76 Aryana K et al. / Efficacy of high energy collimator FIGURE 1. Low energy high resolution collimator (LEHR) (upper row) as well as high energy (HE) collimator (lower row) images of a patient. Scatterograms are also shown on the right sides of each original image. There is no star shape artefact in the HE collimator images. TABLE 1. The specifications of high energy (HE) and low energy all purpose collimators Hole shape Number of holes (×1,000) Hole length (mm) Septal thickness (mm) Hole diameter (mm across the flats) Sensitivity at10 cm (count per minute/μCi) for 99mTc photons Spatial resolution (mm at 10 cm) for 99mTc photons Septal penetration (%) for 99m Tc photons site, scatter photons, as well as star shaped arte- facts due to septal penetration.5,6 To avoid this problem many centres used a lead shield on the in- jection site with some success.7 Another approach to decrease the above mentioned problem was to use other types of collimators with thicker septa (such as medium energy) instead of usual low en- ergy ones in order to reduce the septal penetration and decrease the star-shaped artifact.5-10 Although high energy (HE) collimators have thicker septa compared to the medium energy collimators, to the extent of our knowledge the efficacy of this kind of Radiol Oncol 2012; 46(1): 75-80. Low energy all purpose collimator High energy collimator Hexagonal Hexagonal 148 24.05 0.16 1.11 261.5 6.64 1.5 8 2 50.8 3.4 285.4 12.66 Almost none collimator for sentinel node mapping has not been evaluated before. In the current study, we evaluated the feasibility and possible advantages of using HE collimator for lymphoscintigraphy of early stage breast cancer patients. Patients and methods 20 patients with the clinical diagnosis of early (stages I and II) breast carcinoma were included in