Y-90 PET/MR imaging optimization with a Bayesian penalized likelihood reconstruction algorithm.

Positron Emission Tomography (PET) imaging after 90 Y liver radioembolization is used for both lesion identification and dosimetry. Bayesian penalized likelihood (BPL) reconstruction algorithms are an alternative to ordered subset expectation maximization (OSEM) with improved image quality and lesion detectability. The investigation of optimal parameters for 90 Y image reconstruction of Q.Clear, a commercial BPL algorithm developed by General Electric (GE), in PET/MR is a field of interest and the subject of this study. The NEMA phantom was filled at an 8:1 sphere-to-background ratio. Acquisitions were performed on a PET/MR scanner for clinically relevant activities between 0.7 and 3.3 MBq/ml. Reconstructions with Q.Clear were performed varying the ß penalty parameter between 20 and 6000, the acquisition time between 5 and 20 min and pixel size between 1.56 and 4.69 mm. OSEM reconstructions of 28 subsets with 2 and 4 iterations with and without Time-of-Flight (TOF) were compared to Q.Clear with ß = 4000. Recovery coefficients (RC), their coefficient of variation (COV), background variability (BV), contrast-to-noise ratio (CNR) and residual activity in the cold insert were evaluated. Increasing ß parameter lowered RC, COV and BV, while CNR was maximized at ß = 4000; further increase resulted in oversmoothing. For quantification purposes, ß = 1000-2000 could be more appropriate. Longer acquisition times resulted in larger CNR due to reduced image noise. Q.Clear reconstructions led to higher CNR than OSEM. A ß of 4000 was obtained for optimal image quality, although lower values could be considered for quantification purposes. An optimal acquisition time of 15 min was proposed considering its clinical use.

Same-day comparative protocol PET/CT-PET/MRI [68 Ga]Ga-DOTA-TOC in paragangliomas and pheochromocytomas: an approach to personalized medicine.

BACKGROUND: PET/MRI is an emerging imaging modality which enables the evaluation and quantification of biochemical processes in tissues, complemented with accurate anatomical information and low radiation exposure. In the framework of theragnosis, PET/MRI is of special interest due to its ability to delineate small lesions, adequately quantify them, and therefore to plan targeted therapies. The aim of this study was to validate the diagnostic performance of [68 Ga]Ga-DOTA-TOC PET/MRI compared to PET/CT in advanced disease paragangliomas and pheochromocytomas (PGGLs) to assess in which clinical settings, PET/MRI may have a greater diagnostic yield. METHODS: We performed a same-day protocol with consecutive acquisition of a PET/CT and a PET/MRI after a single [68 Ga]Ga-DOTA-TOC injection in 25 patients. Intermodality agreement, Krenning Score (KS), SUVmax (Standard Uptake Value), target-to-liver-ratio (TLR), clinical setting, location, and size were assessed. RESULTS: The diagnostic accuracy with PET/MRI increased by 14.6% compared to PET/CT especially in bone and liver locations (mean size of new lesions was 3.73 mm). PET/MRI revealed a higher overall lesion uptake than PET/CT (TLR 4.12 vs 2.44) and implied an upward elevation of the KS in up to 60% of patients. The KS changed in 30.4% of the evaluated lesions (mean size 11.89 mm), in 18.4% of the lesions it increased from KS 2 on PET/CT to a KS ≥ 3 on PET/MRI and 24.96% of the lesions per patient with multifocal disease displayed a KS ≥ 3 on PET/MR, that were not detected or showed lower KS on PET/CT. In 12% of patients, PET/MRI modified clinical management. CONCLUSIONS: PET/MRI showed minor advantages over conventional PET/CT in the detection of new lesions but increased the intensity of SSRs expression in a significant number of them, opening the door to select which patients and clinical settings can benefit from performing PET/MRI.

[Sentinel lymph node selective biopsy in prostate cancer.] / Ganglio centinela en cáncer de próstata.

OBJECTIVE: To validate the sentinel lymph node selective biopsy (SLNSB) in the staging of Prostate Cancer with Briganti Index > 5 by comparison with extended lymphadenectomy (ePLND) in a prospective longitudinal study. METHODS: SLNSB has been performed in 84 patients, the first 70 by injection of nanocoloids marked with Tc99m and preoperative SPECT-CT, and in the last 14 with mixed radiotracer (99mTc + ICG). After laparoscop ic removal of sentinel nodes all patients underwent an ePLND. RESULTS: SPECT-CT showed radiotracer deposits outside the territory of the ePLND in 76% of patients and laparoscopic gamma probe in 57%. The median number of sentinel nodes removed was 5.2 with a total average number of lymph nodes removed of 22. In all cases with metastatic nodes (28% in the series) there was at least one positive sentinel node but metastatic sentinel nodes outside of the territory of the ePLND were found in 6/24 patients (25%). The sensitivity, specificity, PPV and NPV of 99mTc were 100%, 96.07%, 90.47% and 100%, respectively. In 5 out of 14 patients with mixed radiotracer, lymph node involvement was detected. In all of them there was at least one sentinel node affected with 99mTc, and only 3 showed fluorescence with 100% sensitivity and 100% NPV for 99mTc and 60% sensitivity and 77.77% NPV for ICG. CONCLUSION: The SLNSB with 99mTc has a high sensitivity and a VPN of 100%, increasing the identification of lymphatic metastases outside the territory of the ePLND. Fluorescence can facilitate the visualization of the sentinel nodes when they have been previously located by the SPECT-CT, although the sensitivity and the NPV of the ICG are lower than that of the 99mTc.

OBJETIVO: Validar la biopsia selectiva de ganglio centinela (BSGC) en la estadificación del Cáncer de Próstata con Indice de Briganti > 5 mediante comparación con la linfadenectomía extendida (LFDe) en un estudio prospectivo longitudinal.MÉTODOS: Se ha realizado BSGC a 84 pacientes, los 70 primeros mediante inyección de nanocoloides marcados con Tc99m y SPECT-TC preoperatoria, y en los 14 últimos con radiotrazador mixto (Tc99m + ICG). A todos los pacientes tras la extracción laparoscópica de los ganglios centinelas se les realizó una LFDe. RESULTADOS: La SPECT-TC mostró depósitos del radiotrazador fuera del territorio de la LFDe en el 76% de los pacientes y la gammasonda laparoscópica en el 57%.La media de ganglios centinelas extraídos fue 5,2 con una media total de ganglios linfáticos extraídos de 22. En todos los casos con ganglios metastáticos (28% de la serie) hubo, al menos, un ganglio centinela positivo, encontrando ganglios centinela metastásicos fuera del territorio de la LFDe en 6/24 pacientes (25%). La sensibilidad, especificidad, VPP y VPN del Tc99m fue del 100%, 96,07%, 90,47% y 100%, respectivamente. En 5 de los 14 pacientes con radiotrazador mixto se detectó afectación ganglionar. En todos ellos hubo como mínimo un ganglio centinela afecto con Tc99m y sólo 3 mostraron fluorescencia, con sensibilidad del 100% y VPN del 100% para el Tc99m y sensibilidad del 60% y VPN del 77,77% para el ICG.CONCLUSIÓN: La BSGC con Tc99m tiene una alta sensibilidad y un VPN del 100%, aumentando la identificación de metástasis linfáticas fuera del territorio de la LFDe. La fluorescencia puede facilitar la visualización de los centinelas cuando se tiene una localización previa de los mismos con el SPECT-TAC, aunque la sensibilidad y el VPN del ICG es inferior al del Tc99m.