One of the great advantages of digital templating is the ability to correct image magnification.
The impact of patient size on image magnification is an important factor in most orthopedic procedures and particularly significant with pre-operative x-rays for hip replacement surgery.
Materialise OrthoView pre-operative planning software offers simple, one-click scaling. The software automatically detects the calibration object (scaling marker) with one click of the mouse, allowing the user to enter the known size of the object.
Any radiology service that performs pre-operative x-rays for digital templating must provide a method to measure image magnification.
Measuring Image Magnification
Image magnification is measured by placing a calibration object, or a radiopaque object of known dimensions, 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.