Quantitative performance and optimal regularization parameter in block sequential regularized expectation maximization reconstructions in clinical 68Ga-PSMA PET/MR.

BACKGROUND: In contrast to ordered subset expectation maximization (OSEM), block sequential regularized expectation maximization (BSREM) positron emission tomography (PET) reconstruction algorithms can run until full convergence while controlling image quality and noise. Recent studies with BSREM and F-FDG PET reported higher signal-to-noise ratios and higher standardized uptake values (SUV). In this study, we investigate the optimal regularization parameter (β) for clinical Ga-PSMA PET/MR reconstructions in the pelvic region applying time-of-flight (TOF) BSREM in comparison to TOF OSEM. Two-minute emission data from the pelvic region of 25 patients who underwent Ga-PSMA PET/MR were retrospectively reconstructed. Reference OSEM reconstructions had 28 subsets and 2 iterations. BSREM reconstructions were performed with 15 β values between 150 and 1200. Regions of interest (ROIs) were drawn around lesions and in uniform background. Background SUVmean (average) and SUVstd (standard deviation), and lesion SUVmax (average of 5 hottest voxels) were calculated. Differences were analyzed using the Wilcoxon matched pairs signed-rank test. RESULTS: A total of 40 lesions were identified in the pelvic region. Background noise (SUVstd) and lesions SUVmax decreased with increasing β. Image reconstructions with β values lower than 400 have higher (p < 0.01) background noise, compared to the reference OSEM reconstructions, and are therefore less useful. Lesions with low activity on images reconstructed with β values higher than 600 have a lower (p < 0.05) SUVmax compared to the reference. These reconstructions are likely visually appealing due to the lower background noise, but the lower SUVmax could possibly render small low-uptake lesions invisible. CONCLUSIONS: In our study, we showed that PET images reconstructed with TOF BSREM in combination with the Ga-PSMA tracer result in lower background noise and higher SUVmax values in lesions compared to TOF OSEM. Our study indicates that a β value between 400 and 550 might be the optimal compromise between high SUVmax and low background noise

The Monocle Sign in FDG-PET: A Sign of Contralateral Facial Nerve Palsy

We report three cases of unilateral F-FDG uptake in the orbicularis oculi muscle in subjects with contralateral peripheral facial nerve palsy. We argue that this asymmetric uptake pattern in fact reflects lack of metabolism on the side affected by facial nerve palsy, owing to denervation. Since the unilateral periorbital uptake resembles a monocle, we chose to call this finding the monocle sign. The monocle sign should not be confused with inflammation or tumor, but should prompt a neurological assessment for facial nerve palsy and a potential underlying disease

Positron Emission Tomography

Positron emission tomography (PET) was clinically introduced in the 1970s and has since become one of the most important diagnostic imaging modalities in oncology. Today, it is exclusively used as a hybrid imaging modality in conjunction with either computed tomography (CT) as PET/CT, introduced in 2001, or magnetic resonance (MR) imaging as PET/MR, introduced in 2011 (Beyer et al., J Nucl Med 41:1369–1379, 2000; Ng et al., Med Phys 37:1995–2003, 2010). The anatomic imaging component (CT or MR) complements PET with the spatial location of structures and morphological features of tissues, such as the texture of parenchymal organs or the contrast enhancement of vessels, which essentially depends on the electron density of the tissue (CT) or its proton density and relaxation properties (MR). Keywords Positron emission tomography Fluorodeoxyglucose Radiopharmaceuticals Neuroimagin

l-Lactate metabolism in HEP G2 cell mitochondria due to the l-lactate dehydrogenase determines the occurrence of the lactate/pyruvate shuttle and the appearance of oxaloacetate, malate and citrate outside mitochondria

As part of an ongoing study of l-lactate metabolism both in normal and in cancer cells, we investigated whether and how l-lactate metabolism occurs in mitochondria of human hepatocellular carcinoma (Hep G2) cells. We found that Hep G2 cell mitochondria (Hep G2-M) possess an l-lactate dehydrogenase (ml-LDH) restricted to the inner mitochondrial compartments as shown by immunological analysis, confocal microscopy and by assaying ml-LDH activity in solubilized mitochondria. Cytosolic and mitochondrial l-LDHs were found to differ from one another in their saturation kinetics. Having shown that l-lactate itself can enter Hep G2 cells, we found that Hep G2-M swell in ammonium l-lactate, but not in ammonium pyruvate solutions, in a manner inhibited by mersalyl, this showing the occurrence of a carrier-mediated l-lactate transport in these mitochondria. Occurrence of the l-lactate/pyruvate shuttle and the appearance outside mitochondria of oxaloacetate, malate and citrate arising from l-lactate uptake and metabolism together with the low oxygen consumption and membrane potential generation are in favor of an anaplerotic role for l-LAC in Hep G2-M

Detection Rate of ¹⁸F-Labeled PSMA PET/CT in Biochemical Recurrent Prostate Cancer: A Systematic Review and a Meta-Analysis

Background: The use of radiolabeled prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) for biochemical recurrent prostate cancer (BRPCa) is increasing worldwide. Recently, 18F-labeled PSMA agents have become available. We performed a systematic review and meta-analysis regarding the detection rate (DR) of 18F-labeled PSMA PET/CT in BRPCa to provide evidence-based data in this setting. Methods: A comprehensive literature search of PubMed/MEDLINE, EMBASE, and Cochrane Library databases through 23 April 2019 was performed. Pooled DR was calculated on a per-patient basis, with pooled proportion and 95% confidence interval (95% CI). Furthermore, pooled DR of 18F-PSMA PET/CT using different cut-off values of prostate-specific antigen (PSA) was obtained. Results: Six articles (645 patients) were included in the meta-analysis. The pooled DR of 18F-labeled PSMA PET/CT in BRPCa was 81% (95% CI: 71&#8722;88%). The pooled DR was 86% for PSA &#8805; 0.5 ng/mL (95% CI: 78&#8722;93%) and 49% for PSA &lt; 0.5 ng/mL (95% CI: 23&#8722;74%). Statistical heterogeneity was found. Conclusions: 18F-labeled PSMA PET/CT demonstrated a good DR in BRPCa. DR of 18F-labeled PSMA PET/CT is related to PSA values with significant lower DR in patients with PSA &lt; 0.5 ng/mL. Prospective multicentric trials are needed to confirm these findings

Fluoro-deoxy-glucose uptake in the mylohyoid muscle: a common misconception

AIM The mylohyoid muscle is often believed to exhibit high physiologic fluoro-deoxy-glucose (FDG) uptake. Aim of this study was to use PET/MR for adequately assessing the normal FDG distribution in floor of the mouth (FOM) muscles and neighboring major salivary glands. MATERIALS AND METHODS Patients scanned with a simultaneous PET/MRI system for initial staging or follow-up of head and neck tumors, with no malignant lesions in salivary glands or in FOM, were included. Volumes-of-interest (VOIs) were positioned separately for bilateral mylohyoid, digastric, genioglossus, and geniohyoid muscles, based on T2-weighted and T1-weighted images, and for bilateral parotid, submandibular, and sublingual glands in the same way. SUVmax was measured for each VOI. RESULTS Six hundred and ninety-two VOIs were positioned. FDG uptake in mylohyoid (SUVmax = 1.94 ± 0.37) and digastric muscles (SUVmax = 2.01 ± 0.37) were significantly higher compared to that in geniohyoid (SUVmax = 1.67 ± 0.53) and genioglossus muscles (SUVmax = 1.75 ± 0.54) (Friedman's test; P < 0.001). FDG uptake in the sublingual glands (SUVmax = 3.77 ± 1.63) was significantly higher compared to the parotid glands (SUVmax = 2.34 ± 0.60) and submandibular glands (SUVmax = 2.51 ± 0.59) (Wilcoxon signed-ranks test; P < 0.001). FDG uptake in sublingual glands was significantly higher than FDG uptake in the mylohyoid muscles (P < 0.001). FDG uptake in the parotid, submandibular, and sublingual glands was inversely correlated to the age of subjects (Spearman' rho coefficient: -0.397/P = 0.004; -0.329/P = 0.021; -0.535/P < 0.001, respectively). CONCLUSION The sublingual glands yield the highest physiologic FDG uptake in the FOM. High FDG uptake in the mylohyoid muscle is a common misconception

Quantitative performance and optimal regularization parameter in block sequential regularized expectation maximization reconstructions in clinical 68Ga-PSMA PET/MR

Abstract Background In contrast to ordered subset expectation maximization (OSEM), block sequential regularized expectation maximization (BSREM) positron emission tomography (PET) reconstruction algorithms can run until full convergence while controlling image quality and noise. Recent studies with BSREM and 18F-FDG PET reported higher signal-to-noise ratios and higher standardized uptake values (SUV). In this study, we investigate the optimal regularization parameter (β) for clinical 68Ga-PSMA PET/MR reconstructions in the pelvic region applying time-of-flight (TOF) BSREM in comparison to TOF OSEM. Two-minute emission data from the pelvic region of 25 patients who underwent 68Ga-PSMA PET/MR were retrospectively reconstructed. Reference OSEM reconstructions had 28 subsets and 2 iterations. BSREM reconstructions were performed with 15 β values between 150 and 1200. Regions of interest (ROIs) were drawn around lesions and in uniform background. Background SUVmean (average) and SUVstd (standard deviation), and lesion SUVmax (average of 5 hottest voxels) were calculated. Differences were analyzed using the Wilcoxon matched pairs signed-rank test. Results A total of 40 lesions were identified in the pelvic region. Background noise (SUVstd) and lesions SUVmax decreased with increasing β. Image reconstructions with β values lower than 400 have higher (p < 0.01) background noise, compared to the reference OSEM reconstructions, and are therefore less useful. Lesions with low activity on images reconstructed with β values higher than 600 have a lower (p < 0.05) SUVmax compared to the reference. These reconstructions are likely visually appealing due to the lower background noise, but the lower SUVmax could possibly render small low-uptake lesions invisible. Conclusions In our study, we showed that PET images reconstructed with TOF BSREM in combination with the 68Ga-PSMA tracer result in lower background noise and higher SUVmax values in lesions compared to TOF OSEM. Our study indicates that a β value between 400 and 550 might be the optimal compromise between high SUVmax and low background noise

Improved detection of in-transit metastases of malignant melanoma with BSREM reconstruction in digital [18F]FDG PET/CT

Objectives: To compare block sequential regularized expectation maximization (BSREM) and ordered subset expectation maximization (OSEM) for the detection of in-transit metastasis (ITM) of malignant melanoma in digital [18F]FDG PET/CT. Methods: We retrospectively analyzed a cohort of 100 [18F]FDG PET/CT scans of melanoma patients with ITM, performed between May 2017 and January 2020. PET images were reconstructed with both OSEM and BSREM algorithms. SUVmax, target-to-background ratio (TBR), and metabolic tumor volume (MTV) were recorded for each ITM. Differences in PET parameters were analyzed with the Wilcoxon signed-rank test. Differences in image quality for different reconstructions were tested using the Man-Whitney U test. Results: BSREM reconstruction led to the detection of 287 ITM (39% more than OSEM). PET parameters of ITM were significantly different between BSREM and OSEM reconstructions (p < 0.001). SUVmax and TBR were higher (76.5% and 77.7%, respectively) and MTV lower (49.5%) on BSREM. ITM missed with OSEM had significantly lower SUVmax (mean 2.03 vs. 3.84) and TBR (mean 1.18 vs. 2.22) and higher MTV (mean 2.92 vs. 1.01) on OSEM compared to BSREM (all p < 0.001). Conclusions: BSREM detects significantly more ITM than OSEM, owing to higher SUVmax, higher TBR, and less blurring. BSREM is particularly helpful in small and less avid lesions, which are more often missed with OSEM. Key points: • In melanoma patients, [18F]FDG PET/CT helps to detect in-transit metastases (ITM), and their detection is improved by using BSREM instead of OSEM reconstruction. • BSREM is particularly useful in small lesions. Keywords: Algorithms; Fluorodeoxyglucose F18; Melanoma; Positron Emission Tomography / Computed Tomography; Skin neoplasms