Performance characteristics of a second generation micro crystal element (MiCE2) detector

Abstract

A b s t r a c t --This work reports on performance characteristics of a second generation micro crystal element (MiCE2) detector for a dedicated PET system to image mice. Our MiCE2 detector consists of a 22x22 array of 0.8x0.8x6 mm mixed lutetium silicate (MLS) crystals. Five sides of the crystals are polished with one 0.8x0.8 mm face left unpolished. The crystals are placed within a grid made of a highly reflective polymer film material. The grid optically isolates the crystals and also functions as a reflective wrap. The detector unit is directly coupled to a 6+6 cross-anode position sensitive PMT. The crystal of interaction is determined using simple Anger style logic. Crystal maps have been created for a 22x22 crystal array. All 484 crystals are visualized in the full detector module's crystal map. The average peak to valley ratio between neighboring crystals was 6.4. There was greater than a factor of two difference between the photopeak energy channel for high versus low light collection efficiency crystals. The energy resolution for individual crystals varied between 14% and 23%. Partial detector arrays (e.g., 22x4) using 0.8x0.8x10 mm crystals with an etched surface finish have also been built and decoded. A miniature line source phantom consisting of five 1 mm diameter lines with 2 mm center-tocenter spacing has been imaged using two partial MiCE2 detectors. All lines are distinguished and the average peak to valley ratio between lines is 2.7.

Copyright

“…Detectors rPET detectors are based on 1.5x1.5x12 mm 3 MLS crystals (Glendfield Partners, Canada) with all the facets mechanically polished. MLS is a not hygroscopic and rugged material based on Lutetium, what makes it radioactive, producing a background of 260 cps per cubic centimeter [13,17]. The individual crystals are assembled on a 30 x 30 matrix with 100 microns thick Lumirror reflector (Toray Corp., Japan) between crystals, achieving a packing fraction of 88%.…”

“…Previous works referenced in the literature [13,16,25] have demonstrated that this combination of PS-PMTs, high light output scintillators arrays and charge sensitive readouts schemes is well suited for high resolution, high sensitivity PET imaging systems.…”

“…Different designs can be found in the literature using different scintillator materials, crystal sizes and coupling methods. Simultaneous high sensitivity and high spatial resolution constrains the engineering of these types of detectors since state-of-the-art technology usually confronts both requirements [10][11][12][13][14][15][16]. The detector presented in this paper was envisioned for high resolution small imaging (mice and rats mainly) looking for the maximum performance achievable at a reasonable cost since the system that will integrate these detectors should be kept simple and small.…”

Limitaciones tecnológicas de la tomografía por emisión de positrones (PET) para pequeños animales de laboratorio

“…Para lo primero se precisan cristales pequeños y detectores sensibles a posición, con un fino muestreo espacial 30 . Para aumentar la sensibilidad esos mismos cristales deberían ser grandes y densamente empaquetados en una configuración geométrica compacta.…”

“…3), lo que mejora la resolución intrínseca (resolución propia del detector; en la global del sistema intervienen más factores) respecto a la de los detectores de bloque 28,30,[34][35][36][37][38][39] . Estos diseños, sin embargo, tienen un coste más elevado, razón por la cual su uso se ha limitado a los sistemas de animales, con un número de detectores mucho menor que en los sistemas para humanos.…”