Rauni Rossi Norrlund

Image quality dependency on system configuration and tube voltage in chest tomosynthesis—A visual grading study using an anthropomorphic chest phantom

PURPOSE To investigate the potential benefit of increasing the dose per projection image in chest tomosynthesis, performed at the current standard dose level, by reducing the angular range covered or the projection image density and to evaluate the influence of the tube voltage on the image quality. METHODS An anthropomorphic chest phantom was imaged using nine different projection image configurations and ten different tube voltages with the GE VolumeRAD tomosynthesis system. The resulting image sets were representative of being acquired at the same total effective dose. This was achieved partly by applying a simulated dose reduction to the projection images due to restrictions concerning the tube load settings on the VolumeRAD system. Four observers were included in a visual grading study where the reconstructed tomosynthesis section images were rated according to a set of image quality criteria. Image quality was evaluated relative to the default configuration and default tube voltage on the VolumeRAD system. RESULTS Overall, the image quality decreased with decreasing projection image density. Regarding angular range covered by the projection images, the image quality increased with decreasing angular range for two of the criteria, whereas for a criterion related to the depth resolution in the section images the reduced angular ranges resulted in inferior image quality as compared to the default configuration. The image quality showed little dependence on the tube voltage. CONCLUSIONS At the standard dose level of the VolumeRAD system, the potential benefits from increasing the dose per projection do not fully compensate for the negative effects resulting from a reduction in the number of projection images. Consequently, the default configuration consisting of 60 projection images acquired over 30° is a good alternative. The tube voltage used in tomosynthesis does not have a large impact on the image quality.

Evaluation of Accuracy and Precision of Manual Size Measurements in Chest Tomosynthesis using Simulated Pulmonary Nodules

RATIONALE AND OBJECTIVES To investigate the accuracy and precision of pulmonary nodule size measurements on chest tomosynthesis images. MATERIALS AND METHODS Artificial ellipsoid-shaped nodules with known sizes were inserted in clinical chest tomosynthesis images. The volume of the nodules corresponded to that of a sphere with a diameter of 4.0, 8.0, or 12.0 mm. Four thoracic radiologists were given the task to determine the longest diameter of the nodules. All nodules were measured twice. Measurement accuracy in terms of the mean measurement error was determined. Intraobserver and interobserver variabilities, as well as variability because of differences between nodules and their locations, were used as measures of precision. RESULTS The mean measurement error ranged from -0.3 to 0.1 mm for the nodule size groups and observers. Of the smallest nodules, the observers found 7-17 of total 50 nodules nonmeasurable. The intraobserver and interobserver variabilities were of similar magnitude, indicating relatively small differences between the observers. The internodule variability was in general larger, indicating that the different characteristics of the nodules and their location are sources of variability. CONCLUSIONS The results suggest a high accuracy and precision for manual measurements of the nodules in chest tomosynthesis images. However, small nodules (<5.0 mm) may be difficult to measure at all because of poor visibility.

EFFECT OF RADIATION DOSE LEVEL ON ACCURACY AND PRECISION OF MANUAL SIZE MEASUREMENTS IN CHEST TOMOSYNTHESIS EVALUATED USING SIMULATED PULMONARY NODULES

The aim of the present study was to investigate the dependency of the accuracy and precision of nodule diameter measurements on the radiation dose level in chest tomosynthesis. Artificial ellipsoid-shaped nodules with known dimensions were inserted in clinical chest tomosynthesis images. Noise was added to the images in order to simulate radiation dose levels corresponding to effective doses for a standard-sized patient of 0.06 and 0.04 mSv. These levels were compared with the original dose level, corresponding to an effective dose of 0.12 mSv for a standard-sized patient. Four thoracic radiologists measured the longest diameter of the nodules. The study was restricted to nodules located in high-dose areas of the tomosynthesis projection radiographs. A significant decrease of the measurement accuracy and intraobserver variability was seen for the lowest dose level for a subset of the observers. No significant effect of dose level on the interobserver variability was found. The number of non-measurable small nodules (≤5 mm) was higher for the two lowest dose levels compared with the original dose level. In conclusion, for pulmonary nodules at positions in the lung corresponding to locations in high-dose areas of the projection radiographs, using a radiation dose level resulting in an effective dose of 0.06 mSv to a standard-sized patient may be possible in chest tomosynthesis without affecting the accuracy and precision of nodule diameter measurements to any large extent. However, an increasing number of non-measurable small nodules (≤5 mm) with decreasing radiation dose may raise some concerns regarding an applied general dose reduction for chest tomosynthesis examinations in the clinical praxis.

Automatic pericardium segmentation and quantification of epicardial fat from computed tomography angiography

Abstract. Recent findings indicate a strong correlation between the risk of future heart disease and the volume of adipose tissue inside of the pericardium. So far, large-scale studies have been hindered by the fact that manual delineation of the pericardium is extremely time-consuming and that existing methods for automatic delineation lack accuracy. An efficient and fully automatic approach to pericardium segmentation and epicardial fat volume (EFV) estimation is presented, based on a variant of multi-atlas segmentation for spatial initialization and a random forest classifier for accurate pericardium detection. Experimental validation on a set of 30 manually delineated computer tomography angiography volumes shows a significant improvement on state-of-the-art in terms of EFV estimation [mean absolute EFV difference: 3.8 ml (4.7%), Pearson correlation: 0.99] with run times suitable for large-scale studies (52 s). Further, the results compare favorably with interobserver variability measured on 10 volumes.

Application of a computed tomography based cystic fibrosis scoring system to chest tomosynthesis

In the monitoring of progression of lung disease in patients with cystic fibrosis (CF), recurrent computed tomography (CT) examinations are often used. The relatively new imaging technique chest tomosynthesis (CTS) may be an interesting alternative in the follow-up of these patients due to its visualization of the chest in slices at radiation doses and costs significantly lower than is the case with CT. A first step towards introducing CTS imaging in the diagnostics of CF patients is to establish a scoring system appropriate for evaluating the severity of CF pulmonary disease based on findings in CTS images. Previously, several such CF scoring systems based on CT imaging have been published. The purpose of the present study was to develop a CF scoring system for CTS, by starting from an existing scoring system dedicated for CT images and making modifications regarded necessary to make it appropriate for use with CTS images. In order to determine any necessary changes, three thoracic radiologists independently used a scoring system dedicated for CT on both CT and CTS images from CF patients. The results of the scoring were jointly evaluated by all the observers, which lead to suggestions for changes to the scoring system. Suggested modifications include excluding the scoring of air trapping and doing the scoring of the findings in quadrants of the image instead of in each lung lobe.

Evaluation of a corrected implementation of a method of simulating pulmonary nodules in chest tomosynthesis

Background A method of simulating pulmonary nodules in tomosynthesis images has previously been developed and evaluated. An unknown feature of a rounding function included in the computer code was later found to introduce an artifact, affecting simulated nodules in low-signal regions of the images. The computer code has now been corrected. Purpose To perform a thorough evaluation of the corrected nodule-simulation method, comparing the detection rate and visual appearance of artificial nodules with those of real nodules in an observer performance experiment. Material and Methods A cohort of 64 patients with a total of 129 pulmonary nodules was used in the study. Artificial nodules, each matching a corresponding real nodule by size, attenuation, and anatomical location, were generated and simulated into the tomosynthesis images of the different patients. The detection rate and visual appearance of artificial nodules generated using both the corrected and uncorrected computer code were compared to those of real nodules. The results were evaluated using modified receiver operating characteristic (ROC) analyses. Results The difference in detection rate between artificial and real nodules slightly increased using the corrected computer code (uncorrected code: area under the curve [AUC], 0.47; 95% CI, 0.43–0.51; corrected code: AUC, 0.42; 95% CI, 0.38–0.46). The visual appearance was however substantially improved using the corrected computer code (uncorrected code: AUC, 0.70; 95% CI, 0.63–0.76; corrected code: AUC, 0.49; 95% CI, 0.29–0.65). Conclusion The computer code including a correct rounding function generates simulated nodules that are more visually realistic than simulated nodules generated using the uncorrected computer code, but have a slightly different detection rate compared to real nodules.

INFLUENCE OF THE IN-PLANE ARTEFACT IN CHEST TOMOSYNTHESIS ON PULMONARY NODULE SIZE MEASUREMENTS.

The aim of the present study was to investigate how the in-plane artefact present in the scan direction around structures in tomosynthesis images should be managed when measuring the size of nodules in chest tomosynthesis images in order to achieve acceptable measurement accuracy. Data from measurements, performed by radiologists, of the longest diameter of artificial nodules inserted in chest tomosynthesis images were used. The association between the measurement error and the direction of the longest nodule diameter, relative to the scan direction, was evaluated using the Kendall rank correlation coefficient. All of the radiologists had chosen to not include the artefact in the measurements. Significant association between measurement error and the direction of the longest diameter was found for nodules larger than 12 mm, which indicates that, for these nodules, there is a risk of underestimating the nodule size if the in-plane artefact is omitted from manual diameter measurements.

Detection of pulmonary nodule growth with dose reduced chest tomosynthesis: a human observer study using simulated nodules

Chest tomosynthesis may be a suitable alternative to computed tomography for the clinical task of follow up of pulmonary nodules. The aim of the present study was to investigate the detection of pulmonary nodule growth suggestive of malignancy using chest tomosynthesis. Previous studies have indicated remained levels of detection of pulmonary nodules at dose levels corresponding to that of a conventional lateral radiograph, approximately 0.04 mSv, which motivated to perform the present study this dose level. Pairs of chest tomosynthesis image sets, where the image sets in each pair were acquired of the same patient at two separate occasions, were included in the study. Simulated nodules with original diameters of approximately 8 mm were inserted in the pairs of image sets, simulating situations where the nodule had remained stable in size or increased isotropically in size between the two different imaging occasions. Four different categories of nodule growth were included, corresponding to a volume increase of approximately 21 %, 68 %, 108 % and 250 %. All nodules were centered in the depth direction in the tomosynthesis images. All images were subjected to a simulated dose reduction, resulting in images corresponding to an effective dose of 0.04 mSv. Four observers were given the task of rating their confidence that the nodule was stable in size or not on a five-level rating scale. This was done both before any size measurements were made of the nodule as well as after measurements were performed. Using Receiver operating characteristic analysis, the rating data for the nodules that were stable in size was compared to the rating data for the nodules simulated to have increased in size. Statistically significant differences between the rating distributions for the stable nodules and all of the four nodule growth categories were found. For the three largest nodule growths, nearly perfect detection of nodule growth was seen. In conclusion, the present study indicates that during optimal imaging conditions and for nodules with diameters of approximately 8 mm that grow fairly symmetrically, chest tomosynthesis performed at a dose level corresponding to that of a lateral chest radiograph can, with high sensitivity, differentiate nodules stable in size from nodules growing at rates associated with fast growing malignant nodules.

Detection and Characterization of Solid Pulmonary Nodules at Digital Chest Tomosynthesis: Data from a Cohort of the Pilot Swedish Cardiopulmonary Bioimage Study

Purpose To investigate the performance of digital tomosynthesis (DTS) for detection and characterization of incidental solid lung nodules. Materials and Methods This prospective study was based on a population study with 1111 randomly selected participants (age range, 50-64 years) who underwent a medical evaluation that included chest computed tomography (CT). Among these, 125 participants with incidental nodules 5 mm or larger were included in this study, which added DTS in conjunction with the follow-up CT and was performed between March 2012 and October 2014. DTS images were assessed by four thoracic radiologists blinded to the true number of nodules in two separate sessions according to the 5-mm (125 participants) and 6-mm (55 participants) cut-off for follow-up of incidental nodules. Pulmonary nodules were directly marked on the images by the readers and graded regarding confidence of presence and recommendation for follow-up. Statistical analyses included jackknife free-response receiver operating characteristic, receiver operating characteristic, and Cohen κ coefficient. Results Overall detection rate ranges of CT-proven nodules 5 mm or larger and 6 mm or larger were, respectively, 49%-58% and 48%-62%. Jackknife free-response receiver operating characteristics figure of merit for detection of CT-proven nodules 5 mm or larger and 6 mm or larger was 0.47 and 0.51, respectively, and area under the receiver operating characteristic curve regarding recommendation for follow-up was 0.62 and 0.65, respectively. Conclusion Routine use of DTS would result in lower detection rates and reduced number of small nodules recommended for follow-up.

CT-lung volume estimates in trauma patients undergoing stabilizing surgery for flail chest

AIM To estimate and compare lung volumes from pre- and post-operative computed tomography (CT) images and correlate findings with post-operative lung function tests in trauma patients with flail chest undergoing stabilizing surgery. PATIENTS AND METHODS Pre- and post-operative CT images of the thorax were used to estimate lung volumes in 37 patients who had undergone rib plate fixation at least 6 months before inclusion for flail chest due to blunt thoracic trauma. Computed tomography lung volumes were estimated from airway distal to each lung hilum by outlining air-filled lung tissue either manually in images of 5 mm slice thickness or automatically in images of 0.6 mm slice thickness. Demographics, pain, range of motion in the thorax, breathing movements and Forced Vital Capacity (FVC) were assessed. Total Lung Capacity (TLC) measurements were also made in a subgroup of patients (n = 17) who had not been intubated at time of the initial CT. Post-operative CT lung volumes were correlated to FVC and TLC. RESULTS Patients with a median age of 62 (19-90) years, a median Injury Severity Score (ISS) of 20 (9-54), and a median New Injury Severity Score (NISS) of 27 (17-66) were enrolled in the study. Median follow-up time was 3.9 (0.5-5.6) years. Two patients complained of pain at rest and when breathing. Pre-operative CT lung volumes were significantly different (p < 0.0001) from post-operative CT lung volumes, 3.51 l (1.50-6.05) vs. 5.59 l (2.18-7.78), respectively. At follow-up, median FVC was 3.76 l (1.48-5.84) and median TLC was 6.93 l (4.21-8.42). Post-operative CT lung volumes correlated highly with both FVC [rs = 0.75 (95% CI 0.57‒0.87, p < 0.0001)] and TLC [rs = 0.90 (95% CI 0.73‒0.96, p < 0.0001)]. The operated thoracic side showed decreased breathing movements. Range of motion in the lower thorax showed a low correlation with FVC [rs = 0.48 (95% CI 0.19‒0.70, p = 0.002)] and a high correlation with TLC [rs = 0.80 (95% CI 0.51‒0.92, p < 0.0001)]. CONCLUSIONS Post-operative CT-lung volume estimates improve compared to pre-operative values in trauma patients undergoing stabilizing surgery for flail chest, and can be used as a marker for lung function when deciding which patient with chest wall injuries can benefit from surgery.