Acquisition of attenuation map for brain PET study using optical tracking system

Attenuation correction (AC) is essential in order to get quantitative data with positron emission tomography (PET). AC is normally carried out using transmission scan, which is obtained by scanning a subject with external radiation source before the administration of radiopharmaceuticals. The transmission scan makes longer time of PET study and additional radiation exposure to the subject. To avoid these inconveniences, we have aimed to develop a technique to generate attenuation map without the transmission scan for brain PET study. In the procedure, a special cap was designed to put on the head of the subject to be scanned for brain PET study. The surface of the cap has 22 points of markers. An optical tracking system was utilized to determine positions of these 22 markers. In order to obtain the reference attenuation map and positions of 22 markers, the cap was put on the head of a reference subject and the transmission scan was performed. In order to generate a subject´s attenuation map, the subject put on the cap and the positions of 22 markers were determined by the optical tracking system. The thin plate spline (TPS) technique was employed to transform from the reference attenuation map to a target subject´s attenuation map using 22 markers as control points. Preliminary experiment showed good agreement between the attenuation map computed by the present method and the actual attenuation map by the transmission scan. The present method has potential to shorten brain PET study and reduce the exposure of radiation to the subject. The method might provide an accurate attenuation map for single-photon emission computed tomography (SPECT) study.