthy tissue uptake of half-dose 18F-FDG total-body positron emission tomography-computed tomography: a prospective study

Background

This study aimed to investigate the effects of the volume and time of hydration on the quantification of healthy tissue uptake for 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) total-body positron emission tomography (PET)-computed tomography (CT) with half-dose activity.

Methods

This study prospectively enrolled 180 patients who underwent a total-body PET-CT scan 10 min after injection of a half-dose (1.85 MBq/kg) of 18F-FDG. These patients were placed in hydration groups (30 patients in each group) according to different hydration volumes and times: oral hydration with 500 mL of water 20 min before (G1), 5 min after (G2), and 30 min after (G3) the 18F-FDG injection; and oral hydration with 200 mL of water 20 min before (G4), 5 min after (G5), and 30 min after (G6) the 18F-FDG injection. Another 30 patients underwent dynamic imaging without hydration and were used a nonhydration group. The analysis of quantification of healthy tissue uptake included the maximum standardized uptake value (SUVmax) and the mean SUV (SUVmean) of the blood pool and muscle, as well as the SUVmax, SUVmean, and signal-to-noise ratio (SNR) of the liver.

Results

The SUVmax of the blood pool (2.33±0.36), liver (3.03±0.42), and muscle (0.81±0.15) was significantly higher in the nonhydration group than in any of the 6 hydrated groups (P<0.05 for all hydration groups vs. nonhydration group). Muscle SUVmax and SUVmean were significantly (P<0.05) lower in G1 and G2 than in G3 and were lower in G4 and G5 than in G6. The SUVmax and SUVmean of the blood pool were significantly (P<0.05) lower in G1 than in G3 and G4 and lower in G3 than in G6.

Conclusions

When total-body PET-CT with a half dose of 18F-FDG activity is performed, hydration can significantly affect the quantification of healthy tissue uptake. Oral administration of 500 mL of water 20 min before injection could reduce background radioactivity.

Impact of Reduced Image Noise on Deauville Scores in Patients with Lymphoma Scanned on a Long-Axial Field-of-View PET/CT-Scanner

BACKGROUND

Total body and long-axial field-of-view (LAFOV) PET/CT represent visionary innovations in imaging enabling either improved image quality, reduction in injected activity-dose or decreased acquisition time. An improved image quality may affect visual scoring systems, including the Deauville score (DS), which is used for clinical assessment of patients with lymphoma. The DS compares SUVmax in residual lymphomas with liver parenchyma, and here we investigate the impact of reduced image noise on the DS in patients with lymphomas scanned on a LAFOV PET/CT.

METHODS

Sixty-eight patients with lymphoma underwent a whole-body scan on a Biograph Vision Quadra PET/CT-scanner, and images were evaluated visually with regard to DS for three different timeframes of 90, 300, and 600 s. SUVmax and SUVmean were calculated from liver and mediastinal blood pool, in addition to SUVmax from residual lymphomas and measures of noise.

RESULTS

SUVmax in liver and in mediastinal blood pool decreased significantly with increasing acquisition time, whereas SUVmean remained stable. In residual tumor, SUVmax was stable during different acquisition times. As a result, the DS was subject to change in three patients.

CONCLUSIONS

Attention should be drawn towards the eventual impact of improvements in image quality on visual scoring systems such as the DS.

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.

Rapid Standardized CT-Based Method to Determine Lean Body Mass SUV for PET-A Significant Improvement Over Prediction Equations

In 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) studies, maximum standardized uptake value (SUVmax) is the parameter commonly used to provide a measurement of the metabolic activity of a tumor. SUV normalized by body mass is affected by the proportions of body fat and lean tissue, which present high variability in patients with cancer. SUV corrected by lean body mass (LBM), denoted as SUL, is recommended to provide more accurate, consistent, and reproducible SUV results; however, LBM is frequently estimated rather than measured. Given the increasing importance of a quantitative PET parameter, especially when comparing PET studies over time to evaluate disease response clinically, and its use in oncological clinical trials, we set out to evaluate the commonly used equations originally derived by James (1976) and Janmahasatian et al. (2005) against computerized tomography (CT)-derived measures of LBM.

METHODS

Whole-body 18F-FDG PET images of 195 adult patients with cancer were analyzed retrospectively. Representative liver SUVmean was normalized by total body mass. SUL was calculated using a quantitative determination of LBM based on the CT component of the PET/CT study (LBMCT) and compared against the equation-estimated SUL. Bland and Altman plots were generated for SUV-SUL differences.

RESULTS

This consecutive sample of patients undergoing usual care (men, n = 96; women, n = 99) varied in body mass (38-127 kg) and in Body Mass Index (BMI) (14.7-47.2 kg/m2). LBMCT weakly correlated with body mass (men, r2 = 0.32; women, r2 = 0.22), and thus SUV and SULCT were also weakly correlated (men, r2 = 0.24; women, r2 = 0.11). Equations proved inadequate for the assessment of LBM. LBM estimated by James' equation showed a mean bias (overestimation of LBM compared with LBMCT) in men (+6.13 kg; 95% CI 4.61-7.65) and in women (+6.32 kg; 95% CI 5.26-7.39). Janmahasatian's equation provided similarly poor performance.

CONCLUSIONS

CT-based LBM determinations incorporate the patient's current body composition at the time of a PET/CT study, and the information garnered can provide care teams with information with which to more accurately determine FDG uptake values, allowing comparability over multiple scans and treatment courses and will provide a robust basis for the use of PET Response Criteria in Solid Tumors (PERCIST) in clinical trials.

Utility of 68 Ga-DOTA-Exendin-4 positron emission tomography-computed tomography imaging in distinguishing between insulinoma and nesidioblastosis in patients with confirmed endogenous hyperinsulinaemic hypoglycaemia

BACKGROUND

Because management is very different, it is important to differentiate between small focal insulinomas and diffuse pancreatic dysplasia (nesidioblastosis) in patients with confirmed endogenous hyperinsulinaemic hypoglycaemia (EHH). Most insulinomas highly express glucagon-like peptide-1 receptors enabling positron emission tomography-computed tomography imaging with its radiolabelled analogue; ⁶⁸ Ga-DOTA-Exendin-4 (Exendin).

AIM

To determine: (i) the utility of Exendin in EHH patients in a clinical setting; and (ii) whether the degree of Exendin uptake differentiates non-insulinoma pancreatogenous hypoglycaemia syndrome (NIPHS) from post-gastric bypass hypoglycaemia (PGBH).

METHODS

This retrospective study reviewed the clinical, biochemistry and prior imaging findings in confirmed EHH patients referred for Exendin. Accuracy of Exendin was based on surgical findings and treatment outcomes. Finally, average Exendin uptake (SUVmax) of five PGBH studies was compared with the SUVmax of a key NIPHS case report.

RESULTS

Twenty of 25 consecutive patients had confirmed EHH. Exendin located insulinomas in eight of nine patients enabling successful surgical excision with rapid and durable cure. Exendin correctly identified diffuse nesidioblastosis in two of three cases requiring partial pancreatectomy for hypoglycaemia control. All three relapsed within 1.7 years with one needing completion pancreatectomy. Establishing the cause in the remainder relied on other investigations, clinical correlation and response to empirical treatment. Finally, Exendin SUVmax could not distinguish between NIPHS and PGBH.

CONCLUSION

In EHH patients, Exendin accurately identifies the site of insulinoma and thereby differentiates it from nesidioblastosis but negative findings should not be ignored. Exendin is unlikely to differentiate between normal pancreatic uptake, NIPHS and PGBH.