Dynamic Changes of FDG Uptake and Clearance in Normal Tissues

Total-body dynamic PET/CT imaging reveals kinetic distribution of [13N]NH3 in normal organs

PURPOSE

To systematically investigate kinetic metrics and metabolic trapping of [13N]NH3 in organs.

METHODS

Eleven participants performed total-body [13N]NH3 dynamic positron emission tomography (PET). Regions of interest were drawn in organs to obtain time-to-activity curves (TACs), which were fitted with an irreversible two-tissue compartment model (2TC) to investigate constant rates K1, k2 and k3, and to calculate Ki. Additionally, one-tissue compartment model using full data (1TCfull) and the first four minutes of data (1TC4min) were fitted to TAC data. K1 and k2 were compared among different models to assess [13N]NH3 trapping in organs.

RESULTS

Kinetic rates of [13N]NH3 varied significantly among organs. The mean K1 ranged from 0.049 mL/cm3/min in the muscle to 2.936 mL/cm3/min in the kidney. The k2 and k3 were lowest in the liver (0.001 min- 1) and in the pituitary (0.009 min- 1), while highest in the kidney (0.587 min- 1) and in the liver (0.800 min- 1), respectively. The Ki was largest in the myocardium (0.601 ± 0.259 mL/cm3/min) while smallest in the bone marrow (0.028 ± 0.022 mL/cm3/min). Three groups of organs with similar kinetic characteristics were revealed: (1) the thyroid, the lung, the spleen, the pancreas, and the kidney; (2) the liver and the muscle; and (3) the cortex, the white matter, the cerebellum, the pituitary, the parotid, the submandibular gland, the myocardium, the bone, and the bone marrow. Obvious k3 was identified in multiple organs, and significant changes of K1 in multiple organs and k2 in most organs were found between 2TC and 1TCfull, but both K1 and k2 were comparable between 2TC and 1TC4min.

CONCLUSION

The kinetic rates of [13N]NH3 differed among organs with some have obvious 13N-anmmonia trapping. The normal distribution of kinetic metrics of 13N-anmmonia in organs can serve as a reference for its potential use in tumor imaging.

Analyzing the value of delayed 18 F-FDG PET/CT images in diagnosing small colorectal cancer liver metastases in patients with hypothyroidism based on diagnostic accuracy and image standardized uptake value

PURPOSE

The objective of this study was to investigate the value of delayed 18F fluorodeoxyglucose PET/computed tomography (18F-FDG PET/CT) images in patients with small colorectal cancer liver metastases (CRLMs) with hypothyroidism.

METHOD

We performed a retrospective analysis of 66 small-CRLM patients with hypothyroidism and 66 small-CRLM patients with euthyroidism, all of whom underwent dual-time-point 18 F-FDG PET/CT imaging. First, the diagnostic accuracy of PET/CT early imaging and PET/CT delayed imaging on lesions was analyzed. Next, the correlation of metabolic parameters between PET/CT early imaging and PET/CT delayed imaging was analyzed according to the grouping of all lesions. Finally, PET/CT parameters were analyzed for correlation with thyroid hormones.

RESULTS

The diagnostic accuracy of delayed imaging in small-CRLM patients with hypothyroidism is not as good as that in small-CRLM patients with euthyroidism; PET/CT metabolic parameters are also unfavorable for the diagnosis of small-CRLM. For small-CRLM patients with hypothyroidism, the greater the thyroid-stimulating hormone level, the greater the uptake of 18 F-FDG in normal liver tissue, and the smaller the ratio of tumor lesion uptake to normal liver tissue uptake.

CONCLUSION

PET/CT-delayed imaging has better performance than early imaging in small-CRLM patients with euthyroidism. However, the more severe the hypothyroidism, the worse the diagnostic delayed imaging performance. The scan time can be extended appropriately to optimize the imaging efficacy.

The role of dynamic, static, and delayed total-body PET imaging in the detection and differential diagnosis of oncological lesions

OBJECTIVES

Commercialized total-body PET scanners can provide high-quality images due to its ultra-high sensitivity. We compared the dynamic, regular static, and delayed 18F-fluorodeoxyglucose (FDG) scans to detect lesions in oncologic patients on a total-body PET/CT scanner.

MATERIALS & METHODS

In all, 45 patients were scanned continuously for the first 60 min, followed by a delayed acquisition. FDG metabolic rate was calculated from dynamic data using full compartmental modeling, whereas regular static and delayed SUV images were obtained approximately 60- and 145-min post-injection, respectively. The retention index was computed from static and delayed measures for all lesions. Pearson's correlation and Kruskal-Wallis tests were used to compare parameters.

RESULTS

The number of lesions was largely identical between the three protocols, except MRFDG and delayed images on total-body PET only detected 4 and 2 more lesions, respectively (85 total). FDG metabolic rate (MRFDG) image-derived contrast-to-noise ratio and target-to-background ratio were significantly higher than those from static standardized uptake value (SUV) images (P < 0.01), but this is not the case for the delayed images (P > 0.05). Dynamic protocol did not significantly differentiate between benign and malignant lesions just like regular SUV, delayed SUV, and retention index.

CONCLUSION

The potential quantitative advantages of dynamic imaging may not improve lesion detection and differential diagnosis significantly on a total-body PET/CT scanner. The same conclusion applied to delayed imaging. This suggested the added benefits of complex imaging protocols must be weighed against the complex implementation in the future.

CLINICAL RELEVANCE

Total-body PET/CT was known to significantly improve the PET image quality due to its ultra-high sensitivity. However, whether the dynamic and delay imaging on total-body scanner could show additional clinical benefits is largely unknown. Head-to-head comparison between two protocols is relevant to oncological management.

The feasibility of quantitative assessment of dynamic 18F-fluorodeoxyglucose PET in Takayasu's arteritis: a pilot study

PURPOSE

PET has been demonstrated to be sensitive for detecting active inflammation in Takayasu's arteritis (TAK) patients, but semi-quantitative-based assessment may be susceptible to various biological and technical factors. Absolute quantification via dynamic PET (dPET) may provide a more reliable and quantitative assessment of TAK-active arteries. The purpose of this study was to investigate the feasibility and efficacy of dPET in quantifying TAK-active arteries compared to static PET.

MATERIALS AND METHODS

This prospective study enrolled 10 TAK-active patients (fulfilled the NIH criteria) and 5 control participants from March to October 2022. One-hour dPET scan (all TAK and control participants) and delayed static PET scan at 2-h (all TAK patients) were acquired. For 1-h static PET, summed images from 50 to 60 min of the dPET were extracted. PET parameters derived from 1- and 2-h static PET including SUV (SUV1H and SUV2H), target-to-background ratio (TBR) (TBR1H and TBR2H), net influx rate (Ki), and TBRKi extracted from dPET were obtained. The detectability of TAK-active arteries was compared among different scanning methods using the generalized estimating equation (GEE) with a logistic regression with repeated measures, and the GEE with gamma distribution and log link function was used to evaluate the different study groups or scanning methods.

RESULTS

Based on the disease states, 5 cases of TAK were classified as untreated and relapsed, respectively. The SUVmax on 2-h PET was higher than that on 1-h PET in the untreated patients (P < 0.05). However, no significant differences were observed in the median SUVmax between 1-h PET and 2-h PET in the relapsed patients (P > 0.05). The TBRKi was significantly higher than both TBR1H and TBR2H (all P < 0.001). Moreover, the detectability of TAK-active arteries by dPET-derived Ki was significantly higher than 1-h and 2-h PET (all P < 0.001). Significant differences were observed in Kimax, SUVmax-1H, TBR1H, and TBRKi among untreated, relapsed, and control groups (all P < 0.05).

CONCLUSIONS

Absolute quantitative assessment by dPET provides an improved sensitivity and detectability in both visualization and quantification of TAK-active arteries. This elucidates the clinical significance of dPET in the early detection of active inflammation and monitoring recurrence.

Prone position PET/CT is useful in reducing gravity-dependent opacity-related [18F]fluorodeoxyglucose uptake

OBJECTIVES

This study aimed to investigate whether performing [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) in the prone position could reduce [18F]FDG uptake in dependent lungs.

METHODS

Patients who underwent [18F]FDG PET/CT in both supine and prone positions from October 2018 to September 2021 were reviewed retrospectively. [18F]FDG uptake of dependent and nondependent lungs was analysed visually and semi-quantitatively. A linear regression analysis was performed to examine the association between the mean standardised uptake value (SUVmean) and the Hounsfield unit (HU).

RESULTS

A total of 135 patients (median age, 66 years [interquartile range: 58-75 years]; 80 men) were included. Dependent lungs showed significantly higher SUVmean and HU than nondependent lungs on supine position PET/CT (sPET/CT, 0.59 ± 0.14 vs. 0.36 ± 0.09, p < 0.001; - 671 ± 66 vs. - 802 ± 43, p < 0.001, respectively) and prone position PET/CT (pPET/CT, 0.45 ± 0.12 vs. 0.42 ± 0.08, p < 0.001; - 731 ± 67 vs. - 790 ± 40, p < 0.001, respectively). Linear regression analysis revealed a strong association between the SUVmean and HU in sPET/CT (R = 0.86, p < 0.001) and moderate association in pPET/CT (R = 0.65, p < 0.001). One hundred and fifteen patients (85.2%) had visually discernible [18F]FDG uptake in the posterior lung on sPET/CT, which disappeared on pPET/CT in all but one patient (0.7%, p < 0.001).

CONCLUSIONS

[18F]FDG uptake of the lung had moderate-to-strong associations with HU. Gravity-dependent opacity-related [18F]FDG uptake can be effectively reduced on prone position PET/CT.

CLINICAL RELEVANCE STATEMENT

Prone position PET/CT effectively reduces gravity-dependent opacity-related [18F]fluorodeoxyglucose uptake in the lung, potentially improving diagnostic accuracy in evaluating nodules in dependent lungs and offering a more accurate assessment of lung inflammation parameters in interstitial lung disease evaluations.

KEY POINTS

• The study evaluated whether performing [18F]fluorodeoxyglucose ([18F]FDG) PET/CT could reduce [18F]FDG uptake in lungs. • In prone and supine position PET/CT, the [18F]FDG uptake and Hounsfield unit were moderately to strongly associated. • Prone position PET/CT can reduce gravity-dependent opacity-related [18F]FDG uptake by the posterior lung.

Current and Future Use of Long Axial Field-of-View Positron Emission Tomography/Computed Tomography Scanners in Clinical Oncology

The latest technical development in the field of positron emission tomography/computed tomography (PET/CT) imaging has been the extension of the PET axial field-of-view. As a result of the increased number of detectors, the long axial field-of-view (LAFOV) PET systems are not only characterized by a larger anatomical coverage but also by a substantially improved sensitivity, compared with conventional short axial field-of-view PET systems. In clinical practice, this innovation has led to the following optimization: (1) improved overall image quality, (2) decreased duration of PET examinations, (3) decreased amount of radioactivity administered to the patient, or (4) a combination of any of the above. In this review, novel applications of LAFOV PET in oncology are highlighted and future directions are discussed.

The Spectrum of Solitary Benign Splenic Lesions-Imaging Clues for a Noninvasive Diagnosis

Cross-sectional imaging of the upper abdomen, especially if intravenous contrast has been administered, will most likely reveal any acute or chronic disease harbored in the spleen. Unless imaging is performed with the specific purpose of evaluating the spleen or characterizing a known splenic lesion, incidentally discovered splenic lesions pose a small challenge. Solitary benign splenic lesions include cysts, hemangiomas, sclerosing angiomatous nodular transformation (SANT), hamartomas, and abscesses, among others. Sarcoidosis and tuberculosis, although predominantly diffuse micronodular disease processes, may also present as a solitary splenic mass lesion. In addition, infarction and rupture, both traumatic and spontaneous, may take place in the spleen. This review aims to describe the imaging features of the most common benign focal splenic lesions, with emphasis on the imaging findings as these are encountered on routine cross-sectional imaging from a multicenter pool of cases that, coupled with clinical information, can allow a definite diagnosis.

Evaluation of physiological Waldeyer's ring, mediastinal blood pool, thymic, bone marrow, splenic and hepatic activity with 18F-FDG PET/CT: exploration of normal range among pediatric patients

INTRODUCTION

While ¹⁸F-FDG PET/CT pediatrics applications have increased in number and indications, few studies have addressed normal maximum standardized uptake values (SUV_max) of referral organs in children. The purpose of this study is to assess these in a cohort of pediatric patients.

MATERIAL AND METHODS

285 ¹⁸F-FDG PET/CT scans in 229 patients were reviewed. SUV_max were assessed for mediastinal blood pool (MBP), thymus (T), liver (L), spleen (S), bone marrow (BM) and Waldeyer's Ring (Wald). L/MBP and S/L ratios were calculated. Same day complete blood counts (CBC) were available for 132 studies and compared to BM and S. Means, standard deviations and correlation coefficients with age, weight and body surface area (BSA) were calculated.

RESULTS

Weak correlation with age, weight or BSA was found for Wald. Strong correlations with weight/BSA more than with age were demonstrated for MBP, L and BM and moderate for S and T. After initial decrease between age 0 and 2, thymic activity peaked at age 11 years then involuted. No correlation was found between CBC ad BM or S. In 28 studies, L was less or equal to MBP. In 74 S was superior to L.

CONCLUSIONS

Referral organs ¹⁸F-FDG uptake varies in children more in relation with weight and BSA than with age for key referral organs, such as L, S and MBP. In a significant number of studies, L activity may impede evaluation of treatment response in comparison with MBP or inflammation/infection evaluation in comparison with S.

Dual time point imaging in locally advanced head and neck cancer to assess residual nodal disease after chemoradiotherapy

Background

FDG-PET/CT has a high negative predictive value to detect residual nodal disease in patients with locally advanced squamous cell head and neck cancer after completing concurrent chemoradiotherapy (CCRT). However, the positive predictive value remains suboptimal due to inflammation after radiotherapy, generating unnecessary further investigations and possibly even surgery. We report the results of a preplanned secondary end point of the ECLYPS study regarding the potential advantages of dual time point FDG-PET/CT imaging (DTPI) in this setting. Standardized dedicated head and neck FDG-PET/CT images were obtained 12 weeks after CCRT at 60 and 120 min after tracer administration. We performed a semiquantitative assessment of lymph nodes, and the retention index (RI) was explored to optimize diagnostic performance. The reference standard was histology, negative FDG-PET/CT at 1 year, or > 2 years of clinical follow-up. The time-dependent area under the receiver operator characteristics (AUROC) curves was calculated.

Results

In total, 102 subjects were eligible for analysis. SUV values increased in malignant nodes (median SUV₁ = 2.6 vs. SUV₂ = 2.7; P = 0.04) but not in benign nodes (median SUV₁ = 1.8 vs. SUV₂ = 1.7; P = 0.28). In benign nodes, RI was negative although highly variable (median RI = − 2.6; IQR 21.2), while in malignant nodes RI was positive (median RI = 12.3; IQR 37.2) and significantly higher (P = 0.018) compared to benign nodes. A combined threshold (SUV₁ ≥ 2.2 + RI ≥ 3%) significantly reduced the amount of false-positive cases by 53% (P = 0.02) resulting in an increased specificity (90.8% vs. 80.5%) and PPV (52.9% vs. 37.0%), while sensitivity (60.0% vs. 66.7%) and NPV remained comparably high (92.9% vs. 93.3%). However, AUROC, as overall measure of benefit in diagnostic accuracy, did not significantly improve (P = 0.62). In HPV-related disease (n = 32), there was no significant difference between SUV₁, SUV₂, and RI in malignant and benign nodes, yet this subgroup was small.

Conclusions

DTPI did not improve the overall diagnostic accuracy of FDG-PET/CT to detect residual disease 12 weeks after chemoradiation. Due to differences in tracer kinetics between malignant and benign nodes, DTPI improved the specificity, but at the expense of a loss in sensitivity, albeit minimal. Since false negatives at the 12 weeks PET/CT are mainly due to minimal residual disease, DTPI is not able to significantly improve sensitivity, but repeat scanning at a later time (e.g. after 12 months) could possibly solve this problem. Further study is required in HPV-associated disease.

What's in a node? The clinical and radiologic significance of Virchow's node

In 1848, Rudolf Ludwig Karl Virchow described an association of left supraclavicular lymphadenopathy with abdominal malignancy. The left supraclavicular lymph node later became commonly referred to as Virchow's node. Charles-Emile Troisier went on to describe the physical exam finding of an enlarged left supraclavicular lymph node, later termed Troisier's sign. Subsequent studies confirmed a predilection of abdominal and pelvic malignancies to preferentially metastasize to the left supraclavicular node. Identification of a pathologically enlarged left supraclavicular node raises the suspicion for abdominopelvic malignancy, particularly in the absence of right supraclavicular lymphadenopathy, and provides a safe and easy target for biopsy. Supraclavicular lymph nodes also represent a great target for diagnosis of metastatic thoracic malignancies, although thoracic malignancies can involve either right or left supraclavicular nodes and do not show a predilection for either. This article presents a review of the history, anatomy, pathophysiology, clinical significance, radiological appearance, and biopsy of Virchow's node. Key points are illustrated with relevant cases.

Test-retest repeatability and interobserver variation of healthy tissue metabolism using 18F-FDG PET/CT of the thorax among lung cancer patients

OBJECTIVES

The aim of this study was to assess the test-retest repeatability and interobserver variation in healthy tissue (HT) metabolism using 2-deoxy-2-[18F]fluoro-d-glucose (18F-FDG) PET/computed tomography (PET/CT) of the thorax in lung cancer patients.

METHODS

A retrospective analysis was conducted in 22 patients with non-small cell lung cancer who had two PET/CT scans of the thorax performed 3 days apart with no interval treatment. The maximum, mean and peak standardized uptake values (SUVs) in different HTs were measured by a single observer for the test-retest analysis and two observers for interobserver variation. Bland-Altman plots were used to assess the repeatability and interobserver variation. Intrasubject variability was evaluated using within-subject coefficients of variation (wCV).

RESULTS

The wCV of test-retest SUVmean measurements in mediastinal blood pool, bone marrow, skeletal muscles and lungs was less than 20%. The left ventricle (LV) showed higher wCV (>60%) in all SUV parameters with wide limits of repeatability. High interobserver agreement was found with wCV of less than 10% in SUVmean of all HT, but up to 22% was noted in the LV.

CONCLUSION

HT metabolism is stable in a test-retest scenario and has high interobserver agreement. SUVmean was the most stable metric in organs with low FDG uptake and SUVpeak in HTs with moderate uptake. Test-retest measurements in LV were highly variable irrespective of the SUV parameters used for measurements.

Advantages and Applications of Total-Body PET Scanning

Recent studies have focused on the development of total-body PET scanning in a variety of fields such as clinical oncology, cardiology, personalized medicine, drug development and toxicology, and inflammatory/infectious disease. Given its ultrahigh detection sensitivity, enhanced temporal resolution, and long scan range (1940 mm), total-body PET scanning can not only image faster than traditional techniques with less administered radioactivity but also perform total-body dynamic acquisition at a longer delayed time point. These unique characteristics create several opportunities to improve image quality and can provide a deeper understanding regarding disease detection, diagnosis, staging/restaging, response to treatment, and prognostication. By reviewing the advantages of total-body PET scanning and discussing the potential clinical applications for this innovative technology, we can address specific issues encountered in routine clinical practice and ultimately improve patient care.

Potential and Most Relevant Applications of Total Body PET/CT Imaging

ABSTRACT

The introduction of total body (TB) PET/CT instruments over the past 2 years has initiated a new and exciting era in medical imaging. These instruments have substantially higher sensitivity (up to 68 times) than conventional modalities and therefore allow imaging the entire body over a short period. However, we need to further refine the imaging protocols of this instrument for different indications. Total body PET will allow accurate assessment of the extent of disease, particularly, including the entire axial and appendicular skeleton. Furthermore, delayed imaging with this instrument may enhance the sensitivity of PET for some types of cancer. Also, this modality may improve the detection of venous thrombosis, a common complication of cancer and chemotherapy, in the extremities and help prevent pulmonary embolism. Total body PET allows assessment of atherosclerotic plaques throughout the body as a systematic disease. Similarly, patients with widespread musculoskeletal disorders including both oncologic and nononcologic entities, such as degenerative joint disease, rheumatoid arthritis, and osteoporosis, may benefit from the use of TB-PET. Finally, quantitative global disease assessment provided by this approach will be superior to conventional measurements, which do not reflect overall disease activity. In conclusion, TB-PET imaging may have a revolutionary impact on day-to-day practice of medicine and may become the leading imaging modality in the future.

Diagnosis of bone metastases in breast cancer: Lesion-based sensitivity of dual-time-point FDG-PET/CT compared to low-dose CT and bone scintigraphy

We compared lesion-based sensitivity of dual-time-point FDG-PET/CT, bone scintigraphy (BS), and low-dose CT (LDCT) for detection of various types of bone metastases in patients with metastatic breast cancer. Prospectively, we included 18 patients with recurrent breast cancer who underwent dual-time-point FDG-PET/CT with LDCT and BS within a median time interval of three days. A total of 488 bone lesions were detected on any of the modalities and were categorized by the LDCT into osteolytic, osteosclerotic, mixed morphologic, and CT-negative lesions. Lesion-based sensitivity was 98.2% (95.4-99.3) and 98.8% (96.8-99.5) for early and delayed FDG-PET/CT, respectively, compared with 79.9% (51.1-93.8) for LDCT, 76.0% (36.3-94.6) for BS, and 98.6% (95.4-99.6) for the combined BS+LDCT. BS detected only 51.2% of osteolytic lesions which was significantly lower than other metastatic types. SUVs were significantly higher for all lesion types on delayed scans than on early scans (P<0.0001). Osteolytic and mixed-type lesions had higher SUVs than osteosclerotic and CT-negative metastases at both time-points. FDG-PET/CT had significantly higher lesion-based sensitivity than LDCT and BS, while a combination of the two yielded sensitivity comparable to that of FDG-PET/CT. Therefore, FDG-PET/CT could be considered as a sensitive one-stop-shop in case of clinical suspicion of bone metastases in breast cancer patients.

PET/CT Variants and Pitfalls in Liver, Biliary Tract, Gallbladder and Pancreas

A wide variety of pathological anomalies may occur in the liver, biliary system, and pancreas. It is a necessity to use many different imaging techniques in order to distinguish such varied pathologies, especially those from malignant processes. Positron Emission Tomography/Computed Tomography (PET/CT) is an imaging method that has proven its diagnostic value in oncology and can be used for different clinical purposes. Fluoro-18 fluoro-2-deoxy-D-glucose has a wide range of uses as a dominant radiopharmaceutical in routine molecular imaging, however, molecular imaging has started to play a more important role in personalized cancer treatment in recent years with new Fluoro-18 and Gallium-68 labeled tracers. Although molecular imaging has a strong diagnostic effect, the surprises and pitfalls of molecular imaging can lead us to unexpected and misleading results. Prior to PET/CT analysis and reporting, information about possible technical and physiological pitfalls, normal histological features of tissues, inflammatory pathologies, specific clinical features of the case, treatment-related complications and past treatments should be evaluated in advance to avoid misinterpretation. In this review, the physiological and pathophysiological variants as well as pitfalls encountered in PET/CT imaging of the liver, biliary tract, gallbladder, and pancreas will be examined. Other benign and malignant pathologies that have been reported to date and that have led to incorrect evaluation will be listed. It is expected that the devices, software, and artificial intelligence applications that will be developed in the near future will enable much more effective and faster imaging that will reduce the potential causes of error. However, as a result of the dynamic and evolving structure of the information obtained by molecular imaging, the inclusion of the newly developed radiopharmaceuticals in routine practice will continue to carry new potentials as well as new troubles. Although molecular imaging will be the flagship of diagnostic oncology in the 21st century, the correct analysis and interpretation by the physician will continue to form the basis of achieving optimal performance.

Age-related changes of standardized uptake values in the blood pool and liver: a decade-long retrospective study of the outcomes of 2,526 subjects

Background

Background activity on fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is often used as a reference to assess a patient's response to tumor treatment. To produce a suitable background activity reference, we examined the variations in standardized uptake values (SUVs) in the blood pool and liver of a large multi-aged population.

Methods

A total of 2,526 subjects underwent ¹⁸F-FDG PET/CT examinations and were divided into 12 age groups. Pearson's partial correlation and multivariate regression analyses were performed to assess the associations between individual factors and SUVs of the blood pool and liver and to identify the factor that most influenced the SUVs. The mean SUVs across the age groups were also determined.

Results

Positive correlations were found between individual factors and SUVs. Age appeared to be the most important predictor of SUVs and was significantly associated with the blood pool SUV_max (ß=0.466, P=0.000), blood pool SUV_mean (ß=0.393, P=0.000), liver SUV_max (ß=0.347, P=0.000), and liver SUV_mean (ß=0.354, P=0.000). Blood pool and liver SUVs rose rapidly until the age of 20 and then showed a slow upward trend without reaching a plateau.

Conclusions

Age is an important factor that influences variations in the blood pool and liver SUVs. Our study clarified this understanding of age-related variations in SUVs and provided a normal range of blood pool and liver SUVs that may aid clinicians in evaluating tumors with greater accuracy.

Correlation of the apparent diffusion coefficient (ADC) and standardized uptake values (SUV) with overall survival in patients with primary non-small cell lung cancer (NSCLC) using 18F-FDG PET/MRI

OBJECTIVES

To investigate if the combined analysis of the apparent diffusion coefficient (ADC) and standardized uptake values (SUV) measured in ¹⁸F-fluoro-deoxy-glucose-positron emission tomography/magnetic resonance imaging (¹⁸F-FDG PET/MRI) examinations correlates with overall survival in non-small cell lung cancer (NSCLC).

MATERIAL AND METHODS

A total of 92 patients with newly diagnosed, histopathologically proven NSCLC (44 women and 48 men, mean age 63.1 ± 9.9y) underwent a dedicated thoracic ¹⁸F-FDG PET/MRI examination. A manually drawn polygonal region of interest (ROI), encompassing the entire primary tumor mass, was placed over the primary tumor on fused PET/MR images to determine the maximum and mean standardized uptake values (SUV_max; SUV_mean) as well as on the ADC maps to quantify the mean and minimum ADC values (ADC_mean, ADC_min). The impact of these parameters to predict patient's overall survival was tested using hazard ratios (HR). Pearson's correlation coefficients were calculated to assess dependencies between the different values. A p-value < 0.05 indicated statistical significance.

RESULTS

In all 92 patients (n = 59 dead at time of retrospective data collection, mean time till death: 19 ± 16 month, n = 33 alive, mean time to last follow-up: 56 ± 22 month) the Hazard ratios (HR) as independent predictors for overall survival (OS) of SUV_max were 2.37 (95 % CI: 1.23-4.59, p = 0.008) and for SUV_mean 1.85 (95 % CI: 1.05-3.26, p = 0.03) while ADC_min showed a HR of 0.95 (95 % CI: 0.57-1.59, p = 0.842) and ADC_mean a HR of 2.01 (95 % CI: 1.2-3.38, p = 0.007). Furthermore, a combined analysis for SUV_max/ADC_mean, SUV_max / ADC_min and SUV_mean/ADC_mean revealed a HR of 2.01 (95 % CI: 1.10-3.67, p = 0.02), 1.75 (95 % CI: 0.97-3.15, p = 0.058) and 1.78 (95 % CI: 1.02-3.10, p = 0.04).

CONCLUSION

SUV_max and SUV_mean of the primary tumor are predictors for OS in therapy-naive NSCLC patients, whereas the combined analysis of SUV and ADC values does not improve these results. Therefore, ADC values do not further enhance the diagnostic value of SUV as a prognostic biomarker in NSCLC.

Imaging Atherosclerosis by PET, With Emphasis on the Role of FDG and NaF as Potential Biomarkers for This Disorder

Molecular imaging has emerged in the past few decades as a novel means to investigate atherosclerosis. From a pathophysiological perspective, atherosclerosis is characterized by microscopic inflammation and microcalcification that precede the characteristic plaque buildup in arterial walls detected by traditional assessment methods, including anatomic imaging modalities. These processes of inflammation and microcalcification are, therefore, prime targets for molecular detection of atherosclerotic disease burden. Imaging with positron emission tomography/computed tomography (PET/CT) using 18F-fluorodeoxyglucose (FDG) and 18F-sodium fluoride (NaF) can non-invasively assess arterial inflammation and microcalcification, respectively. FDG uptake reflects glucose metabolism, which is particularly increased in atherosclerotic plaques retaining macrophages and undergoing hypoxic stress. By contrast, NaF uptake reflects the exchange of hydroxyl groups of hydroxyapatite crystals for fluoride producing fluorapatite, a key biochemical step in calcification of atherosclerotic plaque. Here we review the existing literature on FDG and NaF imaging and their respective values in investigating the progression of atherosclerotic disease. Based on the large volume of data that have been introduced to the literature and discussed in this review, it is clear that PET imaging will have a major role to play in assessing atherosclerosis in the major and coronary arteries. However, it is difficult to draw definitive conclusions on the potential role of FDG in investigating atherosclerosis given the vast number of studies with different designs, image acquisition methods, analyses, and interpretations. Our experience in this domain of research has suggested that NaF may be the tool of choice over FDG in assessing atherosclerosis, especially in the setting of coronary artery disease (CAD). Specifically, global NaF assessment appears to be superior in detecting plaques in tissues with high background FDG activity, such as the coronary arteries.

Reinventing Molecular Imaging with Total-Body PET, Part II: Clinical Applications

Total-body PET scans will initiate a new era for the PET clinic. The benefits of 40-fold effective sensitivity improvement provide new capabilities to image with lower radiation dose, perform delayed imaging, and achieve improved temporal resolution. These technical features are detailed in the first of this 2-part series. In this part, the clinical impacts of the novel features of total-body PET scans are further explored. Applications of total-body PET scans focus on the real-time interrogation of systemic disease manifestations in a variety of practical clinical contexts. Total-body PET scans make clinical systems biology imaging a reality.

The added value of dual-time-point 18F-FDG PET/CT imaging in the diagnosis of colorectal cancer liver metastases

PURPOSE

To investigate the added value of dual-time-point ¹⁸F-FDG PET/CT imaging in the diagnosis of colorectal cancer liver metastases (CRLM).

METHODS

One hundred and eight patients with CRLM preoperatively underwent a dual-time-point ¹⁸F-FDG PET/CT scan. All hepatic lesions were diagnosed by histopathology. The diagnostic sensitivity of ¹⁸F-FDG PET/CT for CRLM was calculated on early scan and delayed scan, respectively. The McNemar test was used to test the differences of the sensitivity and the specificity between early scan and delayed scan.

RESULTS

On a per-patient basis, no significant difference in sensitivity was found between early scan and delayed scan (92.93% vs. 96.97%, P = 0.125). The per-patient specificity of early and delayed scans was 77.78%. On a per-lesion basis, overall sensitivity of delayed scan was significantly higher than that of early scan (83.49% vs. 76.61%, P < 0.001). The per-lesion specificity of early and delayed scans was 69.23%. For the lesion size of CRLM ≤ 10 mm, delayed imaging had significantly higher sensitivity than early imaging (47.17% vs. 26.42%, P < 0.001). However, for CRLM > 10 mm, there was no significant difference in sensitivity between early and delayed scans (92.73% vs. 95.15%, P = 0.125). Of the detected 182 liver metastatic lesions on delayed scan, the SUV_max on delayed scan was significantly higher than that on early scan (12.13 ± 7.13 vs. 9.16 ± 4.74, P < 0.001). The SUVmean of the normal liver on delayed scan was significantly lower than that on early scan (1.91 ± 0.29 vs. 2.33 ± 0.31, P < 0.001). The tumor to normal background ratio on delayed scan was significantly higher than that on early scan (6.59 ± 4.43 vs. 4.02 ± 2.23, P < 0.001).

CONCLUSION

The dual-time-point ¹⁸F-FDG PET/CT imaging might detect more CRLM lesions compared with single-time-point imaging, especially for small (< 10 mm) lesions.

Partial volume and motion correction in cardiac PET: First results from an in vs ex vivo comparison using animal datasets

BACKGROUND

In a previous study on ex vivo, static cardiac datasets, we investigated the benefits of performing partial volume correction (PVC) in cardiac 18F-Fluorodeoxyglucose(FDG) PET datasets. In the present study, we extend the analysis to in vivo cardiac datasets, with the aim of defining which reconstruction technique maximizes quantitative accuracy and, ultimately, makes PET a better diagnostic tool for cardiac pathologies.

METHODS

In vivo sheep datasets were acquired and reconstructed with/without motion correction and using several reconstruction algorithms (with/without resolution modeling, with/without non-anatomical priors). Corresponding ex vivo scans of the excised sheep hearts were performed on a small-animal PET scanner (Siemens Focus 220, microPET) to provide high-resolution reference data unaffected by respiratory and cardiac motion. A comparison between the in vivo cardiac reconstructions and the corresponding ex vivo ground truth was performed.

RESULTS

The use of an edge-preserving prior (Total Variation (TV) prior in this work) in combination with motion correction reduces the bias in absolute quantification when compared to the standard clinical reconstructions (- 0.83 vs - 3.74 SUV units), when the end-systolic gate is considered. At end-diastole, motion correction improves absolute quantification but the PVC with priors does not improve the similarity to the ground truth more than a regular iterative reconstruction with motion correction and without priors. Relative quantification was not influenced much by the chosen reconstruction algorithm.

CONCLUSIONS

The relative ranking of the algorithms suggests superiority of the PVC reconstructions with dual gating in terms of overall absolute quantification and noise properties. A well-tuned edge-preserving prior, such as TV, enhances the noise properties of the resulting images of the heart. The end-systolic gate yields the most accurate quantification of cardiac datasets.

The Evolving Role of PET-Based Novel Quantitative Techniques in the Interventional Radiology Procedures of the Liver

Interventional radiology procedures have revolutionized the treatment of cancer and interventional oncology is now the fourth pillar of cancer care. The article discusses the importance of fluorodeoxyglucose (FDG)-PET imaging, and dual time-point imaging in the context of PET/computed tomography as applied to treatments of liver malignancy. The necessary paradigm shift in the adoption of novel segmentation methodologies to express global disease burden is explored.

Adjustment of vascular 2-deoxy-2-[18F]fluoro-D-glucose uptake values over time through a modeling approach

To develop and test a model predicting 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) standardized uptake value (SUV) changes over time in the aorta and the superior vena cava (SVC). Maximum aortic SUV and mean SVC SUV were determined at two time points (T1 and T2) in the ascending (ASC), descending (DSC), abdominal (ABD) aorta, aortic arch (ARC) and SVC of patients who have undergone [18F]FDG PET/CT for clinical purposes. For SUV prediction at T2, linear and non-linear models of SUV difference for a given time change were developed in a derivation group. The results were tested in an independent validation group, whilst model reproducibility was tested in patients of the validation group who have undergone a second clinically indicated scan. Applying the linear model in the derivation group, there were no statistically significant differences in measurements obtained in the examined segments: mean differences ranged from 0 ± 0.10 in SVC to 0.01 ± 0.13 in ARC between measured and predicted SUV. In contrast, in the non-linear model, there were statistically significant differences in measurements, except in ARC, with mean differences ranging from 0.04 ± 0.14 in ARC to 0.28 ± 0.13 in ABD. In the validation group using the linear model, there were no statistically significant differences, with mean differences ranging from - 0.01 ± 0.08 in ASC to - 0.03 ± 0.11 in ABD. Regarding reproducibility, mean differences were no statistically significant, ranging from 0.004 ± 0.06 in ASC to - 0.02 ± 0.16 in ABD. We have developed a linear model allowing accurate and reproducible prediction of SUV changes over time in the aorta and SVC.

Dynamics of fluorine-18-fluorodeoxyglucose uptake in the liver and its correlation with hepatic fat content and BMI

PURPOSE

The aim of this study was to explore the rate of elimination of fluorine-18-fluorodeoxyglucose (F-FDG) from the liver and assess the impact of hepatic fat and obesity on F-FDG clearance in early and delayed PET scans. We hypothesized that an increase in liver fat may cause a decline in hepatic F-FDG elimination with potential consequences as measured by dual time-point F-FDG PET/CT imaging.

PATIENTS AND METHODS

A total of 32 patients from the Cardiovascular Molecular Calcification Assessed by F-NaF PET/CT (CAMONA) clinical trial (17 males, 15 females; mean age: 47.2 years, range: 23-69 years, mean BMI: 27.2 kg/m) were enrolled and underwent F-FDG PET/CT 90 and 180 min after tracer injection. Global mean standardized uptake value (SUVmean) (i.e. the average of SUVmean in segmented liver slices) and average maximum standardized uptake value (SUVmax) (i.e. the average of the SUVmax values recorded in same slices) were calculated for semiquantification of liver F-FDG uptake at both time-points. Percentage difference in global SUVmean and average SUVmax were also calculated to yield respective retention indices (RImean and RImax). Changes in global SUVmean, average SUVmax, RImean, and RImax from 90 to 180 min were correlated with BMI and liver fat content as measured by CT Hounsfield units.

RESULTS

There was a 12.2±3.5 percent reduction in global liver SUVmean and a 4.1±5.8 percent reduction in average SUVmax at 180 min scan as compared with the 90 min time-point. RImean and RImax were inversely correlated with liver fat content and positively correlated with BMI.

CONCLUSION

We observed a time-dependent decrease in global hepatic SUVmean and average SUVmax, which was affected by the amount of liver fat. Patients with higher BMI and hepatic fat content tended to retain F-FDG.

Evaluation of the most commonly used (semi-)quantitative parameters of 18F-FDG PET/CT to detect malignant transformation of neurofibromas in neurofibromatosis type 1

In patients with neurofibromatosis type 1, transformation of neurofibromas into a malignant peripheral nerve sheath tumor (MPNST) is a severe complication of the disease. Fluorine-18-fluorodeoxyglucose PET/computed tomography (PET/CT) is a viable option for detecting malignant tumors in neurofibromatosis type 1 patients. The aim of this review was to assess the diagnostic performance of the most frequently used parameters of PET/CT in detecting MPNST. An extensive computer search was performed using the Cochrane Library, Pubmed, and Medline/Embase databases. Two reviewers independently extracted data of relevant studies and assessed the methodological quality (QUADAS-2). The diagnostic performance of PET/CT parameters in individual studies was determined by calculating a diagnostic odds ratio (DOR) using the absolute numbers of true-positive, true-negative, false-positive, and false-negative test results. A total of eight studies were included, of which three evaluated the standardized uptake value as a diagnostic parameter, two assessed the tumor-to-liver (T/L) ratio, and three articles described both parameters. The cut-off values for maximum standardized uptake value (SUVmax) ranged from 3.2 to 4.5; for the T/L ratio, the cut-off values were between 1.0 and 4.3. The sensitivity and specificity ranged from 90 to 100% and from 80 to 100%, respectively (SUVmax). T/L ratios were associated with 92-100% sensitivity and 72-94% specificity. The corresponding DORs ranged from 57 to 145 (SUVmax) and 35 to 655 (T/L ratio). Both the SUV and the T/L ratio are associated with high sensitivity combined with acceptable specificity in detecting MPNST. There is a tendency toward higher DORs using the T/L ratio, but the number of studies is limited.

Quantification of FDG-PET/CT with delayed imaging in patients with newly diagnosed recurrent breast cancer

Background

Several studies have shown the advantage of delayed-time-point imaging with 18F-FDG-PET/CT to distinguish malignant from benign uptake. This may be relevant in cancer diseases with low metabolism, such as breast cancer. We aimed at examining the change in SUV from 1 h (1h) to 3 h (3h) time-point imaging in local and distant lesions in patients with recurrent breast cancer. Furthermore, we investigated the effect of partial volume correction in the different types of metastases, using semi-automatic quantitative software (ROVER™).

Methods

One-hundred and two patients with suspected breast cancer recurrence underwent whole-body PET/CT scans 1h and 3h after FDG injection. Semi-quantitative standardised uptake values (SUVmax, SUVmean) and partial volume corrected SUVmean (cSUVmean), were estimated in malignant lesions, and as reference in healthy liver tissue. The change in quantitative measures from 1h to 3h was calculated, and SUVmean was compared to cSUVmean. Metastases were verified by biopsy.

Results

Of the 102 included patients, 41 had verified recurrent disease with in median 15 lesions (range 1-70) amounting to a total of 337 malignant lesions included in the analysis. SUVmax of malignant lesions increased from 6.4 ± 3.4 [0.9-19.7] (mean ± SD, min and max) at 1h to 8.1 ± 4.4 [0.7-29.7] at 3h. SUVmax in breast, lung, lymph node and bone lesions increased significantly (p < 0.0001) between 1h and 3h by on average 25, 40, 33, and 27%, respectively. A similar pattern was observed with (uncorrected) SUVmean. Partial volume correction increased SUVmean significantly, by 63 and 71% at 1h and 3h imaging, respectively. The highest impact was in breast lesions at 3h, where cSUVmean increased by 87% compared to SUVmean.

Conclusion

SUVs increased from 1h to 3h in malignant lesions, SUVs of distant recurrence were in general about twice as high as those of local recurrence. Partial volume correction caused significant increases in these values. However, it is questionable, if these relatively modest quantitative advances of 3h imaging are sufficient to warrant delayed imaging in this patient group.

Trial registration

ClinicalTrails.gov NCT01552655. Registered 28 February 2012, partly retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12880-018-0254-8) contains supplementary material, which is available to authorized users.

Detection of Distant Metastases in Head and Neck Cancer: Changing Landscape

As head and neck squamous cell carcinoma (HNSCC) patients with distant metastases (DM) were generally treated only palliatively, the value of screening for DM was usually limited to attempts to avoid extensive locoregional treatment when DM were present pretreatment. Recently, the concept of treating oligometastases, e.g., by metastatectomy or stereotactic body radiotherapy, has been reintroduced for HNSCC and may cause a change in the treatment paradigm. Although whole body ¹⁸F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) combined with computed tomography (CT; WB-FDG-PET/CT) is still the mainstay diagnostic technique, there is a growing body of evidence supporting implementation of whole body magnetic resonance imaging (WB-MRI) as an important diagnostic technique for screening for DM. Also, FDG-PET/MRI may become a valuable technique for the detection of DM in HNSCC patients. Because the yield of examinations for detection of DM is too low to warrant routine screening of all HNSCC patients, only patients with high risk factors should be selected for intense screening for DM. Clinical and histopathological risk factors are mainly related to the extent of lymph node metastases. Risk for development of DM may also be assessed by molecular characterization of the primary tumor using genomic and proteomic technologies and radiomics. More research is needed to develop a new protocol for screening for DM after introduction of the concept of treating oligometastases in HNSCC.

The extent to which standardized uptake values reflect FDG phosphorylation in the liver and spleen as functions of time after injection of 18F-fluorodeoxyglucose

Purpose

In FDG PET/CT, standardized uptake value (SUV) is used to measure metabolic activity but detects un-phosphorylated FDG as well as phosphorylated FDG (FDG6P). Our aim was to determine the proportions of intrahepatic and intrasplenic FDG that are phosphorylated after FDG injection and compare them with SUVs.

Methods

Sixty patients undergoing whole-body PET/CT 60 min post-injection of FDG first had dynamic PET imaging for 30 min with measurement of hepatic and splenic FDG clearances using Patlak-Rutland analysis. The gradient of the Patlak-Rutland plot, which is proportional to clearance (Ki), was normalized to the intercept, which is proportional to FDG distribution volume (V(0)) with the same proportionality constant. Using measured values of Ki/V(0), FDG6P/FDG ratios as functions of time in the two organs were measured for assumed FDG blood disappearance half-times of 40, 50 and 60 min. Hepatic and splenic SUVs were measured from whole-body PET/CT.

Results

The mean (SD) Ki/V(0) was 0.0036 (0.0021) and 0.0060 (0.0041) ml/min/ml for the liver and spleen, respectively, but the hepatic SUV was 1.36-fold higher than the splenic SUV. This discrepancy was explained by the hepatic V(0) being 1.6-fold higher than the splenic V(0). The percentages of FDG phosphorylated 60 min post-injection were 27, 25 and 23% for the liver and 39, 36 and 34% for the spleen, for blood clearance half-times of 40, 50 and 60 min, respectively. SUV indices correlated poorly with Ki/V(0) for both organs.

Conclusions

SUV is largely determined by un-phosphorylated FDG in dynamic exchange with blood FDG, explaining the poor correlations between SUV indices and Ki/V(0).

The performance of quantitation methods in the evaluation of cardiac implantable electronic device (CIED) infection: A technical review

BACKGROUND

Quantitative assessment of [18F]-FDG PET/CT images has been shown to be useful in the diagnosis of cardiac implantable electronic device (CIED) infection. This study aimed to compare the accuracy of various quantitative methods, using the same patient cohort and to assess the utility of dual time point imaging.

METHODS

The study comprised a retrospective review of 80 [18F]-FDG PET/CT studies. Of these, 41 were oncological patients with an asymptomatic CIED in situ (Group 1), and 39 were studies performed in patients with symptomatic devices. Of these, 14 were subsequently deemed on follow-up to be non-infected (Group 2), and 25 confirmed as infected post-device extraction (Group 3). Ratios of maximal uptake around the CIED in both the attenuation corrected and non-attenuation corrected images were calculated to regions of normal physiological uptake, along with the maximal standardized uptake value (SUVmax) alone. Receiver operating characteristic analysis was performed for all methods at both time points. Measurement reliability was assessed using the intraclass correlation coefficient (ICC).

RESULTS

Using Group 1 as a reference, all methods gave an area under the curve (AUC) greater than 0.93. Using Group 2 as reference, the accuracy varied greatly, with AUC values ranging from 0.71 to 0.97. The hepatic blood pool (HBP) ratio gave the highest AUC values. The calculated ICC values for each method showed the SUVmax and HBP measurement to have the greatest reliability, with values of 1.0 and 0.97, respectively.

CONCLUSIONS

Quantitation of [18F] FDG uptake was found to have a high degree of accuracy in confirming the diagnosis of CIED infection. Normalization to HBP uptake was found to give the greatest AUC and demonstrated excellent reliability. Inconsistencies from published data indicate that individual imaging centers should only use published data for guidance.

Do myocardial PET-MR and PET-CT FDG images provide comparable information?

INTRODUCTION

Although positron emission tomography PET-MR imaging is emerging into clinical practice, many aspects of this imaging technique such as attenuation correction have yet to be validated for myocardial imaging. Thus, it is uncertain whether PET-MR FDG images provide clinical information which is comparable to PET-CT FDG images. The study goal was to systematically compare relative myocardial FDG concentrations obtained from cardiac PET-MR images to those derived from same day PET-CT images.

METHODS

Myocardial FDG images of 27 patients undergoing PET-CT imaging, followed by PET-MR imaging 42 ± 13 minutes later as part of a prospective oncology study were analyzed. Mean segmental standardized uptake measurements (SUVmean) were obtained in each of the 17 standard myocardial segments and normalized to the brightest segment.

RESULTS

Normalized segmental SUVmean values did not differ significantly between the PET-MR and PET-CT images (mean difference 0.002, P = .826). The specific segment was a marginally significant predictor of the differences (P = .057), with the largest difference in the anteroseptal basal segment.

CONCLUSIONS

PET-MR, vis-à-vis PET-CT, does not significantly raise segmental uptake relative to the brightest segment, suggesting that PET-MR can be used similarly to PET-CT for applications where relative uptake is important.

What approach should we take for the incidental finding of increased 18F-FDG uptake foci in the colon on PET/CT?

INTRODUCTION

F-Fluorodeoxyglucose (F-FDG) PET/CT represents an imaging modality that is gaining increasingly more prominence in screening, staging, and therapeutic monitoring of malignant diseases. An incidental focus of uptake in different regions of the body is not an uncommon finding during PET/CT imaging. Patients with incidental gastrointestinal tract findings comprise ∼3% of the overall patient group. The aim of the current study was to provide contributory information in relation to the answer on the most appropriate approach in cases with incidental colonic F-FDG uptake.

PATIENTS AND METHODS

A retrospective examination was performed on PET/CT results of 5258 patients. Of these, 152 were recommended to undergo colonoscopy because of the presence of suspicious foci and 31 underwent colonoscopy within 60 days with biopsy from all visible lesions. These dates were also examined.

RESULTS

Of the 24 patients undergoing colonoscopy with a suspicion of malignancy, five (20.83%) had no pathological findings. Of the 19 (79.17%) cases with a pathological finding in endoscopy, histopathology showed a benign lesion in five (20.83%), premalignant lesion in seven (29.17%), and a malignant lesion in seven (29.17%). Among seven patients undergoing colonoscopy because of a suspicion of inflammatory bowel disease, five were free of pathological signs and two patients with pathological endoscopy findings had nonspecific inflammation as documented by histopathological examination.

CONCLUSION

Colonoscopic and histopathological examination of the increased foci of colonic F-FDG uptake incidentally detected at PET/CT seems to be a plausible approach.

Clinical Evaluation of PET Image Quality as a Function of Acquisition Time in a New TOF-PET/MRI Compared to TOF-PET/CT--Initial Results

PURPOSE

The purpose of this study was to compare only the performance of the PET component between a TOF-PET/CT (henceforth noted as PET/CT) scanner and an integrated TOF-PET/MRI (henceforth noted as PET/MRI) scanner concerning image quality parameters and quantification in terms of standardized uptake value (SUV) as a function of acquisition time (a surrogate of dose). The CT and MR image quality were not assessed, and that is beyond the scope of this study.

PROCEDURES

Five brain and five whole-body patients were included in the study. The PET/CT scan was used as a reference and the PET/MRI acquisition time was consecutively adjusted, taking into account the decay between the scans in order to expose both systems to the same amount of the emitted signal. The acquisition times were then retrospectively reduced to assess the performance of the PET/MRI for lower count rates. Image quality, image sharpness, artifacts, and noise were evaluated. SUV measurements were taken in the liver and in the white matter to compare quantification.

RESULTS

Quantitative evaluation showed strong correlation between PET/CT and PET/MRI brain SUVs. Liver correlation was good, however, with lower uptake estimation in PET/MRI, partially justified by bio-redistribution. The clinical evaluation showed that PET/MRI offers higher image quality and sharpness with lower levels of noise and artifacts compared to PET/CT with reduced acquisition times for whole-body scans while for brain scans there is no significant difference.

CONCLUSION

The TOF-PET/MRI showed higher image quality compared to TOF-PET/CT as tested with reduced imaging times. However, this result accounts mainly for body imaging, while no significant differences were found in brain imaging.

Dual time-point FDG PET/CT and FDG uptake and related enzymes in lymphadenopathies: preliminary results

PURPOSE

The purpose of this study was to determine the ability of dual time-point (DTP) PET/CT with (18)F-FDG to discriminate between malignant and benign lymphadenopathies. The relationship between DTP FDG uptake and glucose metabolism/hypoxia markers in lymphadenopathies was also assessed.

METHODS

Patients with suspected lymphoma or recently diagnosed treatment-naive lymphoma were prospectively enrolled for DTP FDG PET/CT (scans 60 min and 180 min after FDG administration). FDG-avid nodal lesions were segmented to yield volume and standardized uptake values (SUV), including SUVmax, SUVmean, cSUVmean (with partial volume correction), total lesion glycolysis (TLG) and cTLG (with partial volume correction). Expression of glucose transporter-1 (GLUT-1), hexokinase-II (HK-II), glucose-6-phosphatase (G6Pase) and hypoxia-inducible factor-1alpha (HIF-1alpha) were assessed with immunohistochemistry and enzyme activity was determined for HK and G6Pase.

RESULTS

FDG uptake was assessed in 203 lesions (146 malignant and 57 benign). Besides volume, there were significant increases over time for all parameters, with generally higher levels in the malignant lesions. The retention index (RI) was not able to discriminate between malignant and benign lesions. Volume, SUVmax, TLG and cTLG for both scans were able to discriminate between the two groups statistically, but without complete separation. Glucose metabolism/hypoxia markers were assessed in 15 lesions. TLG and cTLG were correlated with GLUT-1 expression on the 60-min scan. RI-max and RI-mean and SUVmax, SUVmean and cSUVmean on the 60-min scan were significantly correlated with HK-II expression.

CONCLUSION

RI was not able to discriminate between malignant and benign lesions, but some of the SUVs were able to discriminate on the 60-min and 180-min scans. Furthermore, FDG uptake was correlated with GLUT-1 and HK-II expression.

Optimizing 18F-FDG Uptake Time Before Imaging Improves the Accuracy of PET/CT in Liver Lesions

(18)F-FDG PET/CT has emerged as one of the fastest-growing imaging modalities. A shorter protocol results in a lower target-to-background ratio, which can increase the challenge of identifying mildly (18)F-FDG-avid lesions and differentiating inflammatory or physiologic activity from malignant activity. The purpose of this study was to determine the delay between radiotracer injection and imaging that optimizes target-to-background ratio while maintaining counts high enough to ensure scan sensitivity.

METHODS

The study included 140 patients (66 male and 74 female; age range, 42-95 y) with suspected hepatic lesions as seen on an (18)F-FDG PET scan. SUV was determined as region-of-interest activity/(dose/total body weight).

RESULTS

The mean injected dose was 610 ± 66.6 MBq (16.5 ±1.8 mCi), with a mean glucose level of 107 ± 26.6 mg/dL (standardized to 90 mg/dL). The uptake time before imaging ranged from 61 to 158 min, with a mean of 108.8 ± 24.8 min. The P values for the correlation of SUV to time were 0.004, 0.003, and 0.0001 for malignant lesions, benign lesions, and background hepatic tissue, respectively.

CONCLUSION

An approximately 90-min time window from (18)F-FDG injection to PET imaging would significantly improve target-to-background ratio and, thus, quantitation and visual interpretation. This benefit outweighs the minimal loss in patient throughput.

Dual-time-point Imaging and Delayed-time-point Fluorodeoxyglucose-PET/Computed Tomography Imaging in Various Clinical Settings

The techniques of dual-time-point imaging (DTPI) and delayed-time-point imaging, which are mostly being used for distinction between inflammatory and malignant diseases, has increased the specificity of fluorodeoxyglucose (FDG)-PET for diagnosis and prognosis of certain diseases. A gradually increasing trend of FDG uptake over time has been shown in malignant cells, and a decreasing or constant trend has been shown in inflammatory/infectious processes. Tumor heterogeneity can be assessed by using early and delayed imaging because differences between primary versus metastatic sites become more detectable compared with single time points. This article discusses the applications of DTPI and delayed-time-point imaging.

Metabolic effects of pulmonary obstruction on myocardial functioning: a pilot study using multiple time-point 18F-FDG-PET imaging

RATIONALE

The aim of this study was to evaluate fluorine-18 fluorodeoxyglucose (18F-FDG) uptake in the right ventricle (RV) of patients with chronic obstructive pulmonary disease (COPD) and to characterize the variability of 18F-FDG uptake in the RV at different time points following radiotracer administration using PET/computerized tomography (CT). Impaired RV systolic function, RV hypertrophy, and RV dilation are associated with increases in mean pulmonary arterial pressure in patients with COPD. Metabolic changes in the RV using 18F-FDG-PET images 2 and 3 h after tracer injection have not yet been investigated.

METHODS

Twenty-five patients with clinical suspicion of lung cancer underwent 18F-FDG-PET/CT imaging at 1, 2, and 3 h after tracer injection. Standardized uptake values (SUVs) and volumes of RV were recorded from transaxial sections to quantify the metabolic activity.

RESULTS

The SUV of RV was higher in patients with COPD stages 1-3 as compared with that in patients with COPD stage 0. RV SUV was inversely correlated with FEV1/FVC pack-years of smoking at 1 h after 18F-FDG injection. In the majority of patients, 18F-FDG activity in RV decreased over time. There was no significant difference in the RV myocardial free wall and chamber volume on the basis of COPD status.

CONCLUSION

The severity of lung obstruction and pack-years of smoking correlate with the level of 18F-FDG uptake in the RV myocardium, suggesting that there may be metabolic changes in the RV associated with lung obstruction that can be detected noninvasively using 18F-FDG-PET/CT. Multiple time-point images of the RV did not yield any additional value in this study.