Head-to-head comparison of [68Ga]Ga-DOTA.SA.FAPi with [18F]F-FDG PET/CT in radioiodine-resistant follicular-cell derived thyroid cancers.

PURPOSE: In the context of radioiodine-resistant follicular-cell derived thyroid cancers (RAI-R-FCTC), [18F]F-FDG PET/CT serves as a widely used and valuable diagnostic imaging method. However, there is growing interest in utilizing molecular imaging probes that target cancer-associated fibroblasts (CAFs) as an alternative approach. This study sought to compare the diagnostic capabilities of [68Ga]Ga-DOTA.SA.FAPi and [18F]F-FDG PET/CT in patients with RAI-R-FCTC. METHODS: In this retrospective study, a total of 117 patients with RAI-R-FCTC were included. The study population consisted of 68 females and 49 males, with a mean age of 53.2 ± 11.7 years. The aim of the study was to perform a comprehensive qualitative and quantitative assessment of [68Ga]Ga-DOTA.SA.FAPi and [18F]F-FDG PET/CT scans in RAI-R-FCTC patients. The qualitative assessment involved comparing patient-based and lesion-based visual interpretations of both scans, while the quantitative assessment included analyzing standardized uptake values corrected for lean body mass (SULpeak and SULavg). The findings obtained from the scans were validated by correlating them with morphological findings from diagnostic computed tomography and/or histopathological examination. RESULTS: Among the 117 RAI-R-FCTC patients, 60 had unilateral local disease, and 9 had bilateral lesions with complete concordance in the detection rate on both PET scans. [68Ga]Ga-DOTA.SA.FAPi had a higher detection rate for lymph nodes (95.4% vs 86.6%, p<0.0001), liver metastases (100% vs. 81.3%, p<0.0001), and brain metastases (100% vs. 39%, p<0.0001) compared to [18F]F-FDG. The detection rates for pleural and bone metastases were similar between the two radiotracers. For lung metastases, [68Ga]Ga-DOTA.SA.FAPi showed a detection rate of 81.7%, whereas [18F]F-FDG had a detection rate of 64.6%. Remarkably, [68Ga]Ga-DOTA.SA.FAPi was able to detect a bowel metastasis that was missed on [18F]F-FDG scan. The median standardized uptake values (SUL) were generally comparable between the two radiotracers, except for brain metastases (SULpeak [68Ga]Ga-DOTA.SA.FAPi vs. [18F]F-FDG: 13.9 vs. 6.7, p-0.0001) and muscle metastases (SULpeak [68Ga]Ga-DOTA.SA.FAPi vs. [18F]F-FDG: 9.56 vs. 5.62, p-0.0085), where [68Ga]Ga-DOTA.SA.FAPi exhibited higher uptake. CONCLUSION: The study results demonstrate the superior performance of [68Ga]Ga-DOTA.SA.FAPi compared to [18F]F-FDG PET/CT in detecting lymph nodal, liver, bowel, and brain metastases in patients with RAI-R-FCTC. These findings highlight the potential of [68Ga]Ga-DOTA.SA.FAPi as a theranostic tool that can complement the benefits of [18F]F-FDG PET/CT in the imaging of RAI-R-FCTC.

Molecular imaging as a tool for evaluation of COVID-19 sequelae - A review of literature.

Coronavirus disease 2019 (COVID-19) is caused by the novel viral pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 primarily involves the lungs. Nucleic acid testing based on reverse-transcription polymerase chain reaction of respiratory samples is the current gold standard for the diagnosis of SARS-CoV-2 infection. Imaging modalities have an established role in triaging, diagnosis, evaluation of disease severity, monitoring disease progression, extra-pulmonary involvement, and complications. As our understanding of the disease improves, there has been substantial evidence to highlight its potential for multi-systemic involvement and development of long-term sequelae. Molecular imaging techniques are highly sensitive, allowing non-invasive visualization of physiological or pathological processes at a cellular or molecular level with potential for detection of functional changes earlier than conventional radiological imaging. The purpose of this review article is to highlight the evolving role of molecular imaging in evaluation of COVID-19 sequelae. Though not ideal for diagnosis, the various modalities of molecular imaging play an important role in assessing pulmonary and extra-pulmonary sequelae of COVID-19. Perfusion imaging using single photon emission computed tomography fused with computed tomography (CT) can be utilized as a first-line imaging modality for COVID-19 related pulmonary embolism. 18F-fluorodeoxyglucose positron emission tomography (PET)/CT is a sensitive tool to detect multi-systemic inflammation, including myocardial and vascular inflammation. PET in conjunction with magnetic resonance imaging helps in better characterization of neurological sequelae of COVID-19. Despite the fact that the majority of published literature is retrospective in nature with limited sample sizes, it is clear that molecular imaging provides additional valuable information (complimentary to anatomical imaging) with semi-quantitative or quantitative parameters to define inflammatory burden and can be used to guide therapeutic strategies and assess response. However, widespread clinical applicability remains a challenge owing to longer image acquisition times and the need for adoption of infection control protocols.