68Ga-FAPI PET/CT safely detects multifocal endometriosis: a case report

TVS and MRI identified a right ovarian endometrioma (Fig. 1 A). 68 Ga-FAPI-46 PET/CT confirmed intense uptake in this lesion (SUVmax 9.5) and revealed two additional FAPI-avid nodules in the left adnexa (SUVmax 9.6, Fig. 1 B) not visualized on MRI. Surgical pathology subsequently verified the presence of multifocal endometriosis. Dosimetry results revealed that the bladder received the highest absorbed dose (10.17 × 10 − 2 Gy/GBq), whereas the ovaries exhibited markedly lower doses (0.73 × 10 − 2 Gy/GBq; Table 2 ), confirming a favorable safety profile for clinical application. Figure 2 illustrates the 3D-segmented organs generated in 3D Slicer, and Figure 3 displays the axial, coronal, and sagittal dose-rate maps derived from GATE Monte Carlo simulations. Fig. 1 ( A ) MRI (T2-weighted) showing right ovarian endometrioma (red arrow). ( B ) 68 Ga-FAPI-46 PET/CT fusion image showing right endometrioma (SUVmax 9.5, red arrow) and left adnexal nodules (SUVmax 9.6, white arrowheads). Physiological uptake is noted in the uterine endometrium (blue arrows)((suvmax 17.1), which is known normal finding Table 2 Organ volumes and estimated absorbed doses (Gy/GBq) based on 68 Ga-FAPI-46 PET/CT and Monte Carlo simulations and Meyer et al. results Organ Volume (mm 3 ) Absorbed Dose (Gy/GBq)±SD Meyer et al. Absorbed Dose (Gy/GBq) ±SD (Gustafsson and Taprogge 2022 ) Liver 1188161 2.98 × 10 −2  ± 0.0001 1.01 × 10 −2 ±7.96 × 10 −3 Kidneys 113738 2.85 × 10 −2  ± 0.002 1.60 × 10 −2 ±4.60 × 10 −3 Ovaries 17315 0.73 × 10 −2  ± 0.001 5.76 × 10 −3 ±6.91 × 10 −4 Uterus 88990 4.03 × 10 −2  ± 0.0003 9.54 × 10 −3 ±5.36 × 10 −3 Bladder 391426 10.17 × 10 −2  ± 0.005 4.83 × 10 −2 ±8.55 × 10 −3 Fig. 2 Axial view images of the liver ( a ), right kidney ( a ), left kidney ( a ), uterus, right adnexal ( b ), left adnexal ( b ) and bladder ( c ) in pink, cream, indigo, yellow, blue, red, green colors respectively using the 3D Slicer software Fig. 3 Images of axial ( a ), coronal ( b ), and sagittal ( c ) views of the dose rate maps obtained from GATE Monte Carlo Toolkit ( A ) MRI (T2-weighted) showing right ovarian endometrioma (red arrow). ( B ) 68 Ga-FAPI-46 PET/CT fusion image showing right endometrioma (SUVmax 9.5, red arrow) and left adnexal nodules (SUVmax 9.6, white arrowheads). Physiological uptake is noted in the uterine endometrium (blue arrows)((suvmax 17.1), which is known normal finding Organ volumes and estimated absorbed doses (Gy/GBq) based on 68 Ga-FAPI-46 PET/CT and Monte Carlo simulations and Meyer et al. results Axial view images of the liver ( a ), right kidney ( a ), left kidney ( a ), uterus, right adnexal ( b ), left adnexal ( b ) and bladder ( c ) in pink, cream, indigo, yellow, blue, red, green colors respectively using the 3D Slicer software Images of axial ( a ), coronal ( b ), and sagittal ( c ) views of the dose rate maps obtained from GATE Monte Carlo Toolkit

A 28-year-old woman experiencing severe menstrual pain was referred to our center for suspected endometriosis. After giving her informed consent, the study was approved by our institutional ethics committee (IR.IUMS.FMD.REC0.1403.585). She first underwent TVS and pelvic MRI (1.5T, using contrast-enhanced T 1 - and T 2 -weighted images) to check for endometriotic lesions. To get a clearer picture of the disease’s extent, we performed a 68 Ga-FAPI-46 PET/CT scan 60 minutes after injecting 3 mCi (111 MBq) of the tracer, following EANM guidelines (Hope et al. 2025 ). We used 3D Slicer software to map organ volumes and Monte Carlo simulations to estimate radiation doses to organs. We also measured SUVmax to assess the tracer’s uptake in lesions. Monte Carlo dose calculations were performed in GATE using the DoseActor, enabling recording of deposited energy and statistical uncertainty. A total of 1 × 10 9 primaries were simulated, achieving ~0.5% uncertainty with a runtime of about 190 hours. The parameters/dimensions of data are shown in Table 1 . Table 1 Data characteristics Modality Image Dimension Pixel Spacing (mm 2 ) Slice Thickness (mm) CT 512 × 512 × 878 0.9765625 × 0.9765625 1 PET 200 × 200 × 293 4.07283 × 4.07283 3 Dose Map 200 × 200 × 293 4.07283 × 4.07283 3 Data characteristics

This case report shows 68 Ga-FAPI PET/CT can detect multifocal endometriosis, but larger prospective studies are needed. An ongoing trial is registered ( NCT06792318 ). Our group is also conducting a prospective study (Ethics Code: IR.IUMS.FMD.REC0.1403.585), planned for IRCT registration.

This case shows that 68 Ga-FAPI-46 PET/CT can spot multifocal endometriosis that MRI misses, like hidden lesions in the left adnexa. It works by targeting fibroblast activation protein (FAP), which is abundant in the fibrotic tissue of endometriotic lesions (Zou et al. 2025 ; Burgard et al. 2025 ). Unlike MRI, which focuses on structural changes, FAPI PET/CT picks up molecular activity, making it a valuable tool for planning surgery (Burgard et al. 2025 ). Incomplete surgical excision is a leading cause of endometriosis recurrence, as residual lesions can regrow and cause persistent symptoms (Bendifallah et al. 2022 ). 68 Ga-FAPI PET/CT enhances surgical planning by detecting multifocal endometriotic lesions missed by MRI, enabling more complete resection. By improving lesion localization, this imaging modality may reduce the risk of recurrence, offering a promising tool for precise surgery (Burgard et al. 2025 ). Physiological intense uptake was observed in the uterine endometrium (SUVmax = 17.1), consistent with normal biodistribution of 68 Ga-FAPI-46 in women of reproductive age and not indicative of disease (Hope et al. 2025 ). Compared with Meyer et al., who used three imaging time points and OLINDA/EXM phantom-based calculations, our voxel-wise Monte Carlo approach reflects patient-specific organ sizes and tracer uptake, explaining the differences between dose values. Nevertheless, the general pattern of higher bladder dose is consistent with previous findings (Meyer et al. 2020 ; Gustafsson and Taprogge 2022 ; Kline et al. 2024 ). Our dosimetry data confirm it’s safe, with low radiation doses to the ovaries, which is crucial for young women. However, this is just one case, so larger studies are needed to confirm these findings.

Endometriosis affects about 1 in 10 women of reproductive age, often causing severe pelvic pain and challenges with fertility (Fauconnier and Chapron 2005 ; Viganò et al. 2004 ). Standard imaging tools like transvaginal ultrasound (TVS) and MRI can miss hidden, multifocal lesions, making surgical planning tricky (Bazot and Daraï 2017 ). A new imaging approach, 68 Ga-FAPI PET/CT, targets fibroblast activation protein (FAP), which is abundant in the fibrotic tissue of endometriotic lesions (Kellers et al. 2025 ). Recent studies suggest this technique could spot lesions that conventional methods overlook (Zou et al. 2025 ; Burgard et al. 2025 ). In this case report, we show how 68 Ga-FAPI-46 PET/CT can reveal these hidden lesions, offering a clearer picture for diagnosis and surgery.