Paper presented by Dr.Jerome Kalister and  Dr.K.K.Krishnamma 

at 54 NATCON -06 at AIMS , COCHIN


The anatomical positions of organs and spaces in the body
have been traditionally described in relation to one another.

For eg.let's see the position of Gall bladder .
'It is situated on the right side of the body closely in contact
with the inferior surface of the liver,along the right edge of the
quadrate lobe in a shallow fossa extending from the right edge
of the porta hepatis to the inferior lobe of the liver'.

In this statement reference has been made to many other structures
like the liver ,quadrate lobe ,porta hepatis etc.Thus to locate the
gall bladder you ought to know where these structures are!

Now let's see where the liver is --
'The liver lies in the upper part of the abdominal cavity
mostly under cover of the ribs and costal cartilages in relation with the
diaphragm, part of the right kidney, right supr renal gland and the stomach'.

So you see it goes on like this. To know where the liver is , you should know the position of so many other structures.As a system of locating an organ or space, in the body ,this approach is quite crude , undetailed and totally beyond the comprehension of any digital system. A computer does'nt understand if you say something is above or something is below something.

A system of projecting the inner organs to the body surface and describing them in relation with the landmarks on the surface , called surface anatomy ,has been quite popular for sometime. Here again things are taken in two dimensions only.Usually no depth is specified. It gives you only a rough idea of where something is located.

Perhaps it must have been sufficient for this long.Some of you must be remembering a time
when a 4-6 inch long incision used to be put for an Appendicectomy. Techniques are becoming more and more accurate and less and less invasive. Appendicectomy is a key hole surgery today!Advancements in medical and surgical procedures demand a far more accurate approach in defining a point in the body.

This is our problem statement. An absolute system of locating, positioning or naming the position of a space or mass in the body does not exist.

Now let us call your attention to something called Stereotaxy about which most of you must be knowing. The neurosurgeons throughout the world have come to a consensus on fixing a central reference line called ACPC line and the space around the line is callibrated in axial ,coronal and sagittal planes. They have begun to use it extensively with a far better output.


The concept of volumetric anatomy defines a point in the body in the 3D space using three intersecting planes


Fig. A shows how a line can be defined by using two intersecting planes.

Fig.B demonstrates how a point can be defined in that line by bringing in a third perpendicular plane.



Fig.A             Fig.B

How can a value be obtained  for such a point ?




As we see, we need to have two opposing planes to define a line. To come to that line ,the blue plane (imagine that is the coronal plane) has to shift by 3 units. The red plane (take that to be the sagittal plane) has to move by say 4 units, and the green plane(say the axial plane) has to travel by 5 units to reach the specified point in that line.Thus the point can be represented by a three set number like



This  number is very very specific for the point . It is quite legible to any digital  system,
because this corresponds to x-y-z axes .

The concept of 3D grid

Now let's forget about the moving planes. Let's imagine a 3D grid superimposed into the whole volume of the body. Each intersecting point will be having a fixed three set number all for itself, just like we discussed now. Each organ may be positioned with reference to the nearest intersecting points. Thus the entire body may be mapped to a very high level of accuracy. Of course these points may vary with age, sex, race etc. This problem could easily be solved by linking the individual in question to the Anthropometric data that is available in extensive detail today, with a digital system that can bring in the appropriate correction factor .

The applications of having extreme accuracy in locating any point in the body with a computer assistance should be quite vast; right from the diagnostic insertion of a needle into any part of the body to the much fantasized telesurgery.