Pseudo-Random Attenuating Screen

The Pseudo-Random Attenuating Screen (Figure 1) will take the place of the current gamma filter that is placed over the SPECT camera. This will allow for more gamma rays to pass through to the detectors thus facilitating rapid imaging. The current gamma filter (the collimator shown in Figure 2) is quite inefficient because it only allows gamma rays arriving parallel to its lead tubes to go through. The attenuation screen must be able to appropriately attenuate gamma rays within an energy range of 50-350 keV, not have pattern overlap between different gamma detectors on the camera, and fit directly over the camera where the current filter is placed.

As shown in Figure 1, the Screen is comprised of two key elements: the Screen Case and the Gel Mixture.

SCREEN CASE

The case was designed to fit over the Digirad Camera Head at Thornton Hospital (Figure 3) and was constructed out of acrylic.

Acrylic was chosen chiefly because it provided minimal to no gamma ray attenuation. The fit requirement determined the dimensions of the parts of the case/container as described below:

[ALL UNITS ARE IN MILLIMETERS]

Attenuating Screen Short Side           Specs (View    Download SolidWorks)

Attenuating Screen Long Side           Specs (View    Download SolidWorks)

Attenuating Screen Base                   Specs (View    Download SolidWorks)

In order to build the case/container, two of each components is needed. The long sides, the short sides, and one base are then glued together using acrylic glue. The second base is then used as a cover for the entire case. 

The handles of the case were 3-D printed and designed such that they fit in the handle cutout of the Camera Head as can be seen in Figure 3. The parameters of the different handle components are described below:

[ALL UNITS ARE IN MILLIMETERS]

                             Handle                 Specs (View      Download SolidWorks)

                      Handle Bar                 Specs (View      Download SolidWorks)

                      Handle Pin                 Specs (View      Download SolidWorks)

Two sets of handle and handle bar are needed along with four sets of the pin to complete the pair of Screen Handles.

GEL MIXTURE

The Gel Mixture is comprised of Ballistic Gel, 4-mm Steel Ball Bearings, and Polycarbonate Pellets. Information on each component can be found by clicking on the item. The procedure for creating the gel is detailed below: