Eman Shaheen

Investigation of the effect of tube motion in breast tomosynthesis: continuous or step and shoot?

Digital breast tomosynthesis (DBT) is a 3D modality that may have the potential to complement or replace 2D mammography. One major design aspect of DBT systems is the choice of tube motion: continuous tube motion during x-ray exposure or the step and shoot method where the tube is held fixed while x-rays are released. Systems with continuous tube motion experience focal spot motion blurring but a reduced patient motion blurring due to potentially faster total acquisition times when compared to the step and shoot approach. In order to examine the influence of focus motion on lesion detectability, a simulation environment was developed where lesions such as microcalcifications and masses are inserted into different thicknesses of theoretical materials. A version of the power law noise method was employed to approximate realistic anatomical breast volumes. The simulated projection images were reconstructed and appropriate metrics (peak contrast, contrast and signal-difference-to-noise ratio) of the lesions in the two different modes were compared. Results suggest an increase of the peak contrasts in the microcalcification data sets by 8 - 9 % for the step-and-shoot method when compared to the continuous mode (p <0.05). While the contrast and signal-difference-to-noise- ratio calculated for the same two modes almost overlapped for the mass datasets showing a difference of only 1-2%.

The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis.

PURPOSE This work proposes a new method of building 3D breast mass models with different morphological shapes and describes the validation of the realism of their appearance after simulation into 2D digital mammograms and breast tomosynthesis images. METHODS Twenty-five contrast enhanced MRI breast lesions were collected and each mass was manually segmented in the three orthogonal views: sagittal, coronal, and transversal. The segmented models were combined, resampled to have isotropic voxel sizes, triangularly meshed, and scaled to different sizes. These masses were referred to as nonspiculated masses and were then used as nuclei onto which spicules were grown with an iterative branching algorithm forming a total of 30 spiculated masses. These 55 mass models were projected into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. The realism of the appearance of these mass models was assessed by five radiologists via receiver operating characteristic (ROC) analysis when compared to 54 real masses. All lesions were also given a breast imaging reporting and data system (BIRADS) score. The data sets of 2D mammography and tomosynthesis were read separately. The Kendalls coefficient of concordance was used for the interrater observer agreement assessment for the BIRADS scores per modality. Further paired analysis, using the Wilcoxon signed rank test, of the BIRADS assessment between 2D and tomosynthesis was separately performed for the real masses and for the simulated masses. RESULTS The area under the ROC curves, averaged over all observers, was 0.54 (95% confidence interval [0.50, 0.66]) for the 2D study, and 0.67 (95% confidence interval [0.55, 0.79]) for the tomosynthesis study. According to the BIRADS scores, the nonspiculated and the spiculated masses varied in their degrees of malignancy from normal (BIRADS 1) to highly suggestive for malignancy (BIRADS 5) indicating the required variety of shapes and margins of these models. The assessment of the BIRADS scores for all observers indicated good agreement based on Kendalls coefficient for both the 2D and the tomosynthesis evaluations. The paired analysis of the BIRADS scores between 2D and tomosynthesis for each observer revealed consistent behavior for the real and simulated masses. CONCLUSIONS A database of 3D mass models, with variety of shapes and margins, was validated for the realism of their appearance for 2D digital mammography and for breast tomosynthesis. This database is suitable for use in future observer performance studies whether in virtual clinical trials or in patient images with simulated lesions.

Simulation of 3D objects into breast tomosynthesis images.

Digital breast tomosynthesis is a new three-dimensional (3D) breast-imaging modality that produces images of cross-sectional planes parallel to the detector plane from a limited number of X-ray projections over a limited angular range. Several technical and clinical parameters have not yet been completely optimised. Some of the open questions could be addressed experimentally; other parameter settings cannot be easily realised in practice and the associated optimisation process requires therefore a theoretical approach. Rather than simulating the complete 3D imaging chain, it is hypothesised that the simulation of small lesions into clinical (or test object) images can be of help in the optimisation process. In the present study, small 3D objects have been simulated into real projection images. Subsequently, these hybrid projection images are reconstructed using the routine clinical reconstruction tools. In this study, the validation of this simulation framework is reported through the comparison between simulated and real objects in reconstructed planes. The results confirm that there is no statistically significant difference between the simulated and the real objects. This suggests that other small mathematical or physiological objects could be simulated with the same approach.

Two examples of indication specific radiation dose calculations in dental CBCT and Multidetector CT scanners

PURPOSE To calculate organ doses and estimate the effective dose for justification purposes in patients undergoing orthognathic treatment planning purposes and temporal bone imaging in dental cone beam CT (CBCT) and Multidetector CT (MDCT) scanners. METHODS The radiation dose to the ICRP reference male voxel phantom was calculated for dedicated orthognathic treatment planning acquisitions via Monte Carlo simulations in two dental CBCT scanners, Promax 3D Max (Planmeca, FI) and NewTom VGi evo (QR s.r.l, IT) and in Somatom Definition Flash (Siemens, DE) MDCT scanner. For temporal bone imaging, radiation doses were calculated via MC simulations for a CBCT protocol in NewTom 5G (QR s.r.l, IT) and with the use of a software tool (CT-expo) for Somatom Force (Siemens, DE). All procedures had been optimized at the acceptance tests of the devices. RESULTS For orthognathic protocols, dental CBCT scanners deliver lower doses compared to MDCT scanners. The estimated effective dose (ED) was 0.32mSv for a normal resolution operation mode in Promax 3D Max, 0.27mSv in VGi-evo and 1.18mSv in the Somatom Definition Flash. For temporal bone protocols, the Somatom Force resulted in an estimated ED of 0.28mSv while for NewTom 5G the ED was 0.31 and 0.22mSv for monolateral and bilateral imaging respectively. CONCLUSIONS Two clinical exams which are carried out with both a CBCT or a MDCT scanner were compared in terms of radiation dose. Dental CBCT scanners deliver lower doses for orthognathic patients whereas for temporal bone procedures the doses were similar.

Comparison of digital breast tomosynthesis and 2D digital mammography using a hybrid performance test

This paper introduces a hybrid method for performing detection studies in projection image based modalities, based on image acquisitions of target objects and patients. The method was used to compare 2D mammography and digital breast tomosynthesis (DBT) in terms of the detection performance of spherical densities and microcalcifications. The method starts with the acquisition of spheres of different glandular equivalent densities and microcalcifications of different sizes immersed in a homogeneous breast tissue simulating medium. These target objects are then segmented and the subsequent templates are fused in projection images of patients and processed or reconstructed. This results in hybrid images with true mammographic anatomy and clinically relevant target objects, ready for use in observer studies. The detection study of spherical densities used 108 normal and 178 hybrid 2D and DBT images; 156 normal and 321 hybrid images were used for the microcalcifications. Seven observers scored the presence/absence of the spheres/microcalcifications in a square region via a 5-point confidence rating scale. Detection performance in 2D and DBT was compared via ROC analysis with sub-analyses for the density of the spheres, microcalcification size, breast thickness and z-position. The study was performed on a Siemens Inspiration tomosynthesis system using patient acquisitions with an average age of 58 years and an average breast thickness of 53 mm providing mean glandular doses of 1.06 mGy (2D) and 2.39 mGy (DBT). Study results showed that breast tomosynthesis (AUC = 0.973) outperformed 2D (AUC = 0.831) for the detection of spheres (p  <  0.0001) and this applied for all spherical densities and breast thicknesses. By way of contrast, DBT was worse than 2D for microcalcification detection (AUC2D = 0.974, AUCDBT = 0.838, p  <  0.0001), with significant differences found for all sizes (150-354 µm), for breast thicknesses above 40 mm and for heights above the detector of 20 mm and above. In conclusion, the hybrid method was successfully used to produce images for a detection study; results showed breast tomosynthesis outperformed 2D for spherical densities while further optimization of DBT for microcalcifications is suggested.

A modelling framework for evaluation of 2d-mammography and breast tomosynthesis systems

Planar 2D X-ray mammography is the most common screening technique used for breast cancer detection. Digital breast tomosynthesis (DBT) is a new and emerging technology that overcomes some of the limitations of conventional planar imaging. However, it is important to understand the impact of these two modalities on cancer detection rates and patient recall. Since it is difficult to adequately evaluate different modalities clinically, a collection of modeling tools is introduced in this paper that can be used to emulate the image acquisition process for both modalities. In this paper, we discuss image simulation chains that can be used for the evaluation of 2D-mammography and DBT systems in terms of both technical factors and observer studies.

The influence of position within the breast on microcalcification detectability in continuous tube motion digital breast tomosynthesis

In digital breast tomosynthesis (DBT), the detectability and characterization of all lesions, especially microcalcifications, is still an issue under investigation. For DBT systems equipped with an x-ray tube that moves continuously during exposure, theory predicts some influence of the focal spot motion blur on detectability and diagnosis of small lesions, such as microcalcifications. Motion blur experienced by a lesion at some position in the breast is known to depend on the height of the lesion above the table within the breast. In this study, we investigated the influence of position above the table on microcalcification contrast and signal difference to noise ratio (SdNR) (as a surrogate for detectability) in tomosynthesis images, by means of a hybrid simulation method. Microcalcifications, represented by spheres of calcium with 400 μm diameter, were simulated into projection images of homogeneous objects and into anatomical backgrounds. The influence of system sharpness was included via the modulation transfer function (MTF) model that included detector, focus size, tube motion and x-ray oblique entry components. Results show contrast reductions for spheres at increasing heights above the detector in all datasets. For example, contrast drops of 31.5% and 43.1% for a sphere inserted at 1 mm height compared to insertions at 40 mm and 69 mm above the table, respectively, were found for spheres simulated near the chest wall for homogeneous background. For the same cases, the corresponding drops in SdNR were 30.6% and 40.3%, respectively. Similar trends were also seen for sphere contrasts measured in anatomical backgrounds.

Software framework for simulating clusters of microcalcifications in digital mammography

Observer performance experiments for lesion detection are an accepted means of assessing the imaging performance of radiological imaging systems Simulation methods for clusters of microcalcifications have been proposed for creating images with abnormal pathology for its use in such experiments We report on a software tool that can generate simulated clusters of microcalcifications for different exposure parameters and different digital mammography systems The effect of the simulation steps on microcalcification templates, (namely exposure settings, breast thickness, modulation transfer function (MTF) and pixel size) is demonstrated and validated Results were evaluated in terms of the clusters peak contrast (PC) for three cases: for different exposure conditions within a given system, for different systems and for different system MTF calculation methods As expected, with higher tube voltage and for insertion into thicker breast simulating material, the lesion contrast decreases while the position of the peak remains unchanged When different systems are considered with the same exposure settings, the observed difference in the PCs is related to the blurring due to the different MTF and the pixel size of the systems; a shift in the peak position is also observed, due to resampling This functional and user-friendly system could be used by other researchers for performing comparative studies of mammographic imaging systems.

Realistic simulation of microcalcifications in breast tomosynthesis

Digital breast tomosynthesis (DBT) provides a possible solution to overcome the problem of overlapping tissue since it provides a 3D volume representation of the imaged object In order to study the detectability of lesions in DBT, we have developed a simulation tool where objects are simulated into real projection DBT images The methodology has already been validated for 3D geometrical shapes and has now been extended to irregularly shaped lesions The work focuses on the simulation of clusters of microcalcifications that are modeled using micro-CT images of biopsy specimens containing such lesions The compilation of a database of microcalcifications clusters classified following Le Gal nomenclature is ongoing These extracted model lesions were then simulated into images of biopsy specimens next to the original real cluster in order to confirm the realism of the simulation.

Validation of a novel imaging approach using multi-slice CT and cone-beam CT to follow-up on condylar remodeling after bimaxillary surgery

The main goal of this study was to introduce a novel three-dimensional procedure to objectively quantify both inner and outer condylar remodelling on preoperative multi-slice computed tomography (MSCT) and postoperative cone-beam computed tomography (CBCT) images. Second, the reliability and accuracy of this condylar volume quantification method was assessed. The mandibles of 20 patients (11 female and 9 male) who underwent bimaxillary surgery were semi-automatically extracted from MSCT/CBCT scans and rendered in 3D. The resulting condyles were spatially matched by using an anatomical landmark-based registration procedure. A standardized sphere was created around each condyle, and the condylar bone volume within this selected region of interest was automatically calculated. To investigate the reproducibility of the method, inter- and intra-observer reliability was calculated for assessments made by two experienced radiologists twice five months apart in a set of ten randomly selected patients. To test the accuracy of the bone segmentation, the inner and outer bone structures of one dry mandible, scanned according to the clinical set-up, were compared with the gold standard, micro-CT. Thirty-eight condyles showed a significant (P<0.05) mean bone volume decrease of 26.4%±11.4% (502.9 mm3±268.1 mm3). No significant effects of side, sex or age were found. Good to excellent (ICC>0.6) intra- and inter-observer reliability was observed for both MSCT and CBCT. Moreover, the bone segmentation accuracy was less than one voxel (0.4 mm) for MSCT (0.3 mm±0.2 mm) and CBCT (0.4 mm±0.3 mm), thus indicating the clinical potential of this method for objective follow-up in pathological condylar resorption.