New brain phantoms suitable for brain scanners with hemisphere detector arrangement

We have developed the brain-dedicated compact PET scanner which has a hemispherical helmet detector unit and an add-on detector unit located at the neck position (helmet-neck PET). To realize clinical applications of the helmet-neck PET scanner, we need to evaluate the performance regarding their absolute quantitation, image contrast, noise and uniformity using appropriate phantoms. However, existing standard phantoms are not applicable for the helmet-neck PET scanner because of its hemisphere geometry. Therefore, in this study, we developed two new phantoms, a small sphere contrast phantom and a 3-dimensional hemispherical Hoffman brain phantom, which model a brain tumor and static regional cerebral blood flow, respectively. These phantoms have an adaptive structure for use with the PET scanner with hemispherical detector arrangement. In addition, we tested the developed contrast phantom using the helmet-neck PET prototype. The PET image obtained by the helmet-neck PET prototype showed high image contrast and acceptable noise level. These phantoms are useful for evaluating the imaging performance of compact helmet-shape scanners.