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


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


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.


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.


Computed Tomography Magnetic Resonance Imaging Positron Emission Tomography


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


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.


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


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




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


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


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


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.


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


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.


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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