Each analysis begins with two scans, one interictal SPECT scan and one ictal SPECT scan for the same patient, and ends with ISAS results as summarized below. Detailed step-by-step instructions for performing the ISAS Analysis are found in the Details section.

Sample Analysis

We recommend that before processing your own images, you should run a complete analysis on the sample patient (see Downloads page) using the instructions below, and confirm that the results obtained agree with those shown on the Sample Analysis results page.

File Format

For scans to be analyzed by SPM they must be in Analyze format. Refer to the Setup page for details on converting image files. Note that the sample analysis scans are already in Analyze format, and are ready for pre-processing (next step).

Pre-processing Scans

  1. Reorient the scan to the same orientation as the SPM SPECT template.
  2. Set the cross hairs to the anterior commissure.
  3. Using the set defaults for SPECT/PET analysis, realign the ictal scan to the interictal and create a mean image.
  4. Leave all of the normalization defaults as set, except change the bounding box to template (-0:90 -126:90 -72:108). Normalize the realigned ictal and interictal scans to the SPECT template, using the mean image created during realignment as the image to determine the normalization parameters from.
  5. Apply the apriori brain mask to the normalized ictal and interictal scans, using the image calculator (multiply the brainmask.img (found in spm2/apriori) by your normalized images).
  6. Smooth your realigned, normalized, and masked images with a kernel of 16x16x16 mm.

The Statistical Model

  1. To set up the statistical model select PET from the SPM menu. Then choose Multi Groups Conditions & Covariates
  2. For number of groups, enter 2.
  3. Group#1, number of subjects should be 1. Then for subject #1, enter pre-processed interictal then ictal scan for your patient. For condition enter 0 (corresponding the interictal baseline) and 1 (corresponding to the activated, or ictal scan).
  4. Then for Group#2, number of subjects, enter 99. This prompts SPM to automatically enter your pre-processed healthy normal scans (If you have correctly done steps 1-3).
  5. Number of Covariates = 0;
    Number of Nuisance Variables = 0;
    Global normalization = proportional scaling;
    Prop scan global mean = 50;
    Threshold Masking = proportional;
    Analysis Threshold = 0.8;
    Global Calculation = mean voxel value;
    Non-Sphericty Correction = no.
  6. Estimate your model and set up contrasts.

Display and Interpret Results

  1. Display results using glass brain, cross sections, and 3-D renderings. Repeat analysis and check with RView.
  2. For SPECT scans injected during seizures (true ictal SPECT), localize the lobe of seizure onset based on the “Reading Rules.”
  3. For SPECT scans injected post-ictally, lateralize the hemisphere of seizure onset based on the hypoperfusion asymmetry index.
  4. If you are performing the sample analysis, compare your results to those on the Sample Analysis page to ensure they match.

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