On-axis Fresnel zone plate imaging system with a germanium gamma ray camera and computer reconstruction

This study examines the feasibility of obtaining germanium gamma camera images by using a Fresnel zone plate aperture to produce shadowgrams and by digital reconstruction of images from the shadowgrams produced. The germanium camera is expected to provide high resolution images in nuclear medicine, but a conventional aperture for forming a high resolution image would result in very low gamma ray collection efficiency. The zone plate aperture is intended to improve this efficiency for imaging small sources, and in addition, to provide three-dimensional information about the source of radiation. The Fresnel zone plate imaging system is designed and evaluated by means of computer studies. Parametric equations relating zone plate, detector, and field of view parameters are derived. Based on these equations, a general method of designing a zone plate system for any detector is established, and this method is applied to a system with a square high-purity germanium detector, measuring 15.3 cm on a side. The zone plate parameters for optimum system resolution are calculated. The theoretical spatial resolution of the system considered here is 1.7 mm, which is better than that of the camera itself, 2.4 mm. In this case, the field of view of the system is restricted to a square field, 11 cm on a side. The field of view can be increased at the expense of degrading system resolution. For resolutions of 2.4 mm and 3.7 mm, the fields of view are squares of length 15.3 cm and 23.6 cm, respectively