Preliminary test of an imaging probe for nuclear medicine using hybrid pixel detectors.

We are investigating the feasibility of an intraoperative imaging probe for lymphoscintigraphy withTc-99m tracer, for sentinel node radioguided surgery, using the Medipix series of hybrid detectors coupled to a collimator. These detectors are pixelated semiconductor detectors bump-bonded to the Medipix1 photon counting read-out chip (64x64 pixel, 170 mm pitch) or to the Medipix2 chip (256x256 pixel, 55 um pitch), developed by the European Medipix collaboration. The pixel detector we plan to use in the final version of the probe is a semi-insulating GaAs detector or a 1–2mm thick CdZnTe detector. For the preliminary tests presented here, we used 300-um thick silicon detectors, hybridized via bump-bonding to the Medipix1 chip. We used a tungsten parallel-hole collimator (7mm thick, matrix array of 6464 100 mm circular holes with 170 um pitch), and a 22, 60 and 122 keV point-like (1mm diameter) radioactive sources, placed at various distances from the detector. These tests were conducted in order to investigate the general feasibility of this imaging probe and its resolving power. Measurements show the high resolution but low efficiency performance of the detector–collimator set, which is able to image the 122 keV source with <1 mm FWHM resolution.