Introduction to PET/CT Imaging

Introduction to PET/CT Imaging

Todd M. Blodgett, MD

Alex Ryan, MD

Marios Papachristou, MD

Graphic depicts a typical PET/CT scanner, which houses both CT and PET scanners in a single unit.

Graphic shows the metabolic pathway for FDG. It enters the cell, undergoes the first step of cellular metabolism, but is not further metabolized. FDG is trapped in the cell long enough to appear on images of the patient.



  • Fluorodeoxyglucose (FDG), standard uptake value (SUV), Hounsfield unit (HU), attenuation correction (AC), fine-needle aspiration (FNA)

  • Positive predictive value (PPV), negative predictive value (NPV)


General Anatomic Considerations

  • Hardware approach to image fusion allows accurate registration of anatomic and metabolic images

    • PET and CT scanners are housed in single device

    • Single gantry passes patient through both scanners without interim repositioning

    • Motion between the CT and PET portions of a PET/CT scan will cause significant misregistration


FDG Uptake

  • Enhanced glycolysis in many malignant cells leads to increased FDG uptake

    • Glucose transmembrane transporter glut-1 is overexpressed

  • Not all malignant cells overexpress glut-1 transporter

    • These malignancies may not take up significantly elevated levels of glucose or FDG

  • FDG enters the cell and is a substrate for hexokinase, the first enzyme of glycolysis

  • Hexokinase phosphorylates FDG to FDG-6-phosphate

  • Metabolic activity of FDG ceases at that point and FDG remains trapped in the cell long enough to image the patient



  • History

    • First PET/CT scanner became operational in 1998, and first commercial scanners appeared in 2001

    • Current state of the art incorporates multi detector row CT with high resolution PET scanners

      • Larger patient ports (70 cm or larger)

      • Aids in radiation planning and accommodates increasing dimensions of average patient in USA

  • Technical considerations

    • Smaller detectors contribute to improved resolution

      • For example, 4×4 mm lutetium oxyorthosilicate detectors offer slightly higher PET resolution than 6×6 mm detectors

    • Gadolinium oxyorthosilicate and lutetium oxyorthosilicate scintillators

      • Result in lower rates of both scattered photons and random coincidences compared with bismuth germinate scintillators

      • Generally offers improved whole-body 3D imaging

Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Introduction to PET/CT Imaging

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