Impact of Dose on Image Quality in Proximity Mapping Technique

1. The Effect of Dose on Image Quality When Using an Image Based Proximity Mapping Technique Jessica Kishimoto The University of Western Ontario Medical Biophysics Undergrad April 7, 2010

2. The Effect of Dose on Image Quality when using an Image Based Proximity Mapping Technique Jessica Kishimoto The University of Western Ontario Medical Biophysics Undergrad April 7, 2010

3. Introduction • A previously developed technique called proximity mapping has been developed to non-invasively examine joint congruency using reconstructed images acquired using x-ray computed tomography (CT) • One concern with this approach however, is exposure to unnecessarily high amounts of radiation

4. Hypothesis • There will be a dose of CT which will allow for good images, but minimize the risk associated with excess radiation

5. Objectives • To show the differences between high and low dose images, and whether or not these differences might be diagnostically important.

6. What is ‘dose’? • This is value calculated from measured radiation exposure and an estimate of the amount absorbed by different body tissues • This is measured in CTDIvol, which is the CT Dose Index, and measures the average dose over the scanned volume • The normal parameters of a scan are 100mA and a pitch of 0.984, which would result in a dose of around 8 CTDIvol.

7. Methods • Multiple raw images from CT scans at different doses were used to reconstruct a 3D image • Cropping was then used to remove either the humerus/scapula components to isolate the bone of interest • Thresholding was employed to create the best the bone. • Smoothing was used when creating the bone model if the images were really bad • Using a proximity mapping program, it was possible to deteremine where the modeled bones were articulating.

8. Results Low dose High dose

9. Results Super low dose High dose

10. Results Low dose Medium dose High dose

11. Results Overlapping low and medium dose Red – low, beige - medium

12. Results Medium dose Low dose

13. Results Low dose

14. Results Medium dose

15. Discussion • There appears to be large differences between the low, medium andhigh dose images. • Perhaps part of this is due to different thresholds used to create the images • Instead of having the goal of the ‘best’ image • By using the same threshold for all images they could be more similar

16. Conclusion • There appears to be a difference, which could cause diagnostic errors in between high and low dose images. • This needs to be investigated much further before any real conclusions can be made towards the optimal amount of dose needed to create a good image.