Number and Diameter of tantalum beads to reliably determineCarpal Bone orientation

[Anwar Upal]

Dear biomech-L readers:

We have developed software to examine carpal bone kinematics using the
principal axis algorithm. We need to verify that the algorithm can
reliably compute the change in orientation of a bone as it moves from one
position to the next from CT scans. So we are embedding tantalum beads in
each of the carpal bones of one cadaver wrist. We will CT this wrist in
five different positions, pick out the beads, and calculate the change in
orientation from the tantalum beads. We will compare the change in
orientation calculated from the tantalum beads with the change in
orientation calculated by the principal axis algorithm from the CT scans.

Due to the small size of the wrist bones, we must put in the minimum
possible number of beads. However, we must pick up a minimum of 3
non-linear beads to get the orientation of the bones. We will CT the wrist
at 1.25mm slice width with approximately 0.30mm X 0.30mm pixel size. I
have two questions for researchers with experience in using tantalum beads
for a similar experiment:

1) how many beads would you recommend that we put in each bone?
2) what is the smallest bead diameter that you can recommend to reliably
pick up the beads using a 1.25mm CT slice width?

Thanks in advance for your help.

Sincerely,
Anwar

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