Academy of Chiropractic’s

MD Relationship Program

#11 Clinical Information and Documentation

Biomechanical Assessment and Scaling Digital Radiographs

From:  William J Owens Jr DC DAAMLP

In recent years we have see the mass conversion of x-rays from film to digital.  Measurations on radiographs is a large part of the biomechancial assessment of our patients but if you are referring out for radiographs OR your patient comes into the office with a CD of images you have to understand how the films were shot.  The Focal Film Distance (FFD) or also called the Source-Image Distance (SID) is a very important component to consider since it effects the magnification, distortion and x-ray beam intensity (penetration).  Here are more exact definitions of each of these definitions.  Below is an example of where to find this “scale” on your PACS or CD images.  Attached is the OPEN ACCESS article discussing PACS, it is from 2000, but I think it gives a nice review of the concept, the past and the future.  Good learning tool. 

A picture archiving and communication system (PACS) is a computerised means of replacing the roles of conventional radiological film. This review describes the Hammersmith PACS, and discusses the advantages and disadvantages of PACS systems.
(Arch Dis Child 2000;83:82–86)
Keywords: PACS; filmless radiology
Focus film distance (FFD) is the distance between the X-ray source and the film in diagnostic radiography. It has recently been superseded due to the replacement of film with computed radiography or direct digital radiography detectors. There are now various possible alternatives: source to image-receptor distance (SID); focus image distance (FID); source receptor distance (SRD); and focus receptor distance (FRD).
If you do NOT see the scale, call the radiology facility – they will be able to point you in the right direction, unfortunately there is no standardization on PACS technical layout and toolbars, they are “Proprietary” (AKA Pain in the Ass).  Sometimes the tool bars are hidden at the top, so you have to right click on them to activate the FULL TOOLBAR.  Other times the images that are included on the CD (online versions are different as you have access to the server directly) are scaled down d/t limits on space.  If you are seeing CRAPPY images, call them and get ONLINE access.  All MRI Facilities have online access, the only issue you may run into is with hospital systems, often they will not give access to NON-CREDENTIALED providers.  In the image below, you can see there are 19 dashes, each representing 1 cm.  That will vary based on FFD/SID and the facility – this is a way to “standardize” measurements. 

Screen Shot 2017 08 18 at 9.39.37 AM

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