Recent topics in fibroblast activation protein inhibitor-PET/CT: clinical and pharmacological aspects.

Recently, positron emission tomography (PET) with fibroblast activation protein inhibitor (FAPI) has gained significant attention as an advanced tumor diagnostic imaging tool. FAPI PET has a promising potential owing to its ability to accurately depict most malignant tumors. It has an accuracy that is comparable to or surpassing the diagnostic accuracy of PET using 18F-fluorodeoxyglucose (FDG). Moreover, FAPI PET can identify malignant lesions that may be inconclusive on FDG PET. Beyond its application in neoplastic disorders, there have been encouraging reports suggesting the utility of FAPI PET in non-neoplastic conditions such as respiratory or cardiac diseases. This article aimed to provide a comprehensive overview of the recently published articles investigating FAPI and discuss its clinical utility with an emphasis on its application in tumor diagnostics. Numerous radiopharmaceutical FAPIs, including 18F- and 68Ga-labeled compounds, have been developed, and they offer various advantages and applications. With the progress in the FAPI PET synthesis to enhance accumulation and retention in pathological lesions, future studies are expected to provide valuable data on its therapeutic efficacy.

Monte Carlo simulation study to explore optimum conditions for Astatine-211 SPECT.

211At is a promising nuclide for targeted radioisotope therapy. Direct imaging of this nuclide is important for in vivo evaluation of its distribution. We investigated suitable conditions for single-photon emission computed tomography (SPECT) imaging of 211At and assessed their feasibility using a homemade Monte Carlo simulation code, MCEP-SPECT. Radioactivity concentrations of 5, 10, or 20 kBq/mL were distributed in six spheres in a National Electrical Manufactures Association (NEMA) body phantom with a background of 1 kBq/mL. The energy window, projection number, and acquisition time were 71-88 keV, 60, and 60 s, respectively, per projection. A medium-energy collimator and three low-energy collimators were tested. SPECT images were reconstructed using the ordered subset expectation maximization (OSEM) method with attenuation correction (Chang method) and scatter correction (triple-energy-windows method). Image quality was evaluated using the contrast-to-noise ratio (CNR) for detectability and the contrast recovery coefficient (CRC) for quantitavity. The low-energy, high-sensitivity collimator exhibited the best detectability among the four types of collimators, with a maximum CNR value of 43. In contrast, the low-energy, high-resolution collimator exhibited excellent quantitavity, with a maximum CRC value of 102%. Scatter correction improved the image quality. In particular, the CRC value almost doubled after scatter correction. The detection of spheres smaller than 20 mm in diameter was difficult. In summary, low-energy collimators were suitable for the SPECT imaging of 211At. In addition, scatter correction was extremely effective in improving the image quality. The feasibility of 211At SPECT was demonstrated for lesions larger than 20 mm.

A review of harmonization strategies for quantitative PET.

PET can reveal in vivo biological processes at the molecular level. PET-derived quantitative values have been used as a surrogate marker for clinical decision-making in numerous clinical studies and trials. However, quantitative values in PET are variable depending on technical, biological, and physical factors. The variability may have a significant impact on a study outcome. Appropriate scanner calibration and quality control, standardization of imaging protocols, and any necessary harmonization strategies are essential to make use of PET as a biomarker with low bias and variability. This review summarizes benefits, limitations, and remaining challenges for harmonization of quantitative PET, including whole-body PET in oncology, brain PET in neurology, PET/MR, and non-18F PET imaging. This review is expected to facilitate harmonization of quantitative PET and to promote the contribution of PET-derived biomarkers to research and development in medicine.

Clinical Implications of FDG-PET in Pancreatic Ductal Adenocarcinoma Patients Treated with Neoadjuvant Therapy.

PURPOSE: To evaluate the clinical significance of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in patients with pancreatic ductal adenocarcinoma who underwent neoadjuvant therapy. METHODS: Among 285 consecutive patients who underwent pancreatic resection for pancreatic ductal adenocarcinoma between 2015 and 2021, 86 who underwent preoperative 18F-fluorodeoxyglucose positron emission tomography/computed tomography after completion of neoadjuvant treatment were reviewed. Among preoperative factors, including post-treatment maximum standardized uptake value, predictors of early recurrence and poor prognosis were identified using multivariate analysis for decision making in surgery. RESULTS: Nineteen (22%) patients with pancreatic ductal adenocarcinoma demonstrated high maximum standardized uptake (≥ 4.5). High post-treatment maximum standardized uptake (≥ 4.5) predicted early recurrence within 6 months after surgery and correlated with shorter recurrence-free survival. Elevated post-treatment CA19-9 level (> 37 U/ml) and maximum standardized uptake ≥ 4.5 were independent prognostic factors. Post-treatment, a high maximum standardized uptake value indicated a poorer prognosis than a low maximum standardized uptake value in both patients with elevated CA19-9 and normal CA19-9 levels. The median overall survival in patients with elevated post-treatment CA19-9 and high maximum standardized uptake was only 17 months; 67% experienced early recurrence. Dynamic changes in maximum standardized uptake during neoadjuvant therapy were correlated with pathological response to neoadjuvant therapy, but not with radiological response or change in CA19-9 level. CONCLUSIONS: Post-treatment assessment using maximum standardized uptake value is useful for stratifying patients with pancreatic ductal adenocarcinoma who will benefit from surgery. Instead of subsequent curative resection, additional neoadjuvant therapy should be considered in patients with a persistently high maximum standardized uptake value.

A deep learning model based on fusion images of chest radiography and X-ray sponge images supports human visual characteristics of retained surgical items detection.

PURPOSE: Although a novel deep learning software was proposed using post-processed images obtained by the fusion between X-ray images of normal post-operative radiography and surgical sponge, the association of the retained surgical item detectability with human visual evaluation has not been sufficiently examined. In this study, we investigated the association of retained surgical item detectability between deep learning and human subjective evaluation. METHODS: A deep learning model was constructed from 2987 training images and 1298 validation images, which were obtained from post-processing of the image fusion between X-ray images of normal post-operative radiography and surgical sponge. Then, another 800 images were used, i.e., 400 with and 400 without surgical sponge. The detection characteristics of retained sponges between the model and a general observer with 10-year clinical experience were analyzed using the receiver operator characteristics. RESULTS: The following values from the deep learning model and observer were, respectively, derived: Cutoff values of probability were 0.37 and 0.45; areas under the curves were 0.87 and 0.76; sensitivity values were 85% and 61%; and specificity values were 73% and 92%. CONCLUSION: For the detection of surgical sponges, we concluded that the deep learning model has higher sensitivity, while the human observer has higher specificity. These characteristics indicate that the deep learning system that is complementary to humans could support the clinical workflow in operation rooms for prevention of retained surgical items.

Utility of FDG PET at the Initial Radioiodine Therapy in Differentiated Thyroid Cancer.

BACKGROUND/AIM: Differentiated thyroid cancer (DTC) has a good prognosis, except in the case of patients with radioiodine therapy (RIT)-refractory cancer. However, since DTC is essentially a slowly progressing cancer, it is usually judged to be a DTC with a poor prognosis after multiple RITs and yearly follow-up with echo, computed tomography (CT), and serum thyroglobulin values. This study investigated whether fluorodeoxyglucose-positron emission tomography/CT (FDG PET/CT) combined with initial RIT could identify early-stage patients with poor prognosis. PATIENTS AND METHODS: We evaluated 100 patients with high-risk DTC who underwent total thyroidectomy and received RIT at our institution. We analyzed the clinical outcomes of patients and 18F-FDG accumulation using univariate and multivariate Cox proportional hazards regression models. RESULTS: The 10-year overall survival (OS) was 87.9%, with no significant difference in OS between 18F-FDG accumulation at pre-total or near-total thyroidectomy (NTT) (p=0.180) and 131I accumulation at initial RIT (p=0.577). However, 18F-FDG positive patients had a significantly worse prognosis than negative patients (p=0.005) at initial RIT. CONCLUSION: 18F-FDG PET/CT plays an important role in both the diagnosis and prognostic prediction of RIT refractory disease in DTC patients. 18F-FDG PET/CT can be a useful tool particularly at the time of initial RIT since the 18F-FDG accumulation enables the screening of high-risk DTC with poor prognosis at a very early time stage.

Assessment of cerebral perfusion in moyamoya disease with dynamic pseudo-continuous arterial spin labeling using a variable repetition time scheme with optimized background suppression.

PURPOSE: Accurate assessment of cerebral perfusion in moyamoya disease is necessary to determine the indication for treatment. We aimed to investigate the usefulness of dynamic PCASL using a variable TR scheme with optimized background suppression in the evaluation of cerebral perfusion in moyamoya disease. METHODS: We retrospectively analyzed the images of 24 patients (6 men and 18 women, mean age 31.4 ± 18.2 years) with moyamoya disease; each of whom was imaged with both dynamic PCASL using the variable-TR scheme and 123IMP SPECT with acetazolamide challenge. ASL dynamic data at 10 phases are acquired by changing the LD and PLD. The background suppression timing was optimized for each phase. CBF and ATT were measured with ASL, and CBF and CVR to an acetazolamide challenge were measured with SPECT. RESULTS: A significant moderate correlation was found between the CBF measured by dynamic PCASL and that by SPECT (r = 0.53, P < 0.001). The CBF measured by dynamic PCASL (52.5 ± 13.3 ml/100 mg/min) was significantly higher than that measured by SPECT (43.0 ± 12.6 ml/100 mg/min, P < 0.001). The ATT measured by dynamic PCASL showed a significant correlation with the CVR measured by SPECT (r = 0.44, P < 0.001). ATT was significantly longer in areas where the CVR was impaired (CVR < 18.4%, ATT = 1812 ± 353 ms) than in areas where it was preserved (CVR > 18.4%, ATT = 1301 ± 437 ms, P < 0.001). The ROC analysis showed a moderate accuracy (AUC = 0.807, sensitivity = 87.7%, specificity = 70.4%) when the cutoff value of ATT was set at 1518 ms. CONCLUSION: Dynamic PCASL using this scheme was found to be useful for assessing cerebral perfusion in moyamoya disease.

Efficacy of Dynamic Chest Radiography for Chronic Thromboembolic Pulmonary Hypertension.

Background While current guidelines require lung ventilation-perfusion (V/Q) scanning as the first step to diagnose chronic pulmonary embolism in pulmonary hypertension (PH), its use may be limited by low availability and/or exposure to ionizing radiation. Purpose To compare the performance of dynamic chest radiography (DCR) and lung V/Q scanning for detection of chronic thromboembolic PH (CTEPH). Materials and Methods Patients with PH who underwent DCR and V/Q scanning in the supine position from December 2019 to July 2021 were retrospectively screened. The diagnosis of CTEPH was confirmed with right heart catheterization and invasive pulmonary angiography. Observer tests were conducted to evaluate the diagnostic accuracy of DCR and V/Q scanning. The lungs were divided into six areas (upper, middle, and lower for both) in the anteroposterior image, and the number of lung areas with thromboembolic perfusion defects was scored. Diagnostic performance was compared between DCR and V/Q scanning using the area under the receiver operating characteristic curve. Agreement between the interpretation of DCR and that of V/Q scanning was assessed using the Cohen kappa coefficient and percent agreement. Results A total of 50 patients with PH were analyzed: 29 with CTEPH (mean age, 64 years ± 15 [SD]; 19 women) and 21 without CTEPH (mean age, 61 years ± 22; 14 women). The sensitivity, specificity, and accuracy of DCR were 97%, 86%, and 92%, respectively, and those of V/Q scanning were 100%, 86%, and 94%, respectively. Areas under the receiver operating characteristic curve for DCR and V/Q scanning were 0.92 (95% CI: 0.79, 0.97) and 0.93 (95% CI: 0.78, 0.98). Agreement between the consensus interpretation of DCR and that of V/Q scanning was substantial (κ = 0.79 [95% CI: 0.61, 0.96], percent agreement = 0.9 [95% CI: 0.79, 0.95]). Conclusion Dynamic chest radiography had similar efficacy to ventilation-perfusion scanning in the detection of chronic thromboembolic pulmonary hypertension. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Wandtke and Koproth-Joslin in this issue.

Clinical significance of the combination of preoperative SUVmax and CEA in patients with clinical stage IA lung adenocarcinoma.

BACKGROUND: Preoperative maximum standardized uptake value (SUVmax) of 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography and serum carcinoembryonic antigen (CEA) have been reported as prognostic factors for lung adenocarcinoma. However, the significance of combined SUVmax and CEA in early-stage lung adenocarcinoma is not well known. METHODS: We retrospectively evaluated the relationship between the combination of SUVmax and CEA and the prognosis of 410 patients with clinical stage IA lung adenocarcinoma who underwent resection. The cutoff values for SUVmax and CEA were determined by receiver operating characteristic curve analysis, and patients were categorized into high SC (SUVmax and CEA) group (SUVmax ≥2.96 and CEA ≥5.3), moderate SC group (either SUVmax <2.96 and CEA ≥5.3 or SUVmax ≥2.96 and CEA <5.3) and low SC group (SUVmax <2.96 and CEA <5.3). RESULTS: Kaplan-Meier curve analysis showed that patients with clinical stage IA lung adenocarcinoma in the high SC group had significantly shorter overall survival (OS) and recurrence-free survival (RFS) than the other groups (p = 0.011 and p < 0.0001, respectively). Multivariate analysis showed that high SC was an independent prognostic factor of OS (p = 0.029) and RFS (p < 0.0001). CONCLUSIONS: High values of SUVmax and CEA were associated with poor OS and RFS in patients with stage IA lung adenocarcinoma. Simultaneous evaluation of SUVmax and CEA may be an effective prognostic marker to determine the optimal treatment strategy of early-stage lung adenocarcinoma.

Prognostic value of pre-transplantation total metabolic tumor volume on 18fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography in relapsed and refractory aggressive lymphoma.

Relapsed and refractory aggressive lymphoma have a poor prognosis. High-dose chemotherapy followed by autologous hematopoietic stem cell transplantation (auto-HSCT) is effective in chemosensitive patients. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is among the few options for non-chemosensitive patients. 18Fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (18FDG-PET/CT) is the standard tool for evaluating response to chemotherapy and residual tumor volume. However, accurate assessment of residual tumor volume is not currently being achieved in clinical practice, and its value in prognostic and therapeutic stratification remains unclear. To answer this question, we investigated the efficacy of quantitative indicators, including total metabolic tumor volume (TMTV), in predicting prognosis after auto-HSCT and allo-HSCT. We retrospectively analyzed 39 patients who received auto-HSCT and 28 who received allo-HSCT. In the auto-HSCT group, patients with a higher TMTV had a poor prognosis due to greater risk of relapse. In the allo-HSCT group, patients with a higher TMTV had a lower progression-free survival rate and a significantly higher relapse rate. Neither Deauville score nor other clinical parameters were associated with prognosis in either group. Therefore, pre-transplant TMTV on PET is effective for prognostic prediction and therapeutic decision-making for relapsed or refractory aggressive lymphoma.

Continuous bed motion in a silicon photomultiplier-based scanner provides equivalent spatial resolution and image quality in whole body PET images at similar acquisition times using the step-and-shoot method.

This study investigated the spatial resolution and image quality of the continuous bed motion (CBM) method in a sensitive silicon photomultiplier (SiPM)-based positron emission tomography (PET)/computed tomography (CT) system compared with the traditional step-and-shoot (SS) method. Methods: Siemens Biograph Vision was used in this study. Data acquisition using the SS method was performed for 3 min per bed. In the CBM method, the bed speed ranged from 0.5 to 3.3 mm/s. The acquisition time equivalent to the SS method was 1.1 mm/s for 2-bed ranges and 0.8 mm/s for seven-bed ranges. The spatial resolution was investigated using 18F point sources and evaluated using the full width at half maximum. Image quality was investigated using a National Electrical Manufacturers Association International Electrotechnical Commission body phantom with six spheres 10-, 13-, 17-, 22-, 28-, and 37-mm inner diameters. The radioactivity concentration ratio of the 18F solution in all spheres and the background was approximately 4:1. The detectability of each sphere was visually evaluated on a five-step score. Image quality was physically evaluated using the noise equivalent count rate (NECphantom), contrast percentage of the 10-mm hot sphere (QH,10mm), background variability percentage (N10mm), and contrast-noise ratio (QH,10mm/N10mm). Results: The spatial resolution was not affected by the difference of acquisition methods and bed speeds. The detectability of the 10-mm sphere with a bed speed of 2.2 mm/s or faster was significantly inferior to that of the SS 2-bed method. In evaluating image quality, no significant difference in the contrast percentage was observed among the acquisition methods and speeds in the CBM method. However, the increasing bed speed in the CBM method increased the N10mm and decreased the NECphantom. When comparing the SS 2-bed method with the CBM method at 0.8 mm/s, no significant differences in all parameters were observed. Conclusion: In a SiPM-based PET/CT scanner, the CBM method provides equivalent spatial resolution and image quality in whole body PET images with same acquisition time using the SS method.

Long-term follow up after sentinel node biopsy alone for early-stage cervical cancer.

OBJECTIVE: Sentinel node biopsy alone (SNB) reduces the postoperative complications of pelvic lymphadenectomy, such as lymphedema and lymphangitis; however, the long-term prognosis after SNB is unclear. The objective of this study was to evaluate the long-term outcome and complications of patients with early-stage cervical cancer who underwent SNB for hysterectomy or trachelectomy. METHODS: We performed SNB for cervical cancer using a radioisotope method in 181 patients between 2009 and 2017. If the intraoperative sentinel lymph node evaluation was negative for metastasis, no further lymph nodes were removed. RESULTS: The median age of the patients was 34 years (range, 21-73 years). The International Federation of Gynecology and Obstetrics 2008 stage was IA1 in 6 patients, IA2 in 18, IB1 in 154, and IIA1 in 3. Of the 181 patients (44 with hysterectomy, 137 with trachelectomy), 8 did not undergo pelvic lymphadenectomy because of a false-negative intraoperative diagnosis, 20 received adjuvant therapy after surgery, and 4 (2.2%) experienced recurrence over a median follow-up period of 83.5 months (range, 25-145 months). In the four recurrent cases, recurrence occurred in the pelvis, lung, and bone in one patient each, while the remaining patient developed pelvic and para-aortic lymph node metastases. Of these four patients, one died, and the remaining three are alive without disease after multidisciplinary therapy. The 5-year progression-free and overall survival rates were 98.8% and 99.4%, respectively. Postoperative complications, such as lymphedema, were very low rate. CONCLUSIONS: SNB for early-stage cervical cancer might be safe and effective, with no increase in the recurrence and postoperative complications rate.

Impact of Nuclear Factor Erythroid 2-Related Factor 2 in Hepatocellular Carcinoma: Cancer Metabolism and Immune Status.

We examined phosphorylated nuclear factor erythroid 2-related factor 2 (P-NRF2) expression in surgically resected primary hepatocellular carcinoma (HCC) and investigated the association of P-NRF2 expression with clinicopathological features and patient outcome. We also evaluated the relationship among NRF2, cancer metabolism, and programmed death ligand 1 (PD-L1) expression. In this retrospective study, immunohistochemical staining of P-NRF2 was performed on the samples of 335 patients who underwent hepatic resection for HCC. Tomography/computed tomography using fluorine-18 fluorodeoxyglucose was performed, and HCC cell lines after NRF2 knockdown were analyzed by array. We also analyzed the expression of PD-L1 after hypoxia inducible factor 1α (HIF1A) knockdown in NRF2-overexpressing HCC cell lines. Samples from 121 patients (36.1%) were positive for P-NRF2. Positive P-NRF2 expression was significantly associated with high alpha-fetoprotein (AFP) expression, a high rate of poor differentiation, and microscopic intrahepatic metastasis. In addition, positive P-NRF2 expression was an independent predictor for recurrence-free survival and overall survival. NRF2 regulated glucose transporter 1, hexokinase 2, pyruvate kinase isoenzymes L/R, and phosphoglycerate kinase 1 expression and was related to the maximum standardized uptake value. PD-L1 protein expression levels were increased through hypoxia-inducible factor 1α after NRF2 overexpression in HCC cells. Conclusions: Our large cohort study revealed that P-NRF2 expression in cancer cells was associated with clinical outcome in HCC. Additionally, we found that NRF2 was located upstream of cancer metabolism and tumor immunity.

Usefulness of semi-quantitative analysis in 123I metaiodobenzylguanidine SPECT/CT for the differentiation of pheochromocytoma and cortical adenoma.

OBJECTIVE: 123I metaiodobenzylguanidine (MIBG) scintigraphy is a useful tool for the diagnosis of pheochromocytomas (PHEOs), but some PHEOs are difficult to differentiate from cortical adenoma (CA) or normal adrenal uptake by visual evaluation alone. A new semi-quantitative analysis using 123I MIBG SPECT/CT is thus expected. Herein, we introduce the tumor-to-liver count ratio (T/L) and the tumor-to-muscle count ratio (T/M). METHODS: We examined the cases of 21 patients with PHEOs (10 males, 11 females; age 24-80, median 61 years) and 23 patients with CA (15 males and 8 females, age 30-78, median 58 years). The visual scoring based on 123I MIBG planar images (planar score) and SPECT images (SPECT score) was used as the conventional evaluation. Using 123I MIBG SPECT/CT findings, we calculated the semi-quantitative values of the count ratio using the maximum or mean count of the tumor and the liver or muscle as the reference organ (T/Lmax, T/Lmean, T/Mmax and T/Mmean). Each evaluation of the PHEOs and CAs was compared, and the diagnosing performance was evaluated based on an ROC analysis. RESULTS: The area under curve (AUC) values were as follows: the planar score, 0.833; SPECT score, 0.813; T/Lmax, 0.986; T/Lmean, 0.975; T/Mmax, 0.955; and T/Mmean, 0.933. The AUC for T/Mmax was significantly higher than those of the planar score, and SPECT score by ROC analysis (p < 0.01 each). CONCLUSION: The semi-quantitative value of 123I MIBG SPECT/CT is more useful than the conventional visual evaluation for differentiating PHEOs from CAs.

Alveolar soft part sarcoma of the orbit: A case report.

Alveolar soft part sarcoma is a rare soft tissue neoplasm that accounts for approximately 1% of all sarcomas and is usually identified in the extremities in adults. The occurrence of alveolar soft part sarcoma in the orbit is extremely rare, estimated at approximately 5% - 15% among all cases of alveolar soft part sarcoma . Here, we present a case of 29-year-old woman with orbital alveolar soft part sarcoma. We describe the magnetic resonance and F-18 2-fluoro-2-deoxy-D-glucose-position emission tomography/computed tomography findings of this case. This young woman had a spindle-shaped mass. A higher signal compared to the extraocular muscle on T1-weighted images, numerous flow voids on T2-weighted images, and intense enhancement could be key findings of this disease.

Compared to conventional PET/CT scanners, silicon-photomultiplier-based PET/CT scanners show higher arterial 18F-FDG uptake in whole-body 18F-FDG-PET/CT.

OBJECTIVES: To clarify differences in arterial 18F-FDG (fluorodeoxyglucose) uptake between silicon photomultiplier (SiPM)-based and conventional PET/CT scanners, and to compare clinical and phantom results. PATIENTS AND METHODS: Twenty-six patients with lung tumours underwent serial SiPM-based and conventional PET/CT scans on the same day. We compared the target-to-background ratios [TBRsi (SiPM), TBRc (conventional)] and the percentage difference between TBRsi and TBRc (ΔTBR) in the carotid artery, aorta and peripheral arteries. The correlation between ΔTBR and vessel size was also investigated. In the carotid artery, active segment analyses were performed with the threshold (TBR ≥1.6), and we compared each scanner's ratio of active segments and TBR values. We compared the clinical results with the recovery coefficients (RCs). RESULTS: The TBRsi was significantly higher than the TBRc in the carotid artery, aorta and peripheral arteries (1.63 ± 0.22 vs. 1.43 ± 0.22, 1.65 ± 0.19 vs. 1.53 ± 0.15 and 1.37 ± 0.31 vs. 1.11 ± 0.27, mean ± SD, P ≤ 0.0001 for all), and the peripheral arteries showed the highest ΔTBR (24.4 ± 16.8%). The small (10-15 mm) vessels (26.9 ± 15.9%) showed significantly higher ΔTBRs than the larger vessels (7.3 ± 8.5% for 15-20 mm, 8.0 ± 12.8% for ≥20 mm, P < 0.0001 for both). The carotid artery showed significantly higher ratios of active segment (54.5 vs. 20.5%, P < 0.0001) and TBR values (1.85 ± 0.25 vs. 1.76 ± 0.15, P = 0.0006) for TBRsi vs. TBRc. The differences in RCs were similar to those of ΔTBR for each vessel size. CONCLUSIONS: SiPM-based PET/CT scanners showed higher arterial 18F-FDG uptake (especially in vessels <15 mm) than conventional scanners, and the threshold TBR ≥1.6 is not applicable for the carotid artery for SiPM-based PET/CT systems.

Estimation of the lower limits for feasible Ra-223 SPECT imaging: a Monte Carlo simulation study.

OBJECTIVES: Ra-223 is a promising radionuclide for the treatment of skeletal metastases in castration-resistant prostate cancer patients. This study aims to estimate the lower limits for feasible Ra-223 single-photon emission computerized tomography (SPECT) imaging using a Monte Carlo simulation study. METHODS: The SPECT images were produced on a homemade code: the Monte Carlo simulation of electrons and photons for SPECT (MCEP-SPECT). The National Electrical Manufacturers Association (NEMA) phantom with six hot spheres of diameters of 37, 28, 22, 17, 13, and 10 mm installed inside, was used. The background activity concentration was 0.6 kBq/mL, and the ratios of hot concentrations to the background (R HB) were 25, 20, 15, 10, and 5. When R HB was 15, the background concentrations of 1.5, 0.9, 0.3, and 0.15 kBq/mL were also tested. The energy window was 84 keV±10%. The number of projections was 60/360°, and the acquisition time was 60 s per projection. Two kinds of collimators: middle-energy general-purpose (MEGP) and high-energy general-purpose (HEGP), were examined. The SPECT images were evaluated based on two quantitative indexes: contrast-to-noise ratio (CNR) for detectability and contrast recovery coefficient (CRC) for quantitative accuracy. RESULTS: The CRC for the HEGP collimator was 35-40%, while the CRC for the MEGP collimator was 25-30%. The CNRs for the MEGP collimator were larger than those for the HEGP collimator. The CNRs of the hot spheres with diameters less than 22 mm were lower than 5.0 for both collimators, when R HB and the background concentration were 15 and 0.6 kBq/mL, respectively. Based on the obtained results, it was estimated that the lower limit of R HB for the detection of the hot sphere with a diameter of 37 mm would be approximately 20 if the background concentration is 0.05 kBq/mL. CONCLUSIONS: The MEGP collimator is superior in terms of detectability, while the HEGP collimator is superior in terms of quantitative accuracy. When the lesion size is small, the MEGP collimator may be favorable. Based on these results, the estimated lower limit of the activity concentration would be approximately 1 kBq/mL if the background concentration is 0.05 kBq/mL for a large lesion.

Impact of Metabolic Activity in Hepatocellular Carcinoma: Association With Immune Status and Vascular Formation.

We evaluated the prognostic value of fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in hepatocellular carcinoma (HCC). Their association with programmed death ligand 1 (PD-L1) expression and vascular formation was further investigated. In this retrospective study, using a database of 418 patients who had undergone 18F-FDG PET/CT before hepatic resection for HCC, immunohistochemical staining of PD-L1, clusters of differentiation (CD) 8, CD68, and CD34 was performed. Patients with a high maximum standardized uptake value (SUVmax) on 18F-FDG PET/CT showed a significantly worse recurrence-free survival (RFS) (hazard ratio [HR]: 1.500; 95% confidence interval [CI]: 1.088-2.069; P = 0.0133) and overall survival (OS) (HR: 2.259; 95% CI: 1.276-4.000; P = 0.0052) than patients with a low SUVmax. Logistic regression analysis showed that a high SUVmax in HCC was significantly associated with PD-L1-positive expression (odds ratio: 4.407; 95% CI: 2.265-8.575; P < 0.0001). SUVmax values of HCC were associated with intratumoral CD8-positive T-cell counts (P = 0.0044) and CD68-positive macrophage counts (P = 0.0061). Stratification based on SUVmax, PD-L1 expression, and the vessels that encapsulate tumor clusters (VETC) status was also significantly associated with RFS and OS. SUVmax, VETC, and PDL1 expression were independently predictive of survival on multivariable analysis. Conclusion: Our large cohort study showed that a high SUVmax on 18F-FDG PET/CT is associated with a poor clinical outcome and PD-L1 expression in patients with HCC. Additionally, stratification of patients based on the combination of SUVmax, PD-L1 expression, and the VETC status predicts poor clinical outcome.

Monte Carlo simulation of the acquisition conditions for 177Lu molecular imaging of hepatic tumors.

OBJECTIVE: To examine the impact of acquisition time on Lutetium-177 (177Lu) single-photon emission computed tomography (SPECT) images using Monte Carlo simulation. METHODS: A gamma camera simulation based on the Monte Carlo method was performed to produce SPECT images. The phantom was modeled on a NEMA IEC BODY phantom including six spheres as tumors. After the administration of 7.4 GBq of 177Lu, radioactivity concentrations of the tumor/liver at 6, 24, and 72 h after administration were set to 1.85/0.201, 2.12/0.156, and 1.95/0.117 MBq/mL, respectively. In addition, the radioactivity concentrations of the tumor at 72 h after administration varied by 1/2, 1/4, and 1/8 when comparison was made. Acquisition times examined were 1.2, 1.5, 2, 3, 6, and 12 min. To assess the impact of collimators, SPECT data acquired at 72 h after the administration using six collimators of low-energy high-resolution (LEHR), extended low-energy general-purpose (ELEGP), medium-energy, and general-purpose (MEGP-1, MEGP-2, and MEGP-3) and high-energy general-purpose (HEGP) were examined. After prefiltering using a Butterworth filter, projection images were reconstructed using ordered subset expectation maximization. The detected photons were classified into direct rays, scattered rays, penetrating rays, and characteristic X-rays from lead. The image quality was evaluated through visual assessment, and physical assessment of contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR). In this study, the CNR threshold for detectability was assumed to be 5.0. RESULTS: To compare collimators, the highest sensitivity was observed with ELEGP, followed by LEHR and MEGP-1. The highest ratio of direct ray was also observed in ELEGP followed by MEGP-1. In comparison of the radioactivity concentration ratios of tumor/liver, CRC and CNR were significantly decreased with smaller radioactivity concentration ratios. This effect was greater with larger spheres. According to the visual assessment, the acquisition time of 6, 6, and 3 min or longer was required using ELEGP collimator at 6, 24, and 72 h after administration, respectively. Physical assessment based on CNR and CRC also suggested that 6, 6, and 3 min or longer acquisition time was necessary at 6, 24, and 72 h after administration. CONCLUSION: 177Lu-SPECT images generated via the Monte Carlo simulation suggested that the recommended acquisition time was 6 min or longer at 6 and 24 h and 3 min or longer at 72 h after administration.