How do we fill this kind of gap with Matlab (without changing the size of the object)?

I need your help!

I have an image A (see below - left). Can you help me with a matlab function that can produce the image B (see below - right)

(A) (B)

Note that the below Matlab code does not work (since it works on holes inside a closed boundary of an object - which is not the case with image A where the boundary is open):

I = imread('');
B = imbinarize(I);
F = imfill(B,'holes');
figure, imshow(I), title('input')
figure, imshow(F), title('output')

Answer 1

[Matt J]

We don't know thickness of the Image A veins in pixels (it's always good to attach your example images as .mat files), but whatever it is it would go in the appropriate place below.

B=imopen(B,strel('disk',vein_thickness))

[Gobert]

I have attached the images A and B. Thank you! It worked (when I used the thickness equals to 10 approx.)