How can I use the function impoly/imfreehand/imrect to extract Region of Interest (ROI) as well as the background separately of a medical image (Brain MRI) with tumor where tumor portion is the ROI and rest of the image is background or Non-ROI?

Sir, I have a code to extract the ROI (tumor portion) of a brain MRI as below

grayImage = imread('brain_tumor.png');

figure,imshow(grayImage);

h = imrect; position = wait(h);

croppedImage = imcrop(grayImage, position);

figure;

imshow(croppedImage);

BackGround = imsubtract(grayImage - croppedImage);

figure, imshow(BackGround);

But Sir with this code I am not getting the background or Non-ROI, that is the rest of the image portion....But I also need to extract the Non ROI separately using either impoly or imfreehand or imrect so that I can merge them later after compressing ROI losslessly and NON ROI using lossy compression. Sir kindly help me. Debarpita Chaudhuri.