By Alexander R. Margulis
Presented at the STAR Training in Advances in Radiology,
16 June 2002, Hyatt Saujana, Subang, Selangor.

Prof Margulis is Clinical Professor of Radiology and Scientific Director of the STAR programme. He is affiliated with Weill Medical College, Cornell University, New York. He has written over 230 articles on Gastrointestinal Radiology and Books on Magnetic Resonance Imaging Alimentary Tract Radiology. His areas of research are in Gastrointestinal Radiology and Computed Tomography virtual colonoscopy.

This article is reproduced with permission from Prof Margulis
 

Since Roentgen discovered x-rays, more than 100 years ago, medical imaging has undergone and continues to undergo dramatic advances. It has become one of the important mainstays of modern medicine, indispensable for diagnosis, treatment planning and follow-up. The progress in medical imaging has been driven by the continuing increases in computer power, advances in micro-instrumentation, communication technology and lately by the impact of molecular biology.

The increase in computer power has been most impressive even exceeding Moore's Law of doubling the number of transistors per chip every two years. The fact that the price at constant computer power has continuously been dropping by the logarithmic scale has been responsible for the relative affordability of the advances in computer technology. These advances have made much of cross-sectional imaging as well as PACS (Picture Archiving and Communications Systems) and teleradiology possible. PACS has empowered many leading medical centers in the United States, Western Europe and Japan to become filmless and many others are in transition. Teleradiology promises access to sophisticated imaging interpretation worldwide and may help in overcoming the anticipated shortage of radiologists.

The general forward directions of medical imaging aim toward increasing sensitivity and specificity while decreasing invasiveness and minimizing cost.
 

The increasing computer power in cross-sectional imaging has facilitated the acquisition of 3-dimensional data, permitting high resolution volumetric acquisition of images, thus facilitating diagnosis. Multi-row detector Computed Tomography and 3D Magnetic Resonance Imaging (MRI) have also made virtual endoscopy an increasingly accepted clinical imaging technique. This technique is presently being applied to practically every anatomic channel: colon, esophagus, stomach, small bowel, bronchial tree, blood vessels, urinary tract (including the bladder) etc. Virtual endoscopy promises to reduce the number of invasive procedures and limit conventional, invasive endoscopic procedures to targeted biopsy if the virtual studies disclose abnormalities.

Fusion of images generated from different imaging modalities, such as MR, CT and PET is showing that advantages of two techniques can be maximized. Several large equipment manufacturers are already marketing PET-CT scanners for clinical use. The advantages of PET's ability to detect malignant lymph nodes are thus combined with the superior spatial resolution of CT. Several companies are presently designing combined MR-PET instruments which will have important applications particularly in the brain. Fusion of MR and CT is currently used in radiation therapy planning.

Proton spectroscopic MR imaging has presently become clinical in the study of brain tumors and prostate carcinoma. A grid is superimposed on the MR image and the voxels can display in color the ratio of choline and NAA for the study of brain tumors. This is particularly valuable in the differentiation of tumor recurrence from necrosis following therapy. For prostate cancer the use of different three dimensional spectroscopic imaging displays of choline and citrate resulted in improved detection, diagnosis of extra-capsular spread, assessment of tumor aggressiveness and evaluation of treatment. In the future, as MRSI (Magnetic Resonance Spectroscopic Imaging) expands its role, other normal function chemical spectroscopic markers will be identified in addition to NAA for the brain and citrate for the prostate. Other MR spectroscopic markers for cancer even more specific than increased choline levels, will be d proteins. This mechanism needs much more research. It does change the original concept that each disease is related to one mutated gene. These factors will need much more study and they do affect the future of medical imaging. also be identified. Extension of these successful MR spectroscopic techniques to breast cancer and brain development and identification of birth injury in neonates is underway in multiple centers.

Mapping of foci of specific brain activity with functional MRI by displaying images of metabolic activity data, as for instance for heat/pain sensation, motor, memory centers etc. is becoming the basis of functionally based medicine and will have an important future role in the study of mental diseases. The development of new imaging modalities like optical coherence tomography, adds new dimensions to medical imaging. It is expected that it will be possible in the future to identify early dysplastic, precancerous changes in many organs. Examples are changes in Barrett's esophagus as well as in the bronchial mucosa of heavy smokers.
 

Future advances in medicine are going to be closely linked to genomics. The identification of disease predisposing genes in the human genome will result in a better understanding of disease, more rational treatment and will expand the role of medical imaging. Genetic imaging is assuming increased importance in these investigations. To be able to participate in genetic medicine imaging, images will have to be obtained at the molecular or cellular level. The present directions of genetic imaging are:

1. Gene expression using intracellular or extracellular reporter genes. An accepted technique in animal genetic imaging employs reporter genes such as luciferase (the firefly gene). The techniques presently used in molecular imaging are: PET, optical imaging and MR. It is very likely that CT will be used in the future.

2. Screening of populations at known risk (either specific gene identification or family disease history) in order to discover the earliest phase of disease,

3. Providing guidance for and follow-up of gene therapy. Image guided gene therapy, whether introducing good genes carried by adeno or retroviruses or with stem cells carrying the good gene is making slow advances. Another promising approach is the removal of an undesirable gene. Occasional accidents are leading to incrreased caution. All present imaging techniques will be used to guide the micro-catheters or needles to the desired target. While progress is painfully slow there have been successes.

This approach will in the future be an essential component of any imaging screening of genetically susceptible individuals. The reduction and eventually the elimination of perception errors can be achieved by using neural- network computers taught what is normal with all its variations. The computer should eventually be able to identify normal appearing structures making the reading by the radiologist unnecessary for a large proportion of images.

This will be increasingly important with the logarithmic increase in the number of images derived with the new cross-sectional techniques. CAD will thus be an important advance in combating the adverse impact of the shortage of radiologists. It may also help in providing screening at an affordable price. Computer aided diagnosis will be particularly important in the screening of identifiable populations at risk as for instance of heavy smokers after a given period of "pack-years."

High resolution CT computer aided screening in such populations may improve the odds of survival. CAD will be soon used in reading images obtained with new techniques such as Virtual CT colonoscopy and as it is now employed in mammography.
 

The cost of health care in the industrialized world represents a large percentage of the Gross Domestic Product (GDP). In the USA, it exceeds 13.5% and it amounts of more than 1 trillion US dollars! Diagnostic imaging procedures per patient visit to the doctor are increasing every year.

There is no doubt that medical Imaging will continue to play its pivotal role in clinical medicine and biological research. However, in order for this to occur, the profession needs to keep recruiting bright people.
 

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