The purpose of this study is to evaluate the effect of reduced tube current, as a surrogate
for radiation dose, on lung nodule detection in pediatric chest multi-detector CT (MDCT).
Normal chest MDCT images of 13 patients aged 1 to 7 years old were used as templates
for this study. The original tube currents were between 70 mA and 180 mA. Using
proprietary noise addition software, noise was added to the images to create 13 cases at
the lowest common mA (i.e. 70 mA), 13 cases at 35 mA (50% reduction), and 13 cases at
17.5 mA (75% reduction). Three copies of each case were made for a total of 117 series
for simulated nodule insertion. A technique for three-dimensional simulation of small
lung nodules was developed, validated through an observer study, and used to add
nodules to the series. Care was taken to ensure that each of three lung zones (upper,
middle, lower) contained 0 or 1 nodule. The series were randomized and the presence of
a nodule in each lung zone was rated independently and blindly by three pediatric
radiologists on a continuous scale between 0 (definitely absent) and 100 (definitely
present). Receiver operating characteristic analysis of the data showed no general
significant difference in diagnostic accuracy between the reduced mA values and 70 mA,
suggesting a potential for dose reduction with preserved diagnostic quality. To our
knowledge, this study is the first controlled, systematic, and task-specific assessment of
the influence of dose reduction in pediatric chest CT.
In recent years, there has been a desire to reduce CT radiation dose to children because of their susceptibility and
prolonged risk for cancer induction. Concerns arise, however, as to the impact of dose reduction on image quality and
thus potentially on diagnostic accuracy. To study the dose and image quality relationship, we are developing a
simulation code to calculate organ dose in pediatric CT patients. To benchmark this code, a cylindrical phantom was
built to represent a pediatric torso, which allows measurements of dose distributions from its center to its periphery.
Dose distributions for axial CT scans were measured on a 64-slice multidetector CT (MDCT) scanner (GE Healthcare,
Chalfont St. Giles, UK). The same measurements were simulated using a Monte Carlo code (PENELOPE, Universitat de
Barcelona) with the applicable CT geometry including bowtie filter. The deviations between simulated and measured
dose values were generally within 5%. To our knowledge, this work is one of the first attempts to compare measured
radial dose distributions on a cylindrical phantom with Monte Carlo simulated results. It provides a simple and effective
method for benchmarking organ dose simulation codes and demonstrates the potential of Monte Carlo simulation for
investigating the relationship between dose and image quality for pediatric CT patients.