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Fundamentals of Medical Imagining notes
Typology: Lecture notes
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History of medical imaging. Roentgen : Discovered x-rays Nov 8, 1895 at his laboratory in Wurzburg, Germany. Submitted for publication on Dec. 28, 1895 Published Jan. 5, 1896 First clinical image was a needle in a woman's hand. Used to guide surgeons. Jan. 13, 1896 Nobel prize in 1901 Miller : First x-ray imaging in US. Hounsfield : Invented Computed Tomography (CT) Lauterbur : Nobel Prize in MR Imaging, CWRU Grad Energy and radiation. Units : Dose versus exposure : If we record a measurement with an air chamber or other radiation measurement device, we measure exposure. Only if we determine the amount absorbed in a tissue should we speak about dose. X-ray production.
Characteristic radiation : Anode materials: Most common: Tungsten (W, Z = 74) In mammography: Molybdenum (M, Z= 42) and Rhodium (Rh, Z = 45) X-ray tube spectra: Filtration:
Focal spot blurring: Purpose/function of grids and Grid Ratio: Subject contrast : Image quality. Poisson statistics: MTF: A narrow PSF makes a wide MTF and a wide PSF makes a narrow PSF
Automatic exposure controls: DSA and Processing: Computed tomography. Hounsfield units: Window/ level: Partial volume: Fourier slice theorem: Convolution back projection:
Noise: Beam hardening artifact: 3D Medical Image Visualization Ambient : Indirect light that is reflected off other objects. Diffuse : Light that comes from a light source and is spread equally in all directions. Independent of the observer. Specular : Light at comes from a light source and is directly reflected from a surface. Depends on viewer and source.
Ultrasound Compression wave:
Velocity of sound: Attenuation: Wave equation: Reflection: Noise: Speckle Doppler shift:
- When the pulse is turned off, the transverse vector will decay, and the longitudinal vector will regrow. The rate the transverse vector decays is known as the Free Induction Decay (FID)
Mechanisms of image contrast: Slice selection: Spin echo sequence: MRI image reconstruction:
2
− λt At: t = T1/2, e-λt^ = 0.
Radiopharmaceuticals:
Molecular Imaging PET and MR techniques: Reporter genes and probes Bioluminescent imaging Fluorescence imaging Radionuclide imaging with reporter genes; e.g., HSV1-tk OCT imaging