Generating PET Attenuation Maps via Sim2Real Deep Learning-Based Tissue Composition Estimation Combined with MLACF.

Deep learning (DL) has recently attracted attention for data processing in positron emission tomography (PET). Attenuation correction (AC) without computed tomography (CT) data is one of the interests. Here, we present, to our knowledge, the first attempt to generate an attenuation map of the human head via Sim2Real DL-based tissue composition estimation from model training using only the simulated PET dataset. The DL model accepts a two-dimensional non-attenuation-corrected PET image as input and outputs a four-channel tissue-composition map of soft tissue, bone, cavity, and background. Then, an attenuation map is generated by a linear combination of the tissue composition maps and, finally, used as input for scatter+random estimation and as an initial estimate for attenuation map reconstruction by the maximum likelihood attenuation correction factor (MLACF), i.e., the DL estimate is refined by the MLACF. Preliminary results using clinical brain PET data showed that the proposed DL model tended to estimate anatomical details inaccurately, especially in the neck-side slices. However, it succeeded in estimating overall anatomical structures, and the PET quantitative accuracy with DL-based AC was comparable to that with CT-based AC. Thus, the proposed DL-based approach combined with the MLACF is also a promising CT-less AC approach.

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.

Asymmetric diffuse thyroid uptake on 18F-FDG PET/CT in patient with subacute thyroiditis: Case report and literature review.

A 48-year-old man with an intermittent fever of 39.0oC for more than three weeks underwent computed tomography (CT) and blood testing, which revealed no clues. Antibiotics wereadministered, but his condition did not improve. Fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) showed right-lobe-dominant diffuse thyroid uptake. On technetium-99m (99mTc) pertechnetate scintigraphy, the thyroid gland could not be visualized, and he was diagnosed with subacute thyroiditis (SAT). When asymmetric 18F-FDG diffuse thyroid uptake on PET/CT is observed in a patient with a fever of unknown origin (FUO), SAT may need to be considered.

Prognostic role of preoperative fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography with an image-based harmonization technique: A multicenter retrospective study.

Objectives: Despite the prognostic impacts of preoperative fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography examination, fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography-based prognosis prediction has not been used clinically because of the disparity in data between institutions. By applying an image-based harmonized approach, we evaluated the prognostic roles of fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography parameters in clinical stage I non-small cell lung cancer. Methods: We retrospectively examined 495 patients with clinical stage I non-small cell lung cancer who underwent fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography examinations before pulmonary resection between 2013 and 2014 at 4 institutions. Three different harmonization techniques were applied, and an image-based harmonization, which showed the best-fit results, was used in the further analyses to evaluate the prognostic roles of fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography parameters. Results: Cutoff values of image-based harmonized fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography parameters, maximum standardized uptake, metabolic tumor volume, and total lesion glycolysis were determined using receiver operating characteristic curves that distinguish pathologic high invasiveness of tumors. Among these parameters, only the maximum standardized uptake was an independent prognostic factor in recurrence-free and overall survivals in univariate and multivariate analyses. High image-based maximum standardized uptake value was associated with squamous histology or lung adenocarcinomas with higher pathologic grades. In subgroup analyses defined by ground-glass opacity status and histology or by clinical stages, the prognostic impact of image-based maximum standardized uptake value was always the highest compared with other fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography parameters. Conclusions: The image-based fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography harmonization was the best fit, and the image-based maximum standardized uptake was the most important prognostic marker in all patients and in subgroups defined by ground-glass opacity status and histology in surgically resected clinical stage I non-small cell lung cancers.

Prognostic significance of the harmonized maximum standardized uptake value of 18F-FDG-PET/CT in patients with resectable oral tongue squamous cell carcinoma: a multicenter study.

OBJECTIVES: To investigate the usefulness of harmonized 18F-FDG-PET/CT parameters for predicting the postoperative recurrence and prognosis of oral tongue squamous cell carcinoma (OTSCC). METHODS: We retrospectively analyzed the cases of 107 OTSCC patients who underwent surgical resection at four institutions in Japan in 2010-2016 and evaluated the harmonized PET parameters of the maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) for the primary tumor as the pSUVmax, pMTV, and pTLG. For lymph node metastasis, we used harmonized PET parameters of nodal-SUVmax, nodal-total MTV (tMTV), and nodal-total TLG (tTLG). The associations between the harmonized PET parameters and the patients' relapse-free survival (RFS) and overall survival (OS) were evaluated by the Kaplan-Meier method and Cox proportional hazard regression analysis for model 1 (preoperative stage) and model 2 (preoperative + postoperative stages). RESULTS: The harmonized SUVmax values were significantly lower than those before harmonization (p=0.012). The pSUVmax was revealed as a significant preoperative risk factor for RFS and OS. Nodal-SUVmax, nodal-tMTV, and nodal-tTLG were significant preoperative risk factors for OS. The combination of pSUVmax + nodal-SUVmax significantly stratified the patients into a low-risk group (pSUVmax <3.97 + nodal-SUVmax <2.85 or ≥2.85) and a high-risk group (pSUVmax ≥3.97 + nodal-SUVmax <2.85 or pSUVmax ≥3.97 + nodal-SUVmax ≥2.85) for recurrence and prognosis (RFS: p=0.001; OS: p<0.001). CONCLUSIONS: The harmonized pSUVmax is a significant prognostic factor for the survival of OTSCC patients. The combination of pSUVmax and nodal-SUVmax identified OTSCC patients at high risk for recurrence and poor prognosis at the preoperative stage.

Impact of respiratory gating and ECG gating on 18F-FDG PET/CT for cardiac sarcoidosis.

BACKGROUND: The aim of this study was to estimate the impact of respiratory and electrocardiogram (ECG)-gated FDG positron emission tomography (PET)/computed tomography (CT) on the diagnosis of cardiac sarcoidosis (CS). METHODS AND RESULTS: Imaging from thirty-one patients was acquired on a PET/CT scanner equipped with a respiratory- and ECG-gating system. Non-gated PET images and three kinds of gated PET/CT images were created from identical list-mode clinical PET data: respiratory-gated PET during expiration (EX), ECG-gated PET at end diastole (ED), and ECG-gated PET at end systole (ES). The maximum standardized uptake value (SUVmax) and cardiac metabolic volume (CMV) were measured, and the locations of FDG accumulation were analyzed using a polar map. The mean SUVmax of the subjects was significantly higher after application of either respiratory-gated or ECG-gated reconstruction. Conversely, the mean CMV was significantly lower following the application of respiratory-gated or ECG-gated reconstruction. The segment showing maximum accumulation was shifted to the adjacent segment in 25.8%, 38.7%, and 41.9% of cases in EX, ED, and ES images, respectively. CONCLUSION: In FDG PET/CT scanning for the diagnosis of CS, gated scanning is likely to increase quantitative accuracy, but the effect depends on the location and synchronization method.

High 18F-FDG Uptake in a Papillary Craniopharyngioma of the Third Ventricle.

ABSTRACT: Craniopharyngioma is a benign tumor classified as grade 1 by the World Health Organization Classification of Tumors of the Central Nervous System. We present a rare case of a high-18F-FDG-avidity papillary craniopharyngioma of the third ventricle. A 65-year-old man underwent CT and MRI examinations for gait disturbance, lower-limb weakness, and urinary incontinence, and an oval solid tumor that extended from the suprasellar region to the third ventricle was identified. 18F-FDG PET/CT showed high accumulation (SUVmax, 22.3) in the tumor. A transventricular endoscopic tumor biopsy led to the diagnosis of papillary craniopharyngioma.

Visualization of tumor hypoxia and re-oxygenation after stereotactic body radiation therapy in early peripheral lung cancer: A prospective study.

BACKGROUND AND PURPOSE: In this study, fluoromisonidazole positron emission tomography (F-MISO PET/CT) was used to evaluate tumor hypoxia and re-oxygenation in patients with lung tumors treated with stereotactic body radiation therapy (SBRT). MATERIALS AND METHODS: Patients with T1-2 N0 lung cancer were included in this study. The prescribed dose was 48-52 Gy in four fractions. F-MISO PET/CT was performed twice, before SBRT and 1-3 days after the first irradiation. The maximum standardized uptake value (SUVmax) and tumor/muscle ratio (TMR) were evaluated as indicators of hypoxia. The threshold for hypoxia was defined as a TMR of 1.30 or more. RESULTS: Between 2016 and 2021, 15 patients were included. Pre-treatment tumor hypoxia was observed in nine tumors (60 %). TMR in all six tumors without pre-treatment hypoxia rose after single high-dose irradiation. In contrast, TMR in six of nine tumors with pre-treatment hypoxia dropped after irradiation, suggesting re-oxygenation. Although no local recurrence was noted, regional and/or distant relapses were seen in four patients (27 %). Of these, three had tumors with abnormal F-MISO uptake. The remaining patient had a tumor without signs of hypoxia on pre-treatment PET/CT. The 2-year progression free survival of patients with tumors with and without pre-treatment hypoxia were 30 % and 63 %, respectively (p = 0.319). CONCLUSION: Tumor hypoxia reduced after single high-dose irradiation. Tumor with F-MISO uptake seems to be an unfavorable prognostic factor in lung SBRT.

High-Resolution Silicon Photomultiplier Time-of-Flight Dedicated Head PET System for Clinical Brain Studies.

We acquired brain 18F-FDG and 18F-flutemetamol PET images using a time-of-flight system dedicated to the head (dhPET) and a conventional whole-body PET/CT (wbPET) system and evaluated the clinical superiority of dhPET over wbPET. Methods: There were 18 subjects for the 18F-FDG PET study and 17 subjects for the 18F-flutemetamol PET study. 18F-FDG PET images were first obtained using wbPET, followed by dhPET. 18F-flutemetamol PET images were first obtained using wbPET, followed by dhPET. Images acquired using dhPET and wbPET were compared by visual inspection, voxelwise analysis, and SUV ratio (SUVR). Results: All 18F-FDG and 18F-flutemetamol images acquired using dhPET were judged as visually better than those acquired using wbPET. The voxelwise analysis demonstrated that accumulations in the cerebellum, in the lateral occipital cortices, and around the central sulcus area in dhPET 18F-FDG images were lower than those in wbPET 18F-FDG images, whereas accumulations around the ventricle systems were higher in dhPET 18F-FDG images than those in wbPET 18F-FDG images. Accumulations in the cerebellar dentate nucleus, in the midbrain, in the lateral occipital cortices, and around the central sulcus area in dhPET images were lower than those in wbPET images, whereas accumulations around the ventricle systems were higher in dhPET 18F-flutemetamol images than those in wbPET 18F-flutemetamol images. The mean cortical SUVRs of 18F-FDG and 18F-flutemetamol dhPET images were significantly higher than those of 18F-FDG and 18F-flutemetamol wbPET images, respectively. Conclusion: The dhPET images had better image quality by visual inspection and higher SUVRs than wbPET images. Although there were several regional accumulation differences between dhPET and wbPET images, understanding this phenomenon will enable full use of the features of this dhPET system in clinical practice.

Evaluation of the performance of a high-resolution time-of-flight PET system dedicated to the head and breast according to NEMA NU 2-2012 standard.

BACKGROUND: This study evaluated the physical performance of a positron emission tomography (PET) system dedicated to the head and breast according to the National Electrical Manufacturers Association (NEMA) NU2-2012 standard. METHODS: The spatial resolution, sensitivity, scatter fraction, count rate characteristics, corrections for count losses and randoms, and image quality of the system were determined. All measurements were performed according to the NEMA NU2-2012 acquisition protocols, but image quality was assessed using a brain-sized phantom. Furthermore, scans of the three-dimensional (3D) Hoffmann brain phantom and mini-Derenzo phantom were acquired to allow visual evaluation of the imaging performance for small structures. RESULTS: The tangential, radial, and axial full width at half maximum (FWHM) at a 10-mm offset in half the axial field of view were measured as 2.3, 2.5, and 2.9 mm, respectively. The average system sensitivity at the center of the field of view and at a 10-cm radial offset was 7.18 and 8.65 cps/kBq, respectively. The peak noise-equivalent counting rate was 35.2 kcps at 4.8 kBq/ml. The corresponding scatter fraction at the peak noise-equivalent counting rate was 46.8%. The peak true rate and scatter fraction at 8.6 kBq/ml were 127.8 kcps and 54.3%, respectively. The percent contrast value for a 10-mm sphere was approximately 50%. On the 3D Hoffman brain phantom image, the structures of the thin layers composing the phantom were visualized on the sagittal and coronal images. On the mini-Derenzo phantom, each of the 1.6-mm rods was clearly visualized. CONCLUSION: Taken together, these results indicate that the head- and breast-dedicated PET system has high resolution and is well suited for clinical PET imaging.

The usefulness of the total metabolic tumor volume for predicting the postoperative recurrence of thoracic esophageal squamous cell carcinoma.

BACKGROUND: Induction or adjuvant therapies are not always beneficial for thoracic esophageal squamous cell carcinoma (ESCC) patients, and it is thus important to identify patients at high risk for postoperative ESCC recurrence. We investigated the usefulness of the total metabolic tumor volume (TMTV) for predicting the postoperative recurrence of thoracic ESCC. METHODS: We retrospectively analyzed the cases of 163 thoracic ESCC patients (135 men, 28 women; median age of 66 [range 34-82] years) treated at our hospital in 2007-2012. The TMTV was calculated from the fluorine-18 fluorodeoxyglucose (18F-FDG) uptake in the primary lesion and lymph node metastases. The optimal cut-off values for relapse and non-relapse were obtained by the time-dependent receiver operating curve analyses. Relapse-free survival (RFS) was evaluated by the Kaplan-Meier method, and between-subgroup differences in survival were analyzed by log-rank test. The prognostic significance of metabolic parameters and clinicopathological variables was assessed by a Cox proportional hazard regression analysis. The difference in the failure patterns after surgical resection was evaluated using the χ2-test. RESULTS: The optimal cut-off value of TMTV for discriminating relapse from non-relapse was 3.82. The patients with a TMTV ≥3.82 showed significantly worse prognoses than those with low values (p < 0.001). The TMTV was significantly related to RFS (model 1 for preoperative risk factors: TMTV: hazard ratio [HR] =2.574, p = 0.004; model 2 for preoperative and postoperative risk factors: HR = 1.989, p = 0.044). The combination of the TMTV and cN0-1 or pN0-1 stage significantly stratified the patients into low-and high-risk recurrence groups (TMTV cN0-1, p < 0.001; TMTV pN0-1, p = 0.004). The rates of hematogenous and regional lymph node metastasis were significantly higher in the patients with TMTV ≥3.82 than those with low values (hematogenous metastasis, p < 0.001, regional lymph node metastasis, p = 0.011). CONCLUSIONS: The TMTV was a more significantly independent prognostic factor for RFS than any other PET parameter in patients with resectable thoracic ESCC. The TMTV may be useful for the identifying thoracic ESCC patients at high risk for postoperative recurrence and for deciding the patient management.

Attenuation correction for phantom tests: an alternative to maximum-likelihood attenuation correction factor-based correction for clinical studies in time-of-flight PET.

OBJECTIVES: This study evaluates the phantom attenuation correction (PAC) method as an alternative to maximum-likelihood attenuation correction factor (ML-ACF) correction in time-of-flight (TOF) brain positron emission tomography (PET) studies. METHODS: In the PAC algorithm, a template emission image [Formula: see text] and a template attenuation coefficient image [Formula: see text] are prepared as a data set based on phantom geometry. Position-aligned attenuation coefficient image [Formula: see text] is derived by aligning [Formula: see text] using parameters that match the template emission image [Formula: see text] to measured emission image [Formula: see text]. Then, attenuation coefficient image [Formula: see text] combined with a headrest image is used for scatter and attenuation correction in the image reconstruction. To evaluate the PAC algorithm as an alternative to ML-ACF, Hoffman 3D brain and cylindrical phantoms were measured to obtain the image quality indexes of contrast and uniformity. These phantoms were also wrapped with a radioactive sheet to obtain attenuation coefficient images using ML-ACF. Emission images were reconstructed with attenuation correction by PAC and ML-ACF, and the results were compared using contrast and uniformity as well as visual assessment. CT attenuation correction (CT-AC) was also applied as a reference. RESULTS: The contrast obtained by ML-ACF was slightly overestimated due to its unique experimental condition for applying ML-ACF in Hoffman 3D brain phantom but the uniformity was almost equivalent among ML-ACF, CT-AC, and PAC. PAC showed reasonable result without overestimation compared to ML-ACF and CT-AC. CONCLUSIONS: PAC is an attenuation correction method that can ensure the performance in phantom test, and is considered to be a reasonable alternative to clinically used ML-ACF-based attenuation correction.

Automatic detection of primary and metastatic lesions on cervicothoracic region and whole-body bone using a uniform machine-learnable approach for [18F]-FDG-PET/CT image analysis.

We propose a method to detect primary and metastatic lesions with Fluorine-18 fluorodeoxyglucose (FDG) accumulation in the lung field, neck, mediastinum, and bony regions on the FDG-PET/CT images. To search for systemic lesions, various anatomical structures must be considered. The proposed method is addressed by using an extraction process for anatomical regions and a uniform lesion detection approach. The uniform approach does not utilize processes that reflect any region-specific anatomical aspects but has a machine-learnable framework. Therefore, it can work as a lesion detection process for a specific anatomical region if it machine-learns the specific region data. In this study, three lesion detection processes for the whole-body bone region, lung field, or neck-mediastinum region are obtained. These detection processes include lesion candidate detection and false positive (FP) candidate elimination. The lesion candidate detection is based on a voxel anomaly detection with a one-class support vector machine. The FP candidate elimination is performed using an AdaBoost classifier ensemble. The image features used by the ensemble are selected sequentially during training and are optimal for candidate classification. Three-fold cross-validation was used to detect performance with the 54 diseased FDG-PET/CT images. The mean sensitivity for detecting primary and metastatic lesions at 3 FPs per case was 0.89 with a 0.10 standard deviation (SD) in the bone region, 0.80 with a 0.10 SD in the lung field, and 0.87 with a 0.10 SD in the neck region. The average areas under the ROC curve were 0.887 with a 0.125 SD for detecting bone metastases, 0.900 with a 0.063 SD for detecting pulmonary lesions, and 0.927 with a 0.035 SD for detecting the neck-mediastinum lesions. These detection performances indicate that the proposed method could be applied clinically. These results also show that the uniform approach has high versatility for providing various lesion detection processes.

High 11 C-Methionine Uptake in a Parasellar Inflammatory Pseudotumor.

ABSTRACT: A 20-year-old man had left visual impairment and homonymous hemianopsia. MRI findings suggested enlargement of an optic glioma, because optic glioma was indicated by MRI 14 years earlier without a definite pathological diagnosis. 11 C-methionine (MET) PET showed high uptake in the tumor in the parasellar region. Transnasal endoscopic biopsy was performed, and an inflammatory pseudotumor (IPT) was diagnosed based on histopathological findings. High MET uptake in a parasellar IPT has apparently not been previously reported. Clinicians should be aware of the possibility of high MET uptake in IPT, because this image could provide an interpretation pitfall.

Initial evaluation of a new maximum-likelihood attenuation correction factor-based attenuation correction for time-of-flight brain PET.

AIM: The aim of this study was to evaluate an image reconstruction algorithm, including a new maximum-likelihood attenuation correction factor (ML-ACF) for time of flight (TOF) brain positron emission tomography (PET). METHODS: The implemented algorithm combines an ML-ACF method that simultaneously estimates both the emission image and attenuation sinogram from TOF emission data, and a scaling method based on anatomical features. To evaluate the algorithm's quantitative accuracy, three-dimensional brain phantom images were acquired and soft-tissue attenuation coefficients and emission values were analyzed. RESULTS: The heterogeneous distributions of attenuation coefficients in soft tissue, skull, and nasal cavity were sufficiently visualized. The attenuation coefficient of soft tissue remained within 5% of theoretical value. Attenuation-corrected emission showed no lateral differences, and significant differences among soft tissue were within the error range. CONCLUSION: The ML-ACF-based attenuation correction implemented for TOF brain PET worked well and obtained practical levels of accuracy.

Diagnostic utility of fusion 18F-fluorodeoxyglucose positron emission tomography/cardiac magnetic resonance imaging in cardiac sarcoidosis.

BACKGROUND: Although each 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and cardiac magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE) has been used to diagnose cardiac sarcoidosis (CS), active CS is still misdiagnosed. METHODS: Active CS, diagnosed by PET alone, was defined as focal or focal on diffuse FDG uptake pattern. In fusion PET/CMR imaging, using a regional analysis with AHA 17-segment model, the patients were categorized into four groups: (1) PET-/LGE-, (2) PET+/LGE-, (3) PET+/LGE+, and (4) PET-/LGE+. PET+/LGE+ was defined as active CS. RESULTS: 74 Patients with suspected CS were enrolled. Between PET alone and fusion PET/CMR imaging, 20 cases had mismatch evaluations of active CS, and most had diffuse or focal on diffuse FDG uptake pattern on PET alone imaging. 40 Patients fulfilled the 2016 the Japanese Circulation Society diagnostic criteria for CS. The interobserver diagnostic agreement was excellent (κ statistics 0.89) and the overall accuracy for diagnosing CS was 87.8% in fusion PET/CMR imaging, which were superior to those in PET alone imaging (0.57 and 82.4%, respectively). In a sub-analysis of diffuse and focal on diffuse patterns, the agreement (κ statistics 0.86) and overall accuracy (81.8%) in fusion PET/CMR imaging were still better. CONCLUSIONS: Fusion PET/CMR imaging with regional analysis offered reliable and accurate diagnosis of CS, covering low diagnostic area by FDG-PET alone.

Vascular/perivascular inflammation in IgG4-related disease.

BACKGROUND: Immunoglobulin G4-related disease (IgG4-RD) is characterized by the infiltration of IgG4-positive plasma cells and fibrosclerotic inflammation in multiple organs. Although vascular complications are present in some patients with IgG4-RD, vascular and/or perivascular inflammatory activity compared to control subjects remains unknown. This study sought to investigate vascular/perivascular inflammation in IgG4-RD patients compared to control subjects using 18F-fluorodeoxyglucose-positron emission tomography combined with computed tomography (FDG-PET/CT). METHODS: We examined 37 consecutive patients diagnosed as IgG4-RD (29 males, mean age of 64.3 ± 8.3 years old), who underwent FDG-PET/CT. Thirty-seven age- and gender-matched subjects without IgG4-RD were employed as controls. Vascular/perivascular inflammation was quantified by blood-normalized standardized uptake value, known as a target-to-background ratio (TBR). RESULTS: All IgG4-RD patients presented with multiple region involvements. Twelve (32.4%) of the IgG4-RD patients had vascular complications, all of which appeared in the abdominal aorta. IgG4-RD patients had significantly higher TBR values in the descending aorta, abdominal aorta, and common iliac artery than control subjects. Also, IgG4-RD patients with vascular complication exhibited higher TBR values in the infra-renal aorta and common iliac artery than those without vascular complication. CONCLUSIONS: We found that vascular FDG activity is significantly elevated in IgG4-RD patients regardless of vascular complication than control subjects. FDG-PET/CT is a useful modality for assessing vascular/perivascular inflammation, which may contribute vascular complication in IgG4-RD patients.

Localization of myocardial FDG uptake for prognostic risk stratification in corticosteroid-naïve cardiac sarcoidosis.

BACKGROUND: The localization of myocardial 18F-fluorodeoxyglucose (FDG) uptake affecting long-term clinical outcomes has not been elucidated in patients with corticosteroid-naïve cardiac sarcoidosis (CS). OBJECTIVES: This study sought to investigate the localization of myocardial FDG uptake on positron emission tomography (PET) and myocardial perfusion abnormality to predict adverse events (AEs) for a long-term follow-up in patients with corticosteroid-naïve CS. METHODS: Consecutive 90 patients with clinical suspicion of CS who underwent FDG-PET imaging to assess for inflammation were enrolled. AEs were defined as a composite of sustained ventricular tachycardia (VT), heart transplantation, and all-cause death, which were ascertained by medical records, defibrillator interrogation, and telephone interviews. RESULTS: Of 90 patients, 42 patients (mean age 62.9 ± 12.0 years; 76.2% females) were confirmed active cardiac involvement. Over a median follow-up of 4.9 years, 15 patients with CS experienced AEs including 6 sustained ventricular tachycardias (VT) and 9 deaths. Cox proportional-hazards model after adjustment for left ventricular systolic dysfunction revealed that FDG uptake in the right ventricle (RV) or basal anterolateral area of the left ventricle (LV) with myocardial perfusion abnormality was predictive of AEs. CONCLUSIONS: FDG uptake in the RV or basal anterolateral area of the LV with myocardial perfusion abnormality provides long-term prognostic risk stratification in patients with corticosteroid-naïve CS.

Quantitative 67Ga-citrate SPECT/CT for evaluating disease activity in patients with interstitial lung disease.

OBJECTIVE: To determine whether results of a standardized uptake value (SUV)-based semi-quantitative analytic method for gallium-67 (67Ga)-citrate single photon emission tomography/computed tomography (SPECT/CT) reflects disease activity in patients with interstitial lung disease. SUBJECTS AND METHODS: Gallium-67-citrate SPECT/CT was used to evaluate disease activity in 24 patients with interstitial pneumoniaon clinical grounds at a single institution from June 2018 to August 2020. SUV in a given volume of interest over the bilateral pulmonary parenchyma was calculated using a dosimetry software package. Correlations of maximum SUV (SUVmax) and mean SUV (SUVmean) with clinical factors, including KL-6, lactate dehydrogenase (LDH), and C-reactive protein (CRP), were evaluated in all 24, as well as in 15 patients with spirometry results using Pearson's rank correlation test. RESULTS: The mean bilateral pulmonary SUVmax value showed a moderately significant correlation with KL-6 (Pearson's correlation coefficient r=0.51, P=0.012) and LDH (r=0.51, P=0.010), a weak non-significant correlation with DLCO% (r=-0.26, P=0.34), and no correlation with CRP (r=-0.01, P=0.94), FVC% (r=0.11, P=0.71), or FEV1.0% (r=0.14, P=0.62). Eleven patients with high KL-6 (≥1000U/mL) were defined as having disease activity. Maximum SUV sensitivity, specificity, and accuracy for predicting interstitial lung disease activity were 72.7%, 76.9%, and 75.0%, respectively, with a best cut-off value of 3.78. CONCLUSION: Semi-quantitative values obtained with 67Ga-citrate SPECT/CT showed a moderate correlation with KL-6 and moderate diagnostic performance for predicting disease activity of interstitial lung disease. It is rather unlikely that quantitative 67Ga-citrate SPECT/CT will have a role into the algorithm of interstitial lung disease.

Usefulness of respiratory-gated PET acquisition during delayed 18F-FDG PET/CT scanning for patients with liver metastases.

OBJECTIVES: To assess respiratory-gated (RG) positron emission tomography (PET) acquisition for patients with liver metastases during delayed PET/computed tomography (CT) scanning with fluorine-18-fluorodeoxyglucose (18F-FDG). METHODS: Nineteen patients with liver metastases who had undergone early whole-body 18F-FDG PET/CT scans without the RG technique and delayed scans with the RG technique were retrospectively selected. The maximum standardized uptake value (SUVmax) of 41 liver lesions and the tumor-to-liver uptake ratios (TLRs) for these same lesions were compared among three data sets: early non-respiratory-gated (early non-RG) images, delayed non-respiratory-gated (delayed non-RG) images, and delayed respiratory-gated (delayed RG) images. In the delayed non-RG and delayed RG images, the improvements in the TLR, relative to the early non-RG images, were assessed according to lesion size. RESULTS: For liver lesions, the SUVmax of early non-RG, delayed non-RG, and delayed RG images were 6.58±2.34, 7.69±3.08, and 9.47±3.73, respectively. There were significant differences among the three images (P<0.01). The TLR of the delayed RG images was significantly higher than those of the early non-RG and delayed non-RG images (P<0.01). In the delayed RG images, the difference in the TLR improvement for lesions ≤10 mm in size was 15% higher than that for lesions >10 mm in size; in the delayed non-RG images, the difference in the TLR improvement for the same lesion categories was 6%. CONCLUSION: Delayed RG imaging improves the TLR, compared with early non-RG and delayed non-RG imaging, especially for small lesions. RG PET acquisition may be a promising protocol for assessing liver metastases on delayed PET/CT scans.