Diagnostic Value of Volume-Based Fluorine-18-Fluorodeoxyglucose PET/CT Parameters for Characterizing Thyroid Incidentaloma

Value of Semi-Quantitative Parameters of 68Ga-FAPI-04 PET/CT in Primary Malignant and Benign Diseases: A Comparison with 18F-FDG

Objectives: We aimed to compare the value of the semiquantitative parameters of 68Ga-labeled FAP inhibitor (68Ga-FAPI)-04 positron emission tomography/computed tomography (PET/CT) and 18F-fluorodeoxyglucose (18F-FDG) in diagnosing primary malignant and benign diseases. Materials and Methods: 18F-FDG and 68Ga-FAPI-04 PET/CT images of 80 patients were compared. Semiquantitative parameters, including maximum standardized uptake value (SUVmax), mean SUV (SUVmean), peak SUV (SUVpeak), peak SUV by lean body mass (SULpeak), metabolic tumor volume (or tumor volume of FAPI; FAPI-TV), and TLG (or total lesion activity of FAPI; FAPI-TLA), were automatically obtained using the IntelliSpace Portal image processing workstation with a threshold of 40% SUVmax. The liver blood pool was measured as the background, and the tumor-to-background ratio (TBRliver) was calculated. Results: In all malignant lesions, FAPI-TV and FAPI-TLA were higher in 68Ga-FAPI-04 PET/CT than in 18F-FDG. In the subgroup analysis, 68Ga-FAPI-04 had higher FAPI-TV and FAPI-TLA and lower SUVmax than 18F-FDG had in group A, including gynecological tumor, esophageal, and colorectal cancers. However, six semiquantitative parameters were higher in group B (the other malignant tumors). For the benign diseases, SUVmax, SUVmean, SUVpeak, and SULpeak were lower in 68Ga-FAPI-04 PET/CT than in 18F-FDG. 68Ga-FAPI-04 PET/CT showed a lower liver background and a higher TBRliver than 18F-FDG did. 68Ga-FAPI-04 PET/CT had higher accuracy, sensitivity, and specificity than 18F-FDG had. Conclusion: More accurate semiquantitative parameters and lower abdominal background in 68Ga-FAPI-04 PET/CT make it more competitive in the differential diagnosis of malignant and benign diseases than in 18F-FDG.

[18F]FDG PET/MRI combined with chest HRCT in early cancer detection: a retrospective study of 3020 asymptomatic subjects

PURPOSE

PET/MRI has become an important medical imaging approach in clinical practice. In this study, we retrospectively investigated the detectability of fluorine-18 (18F)-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging ([18F]FDG PET/MRI) combined with chest computerized tomography (CT) for early cancer in a large cohort of asymptomatic subjects.

METHODS

This study included a total of 3020 asymptomatic subjects who underwent whole-body [18F]FDG PET/MRI and chest HRCT examinations. All subjects received a 2-4-year follow-up for cancer development. Cancer detection rate, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the [18F]FDG PET/MRI with or without chest HRCT were calculated and analyzed.

RESULTS

Sixty-one subjects were pathologically diagnosed with cancers, among which 59 were correctly detected by [18F]FDG PET/MRI combined with chest HRCT. Of the 59 patients (32 with lung cancer, 9 with breast cancer, 6 with thyroid cancer, 5 with colon cancer, 3 with renal cancer, 1 with prostate cancer, 1 with gastric cancer, 1 with endometrial cancer, and 1 with lymphoma), 54 (91.5%) were at stage 0 or stage I (according to the 8th edition of the tumor-node-metastasis [TNM] staging system), 33 (55.9%) were detected by PET/MRI alone (27 with non-lung cancers and 6 with lung cancer). Cancer detection rate, sensitivity, specificity, PPV, and NPV for PET/MRI combined with chest CT were 2.0%, 96.7%, 99.6%, 83.1%, and 99.9%, respectively. For PET/MRI alone, the metrics were 1.1%, 54.1%, 99.6%, 73.3%, and 99.1%, respectively, and for PET/MRI in non-lung cancers, the metrics were 0.9%, 93.1%, 99.6%, 69.2%, and 99.9%, respectively.

CONCLUSIONS

[18F]FDG PET/MRI holds great promise for the early detection of non-lung cancers, while it seems insufficient for detecting early-stage lung cancers. Chest HRCT can be complementary to whole-body PET/MRI for early cancer detection.

TRIAL REGISTRATION

ChiCTR2200060041. Registered 16 May 2022. Public site: https://www.chictr.org.cn/index.html.

Significance of incidental focal fluorine-18 fluorodeoxyglucose uptake in colon/rectum, thyroid, and prostate: With a brief literature review

BACKGROUND

Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT), a functional imaging method, is usually performed on the entire torso, and regions of unexpected suspicious focal hypermetabolism are not infrequently observed. Among the regions, colon, thyroid, and prostate were found to be the common organs in a recent umbrella review. Some studies reported that a high rate of malignancy was shown in incidentally identified focal hypermetabolic regions and suggested that further examinations should not be ignored.

AIM

To investigate the malignancy rate of incidental focal FDG uptake, useful PET parameters and their cutoffs in discrimination between malignant and benign lesions.

METHODS

Retrospectively, the final reports of 16510 F-18 FDG PET/CT scans performed at our hospital between January 2016 and March 2022 were reviewed to identify incidentally observed FDG uptake in the colon/rectum, thyroid, and prostate. The scans of patients with current or prior malignancies at each corresponding location, without the final reports of histopathology or colonoscopy (for colon and rectum) for the corresponding hypermetabolic regions, or with diffuse (not focal) hypermetabolism were excluded. Finally, 88 regions of focal colorectal hypermetabolism in 85 patients (48 men and 37 women with mean age 67.0 ± 13.4 years and 63.4 ± 15.8 years, respectively), 48 focal thyroid uptakes in 48 patients (12 men and 36 women with mean age 62.2 ± 13.1 years and 60.8 ± 12.4 years, respectively), and 39 focal prostate uptakes in 39 patients (mean age 71.8 ± 7.5 years) were eligible for this study. For those unexpected focal hypermetabolic regions, rates of malignancy were calculated, PET parameters, such as standardized uptake value (SUV), capable of distinguishing between malignant and benign lesions were investigated, and the cutoffs of those PET parameters were determined by plotting receiver operating characteristic curves.

RESULTS

In the colon and rectum, 29.5% (26/88) were malignant and 33.0% (29/88) were premalignant lesions. Both SUVmax and SUVpeak differentiated malignant/premalignant from benign lesions, however, no parameters could distinguish malignant from premalignant lesions. Higher area under the curve was shown with SUVmax (0.752, 95%CI: 0.649-0.856, P < 0.001) and the cutoff was 7.6. In the thyroid, 60.4% (29/48) were malignant. The majority were well-differentiated thyroid cancers (89.7%, 26/29). The results of BRAF mutation tests were available for 20 of the 26 well-differentiated thyroid cancers and all 20 had the mutation. Solely SUVmax differentiated malignant from benign lesions and the cutoff was 6.9. In the prostate, 56.4% (22/39) were malignant. Only SUVmax differentiated malignant from benign lesions and the cutoff was 3.8. Overall, among the 175 focal hypermetabolic regions, 60.6% (106/175) were proven to be malignant and premalignant (in colon and rectum) lesions.

CONCLUSION

Approximately 60% of the incidentally observed focal F-18 FDG uptake in the colon/rectum, thyroid, and prostate were found to be malignant. Of the several PET parameters, SUVmax was superior to others in distinguishing between malignant/premalignant and benign lesions. Based on these findings, incidental focal hypermetabolism should not be ignored and lead physicians to conduct further investigations with greater confidence.

Radiomics Analysis of [18F]FDG PET/CT Thyroid Incidentalomas: How Can It Improve Patients’ Clinical Management? A Systematic Review from the Literature

Background: We performed a systematic review of the literature to provide an overview of the application of PET-based radiomics of [18F]FDG-avid thyroid incidentalomas and to discuss the additional value of PET volumetric parameters and radiomic features over clinical data. Methods: The most relevant databases were explored using an algorithm constructed based on a combination of terms related to our subject and English-language articles published until October 2021 were considered. Among the 247 identified articles, 19 studies were screened for eligibility and 11 met the criteria, with 4 studies including radiomics analyses. Results: We summarized the available literature based on a study of PET volumetric parameters and radiomics. Ten articles provided accurate details about volumetric parameters and their prospective value in tumour assessment. We included the data provided by these articles in a sub-analysis, but could not obtain statistically relevant results. Four publications analyzed the diagnostic potential of radiomics and the possibility of creating precise predictive models, their corresponding quality score being assessed. Conclusions: The use of PET volumetric parameters and radiomics analysis in patients with [18F]FDG-avid thyroid incidentalomas outlines a great prospect in diagnosis and stratification of patients with malignant nodules and may represent a way of limiting the need for unnecessary invasive procedures; however, further studies need to be performed for a standardization of the method.

Comparison between Two Different Scanners for the Evaluation of the Role of 18F-FDG PET/CT Semiquantitative Parameters and Radiomics Features in the Prediction of Final Diagnosis of Thyroid Incidentalomas

The aim of this study was to compare two different tomographs for the evaluation of the role of semiquantitative PET/CT parameters and radiomics features (RF) in the prediction of thyroid incidentalomas (TIs) at ¹⁸F-FDG imaging. A total of 221 patients with the presence of TIs were retrospectively included. After volumetric segmentation of each TI, semiquantitative parameters and RF were extracted. All of the features were tested for significant differences between the two PET scanners. The performances of all of the features in predicting the nature of TIs were analyzed by testing three classes of final logistic regression predictive models, one for each tomograph and one with both scanners together. Some RF resulted significantly different between the two scanners. PET/CT semiquantitative parameters were not able to predict the final diagnosis of TIs while GLCM-related RF (in particular GLCM entropy_log2 e GLCM entropy_log10) together with some GLRLM-related and GLZLM-related features presented the best predictive performances. In particular, GLCM entropy_log2, GLCM entropy_log10, GLZLM SZHGE, GLRLM HGRE and GLRLM HGZE resulted the RF with best performances. Our study enabled the selection of some RF able to predict the final nature of TIs discovered at ¹⁸F-FDG PET/CT imaging. Classic semiquantitative and volumetric PET/CT parameters did not reveal these abilities. Furthermore, a good overlap in the extraction of RF between the two scanners was underlined.

Characterization of focal hypermetabolic thyroid incidentaloma: An analysis with F-18 fluorodeoxyglucose positron emission tomography/computed tomography parameters

BACKGROUND

Incidentally found thyroid tumor (thyroid incidentaloma, TI) on F-18 fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) is reported in 2.5%-5% of patients being investigated for non-thyroid purposes. Up to 50% of these cases have been diagnosed to be malignant by cytological/histological results. Ultrasonography (US) and fine-needle aspiration cytology are recommended for thyroid nodules with high FDG uptake (hypermetabolism) that are 1 cm or greater in size. It is important to accurately determine whether a suspicious hypermetabolic TI is malignant or benign.

AIM

To distinguish malignant hypermetabolic TIs from benign disease by analyzing F-18 FDG PET-CT parameters and to identify a cut-off value.

METHODS

Totally, 12761 images of patients who underwent F-18 FDG PET-CT for non-thyroid purposes at our hospital between January 2016 and December 2020 were retrospectively reviewed, and 339 patients [185 men (mean age: 68 ± 11.2) and 154 women (mean age: 63 ± 15.0)] were found to have abnormal, either focal or diffuse, thyroid FDG uptake. After a thorough review of their medical records, US, and cytological/histological reports, 46 eligible patients with focal hypermetabolic TI were included in this study. The TIs were categorized as malignant and benign according to the cytological/histological reports, and four PET parameters [standardized uptake value (SUV)_max, SUV_peak, SUV_mean, and metabolic tumor volume (MTV)] were measured on FDG PET-CT. Total lesion glycolysis (TLG) was calculated by multiplying the SUV_mean by MTV. Both parametric and non-parametric methods were used to compare the five parameters between malignant and benign lesions. Receiver operating characteristic (ROC) curve analysis was performed to identify a cut-off value.

RESULTS

Each of the 46 patients [12 men (26.1%; mean age: 62 ± 13.1 years) and 34 women (73.9%; mean age: 60 ± 12.0 years)] with focal hypermetabolic TIs had one focal hypermetabolic TI. Among them, 26 (56.5%) were malignant and 20 (43.5%) were benign. SUV_max, SUV_peak, SUV_mean, and TLG were all higher in malignant lesions than benign ones, but the difference was statistically significant (P = 0.012) only for SUV_max. There was a positive linear correlation (r = 0.339) between SUV_max and the diagnosis of malignancy. ROC curve analysis for SUV_max revealed an area under the curve of 0.702 (P < 0.05, 95% confidence interval: 0.550-0.855) and SUV_max cut-off of 8.5 with a sensitivity of 0.615 and a specificity of 0.789.

CONCLUSION

More than half of focal hypermetabolic TIs on F-18 FDG PET-CT were revealed as malignant lesions, and SUV_max was the best parameter for discriminating between malignant and benign disease. Unexpected focal hypermetabolic TIs with the SUV_max above the cut-off value of 8.5 may have a greater than 70% chance of malignancy; therefore, further active assessment is required.

Prostate incidentaloma on 18F-fluorodeoxyglucose positron emission tomography: Diagnostic value of volumetric positron emission tomography parameters

OBJECTIVE

To evaluate whether volumetric PET parameters such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG) contributed to maximum standardized uptake value (SUVmax) in predicting prostate carcinoma in the prostate incidentalomas (PI) in 18F-FDG PET/CT.

MATERIALS AND METHODS

This retrospective study comprised 107 patients with PI of 4723 male patients who had undergone 18F-FDG PET/CT. SUVmax and volumetric PET parameters of PIs were assessed. MTV and TLG were acquired with each SUV threshold as 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0.

RESULTS

The PI incidence was 2.3%, and the malignancy ratio of PI was 15.9%. According to further analysis results, 17 patients were in the malignant group, and 46 patients were in the benign group. Malignant PIs had higher SUVmax (10.6 vs. 6.4 and p<0.01), MTV (all p < 0.01) and TLG (all p < 0.01) than benign incidentalomas. All volumetric PET parameters had higher area under the curve (AUC) than SUVmax. SUVmax AUC was 0.835 [95% confidence interval (CI): 0.728-0.942]. MTV 2.5 and TLG 2.5 had the highest performance for predicting malignant PI.MTV2.5 AUC was 0.871 (95% CI: 0.775-0.968), and TLG2.5 AUC was 0.882 (95% CI: 0.797-0.967). Using TLG 2.5 greater than 29.8 as the cut-off point, the sensitivity and specificity for malignancy prediction were 94.1% and 82.6%, respectively.

CONCLUSION

In this study, in which the effectiveness of volumetric parameters in the diagnosis of PI was evaluated for the first time, it was shown that they could potentially have clinical value along with SUVmax.

Radiomics Analysis of [18F]-Fluorodeoxyglucose-Avid Thyroid Incidentalomas Improves Risk Stratification and Selection for Clinical Assessment

Background: [¹⁸F]-Fluorodeoxyglucose (FDG)-avid thyroid lesions incidentally detected on positron emission tomography/computed tomography (PET/CT) scans represent a tumor lesion in about 30% of cases. The present study evaluated the ability of PET metrics and radiomics features to predict final diagnosis of [¹⁸F]FDG thyroid incidentalomas (TIs). Methods: A total of 104 patients with 107 TIs were retrospectively studied; 30 nodules (28%) were diagnosed as malignant. After volumetric segmentation of each thyroid lesion, metabolic tumor volume (MTV), total lesion glycolysis (TLG), standardized uptake values (SUVs), and metabolic heterogeneity were estimated, and 107 radiomics features were extracted following a standard protocol. Results: MTV, TLG, SUVmax, SUVmean, and SUVpeak among functional PET parameters, and gray-level co-occurrence matrix (GLCM)_InverseDifferenceMoment, shape_Sphericity, GLCM_SumSquares, firstorder_Maximum2DDiameterSlice, firstorder_Energy, and GLCM_Contrast among nonredundant radiomics features, showed significantly different values between malignant and benign TIs (Mann-Whitney U-test, p < 0.01 for all). Univariate logistic regression revealed that these parameters demonstrated good ability to predict final diagnosis of TIs (p < 0.02 for all). Shape_Sphericity was the best predictor classifying 82% of TIs correctly (p < 0.0001). Only TLG, SUVmax, and shape_Sphericity retained significance (p < 0.0001) by multivariate analysis. Malignant lesion prevalence increased from 7% to 100% in accordance with the number (score, 0-3) of the three positive parameters present (χ² trend, p < 0.0001). A score of 0 excludes malignant TIs with a negative predictive value of 93%, while a score of 3 predicted malignancy with a positive predictive value of 100%. Conclusions: PET metrics and radiomics analysis can improve identification of [¹⁸F]FDG-avid TIs at high risk of malignancy. A model based on TLG, SUVmax, and shape_Sphericity may allow prediction of a final diagnosis, providing useful information for the management of TIs.

Evaluating Focal 18F-FDG Uptake in Thyroid Gland with Radiomics

Purpose

The aim of this study was to evaluate the ability of ¹⁸F-FDG PET/CT texture analysis to predict the exact pathological outcome of thyroid incidentalomas.

Methods

¹⁸F-FDG PET/CT images between March 2010 and September 2018 were retrospectively reviewed in patients with focal ¹⁸F-FDG uptake in the thyroid gland and who underwent fine needle aspiration biopsy from this area. The focal uptake in the thyroid gland was drawn in 3D with 40% SUVmax threshold. Features were extracted from volume of interest (VOI) using the LIFEx package. The features obtained were compared in benign and malignant groups, and statistically significant variables were evaluated by receiver operating curve (ROC) analysis. The correlation between the variables with area under curve (AUC) value over 0.7 was examined; variables with correlation coefficient less than 0.6 were evaluated with machine learning algorithms.

Results

Sixty patients (70% train set, 30% test set) were included in the study. In univariate analysis, a statistically significant difference was observed in 6 conventional parameters, 5 first-, and 16 second-order features between benign and malignant groups in train set (p < 0.05). The feature with the highest benign-malignant discriminating power was GLRLM_RLNU (AUC:0.827). AUC value of SUVmax was calculated as 0.758. GLRLM_RLNU and SUVmax were evaluated to build a model to predict the exact pathology outcome. Random forest algorithm showed the best accuracy and AUC (78.6% and 0.849, respectively).

Conclusion

In the differentiation of benign-malignant thyroid incidentalomas, GLRLM_RLNU and SUVmax combination may be more useful than SUVmax to predict the outcome.

Evaluation of Malignancy Risk in 18F-FDG PET/CT Thyroid Incidentalomas

Thyroid incidentalomas detected by 18 fluoro-2-deoxy-d-glucose (FDG)-positron emission tomography/computed tomography (PET/CT) are a real challenge for nuclear medicine physicians and clinicians. This study aimed to evaluate the risk of malignancy for patients with focal thyroid incidentalomas (TIs) diagnosed through FDG PET/CT. Data from 6900 patients, with a known primary tumor, who had an FDG PET/CT investigation performed were analyzed for the presence of incidental thyroid uptake. The focal TIs were reported, and the patients were referred for further investigation to the endocrinology department. There were 126 patients (1.82%) who presented with focal thyroid uptake, and for 87 of them, investigations were completed with ultrasonography (US), and for 29 with a fine needle aspiration biopsy (FNAB) procedure. Malignancy was detected in 7.93% (10/126) of cases. An arbitrary cutoff value of four was established for the standard uptake value lean body mass (SUVlbm Max) to differentiate the malignant nodules from the benign ones, and this value was significantly associated with malignancy (p = 0.0168). TIs are not so frequent, but they have a potential malignancy risk, and a proper evaluation is required. Even though SUVlbm Max is a predictive factor for malignancy, the FNAB remains the main diagnostic method for the therapeutic management of these patients.

Role of multi-modality functional imaging in differentiation between benign and malignant thyroid 18F-fluorodeoxyglucose incidentaloma

PURPOSE

To evaluate the diagnostic performance of multi-modality functional imaging in differentiating malignant and benign thyroid ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) incidentaloma.

METHODS

This study included 87 patients with thyroid ¹⁸F-FDG incidentalomas detected by ¹⁸F-FDG- positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT) and diagnosed at surgery or biopsy, who received ¹⁸F-FDG-PET/CT, diffusion-weighted MR imaging (DWI) and ultrasound elastography (USE). The metabolic tumor volume (MTV), total lesion glycolysis (TLG), apparent diffusion coefficient (ADC) values and ultrasound elasticity scores of thyroid ¹⁸F-FDG incidentalomas were measured and compared in benign and malignant thyroid incidentalomas. The differences of malignant and benign thyroid incidentalomas were tested by χ² test, Fisher's exact test, t test, or Mann-Whitney U test. The diagnostic performance was evaluated and optimal cut-off values were determined in distinguishing malignant from benign thyroid incidentalomas by receiver operating characteristic curve analysis.

RESULTS

MTV, TLG and USE scores of malignant thyroid incidentalomas were significantly higher than benign; but ADC value was significantly lower. We defined the functional imaging parameters TLG < 2.48, ADC > 1.80 × 10^-3mm²/s, and USE score of 1 as markers of benign thyroid incidentalomas and each scored -1 point; TLG ≥ 2.48, ADC ≤ 1.80 × 10^-3mm²/s, and USE score of 4 as markers of malignancy and each scored 1 point. Combined multi-functional imaging parameters achieved the highest performance (84.6% sensitivity and 97.1% specificity) for distinguish malignant from benign thyroid incidentaloma with AUC 0.957 (95% CI 0.917, 0.997).

CONCLUSIONS

Functional imaging might help to distinguishing malignant from benign thyroid ¹⁸F-FDG incidentalomas, and combined multi-functional imaging parameters could improve it.

Diagnostic Value of FDG PET-CT Quantitative Parameters and Deauville-Like 5 Point-Scale in Predicting Malignancy of Focal Thyroid Incidentaloma

Objective: To evaluate the diagnostic value of FDG PET-CT metabolic parameters and Deauville-like 5 point-scale to predict malignancy in a population of patients presenting focal thyroid incidentaloma (fTI).

Design: This retrospective study included 41 fTI, classified according to cytological and histological data as benign (BL) or malignant lesion (ML). FDG PET-CT semi-quantitative parameters (SUVmax, SUVmean, SUVpeak, MTV, TLG), tumor to liver SUVmean ratio (TLRmax and TLRmean), tumor to blood-pool SUVmean ratio (TBRmax and TBRmean) were calculated. Each fTI was also classified on a Deauville-like 5-point scale (DS) currently used in lymphoma. Comparison between BL and ML was performed for each parameter and a ROC analysis was conducted.

Results: All quantitative PET metabolic parameters (SUV parameters, volume based parameters and SUV ratio) were higher in ML compared with BL, yet no significant difference was reported. fTI (uptake) malignancy rate according to DS grades 2, 3, 4, and 5 was, respectively, 25% (1 of 4), 28.6% (2 of 7), 8.3% (1 of 12), and 33.3% (6 of 18) with no significant difference between ML and BL groups. Results of ROC analysis showed that mean TBR had the highest AUC in our cohort (0.66 95%CI [0.41; 0.91]) with a cut-off value of 2.2. Specificity of MTV and TLG was 100% (cut-off values: MTV 9.6 ml, TLG 22.9 g) and their sensitivity was 30 and 40%, respectively.

Conclusion: Our study did not highlight any FDG PET/CT parameter predictor of fTI malignancy.