Variability of ¹8F-FDG-positive lung lesion volume by thresholding.

OBJECTIVES: To assess the variability of (18)F-FDG-positive volume measurements in lung cancer patients, obtained with different fixed percentages of maximum standard uptake value (SUVmax) thresholds. METHODS: PET dynamic acquisition involving ten frames was performed within 60-110 min post-injection in eight patients. In each lesion (n = 11), volume was automatically outlined in each frame with fixed 40-50-60-70 % of the SUVmax thresholds. Thus, ten volume values for each threshold (V40-50-60-70) were available to calculate relative SD (SDr), and hence relative measurement error (MEr) and repeatability (R). Dependence on SUVmax variability was also assessed. RESULTS: Mean SDr (; %) of volume estimates was found to strongly correlate with threshold value (T; %): = 1.626 × exp(0.044 × T) (r = 0.999; P < 0.01). MEr and R for V40 were found to be (95 % CL) 18.9 % and 26.7 %. For all fixed thresholds, in successive frames of an arbitrary lesion, volume estimate inversely correlated with SUVmax (P ≤ 0.02). CONCLUSIONS: A formula allows estimation of the variability of (18)F-FDG-positive volumes provided by any fixed percentage of SUVmax threshold, and hence by any thresholding method. It only necessitates conversion of the threshold value into the SUVmax percentage in order to aid quick estimation of volume variability magnitude in current clinical practice.

A method of adjusting SUV for injection-acquisition time differences in (18)F-FDG PET imaging.

OBJECTIVE: A time normalisation method of tumour SUVs in (18) F-FDG PET imaging is proposed that has been verified in lung cancer patients. METHODS: A two-compartment model analysis showed that, when SUV is not corrected for (18) F physical decay (SUV(uncorr)), its value is within 5% of its peak value (t = 79 min) between 55 and 110 min after injection, in each individual patient. In 10 patients, each with 1 or more malignant lesions (n = 15), two PET acquisitions were performed within this time delay, and the maximal SUV of each lesion, both corrected and uncorrected, was assessed. RESULTS: No significant difference was found between the two uncorrected SUVs, whereas there was a significant difference between the two corrected ones: mean differences were 0.04 ± 0.22 and 3.24 ± 0.75 g.ml(-1), respectively (95% confidence intervals). Therefore, a simple normalisation of decay-corrected SUV for time differences after injection is proposed: SUV(N) = 1.66 SUV(uncorr), where the factor 1.66 arises from decay correction at t = 79 min. CONCLUSIONS: When (18) F-FDG PET imaging is performed within the range 55-110 min after injection, a simple SUV normalisation for time differences after injection has been verified in patients with lung cancer, with a ±2.5% relative measurement uncertainty.

An abbreviated therapy-dosimetric equation for the companion diagnostic/therapeutic [64/67Cu]Cu-SARTATE.

In a preclinical model of neuroblastoma, Dearling et al. recently demonstrated the potential interest for a theranostic approach of [64/67Cu]Cu-SARTATE for the detection and treatment of SSTR2-positive neuroblastoma lesions in pediatric patients whose widespread metastases survive initial therapy as minimal residual disease (MRD). MRD may be detected by [64Cu]Cu-SARTATE and subsequently treated by [67Cu]Cu-SARTATE. Since therapeutic dosimetry estimation of the latter agent from the uptake of the former one in the initial diagnostic scan was not addressed, the present theoretical commentary proposes the derivation of an abbreviated therapy-dosimetric equation for the companion diagnostic/therapeutic [64/67Cu]Cu-SARTATE that might be of interest for future clinical theranostic practice.

The effect of renal failure on 18F-FDG uptake: a theoretic assessment.

UNLABELLED: This work addresses the issue of using (18)F-FDG PET in patients with renal failure. METHODS: A model analysis has been developed to compare tissue (18)F-FDG uptake in a patient who has normal renal function with uptake in a theoretic limiting case that assumes tracer plasma decay is tracer physical decay and is trapped irreversibly. RESULTS: This comparison has allowed us to propose, in the limiting case, that the usually injected activity be lowered by a factor of 3. We also proposed that the PET static acquisition be obtained at about 160 min after tracer injection. These 2 proposals were aimed at obtaining a similar patient radiation dose and similar tissue (18)F-FDG uptake. CONCLUSION: In patients with arbitrary renal failure (i.e., between the 2 extremes of normal function and the theoretic limiting case), we propose that the injected activity be lowered (without exceeding a factor of 3) and that the acquisition be started between 45 and 160 min after tracer injection, depending on the severity of renal failure. Furthermore, the model also shows that the more severe the renal failure is, the more overestimated is the standardized uptake value, unless the renal failure indirectly impairs tissue sensitivity to insulin and hence glucose metabolism.

SUVpeak Performance in Lung Cancer: Comparison to Average SUV from the 40 Hottest Voxels.

UNLABELLED: The performance of an average SUV over a 1-mL-volume sphere within an (18)F-FDG-positive lesion resulting in the highest possible value (SUVpeakW) was compared with that of an average SUV computed from the 40 hottest voxels, irrespective of their location within the lesion (SUVmax-40). METHODS: Dynamic PET performed in 20 lung cancer lesions yielded for each SUV metric its mean value, relative measurement error, and repeatability (MEr-R). RESULTS: SUVpeakW mean value was significantly 9.66% lower than that of SUVmax-40 (P < 0.0001). SUVpeakW and SUVmax-40 MEr-R were significantly lower than the MEr-R of SUVmax (the hottest voxel): 9.35%-13.21% and 8.84%-12.49% versus 13.86%-19.59%, respectively, (95% confidence limit; P < 0.0001). Although being marginal, SUVpeakW MEr-R was not significantly greater than SUVmax-40 MEr-R (P = 0.086). CONCLUSION: SUVmax-40 is more likely to represent the most metabolically active portions of tumors than SUVpeakW, with close variability performance.

Anthracosis mimicking mediastinal lymph node metastases with 18F-FCholine in high-risk prostate cancer.

A 62-year-old patient with prostate adenocarcinoma underwent PET with radiolabeled choline (18F-Fcholine) for pretreatment staging of a high-risk prostate cancer. Images showed a significant mediastinal lymph node uptake of 18F-Fcholine. Owing to the rarity of spread to supradiaphragmatic lymph nodes, a surgical removal was performed, revealing anthracosis and no malignant cells. Even if its specificity seems better than 18F-FDG, false positives have been reported and other pathologies could mimic lymph node metastases. Consequently, histology should be performed so that the appropriate treatment can be initiated.

Variability of total lesion glycolysis by 18F-FDG-positive tissue thresholding in lung cancer.

UNLABELLED: The aim of this work was to assess the variability of total lesion glycolysis (TLG) measurements in lung cancer patients, obtained with fixed percentages of the maximum standardized uptake value (SUVmax) thresholds. METHODS: Thirteen lesions (10 patients) were analyzed in 10 successive 2.5-min frames of an (18)F-FDG PET dynamic acquisition obtained between 60 and 110 min after injection. (18)F-FDG-positive lesion volume, associated average SUV (SUVmean), and TLG (volume × SUVmean) were assessed in each frame using thresholds of 40%, 50%, 60%, 70%, and 80%. For each threshold, the average relative SD of TLG, leading to relative measurement error and repeatability, was calculated over the lesion series. The dependence of TLG variability on volume and SUVmean variability was also assessed. RESULTS: The average relative SD of TLG correlated strongly with threshold: 1.0866 × exp(0.0472 × threshold) (r = 0.999; P < 0.01). For the 40% threshold, average TLG over the series was 225.9 g (range, 41.7-1,086.3), relative measurement error and repeatability were 14.5%-20.4% (95% confidence interval), and no significant difference was found between TLG and volume variability. For the other thresholds, TLG variability was significantly lower or greater than volume or SUVmean variability, respectively. CONCLUSION: In current clinical practice, a formula allows quick estimation of TLG variability for any percentage of the SUVmax threshold: the higher the threshold the greater the TLG variability.

Is liver SUV stable over time in ¹8F-FDG PET imaging?

UNLABELLED: This work investigated whether (18)F-FDG PET standardized uptake value (SUV) is stable over time in the normal human liver. METHODS: The SUV-versus-time curve, SUV(t), of (18)F-FDG in the normal human liver was derived from a kinetic model analysis. This derivation involved mean values of (18)F-FDG liver metabolism that were obtained from a patient series (n = 11), and a noninvasive population-based input function was used in each individual. RESULTS: Mean values (±95% reliability limits) of the (18)F-FDG uptake and release rate constant and of the fraction of free tracer in blood and interstitial volume were as follows: K = 0.0119 mL·min(-1)·mL(-1) (±0.0012), k(R) = 0.0065·min(-1) (±0.0009), and F = 0.21 mL·mL(-1) (±0.11), respectively. SUV(t) (corrected for (18)F physical decay) was derived from these mean values, showing that it smoothly peaks at 75-80 min on average after injection and that it is within 5% of the peak value between 50 and 110 min after injection. CONCLUSION: In the normal human liver, decay-corrected SUV(t) remains nearly constant (with a reasonable ±2.5% relative measurement uncertainty) if the time delay between tracer injection and PET acquisition is in the range of 50-110 min. In current clinical practice, the findings suggest that SUV of the normal liver can be used for comparison with SUV of suspected malignant lesions, if comparison is made within this time range.

Feasibility of assessing [(18)F]FDG lung metabolism with late dynamic PET imaging.

PURPOSE: The aim of this work was to non-invasively establish the feasibility of assessing 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) lung metabolism with the use of a late dynamic positron emission tomograpy (PET) acquisition, i.e., beyond 2 h after injection. PROCEDURES: The present method has been probed in 11 patients without any respiratory disease, under fasting conditions, by assessing mean values of (18)F-FDG lung metabolism. A kinetic model analysis has been implemented on a simple calculation sheet. An arbitrary (population based) input function has been used in each individual, which was obtained from literature data. RESULTS: In the healthy lung, no (18)F-FDG release was found, and the mean values (±SD) of the (18)F-FDG uptake rate constant and of the fraction of the free tracer in blood and interstitial volume were: K = 0.0016 min(-1) (±0.0005), and F = 0.18 (±0.10), respectively. These results were in very close agreement with literature data that were obtained by both three-compartment model analysis and Patlak graphical analysis (gold standards), and that used an invasive blood sampling. Furthermore, K and the standard uptake value index have been compared. CONCLUSION: We conclude that assessing lung metabolism of (18)F-FDG in humans with the use of late dynamic PET imaging is feasible. The arbitrary input function of this non-invasive feasibility study could be replaced in further experiments by an input function obtained by arterial sampling. It is suggested that this method may prove useful to quantify (18)F-FDG lung metabolism under pathological conditions.

Assessment of dual-time-point 18F-FDG-PET imaging for pulmonary lesions.

OBJECTIVE: The objective of this study was to assess suitability of dual-time-point 18F-FDG [(18F)-fluoro-2-deoxyglucose]-PET imaging for differentiating between malignant and benign pulmonary lesions, whose size and maximal standardized uptake values (SUVs) are greater than 10 mm and 2.5, respectively. METHODS: A total of 38 patients, 27 with malignant lesions (n = 30), and 11 with benign lesions (n = 22), were investigated by performing two static acquisitions started at mean times t = 79 and t = 158 min after the tracer injection. A model analysis involving tissue 18F-FDG uptake and release has been developed and applied. RESULTS: Malignant lesions showed a SUV increase between the two acquisitions for 27 of 30 lesions, and a SUV decrease or constancy for the other three. Benign lesions showed a SUV increase in 19 of 22 lesions, and a SUV decrease in three (both increase and decrease were observed for multiple benign lesions in two patients). CONCLUSION: It is recommended that dual-time-point 18F-FDG-PET imaging is not indicated to differentiate between malignant and benign pulmonary lesions, whose size and maximal SUV are greater than 10 mm and 2.5, respectively. Furthermore, a model analysis suggests that the variation in SUV observed between early and delayed scans may be explained by different values of the 18F-FDG release/uptake ratio.