Overlay to Measure Angles

OsiriX and Horos Course · MPR and Centerline

In this video I answer a question about how to measure angles using image "overlay" in OsiriX, with a knee example (orthopedics). I test overlay methods (such as MIP and mean, adjusting the slice thickness), but explain why this can blur the image and make analysis harder. The most practical and precise solution in OsiriX, in most cases, is not to rely on overlay — but rather to measure the angle across different slices, keeping the same ROI while navigating between images. Overlay attempt (and limitations) Enable overlay and use: MIP (Maximum Intensity Projection): sums intensities over a greater thickness → can become very blurred Mean: sometimes helps, but can still lose sharpness depending on the case These methods overlay several images, which is not always ideal for measuring an angle precisely. The method that solves it: persistent ROI across slices (Shift key) Select the Angle tool (angle ruler) Hold down the Shift key on the keyboard While keeping Shift pressed, draw the angle Now you can change the slice/image and continue the measurement (the ROI "persists") Finish the angle on the desired slice — with more control and no need for "transparency" This tip is useful not only for orthopedics, but also for many measurements in other areas (including vascular), whenever you need to "complete" a measurement using different slices.