SiPM based technology with Time-of-Flight capability

What is the benefit of Time-of-Flight?

PETsys Electronics technology is based on the TOFPET ASIC (Figure 1). It provides a cost effective way to use Time-of-Flight (ToF)  to improve the “equivalent sensitivity” of PET systems. The gain in sensitivity implies sharper images with substantially less noise (see Figure 2).  The ratio of the patient torso diameter to the uncertainty of the location of the gamma rays emission along the Line-of-Response (line joining the interaction points of the two gammas in the detector) determined by the ToF measurements, has been shown to be representative of the sensitivity gain. The signal-to-noise ratio (SNR) of the PET images is improved by the square-root of the sensitivity gain factor.


Figure 2 - Simulation of the PET image of an uniform cylinder filled with FDG for different assumptions of the time resolution. The statistical noise is substantially reduced when using better ToF information.

 What is the ToF performance of PETsys detectors?

PETsys Detector Modules, based on LYSO crystal arrays (3x3x15 mm pixels), MPPC silicon photomultipliers and PETsys TOFPET ASICs, have Coincidence Time Resolution (CTR) of ~300 ps FWHM (Full Width Half Maximum) – see Figures 3 and 4. The corresponding uncertainty of the emission point is about 4.5 cm FWHM. Knowing that the torso diameter of a typical patient is ~30 cm we conclude that PETsys technology allows a gain in sensitivity of a factor 6.5, and a gain in SNR of a factor 2.5. This also means that the same image quality as with non-ToF PET is achieved with shorter exam time or with lower radiation dose to the patient by a factor 6.5.


Figure 4: Coincidence time resolution (CTR) measured with two LYSO 4x4 crystal arrays (crystal pixels with 3.5x3.5x15 mm) coupled to Hamamatsu S12642-0404PB-50 4x4 MPPC arrays at room temperature. Area matching between silicon and crystal pixels is ~70%. The result shown was obtained with TOFPET1.

 

Application to small animal or breast PET

In some applications, e.g. in small animal PET systems or breast PET, the sensitivity gains from ToF are smaller but a better coincidence time resolution allows the reduction of random coincidences noise. This is an important consideration in high rate applications. Also in this case scanners based on SiPM will lead to a more compact and cost effective solution.

Straightforward integration of SiPM-based PET scanners

PETsys state of the art data acquisition technology based on high-speed point-to-point links allows the straightforward integration of SiPM-based PET scanners. The technology is scalable to systems with several tens of thousand channels and allows for a staggering total rate of singles in the PET scanner of 1 Giga hit per second.

 

ASIC2Figure 1 - TOFPET2 ASIC for time and amplitude measurements of 64 SiPM channels.

  


Figure 3: Coincidence time resolution (CTR) measured with two LYSO crystals 3x3x15 mm coupled to Hamamatsu S12642-0404PB-50 MPPCs at room temperature. Area matching between silicon and crystal pixels is ~100%. The result shown was obtained with TOFPET1.