Fully automated 3D basal ganglia activity measurement in dopamine transporter scintigraphy (Spectalyzer)

Semiquantitative evaluation of tracer uptake in basal ganglia is superior to visual assessment of images in dopamine transporter (DAT) scintigraphy especially in follow-up of the patients. Manual drawing of regions of interest (ROIs) in two-dimensional (2D) transaxial slices of the single photon emission computed tomography (SPECT) datasets leads to a large inter- and intra-reader variability, while being time consuming. Our aim was to investigate a technique that extracts 3D ROIs in a fully automated fashion and thus might provide reproducible user-independent results allowing better follow-up control and large-scale clinical studies.

The highest activity of 123IFP-CIT is expected in the basal ganglia. The proposed method (Spectalyzer) uses the following steps to localize this maximum and extract the ROIs in 3D: (1) Dithers the SPECT volume to obtain a 3D volume with binary only. (2) Models the obtained point distributions as two multivariate Gaussian distributions and estimated their parameters using the expectation maximization algorithm. (3) Using the original SPECT activity values, thresholding is performed using a fixed percentage of maximum activity as a parameter to obtain the 3D ROIs. (4) A reference volume in the occipital region is automatically found based on the location of the two ROIs. (5) From the 3D ROIs, statistical information like mean and median activity and the volume is extracted, relative to the activity in the reference region. The resulting values are compared with values from manual 2D ROIs. Further validation is performed by means of an anthropomorphic striatal phantom.

The method was evaluated on 12 SPECT volumes including anthropomorphic striatal phantoms. In all cases the two basal-ganglia were successfully localized and the 3D ROIs estimated, with perfect reproducibility. The obtained values for the mean activity showed the same trend with the values obtained manually and also with the results of the 2D semiautomatic software, but without the substantial inter- and intra-reader variations.

The proposed method is successful in finding the 3D ROIs and performing the subsequent measurements automatically. It is proposed as an automatic reproducible approach for semiquantitative analysis of DAT scintigraphy.