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: MRI AND PET-MRI FUSION IMAGES OF PATIENTS WITH DIPG. Top row: Zr-89-bevacizumab PET (144 hrs p.i.) fused with T1-Gd weighted MRI per patient; middle row: T1-Gd weighted MRI; lower row: T2-weighted/FLAIR MR-images. Five tumors show variable uptake of Zr-89-bevacizumab (white arrows), with both PET negative and positive areas within each tumor. Two primary tumors are completely PET negative (Fig. 1C and 1E), while the T2 weighted images show tumor infiltration in the whole pons of both patients. In the middle row, the red arrows represent the areas of contrast enhancement within the tumor. In four out of five primary tumors, the PET-positive area corresponds with the contrast-enhancing area on MRI of the tumors (Fig. 1A, 1B, 1F and 1G). In Fig. 1C, the tumor shows an MRI contrast-enhancing area, while there is no Zr-89-bevacizumab uptake. Fig. 1D shows a PET positive tumor, while no Gd-enhancement is observed on MRI. Credit: Sophie Veldhuijzen van Zanten and Marc Jansen, VU University Medical Center, Amsterdam, The Netherlands.
From left to right are patients with EGFR mutation, KRAS mutation, and EGFR– and KRAS– tumors, respectively. Stage I and III tumors are shown in the top and bottom rows, respectively. Arrows indicate the locations of the lung tumors. Credit: Stephen S.F. Yip, Ph.D., and Hugo Aerts, Ph.D., Dana-Farber Cancer Institute, Brigham and Women’s Hospital, and Harvard Medical School, Boston; John Kim, M.D., University of Michigan Health System, Ann Arbor, Mich.
CTVPOST (red) = CTVPRE (yellow) union CTVPET (pink). Also shown (upper right corner) are the PRE (square) vs POST (triangle) dose volume histograms for PTV1, PTV2, rectum, bladder, and penile bulb, showing minimal impact on target coverage or organs at risk dose with the modified targets. Image courtesy of Ashesh B. Jani, M.D., and David Schuster, M.D., Emory University.