Transmission imaging for registration of ictal and interictal single-photon emission tomography, magnetic resonance imaging and electroencephalography

A method developed for registration of ictal and interictal single-photon e mission tomography (SPET), magnetic resonance imaging (MRI) and electroence phalography (EEG) is described. For SPET studies. technetium-99m ethyl cyst einate dimer (ECD) was injected intravenously while the patient was monitor ed on video-EEG to document the ictal or interictal state, Imaging was perf ormed using a triple-head gamma camera equipped with a transmission imaging device using a gadolinium-153 source. The images (128x128 pixels, voxel si ze 3.7x3.7x3.6 mm(3)) were reconstructed using an iterative algorithm and p ostfiltered with a Wiener filter. The gold-plated silver electrodes on the patient's scalp were utilized as markers for registration of the ictal and interictal SPET images, as these metallic markers were clearly seen on the transmission images, Fitting of the marker sets was based on a non-iterativ e least squares method. The interictal SPET image was subtracted from the i ctal image after scaling. The Tl-weighted MPRAGE MR images with voxel size of 1.0x1.0x1.0 mm(3) were obtained with a 1.5-T scanner. For registration o f MR and subtraction SPET images, the external marker set of the ictal SPET study was fitted to the surface of the head segmented from MR images. The SPET registration was tested with a phantom experiment. Registration of ict al and interictal SPET in five patient studies resulted in a 2-mm RMS resid ual of the marker sets, The estimated RMS error of registration in the fina l result combining locations of the electrodes, subtraction SPET and MR ima ges was 3-5 mm, In conclusion, transmission imaging can be utilized for an accurate and easily implemented registration procedure for ictal and interi ctal SPET, MRI and EEG.