# Low Radiation Dose Implications in Obese Abdominal Computed Tomography Imaging
## 4 Discussion  
Our study showed that adding 6 cm of fat tissue to the anthropomorphic phantom caused up to 20% lower organ and effective doses when the same exposure settings were applied. Such a finding was expected due to the fat shielding, which attenuates the photons before reaching the internal organs. Given that no evidence currently attests to the radiosensitivity of fat, our findings could be positive for obese patients [16]. Therefore, using DLP values to estimate effective patient doses may not be as accurate as the actual absorbed doses measured in the organs [17]. Given the introduction of iterative algorithms that facilitate noise reductions for low-dose scans, the use of scanning techniques delivering relatively higher radiation doses for obese patients may not be justified any longer. Indeed, the use of this software can permit the use of low-dose scans that allow for dose reduction while maintaining diagnostic images for abdominal CT scans. This study showed that the abdominal protocol for the  
Figure 5: (**a**). Mean noise values \(\pm\) SDs for both phantoms (normal-weighted and obese) across the kVp applied selections (**b**). Mean noise values \(\pm\) SDs for both phantoms (normal-weighted and obese) across the applied reconstruction types. Figure 6: Mean signal to noise ratio (SNR) values for obese phantoms (at 200 mA) across the applied tube voltages selections and different reconstruction types. obese phantom at 100 kVp and with iterative reconstruction results in a 77.7% increase in SNR (at SAFIRE5) compared to at 120 kVp and with FBP for the matched tube current selection. This improvement in SNR is associated with up to 40% lower radiation dose. Furthermore, it is worth noting the scale of the individual mean values shown in Figure 5, which would seem to be in the diagnostic range, although no recommendation has been issued for an acceptable level of image noise for abdominal CT. The presence of internal fat can be beneficial for obese patients due to the potential improvement in natural contrast between organs. Hence, relatively higher noise can be acceptable, which facilitates the use of lower radiation doses. Although there is no widely accepted threshold for noise in the abdomen, the noise level values measured for obese patients in this study were all below 15 SD, which would likely be an acceptable level for most clinical indications. Therefore, radiographers should be careful not to aim for higher than necessary values for specific clinical indications. The deterioration in image quality for obese patients with low-dose protocols with FBP results from poorer image noise caused by increased photon absorption and scattering [1, 18, 19]. The use of IR, on the other hand, can cause noise reduction, which could be an alternative to the use of higher kVp of at least 120 and up to 140 when scanning patients of larger size to improve image noise at the price of higher dosage, as recommended by different studies [9, 20, 21]. However, this approach was used without an IR algorithm, which allows further dose and noise reductions while maintaining diagnostic acceptability, which has been proven in abdominal CT scans of obese patients [6]. Furthermore, lower kVps have the advantage of improving the contrast resolution of image [22]. For all abdominal organs, higher doses were received by the normal-weighted phantom when compared to the obese phantom, without reaching a statistical difference due to less attenuation of the beam. In a similar study, a significant dose increase was delivered to the overweight simulated phantom when higher image quality was requested by CT users by reducing the noise index by about 20% (15-12.5 H) [23]. This finding is in parallel to the difference in dosage seen in this study when the mA value selections were increased from 150 to 300 for the obese phantom. DLP and organ doses were increased by almost two-fold, which was expected.