Baumkuchen map analysis to detect postural cerebral hypoperfusion with upright 99Tcm-HMPAO brain SPET

We have evaluated a polar cortical flow Baumkuchen map (BK map), constructed from projection data by inwardly layering cortical flow stripes from the base to the apex, to detect postural cerebral hypoperfusion using 99Tcm-HMPAO brain SPET. A circular cortical perfusion outline was constructed from sinogram data at a 20% threshold; a ring was then formed by constructing an inner line with a radius equal to half that of the outer line. This ring on the transaxial image was superimposed onto the cortical image, then divided into 60 portions at 6 degrees intervals from the centre. The maximal number of counts per pixel within each sector was determined, translated into polar coordinate profiles and displayed as a polar map. We studied 11 patients with unilateral stenosis of the internal carotid artery or middle cerebral artery (MCA) and 7 patients without stenosis, using upright and supine (rest) 99Tcm-HMPAO brain SPET Cerebral perfusion was visibly altered on the BK maps of all 11 patients with arterial stenosis and on the transaxial images of 8 of them. A semi-quantitative analysis of the BK maps using a ratio of the counts in the regions of interest over the right and left MCA areas, showed that the mean of the ratios was significantly lower in the upright images than in the upright + rest and rest images (P = 0.0044 and 0.0033, respectively). Although the difference in the means of the ratios between the upright and upright + rest images was significant for both the BK map and transaxial image data (P = 0.0044 and 0.0051, respectively), the BK map was accurate in detecting changes in perfusion in the upright position. We conclude that BK map analysis is useful for detecting changes in patients examined using upright brain SPET.