Positron emission tomography (PET) is a nuclear imaging technology (also referred to as molecular imaging) that enables visualization of metabolic processes in the body. The basics of PET imaging is that the technique detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (also called radiopharmaceuticals, radionuclides or radiotracer). The tracer is injected into a vein on a biologically active molecule, usually a sugar that is used for cellular energy. PET systems have sensitive detector panels to capture gamma ray emissions from inside the body and use software to plot to triangulate the source of the emissions, creating 3-D computed tomography images of the tracer concentrations within the body.
Figure 1. Case example: A 54-year-old man with a history of RP+LND and a subsequent PSA of 1.25 ng/mL had no evidence of disease by baseline imaging. Piflufolastat F 18 (18F-DCFPyL)- PET/CT accurately detected biochemically recurrent prostate cancer with the PSMA PET/CT scan identifying positive left (left panel) and right peri-rectal lymph nodes (right panel).
Figure 1. Tau accumulation over one year measured in composite A) mesial temporal ROI; and B) temporoparietal ROI in cognitively unimpaired participants (blue) and cognitively impaired participants (red). The CI group included participants with clinical mild cognitive impairment and dementia. Higher rates of tau accumulation were observed in participants on the AD continuum (CU Aβ+ve and CI Aβ+ve). Participants with the highest baseline tau and rates of tau accumulation were younger and more likely to be CI Aβ+ve. Image courtesy of SNMMI
Figure 1. A: COVID-19-related spatial covariance pattern of cerebral glucose metabolism overlaid onto an MRI template. Voxels with negative region weights are color-coded in cool colors, and regions with positive region weights in hot colors. B: Association between the expression of COVID-19-related covariance pattern and the Montreal Cognitive Assessment (MoCA) score adjusted for years of education. Each dot represents individual patient. C: Results of a statistical parametric mapping analysis. Upper row illustrates regions that show significant increases of normalized FDG uptake in COVID-19 patients at 6-months follow-up compared to the subacute stage (paired t test, p < 0.01, false discovery rate-corrected). Bottom row depicts regions that still show significant decreases of normalized FDG uptake in COVID-19 patients at 6-months follow-up compared to the age-matched control cohort at an exploratory statistical threshold (two-sample t test, p < 0.005). Image Credit: G Blazhenets et al., Department of Nuclear Medicine, Medical Center – University of Freiburg, Faculty of Medicine, University of Freiburg
Result of the Hoffman brain phantom study. Top row: same PET slice reconstructed with A) 2mm static OSEM, B) 1mm static OSEM, C) proposed SR method and D) corresponding CT slice (note that the CT image can be treated as a high-resolution reference). Middle row: zoom on region of interest for corresponding images. Bottom row: Line profiles for corresponding data. Image created by Y Chemli, et al., Gordon Center for Medical Imaging: Department of Radiology Massachusetts General Hospital, Harvard Medical School, Boston, MA.
A) Axial CT images through the mouse lungs at 7 and 14 days after intratracheal administration of bleomycin or saline (as a control), demonstrating increased lung fibrosis in the bleomycin group (white arrows). (B) CT attenuation histograms in Hounsfield units (HU) after lung segmentation demonstrate increased attenuation in the lungs in the bleomycin group than the control group (p <0.05), consistent with increasing fibrosis (n=3). (C) Representative axial PET/CT fusion images at 20 and 60 min demonstrating increased FAPI uptake in the lungs of the bleomycin group (white arrows) with no significant uptake in the control group (yellow arrows). (D) Time-activity curve of lung uptake ROI analysis demonstrating higher FAPI uptake in the lungs of the bleomycin group than the control (p < 0.05), 14 days after bleomycin (n=3). (E) Ex vivo biodistribution data of lung tissue demonstrating higher radiotracer uptake in the lungs of the bleomycin group than the control (n=3). *p<0.05, **p<0.01. Image created by CA Ferreira et al., University of Wisconsin-Madison, Madison, WI.
(A) 57-year-old woman with right upper arm melanoma who received the first dose of the COVID-19 vaccine (Pfizer-BioNTech) in the left deltoid 15 days prior to FDG PET/CT. FDG uptake is observed within left axillary lymph nodes (arrow, SUVmax = 9.3).
(B) 62-year-old man with metastatic prostate carcinoma who received the second dose of COVID-19 vaccine (Pfizer-BioNTech) in the right deltoid 7 days prior to 11C-choline PET/CT. 11C-choline uptake is observed within right axillary lymph nodes (arrows, SUVmax = 3.1) as well as the right deltoid muscle (circle, SUVmax = 1.7).
After radiosurgery concurrent with nivolumab in 59-year-old patient with melanoma BM (patient 1; Supplemental Tables 3 and 5), F-18 FET PET at follow-up 12 weeks after treatment initiation (bottom row) shows significant decrease of metabolic activity (TBRmean, ?28%) compared with baseline (top row), although MRI changes were consistent with progression according to iRANO criteria. Reduction of metabolic activity was associated with stable clinical course over 10 mo. CE = contrast-enhanced. Image created by N. Galldiks et al., Research Center Juelich, Juelich, Germany.
Axial fused PET/CT image shows intense uptake (arrowhead) in the deep pelvis corresponding to the left lobe of the prostate in a 62-year-old with a history of prostate cancer treated with radiation therapy. The CT scan does not show the tumor. Image courtesy of the the Radiological Society of North America.