Calculating Center of Mass Using List Mode Data from PET Biograph128 mCT-1104

Sammanfattning: A common problem within positron emission tomography examinations of the brain is the motion of the patient. If the patients ́ head moves during an examination all the data acquired after the movement will not be suited for clinical use. This means that a lot of data recovered from PET is not used at all. Motion tracking during PET acquisitions of the brain is not a well explored issue within medical imaging in relation to the magnitude of the problem. Due to the radiation risks of the examination and the logistics at the hospital, a second acquisition is not preferred. Therefore a method to avoid a second acquisition would be welcome. PET data saved in list mode makes it possible to analyze the data during an examination. By calculating the center of mass of the object examined in list mode only using the raw data from PET and use it as a tracking point, it would be possible to track a motion during an acquisition. The center of mass could therefore possibly be used as a reference to connect two different time intervals on each side of the moment were the motion occurred. The raw PET data used for this project was acquired in the Nuclear Medicine Department in Karolinska University Hospital in Huddinge and covered four turns of one minute acquisitions in different positions and with two different objects that were saved in list mode. The acquisitions were analyzed with the Siemens software e7-tools and sliced into time intervals. To calculate the center of mass within these time intervals, two methods were developed. One method only used the Siemens software e7-tools and histogrammed the time of flight bin position. The other method used each event position in its sinogram to calculate a center of mass sinusoidal equation. This equation lead to coordinates describing the center of mass in a specific slice.