Working with image overlays

Subtopics in this section

Loading Image Overlays
Modify Image Overlays
Image Co-registration from DICOM geometry parameters

General introduction

nordicICE supports the use of multiple image overlays. This function is particularly useful for viewing functional MRI analyses of brain activation overlaid on structural images, and for comparing parametric maps with the original anatomical image, and with each other. Images can be overlayed using either Drag & Drop of one image set onto another or by loading an Nifti image file as overlay. The rendering of the overlay is based on the geometric information contained in the header (for DICOM images) or the information contained in the Nifti file header. Consequently, the overlay is only correctly coregistered for these image formats where the image orientation and dimensions are available as part of the file information. Any combination of DICOM/Nifti overlay/underlay can be used. See the section called Image Co-registration from DICOM geometry parameters for more information.

For DICOM images, each image has an associated image orientation and position field in the DICOM header. This is not the case for Nifti images and nICE assumes that the slice in an SPM dataset is ordered in a specified way: Axial datasets should be ordered feet-head; coronal datasets should be ordered anterior-posterior and sagittal datasets should be ordered left-right. Care should, therefore, be taken to ensure that the Nifti images are loaded in this order. If Nifti images are generated in nICE (from DICOM images) correct slice order is ensured but the slice order cannot be tested if generated by another program and the above defined slice order is therefore always assumed.

Images may be overlaid on the active window or on MPR images in the MPR module. Multiple overlays may be superimposed on a given image volume or image series. The color palette may be individually varied to differentiate between the different overlays. The degree of overlay transparency may be set individually for each overlay on a gliding scale from None to Max, where Max is completely transparent (i.e. not visible) and None means completely opaque. The transparency is set for each overlay individually and may be varied in real time to aid viewing and examination.