A simple method for the correction of distorted digital angiographic images for stereotactic target localization

The most commonly used imaging modality for the diagnosis and localization of arteriovenous malformations (AVMs) treated with stereotactic radiotherapy is traditional angiography, but it would be desirable to also use digital subtraction angiography (DSA). However, DSA images are distorted due to the electron-optical characteristics of the X-ray image intensifier. For that reason, we have developed a method for the correction of the image distortion. The ISIS II Treatment Planning System (ISIS II TPS), developed at the Curie Institute, has been used for image acquisition and stereotactic localization. A grid phantom has been constructed for determining the distortion of the DSA images. The software developed for the correction has been implemented into the TPS and is based on a correction vector produced by matching the distorted and corrected grid points. The method has been tested for its ability to correct the position of all grid points as well as its effectiveness in real cases as compared to traditional angiography. The maximum displacement of the corrected grid points compared with their original position is measured to be 0.1 mm. The accuracy of the target localization using the corrected DSA images is comparable with traditional angiography localization and falls inside acceptable accuracy limits. In conclusion, this method offers the possibility of using DSA images for stereotactic localization without limiting the requested accuracy.