A Readout ASIC for SPECT

Abstract

A new low noise multi-channel application specific integrated circuit (ASIC) has been designed for use in nuclear medical imaging single photon emission computed tomography (SPECT), and prototypes have been produced and tested. The ASIC has 128 charge sensitive amplifiers (CSA) followed by shapers, threshold discriminators and sample-and-hold. The ASIC delivers analog signal amplitude and digital address from channels with signals above threshold, and optionally allows one to read signals from any channel using a random-access readout. The total power consumption is 358 mW. The ASIC parameters have been specified and measured as follows: each amplifier measures charge within a linear dynamic range from -40000 e to +40000 e. The pre-amplifier noise is 56 e+11.6 e/pF at 10 µs shaping time. The ASIC is ideally suited for readout of radiation sensors with a few pF capacitance and less than 100 pA dc input current. The ASIC has been tested with silicon diode pad sensors. The diode had a capacitance of ≈ 1 pF and a leakage current of 20 pA. We measure an equivalent noise charge of 85 e, and achieve a triggering threshold of 800 e. Energy spectra from radioactive isotopes have been measured with energy resolution of 823 eV FWHM for 5.9 keV x-rays.

High-Resolution Anamorphic SPECT Imaging

“…The triggering and readout of the signals detected at strips are accomplished by VaTaGP6 application-specific integrated circuits (ASICs) from IDEAS [13]. Each ASIC is responsible for monitoring 128 conducting strips; eight ASICs are required on each side of the detector.…”

SPECT detectors: the Anger Camera and beyond

“…In a self-triggering, event-driven ASIC such as the one described in (Pettersen et al, 2005), each electronics channel includes a discriminator that generates a logic pulse initiating the readout cycle whenever a signal exceeds a threshold. Leading-edge discriminators are the most common choice because they require less power than constant-fraction discriminators, and often trim DACs are included for each channel to allow for compensation of threshold variations arising from gain and offset differences among channels.…”

Thick Silicon Double-Sided Strip Detectors for Low-Energy Small-Animal SPECT

“…The readout of the silicon DSSD is accomplished using a custom-designed 128-channel ASIC, the VaTaGP6, manufactured by Gamma Medica-Ideas. This ASIC is the latest version of the VaTa family [27], which features self-triggering capabilities with sparse readout [30]. It was specifically tailored to offer stable triggering at low energies with enhanced capabilities for making adjustments to individual trigger levels to minimize channel-to-channel threshold variations.…”

“…This can be achieved by increasing the thickness of the silicon wafer. We are proposing a dual-headed, stationary SPECT system that utilizes a new generation of silicon DSSDs with a thickness of one millimeter, an active area of 60.4 mm × 60.4 mm and a new ASIC [30]. We previously demonstrated some preliminary performance characteristics [26] of thick silicon DSSDs.…”