IntroductionIn idiopathic scoliosis, biomechanical, biological and clinical views confirm that the deformity in the sagittal plane is of primary pathogenetic significance [8]. A fixed lordotic section causes rotation and increased lateral curvature of the spine as a result of the asymmetry in the coronal plane [2]. Various studies confirm that lordosis of the thoracic vertebrae is characteristic for idiopathic scoliosis in adolescents [3,8,11].The scoliotic deformity in the follow-up of scoliosis patients is usually examined using anteroposterior (AP) radiographs. An additional lateral radiograph, while providing additional information, would result in increased X-ray exposure. On the lateral X-ray projection, the mean entrance surface radiation dose for the thoracic spine is 6.1 mGy and for the lumbar spine 6.7 mGy [1]. However, monitoring the scoliotic deformity on a lateral view can provide additional information, useful, for example, for assessing the effect of brace treatment in two planes or determining further prognostic factors.The technique of MR total spine imaging developed by the authors allows visualization of the whole spine in the coronal and sagittal planes [4,5]. The present study aimed to establish whether MR total spine imaging is a reliable and useful method to image scoliosis in the sagittal plane.
AbstractThe purpose of the present study was to introduce a new magnetic resonance imaging (MRI) procedure showing the whole spine in a coronal and sagittal plane, and to study the assessment of sagittal Cobb angle measurements using this technique. Prospectively we studied 32 patients (average age 14.8 years) with idiopathic scoliosis (mean thoracic Cobb angle 33°on radiograph) and 18 patients (average age 14.5 years) without scoliosis. The MRI investigation was carried out in a standard supine position. The cervical and upper thoracic spine and the lower thoracic and lumbar spine were measured on a 1.5-T Gyroscan ACS-NT Powertrak 6000 system. An algorithm was developed to combine the results of the cranial and caudal scans into a coronal and a sagittal image of the whole spine (MR total spine imaging). Measurement of the sagittal Cobb angle conducted ten times by four independent investigators revealed an intraobserver variance of 1.6°and an interobserver variance of 1.8°. In the group with scoliosis the mean sagittal Cobb angle from T4 to T12 was 12°(range -3°to 24°) and in the group without scoliosis 22°(range 16°to 30°), which was a significant difference. MR total spine imaging makes it possible to image scoliosis in the sagittal plane. On these MR projections, idiopathic thoracic scoliosis was identified by a reduced sagittal Cobb angle. MR total spine imaging would allow monitoring of scoliosis in the sagittal plane, which can reveal relevant clinical data without radiation exposure.
In patients with drug-resistant focal epilepsies subdural grid electrodes may be implanted to determine the seizure onset zone and eloquent cortex areas. Since the spatial relationship of the grid to the underlying brain is poorly visualized on MRI, we co-registered MRI before and CT after implantation of subdural grid electrodes. In this study we sought an appropriate algorithm to combine both imaging modalities. We compared six different co-registration algorithms including surface-oriented, mutual information-based and landmark-based methods. The resulting overlay matrices were analyzed by calculating rotational and translational shifts and by judging co-registered MRI and CT scans visually. A brain surface oriented method had the lowest rotational (axial 0.7 +/- 0.6 degrees; coronal 1.7 +/- 1.1 degrees; sagittal 1.9 +/- 1.8 degrees) and translational shifts (3.7 +/- 1.3 mm). It was judged visually to be the best, had a low intra- and inter-observer variability, and lasted approximately 15 minutes. This algorithm is recommended when co-registering MRI before and CT after implantation of subdural grid electrodes. Skin-, voxel-, and landmark-based algorithms are less accurate, which is most likely due to postsurgical deformation of extra- and intracranial soft tissue.
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