Development of a miniature scintillation camera using an NaI(Tl) scintillator and PSPMT for scintimammography

Abstract

We have developed a small scintillation camera dedicated to breast imaging and have evaluated the performance of the system. In order to increase the limited field of view (FOV) determined by the size of a position-sensitive photomultiplier tube (PSPMT), the imaging characteristics of a diverging-hole collimator (DHC) were also investigated. The small scintillation camera system consists of an NaI(Tl) crystal (60 mm × 60 mm × 6 mm) coupled to a Hamamatsu R3941 PSPMT, a resistor chain circuit, preamplifiers, nuclear instrument modules, an analogue to digital converter and a PC for control and display. The intrinsic energy resolution of the system was 12.9% FWHM at 140 keV. The spatial resolution was measured using a line-slit mask and 99mTc point sources and was 3.1 mm FWHM. The intrinsic sensitivity of the system was approximately 162 counts/s kBq-1. The DHC made it possible to image a larger FOV (75×75 mm2 at the surface of collimator) than a parallel-hole collimator (60×60 mm2). The system sensitivity obtained using the DHC gradually decreased with distance (3% at 1 cm, 6% at 2 cm and 9% at 3 cm). The results demonstrate that the system developed in this study could be utilized clinically to image malignant breast tumours. A DHC can be employed to expand the FOV of the system confined by the size of PSPMT with a modest compromise in the performance of the system.

Performance evaluation of a hand-held, semiconductor (CdZnTe)-based gamma camera

“…Recent and comparable sensitivity data are available for other gamma camera detector systems [1,2,3,4]. As stated previously, CdZnTe has a high density and therefore high efficiency for stopping gamma rays.…”

“…With the NaI scintillation camera, the intrinsic energy resolution is about 10% FWHM at 140 keV at best [2,3,4,13]. As compared with the recently developed semiconductor systems based on CsI/PIN diode detector technology, we obtained superior results with the CdZnTe-based, semiconductor detector system [1,4].…”

“…When compared with conventional gamma cameras using NaI/PMT detector systems, the result was an improvement [2,3,4]. Both the CsI/PIN and the CdZnTe detector technology use discrete channels of electronic signal processing for every pixel.…”

“…This represents a significant difference as compared with both the CsI/PIN and the NaI/PMT detection technology [1,2,3,4]. By comparison, FWHM was found to be 3.5 mm at the surface of the collimator when using the best-performing currently available NaI scintillation camera with a parallel-hole collimator [2]. CsI/PIN detector features and pixel sizes are limited by several factors, the most significant being the cross-talk in the energy to light conversion process and the size limitations of the PIN structure.…”

“…Digirad has recently developed a portable gamma camera, the 2020tc Imager, that uses CsI(Ti) multi-crystal scintillators and photodiode sensors. The basic performance of the Digirad 2020tc Imager is superior to that of conventional gamma cameras using the NaI/PMT technology [1,2,3,4,5], but not to an extent that permits its use for sentinel node detection and radiopharmaceutical-guided surgery applications [6,7,8,9,10].…”