Download Medical Imaging detailed

MEDICAL IMAGING
RADIOLOGY
• Radiology is a medical specialty that uses
imaging techniques to both diagnose and
treat disease visualized within the human
body.
• Imaging technologies include x-rays,
ultrasound, computed tomography, nuclear
medicine, positron emission tomography and
magnetic resonance imaging, all of which are
used to diagnose or treat diseases.
Ultrasounds
• Uses high-frequency sound
waves to image organs and
body structures
• Can look at heart, blood vessles,
kidneys, liver and other organs
as well as soft tissues
• Sounds waves are reflected
(echo) off of different density
tissues differently
Ultrasound cont’d
• A transducer sends out sound waves, which
bounce off at different speeds depending on
the density of the tissue or organ
• The transducer also receives the sound waves
that are bounced back
Why ultrasound?
• Condition of a fetus
• Check thyroid gland
• Diagnose some forms of cancer (e.g. breast,
prostate, GI tract)
• Evaluate abnormalities of muscles and
tendons
• Cardiac problems
• Abnormalities in reproductive organs
Risks?
• No documented risks; no ionizing radiation
• higher power sound waves are used (for
treatment); they could can heat and destroy
tissue
X-Rays
• Based on the fact that larger
atoms (as in bone-Calcium)
absorb X-rays than smaller ones
(as in soft tissues)
• X-ray machine generates X-ray
photons which are funnelled into
a narrow beam
X-rays cont’d
• Camera on the other side of patient records patterns of X-ray
absorption
• Hard materials like bone appear white and softer materials
appear black or gray
• Contrast media is used if soft tissues are of interest – e.g
Barium – absorbs X-rays better
• Can even trace the path of a contrast media through the body
using fluoroscopy
• Can also be used to see soft tissues with the
help of stains (ex. barium)
Risks?
• Considered safe and benefits of early detection are thought to
outweigh risks of x-ray exposure
• It is possible that there is cell damage – most would die
• If you had 300 medical x-rays a year, increase in cancer risk by
1 percent (USDA)
• Caution for pregnant women – no CT scans
• Question of cummulative exposure?
CAT Scans: computerized axial
tomography scan
• An X-ray machine rotates around the patient
taking hundreds of individual pictures form
many angles
• More sensitive than an X-ray alone
• Computer re-assembles the picture into a 3-D
image, allowing for organs to be viewed
section-by-section
A CT or CAT scan (computed tomography) is a much more sensitive imaging technique
than x-ray, allowing high definition not only of the bony structures, but of the soft
tissues. Clear images of organs such as the brain, muscles, joint structures, veins and
arteries, as well as anomalies like tumors and hemorrhages may be obtained with or
without the injection of contrasting dye.
Radiation exposure comparison
Type
Radiation reading (mSV)
Single fatal dose, fatal within weeks
10,000
Accumulated dosage that could cause
Fatal cancer in 5 % of people
1,000
Recommended limit for radiation workers
Every 5 years
100
CT scan: heart
16
CT scan: abdomen & pelvis
15
Dose in full-body CT scan
10
Mammogram
0.40
Chest x-ray
0.10
Dental x-ray
0.01
Daily background dose in Ottawa
0.00040
Yearly background dose in Ottawa
0.146
MRI
• Magnetic Resonance Imaging
An imaging technology that uses magnetism,
radio waves adn a computer to produce
images of body structures.
The MRI scanner is a tube
surrounded by a giant
circular magent.
• The magnet creates a strong magnetic filed
that aligns the protons of hydrogen atoms.
• The protons are then exposed to radio waves,
which make them spin. This spinning produces
a signal from which an image is produced.
What is MRI good for?
• Accurate disease detection throughout the
body
e.g. tumours of the brain, inflammation of the
spine, structure of the heart
CT vs. MRI
Depends on what is being diagnosed:
MRI - For brain tumour detection
- For multiple exams
- Best for soft tissues (e.g heart)
CT - For solid tumours in the chest and
abdomen
- for bone abnormalities and injuries
- cheaper than MRI
Nuclear medicine
This is a branch of medicine and medical
imaging that uses radionuclides (unstable
atoms) that undergo radioactive decay; it is
used for the diagnosis and treatment of
disease.
Radionuclides are combined with other
elements or medication to form
radiopharmaceuticals.
Nuclear medicine cont’d
Radiopharmaceuticals localize in specific organs
or cellular receptors so information can be
obtained about diseases process/progress
Nuclear medicine is based on cellular function
and physiology rather than physical changes
that are detected with X-rays and MRIs.
Nuclear Medicine cont’d
• Measures radiation emitted from within the
body and provides information about the
function of the organ, not just its structure
• Large amounts of isotopes collect at site of
damage “lighting” it up
• Can be detected by special cameras
• Ex. PET scan: positron emission tomography
PET
Produces a three-dimensional image of
functional processes in the body.
Gamma rays are emitted by a positron-emitting
radionucleotide tracer, which is injected into
the patient.
Used for imaging of tumours and metastases,
also for brain and heart function
• PET scan are often used in combination with
MRI or CT scans to give a complete metabolic
and anatomic picture