Compared to 3D imaging, how does the sensitivity of 2D imaging differ due to septa usage?

In the context of positron emission tomography (PET), the use of septa in 2D imaging significantly influences the system's sensitivity. When septa are used in the detection of gamma rays, they help to collimate the incoming radiation, effectively blocking scatter and subsequently allowing for more accurate detection of coincident events. However, this collimation comes at a cost.

The presence of septa in 2D imaging restricts the number of detected events because the system can only collect data from photons that travel through specific paths defined by the openings of the septa. This limits the effective area available for photon detection compared to a 3D imaging setup, where no septa are employed. In 3D imaging, the system can utilize all detected photons, including those that might scatter, thereby enhancing the overall sensitivity.

As a result, due to this restriction, 2D imaging actually achieves lower sensitivity when compared to 3D imaging, often quoted as being 4 to 10 times less sensitive. This is because it captures a smaller fraction of the available coincidence events, which can ultimately lead to lower-quality images and reduced diagnostic capability in clinical practice. Therefore, the answer accurately reflects the fundamental differences in sensitivity attributed to the sept