import re
regex = r"(?<!\S)(\d+\.\d+)x(\d+\.\d+)x(\d+\.\d+) [cm]m(?!\S)"
test_str = "The study reveals a speculated nodule with pleural tagging at anterior basal segment of LLL, measured 1.9x1.4x2.0 cm in size"
print(re.findall(regex, test_str))
aW1wb3J0IHJlCgpyZWdleCA9IHIiKD88IVxTKShcZCtcLlxkKyl4KFxkK1wuXGQrKXgoXGQrXC5cZCspIFtjbV1tKD8hXFMpIgp0ZXN0X3N0ciA9ICJUaGUgc3R1ZHkgcmV2ZWFscyBhIHNwZWN1bGF0ZWQgbm9kdWxlIHdpdGggcGxldXJhbCB0YWdnaW5nIGF0IGFudGVyaW9yIGJhc2FsIHNlZ21lbnQgb2YgTExMLCBtZWFzdXJlZCAxLjl4MS40eDIuMCBjbSBpbiBzaXplIgoKcHJpbnQocmUuZmluZGFsbChyZWdleCwgdGVzdF9zdHIpKQ==