PET Imaging Research Articles

323. LONG-TERM SURVIVAL OUTCOME OF PATIENTS WITH EARLY ESOPHAGEAL CANCER AFTER ESD (ENDOSCOPIC SUBMUCOSAL DISSECTION) AND ESOPHAGECTOMY

Abstract Endoscopic submucosal dissection (ESD) has been gradually accepted as an effective treatment option for patients with early esophageal cancer. However, its long-term outcome is limited in literature. Method This study compare the overall survival for the patients with early esophageal cancer (T1N0M0) treated with ESD and esophagectomy. The tumor staging was confirmed with EUS, PET and CT imaging. The indication of ESD was T1aN0M0 in clinical staging studies. Three-field lymph node dissection with intrathoracic (Ivor Lewis) or cervical esophagogastrostomy (McKeown) was performed for the patients undergoing esophagectomy under thoracoscopic (minimally invasive esophagectomy) laparoscopic approaches. Result There were 82 patients enrolled in the study including 22 and 60 undergoing esophagectomy and ESD respectively. There is no difference of overall survival in 3 and 5 years with 89.1 % and 81.8 % for patients after ESD, 78.1 % and 78.1 % after esophagectomy (P=0.6) Conclusion For early esophageal cancer with T1aN0M0, ESD can provide an equivalent long-term survival outcome as compared to that with esophagectomy with three-field lymph node dissection.

Abstract P374: Systolic blood pressure burden better predicts tau accumulation than a one-time measurement

In our past work, our group identified a significant relationship between uncontrolled hypertension and greater accumulations of total-tau and phospho-tau181 in cerebrospinal fluid over time. Here, we tested whether blood pressure is related to brain tau deposition assessed using MK-6240 PET. Blood pressure is dynamic in nature, making it difficult to draw conclusions about their risk from a single measurement. To address this issue, different measurement methods have surfaced to better utilize blood pressure as a predictor of disease pathology. Previous studies have found cumulative diastolic blood pressure to increase cardiovascular disease stratification beyond that of a single diastolic blood pressure measurement. In this project, we studied another method of quantifying blood pressure. We examined whether systolic blood pressure (SBP) burden was better related to tau accumulation than a one-time BP measurement taken at the time of PET scan. SBP load was defined as the percentage of SBP values >=140 mmHg taken in the period spanning from 6 months before tau imaging to 6 months after. SUVR (standardized uptake value ratio) was created using the cerebellar gray matter as the reference region. We assessed SUVR in Braak regions 1-6. Pearson correlation was used to test the associations between the variables of interest. We studied cognitively healthy subjects from a brain aging research center (n=72, 40% women, 60% with hypertension). Medians of our group were 72 years of age (interquartile range (IQR) 10.6), education of 18 years (IQR 2), and 8 BP measurements (IQR 14). While one-time SBP measurements and tau were not related, SBP load was progressively correlated with SUVR across Braak stages. In the entire group, the correlations ranged from -0.18 (p = 0.133) in Braak region 1 to 0.19 (p = 0.114) in Braak region 3 to 0.24 (p = 0.042) in Braak region 6. In the hypertensive group, these correlations were stronger and ranged from -0.06 (p = 0.713) in Braak region 1 to 0.38 (p = 0.012) in Braak region 3 to 0.50 (p < 0.001) in Braak region 6. We show that SBP load instead of singular SBP measurements is a stronger predictor of tau accumulation. Furthermore, stronger associations with brain regions known to be affected in more advanced stages suggest that blood pressure control is more critical to tau progression than initial deposition.

369. IMPACT OF THE COVID-19 PANDEMIC ON ESOPHAGEAL CANCER PATIENTS UNDERGOING ESOPHAGECTOMY: AN ACS-NSQIP DATABASE ANALYSIS

Abstract Background To cope with the increasing number of infected patients, medical access was restricted, and public facilities were closed throughout the COVID-19 pandemic. Early detection and treatment of esophageal cancer is critical for improved prognosis. However, the impact of pandemic-related medical access restrictions has not be evaluated to date for esophageal cancer. Therefore, the purpose of this research is to determine how the lockdown policy affected the surgical outcome of patients with esophageal cancer. Methods We analyzed patients who underwent esophagectomy for esophageal cancer between 2016-2022 using data obtained from the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP), including the procedure targeted esophagectomy database. The patients were stratified into two groups based on their operation date relative to pandemic (BEFORE COVID group: 2016-2019 vs AFTER COVID group: 2020-2022). Demographic data and perioperative outcomes were compared between the two groups. Statistical analysis included Chi-square tests for categorical variables and independent student T-tests for continuous data, with a significance threshold set at p < 0.05. Results Between 2016-2022, 7,198 esophageal cancer patients underwent esophagectomy. Clinical T4 increased significantly, but clinical N and pathologic T and N stages showed no impact. PET scan imaging, neoadjuvant chemotherapy and radiotherapy remained unchanged. The utilization of a minimally invasive approach rose substantially from 32.6% to 47.2% (p < 0.001). Positive margin rates increased from 7.5% to 9% (p = 0.03), and anastomotic leak rates increased from 14.1% to 17.2% (p < 0.001). Operative time, blood loss, and conversion rate showed no significant differences. Perioperative complications, including organ space surgical site infections and myocardial infarctions, significantly increased after COVID-19. Conclusion The COVID-19 pandemic altered the clinical staging of esophageal cancer patients undergoing esophagectomy, but it did not disrupt access to essential investigations and treatment. A notable increase in the implementation of minimally invasive techniques was observed after the pandemic. However, significant impacts were noticed on operative outcomes, including positive margin and leak rates.

Cardiac positron emission tomography and other modalities for coronary artery disease assessment: A snapshot from the medicare data

BackgroundPositron emission tomography (PET) is an important tool for assessing coronary artery disease (CAD), but its widespread utilization is limited due to various factors, including limited local champion availability. This study aims to compare the frequency of PET procedures and their interpreters with other common CAD assessment modalities. MethodsUsing Medicare data, we examined the number of cardiac PET procedures billed and compared them with single-photon emission computed tomography (SPECT), coronary computed tomography angiography (CCTA), stress magnetic resonance imaging (MRI), and stress echocardiography. Healthcare Common Procedure Coding System codes were used to identify procedures. We calculated the total number of PET myocardial perfusion imaging (MPI) procedures, the proportion of PET/CT and myocardial blood flow (MBF) assessments, and the median number of studies read per physician. We also analyzed the trends in the use of different CAD assessment modalities between 2018 and 2022. Descriptive statistics summarized the data. ResultsIn 2022, Medicare billed for 212,106 PET MPI scans. SPECT was six times more frequent (1,343,519), whereas stress echocardiography (201,676) and CCTA (118,734) had similar or lower use. Stress MRI (3,932) was least used. Of the PET MPI scans, 46% were PET/CT, and 39% included MBF measurements. Cardiologists interpreted 86% of PET scans, with a median of 58 studies per reader; 23% interpreted ≤25 studies annually. SPECT had a median of 63 studies per reader, and CCTA, stress MRI, and stress echocardiography had medians of 27, 20, and 24, respectively. PET, CT, and MRI use increased from 2018 to 2022, whereas SPECT and stress echocardiography declined. ConclusionIn the Medicare population, radionuclide perfusion imaging (SPECT and PET) remained the preferred method for assessment of CAD, with SPECT being the most frequently used modality and PET being the second most frequently used modality for this application. However, PET/CT and MBF are underutilized, limiting diagnostic and prognostic capabilities. Efforts to enhance education and awareness of PET's advantages and to address barriers to its wider adoption are essential to maximize its clinical benefits and improve patient outcomes.

"One Method to Label Them All": A Single Fully Automated Protocol for GMP-Compliant 68Ga Radiolabeling of PSMA-11, Transposable to PSMA-I&T and PSMA-617.

Prostate-specific membrane antigen (PSMA) is an ideal target for molecular imaging and targeted radionuclide therapy in prostate cancer. Consequently, various PSMA ligands were developed. Some of these molecules are functionalized with a chelator that can host radiometals, such as 68Ga for PET imaging. The 68Ga radiolabeling step benefits from process automation, making it more robust and reducing radiation exposure. To design a single automated radiolabeling protocol for the GMP-compliant preparation of [68Ga]Ga-PSMA-11, transposable to the production of [68Ga]Ga-PSMA-617 and [68Ga]Ga-PSMA-I&T. A GAIA® synthesis module and a GALLIAD® generator were used. Radio-TLC and radio-HPLC methods were validated for radiochemical purity (RCP) determination. Three [68Ga]Ga-PSMA-11 validation batches were produced and thoroughly tested for appearance and pH, radionuclide identity and purity, RCP, stability, residual solvent and sterility. Minimal modifications were made to the reagents and disposables for optimal application to other PSMA ligands. [68Ga]Ga-PSMA-11 for clinical application was produced in 27 min. The 3 validation batches met the quality criteria expected by the European Pharmacopoeia to allow routine production. For optimal transposition to PSMA-617, the solid phase extraction cartridge was changed to improve purification of the radiolabeled product. For application to PSMA-I&T, the buffer solution initially used was replaced by HEPES 2.7 M to achieve good radiochemical yields. Residual HEPES content was checked in the final product and was below the Ph. Eur. threshold. A single automated radiolabeling method on the GAIA® module was developed and implemented for 68Ga radiolabeling of 3 PSMA ligands, with slight adjustments for each molecule.

Automated Synthesis of [11C]PiB via [11CH3OTf]-as Methylating Agent for PET Imaging of β-Amyloid.

Efficient synthesis of precursor from commercially available starting materials and automated radiosynthesis of [11C]PiB using commercially available dedicated [11C]- Chemistry module from the synthesized precursor. [11C]PiB is a promising radiotracer for PET imaging of β-Amyloid, advancing Alzheimer's disease research. The availability of precursors and protocols for efficient radiolabelling foster the applications of any radiotracer. Efficient synthesis of PiB precursor was performed using anisidine and 4-nitrobenzoyl chloride as starting materials in 5 steps, having addition, substitutions, and cyclization chemical methodologies. This precursor was used for fully automated radiosynthesis of [11C]PiB in a commercially available synthesizer, MPS-100 (SHI, Japan). The synthesized [11C]PiB was purified via solid-phase methodology, and its quality control was performed by the quality and safety criteria required for clinical use. The synthesis of desired precursors and standard authentic compounds started with commercially available materials with 70-80% yields. The standard analytical methods were characterized all synthesized compounds. The fully automated [11C]-chemistry synthesizer (MPS-100) used for radiosynthesis of [11C]PiB with [11C]CH3OTf acts as a methylating agent. For radiolabelling, varied amounts of precursor and time of reaction were explored. The resulting crude product underwent purification through solid-phase cartridges. The synthesized radiotracer was analyzed using analytical tools such as radio TLC, HPLC, pH endo-toxicity, and half-life. The precursor for radiosynthesis of [11C]PiB was achieved in excellent yield using simple and feasible chemistry. A protocol for radiolabelling of precursor to synthesized [11C]PiB was developed using an automated synthesizer. The crude radiotracer was purified by solid-phase cartridge, with a decay-corrected radiochemical yield of 40±5% and radiochemical purity of more than 97% in approx 20 minutes (EOB). The specific activity was calculated and found in a 110-121 mCi/μmol range. A reliable methodology was developed for preparing precursor followed by fully automated radiolabeling using [11C]MeOTf as a methylating agent to synthesize [11C]PiB. The final HPLC-free purification yielded more than 97% radiochemical purity tracer within one radionuclide half-life. The method was reproducible and efficient for any clinical center.

Investigation of Nuclear Reaction Cross Section by Proton, Deuteron, and alpha Particles Induced Reaction for the Production of Important Radioisotopes for PET Imaging

Investigation of Nuclear Reaction Cross Section by Proton, Deuteron, and alpha Particles Induced Reaction for the Production of Important Radioisotopes for PET Imaging

Nuclear Imaging Modalities in the Diagnosis and Management of Thyroid Cancer.

In this review we have brought forward various nuclear imaging modalities used in the diagnosis, staging, and management of thyroid cancer. Thyroid cancer is the most common endocrine malignancy, accounting for approximately 3% of all new cancer diagnoses. Nuclear imaging plays an important role in the evaluation of thyroid cancer, and the use of radioiodine imaging, FDG imaging, and somatostatin receptor imaging are all valuable tools in the management of this disease. Radioiodine imaging involves the use of Iodine-123 [I-123] or Iodine-131 [I-131] to evaluate thyroid function and detect thyroid cancer. I-123 is a gamma-emitting isotope that is used in thyroid imaging to evaluate thyroid function and detect thyroid nodules. I-131 is a beta-emitting isotope that is used for the treatment of thyroid cancer. Radioiodine imaging is used to detect the presence of thyroid nodules and evaluate thyroid function. FDG imaging is a PET imaging modality that is used to evaluate the metabolic activity of thyroid cancer cells. FDG is a glucose analogue that is taken up by cells that are metabolically active, such as cancer cells. FDG PET/CT can detect primary thyroid cancer and metastatic disease, including lymph nodes and distant metastases. FDG PET/CT is also used to monitor treatment response and detect the recurrence of thyroid cancer. Somatostatin receptor imaging involves the use of radiolabeled somatostatin analogues to detect neuroendocrine tumors, including thyroid cancer. Radiolabeled somatostatin analogues, such as Indium-111 octreotide or Gallium-68 DOTATATE, are administered to the patient, and a gamma camera is used to detect areas of uptake. Somatostatin receptor imaging is highly sensitive and specific for the detection of metastatic thyroid cancer. A comprehensive search of relevant literature was done using online databases of PubMed, Embase, and Cochrane Library using the keywords "thyroid cancer," "nuclear imaging," "radioiodine imaging," "FDG PET/CT," and "somatostatin receptor imaging" to identify relevant studies to be included in this review. Nuclear imaging plays an important role in the diagnosis, staging, and management of thyroid cancer. The use of radioiodine imaging, thyroglobulin imaging, FDG imaging, and somatostatin receptor imaging are all valuable tools in the evaluation of thyroid cancer. With further research and development, nuclear imaging techniques have the potential to improve the diagnosis and management of thyroid cancer and other endocrine malignancies.

Using Integrin αvβ6–Targeted Positron Emission Tomography Imaging to Longitudinally Monitor Radiation-Induced Pulmonary Fibrosis In Vivo

PurposeRadiation-induced pulmonary fibrosis (RIPF) is a potentially serious and disabling late complication of radiation therapy. Monitoring RIPF progression is challenging due to the absence of early detection tools and the difficulty in distinguishing RIPF from other lung diseases using standard imaging methods. In the lungs, integrin αvβ6 is crucial in the development of RIPF, acting as a significant activator of TGF-β after radiation injury. This study aims to investigate integrin αvβ6-targeted PET imaging ([64Cu]Cu-αvβ6-BP) to study RIPF development in vivo. Methods and MaterialsWe used a focal RIPF model (70 Gy delivered focally to a 3 mm spot in the lung) and a whole lung RIPF model (14 Gy delivered to the whole lung) in adult C57BL/6J mice. Small animal PET/CT images were acquired 1h post-injection of 11.1 MBq of [64Cu]Cu-αvβ6-BP. Animals were imaged for eight weeks in the focal RIPF model and six months for the whole lung RIPF model. Immunohistochemistry for integrin αvβ6 and trichrome staining were performed. ResultsIn the focal RIPF model, there was focal uptake of [64Cu]Cu-αvβ6-BP in the irradiated region at week four that progressively increased at week 6 and 8. In the whole lung RIPF model, minimal uptake of the probe was observed at four months post-RT, which significantly increased at months five and six. Expression of integrin αvβ6 was validated histologically by immunohistochemistry in both models. ConclusionsIntegrin αvβ6-targeted PET imaging using [64Cu]Cu-αvβ6-BP can serve as a useful tool to identify radiation-induced pulmonary fibrosis in vivo.

Quantitative Total-Body Imaging of Blood Flow with High Temporal Resolution Early Dynamic 18F-Fluorodeoxyglucose PET Kinetic Modeling.

The first two minutes of dynamic PET scans were reconstructed at high temporal resolution (60×1 s, 30×2 s) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate ( ) as a surrogate of blood flow, our method directly estimates blood flow using a distributed kinetic model (adiabatic approximation to the tissue homogeneity model; AATH). To validate our 18F-FDG measurements of blood flow against a flow radiotracer, we analyzed total-body dynamic PET images of six human participants scanned with both 18F-FDG and 11C-butanol. An additional thirty-four total-body dynamic 18F-FDG PET scans of healthy participants were analyzed for comparison against literature blood flow ranges. Regional blood flow was estimated across the body and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared by the Akaike Information Criterion at different temporal resolutions. 18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson R=0.955, p<0.001; linear regression y=0.973x-0.012), which was visually corroborated by total-body blood flow parametric imaging. Our method resolved a wide range of blood flow values across the body in broad agreement with literature ranges (e.g., healthy cohort average: 0.51±0.12 ml/min/cm3 in the cerebral cortex and 2.03±0.64 ml/min/cm3 in the lungs, respectively). High temporal resolution (1 to 2 s) was critical to enabling AATH modeling over standard compartment modeling. Total-body blood flow imaging was feasible using early-dynamic 18F-FDG PET with high-temporal resolution kinetic modeling. Combined with standard 18F-FDG PET methods, this method may enable efficient single-tracer flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.

Evaluation of [68Ga]Ga-DOTA-AeK as a Potential Imaging Tool for PET Imaging of Cell Wall Synthesis in Bacterial Infections.

The ability of bacteria to recycle exogenous amino acid-based peptides and amino sugars for peptidoglycan biosynthesis was extensively investigated using optical imaging. In particular, fluorescent AeK-NBD was effectively utilized to study the peptidoglycan recycling pathway in Gram-negative bacteria. Based on these promising results, we were inspired to develop the radioactive AeK conjugate [68Ga]Ga-DOTA-AeK for the in vivo localization of bacterial infection using PET/CT. An easy-to-implement radiolabeling procedure for DOTA-AeK with [68Ga]GaCI3 followed by solid-phase purification was successfully established to obtain [68Ga]Ga-DOTA-AeK with a radiochemical purity of ≥95%. [68Ga]Ga-DOTA-AeK showed good stability over time with less protein binding under physiological conditions. The bacterial incorporation of [68Ga]Ga-DOTA-AeK and its fluorescent Aek-NBD analog were investigated in live and heat-killed Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Unfortunately, no conclusive in vitro intracellular uptake of [68Ga]Ga-DOTA-AeK was observed for E. coli or S. aureus live and heat-killed bacterial strains (p > 0.05). In contrast, AeK-NBD showed significantly higher intracellular incorporation in live bacteria compared to the heat-killed control (p < 0.05). Preliminary biodistribution studies of [68Ga]Ga-DOTA-AeK in a dual-model of chronic infection and inflammation revealed limited localization at the infection site with non-specific accumulation in response to inflammatory markers. Finally, our study demonstrates proof that the intracellular incorporation of AeK is necessary for successful bacteria-specific imaging using PET/CT. Therefore, Ga-68 was not a suitable radioisotope for tracing the bacterial uptake of AeK tripeptide, as it required chelation with a bulky metal chelator such as DOTA, which may have limited its active membrane transportation. An alternative for optimization is to explore diverse chemical structures of AeK that would allow for radiolabeling with 18F or 11C.

Correlation between dopaminergic and metabolic asymmetry in Lewy body disease – A dual-imaging study

IntroductionThe a-Synuclein Origin and Connectome (SOC) model of Lewy body diseases postulates that a-syuclein will be asymmetrically distributed in some patients with Lewy body diseases, potentially leading to asymmetric neuronal dysfunction and symptoms. MethodsWe included two patient groups: 19 non-demented Parkinson's disease (nPD) patients with [18F]FDG PET and motor symptoms assessed by UPDRS-III, and 65 Lewy body dementia (LBD) patients with [18F]FDG PET and dopamine radioisotope imaging. Asymmetry indices were calculated for [18F]FDG PET by including the cortex for each hemisphere, for dopamine radioisotope imaging by including the putamen and caudate separately, and for motor symptoms by using the difference between right-left UPDRS-III score. Correlations between these asymmetry indices were explored to test the predictions of the SOC model. To identify cases with a more typical LBD imaging profile, we calculated a Cingulate Island Sign (CIS) index on the [18F]FDG PET image. ResultsWe found a significant correlation between cortical interhemispheric [18F]FDG asymmetry and motor-symptom asymmetry in nPD patients (r = 0.62, P = 0.004). In patients with LBD, we found a significant correlation between cortical interhemispheric [18F]FDG asymmetry and dopamine transporter asymmetry in the caudate (r = 0.37, P = 0.0019), but not in the putamen (r = 0.15, P = 0.22). We observed that the correlation in the caudate was stronger in LBD subjects with the highest CIS index, i.e., with more typical LBD imaging profiles. ConclusionOur study partly supports the SOC model, but further investigations are needed – ideally of de novo, non-demented PD patients.

Visual field defects in neurocysticercosis: A rare presentation

Neurocysticercosis is one of the commonest helminthic infections which affects central nervous system in humans and is caused by a tapeworm , Taenia solium. A 46-year-old male patient reported with complaint of restricted visual field in the left eye for one week. His best-corrected visual acuity was 6/6 partial, N6 in both eyes. Perimetry confirmed left homonymous hemianopia. The patient was referred to a neurophysician and based on magnetic resonance imaging brain and positron emission tomography scan, the patient was diagnosed with neurocysticercosis. The subject was started on oral medications following which the lesion resolved and improvement in visual fields was seen at one month follow-up. Ophthalmic manifestations of neurocysticercosis are variable and may include rare symptoms like visual field defects. A multimodal imaging and multidisciplinary approach can be helpful in the early diagnosis and faster recovery in patients with neurocysticercosis.

An Uncommon Culprit: Pancreatic Neuroendocrine Tumor in a Patient with Uncontrolled Diabetes

Pancreatic Neuro Endocrine Tumors (NETs) are rare neoplasms that originate from the endocrine tissues of the pancreas, accounting for only 1-2% of pancreatic tumors. Despite their low incidence, these tumors present with a wide range of symptoms and have the ability to secrete hormones, posing significant challenges for their diagnosis and treatment. There are two distinct types of pancreatic NETs: functioning and nonfunctioning. Functioning tumors are characterized by hormone-related clinical syndromes, while nonfunctioning tumors are often found incidentally. The pathogenesis of pancreatic NETs involves both sporadic and hereditary factors, including syndromes such as MEN1, VHL, and NF1. Typically, these tumors are diagnosed in individuals between the ages of 40 and 60, and their effective management requires a multidisciplinary approach. Diagnostic imaging techniques, such as CT and EUS, play a crucial role in accurate diagnosis, while PET scans aid in staging and treatment planning. Histological analysis is essential for determining the tumor grade and predicting prognosis. Treatment strategies are tailored to the tumor's characteristics and the patient's overall health. These may include the use of somatostatin analogs, such as Lanreotide and Octreotide, to control hormone secretion and inhibit tumor growth, as well as systemic therapies like everolimus, sunitinib, and PRRT for metastatic disease. This case report describes the clinical course of a 66-year-old male with a well-differentiated pancreatic NET who initially presented with persistent hyperglycemia. Further investigations revealed a sizable pancreatic mass and liver metastases. Diagnostic evaluation confirmed a grade 1 Neuro Endocrine Tumor, and the patient was started on treatment with Lanreotide. However, his management was complicated by the development of hepatic encephalopathy, which necessitated treatment with lactulose and rifaximin. This case highlights the importance of considering pancreatic NETs in cases of atypical diabetes presentations and emphasizes the need for a multidisciplinary team to provide optimal care. Given the complex nature of pancreatic NETs, a comprehensive diagnostic workup and personalized treatment approach are essential for improving patient outcomes.

Low dose optimization for total-body 2-[18F]FDG PET/CT imaging: a single-center study on feasibility based on body mass index stratification.

Implementing personalization protocol in clinical routine necessitates diverse low-dose PET/CT scan protocols. This study explores the clinical feasibility of one-third (1/3) dose regimen and evaluates the diagnostic image quality and lesion detectability of BMI-based 1/3-injection doses for 2-[18F]FDG PET/CT imaging. Seventy-four cancer patients underwent total-body 2-[18F]FDG PET/CT examination, with 37 retrospectively enrolled as full-dose group (3.7 MBq/kg) and 37 prospectively enrolled as the 1/3-dose group (1.23 MBq/kg). The 1/3-dose group was stratified by BMI, with an acquisition time of 5 min (G5), 6 min (G6), and 8 min (G8) for BMI < 25, 25 ≤ BMI ≤ 29, and BMI > 29, respectively. Image quality was subjectively and objectively assessed, and lesion detectability was quantitatively analyzed. Subjective assessments of 1/3-dose and full-dose PET images showed strong agreement among readers (κ > 0.88). In the 1/3-dose group, the Likert scores were above 4. G5, G6, and G8 showed comparable image quality, with G5 demonstrating higher lesion conspicuity than G6 and G8 (p = 0.045). Objective evaluation showed no significant differences in SUVmax, liver SUVmean and TBR between 1/3- and full-dose groups (p > 0.05). No statistical differences were observed in the SUVmax of primary tumor, SUVmean of liver and TBR across all BMI categories between the 1/3-dose and full-dose groups. Lesion detection rates showed no significant difference between the 1/3-dose (93.24%, 193/207) and full-dose groups (94.73%, 198/209) (p = 0.520). A BMI-stratified 1/3-dose regimen is a feasible low-dose alternative with clinically acceptable lesion detectability equivalent to full-dose protocol, potentially expanding the applicability of personalized protocols. This study demonstrated that BMI-stratified 1/3-dose regimens for [18F]FDG total-body PET/CT yielded equivalent outputs compared to the full-dose regimen, which aligns with clinical needs for personalization in dose and BMI. Currently, limited personalized low-dose total-body PET/CT protocols are available, particularly for patients with varied BMI. Reducing the radiotracer dose to 1/3 the standard demonstrated comparable image quality and lesion detectability equivalent to full dose. BMI-stratified 1/3-dose regimen is a clinically feasible low-dose alternative.

1563: Towards real-time range verification for head and neck treatments based on in-beam PET imaging

1563: Towards real-time range verification for head and neck treatments based on in-beam PET imaging

Improving 18F-FDG PET Quantification Through a Spatial Normalization Method.

Quantification of 18F-FDG PET images is useful for accurate diagnosis and evaluation of various brain diseases, including brain tumors, epilepsy, dementia, and Parkinson disease. However, accurate quantification of 18F-FDG PET images requires matched 3-dimensional T1 MRI scans of the same individuals to provide detailed information on brain anatomy. In this paper, we propose a transfer learning approach to adapt a pretrained deep neural network model from amyloid PET to spatially normalize 18F-FDG PET images without the need for 3-dimensional MRI. Methods: The proposed method is based on a deep learning model for automatic spatial normalization of 18F-FDG brain PET images, which was developed by fine-tuning a pretrained model for amyloid PET using only 103 18F-FDG PET and MR images. After training, the algorithm was tested on 65 internal and 78 external test sets. All T1 MR images with a 1-mm isotropic voxel size were processed with FreeSurfer software to provide cortical segmentation maps used to extract a ground-truth regional SUV ratio using cerebellar gray matter as a reference region. These values were compared with those from spatial normalization-based quantification methods using the proposed method and statistical parametric mapping software. Results: The proposed method showed superior spatial normalization compared with statistical parametric mapping, as evidenced by increased normalized mutual information and better size and shape matching in PET images. Quantitative evaluation revealed a consistently higher SUV ratio correlation and intraclass correlation coefficients for the proposed method across various brain regions in both internal and external datasets. The remarkably good correlation and intraclass correlation coefficient values of the proposed method for the external dataset are noteworthy, considering the dataset's different ethnic distribution and the use of different PET scanners and image reconstruction algorithms. Conclusion: This study successfully applied transfer learning to a deep neural network for 18F-FDG PET spatial normalization, demonstrating its resource efficiency and improved performance. This highlights the efficacy of transfer learning, which requires a smaller number of datasets than does the original network training, thus increasing the potential for broader use of deep learning-based brain PET spatial normalization techniques for various clinical and research radiotracers.

Higher striatal dopamine is related with lower physical performance fatigability in community-dwelling older adults.

Fatigability in community-dwelling older adults is highly prevalent and disabling, but lacks a treatment. Greater nigrostriatal dopaminergic signaling can ameliorate performance fatigability in healthy young adults, but its role in community-dwelling older adults is not known. We hypothesized that higher nigrostriatal dopaminergic integrity would be associated with lower performance fatigability, independent of cardiopulmonary and musculoskeletal energetics and other health conditions. In 125 older adults participating in the Study of Muscle, Mobility and Aging, performance fatigability was measured as performance deterioration during a fast 400 meter walk (% slowing down from the 2nd to the 9th lap). Nigrostriatal DA integrity was measured using (+)-[11C] dihydrotetrabenazine (DTBZ) PET imaging. The binding signal was obtained separately for the subregions regulating sensorimotor (posterior putamen), reward (ventral striatum) and executive control processes (dorsal striatum). Multivariable linear regression models of performance fatigability (dependent variable) estimated the coefficients of dopamine integrity in striatal subregions, adjusted for demographics, comorbidities, and cognition. Models were further adjusted for skeletal muscle energetics (via biopsy) and cardiopulmonary fitness (via cardiopulmonary exercise testing). Higher [11C]-DTBZ binding in the posterior putamen was significantly associated with lower performance fatigability (demographic-adjusted standardized Beta = -1.08, 95% CI: -1.96, -0.20); results remained independent of adjustment for other covariates, including cardiopulmonary and musculoskeletal energetics. Associations with other striatal subregions were not significant. Dopaminergic integrity in the sensorimotor striatum may influence performance fatigability in older adults without clinically overt diseases, independent of other aging systems.

Head-to-Head Comparison of [18F]FDG PET Imaging and MRI for the Detection of Recurrence or Residual Tumor in Patients with Nasopharyngeal Carcinoma: A Meta-Analysis.

This meta-analysis compared the diagnostic performance of [18F] fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) or PET versus Magnetic resonance imaging (MRI) in detecting recurrence or residual tumors at the primary site in patients with nasopharyngeal carcinoma (NPC). A comprehensive literature search was conducted in the PubMed/MEDLINE and CENTRAL databases to find studies with at least 20 patients with NPC undergoing both [18F]FDG PET/CT (or [18F]FDG PET) and MRI for detecting recurrence or assessing residual disease at the primary site. The pooled sensitivity and specificity of PET/CT and MRI were calculated with 95% confidence intervals (CIs) and compared. Five studies, including 1908 patients (six patient groups), were included. PET imaging had higher sensitivity [93.3% (95% CI: 91.3-94.9%); I2 = 52.6%] compared to MRI [80.1% (95% CI: 77.2-82.8%); I2 = 68.3%], but the specificity of the two modalities was similar: 93.8% (95% CI: 92.2-95.2%; I2 = 0%) for PET/CT and 91.8% (95% CI: 90.1-93.4%; I2 = 94.3%) for MRI. The areas under the curve (AUCs) for PET/CT and MRI were 0.978 and 0.924, respectively, without significant difference (p = 0.23). This meta-analysis suggests that [18F]FDG PET imaging and MRI do not significantly differ in diagnostic performance. Nevertheless, [18F]FDG PET imaging shows higher sensitivity than MRI.

Detection of tumour heterogeneity in patients with advanced, metastatic castration-resistant prostate cancer on [68Ga]Ga-/[18F]F-PSMA-11/-1007, [68Ga]Ga-FAPI-46 and 2-[18F]FDG PET/CT: a pilot study.

In metastatic castration-resistant prostate cancer (mCRPC), some patients show low/absent PSMA expression in tumour lesions on positron emission tomography (PET) scans, indicating heterogeneity and heightened risk of non-response to PSMA-RLT (radioligand therapy). Imaging cancer-associated fibroblasts and glucose uptake may further characterise tumour heterogeneity in mCRPC patients. Here, we aimed to evaluate tumour heterogeneity and its potential implications for management in mCRPC patients assessed for PSMA-RLT using [68Ga]Ga-FAPI-46, 2-[18F]FDG and [68Ga]Ga-/[18F]F-PSMA-11/-1007 PET. Patients with advanced, progressive mCRPC underwent clinical [68Ga]Ga-/[18F]F-PSMA-11/-1007, 2-[18F]FDG and [68Ga]Ga-FAPI-46 PET/CT to evaluate treatment with PSMA-directed RLT. Tumour detection/semiquantitative parameters were compared on a per-lesion/-region basis. Two phenotypes were defined: Criteria for the mixed phenotype were: (a) PSMA-negative findings for lymph node metastases ≥ 2.5cm, any solid organ metastases ≥ 1.0cm, or bone metastases with soft tissue component ≥ 1.0cm, (b) low [68Ga]Ga-/[18F]F-PSMA-11/-1007 uptake and/or (c) balanced tumour uptake of all radioligands. The PSMA-dominant phenotype was assigned if the criteria were not met. In ten patients, 472 lesions were detected on all imaging modalities (miTNM regions: M1b: 327 (69.3%), M1a: 95 (20.1%), N1: 26 (5.5%), M1c: 18 (3.8%), T: 5 (1.1%) and Tr: 1 (0.2%). [68Ga]Ga-/[18F]F-PSMA-11/-1007 (n = 453 (96.0%)) demonstrates the highest detection rate, followed by [68Ga]Ga-FAPI-46 (n = 268 (56.8%))/2-[18F]FDG (n = 241 (51.1%)). Semiquantitative uptake was highest for [68Ga]Ga-/[18F]F-PSMA-11/-1007 (mean SUVmax (interquartile range): 22.7 (22.5), vs. [68Ga]Ga-FAPI-46 (7.7 (3.7)) and 2-[18F]FDG (6.8 (4.7)). Seven/three patients were retrospectively assigned to the PSMA-dominant/mixed phenotype. Median overall survival was significantly longer for patients who underwent [177Lu]Lu-PSMA-617 RLT and were retrospectively assigned to the PSMA-dominant phenotype (19.7 vs. 9.3months). Through whole-body imaging, we identify considerable inter- and intra-patient heterogeneity of mCRPC and potential imaging phenotypes. Regarding uptake and tumour detection, [68Ga]Ga-/[18F]F-PSMA-11/-1007 was superior to [68Ga]Ga-FAPI-46 and 2-[18F]FDG, while the latter two were comparable. Patients who underwent [177Lu]Lu-PSMA-617 RLT based on clinical-decision making had a longer overall survival and could be assigned to the PSMA-dominant phenotype.