Modern Diagnostics

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Modern Diagnostics
Cover of Modern Diagnostics
Modern Diagnostics
Author Anil Aggrawal
Country India
Language English
Series Popular Science
Genre(s) Popular Science
Publisher [National Book Trust], India
Publication date 2001
Media type Print (Paperback)
ISBN ISBN 81-237-3317-8
Preceded by 1000 Biology Quiz
Followed by Health Quiz Book

Modern Diagnostics was written by Anil Aggrawal in 2001, in response to a tremendous demand in India for a book which could explain basic facts about some modern diagnostic methods, such as X-rays, CT scan, PET scan etc to the layman in non-technical terms. National Book Trust, India, approached the popular science writer Anil Aggrawal for this work.

Contents

[edit] Areas dealt with

The author has dealt with 12 major diagnostic methods. These are X-rays (chapter 1), ECG and EEG (chapter 2), Endoscopy (chapter 3), Thermography (chapter 4), Mammography (Chapter 5), Angiography (Chapter 6), Computers in modern diagnostics (chapter 7), Digital technology (chapter 8), MRI (Chapter 9), Ultrasound (chapter 10), Nuclear scans (chapter 11) and PET scan (chapter 12). In addition there are two appendices too, the first dealing with minor diagnostic tests which have not been covered in the main book (such as agglutination test, air plethysmography, arthrometry, ballistocardiography, caloric study, capillary fragility test, TORCH test and so on. Appendex II deals with some important dates in the development of Modern Diagnostic procedures. There is a brief glossary also.

[edit] Significance

The main significance of this book is that the subject matter is explained in a completely non technical language. The book has been illustrated with many line diagrams to make the book still more interesting. It has proved quite popular among lay people.

[edit] Sample

Here are sample two pages from chapter 6 entitled "Looking at arteries and veins"

There are many situations when a doctor would like to visualize the various arteries of the body. The doctor may suspect an abnormal dilatation of an artery (aneurysm) or a constriction (caused by atherosclerosis), and may want to view them to confirm or dispel his suspicion. Blood vessels however are not normally visible in conventional radiography, because they don't stop the X-rays, and thus do not cast a shadow on an X-ray plate. To make them visible, a contrast medium (see chapter on X-rays) would have to be injected in them. Seeing the vessels in this way is termed angiography (from Greek aggeion, vessel and graphein, to record; thus literally meaning "recording the vessel"). The picture thus obtained is called the angiogram. If arteries are visualized by this method, it is called arteriography, if veins are visualized, it is called venography. Angiography is a general term emcompassing both these terms. A special technique, fluorescein angiography is used to diagnose certain eye disorders. More about this technique is given in chapter 26 on the diagnosis of eye disorders.

A.The story of angiography

We have seen that angiography was conceived just one month after the announcement of Roentgen's discovery of X-rays . In January 1896, Haschek and Lindenthal had injected a radio-opaque mixture into the blood vessels of an amputated hand to visualize them! This radio-opaque mixture was an emulsion on chalk, which obviously can't be injected in a live person. Since a suitable contrast media was not available, angiography could not be carried out in living people. By the 1920s, researchers had used sodium iodide as a contrast medium. Until the 1950s the contrast medium was most commonly injected through a needle that punctured the vessel. This had many disadvantages. It caused a lot of bleeding. Moreover several deep seated arteries such as aorta could not be reached by this method. In 1952 Seldinger announced an interesting method by which a flexible thin walled catheter could be introduced through the skin. This reduced bleeding and deep seated arteries could be reached, because the catheter could be "snaked" up to any length to any artery of the body. This method had other advantages too. The patient could be positioned as needed (for taking radiographs), and the catheter could be safely left in the body while radiographs were being examined. This new technique, along with the development of new catheters and contrast media, allowed angiography to become the powerful medical tool that it is today.

B.The Seldinger technique

Figure 1: The Seldinger Technique.
Figure 1: The Seldinger Technique.

The following series of diagrams illustrate the Seldinger technique. In this diagram it is shown how a doctor would pass a catheter in the aorta through the femoral artery, a major artery of the thigh (Figure 1).

First of all a proper site is chosen. It is a point high up in the thigh where the thigh just begins (A). A bevelled needle is now passed through the skin in the artery. This needle contains an inner cannula (B). The needle is passed in such a way that it pierces the artery through and through. After this it is slowly withdrawn until there is a gush of blood backwards (C). This tells the doctor that the needle is now inside the artery. Now the needle's inner cannula is removed and a flexible guide wire is inserted (D). The needle is now removed, while the doctor applies pressure on the artery. This reduces bleeding (E). Now a flexible catheter is slipped over the wire into the artery (F). Finally the wire guide is removed leaving the catheter inside the artery (G).

The above procedure would become somewhat clearer by referring to the following diagram. It should be appreciated that in the above procedure, the actual aim is to introduce the catheter. But since it can not be introduced as such, this elaborate technique is devised. It involves introduction - and removal - of two other things first, which finally prepare the stage for introducing the catheter.

First of all the hollow needle is inserted (step 1). Then the guide wire is inserted through the needle (step 2). Needle is retracted (step 3) and the catheter is threaded into the vessel over the guide wire (step 4). Finally the guide wire is removed and the catheter is advanced in the vessel (step 5).

The contrast media used for angiography is usually an organic iodine solution, and it is usually injected by an automatic injector. It is usually necessary to record the flow of contrast medium through the vessel. The abnormal flow can point to disease processes such as atherosclerosis or hardening of arteries. To record the flow of the contrast medium, devices called rapid film changers are used. These devices move the film at a fast rate and permit exposures at intervals of a fraction of a second. Most film changers have a speed of 6 films per second, but some devices have been invented which allow up to 12 films per second. Some film changers use cut film, whereas others use roll film.

We have seen in the chapter on fluoroscopy, that this can also be achieved by cinefluorography. A cine camera can usually take up to 60 frames per second, with the resultant true motion picture radiography . These cameras use 16 or 35 mm film rather than the large size of film used in rapid film changers. The photographic details achieved with cine units is not as great as that seen with rapid film changers. However, many more events can be photographed with the cine attachment, and dynamic function (i.e. movement) can obviously be seen more satisfactorily with cinefluorography. Today angiography is a widely used diagnostic technique for detection of various vessel disorders. Angiography of aorta (aortography), of lung blood vessels (pulmonary angiography), arteries of the thigh (femoral arteriography), arteries of the brain (cerebral angiography), and arteries of the kidney (renal arteriography) have proved to be very useful diagnostic techniques. The contrast media is injected directly in these arteries and radiographs taken.

Recently angiography has also been done by an entirely new technique known as Magnetic Resonance Angiography (MRA). We shall be reading more about it in the chapter on Magnetic Resonance Imaging.

[edit] Other Books by Anil Aggrawal

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