Tomosintesi e contrast mammography in Az. Ospedaliera di Reggio Emilia

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1 Tomosintesi e contrast mammography in Az. Ospedaliera di Reggio Emilia A. Nitrosi 1, M. Bertolini 1, D. Tassoni 1, M.Iori 1, P. Pattcini 2, S. Ravaioli 2, C. A. Mori 2 e V. Ginocchi 2 1 Servizio di Fisica Medica 2 Dipartimento Interaziendale di Diagnostica per Immagini Reggio Emilia (IT)

2 REGGIO EMILIA - 11 GE Senographe Essential systems (~57 k exams/year) - Structured report (following the regional statement RER 220/ CAD) Scientific collaboration project: CESM 3 systems DBT 3 systems activation 1 quarter 2012 Progetti di modernizzazione Dr.ssa Ravaioli

3 Journal of Digital Imaging, Vol 24, No 1 (February), 2011: pp Contrast Detail Phantom Comparison on a Commercially AvailableUnit. Breast Tomosynthesis (DBT) versus Full-Field Digital Mammography (FFDM) Marco Bertolini, Andrea Nitrosi, Giovanni Borasi, Andrea Botti, Davide Tassoni, Roberto Sghedoni and Giulio Zuccoli

4 Istituto in tecnologie avanzate e modelli assistenziali in oncologia In breast imaging factors implicated in 2D radiographic technique missing cancers detection are related to sensitivity, the presence of distracting lesions, the tumor growth rate / pattern and especially the background (breast structures) The anatomic background is probably the main limiting factor in cancer detection. To overcome the effect of overlying and underlying breast tissues, DBT is being considered to improve sensitivity compared to 2D

5 Istituto in tecnologie avanzate e modelli assistenziali in oncologia PURPOSE To evaluate the performance of a digital mammographic system working in 2D planar versus tomosynthesis mode in terms of image signal to noise ratio (SDNR). DBT Vs FFDM sensitivity has been evaluated using contrast detail phantoms sandwiched between confounding breast simulating material

6 Istituto in tecnologie avanzate e modelli assistenziali in oncologia Abstract A contrast detail phantom was obtained embedding 1 cm Plexiglas, including 49 holes of different diameter and depth, between two layers containing a breast-simulating material. The phantom was exposed with the details plane perpendicular to the X-ray beam using the manufacturer s standard clinical breast acquisition parameters. SDNR in the digital breast tomosynthesis (DBT) images was higher than that of the full-field digital mammography (FFDM) for 38 out of 49 details in complex background conditions. These differences (p<0.05) are statistically significant for 19 details out of 38. The relative SDNR results for DBT and FFDM images showed a dependence on the diameter of the details considered. This work proposes an initial framework for a global image quality evaluation for commercial systems that can operate with different image acquisition modality using the same detector.

7 METHODS AND MATERIALS All FFDM and DBT images were acquired on a CEmarked digital unit (Selenia Dimensions Tomosynthesis System, Hologic, Bedford, MA) in march The systems use a Selenium based detector, enabling X-ray direct detection (detector 24 cm x 29 cm, pixel pitch size 70 µm) Tomosynthesis is performed acquiring 15 low dose projections over a ±7.5 angular range in less than 5 seconds. The DBT image reconstructed pixel size is approximately 88µm at 1-mm in-plane spacing.

8 Phantom design Istituto in tecnologie avanzate e modelli assistenziali in oncologia A contrast detail (CD) phantom was developed from a Nuclear Associates CD phantom Model that included 49 holes of different diameter φ (from 4.3 to 0.18 mm) and depth (from to mm). In terms of lesions simulations the objects can be categorized in masses (φ 0.5 mm) or calcifications (φ < 0.5 mm). (1) Ideal condition (2) Pseudo-clinical condition Phantom set #1 - ideal conditions - obtained placing the holes matrix between two uniform thick plexiglas layers. Phantom set #2 - pseudo-clinical conditions - obtained placing the holes matrix between two thick layers containing a breast simulating material.

9 Phantom sets In both acquisition modalities (FFDM and DBT) and phantom sets automatic exposure control was used. - FFDM 29 kvp, cellular anti-scatter grid in - DBT 32kVp, cellular anti-scatter grid out The ESAK delivered for FFDM and DBT acquisitions were near the same (7.73 ± 0.01 mgy for DBT and 7.63 ± 0.01 mgy for FFDM). The corresponding average glandular doses (AGD) were about 2.2 mgy for FFDM and 2.3 mgy for DBT.

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11 Quality evaluation The 1 mm slices obtained with the DBT and the FFDM images were evaluated for image quality. In-plane image quality was evaluated calculating the signal difference to noise ratio (SDNR) defined by SDNR = S bg S t σ where S t is the average pixel intensity of the target, S bg is the average background pixel intensity and σ bg is the standard deviation of the background pixel intensity close to the target. bg A contrast detail (CD) curve (in function of target diameters d and depths) was computed for each target size calculating the inverse of the ratio of signal-to-noise ratio (SNR) and target depth lower CD(d) value means superior detectability of a target, being proportional to the minimum perceivable contrast

12 Global quality evaluation The whole results were summarized by averaging all the SDNRs for a fixed diameter, where d and c are referred to target diameter and contrast, n is the number of details per diameter ISDNR d = n c=1 SDNR n d, c

13 Image type Only DICOM for presentation images were analyzed these conditions included, for 2D and 3D, proprietary denoising and histogram equalization algorithms. 3D images were obtained with a filtered backprojection algorithm. The reported results then refer to the real working condition of the system in the clinical setting. The use of different diameters allowed to tentatively consider the resolution of the systems tested. Images were evaluated using an automatic software analysis tool (CD-Eval) also thanks to the known geometry of the phantom/holes

14 An automatic software analysis tool (CD-Eval) supporting a clinical-like methodology to compare FFDM and DBT system performance was developed. The software can automatically segment and analyze images from contrast detail phantoms embedded between layers containing a breast simulating material or uniform plexiglas. CD-Eval software

15 Istituto in tecnologie avanzate e modelli assistenziali in oncologia Statistical Analysis Distribution characteristics of SDNR and ISDNR measures were evaluated by using the Kolmogorov Smirnov one-sample test for normality* Two different t tests were performed. 1. One was applied to the SDNR values for both modalities and each diameter/contrast. 2. one was applied to ISDNR values. * SDNRs of the same detail (corresponding to a definite diameter and contrast for 16 different realizations) obtained with DBT was compared with SDNRs obtained with FFDM using Student s two-sided paired t (using the paired samples t test with a two-sided PG0.05 being statistically significant).

16 DBT vs FFDM in ideal conditions Differences in SDNR were statistically significant considering all diameters together (P = 9.60E-15) and diameters bigger then 0.5 mm (P = 6.83E-22) but not for diameters smaller than 0.5 mm (P = 0.57). (lower CD(d) value means superior detectability of a target)

17 DBT vs FFDM in pseudo clinical conditions SDNR differences were always statistically significant demonstrating the DBT s capability in anatomical noise reduction also for smaller target diameters. (lower CD(d) value means superior detectability of a target)

18 DBT in pseudo clinical conditions vs FFDM in ideal conditions Differences in SDNR were statistically significant considering all diameters together (P = 2.59E-3) and for the diameters bigger than 0.5 mm (P = 1.78E-03). (lower CD(d) value means superior detectability of a target)

19 Results

20 SDNR results discussion The SDNR values for the DBT images were higher than the FFDM s for 38 out of 49 details. The DBT s SDNR values were higher for details with diameters greater than mm over the entire contrast range covered by the phantom. For details with diameters smaller than 1 mm, the DBT SDNR values remained higher than the FFDM s only for higher contrasts. For the smallest detail, the presence of negative SDNR values probably depended on the mixing effect of the complex background (breast tissue) and the resolution of the system (with DBT pixel size very close to the detail diameter).

21 ISDNR results The ISDNR results showed a dependence on the size of the objects. The ISDNR values in function of target diameters showed higher values for DBT with respect to FFDM. The differences for ISDNR are statistically significant for all the details diameters with the exception of the smallest one (0.177 mm).

22 Limitation The results discussed above are somewhat depending on the proprietary processing algorithms: this is, however, an unavoidable consequence when dealing with commercial systems and for presentation images. The planar configuration of the contrast detail slab did not perfectly mimic a real breast. An actual 3D detail distribution into the phantom would be of great interest and the presence of structured noise, also in the detail plane, could make more realistic the DBT versus FFDM comparison.

23 CONCLUSIONS These results suggested that the complex background plays a less important role in lesion conspicuity for DBT than for FFDM. This should offer an initial framework for a global image quality evaluation, which takes into account the mixing effects of noise, contrast, and spatial system resolution, typical of a real imaging system. To apply the conclusions of this study to clinical practice, several issues should be addressed, such as further perception studies that are needed to point out any conclusion on tomosynthesis benefits in the visualization of simulated pathologic lesions with respect to FFDM.

24 Istituto in tecnologie avanzate e modelli assistenziali in oncologia

25 CIRS PROJECT , Tomosynthesis Mammo Phantom Set Istituto in tecnologie avanzate e modelli assistenziali in oncologia

26 Istituto in tecnologie avanzate e modelli assistenziali in oncologia Cirs Mammography BR3D Phantom Model 020 BACKGROUND SLABS Epoxy resin: equivalent to 50% glandular / 50% adipose tissue (Size: 100 x 180 x 100 mm, semicircular shape - Quantity: 5 slabs) TARGET SLAB Epoxy resin: equivalent to 50% glandular / 50% adipose tissue - Size: 100 x 180 x 100 mm, semicircular shape - Quantity: 1 slab LESIONS (CaCO3 SPECKS) Grain size: 0.130, 0.165, 0.196, 0.230, & mm SPHEROIDAL MASSES Epoxy resin: equivalent to breast carcinoma (Diameters: 1.80, 2.38, 3.18, 3.96, 4.76 & 6.32 mm) FIBERS 10 mm length (Diameters: 0.15, 0.18, 0.23, 0.28, 0.38,0.41 & 0.60 mm)

27 Med. Phys. 37 (2) February 2010: pp Phantom study to evaluate contrast-medium-enhanced digital subtraction mammography with a full-field indirect-detection system B. A. Palma et al