Semiautomated analysis of the extent and severity of perfusion defects on brain SPECT images: validation studies

Single photon emission computed tomography (SPECT) is a widely available an d practical functional imaging technique with established clinical and rese arch applications in neurological disorders such as epilepsy and stroke. SP ECT images are usually analysed visually, or semiquantitatively by measurin g side-to-side asymmetries. In order to evaluate perfusion change after thr ombolytic therapy in patients with acute ischaemic stroke we developed a se miautomated, weighted volumetric analysis (the ischaemic index) that measur ed the extent and severity of tracer uptake abnormalities on brain SPECT im ages semiquantitatively. The unaffected cerebral hemisphere was used as the reference region of interest. The analysis was validated in a phantom brai n model incorporating 'strokes' varying in size and degree. The phantom 'st roke' sizes measured with the ischaemic index analysis correlated closely w ith the true values (r=0.994, P < 0.01) and this correlation was maintained under low count conditions acquired to simulate the clinical setting. The overall operator dependent error of the analysis was +/-3.4%. in 30 patient s treated with thrombolytic therapy who were studied serially with Tc-99m-h examethylpropyleneamine oxime (HMPAO) SPECT, the analysis was used to measu re hypoperfusion volume and provide indices of perfusion change. This analy sis has the advantages of semiautomation, ease of use and validation and ha s a potentially wide range of applications for both SPECT and PET.