Manuel Rolo

A 64-channel ASIC for TOFPET applications

A 64-channel ASIC for TOF PET imaging is presented. The circuit provides time and energy measurements of events produced by a SiPM coupled to a L(Y)SO fast scintillator. This ASIC is developed in the framework of the EndoTOFPETUS collaboration as an option for the readout of external 200×200 mm plate detector, which consists of 3×3×15 mm crystals and 3×3 mm (active area) SiPMs. Using the chip with non-segmented and/or higher light yield crystals is possible. The same applies for photodetectors with different gain, polarity, or even higher dark count rate. The targeted 200 ps timing resolution for the system and the need for a low power consumption have driven the choice of a closed-loop amplifier input stage and a 50 ps time binning TDC based on analogue interpolation. A power consumption between 5 to 10 mW per channel is expected to guarantee a SNR of at least 20 dB for the single photon, using a SiPM with 320 pF terminal capacitance.

A low-power low-noise synchronous pixel front-end chain in 65 nm CMOS technology with local fast ToT encoding and autozeroing for extreme rate and radiation at HL-LHC

A low-power and low-noise synchronous front-end chain in a commercial 65 nm CMOS technology suitable for the future pixel upgrades at the CERN Large Hadron Collider (LHC) is presented. A shaper-less Charge-Sensitive Amplifier (CSA) with constant current feedback provides triangular pulse shaping for linear Time-over-Threshold (ToT) charge measurement. The sensor leakage current is compensated by the same feedback network. A track-and-latch voltage comparator is adopted for the hit discrimination. The hit generation is synchronized with a 40 MHz clock, minimizing time-walk issues in the time-stamp assignment. Fast ToT charge encoding up to 8-bit resolution can be retrieved at the pixel level exploiting a high-frequency self-generated clock signal. This is obtained by turning the latch into a voltage-controlled oscillator (VCO) using asynchronous logic. Pixel-to-pixel threshold variations are compensated by means of an autozeroed scheme, thus avoiding the need of a on-pixel D/A converter. An array of 8 × 8 cells with 50 μm × 50 μm pixel size has been prototyped. Design specifications, implementation and test results are discussed.

INSIDE in-beam positron emission tomography system for particle range monitoring in hadrontherapy

Abstract. The quality assurance of particle therapy treatment is a fundamental issue that can be addressed by developing reliable monitoring techniques and indicators of the treatment plan correctness. Among the available imaging techniques, positron emission tomography (PET) has long been investigated and then clinically applied to proton and carbon beams. In 2013, the Innovative Solutions for Dosimetry in Hadrontherapy (INSIDE) collaboration proposed an innovative bimodal imaging concept that combines an in-beam PET scanner with a tracking system for charged particle imaging. This paper presents the general architecture of the INSIDE project but focuses on the in-beam PET scanner that has been designed to reconstruct the particles range with millimetric resolution within a fraction of the dose delivered in a treatment of head and neck tumors. The in-beam PET scanner has been recently installed at the Italian National Center of Oncologic Hadrontherapy (CNAO) in Pavia, Italy, and the commissioning phase has just started. The results of the first beam test with clinical proton beams on phantoms clearly show the capability of the in-beam PET to operate during the irradiation delivery and to reconstruct on-line the beam-induced activity map. The accuracy in the activity distal fall-off determination is millimetric for therapeutic doses.

First results of the INSIDE in-beam PET scanner for the on-line monitoring of particle therapy treatments

Quality assessment of particle therapy treatments by means of PET systems has been carried out since late `90 and it is one of the most promising in-vivo non invasive monitoring techniques employed clinically. It can be performed with a diagnostic PET scanners installed outside the treatment room (off-line monitoring) or inside the treatment room (in-room monitoring). However the most efficient way is by integrating a PET scanner with the treatment delivery system (on-line monitoring) so that the biological wash out and the patient repositioning errors are minimized. In this work we present the performance of the in-beam PET scanner developed within the INSIDE project. The INSIDE PET scanner is made of two planar heads, 10 cm wide (transaxially) and 25 cm long (axially), composed of pixellated LFS crystals coupled to Hamamatsu MPPCs. Custom designed Front-End Electronics (FE) and Data AcQuisition (DAQ) systems allow an on-line reconstruction of PET images from separated in-spill and inter-spill data sets. The INSIDE PET scanner has been recently delivered at the CNAO (Pavia, Italy) hadrontherapy facility and the first experimental measurements have been carried out. Homogeneous PMMA phantoms and PMMA phantoms with small air and bone inserts were irradiated with monoenergetic clinical proton beams. The activity range was evaluated at various benchmark positions within the field of view to assess the homogeneity of response of the PET system. Repeated irradiations of PMMA phantoms with clinical spread out Bragg peak proton beams were performed to evaluate the reproducibility of the PET signal. The results found in this work show that the response of the INSIDE PET scanner is independent of the position within the radiation field. Results also show the capability of the INSIDE PET scanner to distinguish variations of the activity range due to small tissue inhomogeneities. Finally, the reproducibility of the activity range measurement was within 1 mm.

A free-running, time-based readout method for particle detectors

For the EndoTOFPET-US experiment, the TOFPET ASIC has been developed as a front-end chip to read out data from silicon photomultipliers (SiPM) [1]. It introduces a time of flight information into the measurement of a PET scanner and hence reduces radiation exposure of the patient [2]. The chip is designed to work with a high event rate up to 100 kHz and a time resolution of 50 ps LSB. Using two threshold levels, it can measure the leading edge of the event pulse precisely while successfully suppressing dark counts from the SiPM. This also enables a time over threshold determination, leading to a charge measurement of the signals pulse. The same, time-based concept is chosen for the PASTA chip used in the PANDA experiment. This high-energy particle detector contains sub-systems for specific measurement goals. The innermost of these is the Micro Vertex Detector, a silicon-based tracking system. The PASTA chips approach is much like the TOFPET ASIC with some differences. The most significant ones are a changed amplifying part for different input signals as well as protection for radiation effects of the high-radiation environment. Apart from that, the simple and general concept combined with a small area and low power consumption support the choice for using this approach.

First results of the front-end ASIC for the strip detector of the PANDA MVD

PANDA is a key experiment of the future FAIR facility and the Micro Vertex Detector (MVD) is the innermost part of its tracking system. PASTA (PAnda STrip ASIC) is the readout chip for the strip part of the MVD. The chip is designed to provide high resolution timestamp and charge information with the Time over Threshold (ToT) technique. Its architecture is based on Time to Digital Converters with analog interpolators, with a time bin width of 50 ps. The chip implements Single Event Upset (SEU) protection techniques for its digital parts. A first full-size prototype with 64 channels was produced in a commercial 110 nm CMOS technology and the first characterizations of the prototype were performed.

A time-based front-end ASIC for the silicon micro strip sensors of the P̄ANDA Micro Vertex Detector

The ANDA (Antiproton Annihilation at Darmstadt) experiment foresees many detectors for tracking, particle identification and calorimetry. Among them, the innermost is the MVD (Micro Vertex Detector) responsible for a precise tracking and the reconstruction of secondary vertices. This detector will be built from both hybrid pixel (two inner barrels and six forward disks) and double-sided micro strip (two outer barrels and outer rim of the last two disks) silicon sensors. A time-based approach has been chosen for the readout ASIC of the strip sensors. The PASTA (ANDA Strip ASIC) chip aims at high resolution time-stamping and charge information through the Time over Threshold (ToT) technique. It benefits from a Time to Digital Converter (TDC) allowing a time bin width down to 50 ps. The analog front-end was designed to serve both n-type and p-type strips and the performed simulations show remarkable performances in terms of linearity and electronic noise. The TDC consists of an analog interpolator, a digital local controller, and a digital global controller as the common back-end for all of the 64 channels.

The readout chain for the P̄ANDA MVD strip detector

The ANDA (antiProton ANnihilation at DArmstadt) experiment will study the strong interaction in annihilation reactions between an antiproton beam and a stationary gas jet target. The detector will comprise different sub-detectors for tracking, particle identification and calorimetry. The Micro-Vertex Detector (MVD) as the innermost part of the tracking system will allow precise tracking and detection of secondary vertices. For the readout of the double-sided silicon strip sensors a custom-made ASIC is being developed, employing the Time-over-Threshold (ToT) technique for digitization and utilize time-to-digital converters (TDC) to provide a high-precision time stamp of the hit. A custom-made Module Data Concentrator ASIC (MDC) will multiplex the data of all front-ends of one sensor towards the CERN-developed GBT chip set (GigaBit Transceiver). The MicroTCA-based MVD Multiplexer Board (MMB) at the off-detector site will receive and concentrate the data from the GBT links and transfer it to FPGA-based compute nodes for global event building.