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University of Wisconsin Diagnostic Imaging Research

Lecture 1: Introduction (1/2) ? History, basic principles, modalities. Class consists of:Deterministic Studies - distortion- impulse response- transfer functionsAll modalities are non-linear and space variant to some degree.Approximations are made to yield a linear, space-invariant system.

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University of Wisconsin Diagnostic Imaging Research

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    1. University of Wisconsin Diagnostic Imaging Research

    2. Lecture 1: Introduction (1/2) – History, basic principles, modalities Class consists of: Deterministic Studies - distortion - impulse response - transfer functions All modalities are non-linear and space variant to some degree. Approximations are made to yield a linear, space-invariant system. Stochastic Studies SNR (signal to noise ratio) of the resultant image - mean and variance

    3. Course Objectives Learn basics of 2D to n-dimensional system theory and signal processing Emphasis on duals between space and frequency domain Emphasis on intuitive understanding Understand underlying physics of medical imaging modalities Study the deterministic and stochastic descriptions of medical imaging systems Theory is applicable beyond medical imaging

    4. Prerequisites and Postrequisites System Theory ECE 330, BME/MP 573 Statistics Helpful but Not Required Mean and variance of stochastic processes ECE 331, BME/MP 574, ECE 730 Other Courses Microscopy of Life BME 568/ MP 568 MRI ( less math)

    5. Nov. 1895 – Announces X-ray discovery Jan. 13, 1896 – Images needle in patient’s hand – X-ray used presurgically 1901 – Receives first Nobel Prize in Physics – Given for discovery and use of X-rays. Wilhelm Röntgen, Wurtzburg

    6. Röntgen detected: No reflection No refraction Unresponsive to mirrors or lenses His conclusions: X-rays are not an EM wave Dominated by corpuscular behavior Röntgen’s Setup

    7. Projection X-Ray Disadvantage: Depth information lost Advantage: Cheap, simple

    9. Early Developments Intensifying agents, contrast agents all developed within several years. Creativity of physicians resulted in significant improvements to imaging. - found ways to selectively opacify regions of interest - agents administered orally, intraveneously, or via catheter

    10. Later Developments More recently, physicists and engineers have initiated new developments in technology, rather than physicians. 1940’s, 1950’s Background laid for ultrasound and nuclear medicine 1960’s Revolution in imaging – ultrasound and nuclear medicine 1970’s CT (Computerized Tomography) - true 3D imaging (instead of three dimensions projected down to two) 1980’s MRI (Magnetic Resonance Imaging) PET ( Positron Emission Tomography) 2000’s PET/ CT

    11. Computerized Tomography (CT) 1972 Hounsfield announces findings at British Institute of Radiology Hounsfield, Cormack receive Nobel Prize in Medicine (CT images computed to actually display attenuation coefficient m(x,y)) Important Precursors: 1917 Radon: Characterized an image by its projections 1961 Oldendorf: Rotated patient instead of gantry

    12. First Generation CT Scanner Acquire a projection (X-ray) Translate x-ray pencil beam and detector across body and record output Rotate to next angle Repeat translation Assemble all the projections.

    13. Reconstruction from Back Projection

    14. Modern CT Scanner

    15. Computerized Tomography (CT), continued

    17. Nuclear Medicine - Grew out of the nuclear reactor research of World War II Discovery of medically useful radioactive isotopes 1948 Ansell and Rotblat: Point by point imaging of thyroid 1952 Anger: First electronic gamma camera

    18. Nuclear Medicine, continued Very specific in imaging physiological function - metabolism - thyroid function - lung ventilation: inhale agent Advantage: Direct display of disease process. Disadvantage: Poor image quality (~ 1 cm resolution) Why is resolution so poor? Very small concentrations of agent used for safety. - source within body Quantum limited: CT 109 photons/pixel Nuclear ~100 photons/pixel Tomographic systems: SPECT: single photon emission computerized tomography PET: positron emission tomography

    20. Necessary Probe Properties Probe can be internal or external. Requirements: Wavelength must be short enough for adequate resolution. bone fractures, small vessels < 1 mm large lesions < 1 cm Body should be semi-transparent to the probe. transmission > 10-1 - results in contrast problems transmission < 10 -3 - results in SNR problems ? > 10 cm - results in poor resolution ? < .01Ĺ - negligible attenuation Standard X-rays: .01 Ĺ < ? < .5 Ĺ corresponding to ~ 25 kev to 1.2 Mev per photon

    21. Necessary Probe Properties: Transmission vs. ?

    22. Probe properties of different modalities NMR Nuclear magnetic moment ( spin) Makes each spatial area produce its own signal Process and decode Ultrasound Not EM energy Diffraction limits resolution resolution proportional to ? ~~~~~~~~~~~~~~~~~~

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