A novel silicon array designed for intraoperative charged particle imaging

Abstract

A novel Si-PIN imaging array is under investigation for a charged particle (beta, positron, or alpha) sensitive intraoperative camera to be used for (residual) tumor identification during surgery. This class of collimator-less nuclear imaging device has a higher signal response for direct interactions than its scintillator-optical detector-based counterparts. Monte Carlo simulations with 635 keV betas were performed, yielding maximum and projected ranges of 1.64 and 0.55 mm in Si. Up to 90% of these betas were completely absorbed in the first 0.30 mm. Based on these results, 300 microm thick prototype Si detector arrays were designed in a 16 x 16 crossed-grid arrangement with 0.8 mm wide orthogonal strips on 1.0 mm pitch. A NIM- and CAMAC-based high-density data acquisition and processing system was used to collect the list mode data. The system was calibrated by comparisons of measured spectra to energy deposition simulations or by direct measurement of various >100 keV conversion electron or beta emitters. Mean electronic noise per strip was <3.6 keV FWHM at room temperature. When detecting positrons, which have an accompanying 511 keV annihilation background, the flood irradiated beta/gamma ratio was approximately 40, indicating that beta images could be made without the use of background rejection techniques. The intrinsic spatial resolution corresponds to the 1 x 1 mm2 pixel size, and measurements of beta emitting point and line sources yielded FWHM resolutions of 1.5 (lateral) and 2.5 mm (diagonal), respectively, with the larger widths due to particle range blurting effects. Deconvolution of the finite source size yielded intrinsic resolutions that corresponded to the image pixel size. Transmission images of circle and line phantoms with various hole sizes and pitch were resolved with either pure beta or positron irradiation without a background correction. This novel semiconductor imaging device facilitates high charged particle and low gamma sensitivity, high signal/noise ratio, and allows for compact design to potentially aid surgical guidance by providing in situ images of clinical relevance.

Experimental study for an intraoperative probe for 18F imaging with a silicon pixel detector

“…18 F is a radionuclide with half-life of 109.728 min which decays via b + emission and electron capture. The maximum positron range is 1.64 mm in the silicon detector [13].…”

“…Among the semiconductor based detectors, silicon is a good choice for its high sensitivity to charged particles and low efficiency of thin detectors for g-rays. Conceptual designs and implementations for intraoperative imaging b probes based on silicon detectors have been reported [10,13]. In this framework, we present a probe for 18 FDG intraoperative positron imaging based on a silicon hybrid pixel detector.…”

“…In the former (non-imaging) type, a detector with energy-selective response-possibly laterally shielded from background radiation-collects, identifies (pulse height analysis) and counts each particle or g-ray: its instrumental output is the integral counting rate in the region pointed to by the tip of the probe, after suitable subtraction of the background radiation [1,2,[4][5][6][7][8]. Imaging probes, having a segmented sensitive area, are able to spatially resolve the distribution of the radioactive emission [9][10][11][12][13][14]. Non-imaging g-ray probes are largely utilized to locate sentinel lymph nodes and for radioimmunoguided surgery [3,4].…”

Direct Imaging of Radionuclide-Produced Electrons and Positrons with an Ultrathin Phosphor

“…With modern CCDs having large sensors, low noise, and high quantum efficiency, and with lenses of high effective numeric aperture, this tiny amount of light is sufficient for b imaging with excellent sensitivity and resolution. Many b detectors described in the literature (4,8,16,17) are based on the assumption that it is necessary to absorb most or all of the electron energy in the detector. This leads to detector thicknesses and pixel sizes on the order of 1 mm.…”

A 64-pixel positron-sensitive surgical probe

“…There are several types of beta-sensitive devices under development by other groups [3][4][5][6][7][8][9]. Compared to 511 keV gammas from 18 F-FDG, the short interaction length of positrons in tissue gives a measurement representative of just the region immediately in front of the probe (~1 -2 mm).…”