Defining Imaging

• Modality: The difference between different bioimaging methods and machines (ex: CT and MRI are different ______)

  • Four necessary components of a modality: source (illumination), camera (detector), digitizer (frame grabber), imaging processing unit

  • Imaging processing unit (hardware and/or software)

    • acquisition (takes in the data and understands it)

    • preprocessing (combines information from multiple points)

    • segmentation (identifying components, facial recognition)

    • & more

• An image is a 2D representation of a physical quantity as rendered by an imaging modality

  • X-ray attenuation (projection x-ray yor CT)

  • Proton density (MRI)

  • Acoustic reflectivity (ultrasound)

  • An image represents a “finite-thickness” plane within a volume of interest

• Types of imaging

  • Anatomical: Imaging that represents structure/composition of objects (e.g. CT imaging)

  • Functional: Imaging that represents function/physiology of an organ (e.g. PET scans)

  • Projection: Imaging that shoes a single planar representation (e.g. x-ray)

  • Tomographic: Imaging that shows cross-sectional representation (e.g. CT imagings)

• Imaging mechanisms

  • Transmission: The imaging mechanism by which information comes from what travels through the body (e.g. x-ray)

  • Reflection: Transmission: The imaging mechanism by which information that comes from what reflects back from the body (e.g. ultrasound)

Modality Comparison

• Ionizing is when the energy we work with is higher than others, and electrons in the atoms can bump up to unsafe levels; this is something we want to avoid (can lead to cancer)

Digital Imaging

• Digital images are digital files saved on a computer

• 2D arrays of “picture elements” called pixels

  • Voxels are for 3D elements

• Image size = width x height

• Real-world image size (or FOV) is (Ncolumn x pixel width) x (Nrow x pixel height)

• Resolution: Number of pixels per square inch

• Image Pixels

  • Addressed with x,y coordinates

  • Top left corner is (1, 1)

  • (coumn, row)

• Storage type

  • Pixel values depend on the storage type

  • Grayscale images are NOT called black and white

    • 8-Bit: Greyscale images with values from 0 to 2^8 minus 1

    • 16-Bit: Greyscale images with values from 0 to 2^16 minus 1

• Color images: each pixel can have 4 values

  • 1 value per pixel – e.g. indexed image

  • 3 values per pixel e.g. 3x1 bytes – R_G_B, 3x2 bytes – R_G_B, ...

  • 4 values per pixel RGB e.g. 4x1 byte – R_G_B_Alpha, ...

Image Processing

• Enhancement/restoration of image info for human reading

• Segmentation

• Characterization

• Representation of images for machine analysis

• Visualization

• Processing of image data for storage

• Processing of image data for transmission

• Matlab

  • Load the image and info

    • imread()

    • iminfo()

  • Display image

    • imtool()

    • imshow()

    • imagesec()

    • image()

    • imshowpair()

  • Perform needed operation

  • Display and evaluate results

  • Save resulting image

    • imwrite()