br used for preoperative localization before biopsy Similarl

511
used for preoperative localization before biopsy. Similarly, the 512
distance between the centroid of the suspicious lesions on 513
456 suspicious lesions and to eliminate false positives using length of minor axis of the lesion, M1, measured in terms of 515
457 reduced annular search region. Secondly, in order to expose pixels/Euclidean distance as shown in Fig. 6(b). The arc (green 516
458 the maximum portion of the breast for imaging, the nipple line) with radius, mr1, is drawn with nipple tip, Nc, on CC view 517
459 during SQ109 is pulled away from the chest wall equally as centre is shown in Fig. 6(b).
460 in CC and MLO views [28]. This results in an approximately An arc pair (yellow band) around this central arc is drawn 519
461 constant distance between centre of nipple and the centroid of with width DW which is calculated using Eqs. (6) and (7). The 520
462 suspicious lesion on both the views. This distance is useful arc intersects the breast border at two points, the centre of 521
463 during mapping the corresponding lesions on ipsilateral which is used to define breast midline (maroon line) from 522
464 views. The centre of nipple and centroid are marked under nipple tip to centre of chest wall as shown in Fig. 6(c). This 523
465 the supervision of the radiologists involved in this study. A midline divides the CC view in two sections known as Outer 524
466 scatter plot of these radial distances on the radiologist- and Inner quadrants, as shown in Fig. 6(c). The location of the 525
467 identified objects on the ipsilateral views is shown in Fig. 5. It is lesion in a breast quadrant is used for preoperative localization 526
468 revealed that there is a high correlation of the radial distances before biopsy.
469 of the correlated lesions on the ipsilateral views. However, the Thus the annular regions for all the suspicious lesions are 528
470 angular coordinates are found with a significant correlation. drawn to limit the number of lesions to be paired. The square 529
471 Consequently, the radial distance is selected as the metric for templates on each of the paired lesions are selected for 530
472 determining the correlation of a lesion on one view with the extracting the features shown in Fig. 7(a) and (b).
473 same physical lesion on the other view. The template is the square region centred on the centroid 532
The suspicious lesions are found in a wide variety of shapes of the selected suspicious lesion belonging to either view. To 533
475 and size. Moreover, the radial distance of a physical lesion on calculate the similarity features, the templates of the 534
476 CC view is different than that of on MLO view. Thus, both these suspicious lesions on both views must be of equal size. 535
477 facts are considered for deciding the width of annular region The size of the templates is equal to minimum of the minor 536
478 for optimal search. The first coefficient is calculated by axis lengths the respective lesions. The square template 537
479 minimizing mean square error between the radial distance within minor and major axis ensures the maximum of the 538
480 of ith true lesion on CC, Ri , with its jth true distance on a MLO common portion of the lesions is selected for extracting 539
Rj
cc
as given in Eq. (5). similarity features. We conducted a small experiment on few 540
mlo
templates and calculated score by applying similarity 541
features and traditional pixel by pixel template matching 542
¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið
effective instead of pixel by pixel score as like in traditional 544
Ry
485 axis of the lesion on CC view, Lc. The width of annular region,
An important task in two view diagnosis is to find the same 547
abnormal lesion on both CC and MLO views. This is achieved 548
using similarity features of all possible pairs of lesions, one 549
Please cite stigma article in press as: Sapate S, et al. Breast cancer diagnosis using abnormalities on ipsilateral views of digital mammograms.
Fig. 6 – Breast coordinate system (a) CC view measuring R1cc, R2cc; (b) MLO view measuring R1mlo, R2mlo annular region within yellow arcs, midline (red) showing upper/lower quadrants; (c) CC view annular region within yellow arcs, midline (green) showing outer/inner quadrants,.
Fig. 7 – The lengths of minor axis of the sample lesions (a) on CC view and (b) on MLO view.