Jessica KishimotoThe University of Western OntarioMedical Biophysics UndergradApril 7, 2010

The Effect of Dose on Image Quality When Using an Image Based Proximity Mapping Technique

The Effect of Dose on Image Quality

when using an Image Based

Proximity Mapping TechniqueJessica KishimotoThe University of Western OntarioMedical Biophysics UndergradApril 7, 2010

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

Hypothesis

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

Objectives

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

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.

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.

Results

Low dose High dose

Results

Super low dose High dose

Results

Low dose

Medium dose

High dose

ResultsOverlapping low and medium dose Red – low, beige - medium

Results

Medium dose Low dose

Results

Low dose

Results

Medium dose

Discussion

There appears to be large differences between the low, medium and high 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

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.