Hi everyone. Earlier in the course, Positron Emission Tomography
or PET was introduced along with PET/CT scanners like the one that you can see in the picture here.
This particular scanner has separate PET and CT rings or gantries, however many other modern
PET/CT systems encapsulate these within one gantry. So now let's discuss and take a
look at what happens during a typical PET/CT imaging process, from the time a patient arrives
at the PET centre to when the imaging process is complete. After arriving at the PET centre,
the patient is usually interviewed by a clinician to discuss aspects of their medical history
and the reason for the scan. Often factors like diet are important as these may influence
uptake of the radiopharmaceutical in the patient's body. For instance, patients are often required
to fast for a prescribed time before a PET scan, particularly when a radiopharmaceutical
such as fluorodeoxyglucose or FDG is to be used.
The patient then changes out of their street clothes into a gown and removes any metal
objects that may appear in the scanning field. You might remember from the earlier section
on computerised tomography or CT that dense objects are seen on CT scans. Because this
scanner uses PET combined with CT, metal objects such as jewellery may interfere with the imaging.
The patient is weighed and transferred to an injection room.
The quantity of radiopharmaceutical injected into the patient is usually determined by
the patient's weight. The radiopharmaceutical injection is prepared accordingly and the
radiopharmaceutical is then administered intravenously by a nuclear medicine technologist, just as
you can see in the video. When using FDG, the patient rests for up to
an hour while the radiopharmaceutical distributes around the body. In this case, it is important
that the patient remains relaxed because along with diseases like many cancers, active muscle
will take up FDG which may be detrimental to the image quality.
The patient is then transferred onto the bed of the PET/CT scanner. This bed is then moved
into the gantry of the scanner so that the patient can be positioned correctly for the
scan. The red beams of light that you can see are
to assist with the positioning of the patient. The technologist sets up the scan along with
the imaging protocols from a workstation in the control room.
A low dose CT scan called a scout scan is then performed to further assist with the
positioning of the patient and the set-up of the scanner. This scout scan is completed
relatively quickly. Once the settings have been optimised, scanning begins, first with
a CT scan and then a PET scan. During this process, the patient is moved through the two
rings or gantries of the scanner: one for CT and the other for PET. The CT component
emits X-rays from one side of its gantry that pass through the patient and are detected by
the CT's receiver at the opposite side. Conversely for PET, the detectors located
in the gantry detect gamma rays that are emitted from the radiopharmaceutical that is distributed
inside the patient. During the PET scan, the patient moves through
the gantry relatively slowly, at a rate of about 1 small bed movement every 1 to two
minutes. So depending on what areas of the patient's body are to be scanned, for instance
whether the scan is a whole body or head and neck scan, determines how long the patient
needs to be on the scanner. So a PET/CT scan may take about 20 minutes to an hour.
After the scanning is complete, the technologist or nursing staff remove the canula from the
patients arm. The patient is then allowed to get changed back into their clothes and
are free to go. The images acquired during the scan are reconstructed
to appear as multiple slices, as three dimensional images, and as fused images where the PET
and CT image are combined to give information on function and structure within the patient.
The clinician uses these images to assess disease such as cancer and provides a report
of the findings of the PET/CT scan to assist with patient management.
So now you have an understanding of the patient's experience during a PET/CT scan. I hope that
you enjoyed this video and found it informative.