Noise considerations for PET quantification using maximum and peak standardized uptake value

Quantitative SPECT/CT for dosimetry of peptide receptor radionuclide therapy

Neuroendocrine tumors (NETs) are uncommon malignancies of increasing incidence and prevalence. As these slow growing tumors usually overexpress somatostatin receptors (SSTRs), the use of ⁶⁸Ga-DOTA-peptides (gallium-68 chelated with dodecane tetra-acetic acid to somatostatin), which bind to the SSTRs, allows for PET based imaging and selection of patients for peptide receptor radionuclide therapy (PRRT). PRRT with radiolabeled somatostatin analogues such as ¹⁷⁷Lu-DOTATATE (lutetium-177-[DOTA,Tyr³]-octreotate), is mainly used for the treatment of metastatic or inoperable NETs. However, PRRT is generally administered at a fixed injected activity in order not to exceed dose limits in critical organs, which is suboptimal given the variability in radiopharmaceutical uptake among patients. Advances in SPECT (single photon emission computed tomography) imaging enable the absolute quantitative measure of the true radiopharmaceutical distribution providing for PRRT dosimetry in each patient. Personalized PRRT based on patient-specific dosimetry could improve therapeutic efficacy by optimizing effective tumor absorbed dose while limiting treatment related radiotoxicity.

Machine learning in the differentiation of follicular lymphoma from diffuse large B-cell lymphoma with radiomic [18F]FDG PET/CT features

BACKGROUND

One of the challenges in the management of patients with follicular lymphoma (FL) is the identification of individuals with histological transformation, most commonly into diffuse large B-cell lymphoma (DLBCL). [¹⁸F]FDG-PET/CT is used for staging of patients with lymphoma, but visual interpretation cannot reliably discern FL from DLBCL. This study evaluated whether radiomic features extracted from clinical baseline [¹⁸F]FDG PET/CT and analyzed by machine learning algorithms may help discriminate FL from DLBCL.

MATERIALS AND METHODS

Patients were selected based on confirmed histopathological diagnosis of primary FL (n=44) or DLBCL (n=76) and available [¹⁸F]FDG PET/CT with EARL reconstruction parameters within 6 months of diagnosis. Radiomic features were extracted from the volume of interest on co-registered [¹⁸F]FDG PET and CT images. Analysis of selected radiomic features was performed with machine learning classifiers based on logistic regression and tree-based ensemble classifiers (AdaBoosting, Gradient Boosting, and XG Boosting). The performance of radiomic features was compared with a SUV_max-based logistic regression model.

RESULTS

From the segmented lesions, 121 FL and 227 DLBCL lesions were included for radiomic feature extraction. In total, 79 radiomic features were extracted from the SUVmap, 51 from CT, and 6 shape features. Machine learning classifier Gradient Boosting achieved the best discrimination performance using 136 radiomic features (AUC of 0.86 and accuracy of 80%). SUV_max-based logistic regression model achieved an AUC of 0.79 and an accuracy of 70%. Gradient Boosting classifier had a significantly greater AUC and accuracy compared to the SUV_max-based logistic regression (p≤0.01).

CONCLUSION

Machine learning analysis of radiomic features may be of diagnostic value for discriminating FL from DLBCL tumor lesions, beyond that of the SUV_max alone.

Harmonization of PET image reconstruction parameters in simultaneous PET/MRI

Objective

Simultaneous PET/MRIs vary in their quantitative PET performance due to inherent differences in the physical systems and differences in the image reconstruction implementation. This variability in quantitative accuracy confounds the ability to meaningfully combine and compare data across scanners. In this work, we define image reconstruction parameters that lead to comparable contrast recovery curves across simultaneous PET/MRI systems.

Method

The NEMA NU-2 image quality phantom was imaged on one GE Signa and on one Siemens mMR PET/MRI scanner. The phantom was imaged at 9.7:1 contrast with standard spheres (diameter 10, 13, 17, 22, 28, 37 mm) and with custom spheres (diameter: 8.5, 11.5, 15, 25, 32.5, 44 mm) using a standardized methodology. Analysis was performed on a 30 min listmode data acquisition and on 6 realizations of 5 min from the listmode data. Images were reconstructed with the manufacturer provided iterative image reconstruction algorithms with and without point spread function (PSF) modeling. For both scanners, a post-reconstruction Gaussian filter of 3–7 mm in steps of 1 mm was applied. Attenuation correction was provided from a scaled computed tomography (CT) image of the phantom registered to the MR-based attenuation images and verified to align on the non-attenuation corrected PET images. For each of these image reconstruction parameter sets, contrast recovery coefficients (CRCs) were determined for the SUV_mean, SUV_max and SUV_peak for each sphere. A hybrid metric combining the root-mean-squared discrepancy (RMSD) and the absolute CRC values was used to simultaneously optimize for best match in CRC between the two scanners while simultaneously weighting toward higher resolution reconstructions. The image reconstruction parameter set was identified as the best candidate reconstruction for each vendor for harmonized PET image reconstruction.

Results

The range of clinically relevant image reconstruction parameters demonstrated widely different quantitative performance across cameras. The best match of CRC curves was obtained at the lowest RMSD values with: for CRC_mean, 2 iterations-7 mm filter on the GE Signa and 4 iterations-6 mm filter on the Siemens mMR, for CRC_max, 4 iterations-6 mm filter on the GE Signa, 4 iterations-5 mm filter on the Siemens mMR and for CRC_peak, 4 iterations-7 mm filter with PSF on the GE Signa and 4 iterations-7 mm filter on the Siemens mMR. Over all reconstructions, the RMSD between CRCs was 1.8%, 3.6% and 2.9% for CRC mean, max and peak, respectively. The solution of 2 iterations-3 mm on the GE Signa and 4 iterations-3 mm on Siemens mMR, both with PSF, led to simultaneous harmonization and with high CRC and low RMSD for CRC mean, max and peak with RMSD values of 2.8%, 5.8% and 3.2%, respectively.

Conclusions

For two commercially available PET/MRI scanners, user-selectable parameters that control iterative updates, image smoothing and PSF modeling provide a range of contrast recovery curves that allow harmonization in harmonization strategies of optimal match in CRC or high CRC values. This work demonstrates that nearly identical CRC curves can be obtained on different commercially available scanners by selecting appropriate image reconstruction parameters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00416-0.

Semiautomatic Tumor Delineation for Evaluation of 64Cu-DOTATATE PET/CT in Patients with Neuroendocrine Neoplasms: Prognostication Based on Lowest Lesion Uptake and Total Tumor Volume

Patients with neuroendocrine neoplasms (NENs) have heterogeneous somatostatin receptor expression, with highly differentiated lesions having higher expression. Receptor expression of the total tumor burden may be visualized by somatostatin receptor imaging, such as with 64Cu-DOTATATE PET/CT. Assessment of maximal lesion uptake is associated with progression-free survival (PFS) but not overall survival (OS). We hypothesized that the lesion with the lowest, rather than the highest, 64Cu-DOTATATE uptake would be more prognostic, and we developed a semiautomatic method for evaluating this hypothesis. Methods: Patients with NENs underwent 64Cu-DOTATATE PET/CT. A standardized semiautomatic tumor delineation method was developed and used to identify the lesion with the lowest uptake, that is, with the lowest SUVmean Additionally, we assessed total tumor volume derived from the semiautomatic tumor delineation. Kaplan-Meier and Cox regression analyses were used to determine whether there was any association with OS and PFS. Results: In 116 patients with NENs, median PFS (95% CI) was 23 mo (range, 20-31 mo) and median OS was 85 mo (range, 68-113 mo). Minimum SUVmean and total tumor volume were significantly associated with PFS and OS in univariate Cox regression analyses, whereas SUVmax was significant only for PFS. In multivariate Cox analyses, both minimum SUVmean and total tumor volume remained statistically significant. Minimum SUVmean and total tumor volume were then dichotomized by their median, and patients were categorized into 4 groups: high or low total tumor volume and high or low minimum SUVmean Patients with a low total tumor volume and high minimum SUVmean had a hazard ratio of 0.32 (95% CI, 0.20-0.51) for PFS and 0.24 (95% CI, 0.13-0.43) for OS, both with P values of less than 0.001 (reference: high total tumor volume and low minimum SUVmean). Conclusion: We propose a standardized semiautomatic tumor delineation method to identify the lesion with the lowest 64Cu-DOTATATE uptake and total tumor volume. Assessment of the lowest, rather than the highest, lesion uptake greatly increases prognostication by 64Cu-DOTATATE PET/CT. Combining lesion uptake and total tumor volume, we derived a novel prognostic classification system for patients with NENs.

[Improvement of Standardized Uptake Value Accuracy in the 99mTc Body SPECT and SPECT/CT: Optimization of the Phantom for Calculating Becquerel Calibration Factor and Correction Method]

PURPOSE

The purpose of this study was to evaluate the best phantom for calculating the becquerel calibration factor (BCF) and correction method to obtain the improvement of standardized uptake value (SUV) accuracy in both single photon emission computed tomography (SPECT) and SPECT/CT.

METHOD

A SPECT/CT scanner was used in this study. BCFs were calculated using four phantoms with different cross sections including National Electrical Manufacturers Association International Electrotechnical Commission body phantom (NEMA IEC body phantom) filled with ^99mTcO₄^-, and five correction methods were used for reconstruction. SUVs were calculated by the NEMA IEC body phantom and pediatric phantom in house with these BCFs. We then measured SUV_mean in the background region of the NEMA IEC body phantom, SUV_max and SUV_peak of the 37-mm-diameter sphere.

RESULTS

In the SPECT scanner, SUV_mean and SUV_max measured 1.04 and 4.02, respectively, in the case of BCF calculation and SUV measurement using NEMA IEC body phantoms without corrections. In the SPECT/CT scanner, SUV_mean with CT attenuation correction (AC) was in agreement with the theoretical values using each phantom. SUV_max showed the same trend.

CONCLUSION

In the SPECT scanner, it is possible to obtain a highly accurate SUV by using a phantom that matches the size of the subject for BCF calculation and without correction. In the SPECT/CT scanner, highly accurate SUVs can be obtained by using CT-based attenuation correction, and these values do not depend on the size of the BCF calculation phantom.

Bone Scintigraphy of Vertebral Fractures With a Whole-Body CZT Camera in a PET-Like Utilization

Objective: An image display with a standardized uptake value (SUV) scale is recommended for analyzing PET exams, thus requiring the reconstruction of accurate images for both SUV measurement and visual analysis. This study aimed to determine whether such images may also be obtained with a high-speed CZT-SPECT/CT system, with a further application for the longitudinal monitoring of vertebral fractures. Materials and Methods: SPECT image reconstruction was optimized with an IEC phantom according to both image quality parameters and accuracy of measured activity. The optimized reconstruction process was applied to ≤15 min 99mTc-HDP SPECT spine recordings previously acquired from 25 patients (74 ± 12 years old) at both early (1.3 ± 1.1 months) and late (5.2 ± 2.3 months) stages after an acute vertebral fracture. Results: A SPECT reconstruction with 32 equivalent iterations was selected based on the association of high detectability for spheres down to 0.6 ml in volume, with accurate measured activity, although the latter was affected by partial volume effect for spheres ≤5.6 ml. Coherent measurements were obtained on these high-quality SPECT images for the SUVmax from the intact vertebrae of patients, which were stable between basal SPECT/CT and follow-up SPECT/CT (for T1 vertebrae: 5.7 ± 1.1 vs. 5.8 ± 1.1, p = 0.76), and from initially fractured vertebrae, which were dramatically higher on the basal compared with the follow-up SPECT (21.0 ± 8.5 vs. 11.2 ± 4.2, p < 0.001), whereas inverse changes in SUVmax were observed for newly compacted fractures identified on follow-up SPECT (74.4 ± 2.0 vs. 21.8 ± 10.3, p = 0.002). Finally, an image display with an SUV scale was shown to be advantageous for highlighting areas with >7.5 SUV, a level reached by 98% of vertebral fractures of <7 months and 4% of reference intact vertebrae. Conclusion: Bone scintigraphy of vertebral fractures may be obtained with this CZT-SPECT/CT system with fast 3D acquisitions and high-quality images displayed with a reliable SUV scale, approaching what is achieved and recommended for PET imaging.

SUVs Are Adequate Measures of Lesional 18F-DCFPyL Uptake in Patients with Low Prostate Cancer Disease Burden

In prostate cancer (PCa) patients, the tumor-to-blood ratio (TBR) has been validated as the preferred simplified method for lesional 18F-DCFPyL (a radiolabeled prostate-specific membrane antigen ligand) uptake quantification on PET. In contrast to SUVs, the TBR accounts for variability in arterial input functions caused by differences in total tumor burden between patients (the sink effect). However, TBR depends strongly on tracer uptake interval and has worse repeatability and is less applicable in clinical practice than SUVs. We investigated whether SUV could provide adequate quantification of 18F-DCFPyL uptake on PET/CT in a patient cohort with low PCa burden. Methods: In total, 116 patients with PCa undergoing 18F-DCFPyL PET/CT imaging were retrospectively included. All 18F-DCFPyL-avid lesions suspected of being PCa were semiautomatically delineated. SUVpeak was plotted against TBR for the most intense lesion of each patient. The correlation of SUVpeak and TBR was evaluated using linear regression and was stratified for patients undergoing PET/CT for primary staging, patients undergoing restaging at biochemical recurrence, and patients with metastatic castration-resistant PCa. Moreover, the correlation was evaluated as a function of tracer uptake time, prostate-specific antigen level, and PET-positive tumor volume. Results: In total, 436 lesions were delineated (median, 1 per patient; range, 1-66). SUVpeak correlated well with TBR in patients with PCa and a total tumor volume of less than 200 cm3 (R2 = 0.931). The correlation between SUV and TBR was not affected by disease setting, prostate-specific antigen level, or tumor volume. SUVpeak depended less on tracer uptake time than did TBR. Conclusion: For 18F-DCFPyL PET/CT, SUVpeak correlates strongly with TBR. Therefore, it is a valuable simplified, semiquantitative measurement in patients with low-volume PCa (<200 cm3). SUVpeak can therefore be applied in 18F-DCFPyL PET assessment as an imaging biomarker to characterize tumors and to monitor treatment outcomes.

Semiquantitative analysis of interim 18F-FDG PET is superior in predicting outcome in Hodgkin lymphoma patients compared to visual analysis

PURPOSE

To investigate the prognostic value of interim PET (PETi) in adult HL patients, comparing visual with semiquantitative analysis.

MATERIAL AND METHODS

Retrospective analysis of Hodgkin's lymphoma (HL) patients diagnosed between 2012 and 2016 in the Onco-hematology Department of Instituto Português de Oncologia - Porto (median follow-up: 46.5 months [2.6-66.4]). Fifty-eight patients with available PET at diagnosis (PET0) and PETi data were included. PETi scans were analyzed according to Deauville 5-point scale (5-PS), and cut-off values for changes in maximum standardized uptake value [SUVmax], peak SUV [SUVpeak], metabolic tumour volume [MTV] and total lesion glycolysis index [TLG] between PETi and PET0 were computed using ROC analysis. Visual and semiquantitative data were compared with each other in the prediction of patient outcomes.

RESULTS

Semiquantitative analysis obtained a higher sensitivity for persistent/relapsed disease compared to the 5-PS (70% vs. 10%, respectively), but lower specificity. It also demonstrated better predictive performance for response to first-line therapy (negative predictive value >92%). The positive predictive value was similar for all five measurements. At 60 months of follow-up, there was a significant difference between the progression free survival (PFS) curves of patients with positive and negative PETi according to ΔSUVmax (56.9% vs. 88.0%, p<0.05), ΔSUVpeak (55.9% vs. 88.1%, p<0.05), ΔMTV (35.3% vs. 88.7%, p<0.05), and ΔTLG (42.4% vs. 88.1%, p<0.05). Statistical significance was not reached when considering 5-PS results.

DISCUSSION

PETi interpretation according to a semiquantitative approach appears to discriminate HL patients better than the visual 5-PS analysis. This could allow better detection of persistent or early relapsed disease, while a negative PETi result could support de-escalating therapy intensity.

First-in-human study of 89Zr-pembrolizumab PET/CT in patients with advanced stage non-small-cell lung cancer

Background: Tumor programmed-death ligand-1 (PD-L1) proportion score is the current method to select non-small-cell lung cancer (NSCLC) patients for single agent treatment with pembrolizumab, a programmed cell death-1 (PD-1) monoclonal antibody. However, not all patients respond to therapy. Better understanding of in vivo drug behavior may help to select patients that benefit most. Methods: NSCLC patients eligible for pembrolizumab monotherapy as first or later line therapy were enrolled. Patients received two injections of ⁸⁹Zr-pembrolizumab; one without a preceding dose of pembrolizumab and one with 200 mg pembrolizumab, directly prior to tracer injection. Up to four PET/CT scans were obtained after tracer injection. Post-imaging acquisition, patients were treated with 200 mg pembrolizumab, every three weeks. Tumor uptake and tracer biodistribution were visually assessed and quantified as standardized uptake value (SUV). Tumor tracer uptake was correlated with PD-1 and PD-L1 expression and response to pembrolizumab treatment. Results: Twelve NSCLC patients were included. One patient experienced grade 3 myalgia after tracer injection. ⁸⁹Zr-pembrolizumab was observed in the blood pool, liver and spleen. Tracer uptake was visualized in 47,2% of 72 tumor lesions measuring ≥20 mm long axis diameter, and substantial uptake heterogeneity was observed within and between patients. Uptake was higher in patients with response to pembrolizumab treatment (n = 3) compared to patients without a response (n = 9), although this was not statistically significant (median SUVpeak 11.4 vs 5.7, P = 0.066). No significant correlations were found with PD-L1 or PD-1 immunohistochemistry. Conclusion: ⁸⁹Zr-pembrolizumab injection was safe with only one grade 3 adverse event, possibly immune related, out of 12 patients. ⁸⁹Zr-pembrolizumab tumor uptake was higher in patients with response to pembrolizumab treatment, but did not correlate with PD-L1 or PD-1 immunohistochemistry.

SUV95th as a Reliable Alternative to SUVmax for Determining Renal Uptake in [68Ga] PSMA PET/CT

PURPOSE

Widely used in clinical practice, the maximum standardized uptake value (SUV_max) is a statistical index highly prone to physical and biological variations, which can lead to unpredictable errors. This study has a methodological aim: to identify a more robust SUV-based index representing the tracer accumulation. In particular, the new metric was tested to confirm the potential of mannitol to reduce renal uptake Ga-68 prostate-specific membrane antigen ([₆₈Ga]PSMA).

PROCEDURES

To this aim, our previously published work, proving the efficacy of mannitol, was considered as a background study. Renal SUV_max was calculated in nine patients undergoing [⁶⁸Ga]PSMA positron emission tomography (PET)/X-ray computed tomography (CT) at baseline (b-PET/CT) and at follow-up after intravenous infusion of 500 ml of 10 % mannitol (m-PET/CT). SUV values of kidney volumes were extracted by a new 3D segmentation method. A new parameter, the median computed on the upper 10% of the SUV distribution (SUV_95th), was introduced to better characterize the tracer accumulation. A comparison between SUV_max and SUV_95th was also performed. Kruskal-Wallis test was used to assess the statistical significance of the differences in SUV_95th between b-PET/CT and m-PET/CT.

RESULTS

SUV_95th not only confirmed the efficacy of mannitol as demonstrated in the previous study but improved the separability of b-PET/CT and m-PET/CT examinations, overturning SUV_max findings in two cases. The outcomes of the Kruskal-Wallis test computed for each kidney proved that differences between b-PET/CT and m-PET/CT SUV_95th values were significant (p value < 0.001).

CONCLUSIONS

Our findings indicate that SUV_95th is a more robust index to assess high uptake level, representing a reliable alternative to SUV_max. Independently from the segmentation method, the superiority of SUV_95th and its easy computation could make its clinical impact decisive. The results obtained with SUV_95th, more representative of tracer uptake than those with SUV_max suggest, in our opinion, that mannitol infusion could be used to reduce the adsorbed dose to the kidneys during [⁶⁸Ga]PSMA PET/CT and Lu-177 or Ac-225 therapy. Our future goal will be confirming this effect in a larger cohort of patients, also verifying the role of SUV_95th in the evaluation of tumor response to therapy.

Pitfalls on PET/CT Due to Artifacts and Instrumentation

PET/CT has become a preferred imaging modality over PET-only scanners in clinical practice. However, along with the significant improvement in diagnostic accuracy and patient throughput, pitfalls on PET/CT are reported as well. This review provides a general overview on the potential influence of the limitations with respect to PET/CT instrumentation and artifacts associated with the modality integration on the image appearance and quantitative accuracy of PET. Approaches proposed in literature to address the limitations or minimize the artifacts are discussed as well as their current challenges for clinical applications. Although the CT component can play an important role in assisting clinical diagnosis, we concentrate on the imaging scenarios where CT is used to provide auxiliary information for attenuation compensation and scatter correction in PET.

Correlation of 18F-FDG/PET SUVmax, SUVmean, MTV, and TLG with HIF-1α in Patients with Colorectal Cancer

Objectives:

Post-hypoxia hypoxia-inducible factor (HIF)-1α activation plays a vital role in colorectal cancer (CRC) angiogenesis. Although glucose metabolism is induced in some cancer types via HIF-1α, the prognostic significance of HIF-1α in CRC and its correlation with ¹⁸fluorinefluorodeoxyglucose (¹⁸F-FDG) uptake in positron emission tomography (PET) remain controversial. This study aims to investigate the association between ¹⁸F-FDG/PET parameters and HIF-1α expression in CRC.

Methods:

Thirty-six histopathologically confirmed patients with CRC who had ¹⁸F-FDG/PET scans before surgery were enrolled in the study. The correlations between the maximum standardized uptake value (SUV_max), SUV_mean, metabolic tumor volume (MTV), total lesion glycolysis, HIF-1α overexpression, and histopathological features were evaluated.

Results:

The tumor location, tumor diameter, perineural invasion, lymphovascular invasion, T and N stage were not significantly correlated with HIF-1α overexpression. In contrast, the tumor differentiation was negatively correlated with HIF-1α expression (r=-0.332, p=0.048). None of the ¹⁸F-FDG/PET parameters was significantly correlated with HIF-1α overexpression. A significant relationship was found between tumor differentiation, tumor necrosis percentage, and MTV (p=0.030, p=0.020).

Conclusion:

The expected association between HIF-1α overexpression and ¹⁸F-FDG/PET parameters was not found in this study. However, there was a relationship between MTV, tumor differentiation, and tumor necrosis percentage. Hence, further studies are required to predict the pathological and prognostic courses of CRC using a diagnostic ¹⁸F-FDG/PET evaluation.

Dynamic 18F-fluorocholine PET/CT for parathyroid imaging in patients with primary hyperparathyroidism

OBJECTIVE

In the past few years, F-fluorocholine PET/CT has been established as a promising imaging technique for preoperative localization of parathyroid adenomas, but the optimal time point to start PET/CT acquisition after tracer injection is yet unknown. The aim of the present study was to assess the optimal time frame to acquire the PET/CT images and to evaluate the ability of dynamic imaging to differentiate parathyroid adenomas from active lymph nodes, a common cause for false-positive scan results.

PATIENTS AND METHODS

Patients with primary hyperparathyroidism who had undergone a dynamic F-fluorocholine PET/CT positive for parathyroid disease and who subsequently underwent successful parathyroidectomy were retrospectively included in this study. On the 20 minutes dynamic images, standardized uptake value measurements were acquired per 1 minute frame for the parathyroid adenoma, the thyroid gland, blood pool activity, and, if present, lymph node activity.

RESULTS

A total of 101 patients were included in this study. Time-activity curves showed a decrease of activity in parathyroid and thyroid glands, with faster wash-out from the thyroid gland and on average a stable, lower activity in lymph nodes. Blood pool activity was particularly present in the first 2 minutes. Differentiation of a parathyroid adenoma from active lymph nodes was best before 5 minutes, but no definitive cutoff value could be determined. Differentiation of a parathyroid adenoma from the thyroid gland was best after 10 minutes.

CONCLUSION

Dynamic imaging starting at the early time point of 2 minutes after injection of F-fluorocholine is useful for characterization of hyperfunctioning parathyroid glands.

Semiquantitative analysis of interim 18F-FDG PET is superior in predicting outcome in Hodgkin lymphoma patients compared to visual analysis

PURPOSE

To investigate the prognostic value of interim PET (PETi) in adult HL patients, comparing visual with semiquantitative analysis.

MATERIAL AND METHODS

Retrospective analysis of Hodgkin's Lymphoma (HL) patients diagnosed between 2012 and 2016 in the Onco-Hematology Department of Instituto Português de Oncologia - Porto (median follow-up: 46.5 months [2,6-66,4]). Fifty-eight patients with available PET at diagnosis (PET0) and PETi data were included. PETi scans were analysed according to Deauville 5-point scale (5-PS), and cut-off values for changes in maximum standardized uptake value [SUVmax], peak SUV [SUVpeak], metabolic tumour volume [MTV] and total lesion glycolysis index [TLG] between PETi and PET0 were computed using ROC analysis. Visual and semiquantitative data were compared with each other in the prediction of patient outcomes.

RESULTS

Semiquantitative analysis obtained a higher sensitivity for persistent/relapsed disease compared to the 5-PS (70% vs. 10%, respectively), but lower specificity. It also demonstrated better predictive performance for response to first-line therapy (negative predictive value > 92%). The positive predictive value was similar for all five measurements. At 60 months of follow-up, there was a significant difference between the progression free survival (PFS) curves of patients with positive and negative PETi according to ΔSUVmax (56.9% vs. 88.0%, p < 0.05), ΔSUVpeak (55.9% vs 88.1%, p< 0.05), ΔMTV (35.3% vs. 88.7%, p< 0.05), and ΔTLG (42.4% vs. 88.1%, p< 0.05). Statistical significance wasn't reached when considering 5-PS results.

DISCUSSION

PETi interpretation according to a semiquantitative approach appears to discriminate HL patients better than the visual 5-PS analysis. This could allow better detection of persistent or early relapsed disease, while a negative PETi result could support de-escalating therapy intensity.

Improvement of image quality using amplitude-based respiratory gating in PET-computed tomography scanning

OBJECTIVES

This study sought to provide data supporting the expanded clinical use of respiratory gating by assessing the diagnostic accuracy of breathing motion correction using amplitude-based respiratory gating.

METHODS

A respiratory movement tracking device was attached to a PET-computed tomography scanner, and images were obtained in respiratory gating mode using a motion phantom that was capable of sensing vertical motion. Specifically, after setting amplitude changes and intervals according to the movement cycle using a total of nine combinations of three waveforms and three amplitude ranges, respiratory motion-corrected images were reconstructed using the filtered back projection method. After defining areas of interest in the acquired images in the same image planes, statistical analyses were performed to compare differences in standardized uptake value (SUV), lesion volume, full width at half maximum (FWHM), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR).

RESULTS

SUVmax increased by 89.9%, and lesion volume decreased by 27.9%. Full width at half maximum decreased by 53.9%, signal-to-noise ratio increased by 11% and contrast-to-noise ratio increased by 16.3%. Optimal results were obtained when using a rest waveform and 35% duty cycle, in which the change in amplitude in the respiratory phase signal was low, and a constant level of long breaths was maintained.

CONCLUSIONS

These results demonstrate that respiratory-gated PET-CT imaging can be used to accurately correct for SUV changes and image distortion caused by respiratory motion, thereby providing excellent imaging information and quality.

Usefulness of semi-automatic harmonization strategy of standardized uptake values for multicenter PET studies

This study assessed the possibility of semi-automatic harmonization of standardized uptake values (SUVs) in multicenter studies. Phantom data were acquired using 16 PET/CT scanners (including 3 PET/CT scanners with a silicon photomultiplier detector). PET images obtained using 30-min/bed scans for optimum harmonization filter calculations and using 90–180-s/bed scans for SUV validation under clinical conditions were obtained. Time of flight and a reconstruction method with point-spread function correction were allowed. The optimal full width at half maximum of the 3D-Gaussian filter that minimizes the root mean square error with the median value of the JSNM harmonization range was calculated semi-automatically. The SUVmax and the SUVpeak of the hot spheres were measured, and the inter-scanner coefficient of variation (COV) was calculated before and after harmonization. The harmonization filter was applied to 11 of the 15 PET/CT scanners in which the SUV calibration accuracy had been verified, but not in the remaining 4 scanners. Under noiseless conditions before harmonization, the inter-scanner COVs of the SUVmax and the SUVpeak were as high as 21.57% and 12.20%, respectively, decreasing to 8.79% and 5.73% after harmonization, respectively. Harmonization brought the SUVmax of all the hot spheres to within the harmonization range. Even under clinical conditions affected by image noise, the inter-scanner COVs for the SUVmax and SUVpeak were as high as 8.83% and 5.18% after harmonization, respectively. By applying an optimal harmonization filter that is calculated semi-automatically, the harmonization of SUVs according to the JSNM strategy is possible in multicenter studies, thereby reducing inter-scanner COVs.

Standardized Uptake Value for 18F-Fluorodeoxyglucose Is a Marker of Inflammatory State and Immune Infiltrate in Cervical Cancer

PURPOSE

Chemoradiotherapy for locally advanced cervical cancer fails in over a third of patients. Biomarkers with therapeutic implications are therefore needed. We investigated the relationship between an established prognostic marker, maximum standardized uptake value (SUV_max) on ¹⁸F-fluorodeoxyglucose positron emission tomography, and the inflammatory and immune state of cervical cancers.

EXPERIMENTAL DESIGN

An SUV_max most prognostic for freedom from progression (FFP) was identified and compared with known prognostic clinical variables in a cohort of 318 patients treated with definitive radiation with prospectively collected clinical data. Gene set enrichment analysis (GSEA) and CIBERSORT of whole-transcriptome data from 68 patients were used to identify biological pathways and immune cell subpopulations associated with high SUV_max. IHC using a tissue microarray (TMA, N = 82) was used to validate the CIBERSORT findings. The impact of macrophages on cervical cancer glucose metabolism was investigated in coculture experiments.

RESULTS

SUV_max <11.4 was most prognostic for FFP (P = 0.001). The GSEA showed that high SUV_max is associated with increased gene expression of inflammatory pathways, including JAK/STAT3 signaling. CIBERSORT and CD68 staining of the TMA showed high SUV_max tumors are characterized by a monocyte-predominant immune infiltrate. Coculture of cervical cancer cells with macrophages or macrophage-conditioned media altered glucose uptake, and IL6 and JAK/STAT3 signaling contribute to this effect.

CONCLUSIONS

SUV_max is a prognostic marker in cervical cancer that is associated with activation of inflammatory pathways and tumor infiltration of myeloid-derived immune cells, particularly macrophages. Macrophages contribute to changes in cervical cancer glucose metabolism.See related commentary by Williamson et al., p. 4136.

Digital PET/CT allows for shorter acquisition protocols or reduced radiopharmaceutical dose in [18F]-FDG PET/CT

PURPOSE

To establish the feasibility of shorter acquisition times (and by analogy, applied activity) on tumour detection and lesion contrast in digital PET/CT.

METHODS

Twenty-one randomly selected patients who underwent oncological [18F]-FDG PET/CT on a digital PET/CT were retrospectively evaluated. Scan data were anonymously obtained and reconstructed in list-mode acquisition for a standard 2 min/bed position (bp), 1 min/bp and 30 s/bp (100%, 50% and 25% time or applied activity, respectively). Scans were randomized and read by two nuclear medicine physicians in a consensus read. Readers were blind to clinical details. Scans were evaluated for the number of pathological lesions detected. Measured uptake for lesions was evaluated by maximum and mean standardized uptake value (SUVmax and SUVmean, respectively) and tumour-to-backround ratio (TBR) were compared. Agreement between the three acquisitions was compared by Krippendorf's alpha.

RESULTS

Overall n = 100 lesions were identified in the 2 min and 1 min/bp acquisitions and n = 98 lesions in the 30 s/bp acquisitions. Agreement between the three acquisitions with respect to lesion number and tumour-to-background ratio showed almost perfect agreement (K's α = 0.999). SUVmax, SUVmean and TBR likewise showed > 98% agreement, with longer acquisitions being associated with slightly higher mean TBR (2 min/bp 7.94 ± 4.41 versus 30 s/bp 7.84 ± 4.22, p < 0.05).

CONCLUSION

Shorter acquisition times have traditionally been associated with reduced lesion detectability or the requirement for larger amounts of radiotracer activity. These data confirm that this is not the case for new-generation digital PET scanners, where the known higher sensitivity results in clinically adequate images for shorter acquisitions. Only a small variation in the semi-quantitative parameters SUVmax, SUVmean and TBR was seen, confirming that either reduction of acquisition time or (by analogy) applied activity can be reduced as much as 75% in digital PET/CT without apparent clinical detriment.

Effect of quantitative values on shortened acquisition duration in brain tumor 11C-methionine PET/CT

Background

The amount of signal decreases when the acquisition duration is shortened. However, it is not clear how this affects the quantitative values. This study aims to clarify the effect of acquisition time shortening in brain tumor PET/CT using ¹¹C-methionine on the quantitative values.

Method

This study was a retrospective analysis of 30 patients who underwent clinical ¹¹C-methionine PET/CT examination. PET images were acquired in list mode for 10 min. PET images of acquisition duration from 1 to 10 min with 1-min step were reconstructed. We examined the effect on the quantitative values of acquisition duration. We placed a volume of interest to include the entire tumor and regions of interest in the shape of a large crescent in the contralateral hemisphere in 5 contiguous axial slices as normal tissue. Quantitative values examined were maximum, peak, and mean standardized uptake values (SUVmax, SUVpeak, SUVmean), metabolic tumor volume (MTV), and maximum tumor to normal tissue ratio (TNRmax), with each duration compared to that with 10 min.

Results

SUVmax, MTV, and TNRmax showed the highest values due to the effects of statistical noise when the acquisition time was 1 min. These values were stable when the acquisition duration was > 6 min. SUVpeak and SUVmean showed mostly consistent values regardless of duration.

Conclusions

SUVmax, MTV, and TNRmax are affected by acquisition time. If the acquisition duration was > 6 min, the fluctuation could be suppressed within 5% in these quantitative values. However, SUVpeak was suggested to be a robust index regardless of the acquisition duration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00379-2.

Oncologic significance of unexpected osseous foci on FDG-PET without correlative CT abnormalities

PURPOSE

Our purpose was to explore the clinical significance of unexpected osseous foci on 18F-FDG-PET without correlative CT abnormalities (FWCT) in patients referred for oncologic evaluation. The significance of FDG-avid foci without correlative CT abnormalities has been previously explored in tissues such as breast, lung, liver, and prostate; however, osseous foci without correlative CT abnormalities continue to present challenges in diagnostic interpretations.

METHODS

This study is a retrospective review of 120 osseous FWCT, reported in 91 patients, and their corresponding clinical follow-up. We included only patients with at least 6 months of clinical follow-up leading to a final diagnosis, reviewing bone biopsy results, follow-up imaging, and clinical notes. We excluded those patients on active chemotherapy at the time of the scan. For reports describing > 3 foci, we only analyzed the one with highest maximum standardized uptake value (SUVmax). As a measure of uptake intensity, we obtained focus-to-liver ratios (F/L) utilizing their SUVmax and corresponding hepatic 3D SUVmean.

RESULTS

Of 91 patients, 74 (81%) had biopsy-confirmed primary malignancies and 17 (19%) had suspicious findings on diagnostic imaging, but no proven primary malignancy. 50 of 120 (42%) osseous foci were malignant and 70 (58%) were benign. 49 of 120 (41%) foci were solitary and 71 (59%) were 0 with other foci (non-solitary). Malignancy resulted from 15/49 (31%) solitary foci and 35/71 (49%) non-solitary foci. Malignant lesions had a mean F/L 2.37 ± 0.397 and benign lesions a mean F/L 1.49 ± 0.169. Osseous malignancy correlated with a higher uptake intensity (Spearman = 0.408; P < 0.01) and was significantly associated with F/L ≥ 2.0 (P < 0.001). Osseous FWCT led to restaging and management modification in 12/91 (13%) patients.

CONCLUSION

Osseous FWCT frequently represent early stages of malignancy. A higher index of suspicion is warranted for osseous FWCT associated with underlying myeloproliferative neoplasms, breast and lung cancer, and moderate (F/L 1.0-2.0) or high (F/L > 2.0) uptake intensity. Interpreting physicians encountering these variables can recommend interval follow-up with 18F-FDG-PET/CT or correlation with contrast-enhanced MRI or tissue biopsy. In patients with an altered biodistribution of 18F-FDG in the bone marrow (e.g., recent chemotherapy cycle), follow-up FDG-PET can be obtained at an appropriate time interval following oncologic treatment.

Quantitation of cancer treatment response by 2-[18F]FDG PET/CT: multi-center assessment of measurement variability using AUTO-PERCIST™

Background

The aim of this study was to assess the reader variability in quantitatively assessing pre- and post-treatment 2-deoxy-2-[¹⁸F]fluoro-d-glucose positron emission tomography/computed tomography ([¹⁸F]FDG PET/CT) scans in a defined set of images of cancer patients using the same semi-automated analytical software (Auto-PERCIST™), which identifies tumor peak standard uptake value corrected for lean body mass (SUL_peak) to determine [¹⁸F]FDG PET quantitative parameters.

Methods

Paired pre- and post-treatment [¹⁸F]FDG PET/CT images from 30 oncologic patients and Auto-PERCIST™ semi-automated software were distributed to 13 readers across US and international sites. One reader was aware of the relevant medical history of the patients (read_reference), whereas the 12 other readers were blinded to history but had access to the correlative images. Auto-PERCIST™ was set up to first automatically identify the liver and compute the threshold for tumor measurability (1.5 × liver mean) + (2 × liver standard deviation [SD]) and then detect all sites with SUL_peak greater than the threshold. Next, the readers selected sites they believed to represent tumor lesions. The main performance metric assessed was the percent change in the SUL_peak (%ΔSUL_peak) of the hottest tumor identified on the baseline and follow-up images.

Results

The intra-class correlation coefficient (ICC) for the %ΔSUL_peak of the hottest tumor was 0.87 (95%CI: [0.78, 0.92]) when all reads were included (n = 297). Including only the measurements that selected the same target tumor as the read_reference (n = 224), the ICC for %ΔSUL_peak was 1.00 (95%CI: [1.00, 1.00]). The Krippendorff alpha coefficient for response (complete or partial metabolic response, versus stable or progressive metabolic disease on PET Response Criteria in Solid Tumors 1.0) was 0.91 for all reads (n = 380) and 1.00 including for reads with the same target tumor selection (n = 270).

Conclusion

Quantitative tumor [¹⁸F]FDG SUL_peak changes measured across multiple global sites and readers utilizing Auto-PERCIST™ show very high correlation. Harmonization of methods to single software, Auto-PERCIST™, resulted in virtually identical extraction of quantitative tumor response data from [¹⁸F]FDG PET images when the readers select the same target tumor.

FDG PET/CT for Assessment of Immune Therapy: Opportunities and Understanding Pitfalls

Immune checkpoint blockade has demonstrated the ability to modulate the immune system to produce durable responses in a wide range of cancers and has significantly impacted the standard of care. However, many cancer patients still do not respond to immune checkpoint blockade or have a limited duration of antitumor responses. Moreover, immune-related adverse events caused by immune checkpoint blockade can be severe and debilitating for some patients, limiting continuation of therapy and resulting in severe autoimmune conditions. Standard-of-care conventional anatomic imaging modalities and tumor response criteria have limitations to adequately assess tumor responses, especially early in the course of therapy, for risk-adapted clinical management to inform care of patients treated with immunotherapy. Molecular imaging with position emission tomography (PET) provides a noninvasive functional biomarker of tumor response, and of immune activation, for patients on immune-based therapies to help address these needs. 18F-FDG (FDG) PET/CT is readily available clinically and a number of studies have evaluated the use of this agent for assessment of prognosis, treatment response and immune activation for patients treated with immune checkpoint blockade. In this review paper, we discuss the current oncologic applications and imaging needs of cancer immunotherapy, recent studies applying FDG PET/CT for tumor response assessment, and evaluation of immune-related adverse events for improving clinical management. We largely focus on metastatic melanoma; however, we generalize where applicable to immunotherapy in other tumor types. We also briefly discuss PET imaging and quantitation as well as emerging non-FDG PET imaging radiotracers for cancer immunotherapy imaging.

Positron Emission Tomography for Response Evaluation in Microenvironment-Targeted Anti-Cancer Therapy

Therapeutic response is evaluated using the diameter of tumors and quantitative parameters of 2-[¹⁸F] fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET). Tumor response to molecular-targeted drugs and immune checkpoint inhibitors is different from conventional chemotherapy in terms of temporal metabolic alteration and morphological change after the therapy. Cancer stem cells, immunologically competent cells, and metabolism of cancer are considered targets of novel therapy. Accumulation of FDG reflects the glucose metabolism of cancer cells as well as immune cells in the tumor microenvironment, which differs among patients according to the individual immune function; however, FDG-PET could evaluate the viability of the tumor as a whole. On the other hand, specific imaging and cell tracking of cancer cell or immunological cell subsets does not elucidate tumor response in a complexed interaction in the tumor microenvironment. Considering tumor heterogeneity and individual variation in therapeutic response, a radiomics approach with quantitative features of multimodal images and deep learning algorithm with reference to pathologic and genetic data has the potential to improve response assessment for emerging cancer therapy.

Quantitative accuracy of radiomic features of low-dose 18F-FDG PET imaging

Background

¹⁸F-FDG PET based radiomics is promising for precision oncology imaging. This work aims to explore quantitative accuracies of radiomic features (RFs) for low-dose ¹⁸F-FDG PET imaging.

Methods

Twenty lung cancer patients were prospectively enrolled and underwent ¹⁸F-FDG PET/CT scans. Low-dose PET situations (true counts: 20×10⁶, 15×10⁶, 10×10⁶, 7.5×10⁶, 5×10⁶, 2×10⁶, 1×10⁶, 0.5×10⁶, 0.25×10⁶) were simulated by randomly discarding counts from the acquired list-mode data. Each PET image was created using the scanner default reconstruction parameters. Each lesion volume of interest (VOI) was obtained via an adaptive contouring method with a threshold of 50% peak standardized uptake value (SUVpeak) in the PET images with full count data and VOIs were copied to the PET images at the reduced count level. Conventional SUV measures, features calculated from first-order statistics (FOS) and texture features (TFs) were calculated. Texture based RF include features calculated from gray-level co-occurrence matrix (GLCM), gray-level run length matrix (GLRLM), gray-level size zone matrix (GLSZM), neighboring gray-level dependence matrix (NGLDM) and neighbor gray-tone difference matrix (NGTDM). Bias percentage (BP) at different count levels for each RF was calculated.

Results

Fifty-seven lesions with a volume greater than 1.5 cm³ were found (mean volume, 25.7 cm³, volume range, 1.5–245.4 cm³). In comparison with normal total counts, mean SUV (SUVmean) in the lesions, normal lungs and livers, Entropy and sum entropy from GLCM, busyness from NGTDM and run-length non-uniformity from GLRLM were the most robust features, with a BP of 5% at the count level of 1×10⁶ (equivalent to an effective dose of 0.04 mSv) RF including cluster shade from GLCM, long-run low grey-level emphasis, high grey-level run emphasis and short-run low grey-level emphasis from GLRM exhibited the worst performance with 50% of bias with 20×10⁶ counts (equivalent to an effective dose of 0.8 mSv).

Conclusions

In terms of the lesions included in this study, SUVmean, entropy and sum entropy from GLCM, busyness from NGTDM and run-length non-uniformity from GLRLM were the least sensitive features to lowering count.

Machine learning in quantitative PET: A review of attenuation correction and low-count image reconstruction methods

The rapid expansion of machine learning is offering a new wave of opportunities for nuclear medicine. This paper reviews applications of machine learning for the study of attenuation correction (AC) and low-count image reconstruction in quantitative positron emission tomography (PET). Specifically, we present the developments of machine learning methodology, ranging from random forest and dictionary learning to the latest convolutional neural network-based architectures. For application in PET attenuation correction, two general strategies are reviewed: 1) generating synthetic CT from MR or non-AC PET for the purposes of PET AC, and 2) direct conversion from non-AC PET to AC PET. For low-count PET reconstruction, recent deep learning-based studies and the potential advantages over conventional machine learning-based methods are presented and discussed. In each application, the proposed methods, study designs and performance of published studies are listed and compared with a brief discussion. Finally, the overall contributions and remaining challenges are summarized.

Clinical and prognostic value of tumor volumetric parameters in melanoma patients undergoing 18F-FDG-PET/CT: a comparison with serologic markers of tumor burden and inflammation

BACKGROUND

To investigate the association of tumor volumetric parameters in melanoma patients undergoing 18F-FDG-PET/CT with serologic tumor markers and inflammatory markers and the role as imaging predictors for overall survival.

METHODS

A patient cohort with advanced melanoma undergoing 18F-FDG-PET/CT for planning metastasectomy between 04/2013 and 01/2015 was retrospectively included. The volumetric PET parameters whole-body MTV and whole-body TLG as well as the standard uptake value (SUV) peak were quantified using 50%-isocontour volumes of interests (VOIs) and then correlated with the serologic parameters lactate dehydrogenase (LDH), S-100 protein, c-reactive protein (CRP) and alkaline phosphatase (AP). PET parameters were dichotomized by their respective medians and correlated with overall survival (OS) after PET/CT. OS was compared between patients with or without metastases and increased or not-increased serologic parameters.

RESULTS

One hundred seven patients (52 female; 65 ± 13.1yr.) were included. LDH was strongly associated with MTV (rP = 0.73, p <  0.001) and TLG (rP = 0.62, p <  0.001), and moderately associated with SUVpeak (rP = 0.55, p <  0.001). S-100 protein showed a moderate association with MTV (rP = 0.54, p <  0.001) and TLG (rP = 0.48, p <  0.001) and a weak association with SUVpeak (rP = 0.42, p <  0.001). A strong association was observed between CRP and MTV (rP = 0.66, p <  0.001) and a moderate to weak association between CRP and TLG (rP = 0.53, p <  0.001) and CRP and SUVpeak (rP = 0.45, p <  0.001). For differentiation between patients with or without metastases, receiver operating characteristic (ROC) analysis revealed a cut-off value of 198 U/l for serum LDH (AUC 0.81, sensitivity 0.80, specificity 0.72). Multivariate analysis for OS revealed that both MTV and TLG were strong independent prognostic factors. TLG, MTV and SUVpeak above patient median were accompanied with significantly reduced estimated OS compared to the PET parameters below patient median (e.g. TLG: 37.1 ± 3.2 months vs. 55.9 ± 2.5 months, p <  0.001). Correspondingly, both elevated serum LDH and S-100 protein were accompanied with significantly reduced OS (36.5 ± 4.9 months and 37.9 ± 4.4 months) compared to normal serum LDH (49.2 ± 2.4 months, p = 0.01) and normal S-100 protein (49.0 ± 2.5 months, p = 0.01).

CONCLUSIONS

Tumor volumetric parameters in 18F-FDG-PET/CT serve as prognostic imaging biomarkers in patients with advanced melanoma which are associated with established serologic tumor markers and inflammatory markers.

Value of metabolic parameters in distinguishing primary mediastinal lymphomas from thymic epithelial tumors

Objective: A high rate of unnecessary thymectomies has been reported. This study aimed to distinguish primary mediastinal lymphomas (PMLs) from thymic epithelial tumors (TETs) by evaluating volumetric and metabolic parameters with ¹⁸F-FDG PET/CT.

Methods: A total of 136 patients who were pathologically diagnosed with TETs or PMLs were enrolled, and ¹⁸F-FDG PET/CT was performed before therapy. Volumetric parameters, including the mean SUV (SUVmean), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and SUVmax, were determined and compared between the 2 subtypes. The diagnostic performance of these parameters was evaluated with receiver operating characteristic (ROC) curve analysis.

Results: All parameters significantly differed between patients with PMLs and TETs. Patients with lymphomas were younger and had higher SUVmean, SUVmax, TLG, and MTV values than patients with TETs. The MTV and TLG values had similar diagnostic performance. ROC analysis indicated that the areas under the curves of the SUVmean and SUVmax values performed similarly (approximately 0.76) in differentiating patients with PMLs from TETs, and both values were better than the MTV and TLG values. When age was included with the SUVmax in differentiating TETs from PMLs, the AUC was 0.91, and the sensitivity and specificity increased to 80% and 93%, respectively.

Conclusions: The SUVmax and volumetric parameters of ¹⁸F-FDG PET/CT can be used to distinguish patients with PMLs versus TETs, and thus may aid in preventing unnecessary thymectomies or other invasive operations.

Optimization of injected 68Ga-PSMA activity based on list-mode phantom data and clinical validation

Optimization of injected gallium-68 (⁶⁸Ga) activity for ⁶⁸Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA PET/CT) studies is relevant for image quality, radiation protection, and from an economic point of view. However, no clear guidelines are available for ⁶⁸Ga-PSMA studies. Therefore, a phantom study is performed to determine the highest coefficient of variation (COV) acceptable for reliable image interpretation and quantification.

To evaluate image interpretation, the relationship of COV and contrast-to-noise ratio (CNR) was studied. The CNR should remain larger than five, according to the Rose criterion. To evaluate image quantification, the effect of COV on the percentage difference (PD) between quantification results of two studies was analyzed. Comparison was done by calculating the PD of the SUV_max. The maximum allowable PD_SUVmax was set at 20%. The highest COV at which both criteria are still met is defined as COV_max. Of the NEMA Image Quality phantom, a 20 min/bed (2 bed positions) scan was acquired in list-mode PET (Philips Gemini TF PET/CT). The spheres to background activity ratio was approximately 9:1. To obtain images with different COV, lower activity was mimicked by reconstructions with acquisition times of 10 min/bed to 5 s/bed. Pairs of images were obtained by reconstruction of two non-overlapping parts of list-mode data.

For the 10-mm diameter sphere, a COV of 25% still meets the criteria of CNR_SUVmean ≥ 5 and PD_SUVmax ≤ 20%. This phantom scan was acquired with an acquisition time of 116 s and a background activity concentration of 0.71 MBq/kg. Translation to a clinical protocol results in a clinical activity regimen of 3.5 MBq/kg min at injection. To verify this activity regimen, 15 patients (6 MBq/kg min) with a total of 22 lesions are included. Additional reconstructions were made to mimic the proposed activity regimen. Based on the CNR_SUVmax, no lesions were missed with this proposed activity regimen.

For our institution, a clinical activity regimen of 3.5 MBq/kg min at injection is acceptable, which indicates that activity can be reduced by almost 50% compared with the current code of practice. Our proposed method could be used to obtain an objective activity regimen for other PET/CT systems and tracers.

Quantitative PET/MR imaging of lung cancer in the presence of artifacts in the MR-based attenuation correction maps

Background

Positron emission tomography (PET)/magnetic resonance (MR) imaging may become increasingly important for assessing tumor therapy response. A prerequisite for quantitative PET/MR imaging is reliable and repeatable MR-based attenuation correction (AC).

Purpose

To investigate the frequency and test–retest reproducibility of artifacts in MR-AC maps in a lung cancer patient cohort and to study the impact of artifact corrections on PET-based tumor quantification.

Material and Methods

Twenty-five lung cancer patients underwent single-day, test–retest, 18F-fluorodeoxyglucose (FDG) PET/MR imaging. The acquired MR-AC maps were inspected for truncation, susceptibility, and tissue inversion artifacts. An anatomy-based bone template and a PET-based estimation of truncated arms were employed, while susceptibility artifacts were corrected manually. We report the frequencies of artifacts and the relative difference (RD) on standardized uptake value (SUV) based quantification in PET images reconstructed with the corrected AC maps.

Results

Truncation artifacts were found in all 50 acquisitions (100%), while susceptibility and tissue inversion artifacts were observed in six (12%) and 26 (52%) of the scans, respectively. The RD in lung tumor SUV was < 5% from bone and truncation corrections, while up to 20% RD was introduced after susceptibility artifact correction, with large inconsistencies between test–retest scans.

Conclusion

The absence of bone and truncation artifacts have limited effect on the PET quantification of lung lesions. In contrast, susceptibility artifacts caused significant and inconsistent underestimations of the lung tumor SUVs, between test–retest scans. This may have clinical implications for patients undergoing serial imaging for tumor therapy response assessment.

Evaluating Novel PET-CT Functional Parameters TLG and TMTV in Differentiating Low-grade Versus Grade 3A Follicular Lymphoma

BACKGROUND

Follicular lymphoma (FL) grading, low-grade 1-2 (LG) versus grade 3A (3A), informs management. However, accurate grading is challenging owing to disease heterogeneity and inter-reader variability. The [18F]-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) parameter maximum standardized uptake value (SUVmax) has utility in differentiating LG from 3A FL, but the utility of novel parameters total lesion glycolysis (TLG) and total metabolic tumor volume (TMTV) is unknown.

PATIENTS AND METHODS

Retrospective review of diagnostic pre-treatment PET-CTs of patients aged > 18 years with FL grades 1-3A from 2009-2017 was performed. PET-CT parameters SUVmax, TLG, and TMTV values were generated using manual (MW) and semi-automated workflows (SW). Poisson regression and receiver operating characteristic curves were used to compare PET-CT parameters between LG and 3A.

RESULTS

A total of 49 patients with FL were identified: 38 LG and 11 3A. PET-CT parameters were significantly higher in 3A as compared with LG in both workflows. The cutoff values, sensitivities, and specificities were as follows: SUVmax: 10.4, 64%, and 74% in MW and 11.9, 73%, and 76% in SW; TLG: 543, 82%, and 74% in MW and 371, 73%, and 74% in SW; and TMTV: 141, 73%, and 76% in MW and 93, 64%, and 76% in SW. SUVmax had identical cutoff, sensitivity, and specificity across all 3 SWs, whereas TLG and TMTV had considerable variance across all 3 SWs.

CONCLUSIONS

TLG and TMTV are comparable to SUVmax in differentiating LG versus 3A FL. Cutoffs, sensitivities, and specificities varied in MW versus SW. Novel PET-CT parameters serve as reproducible adjuncts but not replacements for biopsy in differentiating grades of FL.

PET-Derived Quantitative Metrics for Response and Prognosis in Lymphoma

Lymphoma is a potentially curable disease; however, the clinical challenge lies in further improvement of outcomes. PET with fludeoxyglucose is an effective imaging tool. PET-derived quantitative metrics have raised significant interest to be used as a prognostic factor to complement clinical parameters for treatment decisions. The most optimized use of these quantitative PET metrics, however, will be possible with the standardization of imaging procedures. In this article, we review the technical and methodological considerations related to PET-derived quantitative metrics, and the relevant published data to emphasize the potential value of these metrics in patient prognosis and treatment response in lymphoma.

Whole-body PET estimation from low count statistics using cycle-consistent generative adversarial networks

Lowering either the administered activity or scan time is desirable in PET imaging as it decreases the patient's radiation burden or improves patient comfort and reduces motion artifacts. But reducing these parameters lowers overall photon counts and increases noise, adversely impacting image contrast and quantification. To address this low count statistics problem, we propose a cycle-consistent generative adversarial network (Cycle GAN) model to estimate diagnostic quality PET images using low count data. Cycle GAN learns a transformation to synthesize diagnostic PET images using low count data that would be indistinguishable from our standard clinical protocol. The algorithm also learns an inverse transformation such that cycle low count PET data (inverse of synthetic estimate) generated from synthetic full count PET is close to the true low count PET. We introduced residual blocks into the generator to catch the differences between low count and full count PET in the training dataset and better handle noise. The average mean error and normalized mean square error in whole body were  -0.14%  ±  1.43% and 0.52%  ±  0.19% with Cycle GAN model, compared to 5.59%  ±  2.11% and 3.51%  ±  4.14% on the original low count PET images. Normalized cross-correlation is improved from 0.970 to 0.996, and peak signal-to-noise ratio is increased from 39.4 dB to 46.0 dB with proposed method. We developed a deep learning-based approach to accurately estimate diagnostic quality PET datasets from one eighth of photon counts, and has great potential to improve low count PET image quality to the level of diagnostic PET used in clinical settings.

[Importance of FDG-PET/computed tomography in colorectal cancer]

BACKGROUND

Hybrid imaging FDG PET/CT (¹⁸F‑fluordeoxyglucose positron emission tomography/computed tomography) has gained increasing importance in oncology in recent years.

DIAGNOSIS

A focal increase in FDG uptake in the gastrointestinal tract may be due to colorectal carcinoma. Such a finding requires further clarification.

PRIMARY STAGING

Staging of the primary and locoregional lymph nodes remains a domain of established imaging modalities as FDG PET/CT does not provide a clear additional benefit. Liver metastases can be detected with high sensitivity by FDG PET/CT, but MRI is superior in small lesions.

RADIATION THERAPY PLANNING

So far FDG PET/CT plays a subordinate role in the radiation therapy planning of rectal cancer. However, it can potentially contribute to the optimization of planning target volumes.

THERAPY MONITORING

FDG PET/CT is suitable for monitoring therapy because morphological and metabolic changes of the tumor can be detected in early stages. This enables early detection of nonresponders after beginning neoadjuvant chemoradiation therapy of rectal cancer. FDG PET/CT can also be used for therapy control of liver metastases, especially after local therapeutic procedures.

DETECTION OF RECURRENCE

With clinical suspicion of local recurrence and increased tumor markers, FDG PET/CT is a valuable tool as tumor recurrence can be detected with high sensitivity and specificity.

Predictive value of LN metastasis detected by 18F-FDG PET/CT in patients with papillary thyroid cancer receiving iodine-131 radiotherapy

The aim of the present study was to predict the prognostic value of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in the metastatic lymph nodes (mLNs) of patients with papillary thyroid carcinoma (PTC) with a negative iodine-131 (¹³¹I) whole-body scan (WBS). The present retrospective study included 32 patients with PTC undergoing standard surgery and radioiodine treatment. All patients received ¹⁸F-FDG PET/CT imaging prior to and following therapy. All mLNs were divided into an effective treatment group (group A) and ineffective treatment group (group B) based on the PET Response Criteria in Solid Tumors 1.0 guidelines. All the patients were followed up for ≥9 months. A significant difference was identified in the peak standardized uptake value (SULpeak) between group B (7.85±3.20) and group A (5.36±2.19). A cut-off value of 5.85 was used to distinguish ineffective treatment of lesions from mLNs receiving radioactive ablation based on receiver operating characteristic (ROC) curve analysis with an area under the ROC curve of 0.755. Patients with a high SULpeak (P=0.003) and extrathyroidal extension (P=0.030), confirmed by pathology, more frequently exhibited a poor prognosis. In conclusion, tracer uptake of ¹⁸F-FDG for cervical metastatic nodes was revealed as a predictor for the clinical outcome of patients with PTC treated with radioiodine therapy. The present results also indicated that high SULpeak and extrathyroidal extension are poor predictors for patients with mLNs receiving ¹³¹I therapy.

Optimization of parathyroid 11C-choline PET protocol for localization of parathyroid adenomas in patients with primary hyperparathyroidism

PURPOSE

To evaluate the optimal tracer uptake time, the minimal amount of radioactivity and the inter-observer agreement for 11C-choline positron emission tomography/computed tomography (PET/CT) in patients with primary hyperparathyroidism (pHPT).

METHODS

Twenty-one patients with biochemically proven pHPT were retrospectively studied after injection of 6.3 ± 1.2 MBq/kg 11C-choline. PET data of the first nine patients, scanned for up to 60 min, were reconstructed in 10-min frames from 10- to 60-min postinjection (p.i.), mimicking varying 11C-choline uptake times. Parathyroid adenoma to background contrast ratios were calculated and compared, using standardized uptake values (SUVs). Data was reconstructed with varying scan durations (1, 2.5, 5, and 10 min) at 20-30-min p.i. (established optimal uptake time), mimicking less administered radioactivity. To establish the minimal required radioactivity, the SUVs in the shorter scan durations (1, 2.5, and 5 min) were compared to the 10-min scan duration to determine whether increased variability and/or statistical differences were observed. Four observers analyzed the 11C-choline PET/CT in four randomized rounds for all patients.

RESULTS

SUVpeak of the adenoma decreased from 30 to 40 p.i. onwards. All adenoma/background contrast ratios did not differ from 20- to 30-min p.i. onwards. The SUVs of adenoma in the scan duration of 1, 2.5, and 5 min all differed significantly from the same SUV in the 10-min scan duration (all p = 0.012). However, the difference in absolute SUV adenoma values was well below 10% and therefore not considered clinically significant. The inter-observer analysis showed that the Fleiss' kappa of the 1-min scan were classified as "moderate," while these values were classified as "good" in the 2.5-, 5-, and 10-min scan duration. Observers scored lower certainty scores in the 1- and 2.5-min scans compared to the 5- and 10-min scan durations.

CONCLUSION

The optimal time to start PET/CT scanning in patients with pHPT is 20 min after mean injection of 6.3 MBq/kg 11C-choline, with a recommended scan duration of at least 5 min. Alternatively, the radioactivity dose can be lowered by 50% while keeping a 10-min scan duration without losing the accuracy of 11C-choline PET/CT interpretation.

68Ga-DOTATATE PET: temporal variation of maximum standardized uptake value in normal tissues and neuroendocrine tumours

OBJECTIVES

Higher affinity of Ga compounds to somatostatin receptors (SSTRs) and PET better image resolution increased interest in Ga-labelled somatostatin analogs in the management of neuroendocrine tumours (NETs). This study aimed to evaluate the maximum standardized uptake value (SUVmax) variation in sequential somatostatin analogs-PET in NET patients and identify optimal tumour detection and characterization imaging time.

METHODS

Patients with histological or biochemical NET diagnosis performed two to three PET/computed tomography (CT) scans after intravenous injection of Ga-DOTATATE: Early PET [EarlyPET: <15 minutes postinjection (p.i.)], diagnostic PET (DiagPET: 45-90 minutes p.i.) and delayed PET (DelayPE: 90-240 minutes p.i.). Up to five tumour sites and normal tissues had SUVmax determined. Time-SUVmax curves were created for the target lesions and normal organs. Ratios between tumour and liver SUVmax (SUVTU/Liver) and tumour/blood pool (SUVTU/BP) were also calculated.

RESULTS

Twenty-nine patients were included, 16 female, mean age of 46.5 ± 14.3 years. Average administered activity was 129.5 ± 29.6 MBq. Kidneys SUVmax was higher in EarlyPET compared with DiagPET (P = 0.04) and DelayPET showed higher SUVmax compared with DiagPET for normal liver, pancreas and kidneys (P = 0.02). No differences were noted between EarlyPET, DiagPET and DelayPET in tumour SUVmax (P > 0.05). SUVTU/Liver and SUVTU/BP did not change between EarlyPET and DiagPET, with a slight decrease in DelayPET.

CONCLUSION

Stability in tumour SUVmax values measured at different intervals independently of tumour location, as also in normal tissues as kidneys and liver suggest that a more flexible imaging protocol may be adopted.

Evolution of heterotopic bone in fibrodysplasia ossificans progressiva: An [18F]NaF PET/CT study

Fibrodysplasia ossificans progressiva (FOP) is a rare, autosomal dominant disorder characterized by heterotopic ossification (HO) in muscles, ligaments and tendons. Flare-ups often precede the formation of HO, resulting in immobilization of joints. Due to progression of the disease without signs of a flare-up, co-existence of a chronic progression of HO has been postulated, but conclusive evidence is lacking. Recently, it has been shown that [¹⁸F]NaF PET/CT is able to identify early ossifying disease activity during flare-ups. Therefore, the purpose of the present study was to assess whether [¹⁸F]NaF PET/CT might also be able to identify the possible presence of chronic progressive HO in FOP. A total of thirteen [¹⁸F]NaF PET/CT scans from five FOP patients were analysed. Scans were acquired over a period of 0.5 to 2 years. Volumes of HO and standardized uptake values (SUV) were obtained based on manual segmentation of CT images. SUV_peak values, defined as the average SUV value of a 1 mL sphere containing the hottest voxel pixels, were obtained. Two out of five patients experienced ≥1 active clinical flare-ups at the time of the [¹⁸F]NaF PET/CT scan. In addition, in four out of five patients, serial scans showed radiological progression of HO (3 to 8 cm³), as assessed by CT volume, in the absence of a clinical flare-up. This volumetric increase was present in 6/47 (12.8%) of identified HO structures and, in all cases, was accompanied by increased [¹⁸F]NaF uptake, with SUV_peak ranging from 8.4 to 17.9. In conclusion, HO may progress without signs of a flare-up. [¹⁸F]NaF PET/CT is able to identify these asymptomatic, but progressive HO lesions, thereby demonstrating the presence of chronic activity in FOP. Consequently, future drugs should not only target new HO formation, but also this chronic HO progression.

18F-FDG PET/CT for the quantification of inflammation in large carotid artery plaques

BACKGROUND

There is currently no consensus on the methodology for quantification of 18F-FDG uptake in inflammation in atherosclerosis. In this study, we explore different methods for quantification of 18F-FDG uptake in carotid atherosclerotic plaques and correlate the uptake values to histological assessments of inflammation.

METHODS AND RESULTS

Forty-four patients with atherosclerotic stenosis ≥70% of the internal carotid artery underwent 18F-FDG PET/CT. Maximum standardized uptake values (SUVmax) from all plaque-containing slices were collected. SUVmax for the single highest and the mean of multiple slices with and without blood background correction (by subtraction (cSUV) or by division (target-to-background ratio (TBR)) were calculated. Following endarterectomy 30 plaques were assessed histologically. The length of the plaques at CT was 6-32 mm. The 18F-FDG uptake in the plaques was 1.15-2.66 for uncorrected SUVs, 1.16-3.19 for TBRs, and 0.20-1.79 for cSUVs. There were significant correlations between the different uptake values (r = 0.57-0.99, P < 0.001). Methods with and without blood background correction showed similar, moderate correlations to the amount of inflammation assessed at histology (r = 0.44-0.59, P < 0.02).

CONCLUSIONS

In large stenotic carotid plaques, 18F-FDG uptake reflects the inflammatory status as assessed at histology. Increasing number of PET slices or background correction did not change the correlation.

Intra-individual comparison of 68Ga-PSMA-11 and 18F-DCFPyL normal-organ biodistribution

Purpose

Detailed data comparing the biodistribution of PSMA radioligands is still scarce, raising concerns regarding the comparability of different compounds. We investigated differences in normal-organ biodistribution and uptake variability between the two most commonly PSMA tracers in clinical use, ⁶⁸Ga-PSMA-11 and ¹⁸F-DCFPyL.

Methods

This retrospective analysis included 34 patients with low tumor burden referred for PET/CT imaging with ⁶⁸Ga-PSMA-11 and subsequently ¹⁸F-DCFPyL. Images were acquired with 4 cross-calibrated PET/CT systems. Volumes of interest were placed on major salivary and lacrimal glands, liver, spleen, duodenum, kidneys, bladder, blood-pool and muscle. Normal-organ biodistribution of both tracers was then quantified as SUV_peak and compared using paired tests, linear regression and Bland-Altman analysis. Between-patient variability was also assessed. Clinical and protocol variables were investigated for possible interference.

Results

For both tracers the highest uptake was found in the kidneys and bladder and low background activity was noted across all scans. In the quantitative analysis there was significantly higher uptake of ⁶⁸Ga-PSMA-11 in the kidneys, spleen and major salivary glands (p <  0.001), while the liver exhibited slightly higher ¹⁸F-DCFPyL uptake (p = 0.001, mean bias 0.79 ± 1.30). The lowest solid-organ uptake variability was found in the liver (COV 21.9% for ⁶⁸Ga-PSMA-11, 22.5% for ¹⁸F-DCFPyL). There was a weak correlation between ¹⁸F-DCFPyL uptake time and liver SUV_peak (r = 0.488, p = 0.003) and, accordingly, patients scanned at later time-points had a larger mean bias between the two tracers’ liver uptake values (0.05 vs 1.46, p = 0.001).

Conclusion

Normal tissue biodistribution patterns of ⁶⁸Ga-PSMA-11 and ¹⁸F-DCFPyL were similar, despite subtle differences in quantitative values. Liver uptake showed an acceptable intra-patient agreement and low inter-patient variability between the two tracers, allowing its use as a reference organ for thresholding scans in the qualitative comparison of PSMA expression using these different tracers.

Electronic supplementary material

The online version of this article (10.1186/s40644-019-0211-y) contains supplementary material, which is available to authorized users.

Prognostic significance of metabolic parameters measured by 18F-FDG PET/CT in limited-stage small-cell lung carcinoma

PURPOSE

Metabolic parameters measured by [18F]-fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG PET/CT) are important prognostic factors in several types of cancers. We evaluated the predictive value of tumor metabolic parameters measured by 18F-FDG PET/CT in limited-disease small-cell lung cancer (LD-SCLC).

METHODS

This retrospective study included 30 LD-SCLC patients who underwent standard chemotherapy after radiotherapy with 18F-FDG PET/CT. The maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and blood glucose-corrected values were used to evaluate metabolic parameters in primary tumors.

RESULTS

For the median follow-up of 41.1 months, median overall survival (OS) was 75.0 months [95% confidence interval (CI) 20.9-129.1 months], and median progression-free survival (PFS) was 9.5 months (95% CI 6.8-12.1 months). Two-year OS was 78.6%, and PFS was 32.7%. OS analysis indicated that MTV and TLG were significant predictors of OS following standard treatment. High glucose-corrected SUVmax (glu-SUVmax) was related to shorter median PFS. On multivariate analysis, MTV was an independent factor of OS, and glu-SUVmax was significantly related to PFS.

CONCLUSIONS

MTV and glu-SUVmax measured on pretreatment 18F-FDG PET/CT were independent prognostic factors for LD-SCLC patients after chemoradiotherapy with curative intent. These metabolic markers need validation in larger prospective studies but may be useful in the clinical care of LD-SCLC patients.

Absolute radiotracer concentration measurement using whole-body solid-state SPECT/CT technology: in vivo/in vitro validation

The accuracy of recently approved quantitative clinical software was determined by comparing in vivo/in vitro measurements for a solid-state cadmium-zinc-telluride SPECT/CT (single photon emission computed tomography/x-ray computed tomography) camera. Bone SPECT/CT, including the pelvic region in the field of view, was performed on 16 patients using technetium-99m methylene diphosphonic acid as a radiotracer. After imaging, urine samples from each patient provided for the measurement of in vitro radiopharmaceutical concentrations. From the SPECT/CT images, three users measured in vivo radiotracer concentration and standardized uptake value (SUV) for the bladder using quantitative software (Q.Metrix, GE Healthcare). Linear regression was used to validate any in vivo/in vitro identity relations (ideally slope = 1, intercept = 0), within a 95% confidence interval (CI). Thirteen in vivo/in vitro pairs were available for further analysis, after rejecting two as clinically irrelevant (SUVs > 100 g/mL) and one as an outlier (via Cook's distance calculations). All linear regressions (R² ≥ 0.85, P < 0.0001) provided identity in vivo/in vitro relations (95% CI), with SUV averages from all users giving a slope of 0.99 ± 0.25 and intercept of 0.14 ± 5.15 g/mL. The average in vivo/in vitro residual difference was < 20%. Solid-state SPECT/CT imaging can reliably provide in vivo urinary bladder radiotracer concentrations within approximately 20% accuracy. This practical, non-invasive, in vivo quantitation method can potentially improve diagnosis and assessment of response to treatment. Graphical abstract.

Quantitative assessment of metabolic tumor burden in molecular subtypes of primary breast cancer with FDG PET/CT

PURPOSE

We aimed to quantitatively evaluate volumetric metabolic tumor burden including metabolic tumor volume and total lesion glycolysis in different molecular subtypes of breast cancer using 18F-fluorodeoxyglucose (FDG) positron emission tomography/ computed tomography (PET/CT).

METHODS

This study involved 99 female patients with pathologic diagnosis of primary breast cancer, who underwent 18F-FDG PET/CT before any therapy. Patients were divided into subtypes of luminal A, luminal B, ERBB2+, and basal-like based on the immunohistochemistry results. Metabolic tumor volume (MTV) and total lesion glycolysis (TLG) before and after correction for lean body mass were achieved and compared. Correlations between metabolic tumor burden and Ki-67 were analyzed and diagnostic performances of volumetric metabolic parameters were evaluated.

RESULTS

TLG values were significantly different between each molecular subtype, while MTV values were not. Values of TLG were significantly reduced after normalizing for lean body mass in each subtype. Both of them showed correlations with Ki-67 and presented high diagnostic ability in identifying patients with basal-like breast cancer from the rest. TLGs before and after normalizing for the lean body mass had similar diagnostic performances in differentiating patients of basal-like subtype from the rest.

CONCLUSION

Metabolic tumor burden could comprehensively reflect tumor metabolic differences of molecular subtypes of breast cancer, and it can serve to help differentiate patients with basal-like breast cancer.

Prognostic modeling for patients with colorectal liver metastases incorporating FDG PET radiomic features

OBJECTIVE

We aimed to improve prediction of outcome for patients with colorectal liver metastases, via prognostic models incorporating PET-derived measures, including radiomic features that move beyond conventional standard uptake value (SUV) measures.

PATIENTS AND METHODS

A range of parameters including volumetric and heterogeneity measures were derived from FDG PET images of 52 patients with colorectal intrahepatic-only metastases (29 males and 23 females; mean age 62.9 years [SD 9.8; range 32-82]). The patients underwent PET/CT imaging as part of the clinical workup prior to final decision on treatment. Univariate and multivariate models were implemented, which included statistical considerations (to discourage false discovery and overfitting), to predict overall survival (OS), progression-free survival (PFS) and event-free survival (EFS). Kaplan-Meier survival analyses were performed, where the subjects were divided into high-risk and low-risk groups, from which the hazard ratios (HR) were computed via Cox proportional hazards regression.

RESULTS

Commonly-invoked SUV metrics performed relatively poorly for different prediction tasks (SUVmax HR = 1.48, 0.83 and 1.16; SUVpeak HR = 2.05, 1.93, and 1.64, for OS, PFS and EFS, respectively). By contrast, the number of liver metastases and metabolic tumor volume (MTV) each performed well (with respective HR values of 2.71, 2.61 and 2.42, and 2.62, 1.96 and 2.29, for OS, PFS and EFS). Total lesion glycolysis (TLG) also resulted in similar performance as MTV. Multivariate prognostic modeling incorporating different features (including those quantifying intra-tumor heterogeneity) resulted in further enhanced prediction. Specifically, HR values of 4.29, 4.02 and 3.20 (p-values = 0.00004, 0.0019 and 0.0002) were obtained for OS, PFS and EFS, respectively.

CONCLUSIONS

PET-derived measures beyond commonly invoked SUV parameters hold significant potential towards improved prediction of clinical outcome in patients with liver metastases, especially when utilizing multivariate models.

Assessment of artery calcification in atherosclerosis with dynamic 18F-FDG-PET/CT imaging in elderly subjects

Glucose metabolism in atherosclerotic arteries has been shown to be an indicator of inflammation, which might be a precursor of plaque rupture. In this prospective study, we assessed the correlation between artery calcification and glucose metabolism by means of 18F-FDG PET/CT imaging in elderly subjects. Nineteen elderly subjects, with age ranging from 65 to 85 years, underwent CT and dynamic 18F-FDG-PET imaging. The artery calcification was determined with a threshold of 130 Hounsfield units. Intensity of calcification and ratio of calcification area to total artery area were classified in four sequential classes from CT images. The CT artery images were also classified as having single or multi-spot calcifications. Their respective glucose metabolism was assessed with fractional uptake rate (FUR). Factor analysis was used in this study to separate blood images from tissue to extract the blood time activity curves for FUR calculations. The artery images in PET data were corrected for partial volume effect. The total arterial segments analyzed were 1332, with 1085 without calcification (81%), 247 (19%) with calcification, and 94 segments were having multi-spot of calcifications. There was a statistically significant difference in FUR values between non-calcified to calcified segments and between subjects under medication to non-medication when comparing the subjects based on calcification area. No statistically significant differences of FUR were found between single spot as a function of intensity, while in the multi-spots, there was a statistically significant difference for all artery segments. Metabolism activity varies for non-calcified to calcified segments. Based on the metabolic activity represented by FUR, calcifications in multi-spots have different effects than in single spots.

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

Aim

To compare weight, lean body mass and body surface area for calculation of standardised uptake value (SUV) in fluorine-18-fluorodeoxyglucose PET/computed tomography, taking sex into account.

Patients and methods

This was a retrospective study of 161 (97 men) patients. Maximum standardised uptake value (SUV_max) and mean standardised uptake value (SUV_mean) were obtained from a 3-cm region of interest over the right lobe of the liver and scaled to weight, scaled to lean body mass (SUL) and scaled to body surface area (SUA). Mean hepatic computed tomography density was used to adjust SUV_mean for hepatic fat (SUV_FA). Hepatic SUV indices were divided by SUV from left ventricular cavity, thereby, eliminating whole body metric, to obtain a surrogate of blood fluorine-18-fluorodeoxyglucose clearance into liver, and multiplied by blood glucose to give a surrogate of hepatic glucose uptake rate (mSUV).

Results

SUL_max, SUA_max and all scaled to weight indices correlated strongly with weight. SUL_mean, SUL_FA, SUA_mean and SUA_FA, however, correlated weakly or not at all with weight, nor with their corresponding whole body metric in men or women, but correlated strongly when the sexes were combined into one group. This was the result of sex differences in SUL (greater in men) and SUA (greater in women). There was, however, no sex difference in mSUV.

Conclusion

Weight is unsuitable for calculating SUV. SUL and SUA are also inappropriate as maxima but appropriate as mean and fat-adjusted values. However, SUL is recommended for both sexes because SUA is influenced by both body fat and weight. Sex differences in SUL and SUA give rise to misleading correlations when sexes are combined into one group.