ABSTRACT
@#Introduction: A custom-made Perspex male pelvic phantom was developed to measure and to compare absorbed, surface and effective doses obtained from Single-Energy and Dual-Energy Computed Tomography (SECT & DECT). Methods: A customised Perspex pelvic phantom that mimicked male Asian reference size was scanned with SECT mode at 80 kV, 100 kV, 120 kV and 140 kV. In addition, the fabricated phantom was also scanned with DECT mode at 80/140 kV. Thermoluminescence dosimeters (TLD) were used to measure the charges and doses obtained from the TLD calibration curve. The absorbed dose, surface dose and effective dose obtained from SECT and DECT were measured and compared between these two modes. Results: The DECT showed 55.9 % dose reduction compared to SECT at 140 kV tube voltage. It shows that DECT can be used with radiation dose sparing, and it is in good agreement with routine CTDI phantom study. The effective dose of DECT of the abdominal imaging was within the acceptable effective dose limit of AAPM Report No. 96. This study also found that the surface dose was lower than values reported in previous studies for both modes. Conclusion: The fabricated Perspex phantom shows a great potential to be considered as an alternative phantom for the commercially existing phantom in CT dosimetry application.
ABSTRACT
Digital mammography has been progressively introduced in screening centers and the concern is to achieve an image of diagnostic value which would be able to detect early changes in the breast tissue. The aim of this study was to evaluate the image quality of mammograms using quantitative and qualitative methods of two FFDM systems with variations in breast thickness and anode/filter combination. This study was done from January to April 2008 with two FFDM systems; Siemens Mammomat NovationDR at Diagnostic Imaging Department, Hospital Kuala Lumpur and Hologic Lorad Selenia at Breast Clinic, National Cancer Society. A CIRS012A tissue equivalent breast phantom (4, 5 and 6 cm) thickness was used to obtain images in the craniocaudal plane with 26-32 kVp and a combination of molybdenum/molybdenum (Mo/Mo) and molybdenum/rhodium (Mo/Rh) anode/filter. For the qualitative evaluation, two independent radiologist with a minimum of five years experience was used to score the images. Wilcoxon Sign Rank Test showed that there are no significant differences (p > 0.05) in image quality between both the FFDM systems. Kappa analysis had a poor agreement between the scores given by the two radiologists. The quantitative analysis using Mann-Whitney test showed that there are significant differences (p < 0.05) between the SNR values of both FFDM systems. Although the qualitative evaluation was similar, the study showed that Lorad Selenia had a significantly superior SNR value, hence would be a better tool to detect early changes in the breast tissue. This study also demonstrated that a lower kVp is more suitable with molybdenum filter and as the breast thickness is increased rhodium filter with higher kVp displayed better quality images.