Many methods have been proposed for the calculation of image-derived input functions from carotid arteries as an alternative to arterial sampling for quantitative PET brain studies. However, these methods are usually validated for standard PET machines. Almost no studies exist for brain-dedicated HRRT scans, which have different resolution and noise characteristics. The aim of this study is to test six previously published image-input methods (three requiring arterial blood samples to scale the image-input (Chen et al., 1998; Mourik et al., 2008; Naganawa et al., 2005) and three blood sample-free methods (Su et al., 2005; Parker and Feng, 2005; Backes et al., 2009)) on HRRT brain studies using two different tracers which have different metabolism rates.