The current rate structure is:
- $134/hr - basic scanning acquisition (includes scanner operator)
- $24/hr - high-resolution reconstruction, data analysis, and visualization.
- For external clients the University imposes an indirect or overhead charge of 45 to 50% depending of the nature of the client.
The immediate question however is what can be accomplished in an hour?
The actual cost of a specific study depends primarily on the time needed to acquire the data and on the extent of analysis needed. We make every effort to design the technique used to provide the needed information at optimal cost. There are several choices and settings that affect image quality, resolution, and time required for scanning. Among these are:
- Medical versus industrial CT
- Length/diameter ratio of object
- Image thickness
- X-ray source power
- Number of views recorded
Other factors that affect the time needed are the object's shape, and its overall X-ray density. As an example, consider a
cylindrical sample of a material with the average density of aluminum. To be more specific, let’s assume its 12 mm in
diameter and 60 mm long. We desire to scan it at maximum possible resolution in the OMNI-X industrial scanner.
We would adjust the magnification so that the diameter of the sample covers the entire width of the detector, approximately
1000 pixels. The in-plane voxel size and the slice thickness would be 12 microns. Collecting 40 or 50 slices at a time, each
sample rotation would cover about 0.6 mm of sample length so that 100 rotations would be needed to cover the entire sample
Using 2400 views (i.e. every 0.15 degrees) results in medium quality data for this type of sample and would take about 10 minutes per rotation for a total of 1000 minutes or 16.7 hours … about $2800 plus about $80 in computer facility usage for off-line high-resolution reconstruction.
How can cost be reduced and what are the tradeoffs?
There are basically two options. One is to reduce image quality by taking fewer views. This decreases the signal-to-noise
ratio and produces a “noisier” image…one with more “snow” in it.
Cutting the number of views in half would reduce acquisition time by about 40% (part of the time needed for
each rotation is taken up in mechanical and computational overhead). This would bring the study cost down
to about $1680.
The other option is to reduce the magnification, say by half, so that the shadow of the object covers only 500 pixels, making each of them 24 x 24 x 24 microns. Now each rotation would cover 1.2 mm of sample length and only 50 rotations would be needed. This reduces the cost directly by 50% down to $1400. If both options were applied, the cost would be about $840, (again plus minor reconstruction costs) at a penalty of lower resolution.
Other cost saving methods
Here are additional ways of reducing the costs of scanning this piece:
- Use the medical scanner. Here the smallest slice thickness is 1 mm, resulting in 60 individual scans. The finest voxel dimensions would be 250 x 250 x 1000 microns and the sample would be only 48 pixels across. On the other hand, the scanning time could be as little as 15 minutes costing about $50.
- Staying with the industrial scanner, it would be possible to increase the number of slices taken with each rotation. This increases the axial angle at which the X-rays are passing through the sample resulting in parallax and less clear connections between the last image of one rotation and the first image of the next. It again decreases the number of rotations needed to cover the sample, decreasing the cost proportionally.
Explanation of Cost Structure
As a public institution frequently engaged in government contracts, and whose equipment has been partially obtained using government funds, our rate structure must comply with Defense Contract Audit Agency rules. Specifically, the facility itself is operated on a cost-recovery-only basis. The hourly rate is negotiated based on actual annual operating expense prorated by the number of hours it is in use annually. This rate is reviewed periodically to assure its current accuracy.
The current rate structure covers our X-ray CT and Computer facilities separately to allow unbundling of data acquisition and data analysis functions. Both rates cover facility maintenance, and routine expendables. The data acquisition rate also includes operator costs. However the computer facility rate covers only the minimal operator costs needed for high-resolution reconstruction, data preparation, transmittal, and archiving. More extensive data handling, including visualization and quantitative analysis, require negotiation of faculty time needed for the analysis. The current rates are $134/hr (US) for data acquisition and $28/hr for use of the computer facility. Both rates are subject to applicable overhead charges for clients outside the Pennsylvania State University. These overhead rates change annually and are currently 45% for academic and government contracts and 50% for commercial contracts.