medical - Medical Imaging Types of imaging X-rays Computed...

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Unformatted text preview: Medical Imaging Types of imaging X-rays Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Fluoroscopy Gamma cameras Positron emission tomography Thermography Ultrasound X-ray images Projectional radiography Mammograms Dental x-rays Notice fine details: Resolution better than 1mm Tens of shades of grey (if not more) QuickTime and a decompressor are needed to see this picture. X-ray images Resolution better than 1mm Tens of shades of grey (if not more) Requires of order 100 absorptions of an X-ray per mm QuickTime and a decompressor are needed to see this picture. X-ray images Resolution better than 1mm Tens of shades of grey (if not more) Requires at least of order 100 X-rays per mm square Roughly 10 000 per 1 cm x 1 cm area 10 million per 30 cm x 30 cm area Background at sea level (all high energy particles): ~ 200 per cm 2 per s QuickTime and a decompressor are needed to see this picture. Radiation Dosage Radiation unit: Roentgen Amount of radiation required to generate about 2 billion charges in 1 cm 3 of dry air Roentgen equivalent in man (or mammal): rem Adjust for biological effects: 1 rem=1.07 R Preferred unit: Sievert: 100 rem=1 Sv Background: 1-3 mSv (1/1000 Sv) per year QuickTime and a decompressor are needed to see this picture. Why X-rays? QuickTime and a decompressor are needed to see this picture. Soft X-rays Hard X-rays More damaging More get absorbed Cross-section Absorption cross- section typically near 1 cm 2 per g If you spread 1 g of material over 1 cm 2 and irradiate it with X-rays then many of the X-rays will be absorbed For density of water, this means most X-rays will only penetrate a few cm Why X-rays?Why X-rays?...
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medical - Medical Imaging Types of imaging X-rays Computed...

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