Hi,
My
name is Franz Devantier, creator of this blog. I
am an Herbalist, who uses local and indigenous herbs when available, in
preference to imported herbs. Because
Herbalists deal with living human beings, it is important to have an
understanding of Anatomy and Physiology, as well as many other related
subjects
Medical
Imaging: Illuminating the body
Before the 1950s, the X-Ray was the only way of extracting
information about the internal state of the human body. Unfortunately the images were a bit murky,
but fairly useful. For the rest of it,
physicians had to examine the internal organs for evidence of disease by means
of exploratory surgery. Exploratory
surgery subjected the patients to all the pain, shock and trauma of major
surgery, but potentially without the benefit of any improvement to their
condition.
An X-ray image is obtained by directing, X-rays, which are
waves of a very short electromagnetic wavelength at the body. The X-ray or radiograph is a shadowy negative
of the internal structures of the body.
The denser structures absorb more X-rays, and so appear as lighter areas
in the radiograph. Hollow air containing
structures and fat, absorb the X-rays to a lesser extent, and so appear as
darker areas in the radiograph. X-ray
images can be viewed on a fluorescent screen or fluoroscope as they are being
generated.
X-rays are best at helping to visualize hard bony
structures, and at locating abnormally dense structures, such as tumors and
tuberculosis nodules in the lungs.
In the 1950s the use of nuclear medicine started. Nuclear medicine uses radioisotopes to scan
the body. Also in this same period, we
saw the advent of ultrasound techniques for scanning the human body.
In the 1970s CT,
PET, and MRI scanning techniques were introduced. These new imaging techniques were able to
reveal the structure of our insides.
Also using these techniques it was possible for the first time to get
information about how the molecules were working inside our organs.
The best known of these three new techniques is the
Computed Tomography (CT), which was originally known as Computerized Axial
Tomography (CAT). The CT is a refined
version of the old X-ray equipment. The
patient is slowly moved through the doughnut shaped CT machine, while its X-ray
tubes rotate around the body, and send beams from all directions to a specific
level of the patient’s body.
At any point in time, the an-shaped beam of the CT machine
is confined to a slice of the human
body, about as thick as a coin. In
conventional X-rays, there can be confusion because of overlapping
structures. In CT, the devices computer
translates this information into a detailed cross sectional picture of each of
the consecutive body regions scanned. In
other words the result could look similar to thin slices cut through the body
for examination.
The CT scan has eliminated the need for exploratory surgery
to a very large degree. CT scans are the
chosen method for evaluating most problems involving the brain. CT is also fairly useful in examining the
abdomen and certain skeletal problems.
Dynamic Spatial Reconstruction (DSR), is a special high
speed CT device. This technique
provides three dimensional images of
the body organs, from any angle. This
technique also allows the movements and changes in the internal volumes of the
organs to be scrutinized at normal body speed.
You can also see the internal body movements in slow motion, or examine
them at a specific point in time. DSR
can be used to evaluate the lungs and other mobile organs. The greatest value of DSR has been to
visualize the heart beating, and blood flowing through the blood vessels; which
allows heart defects, constricted blood vessels, and the status of a coronary
heart bypass graft to be evaluated.
There is another computer assisted X-ray technique that is
called Digital Subtraction Angiography (DSA).
Angiography refers to vessel pictures.
This technique will provide an unobstructed view of diseased blood
vessels. The principle is straight
forward: Conventional radiographs
(X-rays) are taken before and after a contrast medium has been injected into an
artery. The computer subtracts the
before image from the after image, which eliminates all the body structures
that obscure the vessel. The result is
an unobstructed view of a diseased blood vessel. DSA is very useful in identifying blockages
of the arteries that supply the heart wall and the brain.
So we can see that there have been a number very useful
technologies based on X-rays. In the
same way nuclear medicine gave rise to a technology called Positron Emission
Tomography (PET).
PET is a nuclear medical imaging technique that produces a
three-dimensional image or picture of functional processes in the body. The technology works by detecting pairs of
gamma rays, that are emitted indirectly from a positron emitting radionuclide
or tracer. This tracer is introduced
into the body on a chosen biologically active molecule. Three dimensional images of the tracer
concentration is created by computer programs.
In some machines a CT scan is run at the same time from the same
machine.
One biologically active molecule that is chosen is an
analogue of glucose. The aim with this
tracer is to indicate the tissue metabolic activity, based on the concentration
of the regional glucose uptake. This
technology can be used to detect cancer metastasis, which is when cancer starts
spreading to other areas in the body.
Besides glucose, there are other radiotracers that can be used to study
many types of molecules and imaging of tissue concentrations.
The gamma ray is indicated by that funny looking “y”
symbol. This technology can produce
vivid coloured pictures of the brains chemical activities. PET has been very useful in studying brain
activity in Alzheimer’s disease, and Epilepsy.
Visualizations of which part of the brain is active during talking,
listening, problem solving etc, and be created with PET. Before PET this would not have been possible.
My favourite imaging technology is Sonography or Ultrasound
Imaging. Firstly Sonography equipment is
inexpensive, when compared to the other technologies. Secondly it is much safer when compared to
X-ray or nuclear technology. The
high-frequency or ultrasound waves that are used, seem to be safer than the
ionizing forms of radiation used in nuclear medicine, or the X-rays used in CT
technology.
In Sonography, the body is probed with pulses of sound
waves that are reflected and scattered by body tissues and result in echoes
being formed. A computer analyses these
body echoes and creates or constructs visual images of the outlines of body
organs. Often a single hand held device
can be used to emit the sounds and to pick up the echoes. This device can be moved around the body,
allowing sections to be scanned from many different body planes.
Sonography is relatively safe, and because of this it is
the technique that is chosen for obstetrics.
It can be safely used to determine the fetal position and the age of the
fetas, and other information about the fetas.
It is also used to locate the placenta.
On the negative side, sound waves have a very low
penetrating power, and rapidly dissipate in air. Because of this Sonography is of little use
in studying the structures of the lungs, or those structures that are surrounded
by bone, such as the brain and the spinal cord.
Franz Devantier,
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