In places where it is readily available, CT scan has become the diagnostic test of choice, especially in adults. A properly performed CT scan with modern equipment has a detection rate (sensitivity) of over 95% and a similar specificity. Signs of appendicitis on CT scan include lack of contrast (oral dye) in the appendix and direct visualization of appendiceal enlargement (greater than 6 mm in diameter on cross section). The inflammation caused by appendicitis in the surrounding peritoneal fat (so called ""fat stranding"") can also be observed on CT, providing a mechanism to detect early appendicitis and a clue that appendicitis may be present even when the appendix is not well seen. Thus, diagnosis of appendicitis by CT is made more difficult in very thin patients and in children, both of whom tend to lack significant fat within the abdomen. In most cases, however, appendicitis is a clinical diagnosis and, due to the high radiation dose involved, CT scans are only used when the diagnosis is in doubt (e.g. atypical history) or if there are other considerations involved.