SUV and segmentation: pressing challenges in tumour assessment and treatment

A comprehensive review of the role of bone marrow biopsy and PET-CT in the evaluation of bone marrow involvement in adults newly diagnosed with DLBCL

Diffuse large B cell lymphoma (DLBCL) is one of the most prevalent subtypes of non-Hodgkin lymphoma (NHL) and is known for commonly infiltrating extra-nodal sites. The involvement of the bone marrow by lymphoma cells significantly impacts the staging, treatment, and prognosis among the extra-nodal sites in DLBCL. Bone marrow biopsy has been considered the standard diagnostic procedure for detecting bone marrow involvement. However, advancements in imaging techniques, such as positron emission tomography-computed tomography (PET-CT), have shown an improved ability to detect bone marrow involvement, making the need for bone marrow biopsy debatable. This review aims to emphasize the importance of bone marrow evaluation in adult patients newly diagnosed with DLBCL and suggest an optimal diagnostic approach to identify bone marrow involvement in these patients.

Impact of attenuation correction of radiotherapy hardware for positron emission tomography-magnetic resonance in ano-rectal radiotherapy patients

BACKGROUND

Positron Emission Tomography-Magnetic Resonance (PET-MR) scanners could improve ano-rectal radiotherapy planning through improved Gross Tumour Volume (GTV) delineation and enabling dose painting strategies using metabolic measurements. This requires accurate quantitative PET images acquired in the radiotherapy treatment position.

PURPOSE

This study aimed to evaluate the impact on GTV delineation and metabolic parameter measurement of using novel Attenuation Correction (AC) maps that included the radiotherapy flat couch, coil bridge and anterior coil to see if they were necessary.

METHODS

Seventeen ano-rectal radiotherapy patients received a18 F $\mathrm{^{18}F}$ -FluoroDeoxyGlucose PET-MR scan in the radiotherapy position. PET images were reconstructed without (CTAC std $\mathrm{CTAC_{std}}$ ) and with (CTAC cba $\mathrm{CTAC_{cba}}$ ) the radiotherapy hardware included. Both AC maps used the same Computed Tomography image for patient AC. Semi-manual and threshold GTVs were delineated on both PET images, the volumes compared and the Dice coefficient calculated. Metabolic parameters: Standardized Uptake ValuesSUV max $\mathrm{SUV_{max}}$ ,SUV mean $\mathrm{SUV_{mean}}$ and Total Lesion Glycolysis (TLG) were compared using paired t-tests with a Bonferroni corrected significance level ofp = 0.05 / 8 = 0.006 $p = 0.05/8 = 0.006$ .

RESULTS

Differences in semi-manual GTV volumes betweenCTAC cba $\mathrm{CTAC_{cba}}$ andCTAC std $\mathrm{CTAC_{std}}$ were approaching statistical significance (difference- 15.9 % ± 1.6 % $-15.9\%\pm 1.6\%$ ,p = 0.007 $p = 0.007$ ), with larger differences in low FDG-avid tumours (SUV mean < 8.5 g mL - 1 $\mathrm{SUV_{mean}} < 8.5\;\mathrm{g\: mL^{-1}}$ ). TheCTAC cba $\mathrm{CTAC_{cba}}$ andCTAC std $\mathrm{CTAC_{std}}$ GTVs were concordant with Dice coefficients0.89 ± 0.01 $0.89 \pm 0.01$ (manual) and0.98 ± 0.00 $0.98 \pm 0.00$ (threshold). Metabolic parameters were significantly different, withSUV max $\mathrm{SUV_{max}}$ ,SUV mean $\mathrm{SUV_{mean}}$ and TLG differences of- 11.5 % ± 0.3 % $-11.5\%\ \pm 0.3\%$ (p < 0.001 $p < 0.001$ ),- 11.6 % ± 0.3 % $-11.6\% \pm 0.3\%$ (p < 0.001 $p < 0.001$ ) and- 13.7 % ± 0.6 % $-13.7\%\ \pm 0.6\%$ (p = 0.003 $p = 0.003$ ) respectively. The TLG difference resulted in 1/8 rectal cancer patients changing prognosis group, based on literature TLG cut-offs, when usingCTAC cba $\mathrm{CTAC_{cba}}$ rather thanCTAC std $\mathrm{CTAC_{std}}$ .

CONCLUSIONS

This study suggests that using AC maps with the radiotherapy hardware included is feasible for patient imaging. The impact on tumour delineation was mixed and needs to be evaluated in larger cohorts. However using AC of the radiotherapy hardware is important for situations where accurate metabolic measurements are required, such as dose painting and treatment prognostication.

Quantitative myocardial perfusion SPECT/CT for the assessment of myocardial tracer uptake in patients with three-vessel coronary artery disease: Initial experiences and results

BACKGROUND

To evaluate quantitative myocardial perfusion SPECT/CT datasets for routine clinical reporting and the assessment of myocardial tracer uptake in patients with severe TVCAD.

METHODS

MPS scans were reconstructed as quantitative SPECT datasets using CTs from internal (SPECT/CT, Q_INT) and external (PET/CT, Q_EXT) sources for attenuation correction. TPD was calculated and compared to the TPD from non-quantitative SPECT datasets of the same patients. SUVmax, SUVpeak, and SUVmean were compared between Q_INT and Q_EXT SPECT datasets. Global SUVmax and SUVpeak were compared between patients with and without TVCAD.

RESULTS

Quantitative reconstruction was feasible. TPD showed an excellent correlation between quantitative and non-quantitative SPECT datasets. SUVmax, SUVpeak, and SUVmean showed an excellent correlation between Q_INT and Q_EXT SPECT datasets, though mean SUVmean differed significantly between the two groups. Global SUVmax and SUVpeak were significantly reduced in patients with TVCAD.

CONCLUSIONS

Absolute quantification of myocardial tracer uptake is feasible. The method seems to be robust and principally suitable for routine clinical reporting. Quantitative SPECT might become a valuable tool for the assessment of severe coronary artery disease in a setting of balanced ischemia, where potentially life-threatening conditions might otherwise go undetected.

Intrapatient variability of 18F-FDG uptake in normal tissues

Objectives

To investigate the effect of serum glucose level and other confounding factors on the variability of maximum standardized uptake value (SUVmax) in normal tissues within the same patient on two separate occasions and to suggest an ideal reference tissue.

Materials and Methods

We retrospectively reviewed 334 18F-FDG PET/CT scans of 167 cancer patients including 38 diabetics. All patients had two studies, on average 152 ± 68 days apart. Ten matched volumes of interest were drawn on the brain, right tonsil, blood pool, heart, lung, liver, spleen, bone marrow, fat, and iliopsoas muscle opposite third lumber vertebra away from any pathological 18F-FDG uptake to calculate SUVmax.

Results

SUVmax of the lungs and heart were significantly different in the two studies (P = 0.003 and P = 0.024 respectively). Only the brain uptake showed a significant moderate negative correlation with the level of blood glucose in diabetic patients (r = −0.537, P = 0.001) in the first study, while the SUVmax of other tissues showed negligible or weak correlation with the level of blood glucose in both studies.

The liver showed significant moderate positive correlation with body mass index (BMI) in both studies (r = .416, P = <0.001 versus r = 0.453, P = <0.001, respectively), and blood pool activity showed significant moderate positive correlation with BMI in the first study only (r = 0.414, P = <0.001). The liver and blood pool activities showed significant moderate negative correlation with 18F-FDG uptake time in first study only (r = −0.405, P-value = <0.001; and r = −0.409, P-value = <0.001, respectively).

In the multivariate analysis, the liver showed a consistent effect of the injected 18F-FDG dose and uptake duration on its SUVmax on the two occasions. In comparison, spleen and muscle showed consistent effect only of the injected dose on the two occasions.

Conclusion

The liver, muscle, and splenic activities showed satisfactory test/retest stability and can be used as reference activities. The spleen and muscle appear to be more optimal reference than the liver, as it is only associated with the injected dose of 18F-FDG.

Assessment of different quantification metrics of [18F]-NaF PET/CT images of patients with abdominal aortic aneurysm

BACKGROUND

We aim to assess the spill-in effect and the benefit in quantitative accuracy for [18F]-NaF PET/CT imaging of abdominal aortic aneurysms (AAA) using the background correction (BC) technique.

METHODS

Seventy-two datasets of patients diagnosed with AAA were reconstructed with ordered subset expectation maximization algorithm incorporating point spread function (PSF). Spill-in effect was investigated for the entire aneurysm (AAA), and part of the aneurysm excluding the region close to the bone (AAAexc). Quantifications of PSF and PSF+BC images using different thresholds (% of max. SUV in target regions-of-interest) to derive target-to-background (TBR) values (TBRmax, TBR90, TBR70 and TBR50) were compared at 3 and 10 iterations.

RESULTS

TBR differences were observed between AAA and AAAexc due to spill-in effect from the bone into the aneurysm. TBRmax showed the highest sensitivity to the spill-in effect while TBR50 showed the least. The spill-in effect was reduced at 10 iterations compared to 3 iterations, but at the expense of reduced contrast-to-noise ratio (CNR). TBR50 yielded the best trade-off between increased CNR and reduced spill-in effect. PSF+BC method reduced TBR sensitivity to spill-in effect, especially at 3 iterations, compared to PSF (P-value ≤ 0.05).

CONCLUSION

TBR50 is robust metric for reduced spill-in and increased CNR.

Artificial Intelligence in Lymphoma PET Imaging:: A Scoping Review (Current Trends and Future Directions)

Malignant lymphomas are a family of heterogenous disorders caused by clonal proliferation of lymphocytes. 18F-FDG-PET has proven to provide essential information for accurate quantification of disease burden, treatment response evaluation, and prognostication. However, manual delineation of hypermetabolic lesions is often a time-consuming and impractical task. Applications of artificial intelligence (AI) may provide solutions to overcome this challenge. Beyond segmentation and detection of lesions, AI could enhance tumor characterization and heterogeneity quantification, as well as treatment response prediction and recurrence risk stratification. In this scoping review, we have systematically mapped and discussed the current applications of AI (such as detection, classification, segmentation as well as the prediction and prognostication) in lymphoma PET.

Clinical value of baseline 18F-FDG PET/CT in soft tissue sarcomas

Background

The use of ¹⁸F-FDG Positron emission tomography/Computed tomography (PET/CT) in the initial staging of many cancers is clearly established. Most soft tissue sarcoma (STS) has a high affinity for ¹⁸F-FDG, which is why ¹⁸F-FDG PET/CT has been proposed as a non-invasive method, useful in diagnosis and follow-up. The standardized uptake value values (SUV), the volume-based metabolic parameters MTV (metabolic tumor volume), and TLG (total lesion glycolysis) determine tumor viability and provide its total volume and the total activity of metabolically active tumor cells. The histological grade is the most important predictor of metastases and mortality associated with STS, and a significant relationship between the metabolic parameters of ¹⁸F-FDG PET/CT and the histological grade has been described.

Methods

A retrospective study was conducted on STS patients, who had histological grade according to the FNCLCC (Fédération Nationale des Centres de Lutte Contre Le Cancer) criteria, as well as a baseline PET/CT. SUV (SUV_max, SUV_mean, and SUV_peak), MTV, and TLG were quantified. A T-student test was performed to establish the relationship between the metabolic biomarkers and the histological grade. Their usefulness as predictors of the histological grade was verified using receiver operator characteristic (ROC) curves. A survival function study was performed using the Kaplan–Meier method. To assess the prognostic utility of the metabolic biomarkers we use the Log-Rank method.

Results

The SUV values were useful to discriminate high-grade STS. We found a significant relationship between the histological grade and the SUV values. SUV_max, SUV_peak, MTV, and TLG were predictors of overall survival (OS). There were no significant differences in the OS for the SUV_mean, or in the disease-free survival (DFS) for SUV_max, SUV_mean, SUV_peak, MTV, and TLG.

Conclusions

The SUV_max, SUV_mean, and SUV_peak values correlate with the HG and are useful to discriminate high-grade from low-grade STS. Patients with high SUV_max, SUV_peak, MTV, and TLG have a significantly lower OS.

Differences among [18F]FDG PET-derived parameters in lung cancer produced by three software packages

Investigation of differences in derived [18F]FDG PET metabolic and volumetric parameters among three different software programs in lung cancer. A retrospective analysis was performed on a group of 98 lung cancer patients who underwent a baseline [18F]FDG PET/CT study. To assess appropriate delineation methods, the NEMA phantom study was first performed using the following software: Philips EBW (Extended Brilliance Workstation), MIM Software and Rover. Based on this study, the best cut-off methods (dependent on tumour size) were selected, extracted and applied for lung cancer delineation. Several semiquantitative [18F]FDG parameters (SUVmax, SUVmean, TLG and MTV) were assessed and compared among the three software programs. The parameters were assessed based on body weight (BW), lean body mass (LBM) and Bq/mL. Statistically significant differences were found in SUVmean (LBM) between MIM Software and Rover (4.62 ± 2.15 vs 4.84 ± 1.20; p < 0.005), in SUVmean (Bq/mL) between Rover and Philips EBW (21,852.30 ± 21,821.23 vs 19,274.81 ± 13,340.28; p < 0.005) and Rover and MIM Software (21,852.30 ± 21,821.23 vs 19,399.40 ± 10,051.30; p < 0.005), and in MTV between MIM Software and Philips EBW (19.87 ± 25.83 vs 78.82 ± 228.00; p = 0.0489). This study showed statistically significant differences in the estimation of semiquantitative parameters using three independent image analysis tools. These findings are important for performing further diagnostic and treatment procedures in lung cancer patients.

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.

Hepatobiliary MR contrast agent uptake as a predictive biomarker of aggressive features on pathology and reduced recurrence-free survival in resectable hepatocellular carcinoma: comparison with dual-tracer 18F-FDG and 18F-FCH PET/CT

OBJECTIVES

To compare the performance of the quantitative analysis of the hepatobiliary phase (HBP) tumor enhancement in gadobenate dimeglumine (Gd-BOPTA)-enhanced MRI and of dual-tracer 18F-FDG and 18F-fluorocholine (FCH) PET/CT for the prediction of tumor aggressiveness and recurrence-free survival (RFS) in resectable hepatocellular carcinoma (HCC).

METHODS

This retrospective, IRB approved study included 32 patients with 35 surgically proven HCCs. All patients underwent Gd-BOPTA-enhanced MRI including delayed HBP images, 18F-FDG PET/CT, and (for 29/32 patients) 18F-FCH PET/CT during the 2 months prior to surgery. For each lesion, the lesion-to-liver contrast enhancement ratio (LLCER) on MRI HBP images and the SUV_max tumor-to-liver ratio (SUV_T/L) for both tracers were calculated. Their predictive value for aggressive pathological features-including the histological grade and microvascular invasion (MVI)-and RFS were analyzed and compared using area under receiver operating characteristic (AUROC) curves and Cox regression models, respectively.

RESULTS

The AUROCs for the identification of aggressive HCCs on pathology with LLCER, 18F-FDG SUV_T/L, and 18F-FCH SUV_T/L were 0.92 (95% CI 0.78, 0.98), 0.89 (95% CI 0.74, 0.97; p = 0.70), and 0.64 (95% CI 0.45, 0.80; p = 0.035). At multivariate Cox regression analysis, LLCER was identified as an independent predictor of RFS (HR (95% CI) = 0.91 (0.84, 0.99), p = 0.022). LLCER - 4.72% or less also accurately predicted moderate-poor differentiation grade (Se = 100%, Sp = 92.9%) and MVI (Se = 93.3%, Sp = 60%) and identified patients with poor RFS after surgical resection (p = 0.030).

CONCLUSIONS

HBP tumor enhancement after Gd-BOPTA injection may help identify aggressive HCC pathological features, and patients with reduced recurrence-free survival after surgical resection.

KEY POINTS

• In patients with resectable HCC, the quantitative analysis of the HBP tumor enhancement in Gd-BOPTA-enhanced MRI (LLCER) accurately identifies moderately-poorly differentiated and/or MVI-positive HCCs. • After surgical resection for HCC, patients with LLCER - 4.72% or less had significantly poorer recurrence-free survival than patients with LLCER superior to - 4.72%. • Gd-BOPTA-enhanced MRI with delayed HBP images may be suggested as part of pre-surgery workup in patients with resectable HCC.

What and how should we measure in paediatric oncology FDG-PET/CT? Comparison of commonly used SUV metrics for differentiation between paediatric tumours

Background

In clinical routine, SUV_max and SUV_peak are most often used to determine the glucose metabolism in tumours by ¹⁸F-FDG PET/CT. Both metrics can be further normalised to SUVs in reference regions resulting in a SUV ratio (SUV_ratio). The aim of the study was to directly compare several widely used SUVs/SUV_ratios with regard to differentiation between common tumours in paediatric patients; a special focus was put on characteristics of reference region SUVs.

Methods

The final study population consisted of 61 children and adolescents with diagnoses of non-Hodgkin lymphoma (NHL, n = 25), Hodgkin lymphoma (HL, n = 14), and sarcoma (n = 22). SUV metrics included SUV_max and SUV_peak as well as both parameters normalised to liver and mediastinal blood pool, respectively, yielding the SUV_ratios SUV_max/liver, SUV_{max/mediastinum}, SUV_peak/liver, and SUV_{peak/mediastinum}.

Results

The metrics SUV_max, SUV_peak, SUV_max/liver, and SUV_peak/liver all proved to be sensitive for tumour differentiation (p ≤ 0.008); in contrast, SUV_{max/mediastinum} and SUV_{peak/mediastinum} revealed to be non-sensitive approaches. Correlation analyses showed inverse associations between reference region SUVs and SUV_ratios (p < 0.05). Multiple regression analyses demonstrated significant effects of factors as bodyweight and uptake time on reference region SUVs (p < 0.01), and thus indirectly on the corresponding SUV_ratios.

Conclusions

In the paediatric population, the ability to differentiate between common tumours remarkably varies between SUV metrics. When using SUV_ratios, the choice of reference region is crucial. Factors potentially influencing reference region SUVs (and thus SUV_ratios) should be taken into account in order to avoid erroneous conclusions. When not possible, SUV_max and SUV_peak represent less complex, more robust alternatives.

Preoperative [18F]FDG PET/CT tumour heterogeneity index in patients with uterine leiomyosarcoma: a multicentre retrospective study

PURPOSE

We investigated the prognostic value of the tumour heterogeneity index determined on preoperative [¹⁸F]FDG PET/CT in patients with uterine leiomyosarcoma (LMS).

METHODS

We retrospectively reviewed patients with uterine LMS who underwent preoperative [¹⁸F]FDG PET/CT scans at three tertiary referral hospitals. The PET/CT parameters maximum standardized uptake value of the primary tumour (SUV_max), metabolic tumour volume (MTV) and total lesion glycolysis were assessed. The negative values of the MTV linear regression slope (nMLRS) according to the SUV thresholds of 2.5 and 3.0 were determined as the tumour heterogeneity index. The value of PET/CT-derived parameters in predicting progression-free survival (PFS) and overall survival (OS) were determined in regression analyses.

RESULTS

Clinicopathological and PET/CT data from 16 patients were reviewed. The median postsurgical follow-up was 21 months (range 4-82 months), and 12 patients (75.0%) experienced recurrence. Tumour size (P = 0.017), SUV_max (P = 0.019), MTV (P = 0.016) and nMLRS (P = 0.008) were significant prognostic factors for recurrence. MTV (P = 0.048) and nMLRS (P = 0.045) were significant prognostic factors for patient survival. nMLRS was correlated with clinicopathological parameters including tumour size (Pearson's correlation coefficient γ = 0.825, P < 0.001) and lymph node metastasis (γ = 0.721, P = 0.004). Patient groups categorized according to the nMLRS cut-off value showed significant differences in PFS (P = 0.033) and OS (P = 0.044).

CONCLUSION

The preoperative tumour heterogeneity index obtained using the MTV linear regression slope may be a novel and useful prognostic marker in uterine LMS.

Heterogeneity index evaluated by slope of linear regression on 18F-FDG PET/CT as a prognostic marker for predicting tumor recurrence in pancreatic ductal adenocarcinoma

PURPOSE

¹⁸F-Fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) has been investigated as a method to predict pancreatic cancer recurrence after pancreatic surgery. We evaluated the recently introduced heterogeneity indices of ¹⁸F-FDG PET/CT used for predicting pancreatic cancer recurrence after surgery and compared them with current clinicopathologic and ¹⁸F-FDG PET/CT parameters.

METHODS

A total of 93 pancreatic ductal adenocarcinoma patients (M:F = 60:33, mean age = 64.2 ± 9.1 years) who underwent preoperative ¹⁸F-FDG PET/CT following pancreatic surgery were retrospectively enrolled. The standardized uptake values (SUVs) and tumor-to-background ratios (TBR) were measured on each ¹⁸F-FDG PET/CT, as metabolic parameters. Metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were examined as volumetric parameters. The coefficient of variance (heterogeneity index-1; SUVmean divided by the standard deviation) and linear regression slopes (heterogeneity index-2) of the MTV, according to SUV thresholds of 2.0, 2.5 and 3.0, were evaluated as heterogeneity indices. Predictive values of clinicopathologic and ¹⁸F-FDG PET/CT parameters and heterogeneity indices were compared in terms of pancreatic cancer recurrence.

RESULTS

Seventy patients (75.3%) showed recurrence after pancreatic cancer surgery (mean recurrence = 9.4 ± 8.4 months). Comparing the recurrence and no recurrence patients, all of the ¹⁸F-FDG PET/CT parameters and heterogeneity indices demonstrated significant differences. In univariate Cox-regression analyses, MTV (P = 0.013), TLG (P = 0.007), and heterogeneity index-2 (P = 0.027) were significant. Among the clinicopathologic parameters, CA19-9 (P = 0.025) and venous invasion (P = 0.002) were selected as significant parameters. In multivariate Cox-regression analyses, MTV (P = 0.005), TLG (P = 0.004), and heterogeneity index-2 (P = 0.016) with venous invasion (P < 0.001, 0.001, and 0.001, respectively) demonstrated significant results.

CONCLUSIONS

The heterogeneity index obtained using the linear regression slope, could be an effective predictor of pancreatic cancer recurrence after pancreatic cancer surgery, in addition to ¹⁸F-FDG PET/CT volumetric parameters and clinicopathologic parameters.

Influence of PET reconstruction technique and matrix size on qualitative and quantitative assessment of lung lesions on [18F]-FDG-PET: A prospective study in 37 cancer patients

PURPOSE

To evaluate the influence of point spread function (PSF)-based reconstruction and matrix size for PET on (1) lung lesion detection and (2) standardized uptake values (SUV).

METHODS

This prospective study included oncological patients who underwent [18F]-FDG-PET/CT for staging. PET data were reconstructed with a 2D ordered subset expectation maximization (OSEM) algorithm, and a 2D PSF-based algorithm (TrueX), separately with two matrix sizes (168×168 and 336×336). The four PET reconstructions (TrueX-168; OSEM-168; TrueX-336; and OSEM-336) were read independently by two raters, and PET-positive lung lesions were recorded. Blinded to the PET findings, a third independent rater assessed lung lesions with diameters of >4mm on CT. Subsequently, PET and CT were reviewed side-by side in consensus. Multi-factorial logistic regression analyses and two-way repeated measures analyses of variance (ANOVA) were performed.

RESULTS

Thirty-seven patients with 206 lung lesions were included. Lesion-based PET sensitivities differed significantly between reconstruction algorithms (P<0.001) and between reconstruction matrices (P=0.022). Sensitivities were 94.2% and 88.3% for TrueX-336; 88.3% and 85.9% for TrueX-168; 67.8% and 66.3% for OSEM-336; and 67.0% and 67.9% for OSEM-168; for rater 1 and rater 2, respectively. SUV_max and SUV_mean were significantly higher for images reconstructed with 336×336 matrices than for those reconstructed with 168×168 matrices (P<0.001).

CONCLUSION

Our results demonstrate that PSF-based PET reconstruction, and, to a lesser degree, higher matrix size, improve detection of metabolically active lung lesions. However, PSF-based PET reconstructions and larger matrix sizes lead to higher SUVs, which may be a concern when PET data from different institutions are compared.

Role of Optimal Quantification of FDG PET Imaging in the Clinical Practice of Radiology

The combination of fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and computed tomography (CT) for dual-modality imaging (PET/CT) plays a key role in the diagnosis and staging of FDG-avid malignancies. FDG uptake by the tumor cells offers an opportunity to detect cancer in organs that appear normal at anatomic imaging and to differentiate viable tumor from posttreatment effects. Quantification of FDG uptake has multiple clinical applications, including cancer diagnosis and staging. Dedicated FDG PET/CT-based visual and quantitative criteria have been developed to evaluate treatment response. Furthermore, the level of tumor FDG uptake reflects the biologic aggressiveness of the tumor, predicting the risk of metastasis and recurrence. FDG uptake can be measured with qualitative, semiquantitative, and quantitative methods. Qualitative or visual assessment of PET/CT images is the most common clinical approach for describing the level of FDG uptake. Standardized uptake value (SUV) is the most commonly used semiquantitative tool for measuring FDG uptake. SUV can be measured as maximum, mean, or peak SUV and may be normalized by using whole or lean body weight. SUV measurements provide the basis for quantitative response criteria; however, SUVs have not been widely adopted as diagnostic thresholds for discriminating malignant and benign lesions. Volumetric FDG uptake measurements such as metabolic tumor volume and total lesion glycolysis have shown substantial promise in providing accurate tumor assessment. SUV measurement and other quantification techniques can be affected by many technical, physical, and biologic factors. Familiarity with FDG uptake quantification approaches and their pitfalls is essential for clinical practice and research.

Dihydropyrimidine Dehydrogenase Is a Prognostic Marker for Mesenchymal Stem Cell-Mediated Cytosine Deaminase Gene and 5-Fluorocytosine Prodrug Therapy for the Treatment of Recurrent Gliomas

We investigated a therapeutic strategy for recurrent malignant gliomas using mesenchymal stem cells (MSC), expressing cytosine deaminase (CD), and prodrug 5-Fluorocytosine (5-FC) as a more specific and less toxic option. MSCs are emerging as a novel cell therapeutic agent with a cancer-targeting property, and CD is considered a promising enzyme in cancer gene therapy which can convert non-toxic 5-FC to toxic 5-Fluorouracil (5-FU). Therefore, use of prodrug 5-FC can minimize normal cell toxicity. Analyses of microarrays revealed that targeting DNA damage and its repair is a selectable option for gliomas after the standard chemo/radio-therapy. 5-FU is the most frequently used anti-cancer drug, which induces DNA breaks. Because dihydropyrimidine dehydrogenase (DPD) was reported to be involved in 5-FU metabolism to block DNA damage, we compared the survival rate with 5-FU treatment and the level of DPD expression in 15 different glioma cell lines. DPD-deficient cells showed higher sensitivity to 5-FU, and the regulation of DPD level by either siRNA or overexpression was directly related to the 5-FU sensitivity. For MSC/CD with 5-FC therapy, DPD-deficient cells such as U87MG, GBM28, and GBM37 showed higher sensitivity compared to DPD-high U373 cells. Effective inhibition of tumor growth was also observed in an orthotopic mouse model using DPD- deficient U87MG, indicating that DPD gene expression is indeed closely related to the efficacy of MSC/CD-mediated 5-FC therapy. Our results suggested that DPD can be used as a biomarker for selecting glioma patients who may possibly benefit from this therapy.

What Do We Measure in Oncology PET?

Positron emission tomography (PET) has come to the practice of oncology. It is known that ¹⁸F-fluorodeoxyglucose (FDG) PET is more sensitive for the assessment of treatment response than conventional imaging. In addition, PET has an advantage in the use of quantitative analysis of the study. Nowadays, various PET parameters are adopted in clinical settings. In addition, a wide range of factors has been known to be associated with FDG uptake. Therefore, there has been a need for standardization and harmonization of protocols and PET parameters. We will introduce PET parameters and discuss major issues in this review.

Prediction of Posttransplantation Recurrence of Hepatocellular Carcinoma Using Metabolic and Volumetric Indices of 18F-FDG PET/CT

(18)F-FDG PET is an effective method of predicting recurrence of hepatocellular carcinoma (HCC) after liver transplantation. We compared recently introduced metabolic and volumetric (18)F-FDG PET/CT indices with the current clinicopathologic predictors for ability to predict recurrence.

METHODS

In total, 110 HCC patients who underwent (18)F-FDG PET and liver transplantation were enrolled. On PET, SUVs and tumor-to-background ratios (TBRs) were measured as metabolic activity indices. Various metabolic tumor volumes and uptake-volume products (UVP) were also measured as volumetric indices. The ability of these indices and other clinicopathologic factors to predict recurrence was compared.

RESULTS

All metabolic and volumetric indices were significant for recurrence prediction on receiver-operating-characteristic curve analyses (P < 0.001). On univariate survival analyses, all PET indices-as well as tumor size, tumor number, the Milan criteria, tumor grade, vascular invasion, and T-stage-were significant factors. However, on multivariate analyses, tumor size, tumor grade, maximum TBR, and UVP calculated by inferior vena cava activity were significant factors (P = 0.004, 0.014, 0.009, and 0.021, respectively). When the Milan criteria and PET factors were included in the multivariate analysis, the Milan criteria (P = 0.029), maximum TBR (P < 0.001), and UVP (P = 0.016) were significant.

CONCLUSION

Volumetric and metabolic activity indices of (18)F-FDG PET are effective predictors of posttransplantation HCC recurrence. In addition to clinicopathologic factors, these indices need to be considered in the selection of candidates for liver transplantation.

Prognostic value of total lesion glycolysis by 18F-FDG PET/CT in surgically resected stage IA non-small cell lung cancer

Despite the favorable prognosis of stage IA non-small cell lung cancer (NSCLC), the disease recurs after complete surgical resection in 20%-30% of patients. This study determined the prognostic value of various metabolic parameters of (18)F-FDG PET/CT in surgically resected stage IA NSCLC.

METHODS

We retrospectively reviewed 248 patients with stage IA NSCLC who underwent lobectomy and complete lymph node dissection after PET/CT. A region of interest was drawn on the primary lesion, and metabolic indices such as metabolic tumor volume, maximum standardized uptake value (SUV(max)), and total lesion glycolysis (TLG) were measured using an SUV cutoff of 2.5.

RESULTS

The patients included 134 men and 114 women, and the mean age was 63.03 ± 10.01 y; 129 were stage T1a (≤ 2 cm) and 119 were T1b (>2 cm). The median follow-up period was 36.6 mo. Recurrence took place in 15 patients. The mean (± SD) SUV(max), metabolic tumor volume, and TLG were 4.55 ± 3.75, 5.92 ± 5.57, and 14.42 ± 17.35, respectively. The cutoffs of SUV(max) and TLG were 3.7 and 13.76, respectively. The 5-y overall survival (OS) was 95.1% in low-SUV(max) patients and 82.2% in high-SUV(max) patients (P = 0.02). The 5-y OS was 93.7% in low-TLG patients and 78.3% in high-TLG patients (P = 0.01). On multivariate analysis, TLG was a risk factor for OS (hazard ratio, 3.159; P = 0.040), but SUV(max) showed marginal significance (P = 0.064). The concordance index of the TLG model was 0.676 (95% CI, 0.541-0.812).

CONCLUSION

TLG was a significant prognostic factor for OS in patients with stage IA NSCLC.

The effect of volume of interest definition on quantification of lymph node immune response to a monkeypox virus infection assessed by (18)F-FDG-PET

BACKGROUND

2-deoxy-2-[(18)F]fluoro-D-glucose-positron emission tomography ((18)F-FDG-PET) is applied in the clinic for infection assessment and is under consideration for investigating the inflammatory/immune response in lymphoid tissue in animal models of viral infection. Assessing changes in (18)F-FDG uptake of lymph nodes (LNs), primary lymphoid tissues targeted during viral infection, requires suitable methods for image analysis. Similar to tumor evaluation, reliable quantitation of the LN function via multiple (18)F-FDG-PET sessions will depend how the volume of interest is defined. Volume of interest definition has a direct effect on statistical outcome. The current study objective is to compare for the first time agreement between conventional and modified VOI metrics to determine which method(s) provide(s) reproducible standardized uptake values (SUVs) for (18)F-FDG uptake in the LN of rhesus macaques.

METHODS

Multiple (18)F-FDG-PET images of LNs in macaques were acquired prior to and after monkeypox virus intravenous inoculation. We compared five image analysis approaches, SUVmax, SUVmean, SUVthreshold, modified SUVthreshold, and SUVfixed volume, to investigate the impact of these approaches on quantification of the changes in LN metabolic activity denoting the immune response during viral infection progression.

RESULTS

The lowest data repeatability was observed with SUVmax. The best correspondence was between SUVfixed volume and conventional and modified SUVthreshold. A statistically significant difference in the LN (18)F-FDG uptake between surviving and moribund animals was shown using modified SUVthreshold and SUVfixed volume (adjusted p = 0.0037 and p = 0.0001, respectively).

CONCLUSIONS

Quantification of the LN (18)F-FDG uptake is highly sensitive to the method applied for PET image analysis. SUVfixed volume and modified SUVthreshold demonstrate better reproducibility for SUV estimates than SUVmax, SUVmean, and SUVthreshold. SUVfixed volume and modified SUVthreshold are capable of distinguishing between groups with different disease outcomes. Therefore, these methods are the preferred approaches for evaluating the LN function during viral infection by (18)F-FDG-PET. Validation of multiple approaches is necessary to choose a suitable method to monitor changes in LN metabolic activity during progression of viral infection.

Anatomical and functional volume concordance between FDG PET, and T2 and diffusion-weighted MRI for cervical cancer: a hybrid PET/MR study

PURPOSE

To evaluate the concordance among (18)F-FDG PET imaging, MR T2-weighted (T2-W) imaging and apparent diffusion coefficient (ADC) maps with diffusion-weighted (DW) imaging in cervical cancer using hybrid whole-body PET/MR.

METHODS

This study prospectively included 35 patients with cervical cancer who underwent pretreatment (18)F-FDG PET/MR imaging. (18)F-FDG PET and MR images were fused using standard software. The percent of the maximum standardized uptake values (SUV max) was used to contour tumours on PET images, and volumes were calculated automatically. Tumour volumes measured on T2-W and DW images were calculated with standard techniques of tumour area multiplied by the slice profile. Parametric statistics were used for data analysis.

RESULTS

FDG PET tumour volumes calculated using SUV max (14.30 ± 4.70) and T2-W imaging volume (33.81 ± 27.32 cm(3)) were similar (P > 0.05) at 35 % and 40 % of SUV max (32.91 ± 18.90 cm(3) and 27.56 ± 17.19 cm(3) respectively) and significantly correlated (P < 0.001; r = 0.735 and 0.766). The mean DW volume was 30.48 ± 22.41 cm(3). DW volumes were not significantly different from FDG PET volumes at either 35 % SUV max or 40 % SUV max or from T2-W imaging volumes (P > 0.05). PET subvolumes with increasing SUV max cut-off percentage showed an inverse change in mean ADC values on DW imaging (P < 0.001, ANOVA).

CONCLUSION

Hybrid PET/MR showed strong volume concordance between FDG PET, and T2-W and DW imaging in cervical cancer. Cut-off at 35 % or 40 % of SUV max is recommended for (18)F-FDG PET/MR SUV-based tumour volume estimation. The linear tumour subvolume concordance between FDG PET and DW imaging demonstrates individual regional concordance of metabolic activity and cell density.

Comparison of F-18-FDG PET/CT findings between pancreatic solid pseudopapillary tumor and pancreatic ductal adenocarcinoma

OBJECTIVE

Pancreatic solid pseudopapillary tumor (SPT) is a rare benign tumor. Little data are available on positron emission tomographic/computed tomographic (PET/CT) characteristics of this tumor. Therefore, we analyzed the metabolic characteristics of SPT using F-18-FDG PET/CT and compared the results with those of pancreatic ductal adenocarcinoma.

METHODS

We retrospectively reviewed the records of 11 SPT patients and 46 patients with ductal adenocarcinoma. Ten SPT patients had primary tumors and 1 patient had metastatic SPT. Maximum standardized uptake value (max SUV), mean SUV, metabolic tumor volume (MTV), total lesion glycolysis (TLG), and tumor-to-background ratio (TBR) were evaluated. Mann-Whitney U test between pancreatic SPT and ductal adenocarcinoma was performed. In addition, age, gender and tumor size-adjusted analysis of covariance (ANCOVA) was done between pancreatic SPT and ductal adenocarcinoma.

RESULTS

Compared with pancreatic ductal adenocarcinomas, SPTs had significantly higher tumor size-adjusted MTV and TLG. MTV and TLG values were significantly correlated with T-stage of the SPTs. In 1 SPT patient, metastases in the liver and mesentery were revealed by intense uptake of FDG on F-18-FDG PET/CT, and after PET/CT had suggested the presence of pancreatic SPT.

CONCLUSION

We recommend that SPT be considered when a solid pancreatic mass with increased FDG metabolism is encountered on PET/CT. F-18-FDG PET/CT may be useful in detecting subtle metastases of SPT.

Reproducibility of the adaptive thresholding calibration procedure for the delineation of 18F-FDG-PET-positive lesions

OBJECTIVE

The aim of the study was to evaluate the robustness of the calibration procedure against the counting statistics and lesion volumes when using an adaptive thresholding method for the delineation of 2-[18F]fluoro-2-deoxyglucose (18F-FDG)-PET-positive tissue.

MATERIALS AND METHODS

Three data sets obtained from physical and simulated images of a phantom containing hot spheres of known volume and contrast were used to study the robustness of the calibration procedure against the counting statistics and range of volumes and contrasts for a given PET model. The mathematical expression of the adaptive thresholding method used corresponds to a linear relationship between the optimal threshold value and the inverse of the local contrast. Robustness was evaluated by testing whether the slopes and intercepts of the linear expression found under two experimental conditions were significantly different (P<0.05).

RESULTS

It was found that the calibration step was not sensitive to the PET device for the studied PET model, nor to the counting statistics for a signal-to-noise ratio higher than 5.7. No statistical difference was found in the calibration step when using a wide range of volumes (0.2-200 ml) and contrasts (2.0-20.6) or more restricted ones (0.43-97.3 ml and 2.0-7.7, respectively). Therefore, a calibration procedure using limited experimental conditions can be applied to a wider range of volumes and contrasts.

CONCLUSION

These results show that the manufacturer could propose simulated or experimental raw data corresponding to a given PET model with high counting statistics, allowing each clinical center to reconstruct calibration images according to the algorithm parameters used in the clinic.

FDG-PET/CT imaging biomarkers in head and neck squamous cell carcinoma

This article discusses the value of ¹⁸F-fluoro-2-deoxyglucose PET/CT imaging biomarkers in head and neck squamous cell carcinoma. ¹⁸F-fluoro-2-deoxyglucose PET/CT is valuable at baseline staging, radiotherapy planning, therapy response assessment and in the follow-up of patients with head and neck squamous cell carcinoma. Maximum and peak standardized uptake value (SUV_max and SUV_peak), metabolic tumor volume and total lesion glycolysis are the common ¹⁸F-fluoro-2-deoxyglucose quantitative parameters that have been studied, along with qualitative assessments. These parameters will be evaluated with respect to their established or potential role as noninvasive biomarkers for patient risk stratification, treatment response and survival outcome.

Gaussian process models of dynamic PET for functional volume definition in radiation oncology

In routine oncologic positron emission tomography (PET), dynamic information is discarded by time-averaging the signal to produce static images of the "standardised uptake value" (SUV). Defining functional volumes of interest (VOIs) in terms of SUV is flawed, as values are affected by confounding factors and the chosen time window, and SUV images are not sensitive to functional heterogeneity of pathological tissues. Also, SUV iso-contours are highly affected by the choice of threshold and no threshold, or other SUV-based segmentation method, is universally accepted for a given VOI type. Gaussian Process (GP) time series models describe macro-scale dynamic behavior arising from countless interacting micro-scale processes, as is the case for PET signals from heterogeneous tissue. We use GPs to model time-activity curves (TACs) from dynamic PET and to define functional volumes for PET oncology. Probabilistic methods of tissue discrimination are presented along with novel contouring methods for functional VOI segmentation. We demonstrate the value of GP models for voxel classification and VOI contouring of diseased and metastatic tissues with functional heterogeneity in prostate PET. Classification experiments reveal superior sensitivity and specificity over SUV calculation and a TAC-based method proposed in recent literature. Contouring experiments reveal differences in shape between gold-standard and GP VOIs and correlation with kinetic models shows that the novel VOIs contain extra clinically relevant information compared to SUVs alone. We conclude that the proposed models offer a principled data analysis technique that improves on SUVs for oncologic VOI definition. Continuing research will generalize GP models for different oncology tracers and imaging protocols with the ultimate goal of clinical use including treatment planning.

[Metabolically active volumes automatic delineation methodologies in PET imaging: review and perspectives]

PET imaging is now considered a gold standard tool in clinical oncology, especially for diagnosis purposes. More recent applications such as therapy follow-up or tumor targeting in radiotherapy require a fast, accurate and robust metabolically active tumor volumes delineation on emission images, which cannot be obtained through manual contouring. This clinical need has sprung a large number of methodological developments regarding automatic methods to define tumor volumes on PET images. This paper reviews most of the methodologies that have been recently proposed and discusses their framework and methodological and/or clinical validation. Perspectives regarding the future work to be done are also suggested.

PET functional volume delineation: a robustness and repeatability study

PURPOSE

Current state-of-the-art algorithms for functional uptake volume segmentation in PET imaging consist of threshold-based approaches, whose parameters often require specific optimization for a given scanner and associated reconstruction algorithms. Different advanced image segmentation approaches previously proposed and extensively validated, such as among others fuzzy C-means (FCM) clustering, or fuzzy locally adaptive bayesian (FLAB) algorithm have the potential to improve the robustness of functional uptake volume measurements. The objective of this study was to investigate robustness and repeatability with respect to various scanner models, reconstruction algorithms and acquisition conditions.

METHODS AND MATERIALS

Robustness was evaluated using a series of IEC phantom acquisitions carried out on different PET/CT scanners (Philips Gemini and Gemini Time-of-Flight, Siemens Biograph and GE Discovery LS) with their associated reconstruction algorithms (RAMLA, TF MLEM, OSEM). A range of acquisition parameters (contrast, duration) and reconstruction parameters (voxel size) were considered for each scanner model, and the repeatability of each method was evaluated on simulated and clinical tumours and compared to manual delineation.

RESULTS

For all the scanner models, acquisition parameters and reconstruction algorithms considered, the FLAB algorithm demonstrated higher robustness in delineation of the spheres with low mean errors (10%) and variability (5%), with respect to threshold-based methodologies and FCM. The repeatability provided by all segmentation algorithms considered was very high with a negligible variability of <5% in comparison to that associated with manual delineation (5-35%).

CONCLUSION

The use of advanced image segmentation algorithms may not only allow high accuracy as previously demonstrated, but also provide a robust and repeatable tool to aid physicians as an initial guess in determining functional volumes in PET.

A systematic review of the factors affecting accuracy of SUV measurements

OBJECTIVE

There is growing interest in using PET/CT for evaluating early response to therapy in cancer treatment. Although widely available and convenient to use, standardized uptake value (SUV) measurements can be influenced by a variety of biologic and technologic factors. Many of these factors can be addressed with close attention to detail and appropriate quality control. This article will review factors potentially affecting SUV measurements and provide recommendations on ways to minimize when using serial PET to assess early response to therapy.

CONCLUSION

Scanner and reconstruction parameters can significantly affect SUV measurements. When using serial SUV measurements to assess early response to therapy, imaging should be performed on the same scanner using the same image acquisition and reconstruction protocols. In addition, attention to detail is required for accurate determination of the administered radiopharmaceutical dose.