Localization of cerebral arterovenous malformations using digital angiography

Since 1989 we performed stereotactic radiotherapy treatments of cerebral ar terovenous malformations (AVM, estimating three-dimensional (3-D) localizat ion and shape of target volumes by the Leksell stereotactic helmet on two o rthogonal radiographic projections. Due to the limitations of this method, we developed a new technique for the localization of the target volume usin g digital subtraction angiography (DSA) and digital image processing. To ac hieve this result we first developed a method to correct nonlinear distorti on of DSA images using spatial relocation of image pixels based on a calibr ation grid. We then developed an algorithm for localization of the target v olume using two independent DSA projections. Target volume coordinates in t he helmet system are calculated using two DSA acquisitions taken with a foe angle (similar to 90 degrees), one in the AP and the other in the LL direc tion. The helmet can be freely positioned between the x-ray source and the image plane. The projections of eight reference points inserted in the helm et at a known location, are used to calculate the transformation matrix bet ween the two coordinate systems. We performed numerical and experimental va lidation of the system. A hypothetical random error (up to 2 mm) on image c oordinates of the reference points allowed to determine that the error in t arget localization was less than 0.2 mm. Using DSA images of target points with a known location within a phantom, the error between calculated and ac tual location was, on average, 0.30+/-0.13 mm (mean+/-SD), with a maximum e rror of 0.49 mm. The results of numerical and experimental validations show that the system we have developed allows fast and accurate localization of the center of the target volume and it is suitable for efficient guiding d uring stereotactic radiosurgery of AVM. (C) 2000 American Association of Ph ysicists in Medicine. [S0094-2405(00)00709-4].