gms | German Medical Science

Objective: Radiosurgery can be considered a well-established option for treatment of AVMs (arteriovenous malformations). The exact application of the therapeutic dose is based on the availability of imaging data sets with superior image quality that can be superimposed by an image fusion algorithm. The quantitative comparison of the respective image data sets also plays an important role for follow-ups Up to now the digital subtraction angiography (DSA) is a mandatory tool for the treatment planning and follow-up procedures as well. The aim was to investigate whether suitable CT and/or MR angiography procedures can replace digital subtraction angiography (DSA).

Methods: For 34 AVM patients various MR data sets have been used together with the stereotactically localized CT and DSA data sets for treatment planning. In order to define the AVM nidus precisely all available MR data sets have been fused onto the CT data set using an automatic image fusion algorithm. Furthermore a ll available digital follow-up studies were fused for exact comparison purposes.

Results: In all cases the thin-slice MR data sets (1 mm slice width, no gap) that inluded T1-weighted series and TOF (time of flight) angiographies were precisely fused onto the stereotactically localized treatment planning CT. In cases where a previous partial embolization had been performed, the use of superimposed CT sets with and without contrast media was important in order to define the completely embolized partial volumes that are no subject to be treated. The inclusion of the DSA images enabled a better identification of those arterialized veins that did not belong to the nidus. In 6 cases the MR follow-up studies showed contrast media enhancements overlapping the AVM nidus as a result of a brain-blood barrier disorder (T1 series with contrast). In 7 cases perifocal reactions were primarily observed (T2 series) 12 months after treatment with rather low clinical relevance.

Conclusions: By integrating all available imaging modalities, the exact 3-dimensional definition of the AVM nidus was realized safely for all patients. The stereotactic DSA data acquisition remains a crucial tool for safe nidus definition in radiosurgery treatment planning and therefore cannot be done without at present. A quantitative comparison of all MR follow-up studies is recommended.