We suggest that MRI may be helpful to assess the extent of this disease more accurately.

Ventriculoperitoneal shunts have been associated with many different complications. We describe two rare complications in a 10-month-old girl. To the best of our knowledge, protrusion of ventriculoperitoneal shunt through the knee has not been reported before.

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Background With the introduction of hybrid positron emission tomography (PET)/MRI, a new imaging option to acquire multimodality images with complementary anatomical and functional information has become available. Compared with hybrid PET/CT, hybrid PET/MRI is capable of providing superior anatomical detail while removing the radiation exposure associated with CT. The early adoption of hybrid PET/MRI, however, has been limited. Objective To provide a viable alternative to the hybrid PET/MRI hardware by validating a software-based solution for PET/MR image coregistration. Materials and methods A fully automated, graphics processing unit-accelerated 3-dimensional deformable image registration technique was used to align PET (acquired as PET/CT) and MR image pairs of 17 patients (age range: 10 months-21 years, mean: 10 years) who underwent PET/CT and body MRI (chest, abdomen or pelvis), which were performed within a 28-day (mean: 10.5 days) interval. MRI data for most of these cases included single-station post-contrast axial T1-weighted images. Following registration, maximum standardized uptake value (SUVmax) values observed in coregistered PET (cPET) and the original PET were compared for 82 volumes of interest. In addition, we calculated the target registration error as a measure of the quality of image coregistration, and evaluated the algorithm’s performance in the context of interexpert variability. Results The coregistration execution time averaged 97±45 s. The overall relative SUVmax difference was 7% between cPET/MRI and PET/CT. The average target registration error was 10.7±6.6 mm, which compared favorably with the typical voxel size (diagonal distance) of 8.0 mm (typical resolution: 0.66 mm×0.66 mm×8 mm) for MRI and 6.1 mm (typical resolution: 3.65 mm×3.65 mm×3.27 mm) for PET. The variability in landmark identification did not show statistically significant differences between the algorithm and a typical expert. Conclusion We have presented a software-based solution that achieves the many benefits of hybrid PET/MRI scanners without actually needing one. The method proved to be accurate and potentially clinically useful.

Purpose:To evaluate the utility of magnetic resonance cholangiography (MRC) in estimation of gallbladder ejection fraction (GBEF) and to comparing this value to the conventional method, hepatobiliary scintigraphy (HBS). Materials and Methods:Twenty-one healthy volunteers were imaged on sequential weeks to determine GBEF using MRC and HBS. GBEF was calculated by HBS after infusion of 20 ng/kg of sincalide following injection of 111 Mbq of Tc 99 m mebrofenin. For estimation by MRC, imaging of the gallbladder was performed before and after slow infusion of sincalide every 5 minutes, for a total of 60 minutes. Gallbladder imaging was performed using a heavily T2-weighted 2D fast spin echo (FSE) sequence. Data was analyzed using a variance component analysis technique. Results:Mean GBEF by HBS was 65.7%, with an SD of Ϯ27.3%. Mean GBEF by MRC was 62.7%, with an SD of Ϯ 20.4%. If minimum normal GBEF is set at 35%, two of the cases showed discordance, with HBS calculating an abnormally low average GBEF compared to MRC. Additionally, two cases showed abnormally low GBEF for both modalities. The coefficient of correlation between HBS and MRC was 0.72. Inter-and intraobserver variance is acceptable within the two modalities with Ͻ1.1% variation. Conclusion:GBEF can be calculated with MRC, yielding similar values when a group of volunteers are considered. Further study with symptomatic patients is needed to determine the validity of this technique for clinical diagnosis.

Primitive neuroectodermal tumors (PNETs) include a heterogeneous group that originate from primitive neuroepithelial cells. PNETs are prone to cerebrospinal fluid seeding and central nervous system spread. Infratentorial PNET, or medulloblastoma, is a common brain tumor in children and metastatic spread to the abdomen via a ventriculoperitoneal (VP) shunt has been described. Supratentorial PNETs are much less common. We present a rare case of a predominantly supratentorial PNET metastasizing to the abdomen via a VP shunt and discuss the radiological findings. This case demonstrates the small but real risk of metastatic spread, which should be weighed when considering VP shunt placement.