New Imaging Method of Positrons Leaving the Source Application for PET/MR hybrid Scanners -

The
¹¹
CO
₂
tracer is of high interest to study carbon transport in living plants. However, conventional PET images of plant leaves suffer from the poor positron annihilation probability in the targeted structures, thus giving strong bias in reconstructed images. Here, PET/MR hybrid scanner systems offer a new method to detect and quantify escaping positrons as 2D projections by exploiting the directed travelling of positrons parallel to the present B
₀
field of the MR magnet system. Due to the Lorentz force all emitted positrons propagate on spiral trajectories parallel to the B
₀
field with tiny gyroradii. The introduction of a thin absorber screen within the field-of-view of the PET scanner, forces the annihilation of almost all incoming positrons inside the absorber. The annihilation photon pairs can be registered as coincidences and thus directly indicate the positron impact point on the screen by interpolating the Lines-of-Response onto the screen. In this way, 2D images are obtained and the amount of positrons leaving the source can be quantified dynamically.