Dangerous advances in measurements from digital subtraction angiography: when is a millimeter not a millimeter?

Aneurysms need accurate millimeters (mm). Direct millimeters were lost with digital subtraction angiography (DSA) years ago, with measurements in pixels. Advances in DSA can now give inherent millimeters. The Cerecyte aneurysm coiling trial's angiographic core lab assesses images from compact disc (CD). External fiducials for millimeter calibration are required. Of 25 cases with two 10 mm fiducials, near and far from the intensifier, the midline mean is between 9 "mm" to 15 "mm". Yet 10 mm must be 10 mm. This variance is potentially dangerous. Proprietary software seems to prohibit calibration transfer via CD to another vendor's system.