1287
The HYPMED PET/MRI Insert for Breast Cancer
Yannick Kuhl1, Stephan Naunheim1, Bjoern Weissler1,2, Vanessa Nadig1, David Schug1,2, Florian Mueller1, Harald Radermacher1, Pierre Gebhardt1, Nicolas Gross-Weege1, Teresa Nolte1, Martino Borgo3, Marcel de Koning3, Menno Mathlener3, Jeroen Koeleman3, Frank van Duin3, Arold Dekker3, Wout Schut3, Jos van den Berghe3, Daniel Gareis4, Turgay Celik4, André Salomon5, Dennis Schaart6, Dimitri Kuznetsov6, René Bakker6, Karl-Josef Langen7, Christiane Kuhl8, and Volkmar Schulz1,2,9,10
1Physics of Molecular Imaging Systems (PMI), Experimental Molecular Imaging (ExMI), Aachen, Germany, 2Hyperion Hybrid Imaging Systems GmbH, Aachen, Germany, 3Futura Composites B.V., Heerhugowaard, Netherlands, 4NORAS MRI Products GmbH, Hoechberg, Germany, 5Philips Research, Eindhoven, Netherlands, 6Delft University of Technology, Delft, Netherlands, 7Forschungszentrum Juelich, Juelich, Germany, 8Department of Diagnostic and Interventional Radiology, University Hospital Aachen, Aachen, Germany, 9Physics Institute III B, RWTH Aachen University, Aachen, Germany, 10Fraunhofer Institute for Digital Medicine MEVIS, Aachen, Germany
1Physics of Molecular Imaging Systems (PMI), Experimental Molecular Imaging (ExMI), Aachen, Germany, 2Hyperion Hybrid Imaging Systems GmbH, Aachen, Germany, 3Futura Composites B.V., Heerhugowaard, Netherlands, 4NORAS MRI Products GmbH, Hoechberg, Germany, 5Philips Research, Eindhoven, Netherlands, 6Delft University of Technology, Delft, Netherlands, 7Forschungszentrum Juelich, Juelich, Germany, 8Department of Diagnostic and Interventional Radiology, University Hospital Aachen, Aachen, Germany, 9Physics Institute III B, RWTH Aachen University, Aachen, Germany, 10Fraunhofer Institute for Digital Medicine MEVIS, Aachen, Germany
Synopsis
Within the H2020 EU project HYPMED, we have developed a PET insert that can be moved into a 1.5 T MRI Philips Ingenia turning this into a simultaneous MRI-PET device for breast cancer applications. The PET insert consists of two independent PET rings with a field of view of 28$$$\times$$$10 cm² and two dual-channel local receive coils. Each ring consists of 14$$$\times$$$2 detector blocks of which each features a three-layer LYSO crystal array with 1.3 mm pitch. We will present the first PET and MRI results of our system.
INTRODUCTION
Improving the spatial resolution and system sensitivity of PET systems has always been a driver for innovation. Total-body PET/CT systems have been recently introduced that increase sensitivity by at least a factor of four for a single organ [1]. However, they are unfortunately subject to the same physical limitations with respect to the spatial resolution of about 3 to 4 mm [2]. The EU H2020 project HYPMED will address the above needs by developing a PET insert for a clinical 1.5 T MRI for breast cancer imaging.METHODS
The HYPMED insert consists of a combination of two local 2-channel receiver coils and two local PET rings that allow simultaneous imaging of the female breast in the prone position at 1.5 Tesla. The two local PET detector rings are arranged at an out-of-plane angle of $$$\pm$$$ 20° to better follow the thoracic contour. Each ring can be opened and closed (Fig. 1). 2$$$\times$$$14 detector stacks form one ring leading to a field of view of approximately 10 cm. The detector stacks consist of three-layer LYSO crystal arrays with a pitch of 1.3 mm. In this way, the insert is developed to achieve high and homogeneous resolution across the fields of view. The MR-compatible detector is based on the Hyperion III platform [3] (Hyperion hybrid imaging systems GmbH, Aachen, Germany). The platform offers a sensor tile with 12$$$\times$$$12 individual digital SiPM channels (DPC-3200, Philips, the Netherlands) forming a sensitive area of ~ 48$$$\times$$$48 mm² each.RESULTS
All system components are completed (Fig. 1 and 2), and individual investigations will be presented. SNR investigations of the local receive coils show good SNR for biopsy and diagnostics mode (Fig. 3). MR-compatibility studies of the developed Hyperion III detector platform are presented using previously developed protocols [4]. Flood maps of one three-layer detector stack were measured and show excellent ability to identify most of the 3,425 crystals (Fig. 4). The PET electronics have been successfully tested for gradient interference and show B0 interference for the detector stacks < 1 ppm in FOV. At the highest slew rates and duty cycles of the MRI system, a slight temperature effect on the detector stacks was observed, but no data rate loss was noticed (Fig. 5).DISCUSSION
The results demonstrate the feasibility of a dedicated PET insert that can be added as an add-on to an MRI. The use of the B1-Tx concept can be easily seen by the SNR plots of the right receiving coil, which supports both PET configurations (PET ring open and closed). Gradient switching shows no direct effect on the energy and timing resolution of the Hyperion III platform. With ~ 300 ps (FWHM) coincidence timing resolution with clinical detector stacks, the platform shows excellent PET performance in simultaneous operation. More details on the system will be shown during the conference.CONCLUSION
Local PET detectors in combination with a stand-alone clinical 1.5 T MRI system are a promising approach for high-resolution PET/MRI imaging of single organs, e.g., the female breast. With its higher sensitivity and improved spatial resolution, it offers an attractive alternative to commercially integrated PET-MRI.Acknowledgements
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 667211.References
[1] Cherry, S.R., Jones, T., Karp, J.S., Qi, J., Moses, W.W. and Badawi, R.D., 2018. Total-body PET: maximizing sensitivity to create new opportunities for clinical research and patient care. Journal of Nuclear Medicine, 59(1), pp.3-12.
[2] Reddin, J.S., Scheuermann, J.S., Bharkhada, D., Smith, A.M., Casey, M.E., Conti, M. and Karp, J.S., 2018, November. Performance evaluation of the SiPM-based Siemens Biograph Vision PET/CT system. In 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference Proceedings (NSS/MIC) (pp. 1-5).
[3] Weissler, B., Gebhardt, P., Dueppenbecker, P.M., Wehner, J., Schug, D., Lerche, C.W., Goldschmidt, B., Salomon, A., Verel, I., Heijman, E. and Perkuhn, M., 2015. A digital preclinical PET/MRI insert and initial results. IEEE transactions on medical imaging, 34(11), pp.2258-2270.
[4] Wehner, J., Weissler, B., Dueppenbecker, P.M., Gebhardt, P., Goldschmidt, B., Schug, D., Kiessling, F. and Schulz, V., 2015. MR-compatibility assessment of the first preclinical PET-MRI insert equipped with digital silicon photomultipliers. Physics in Medicine & Biology, 60(6), p.2231.
Figures
Figure 1. Concept drawing of the HYPMED insert. The scanner is mounted on a common patient bed. It is designed as a transmit-through concept and therefore has only two local receiver coils (two channels each). The two PET rings are tilted by 20° to adapt to the chest wall contour. For workflow reasons, the two PET rings can be opened and closed easily. Four single processing units (SPUs) control the 2$$$\times$$$2$$$\times$$$14 detector stacks. In addition, the scanner features water cooling for the detectors and SPUs.
Figure 2. The figure shows the module mechanics (unpainted) mounted on a commercial patient trolley. The trolley is driven to the MRI with the scanner and the patient as usual and converts the 1.5 Tesla MRI into a simulated MRI-PET system. The cable management is routed via the cable slapp (black) to the rear end of the scanner, where the power supply unit is located. Below right is the view of dummy detectors (no housing shown here).
Figure 3. The figure shows the investigation of the SNR by means of a water phantom. Figure a) depicts the SNR of both receive channels of the right receive coil in the so-called diagnostic mode of the HYPMED insert (PET ring closed). In figure b), the SNR of both channels for the so-called biopsy mode is shown (PET ring opened). It can be seen that the SNR of both coils is similarly high as in the diagnostic mode supporting MRI investigations in both modes.
Figure 4. The figure shows one of the first flood maps of one of the three-layer LYSO detector blocks. The flood maps show the typical pattern, where the three layers are well distinguishable from each other. The three magnifications at the corner (green), at the edge (red), and in the middle (orange) show the very good identifiability of most of the 3,425 crystals.
Figure 5. The Hyperion III platform shows no direct effect during gradient switching. The plots show the results of a trapezoidal gradient sequence. The left column shows the values as a function of the measurement time. The right column shows the data during the active gradient switching synchronized to the TR which has a higher sensitivity to show direct influences during the actual switching duration. The right plot shows a time difference histogram for clinical detector stacks showing a CRT of 301 ps FWHM.
DOI: https://doi.org/10.58530/2022/1287