# Low Radiation Dose Implications in Obese Abdominal Computed Tomography Imaging
###### Abstract  
The aim of this study was to evaluate the implications of low radiation dose in abdominal computed tomography (CT) when combined with noise reduction filters and to see if this approach can overcome the challenges that arise while scanning obese patients. Anthropomorphic phantoms layered with and without 3-cm-thick circumferential animal fat packs to simulate different sized patients were scanned using a 128-slice multidetector CT (MDCT) scanner. Abdominal protocols (n = 12) were applied using various tube currents (150, 200, 250, and 300 mA) and tube voltages (100, 120, and 140 kVp). MOSFET dosimeters measured the internal organ dose. All images were reconstructed with filtered back projection (FBP) and different iterative reconstruction (IR) strengths (SAFIRE 3, SAFIRE 4, and SAFIRE 5) techniques and objective noise was measured within three regions of interests (ROIs) at the level of L4-L5. Organ doses varied from 0.34-56.2 mGy; the colon received the highest doses for both phantom sizes. Compared to the normal-weighted phantom, the obese phantom was associated with an approximately 20% decrease in effective dose. The 100 kVp procedure resulted in a 40% lower effective dose (\(p<0.05\)) compared to at 120 kVp and the associated noise increase was improved by increasing the IR (5) use, which resulted in a 60% noise reduction compared to when using FBP (\(p<0.05\)). When combined with iterative reconstruction, the low-kVp approach is feasible for obese patients in order to optimize radiation dose and maintain objective image quality.  
ab 2021 11 2456 2021 11 24  
reaching the CT detector. However, this results in higher patient doses, depending on patient shape, size, and composition [5]. Given that CT does not carry an image quality penalty for overexposures, CT personnel should stop erring on the side of lower than necessary noise levels for obese patients, which comes at the price of higher dose level [6; 7]. Indeed, the optimal image quality level for CT examinations with different clinical indications (i.e., the level at which diagnostic images can reliably be produced using the lowest dose level) should be tailored for individual patients and also for relevant groups (e.g., pediatric or obese patients).  
CT scanning techniques must always aim for optimum image quality at the lowest possible radiation exposure to patients. CT personnel are fundamentally responsible for controlling exposure parameters influencing radiation dose [8]. Modifying these parameters can influence image quality, thus causing higher noise levels, which can affect the low-contrast detection ability [9]. The challenge is to identify the acceptable image quality that allows the clinical question to be answered, which has not been done yet for obese patients undergoing abdominal CT [9; 10]. The patients' effective dose for abdominal CT might exceed 100 mSv, which would increase the cancer risk to 1 cancer case per 200 abdominal CT procedures [1]. Therefore, development of a CT dose reduction protocol is recommended to avoid unnecessary radiation risk.  
In this study, abdominal CT protocols were investigated because this area of the body is typically the most prone to compromised image quality due to patient girth. Therefore, an anthropomorphic phantom was used to manipulate the scanning parameters. Both the image quality and radiation doses were measured and the information obtained was used to help optimize scanning protocols for clinical use.