PRINCIPLES AND APPROACHES

3D Medical Imaging

Introduction (I) – Purpose and Sources of Medical Imaging

Purpose Given a set of multidimensional images, output qualitative /

quantitative information about the object/object system under study in these images.

Sources of Images 2D: digital radiography

Computerized tomography (CT) Magnetic resonance imaging (MRI) Positron emission tomography (PET) Single Photon emission computed tomography (SPECT) Ultrasound (US) Functional MRI (fMRI)

3D: A time sequence of 2D images or a volume of tomography 4D: A sequence of 3D images of a dynamic object 5D and up Among tomographic modalities, CT, MRI, and US provide

structural/anatomical information; PET, SPECT, and fMRI as well as doppler US provide functional information

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Introduction (II) – Objects and Classification of Study

Objects of Study Rigid (e.g., bones) vs. deformable (e.g., soft-tissue structures) Static (e.g., skull) vs. dynamic (e.g., heart, joints) Mixed characteristics, such as MRI 3D study of the head:

white matter, gray matter, and cerebrospinal fluid Qualitative (e.g., visually) vs. quantitative information (e.g.,

statistically)Classification

Operations: preprocessing, visualization, manipulation, analysis

Viewing medium: computer monitor, holography, head-mounted display

Systems physician display console (by imaging device vendors) Image processing/visualization workstations supplied by

workstation vendors 3D imaging software (commercial products) University-based 3D imaging software (often freely available)

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Introduction (III) – Schematic Representation of 3D Imaging Systems

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Introduction (IV) – Basics and Terminology

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Introduction (V) – Basics and Terminology

Object, Object system (a collection of objects)Body regionImaging devicePixel, voxelScene, scene domain, intensity, binary sceneK-th slice, pixel size, slice thickness, slice

location, slice spacingStructure, structure systemRendition of a scene/structure/structure systemCoordinate systems: imaging device, scene,

structure, display (viewing)

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Introduction (VI) – Object Characteristics

Graded composition Voxels constituting the femur have a

gradation of density values; however, they “hang together” to form the femur

Hanging-Togetherness (Gestalt) A configuration, pattern, or organized

field having specific properties that cannot be derived from the summation of its component parts; a unified whole

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Preprocessing – ROI/VOI

Region of Interest (ROI)/Volume of Interest (VOI)A sub-scene with reduced sized of the scene domain

and/or the intensityROI/VOI operations may

Specify a rectangle/rectangular volume, or Drawing and painting, or Specify ROI/VOI loosely, indicate a region containing ROI but

exclude unwanted regions with similar property[Figure; from left to right, top to bottom]

A region of interest specified by a rectangular box in the scene (a); the output is shown in (b); region of arbitrary shape by drawing (c) and painting (d)

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Preprocessing – Filtering (Enhancing)

Filtering operations convert a given scene into another scene to enhance wanted (object) information and to suppress unwanted (noise, background) information Edge Enhancing

Gradient

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Preprocessing – Edge Enhancing

A slice of a 3D MR scene ofa patient’s head (a) and itsedge-enhancing filtered output with a 2D (b) and a 3D neighborhood (c).

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Preprocessing – Filtering (Suppressing)

Edge suppressing, smoothing, or averaging – low-pass filtering

Illustration of a smoothing 2D GaussianFilter (b), a 3D Gaussian filter (c), anda median filter (d) for the scene in (a)

Interpolation Scene-Based Interpolation Methods Object-Based Interpolation Methods

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Preprocessing – Diffusion

Intensity gradients in a given scene are considered to cause a “flow” within the scene whose functional dependence on gradient is controlled through a parameter K.

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Preprocessing

Registration Scene-Based Registration Methods

Rigid Deformable

Object-Based Registration Methods Rigid Deformable

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Preprocessing

Segmentation Hard, Boundary-Based, Automatic Methods

Iso-Surfacing Methods Gradient-Based Methods

Fuzzy, Boundary-Based, Automatic Methods Hard, Boundary-Based, Assisted Methods

Active Contours Live Wire/Lane

Hard, Region-Based, Automatic Methods Thresholding Clustering

Fuzzy, Region-Based, Automatic Methods Hard, Region-Based, Assisted Methods Fuzzy, Region-Based, Assisted Methods

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Visualization

Scene-Based Visualization Methods Slice Mode Volume Mode

Maximum Intensity Projection (MIP) Surface Rendering Volume Rendering

Object-Based Visualization Methods Maximum Intensity Projection Surface Rendering Volume Rendering

Misconceptions and Challenges in Visualization

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Further Topics

Manipulation Rigid model Deformable model

Analysis Scene-Based Object-Based

Sources of difficulty in 3D imaging Qualitative validation Quantitative validation

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