The wrist scanner is a small radioactivity detector being developed to image arteries in the wrist for non-invasive estimation of an input function for quantitative positron emission tomography (PET) studies. A prototype four detector LSO-APD array was characterized and tested in a clinical setting. The scanner has a sensitivity of 4 cps/nCi/cc and a resolution at the arterial position of the wrist is 2.3 mm. Tomographic images of the human wrist were acquired using the MicroPET R4 scanner. These images were used to measure the tissue radioactivity interference, study partial volume effects and to estimate an image-derived input function from the radial and ulnar arteries. The metabolic rate of glucose calculated using an image derived input function from the wrist was compared to the values calculated using the invasive arterial input function. A paired two tailed t-test showed that these values did not differ at a significance level of p<0.05.