Abstract
To compare the effective and eye lens radiation dose in helical MDCT brain examinations using automatic tube current modulation in conjunction with either standard filtered back projection (FBP) technique or iterative reconstruction in image space (IRIS). Of 400 adult brain MDCT examinations, 200 were performed using FBP and 200 using IRIS with the following parameters: tube voltage 120 kV, rotation period 1 second, pitch factor 0.55, automatic tube current modulation in both transverse and longitudinal planes with reference mAs 300 (FBP) and 200 (IRIS). Doses were calculated from CT dose index and dose length product values utilising ImPACT software; the organ dose to the lens was derived from the actual tube current-time product value applied to the lens. Image quality was assessed by two independent readers blinded to the type of image reconstruction technique. The average effective scan dose was 1.47±0.26 mSv (FBP) and 0.98±0.15 mSv (IRIS), respectively (33.3% decrease). The average organ dose to the eye lens decreased from 40.0±3.3 mGy (FBP) to 26.6±2.0 mGy (IRIS, 33.5% decrease). No significant change in diagnostic image quality was noted between IRIS and FBP scans (P=0.17). Iterative reconstruction of cerebral MDCT examinations enables reduction of both effective and organ eye lens dose by one third without signficant loss of image quality.
Highlights
Radiation doses resulting from medical exposure are steadily increasing in the population
Image quality and image noise were evaluated on 5 mm axial slices with reconstruction kernel H31s (FBP) and J30s (IRIS)
In terms of radiation dose, IRIS based protocols showed significant (P
Summary
Radiation doses resulting from medical exposure are steadily increasing in the population. Computed tomography (CT) accounts for only about 15% of radiologic examinations in the United States, it delivers two thirds of the entire cumulative exposure from all radiologic studies[1,2]. In order to change this unfavourable trend resulting from the continuously increasing number of CT procedures performed worldwide, adoption of adequate precautions aimed at radiation dose reduction is of great importance. IR was already used on first generation CT scanners in the early 1970s It was rapidly replaced by filtered back projection (FBP) which offered incomparably shorter reconstruction times. As emission tomography methods (SPECT, PET) deal with much less projection data but with increased proportion of noise than CT, image noise supression emerged as the most desirable feature and long reconstruction times of IR were subsidiary[4]
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