Accurate identification of tissue regions of interest (ROIs) is quite challenging in small animal studies. Basically, the goal is to have perfect! coregistration of PET or SPECT data with an anatomical image, i.e. either MR or CT. ROIs are drawn on the anatomical image directly, then saved as an object map, then applied to the PET or SPECT images. ROIs may need to be corrected for partial volume.

Drawing ROIs with Analyze

• Begin Analyze.
• First, ROI’s need to be drawn.  If MRI is present, it can be used to draw a different set of ROI’s (known as an object map, or .obj file) for each subject.
• Load the MRI file using File->”Load as.”
• With the image highlighted in red, press Ctrl-Alt-C to check for the min/max values of the image, which may be necessary if the min/max values are such that the image does not appear.
• With the image still highlighted in red, click on the “ROI tool” button on the top toolbar.
• Zoom in and out using the “+” and “-“ buttons located on the top toolbar.
• To change image brightness, click on the View menu à IntensitiesàLoaded Volume, and adjust the brightness as desired.
• To draw an ROI, many options are available.  To draw a region freehand, click on the “tracer” button on the left toolbar.  One could also use “poly” to draw polygons, or use certain shapes. 
• If a similar set of ROI’s was drawn for another patient, that .obj file could be loaded and manipulated using the bottom toolbar.  For example, the “truck” button allows moving of ROI’s.
• Continue drawing as many ROI’s as desired.  The “Object” button in the lower right screen helps control which object, or ROI, is currently being drawn.  That way, many areas could all contribute to one ROI.
• Save the ROI’s as a .obj map.
• Close the ROI tool.