Question

In a few sentences and include a simple sketch and make it clear if you handwriting

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How does the positron emission tomography (PET scan) work ?

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In a few sentences and include a simple sketch and make it clear if you handwriting

Answer 1

PET scanning uses elements of computer aided cross sectional imaging (similar to CT and MRI scanning) and nuclear medicine imaging.

In CT and MRI, images are obtained by bombarding the area of interest with an outside "force" if you will (in CT - X rays are sent into the body; in MRI - a radiofrequency (RF) wave is sent into the body in the setting of a strong magnetic field). What is measured is how the cells in the body react to these perturbations. In CT, cells absorb the X rays differently and in MRI, cells emit different RF frequencies after the RF pulse is sent in. Mathematical formulae then create images in three dimensions based on the data collected

In PET, a substance is injected into the body and taken up by metabolically active tissue. The tracer injected is most commonly fluorodeoxyglucose (FDG) which the body treats as glucose, a metabolic substrate for all cells (meaning cells use it for "food").

The more active a region of metabolic activity (such as cancer cells), the more uptake of FDG. The gamma rays given off by the labeled FDG are picked up by detectors in a ring around the patient and using complex mathematical formulae a 3D image is obtained.

Conversely, PET can be used to look for decreased metabolic activity in regions of the heart after heart attacks or in the brain with diseases such as Alzheimer's. Abnormal brain activity can be seen in some psychiatric conditions.

Since the spatial orientation of PET scans is limited (i.e., the image acquired is not very detailed), a fusion scan with a near simultaneous CT is often obtained (and less commonly, MRI is used). Now you can overlay the two images obtained so you can see exactly where the PET 'activity" is increased anatomically.

For example, using PET/CT, one can distinguish exactly which lymph node appears to have cancer in it as it has increased activity (it's "glowing" due to increased metabolic activity seen in cancer). Thus a directed biopsy can be performed if necessary for further diagnosis.