High-Resolution $^{125}$I Small Animal Imaging With a Coded Aperture and a Hybrid Pixel Detector

Abstract

We report on tests of a radionuclide imaging system for in vivo investigations in small animals with low-energy photons as from 125 I (27-35 keV). Imaging optics features a high-resolution coded aperture mask and a fine pitch hybrid pixel detector (silicon 300-m or 700-m thick, or CdTe 1 mm thick) of the Medipix2 series (55 m pitch, 256 256 pixels). The coded aperture had 480 70-m holes in 100-m-thick tungsten. Laboratory tests with a 109 Cd 22 keV source and a microfocus X-ray tube (35 kVp, Mo anode) show a system resolution of about 110 m at magnification = 2 12 and a sensitivity improvement of 30:1 as compared to a 300-m pinhole collimator. The field of view also depends on magnification: in the experiments presented, it varied from 6 mm ( = 2 12) to 21 mm ( = 0 66). 125 I in vivo mouse thyroid imaging with the 70 m coded aperture, a 300 m pinhole and a 100 m parallel hole collimator was also performed to obtain a qualitative comparison. This low energy, semiconductor-based, compact gamma-ray imaging system can be used as a gamma-ray sub-millimeter resolution imager for energies below about 35 keV and it is the basic imaging unit of a small animal Single Photon Emission Computed Tomography system (MediSPECT) built at University of Napoli Federico II and Istituto Nazionale Fisica Nucleare (INFN), Napoli.

The effects of object activity distribution on multiplexing multi-pinhole SPECT

“…It was originally proposed and works well for far-field applications, such as high-energy astronomical imaging with bright and isolated sources (Caroli et al 1987). Accorsi et al (2001) validated the relationship between SNR improvement and sensitivity gain with a coded aperture for point sources, and demonstrated its usage in imaging high contrast point-like objects with 125 I tracer when coupled to a hybrid pixel detector (Accorsi et al 2008). However, the majority of tracers for nuclear medicine imaging do not bind to the targets with high specificity, and as a result background activity always exists.…”

Multi-pinhole collimator design for small-object imaging with SiliSPECT: a high-resolution SPECT

“…Higher projection magnification and pinhole density can increase the overlap of pinhole projections, known as multiplexing, which reduces the accuracy of the information about the photon trajectories. Highly multiplexed projections with very dense pinhole distribution require some type of decoding process and are commonly referred to as coded apertures (Garibaldi et al 2005, Accorsi et al 2008). Another way of reducing the problem with multi-pinhole projection overlap is to obtain projections at a number of pinhole-detector distances (Wilson et al 2000).…”

Preliminary evaluation of a novel energy-resolved photon-counting gamma ray detector

“…These detectors offer a combination of good energy resolution, good spatial resolution and adequate detection efficiency for gamma rays emitted by common single photon emitters, such as I-125, Tc-99m, I-123 and Tl-201. Given the recent trend in developing ultrahigh-resolution single photon emission computed tomography (SPECT) instrumentation, several groups have evaluated the use of CZT or CdTe-based imaging sensors to replace scintillation detectors for high-resolution SPECT imaging applications [5][6][7][8].…”