Head and body design

The GammaPen head comprises CsI (Tl) scintillation crystal (Epic Crystal Co., China) with 7.5 mm diameter and 10 mm length coupled to a MicroFC-60035-SMT SiPM (ON Semiconductor Co., USA), with 6 × 6 mm active area [18]. We designed the crystal with 7.5 mm diameter for efficient use of the active area of the SiPM. The GammaPen is primarily optimized for use with 140 keV gamma rays (the dominant gamma energy of Tc-99m). Yet, it can be also used for gamma-ray energies ranging between ∼60 keV (Am-241) and 364 keV (I-131).

The SiPM has proper photon detection efficiency (PDE) between 350 and 550 nm, having good overlap with CsI (Tl) emission spectra which has a high intensity between 480 and 630 nm [18, 19]. The detector is equipped with a Tungsten pinhole collimator with 7.5 mm internal diameter, 2.8 mm lateral thickness, and 225 mm length (Fig. 1b). The detector modules are shielded using 2.8-mm-thick tungsten for side and back faces and placed in a housing. The head tip diameter is about 14.5 mm.

The body of GammaPen consists of two machined parts. The first one is the head housing made of stainless steel whereas the second one is the housing of electronic components made of aluminum (Fig. 2a). The overall weight of these two parts is about 100 g with the center of mass showed in Fig. 2b. The position of the center of mass is near the center of the body which makes the device more stable in hand. The device weight consisting of body, Tungsten, battery and other electronic components is about 170 g, which is a suitable weight for handling. As a result, based on the weight, the center of mass and shape of the body, the device is ergonomic and easy to handle.

a The GammaPen body design and b the position of the center of mass