Automated detection of mismatch in paired V/Q SPECT scans using voxelwise statistical testing: validation and pilot clinical study

V/Q (Ventilation/Perfusion) tests are used to diagnose pulmonary emboli predominantly using planar images. This study presents a quantitative, objective statistical analysis of SPECT V/Q scans for the detection of ventilation-perfusion mismatch. The method is based on a voxelwise statistical assessment of the V/Q images differences. A new acquisition protocol (externally triggered gating) is introduced for acquiring multiple frames for the voxelwise variance estimation. The V/Q data sets are then tested by applying a student´s t-test in a voxelwise fashion seeking areas of mismatch. The resulting probability image is finally thresholded to display the detected differences. Two different datasets were used: 72 different cases of a computerised model of pulmonary embolism with emboli of varying magnitude and in different segments, plus seven clinical cases with physicians´ reports. The method was shown to be robust irrespective of the location of the mismatch for large defects but greater count densities than those used in the simulation studies are needed for the detection of smaller defects. The results from the clinical datasets agree with the clinical reports but in some cases reveal unreported abnormalities.