The Haller index, created in 1987 by Dr. Haller, Dr. Kramer, and Dr. Lietman, is a mathematical relationship that exists in a human chest

Chest

The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...

 section observed with a CT scan. It is defined as the ratio

Ratio

In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 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). It is of diagnostic use in vivo

In vivo

In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

.


where:

HI is the Haller Index

distance1 is the distance of the inside ribcage

distance2 is the distance between the sternum and vertebrae.

A normal Haller index should be about 2.5. Chest wall deformities such as pectus excavatum

Pectus excavatum

Pectus excavatum is the most common congenital deformity of the anterior wall of the chest, in which several ribs and the sternum grow abnormally. This produces a caved-in or sunken appearance of the chest...

can cause the sternum to invert, thus increasing the index, which can reach 3.25 or even as high as 5.5