In chest tomosynthesis, low-dose projections collected over a limited angular range are used for reconstruction of section
images of the chest, resulting in a reduction of disturbing anatomy at a moderate increase in radiation dose compared to
chest radiography. In a previous study, we investigated the effects of learning with feedback on the detection of
pulmonary nodules in chest tomosynthesis. Six observers with varying degrees of experience of chest tomosynthesis
analyzed tomosynthesis cases for presence of pulmonary nodules. The cases were analyzed before and after learning with
feedback. Multidetector computed tomography (MDCT) was used as reference. The differences in performance between
the two readings were calculated using the jackknife alternative free-response receiver operating characteristics
(JAFROC-2) as primary measure of detectability. Significant differences between the readings were found only for
observers inexperienced in chest tomosynthesis. The purpose of the present study was to extend the statistical analysis of
the results of the previous study, including JAFROC-1 analysis and FROC curves in the analysis. The results are
consistent with the results of the previous study and, furthermore, JAFROC-1 gave lower p-values than JAFROC-2 for
the observers who improved their performance after learning with feedback.
Chest tomosynthesis has recently been introduced to healthcare as a low-dose alternative to CT or as a tool for improved
diagnostics in chest radiography with only a modest increase in radiation dose to the patient. However, no detailed
description of the dosimetry for this type of examination has been presented. The aim of this work was therefore to
investigate the dosimetry of chest tomosynthesis. The chest tomosynthesis examination was assumed to be performed
using a stationary detector and a vertically moving x-ray tube, exposing the patient from different angles. The Monte
Carlo based computer software PCXMC was used to determine the effective dose delivered to a standard-sized patient
from various angles using different assumptions of the distribution of the effective dose over the different projections.
The obtained conversion factors between input dose measures and effective dose for chest tomosynthesis for different
angular intervals were then compared with the horizontal projection. The results indicate that the error introduced by
using conversion factors for the PA projection in chest radiography for estimating the effective dose of chest
tomosynthesis is small for normally sized patients, especially if a conversion factor between KAP and effective dose is
used.
Chest tomosynthesis refers to the technique of collecting low-dose projections of the chest at different angles and using
these projections to reconstruct section images of the chest. In this study, a comparison of chest tomosynthesis and chest
radiography in the detection of pulmonary nodules was performed and the effect of clinical experience of chest
tomosynthesis was evaluated. Three senior thoracic radiologists, with more than ten years of experience of chest
radiology and 6 months of clinical experience of chest tomosynthesis, acted as observers in a jackknife free-response
receiver operating characteristics (JAFROC-1) study, performed on 42 patients with and 47 patients without pulmonary
nodules examined with both chest tomosynthesis and chest radiography. MDCT was used as reference and the total
number of nodules found using MDCT was 131. To investigate the effect of additional clinical experience of chest
tomosynthesis, a second reading session of the tomosynthesis images was performed one year after the initial one. The
JAFROC-1 figure of merit (FOM) was used as the principal measure of detectability. In comparison with chest
radiography, chest tomosynthesis performed significantly better with regard to detectability. The observer-averaged
JAFROC-1 FOM was 0.61 for tomosynthesis and 0.40 for radiography, giving a statistically significant difference
between the techniques of 0.21 (p<0.0001). The observer-averaged JAFROC-1 FOM of the second reading of the
tomosynthesis cases was not significantly higher than that of the first reading, indicating no improvement in detectability
due to additional clinical experience of tomosynthesis.
ViewDEX (Viewer for Digital Evaluation of X-ray images) is a Java-based DICOM-compatible software tool for
observer performance studies that can be used to display medical images with simultaneous registration of the observer's
response. The current release, ViewDEX 2.0 is a development of ViewDEX 1.0, which was released in 2007. Both
versions are designed to run in a Java environment and do not require any special installation. For example, the program
can be located on a memory stick or stand alone hard drive and be run from there. ViewDEX is managed and configured
by editing property files, which are plain text files where users, tasks (questions, definitions, etc.) and functionality
(WW/WL, PAN, ZOOM, etc.) are defined. ViewDEX reads all common DICOM image formats and the images can be
stored in any location connected to the computer. ViewDEX 2.0 is designed so that the user in a simple way can alter if
the questions presented to the observers are related to localization or not, enabling e.g. free-response ROC, standard
ROC and visual grading studies, as well as combinations of these, to be conducted in a fast and efficient way. The
software can also be used for bench marking and for educational purposes. The results from each observer are saved in a
log file, which can be exported for further analysis. The software is freely available for non-commercial purposes.
To determine clinical image quality in radiography, visual grading of the reproduction of important anatomical
landmarks is often used. The rating data from the observers in a visual grading study with multiple scale steps is ordinal,
meaning that non-parametric rank-invariant statistical methods are required. However, many visual grading methods
incorrectly use parametric statistical methods. This work describes how the methodology developed in receiver operating
characteristics (ROC) analysis for characterising the difference in the observer's response to the signal and no-signal
distributions can be applied to visual grading data for characterising the difference in perceived image quality between
two systems. The method is termed visual grading characteristics (VGC) analysis. In a VGC study, the task of the
observer is to rate her confidence about the fulfilment of image quality criteria. Using ROC software, the given ratings
for the two systems are then used to determine the VGC curve, which describes the relationship between the proportions
of fulfilled image criteria for the two compared systems for all possible decision thresholds. As a single measure of the
difference in image quality between the two compared systems, the area under the VGC curve can be used.
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