Transcript File medical imaging

Medical Imaging
X-Rays
• What is a Routine X-Ray?
• The X-ray has been called one of the most
significant advances in all of medical history. It is
used in many different ways in medical
diagnosis. An x-ray image is produced when a
small amount of radiation passes through the
body and strikes a sheet of sensitive film placed
on the other side of the body. The ability of xrays to penetrate tissues and bones varies
according to the tissue's composition and mass.
Bone, which contains calcium, does not let much
radiation through and results in white images on
the x-ray film. The lungs, which are filled with air,
allow nearly all x-rays to strike the film resulting
in a black film image.
Medical Imaging Techniques
• X-rays
CT Scan
• What is a CT scanner?
A CT (computerised tomography) scanner is a special kind of X-ray
machine. Instead of sending out a single X-ray through your body as
with ordinary X-rays, several beams are sent simultaneously from
different angles.
How does a CT scanner work?
The X-rays from the beams are detected after they have passed
through the body and their strength is measured.
Beams that have passed through less dense tissue such as the
lungs will be stronger, whereas beams that have passed through
denser tissue such as bone will be weaker.
A computer can use this information to work out the relative density
of the tissues examined. Each set of measurements made by the
scanner is, in effect, a cross-section through the body
CT Scan
CT Scan image
What is a PET scan?
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A positron emission tomography (PET) scan is a unique type of imaging test that helps
doctors see how the organs and tissues inside your body are actually functioning.
The test involves injecting a very small dose of a radioactive chemical, called a radiotracer,
into the vein of your arm. The tracer travels through the body and is absorbed by the
organs and tissues being studied. Next, you will be asked to lie down on a flat examination
table that is moved into the center of a PET scanner—a doughnut-like shaped machine.
This machine detects and records the energy given off by the tracer substance and, with
the aid of a computer, this energy is converted into three-dimensional pictures. A physician
can then look at cross-sectional images of the body organ from any angle in order to detect
any functional problems.
What problems can a PET scan detect?
A PET scan can measure such vital functions as blood flow, oxygen use, and glucose
metabolism, which helps doctors identify abnormal from normal functioning organs and
tissues. The scan can also be used to evaluate the effectiveness of a patient’s treatment
plan, allowing the course of care to be adjusted if necessary.
Currently, PET scans are most commonly used to detect cancer, heart problems (such as
coronary artery disease and damage to the heart following a heart attack), brain disorders
(including brain tumors, memory disorders, seizures) and other central nervous system
disorders.
How is a PET scan different from a CT or MRI scan?
One of the main differences between PET scans and other imaging tests like CT scan or
magnetic resonance imaging (MRI) is that the PET scan reveals the cellular level metabolic
changes occurring in an organ or tissue. This is important and unique because disease
processes often begin with functional changes at the cellular level. A PET scan can often
detect these very early changes whereas a CT or MRI detect changes a little later—as the
disease begins to cause changes in the structure of organs or tissues
PET Scan
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What is an MRI scan?
MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of
the 1980s.
The MRI scan uses magnetic and radio waves, meaning that there is no exposure to X-rays or any other
damaging forms of radiation.
How does an MRI scanner work?
The patient lies inside a large, cylinder-shaped magnet. Radio waves 10,000 to 30,000 times stronger
than the magnetic field of the earth are then sent through the body. This affects the body's atoms, forcing
the nuclei into a different position. As they move back into place they send out radio waves of their own.
The scanner picks up these signals and a computer turns them into a picture. These pictures are based
on the location and strength of the incoming signals.
Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of
the hydrogen atom is often used to create an MRI scan in the manner described above.
What does an MRI scan show?
Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body. The tissue that
has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen
atoms (such as fatty tissue) looks much brighter. By changing the timing of the radiowave pulses it is
possible to gain information about the different types of tissues that are present.
An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone
tissue, so the technique is useful when examining the brain and spinal cord.
Because the MRI scan gives very detailed pictures it is the best technique when it comes to finding
tumours (benign or malignant abnormal growths) in the brain. If a tumour is present the scan can also be
used to find out if it has spread into nearby brain tissue.
The technique also allows us to focus on other details in the brain. For example, it makes it possible to
see the strands of abnormal tissue that occur if someone has multiple sclerosis and it is possible to see
changes occurring when there is bleeding in the brain, or find out if the brain tissue has suffered lack of
MRI
MRI Scan
What is General Ultrasound
Imaging?
• Ultrasound imaging, also called ultrasound scanning or sonography,
is a method of obtaining images from inside the human body
through the use of high-frequency sound waves. The reflected
sound wave echoes are recorded and displayed as a real-time
visual image. No ionizing radiation (x-ray) is involved in ultrasound
imaging. Obstetric ultrasound refers to the specialized use of sound
waves to visualize and thus determine the condition of a pregnant
woman and her embryo or fetus.
• Ultrasound is a useful way of examining many of the body's internal
organs, including but not limited to the heart, liver, gallbladder,
spleen, pancreas, kidneys and bladder. Because ultrasound images
are captured in real time, they can show movement of internal
tissues and organs and enable physicians to see blood flow and
heart valve functions. This can help to diagnose a variety of heart
conditions and to assess damage after a heart attack or other
illness.
Ultrasound