Biomedical Engineering Reference
In-Depth Information
Fig. 3.7
State-of-the-art PET/MRI devices from Siemens Healthcare and Philips Healthcare
are implemented in the device. In order to avoid the residual magnetic field from the
MR, the PET detector is equipped with an annular magnetic soft iron shield and each
PMT (photomultiplier) is also covered with a soft iron shield. PMTs are oriented
to align their photocathode with the flux lines of the magnetic field produced by
the MR. Not only the detectors but also the device electronics can suffer from the
mutual interference between the two scanners. The PET RF-generating circuits can
affect the MRI system. Thus, these components are placed outside the room where
the scanners are installed, and the PMTs power supply is dynamically controlled and
dropped during the MRI acquisition [
72
]. In terms of performance, the ideal goal
would be to obtain similar results from the subsystems in the hybrid scanner and
the originally independent devices. It has been demonstrated that the performance
of PET and MRI subsystems included in the Ingenuity TF PET/MRI scanner fulfills
this requirement [
55
].
Biograph mMR.
Siemens Biograph mMR scanner (Fig.
3.7
) is a hybrid scanner with
the MRI and the PET scanners within the same device. In particular, an APD-based
PET detector is inserted in a Verio MRI. The PET detector is inserted between
the coils in the MRI bore, which has a diameter of 60 cm (the same as the Philips
Ingenuity bore). Crosstalk is avoided in the Ingenuity TF scanner by separating the
two scanners in tandem geometry. In the Biograph mMR scanner the two scanners
are completely integrated, therefore the PET component works inside an intense
electromagnetic field. Due to this, the readout instrumentation of the PET has been
re-designedwith components capable towork under such conditions. Delso et al. [
71
]
compared PET and MRI performance to other PET/CT and PET/MR scanners. They
