A fter an intracerebral hemorrhage (ICH), hematoma expansion by 33% or more has been reported in at least 38% of patients within 24 hours after symptom onset (1), and in up to 50% of patients who are on anticoagulation therapy (2). Early hematoma expansion is strongly associated with neurologic deterioration, worse functional outcome, and mortality after ICH (3). Thus, identification of patients at risk for hematoma expansion may help to direct management, in particular with respect to selecting candidates for early targeted medical or surgical intervention (4). Several imaging markers have been proposed to assess greater risk of hematoma expansion, including spot sign at CT angiography (5), defined as foci of enhancement within a hematoma due to active contrast media extravasation (6). However, the test characteristics of spot sign are not optimal for predicting hematoma expansion (7,8). For example, in the large Prediction of Haemotoma Growth and Outcome in Patients with Intracerebral Haemorrhage using the CT-angiography Spot Sign (PREDICT) trial, when the spot sign was assessed at arterial phase imaging, it demonstrated sensitivity only slightly greater than 50% (9,10). In other words, although presence of the spot sign is highly predictive of hematoma expansion, there is room for improvement in its sensitivity (even including assessment on delayed images and at dynamic CT angiography) so that it may be used as a robust predictor of both stability and expansion of ICH. One of the difficulties in spot sign reading is differentiating hyperdense hemorrhage from contrast media staining of the brain parenchyma due to spotty or diffuse contrast media extravasation from leaky blood vessels (11,12). Dual-energy CT can be helpful in these situations through

Background The pedunculopontine nucleus (PPN) has been studied as a possible target for deep brain stimulation (DBS) for Parkinson’s disease (PD). However, identifying the PPN can be challenging as the PPN is poorly visualized on conventional or even high-resolution MR scans. From histological studies it is known that the PPN is surrounded by major white matter tracts, which could function as possible anatomical landmarks. Methods This study aimed to localize the PPN using 7T magnetic resonance (MR) imaging and diffusion tensor imaging (DTI) of its white matter borders in one post-mortem brain. Histological validation of the same specimen was performed. The PPN was segmented in both spaces, after which the two masks were compared using the Dice Similarity Index (DSI). The DSI compared the similarity of two samples on an inter-individual level and validated the MR findings. The error in distance between the center of the two 3D segmentations was measured by use of the Euclidean distance. Results The PPN can be found in between the superior cerebellar peduncle and the medial lemniscus on both the FA-maps of the DTI images and the histological sections. The histological transverse sections showed to be superior to recognize the PPN (DSI: 1.0). The DTI images have a DSI of 0.82. The overlap-masks of both spaces showed a DSI of 0.32, whereas the concatenation-masks of both spaces showed a remarkable overlap, a DSI of 0.94. Euclidean distance of the overlap- and concatenation-mask in the two spaces showed to be 1.29 mm and 1.59 mm, respectively. Conclusion This study supports previous findings that the PPN can be identified using FA-maps of DTI images. For possible clinical application in DBS localization, in vivo validation of the findings of our study is needed.

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