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Before the injection of the radiopharmaceutical, the assistants inform the patient about the course of the examination. When sufficient time (1 hour) has passed after the injection for the activity distribution to be formed, the patient lies on the table of the PET/CT device.
First a so-called topogram is taken of the patient, the hands are placed above the head. It is practically a rapid X-ray image taken of the patient by pushing them through the CT component of the device. The image below shows a topogram.

Figure 1. Topogram (from Scanomed Ltd. education material)

The specialist can mark the areas to be examined by the PET and the CT scanner on the topogram. After that the acquisition of PET data begins. For a whole-body scan (or even for an abdominal PET/CT) data usually have to be obtained from more, partially overlapping fields of view. The machine collects data for 3 minutes from one field of view, then moves the table to the next position, thus it can collect data from a different field of view. Overlapping is needed because of the sensitivity profile of the field of view (sensitivity is lower at the edge of the field of view). When the PET acquisitions are finished, the patient is moved to the CT component of the device and the CT image is taken of the selected area. The duration of the whole examination is about 20 minutes (it of course depends on the type of the device and on the settings). Software is provided by the manufacturer for each device for performing the examinations and the reconstruction of images.

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