A fiducial skull marker for precise MRI-based stereotaxic surgery in large animal models.

BACKGROUND: Stereotaxic neurosurgery in large animals is used widely in different sophisticated models, where precision is becoming more crucial as desired anatomical target regions are becoming smaller. Individually calculated coordinates are necessary in large animal models with cortical and subcortical anatomical differences. NEW METHOD: We present a convenient method to make an MRI-visible skull fiducial for 3D MRI-based stereotaxic procedures in larger experimental animals. Plastic screws were filled with either copper-sulfate solution or MRI-visible paste from a commercially available cranial head marker. The screw fiducials were inserted in the animal skulls and T1 weighted MRI was performed allowing identification of the inserted skull marker. RESULTS: Both types of fiducial markers were clearly visible on the MRÍs. This allows high precision in the stereotaxic space. COMPARISON WITH EXISTING METHOD: The use of skull bone based fiducial markers gives high precision for both targeting and evaluation of stereotaxic systems. There are no metal artifacts and the fiducial is easily removed after surgery. CONCLUSION: The fiducial marker can be used as a very precise reference point, either for direct targeting or in evaluation of other stereotaxic systems.

[Imaging modalities for finding almonds in rice deserts]. / Billeddiagnostiske metoder til identificering af mandel i risalamande.

INTRODUCTION: In the traditional Danish Christmas dessert, ris à l'amande, one whole almond is hidden. The person who is lucky to find it in his portion is rewarded with a small gift, usually more sweets. We want to find out whether the hidden almond could be found by use of magnetic resonance imaging (MRI), computed tomography (CT) or conventional X-ray examinations. MATERIAL AND METHODS: We made three portions of ris à l'amande containing respectively three, one and zero whole almonds. All three portions were X-rayed and scanned by use of both MRI and CT, and three medical doctors from the neuroradiology department counted the almonds. All the three participants where blinded. RESULTS: We found that conventional X-ray was unsuitable for the purpose of finding whole almonds. In using either CT or MRI though, the hidden almonds were found. DISCUSSION: In a comparison between CT and MRI, the preferred modality is MRI, as diagnostic imaging confidence is higher with MRI as with CT. Ultrasound is another modality not tested, but potentially an excellent method for detecting almonds in ris à l'amande.