medical applications of nuclear physics
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Medical Applications of Nuclear Physics
Nuclear Physics Medical Applications
Diagnostic Imaging
The First “Medical Application”
Source:Radiological Society of North America, Inc (http://www.radiologyinfo.org)
CAT scanComputerized Axial Tomography
Source: Cutnell and Johnson, 7th edition image gallery
CAT scan
X-rays are produced and emitted in thin, fanned out beams
Detected on the opposite side of the patient via arrays of x-ray detectors
Scanner rotates to get the full 2-D picture The patient is passed through the scanner in
small steps to get ‘slices’ for 3-D reconstruction Computer control allows for high level of
precision yield very detailed images
CAT scan advantages
3-D reconstruction of the internal organs High resolution giving doctors very good
details prior to grabbing a knife CAT scans can image soft tissue, bone,
and blood vessels at the same time Often less expensive than an MRI and
can be used with medical implants and metal objects
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
CAT scan reconstructed
Source: Cutnell and Johnson, 7th edition image gallery
CAT scan image of lung
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
CAT scan dangers
Increased exposure to x-ray radiation NBC Nightly News recently reported on an
article in the New England Journal of Medicine that up to as much as 2% of new cancer cases may be caused by CT scans
A CT scan of the chest involves 10 to 15 millisieverts versus 0.01 to 0.15 for a regular chest X-ray
Nevertheless, it’s still a powerful tool … just don’t over use it.
Source: http://www.msnbc.msn.com/id/22012569/
PET scan Positron Emission Tomography A radioactive source (positron emitter) is injected into the
patient usually attached to a sugar Cancers have unusually high metabolic rates so the sugar
solution goes more to the cancer cells than the other tissues
Emitted positron annihilates with an electron to produce two gamma rays
Gamma rays leave traveling in opposite directions Coincident detection of gamma rays can be computer
reconstructed to give high resolution images of the internal organs
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Source: Cutnell and Johnson, 5th edition text
PET scan advantages
Very powerful imaging tool Produces higher resolution images Can detect changes in metabolic activity
before changes in the anatomy are seen in CAT and MRI images
Can be used in combination with CT and MRI images (CT/PET scans are becoming more widely used)
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
PET scanner
Source: Cutnell and Johnson, 7th edition image gallery
PET scan image
Source: Cutnell and Johnson, 7th edition image gallery
CAT/PET scan combined
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
PET scan dangers and limitations PET scan dosages are very small (it’s an
efficient method for imaging) but its still radiation
Must weigh the danger against the rewards These radio-nuclides have short half-lives which
means they must be produced locally or pay huge shipping costs
Sometimes gives false positives if there is chemical imbalances in the patient
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
MRI imaging
Magnetic Resonance Imaging Patient is placed in a powerful non-
uniform magnetic field A electromagnetic wave is transmitted
into the body and at the right frequency it is absorbed. This absorption is detected by the machine.
A computer reconstructs the location of the cells to develop 3-D images
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Source: Cutnell and Johnson, 5th edition
MRI imaging machine
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
MRI image of the knee
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
MRI dangers and limitations
Confined environment No metals allowed! Does not do well with lungs The patient must lie perfectly still so
anxiousness may make the images blurry
MRI’s can be expensive
Nuclear Physics Medical Applications
Treatments
Gamma Knife Radio surgery
Use of gamma rays to treat cancerous tumors
Directs gamma radiation from many directions to a specific location to delivery a powerful dose of radiation
Does not require surgery Can treat cancers where conventional
surgery is not possible
Source: Cutnell and Johnson, 7th edition image gallary
Gamma Knife device
Source: Cutnell and Johnson, 7th edition image gallery
Gamma Knife disadvantages
Exposure to significant radiation Must be aligned to within a millimeter for
accurate treatment Is not guaranteed to destroy all the
cancer (it’s a treatment, after all)
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Linear Accelerator
High energy electrons are crashed into a heavy metal target and emit x-rays
Energy, intensity, and location of the x-rays are controlled to deliver radiation to a tumor
Precision and accuracy are very good and getting better
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Linear Accelerator in Operation
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Linear Accelerator Drawbacks
X-ray radiation can damage healthy tissue
Must be aligned correctly for good accuracy
Movement of internal organs requires larger beam area to get the cancer … you don’t want to do this again
Equipment is expensive … but getting much better
Proton Therapy
Similar to the linear accelerator therapy except energetic protons are directed at the tumor
Varying the energy of the protons results in good deep control
Can be focused to the size of a pin Usually results in less damage to healthy
tissue
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Proton Therapy
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)
Proton Therapy Disadvantages
Radiation exposure to good tissues Requires the cancer to remain still for
good precision and minimization of collateral damage
Very expensive and only used at a few locations in North America
Source: Radiological Society of North America, Inc (http://www.radiologyinfo.org)