How to exclude the limit of ROI from boundaries detection

Hello

A picture is better than a long speech. As you can see my function detects the edges of my ROI and conciders as a limit of my object. How to remove this (the line on the left and the right angle on the right)?

Here there is the code used :

 clear all;
clc;
I = imread('Image1.PNG');
Icrop = imcrop(I);
subplot(2,2,1);
imshow(I);
title('Original Image');
subplot(2,2,2);
imshow(Icrop);
title('Cropped Image'); 
BW = im2bw(Icrop, graythresh(Icrop));
BW = bwareaopen(BW,50);
subplot(2,2,3);
imshow(BW);
title('Cropped BW Image');
[B,L] = bwboundaries(BW,'noholes');
subplot(2,2,4);
imshow(Icrop);
title('Crop Image with Boundaries Detected');
hold on
for k = 1:length(B)
    boundary = B{k};
    plot(boundary(:,2), boundary(:,1), 'r', 'LineWidth', 2)

Thank you !