The sensitivity of a pinhole collimator for gamma ray imaging in nuclear medicine is dependent on the angle of incidence of the gamma rays. The effect of penetration near the pinhole aperture on angle‐dependent sensitivity was investigated using experimental measurements and numerical modeling. Projection data measurements were acquired with Tc‐99m and I‐131 point sources using tungsten pinhole inserts with 1.0 to 4.0 mm diameter apertures. Curves of the form where θ is the angle of the incident ray with the surface of the detector crystal, were fit to sensitivity measurements from the projection data. Experimentally measured values were between 3.3 and 4.1 for Tc‐99m and between 5.1 and 7.2 for I‐131. Penetration near the pinhole aperture was modeled using (1) an expression for effective pinhole diameter that is a generalization of Anger's formula for normally incident photons and (2) a photon transport simulation code. Experimentally measured sensitivity exponents from new and previously reported experimental observations were modeled within 15% by the numerical simulations. For modeling using the generalized expression for effective diameter the average error was 1.4% and the
📖 افتح في inklap 🔗 DOI 📮 اطلب بحثاً