ENGR4223 Ch1

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Ch 1 Basic Imaging Principles: 

Ch 1 Basic Imaging Principles

Basic Imaging Principles: 

Basic Imaging Principles What does the human body look like on the inside? Invasive Techniques: Operation Endoscope Noninvasive Techniques: Magnetic Resonance Imaging (MRI) Ultrasound Imaging x-ray Computed Tomography (CT) Nuclear Medicine Functional Magnetic Resonance Imaging (fMRI) Positron Emission Tomography (PET)

Basic Imaging Principles: 

Basic Imaging Principles What do Images look like, and why? Image reconstruction: the process of creating an image from measurement of signals. Image quality determined by: Portray of the true spatial distribution of the physical parameters. Resolution Noise Contrast Geometric Distortion Artifacts

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x-ray Transmission through the body Gamma ray emission from within the body Ultrasound echoes Nuclear magnetic resonance induction

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Projection Images: The creation of a two-dimensional image “shadow” of the three dimensional body. X-ray are transmitted through a patient, creating a radiograph.

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The three standard orientations of slice (or tomographic) images Axial, Transaxial, Transverse Coronal Frontal Sagittal Oblique Slice: an orientation not corresponding to one of the Standard slice orientation.

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Computed Tomography Magnetic Resonance Imaging Positron Emission Tomography

Introduction: 

Nov. 1895 – Announces X-ray discovery 1901 – Receives first Nobel Prize in Physics – Given for discovery and use of X-rays. Wilhelm Röntgen Radiograph of the hand of Röntgen’s wife, 1895. Introduction

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1940’s, 1950’s Background laid for ultrasound and nuclear medicine 1960’s Revolution in imaging – ultrasound and nuclear medicine 1972 CT (Computerized Tomography) - true 3D imaging - Allan Cormack and Hounsfield win Nobel Prize in 1979 1980’s -In 1952 Felix Bloch and Edward Purcell received Nobel Prize in Physics for describing the phenomena of NMR -In 1991 Richard Ernst received Nobel Prize for a paper describing the use of MRI in medicine in 1973 - In 2003 Paul Lauterbur and Peter Mansfield received Nobel Prize for developing Key method in MRI image construction.

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Physical Signal Detection of physical signals arising from the body and transform these signals to images. Typical signals - Transmission of x-ray through the body ( Projection radiography) - Emission of gamma rays from radiotracer in the body (NM) - Reflection of ultrasonic waves within the body (in ultrasound imaging) - Precession of spin systems in a large magnetic field (MRI) All signals above use Electromagnetic waves (EM) except the ultrasound imaging. f  1/ f  Energy

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Physical Signal Characteristics of spectrum that are useful for medical imaging  > 1 Angstrom (Ao) : Energy is highly attenuated by the body < 0.01 Angstrom : Energy is too high and less contrast Unit of energy for EM is electron volts (eV): 1 eV is the amount of energy an electron gains when accelerated across 1 volt potential. Useful energy for medical imaging: 25 k eV – 500 k eV For Ultrasound Imaging 1 MHz to 20 MHz Resolution is proportional to wavelength

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Spectrum

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Projection Radiography (Chest x-ray) X-ray, fluoroscopy, mammography, motion tomography

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Computed Tomography (CT-scan) The x-rays are collimated (restricted in their geometric spread) to travel within an approximate 2-D “Fan beam” Type of CT scan: single-slice CT, helical CT, multislice CT

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Nuclear Medicine Imaging of gamma rays emitted by radionuclides substance bounded to biochemically active drugs. Example iodine to study thyroid function.

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Nuclear Medicine Modalities of Nuclear Medicine: Conventional radionuclide imaging or scintigraphy Single-photon emission computed tomography (SPECT) Positron emission tomography (PET) In Conventional and SPECT: a radioactive atom’s decay produces a single gamma ray, which may intercept the Anger camera (scintillation detector). In PET, a radionuclide decay produces a positron, which immediately annihilates (with an electron) to produce two gamma rays flying off in opposite directions.

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Ultrasound Imaging Uses electric-to-acoustic transducers to generate repetitive bursts of high-frequency sound. Time-of-return: give information about location Intensity: give information about the strength of a reflector

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Magnetic Resonance Imaging (MRI) - Hydrogen nucleus align itself with an external Magnetic field - Radio frequency pulse cause hydrogen atoms to tip a way from the direction of the external magnetic field. - When excitation pulse end, hydrogen nucleus realign itself with the magnetic field and realize a radio-frequency.

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Magnetic Resonance Imaging (MRI) Modality of MRI Standard MRI Echo-planar imaging (EPI): generate image in real time Magnetic resonance spectroscopic imaging: image other nuclei besides the hydrogen atom. Functional MRI (fMRI): uses oxygenation-sensitive pulse sequence to image blood oxygenation in the brain.

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