PET artifacts from off-plane sources in high magnetic fields

As the intrinsic spatial resolution of small animal PET systems continue to improve into the sub-millimeter regime, the positron range is becoming the dominant factor to the image resolution. This is especially true for higher energy positron emitting radioisotopes such as ⁶⁸Ga and ^94mTc. It has been demonstrated that the range of the positron can be reduced in the plane transverse to an applied magnetic field due to the Lorentz force. However, the component of the positron’s velocity in the direction of the magnetic field is unaffected. Although the resolution in the plane orthogonal to the magnetic field vector is improved, artifacts from positrons emitted by sources positioned outside of the detection plane will be more sharply defined in the presence of a strong magnetic field. In this paper, the artifacts from off-plane ⁶⁸Ga sources are measured at both 0 T and 7 T. A 3-dimensional ML-EM reconstruction algorithm that corrects for the range of the positron is tested with simulated data and the results are compared for 0 T and 7 T for both simple and complex source distributions. Finally, a quantitative study of the noise versus resolution trade-off is discussed.