53. International Winter Meeting on Nuclear Physics

EndoTOFPET-US: an endoscopic Positron Emission Tomography detector for a novel multimodal medical imaging tool

29 Jan 2015, 18:00

20m

Bormio, Italy

Short Contribution Thursday Afternoon

Speaker

Mr Daniele Cortinovis (DESY)

Description

The EndoTOFPET-US collaboration aims to integrate Time-Of-Flight PET with ultrasound endoscopy in a novel multimodal device, capable to support the development of new biomarkers for prostate and pancreatic tumors. The detector consists in two parts: a PET head mounted on an ultrasound probe and an external PET plate, placed outside the body in coincidence with the PET head. The gamma ray detection is performed by scintillating crystals with Silicon PhotoMultiplier (SiPM) readout. Analog SiPM are used in the external plate, while new dedicated multi-digital SiPM have been developed for the internal probe, which also involves other technological solutions due to the high level of miniaturization. The spatial resolution of 1 mm for the PET image requires small crystal size, and therefore high channel density. Moreover, the detector is designed to achieve an unprecedented Coincidence Time Resolution (CTR) of 200 ps FWHM, essential for effective background rejection. Compared to conventional PET scanner, the unusual asymmetric design requires a tracking system with a resolution better than 1 mm, and poses new issues for detector simulation. In addition, the image reconstruction has to cope with the limited field of view. The detector design and the characterization of single components are presented, as well as the results on the first integrated prototype.

Summary

Among the tumors, pancreatic carcinoma is one of the most aggressive and resistant to current therapies, and most often is detected only on an advanced state of development. On the other hand, prostate cancer is the most diffuse cancer among males. The fusion of the high resolution metabolic image from PET and the anatomical image from ultrasound will improve the diagnosis and the therapeutic oncology of the mentioned tumors, especially at the early stages of development.
EndoTOFPET-US aims to push forward the limits of the current PET scanners: the endoscopic approach together with the Time Of Flight (TOF) information with an unprecedented CTR of 200 ps (3 cm along the line of response) allow to define a specific Region Of Interest (ROI), and drastically suppress the background coming from the neighboring organs.
The EndoTOFPET-US detector consists of a PET head extension mounted on a commercial US endoscope placed close to the ROI and an external PET plate facing the patient’s abdomen, in coincidence with the PET head. The internal probe is an highly miniaturized system: the
cooling system, electronics and the LYSO:Ce scintillating crystals coupled to digital SIPMs are housed in a very small volume (15 mm diameter for Pancreas case). The external plate is a square
of 20x20 cm2 and it is made of 256 detector unit modules, each consisting of a 4x4 LYSO:Ce crystal matrix glued to a discrete array of 4x4 analog SiPM from Hamamatsu. SiPM readout is performed
by a fast and low-noise Application-Specific Integrated Circuit (ASIC) developed by the collaboration. FPGAs concentrate event data sent by ASICs and transmit this information to an external Data Acquisition System (DAQ) where the data from the probe are met.
Different options for the tracking system are under study: optical, electromagnetic and mechanical. However, it has to provide at least 1 mm precision, in order to guarantee the requested spatial resolution.
Simulations of the whole detector are performed with the GAMOS framework. They provide a test on sensitivity, time and spatial resolution and therefore guide the detector design. Finally, the image reconstruction has to cope to low sensitivity, high noise and limited angle. GPU computation is used to provide on-line imaging for intraoperative application.

Presentation materials

Slides

EndoTOFPET_Daniele_Cortinovis.pdf