R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

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Medical imaging for rapid prototyping
2.1 Introduction to medical imaging
In order to manufacture a rapid prototype model of any human anatomy
it must fi rst be captured in three dimensions in a manner that allows the
computer processes that control the RP process to be used. A number of
scanning modalities can be used, ranging from substantial hospital facilities
normally found in radiology departments to small hand-held scanners that
can be used in the laboratory or clinic.
There are essentially two main categories of scanning modality for human
bodies, those that capture data from the whole body both internally and
externally and those that capture only external data. Most hospital-based
scanners capture data from the whole body both internally and externally.
These are normally large, sophisticated medical imaging machines capable
of scanning the complete human body. Examples include Computed
Tomography (CT), Magnetic Resonance (MR) imaging and positron emission
tomography. Each modality uses a different physical effect to generate
cross-sectional images through the human body. Typically, the patient is
placed lying down on a table that is fed through the scanner whilst the
images are taken. The cross-sectional images are arranged in order so that
the computer can construct a three-dimensional data set of the patient.
Software can then be used to isolate particular organs or tissues. This data
can then be used to make an exact replica of the organ using RP techniques.
The different physical effects used by each type of scanner result in different
types of tissue being imaged. These machines require highly specialised
staff to operate and require large capital investment. The use of the two
most common modalities in RP will be described in more detail later in this
chapter.
The other type of scanning is used to capture only the external surface
of a patient. There is a wide range of technologies that can be used for
capturing three-dimensional surface data. Three-dimensional surface scanning,
sometimes referred to as digitising, has been used in engineering and
product design for many years as a method of integrating the surfaces of