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 and practical functional imaging technique with established clinical and research applications in neurological disorders such as epilepsy and stroke. SPECT images are usually analysed visually, or semiquantitatively by measuring side-to-side asymmetries. In order to evaluate perfusion change after thrombolytic therapy in patients with acute ischaemic stroke we developed a semiautomated, weighted volumetric analysis (the ischaemic index) that measured the extent and severity of tracer uptake abnormalities on brain SPECT images semiquantitatively. The unaffected cerebral hemisphere was used as the reference region of interest. The analysis was validated in a phantom brain model incorporating ‘strokes’ varying in size and degree. The phantom ‘stroke’ sizes measured with the ischaemic index analysis correlated closely with 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 patients treated with thrombolytic therapy who were studied serially with 99 mTc-hexamethylpropyleneamine oxime (HMPAO) SPECT, the analysis was used to measure hypoperfusion volume and provide indices of perfusion change. This analysis has the advantages of semiautomation, ease of use and validation and has a potentially wide range of applications for both SPECT and PET.