The validity and reliability of the exposure index as a metric for estimating the radiation dose to the patient.

INTRODUCTION: With the introduction of digital radiography, the feedback between image quality and over-exposure has been partly lost which in some cases has led to a steady increase in dose. Over the years the introduction of exposure index (EI) has been used to resolve this phenomenon referred to as 'dose creep'. Even though EI is often vendor specific it is always a related of the radiation exposure to the detector. Due to the nature of this relationship EI can also be used as a patient dose indicator, however this is not widely investigated in literature. METHODS: A total of 420 dose-area-product (DAP) and EI measurements were taken whilst varying kVp, mAs and body habitus on two different anthropomorphic phantoms (pelvis and chest). Using linear regression, the correlation between EI and DAP were examined. Additionally, two separate region of interest (ROI) placements/per phantom where examined in order to research any effect on EI. RESULTS: When dividing the data into subsets, a strong correlation between EI and DAP was shown with all R-squared values > 0.987. Comparison between the ROI placements showed a significant difference between EIs for both placements. CONCLUSION: This research shows a clear relationship between EI and radiation dose which is dependent on a wide variety of factors such as ROI placement, body habitus. In addition, pathology and manufacturer specific EI's are likely to be of influence as well. IMPLICATIONS FOR PRACTICE: The combination of DAP and EI might be used as a patient dose indicator. However, the influencing factors as mentioned in the conclusion should be considered and examined before implementation.

Magnetic resonance colonography in severe attacks of ulcerative colitis.

OBJECTIVES: To evaluate the ability of MR colonography (MRC) to detect lesions in severe attacks of ulcerative colitis (UC) and to assess its concordance with rectosigmoidoscopy. METHODS: Eighteen patients underwent MRC and rectosigmoidoscopy. MRC consisted of a water-filled colonic procedure followed by T1/T2w images. Image quality was recorded. Inflammatory lesions and the existence of signs of severity were analysed. We calculated MR accuracy in the diagnosis of inflammatory lesions, as well as per segment and per patient concordance depending on the presence or absence of severe lesions. RESULTS: The MR image quality of the 108 segments was satisfactory. Endoscopy was used to study 36 segments (rectum and sigmoid). MRC had a positive predictive value of 100% and a sensitivity of 64% in the diagnosis of inflammatory lesions. Concordance for the diagnosis of severe lesions was excellent for the rectum (k = 0.85) and good for the sigmoid (k = 0.64). MRC diagnosed signs of severity in all patients affected at endoscopy. MRC also disclosed signs of severity located higher in the colon in four patients with nonsevere lesions at rectosigmoidoscopy. CONCLUSIONS: MRC can accurately diagnose inflammatory lesions in severe attacks of UC and significantly correlates with rectosigmoidoscopy in the diagnosis of severe lesions.