Delayed 68Ga-FAPI-46 PET/MR imaging confirms ongoing fibroblast activation in patients after acute myocardial infarction.

Purpose of the Report: Combined cardiac 68Ga-Fibroblast-Activation Protein-alpha inhibitor (FAPI) positron-emission tomography (PET) and cardiac magnetic resonance imaging (MRI) constitute a novel diagnostic tool in patients for the assessment of myocardial damage after an acute myocardial infarction (AMI). Purpose of this pilot study was to evaluate simultaneous Ga-68-FAPI-46-PET/MR imaging in the delayed phase after AMI. Material and Methods: Eleven patients underwent hybrid 68Ga-FAPI-46 PET/MRI post AMI. Standardized uptake values and fibroblast activation volume (FAV) were calculated and correlated with serum biomarkers and MRI parameters. Results: Significant 68Ga-FAPI-46 uptake could be demonstrated in 11 (100 %) patients after a mean period of 30.9 ± 22.0 days. FAV significantly exceeded the infarction size in MRI and showed a good correlation to MRI parameters as well as to serum biomarkers of myocardial damage. Conclusions: 68Ga-FAPI-46 PET/MRI offers molecular and morphological imaging of affected myocardium after AMI. This study demonstrates ongoing fibroblast activation in a delayed phase after AMI and generates hypotheses for future studies while aiming for a better understanding of myocardial remodeling following ischemic tissue damage.

First experiences with dynamic renal [68Ga]Ga-DOTA PET/CT: a comparison to renal scintigraphy and compartmental modelling to non-invasively estimate the glomerular filtration rate.

PURPOSE: The determination of the glomerular filtration rate (GFR) is decisive for a variety of clinical issues, for example, to monitor the renal function in radionuclide therapy patients. Renal scintigraphy using glomerularly filtered tracers allows combined acquisition of renograms and GFR estimation but requires repeated blood sampling for several hours. In contrast, dynamic PET imaging using the glomerularly filtered tracer [68Ga]Ga-DOTA bears the potential to non-invasively estimate the GFR by compartmental kinetic modelling. Here, we report the, to our knowledge, first comparison of human renal dynamic [68Ga]Ga-DOTA PET imaging in comparison to renal scintigraphy and compare PET-derived to serum creatinine-derived GFR measurements. METHODS: Dynamic [68Ga]Ga-DOTA PET data were acquired for 30 min immediately after tracer injection in 12 patients. PET and renal scintigraphy images were visually interpreted in a consensus read by three nuclear medicine physicians. The functional renal cortex was segmented to obtain time-activity curves. The arterial input function was estimated from the PET signal in the abdominal aorta. Single-compartmental tracer kinetic modelling was performed to calculate the GFR using complete 30-min (GFRPET-30) and reduced 15-min PET data sets (GFRPET-15) to evaluate whether a shorter acquisition time is sufficient for an accurate GFR estimation. A modified approach excluding minutes 2 to 10 was applied to reduce urinary spill-over effects. Serum creatinine-derived GFRCKD (CKD-EPI-formula) was used as reference standard. RESULTS: PET image interpretation revealed the same findings as conventional scintigraphy (2/12 patients with both- and 1/12 patients with right-sided urinary obstruction). Model fit functions were substantially improved for the modified approach to exclude spill-over. Depending on the modelling approach, GFRCKD and both GFRPET-30 and GFRPET-15 were well correlated with interclass correlation coefficients (ICCs) from 0.74 to 0.80 and Pearson's correlation coefficients (PCCs) from 0.74 to 0.81. For a subgroup of patients with undisturbed urinary efflux (n = 9), correlations were good to excellent (ICCs from 0.82 to 0.95 and PCCs from 0.83 to 0.95). Overall, GFRPET-30 and GFRPET-15 were excellently correlated (ICCs from 0.96 to 0.99 and PCCs from 0.96 to 0.99). CONCLUSION: Renal [68Ga]Ga-DOTA PET can be a suitable alternative to conventional scintigraphy. Visual assessment of PET images and conventional renograms revealed comparable results. GFR values derived by non-invasive single-compartmental-modelling of PET data show a good correlation to serum creatinine-derived GFR values. In patients with undisturbed urinary efflux, the correlation was excellent. Dynamic PET data acquisition for 15 min is sufficient for visual evaluation and GFR derivation.

Pitfalls and Common Findings in 68Ga-FAPI PET: A Pictorial Analysis.

Fibroblast activation protein inhibitor (FAPI) PET/CT is a new tool in the diagnostic workup of cancer. With a growing volume of applications, pitfalls and common findings need to be considered for 68Ga-FAPI PET/CT image interpretation. The aim of this study was to summarize common findings and report pitfalls in 68Ga-FAPI PET/CT. Methods: Ninety-one patients underwent whole-body PET/CT with either FAPI-04 (n = 25) or FAPI-46 (n = 66). Findings were rated in a consensus session of 2 experienced readers. Pitfalls and common findings were defined as focal or localized uptake above the background level and categorized as unspecific or nonmalignant and grouped into degenerative, muscular, scarring/wound-healing, uterine, mammary gland, and head-and-neck findings. The frequency of findings was reported on a per-patient and per-group basis, and SUVmax, SUVmean, and SUVpeak were measured. Results: Non-tumor-specific uptake was found in 81.3% of patients. The most frequent finding was uptake in degenerative lesions (51.6%), with a mean SUVmax of 7.7 ± 2.9, and head-and-neck findings (45.1%). Except for the salivary glands, the uptake values did not differ between 10 and 60 min after injection in most findings. Uterine uptake was found in most women (66.7%), with a mean SUVmax of 12.2 ± 7.3, and uptake correlated negatively with age (SUVmax, r = -0.6, P < 0.01; SUVpeak, r = -0.57, P < 0.01; SUVmean, r = -0.58, P < 0.01). Conclusion: Pitfalls include non-tumor-specific 68Ga-FAPI uptake in degenerative lesions, muscle, the head and neck, scarring, the mammary glands, or the uterus. Here, we summarize the findings to help readers avoid common mistakes at centers introducing 68Ga-FAPI PET/CT.

Post-radiosynovectomy imaging utilizing Erbium-169 citrate.

Currently, there is no imaging procedure for radionuclide therapy utilizing Erbium-169 (Er-169). We have recently published the first post-radiosynovectomy imaging of Er-169 citrate in a case report (Farahati et al., 2017). In this study, we performed in-vitro and in-vivo studies to evaluate the feasibility to assess the distribution of Er-169 citrate after radiosynovectomy in fourteen patients with seventeen affected joints treated for refractory chronic synovitis. Post-radiosynovectomy imaging revealed the feasibility of post-radiosynovectomy detection and distribution utilizing Er-169 citrate in all cases. However, additional in-vitro studies including in-vitro imaging, gamma spectrometry and analysis of half-life indicated that emitted gamma-rays of the Ytterbium-169 in the radiopharmaceutical together with bremsstrahlung induced by Er-169 are the imaging source of emitted counts. Post-radiosynovectomy imaging utilizing Er-169 citrate is feasible and should be implemented in the guidelines for theranostics for quality control, patient safety and therapy monitoring.