Heart and respiratory gating of cardiac microPET®/CT studies in mice

Despite recent developments in high resolution small animal PET, cardiac studies in mice are still of limited quality due to the small size of the imaged organ and motion within the cardiac and respiratory cycle. By gating for one or both motions an improvement of the quantitative PET-data and images can be expected. We used a data acquisition and analysis system with multiple analog channel recording capability, consisting of a general purpose transducer amplifier for respiration and an ECG amplifier. A small plastic pressure pad connected to a pressure transducer served as respiratory sensor. To avoid artifacts in CT and attenuation corrected PET we used carbon electrodes and lead wires for ECG. Two digital trigger units received analog signals from both amplifiers and generated negative trigger impulses. The signal was fed into our microPET^® and integrated into the listmode mode file. For reconstruction microPET^® Manager (Concorde Microsystems) was used. The nongated CT was used for attenuation correction and anatomical orientation. With the system described we were able to generate reliable trigger pulses for both cardiac and respiratory motions. By eliminating inspiratory motion and reducing the influence of systolic spillover better quantitative blood pool values were achieved. A significant visual improvement in image quality was observed in diastole. The reconstruction process was computationally intensive due to the large number of sinograms generated in the histogramming process.