Pitfalls in Positron Emission Tomography/Computed Tomography Imaging:Causes and Their Classifications

Objective To describe the pitfalls in positron emission tomography/computed tomography (PET/CT) imaging and classify them according to the principles of their generation. Methods We summarized retrospectively the 18F-fluorodeoxyglucose (FDP) PET/CT imaging pit-falls through reviewing the PET/CT images of 872 patients. The pitfalls were divided into artifacts and infrequent physiological uptake, and the artifacts were further classified according to their causes. Meanwhile, we calculated the incidences of various pitfalls. Whether the PET/CT pitfalls influenced the diagnostic decision was analyzed. The appearances of pitfalls in PET were also described. Results Pitfalls could be found in PET/CT images of 684 (78.4%) patients. Artifacts were found in 664 (76.15%) patients, and could be classified into self-factor artifacts and equipment-or technology-related artifacts. Among self-factor artifacts, respiratory motion (57.5%), postprandial or hyperglycemia artifacts (2.41%), and metal or high density matter artifacts (1.38%) were frequent. As for equipment- or technology-related factors, injection point outleakage or radiotracer contamination (13.88%) and truncation artifacts (1.83%) were most common ones. Infrequent physiological FDG uptakes, including fatty uptake, endometrial uptake, and bilateral breast feeding period uptake, were found in 20 (2.29%) patients. Among all pitfalls, the artifacts in 92 (13.4%) patients and infrequent physiological uptakes in 6 (0.88%) patients affected the diagnostic results. Artifact images in PET could be described as hot or cold area and the images of infrequent physiological uptake were always shown as hot area. Conclusions The incidence of pitfall in PET/CT imaging was high and the causes of pitfalls are various. Among all causes that artifacts generated, respiratory motion is the most common. Some pitfalls may disturb clinical physicians' decision, so it is important to recognize artifacts and physiological uptake, and distinguish them from pathological uptakes.

COVID-19-associated monocytic encephalitis(CAME):histological and proteomic evidence from autopsy

Severe neurological symptoms are associated with Coronavirus disease 2019(COVID-19).However,the morphologic features,pathological nature and their potential mechanisms in patient brains have not been revealed despite evidence of neurotropic infection.In this study,neuropathological damages and infiltrating inflammatory cells were quantitatively evaluated by immunohistochemical staining,ultrastructural examination under electron microscopy,and an image threshold method,in postmortem brains from nine critically ill COVID-19 patients and nine age-matched cadavers of healthy individuals.Differentially expressed proteins were identified by quantitative proteomic assays.Histopathological findings included neurophagocytosis,microglia nodules,satellite phenomena,extensive edema,focal hemorrhage,and infarction,as well as infiltrating mononuclear cells.Immunostaining of COVID-19 brains revealed extensive activation of both microglia and astrocytes,severe damage of the blood-brain barrier(BBB)and various degrees of perivascular infiltration by predominantly CD14+/CD16+/CD141+/CCR7+/CD11c+monocytes and occasionally CD4+/CD8+T lymphocytes.Quantitative proteomic assays combined with bioinformatics analysis identified upregulated proteins predominantly involved in immune responses,autophagy and cellular metabolism in COVID-19 patient brains compared with control brains.Proteins involved in brain development,neuroprotection,and extracellular matrix proteins of the basement membrane were downregulated,potentially caused by the activation of transforming growth factorβreceptor and vascular endothelial growth factor signaling pathways.Thus,our results define histopathological and molecular profiles of COVID-19-associated monocytic encephalitis(CAME)and suggest potential therapeutic targets.

Comparison of Positron Emission Tomography Using 2-[^18F]-fluoro-2-deoxy-D-glucose and 3-deoxy-3-[^18F]-fluorothymidine in Lung Cancer Imaging

Background： The detection of solitary pulmonary nodules （SPNs） that may potentially develop into a malignant lesion is essential for early clinical interventions. However, grading classification based on computed tomography （CT） imaging results remains a significant challenge. The 2-[^18F]-fluoro-2-deoxy-D-glucose （^18F-FDG） positron emission tomography （PET）/CT imaging produces both false-positive and false-negative findings for the diagnosis of SPNs. In this study, we compared 18F-FDG and 3-deoxy-3-[^18F]-fluorothymidine （^18F-FLT） in lung cancer PET/CT imaging. Methods： The binding ratios of the two tracers to A549 lung cancer cells were calculated. The mouse lung cancer model was established （n = 12）, and micro-PET/CT analysis using the two tracers was performed. Images using the two tracers were collected from 55 lung cancer patients with SPNs. The correlation among the cell-tracer binding ratios, standardized uptake values （SUVs）, and Ki-67 proliferation marker expression were investigated. Results： The cell-tracer binding ratio for the A549 cells using the ^18F-FDG was greater than the ratio using 18F-FLT （P 〈 0.05）. The Ki-67 expression showed a significant positive correlation with the ^18F-FLT binding ratio （r = 0.824, P〈 0.01）. The tumor-to-nontumor uptake ratio of ^18F-FDG imaging in xenografts was higher than that of ^18F-FLT imaging. The diagnostic sensitivity, specificity, and the accuracy of ^18F-FDG for lung cancer were 89%, 67%, and 73%, respectively. Moreover, the diagnostic sensitivity, specificity, and the accuracy of ^18F-FLT for lung cancer were 71%, 79%, and 76%, respectively. There was an obvious positive correlation between the lung cancer Ki-67 expression and the mean maximum SUV of ^18F-FDG and ^18F-FLT （r = 0.658, P〈 0.05 and r = 0.724, P〈 0.01, respectively）. Conclusions： The ^18F-FDG uptake ratio is higher than that of ^18F-FLT in A549 cells at the cellular level.^18F-FLT imaging might be superior for the quantitative diagnosis of lung tumor tissue and could distinguish lung cancer nodules from other SPNs.

Magnetic Resonance Gd？RGD Imaging Study of Hepatocellular Carcinoma with High and Low Metastatic Potential before and after Human Bone Marrow？derived Mesenchymal Stem Cell Intervention

Background： Biotherapy based on human bone marrow-derived mesenchymal stem cells （BMSCs） is currently the focus of research, especially in the field of autologous stem cell transplantation. A novel type of metastasis-associated magnetic resonance （MR） molecular imaging probe was constructed, and the changes in metastasis and proliferation of hepatocellular carcinoma （HCC） before and after BMSC intervention were observed through MR imaging （MRI）. Methods：Metastasis-associatedMRmolecularimagingprobe,integrin αvβ3 ligandcRGD-PEG-DGL-DTPA-Gd （Gd-RGD）,wereconstructed. After human BMSC intervention was performed for 6weeks, tumor weight inhibition rates were calculated, and the RGD molecular probe was imaged through MRI with molecular imaging agent Gd-DTPAas control.The signal-to-noise ratio （SNR） and contrast-to-noise ratio （CNR） in the MRI experiment were used as semi-quantitative indicators. Polymerase chain reaction method was performed to detect proliferation- and metastasis-associated indicators, transforming growth factor β-1 （TGFβ1）, osteopontin （OPN）, and integrin subunit αv and β3. Results： The highest tumor weight inhibition rates were observed 3 weeks after the BMSC transplantation. The MR Gd-RGD in the HCC tissues after the BMSC intervention showed less enhancement than Gd-DTPA. The Gd-DTPAMRI of control group had higher SNR and CNR than Gd-RGD MRI in the experimental groups （P 〈 0.05）. For high metastatic potential hepatocellular carcinoma （MHCC97-H）, significant differenceswereobservedintheSNRsandCNRsofGd-RGDMRIbeforeandaftertheBMSCintervention（P〈0.05）.Forlowmetastaticpotential hepatocellular carcinoma （MHCC97-L）, the CNRs of Gd-RGD MRI were statistically different before and after BMSC intervention （P 〈 0.05）. With regard to MHCC97-H, OPN, β3, and TGFβ1 expression significantly decreased after BMSC intervention （P 〈 0.05）. In MHCC97-L and OPN, β3, TGFβ1, and αv expression after BMSC intervention decreased, and the difference was statistically significant （P 〈 0.05）. Conclusions： The CNR index of MRI is a good indicator for distinguishing high- and low-metastatic potential HCC tissues.After BMSC transplantation of MRI through the two kinds of tracer, the SNR and CNR indexes can distinguish two kinds of high and low metastatic potential HCC tissues, and Gd-RGD imaging is more suitable in distinguishing the metastatic potential changes through BMSC intervention.