(http://topicsinradiography.com/wp-content/upLoads/small-podcast-logo-episode-art-150x150.jpg)The importance of collimation was ingrained in my mind by my instructors and by the technologists who oversaw my clinical education.  Radiologists used to grill me when I failed to collimate an exposure.  To everyone critiquing a radiograph, this was evidence that you did not perform an aspect of basic radiation protection principles that we all learn very early in our education.  But with the adoption of digital imaging and the ability to crop and set the black-surround feature covering the unexposed region of our images, it seems we’ve gotten out of the habit of providing the appropriate amount of collimation.  It seems to be an adopted method for technologists to save time, or improve efficiency to simply open the field and crop later rather than to risk a repeat exposure.  But really, it's a poor excuse which increases patient dose and has a negative effect on image quality.  Now more than ever, appropriate collimation is a practice that should be encouraged by all radiologic technologists for patient safety and its increased impact on digital imaging compared to film/screen.
In this particular episode, you will learn:

* The responsibility of the technologist in providing appropriate collimation
* Similarities and differences in collimation between film/screen and digital imaging
* Why appropriate collimation is essential for digital imaging
* How to tell if collimation was used vs. cropping
* Legal aspects of appropriate collimation
* Accountability for the technologist in failure to collimate appropriately
* Dose impact for patients

Images discussed in this podcast episode:
(http://topicsinradiography.com/wp-content/upLoads/lspine.jpg)

 

These images of a lumbar spine phantom produced in the radiography lab at San Diego Mesa College portray unaltered images post-processing, with black-surround borders removed.  I used 80 kVp and 32 mAs in the table bucky with a 40" SID for both images - the only variable was the collimation.

(http://topicsinradiography.com/wp-content/upLoads/Lspine-Collimation1.jpg)

 

This compares the two images after cropping - notice cropping does not change the appearance of the images.

 

(http://topicsinradiography.com/wp-content/upLoads/foot.jpg)

 

I tried this on a thinner anatomical part here, and there is a noticeable difference, however it is not as extreme.  Both images were exposed using 60 kVp and 1.8 mAs tabletop at a 40" SID.  The image on the left (uncollimated) was about 30% overexposed according to the exposure indicator, while the collimated image on the right was within acceptable limits.

 

(http://topicsinradiography.com/wp-content/upLoads/Evidence-of-Collimation.jpg)

 

Looking for evidence of cropping vs. evidence of collimation.  You should be able to have a super-user or the vendor adjust the distance between the detected edge of the exposure field and where the black-surround region begins.

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