61 Evaluation and comparison of a new low energy high resolution collimator

Abstract

Introduction In order to find an optimum compromise between spatial resolution and sensitivity, GEHC designed a new collimator (LEHRS) and combined it to a new acquisition software for planar images (Clarity2D) and to a new tomographic acquisition method: ”step and shoot continuous”. The objective of the study is to evaluate planar and tomographic performances of this new collimator and to compare them to GEHC LEHR and to Siemens LEHR. Methods In planar mode, sensitivity and spatial resolution were measured for the three collimators according to NEMA NU1–2000 [1] . In tomographic mode, volumetric sensitivity and spatial resolution were also evaluated according to NEMA NU1–2000. Image quality was measured according NEMA NU2-2012 (contrast of 8) [2] . Projections were acquired according to routine protocols and the volumes were reconstructed thanks to and independent software taking into account spatial resolution depth dependence and attenuation correction. Results Planar mode. Maximum sensitivity was measured for Siemens LEHR (100 cps/MBq), LEHRS’s was 9% lower and GEHC LEHR’s was 22% lower. The full width at half maximum of the linear spread function, at source contact, is equivalent for both LEHR and 5% higher for LEHRS. Nevertheless thanks to Clarity2D, LSF’s FWHM degradation is less important when collimator distance increases. With 15 cm of diffusing material, LEHRS spatial resolution is 9,2 mm, GEHC LEHR is 10,1 mm and Siemens LEHR is 10,6 mm. Tomographic mode. LEHRS volumetric sensitivity is superior to both LEHR’s (16% for Siemens LEHR and 25% for GEHC LEHR). Spatial resolution is equivalent for the 3 collimators. The biggest hot sphere contrast recovery is equivalent for both GEHC collimators (41% for LEHR and 39,3% for LEHRS) and superior to Siemens LEHR (35,7%). LEHRS provides a better background variability (7,9%) than both LEHR (10,1% for GEC and 9,8% for Siemens). Conclusions In planar mode, LEHRS collimator associated to clarity 2D provides higher quality images than the other collimators since then enough diffusing material is placed between the source and the camera. In tomographic mode, the increase of volumetric sensitivity allows to reduce noise in the images (low background variability) while maintaining equivalent or superior contrast recovery and spatial resolution.