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)