A CT scan showing a 3.58 index The<unk> , created in 1987 by J. Alex<unk> , S. S. Kramer, and S. A. Lietman, is a mathematical relationship that exists in a human chest section observed with a CT scan. It is defined as the ratio of the transverse diameter (the horizontal distance of the inside of the ribcage) and the anteroposterior diameter (the shortest distance between the vertebrae and sternum). : where: : HI is the<unk>  : distance 1 is the distance of the inside ribcage (at the level of maximum deformity or at the lower third of the sternum) : distance 2 is the distance between the sternal notch and vertebrae. More recent studies show that simple chest x-rays are just as effective as CT scans for calculating the<unk>  and recommend replacing CT scans with CXR to reduce radiation exposure in all but gross deformities. A normal<unk>  should be about 2.5. Chest wall deformities such as pectus excavatum can cause the sternum to invert, thus increasing the index. In severe asymetric cases, where the sternum dips below the level of the vertebra, the index can be a negative value.
Haller index
Mentzer index
Eagle score
Amsler grid
Monoyer chart
Lamellar body count
Nugent score
Stenger test