One of the great advantages of digital templating is the ability to correct for image magnification.
Learn about scaling digital images by selecting from the following topics:
- Significance of Image Scaling
- Measuring Image Magnification
- Positioning Calibration Objects
- OrthoView QuickScale Image Calibration Wizard
- Calibration Object Manufacturers
Traditional acetate templates provided by orthopaedic manufacturers have a fixed magnification and will only allow proper implant sizing if the x-ray image magnification is the same value. Even when a strict imaging protocol is in place, the magnification of the x-ray image will vary according to patient positioning and patient size.
The impact of patient size on image magnification is particularly significant with pre-operative x-rays for hip replacement surgery; however, it is an important factor in most orthopaedic procedures. As such, any radiology service that is performing pre-operative x-rays for digital templating must provide a method to measure image magnification.
For more information on image scaling, read Scaling Digital X-ray Images of the Hip by Grant Shaw, orthopaedic surgeon and leading PACS authority, and our editorial, Why We Recommend the Use of a Calibration Object for Scaling Digital Images for Templating.
Image magnification is measured by placing a calibration object, or a radiopaque object of known dimension, in a precise position in the x-ray’s field of view. The calibration object, sometimes called a scaling marker, is often a 25 mm diameter metal ball that is mounted on a flexible arm. The arm allows the object to be correctly positioned in the same plane as the anatomy of interest.
There are numerous alternative objects and proprietary devices available for image calibration (or scaling). OrthoView software works with most calibration objects and provides tools to measure a variety of objects including balls, discs and rulers. OrthoView supplies the J2 Medical Akucal Image Scaling Device to OrthoView customers in North America. If you are interested in the J2 scaling device, please contact us for more information.
OrthoView pre-operative planning software offers simple, one-click scaling. The software automatically detects the calibration object, allowing the user to enter the size of the calibration object and move on to reduction and templating.
To learn more about image magnification, review our Scaling Digital Images in OrthoView brochure.
QuickScale, OrthoView’s one-click scaling tool, automatically detects the edges of a calibration object to scale the image to size quickly and easily. QuickScale can be used with a spherical or disc shaped calibration object. If a radiographic marker is not available on the digital x-ray image, an estimated oversize can be entered.
Although OrthoView does not endorse any particular radiographic marker device, we are happy to provide these links for further information on examples of markers that are widely available.
Please refer to these manufacturers’ websites for more information on how to use their specific markers:
Learn how OrthoView digital image scaling works with a pre-operative planning software trial or demo. You will have the opportunity to identify your area or areas of orthopaedic interest to help us better assist you:
» Hip, Knee, Shoulder or Small Joint Arthroplasty
» Trauma and Fracture Management
» Pediatrics, including Limb Deformity