Image Modalities

Today, the diagnosis of a patient is rarely done without the use of imaging technology. Imaging allows us to peek inside the body, without resorting to invasive methods. Imaging is not only more comfortable and safe to the patient, it also allows views of anatomy and physiology that cannot be obtained by any other means. Since the first x-ray image of a hand, imaging has significantly evolved. Instead of only bone, we can now visualize organs in motion, such as a beating heart. We can follow chemicals into the brain to their uptake sites and gain information about the very chemical workings of the brain. We can even follow the disappearance of neuronal activity in the brain in diseases such as Parkinson's.

Since the discovery of X-rays by Roentgen just before the dawn of the 20th century, the last 100 years has seen a veritable boom in medical imaging methods and technology. The original, time-honoured x-ray is one of the many methods in a radiologist's arsenal of imaging modalities. Together with CT, MRI, SPECT and PET, the physician can examine the patient in a manner beyond imagination only 50 years ago.

In general, imaging can address two issues: structure and function. One can either view structures in the body and image anatomy or view chemical processes and image biochemistry. Structural imaging techniques include x-rays, CT and MRI. It is the role of SPECT and PET imaging to view the biochemical processes inside.

Magnetic Resonance Imaging Magnetic Resonance Imaging, or MRI, provides the most detailed anatomical information of all the structural imaging modalities. Moreover, MRI is the only imaging method, of the ones described here, where high-energy radiation is not used.  More...	X-Ray X-ray imaging is among the simplest and ubiquitous imaging modalities. X-rays are energetic photons produced by an electron beam incident on a metal target. As the electrons decelerate in the target through interaction, they emit electromagnetic radiation in the form of x-rays. The principle behind the imaging method lies in the fact that bones contain heavy atoms, with many electrons, which act as an absorber of x-rays.  More...
Computerized Tomography This method is also refered to as CAT, short for computer assisted tomography. The CT, or CAT, scan is a natural progression from x-rays. The method is based on the principle that a three-dimensional object can be reconstructed from its two dimensional projections. The mathematics are based on the Radon transform which is a map from an n-dimensional space to an (n-1)-dimensional space. More...	Single Photon Emission Computed Tomography Both SPECT and PET use the idea of a tracer to image chemical processes. A tracer is an analogue of a biologically active compound in which one of the atoms has been replaced by a radioactive atom. When the tracer is introduced into the body, its site-specific uptake can be traced by means of the labeled atom.  More...
Position Emission Tomography PET is the modality which combines principles of CT and SPECT together. The key advantage of PET is added sensitivity which is obtained by naturally collimating the photons through a physical process, without the use of absorbing collimators.  More...