Three Dimensional Computed Tomography: Basic Concepts Chapter 17 Seeram

Three Dimensional Computed Three Dimensional Computed Tomography: Basic ConceptsTomography: Basic Concepts

Chapter 17Chapter 17

SeeramSeeram

Why 3-D?Why 3-D?

Can be used to aid in the study of AIDS, Can be used to aid in the study of AIDS, Huntington’s disease, and schizophreniaHuntington’s disease, and schizophrenia– This is done by using the 3D model as a map to This is done by using the 3D model as a map to

determine areas most affected by disease processesdetermine areas most affected by disease processes

Models can be used to more accurately show Models can be used to more accurately show tumor shape and size for radiation therapy tumor shape and size for radiation therapy planningplanning3D imaging is beginning to gain acceptance as a 3D imaging is beginning to gain acceptance as a tool for virtual colonoscopy by allowing the tool for virtual colonoscopy by allowing the viewer to “fly through” the colonviewer to “fly through” the colon– The downside is that no tissue samples can be The downside is that no tissue samples can be

obtained during this procedureobtained during this procedure

Why 3D?Why 3D?

3D imaging has been used to study Egyptian 3D imaging has been used to study Egyptian mummies without destroying the plaster or mummies without destroying the plaster or bandagesbandages

3D imaging aids in the diagnosis of vascular 3D imaging aids in the diagnosis of vascular pathologypathology

3D imaging can be used to plan surgery and is 3D imaging can be used to plan surgery and is often used during surgical procedures often used during surgical procedures – Real time 3D information shows the surgeon where Real time 3D information shows the surgeon where

the cuts are being made in relation to critical anatomy the cuts are being made in relation to critical anatomy and pathologyand pathology

History of 3DHistory of 3D

Greenleaf et al produced a motion display Greenleaf et al produced a motion display of the ventricles using biplane angiographyof the ventricles using biplane angiography– Greenleaf JF, Tu TS, Wood EH (1970) Computer-generated Greenleaf JF, Tu TS, Wood EH (1970) Computer-generated

three-dimensional oscilloscopic images and associated three-dimensional oscilloscopic images and associated techniques for display and study of the spatial distribution of techniques for display and study of the spatial distribution of

pulmonary blood flow. IEEE Trans Nucl Sci NS-17: 353-359pulmonary blood flow. IEEE Trans Nucl Sci NS-17: 353-359

Using the information gained from Using the information gained from Greenleaf et al, it was clear that Greenleaf et al, it was clear that contiguous CT images could be stacked in contiguous CT images could be stacked in a fashion that would create a 3D imagea fashion that would create a 3D image

History of 3DHistory of 3D

Soon software and hardware became Soon software and hardware became available to ease the production of 3D available to ease the production of 3D imagesimages– Along with the hardware and software came Along with the hardware and software came

algorithms for 3D imagingalgorithms for 3D imaging

By the 1980’s many CT scanners offered By the 1980’s many CT scanners offered 3D software as an optional package3D software as an optional package

Early History of 3D medical imagingEarly History of 3D medical imaging

1969 – Hounsfield and Cormack develop the CT 1969 – Hounsfield and Cormack develop the CT scannerscanner1970 – Greenleaf and colleagues report first 1970 – Greenleaf and colleagues report first biomedical 3D display; computer-generated biomedical 3D display; computer-generated oscilloscope images relating to pulmonary blood oscilloscope images relating to pulmonary blood flowflow1972 - First commercial CT scanner introduced1972 - First commercial CT scanner introduced1975 – Ledley and colleagues report first 3D 1975 – Ledley and colleagues report first 3D rendering of anatomic structures from CT scansrendering of anatomic structures from CT scans1979 – Herman develops technique to render 1979 – Herman develops technique to render bone surface in CT data sets; collaborates with bone surface in CT data sets; collaborates with Hemmy to image spine disordersHemmy to image spine disorders

Early History of 3D Medical Early History of 3D Medical ImagingImaging

1980 – A CT scanner manufactured by General Electric 1980 – A CT scanner manufactured by General Electric features optional 3D imaging softwarefeatures optional 3D imaging software1980 – 1982 – Researchers begin investigating 3D 1980 – 1982 – Researchers begin investigating 3D imaging of craniofacial deformitiesimaging of craniofacial deformities1983 – Commercial CT scanners begin featuring built-in 1983 – Commercial CT scanners begin featuring built-in imaging software packagesimaging software packages1986 – Simulation software developed for craniofacial 1986 – Simulation software developed for craniofacial surgerysurgery1987 – First international conference on 3D imaging in 1987 – First international conference on 3D imaging in medicine organized in Philadelphiamedicine organized in Philadelphia1990 – 1991 – First textbooks on 3D imaging in medicine 1990 – 1991 – First textbooks on 3D imaging in medicine published; atlas of craniofacial deformities illustrated by published; atlas of craniofacial deformities illustrated by 3D CT images published3D CT images published– Taken from Seeram E; Computed Tomography Physical Principles, Clinical Taken from Seeram E; Computed Tomography Physical Principles, Clinical

Applications, and Quality Control, 2001Applications, and Quality Control, 2001

Fundamental 3D ConceptsFundamental 3D Concepts

The following rules should be followed when The following rules should be followed when acquiring data setsacquiring data sets– Field of view, matrix size, and centering must be the Field of view, matrix size, and centering must be the

same for all imagessame for all images– Angulation/orientation must be the same for all slicesAngulation/orientation must be the same for all slices– There should not be any duplicate images within the There should not be any duplicate images within the

datasetdataset– Thinner slices are typically betterThinner slices are typically better– Usually a “standard” algorithm is best for acquiring Usually a “standard” algorithm is best for acquiring

data sets – Edge algorithms are often too noisy data sets – Edge algorithms are often too noisy


Resolution – 3D images and Resolution – 3D images and reconstructions appear best in the planes reconstructions appear best in the planes they were acquiredthey were acquired3D images in the acquisition plane have 3D images in the acquisition plane have the same resolution as the original image the same resolution as the original image set (256x256 or 512x512)set (256x256 or 512x512)3D images in any plane other than the 3D images in any plane other than the original data set, the resolution will depend original data set, the resolution will depend on the inter-slice distanceon the inter-slice distance


When a voxel has the When a voxel has the same dimensions in same dimensions in all planes, it is said to all planes, it is said to be isotropicbe isotropic– Isotropic voxels will Isotropic voxels will

allow the model to allow the model to approximately the approximately the same resolution in all same resolution in all planesplanes

ModelingModeling

The generation of a 3D object using computer The generation of a 3D object using computer software is called modelingsoftware is called modeling

Models can be rotated and viewed from many Models can be rotated and viewed from many different anglesdifferent angles

Several modeling techniques existSeveral modeling techniques exist– The most common is called extrusionThe most common is called extrusion– Extrusion uses computer software to transform a 2D Extrusion uses computer software to transform a 2D

profile into a 3D objectprofile into a 3D object– An example is a square being changed into a boxAn example is a square being changed into a box

ModelingModeling

Several modeling techniques existSeveral modeling techniques exist– The most common is called extrusionThe most common is called extrusion– Extrusion uses computer software to transform a 2D Extrusion uses computer software to transform a 2D

profile into a 3D objectprofile into a 3D object– An example is a square being changed into a boxAn example is a square being changed into a box– Extrusion can also be used to create a wireframe Extrusion can also be used to create a wireframe

modelmodel– Wireframes were more common in the early days of Wireframes were more common in the early days of

medical 3D, but are still commonly used in other medical 3D, but are still commonly used in other applicationsapplications

Wireframe Model of an EmbryoWireframe Model of an Embryo

ModelingModeling

After the wireframe After the wireframe model is created, a model is created, a surface is created by surface is created by placing a layer of placing a layer of pixels and patterns on pixels and patterns on top of the wireframetop of the wireframe

The technologist can The technologist can control various control various attributes such as attributes such as color and texturecolor and texture

Shading and LightingShading and Lighting

Shading and lighting help to add realism to the modelShading and lighting help to add realism to the modelSeveral different types of shading algorithms existSeveral different types of shading algorithms existA few examples are:A few examples are:– Constant shadingConstant shading– Faceted shadingFaceted shading– Gouraud shadingGouraud shading– Phong shadingPhong shading

Each technique has its own advantages and Each technique has its own advantages and disadvantagesdisadvantages

Constant ShadingConstant Shading

One shade or color is assigned to an One shade or color is assigned to an entire object entire object ((

http://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/constant.htmhttp://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/constant.htm))

Faceted ShadingFaceted Shading

Simple and quick but not very realistic Simple and quick but not very realistic ((

http://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/shadfaceted.htmhttp://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/shadfaceted.htm))

Gouraud ShadingGouraud Shading

Better than faceted, looks smoother Better than faceted, looks smoother ((

http://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/shadgou.htmhttp://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/shadgou.htm))

Phong ShadingPhong Shading

Makes images appear smooth and shiny Makes images appear smooth and shiny ((

http://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/shadphong.htmhttp://www.siggraph.org/education/materials/HyperGraph/scanline/shade_models/shadphong.htm))

RenderingRendering

Final step in the process of generating a Final step in the process of generating a 3D object3D object

Rendering is a computer program that Rendering is a computer program that converts the anatomic data collected from converts the anatomic data collected from the patient into the 3D image seen on the the patient into the 3D image seen on the computer screencomputer screen

Rendering adds lighting, texture, and color Rendering adds lighting, texture, and color to the final 3D imageto the final 3D image

RenderingRendering

Two types of rendering are used in Two types of rendering are used in radiologyradiology– Surface rendering: Uses only contour data Surface rendering: Uses only contour data

from the data set. Creates an external from the data set. Creates an external surface that is hollow. Less memory intensive surface that is hollow. Less memory intensive than volume renderingthan volume rendering

– Volume rendering: Uses the entire data set to Volume rendering: Uses the entire data set to create a 3D image. Produces a better image create a 3D image. Produces a better image than surface rendering, but uses more than surface rendering, but uses more computing powercomputing power

Classification of 3D Imaging Classification of 3D Imaging ApproachesApproaches

The primary approaches to 3D imaging The primary approaches to 3D imaging have been identifiedhave been identified– Slice imagingSlice imaging– Projective imagingProjective imaging– Volume imagingVolume imaging

Slice ImagingSlice Imaging

Simplest method of 3D imagingSimplest method of 3D imagingAlso known as multiplanar imaging (MPR)Also known as multiplanar imaging (MPR)Slice imaging doesn’t produce a true 3D Slice imaging doesn’t produce a true 3D image but rather a 2D image displayed on image but rather a 2D image displayed on a computer monitora computer monitorMPR is available on all CT and MR MPR is available on all CT and MR scannersscannersMPR produces coronal, sagittal, and MPR produces coronal, sagittal, and oblique imagesoblique images

MPR MPR

Oblique sagittal Oblique sagittal reconstructionreconstruction

Projective ImagingProjective Imaging

Most popular 3D imaging approachMost popular 3D imaging approachStill doesn’t offer a true 3D modelStill doesn’t offer a true 3D model– Some people classify projective imaging as Some people classify projective imaging as

21/2 D or 2.5D21/2 D or 2.5D

Projective imaging uses the axial stack Projective imaging uses the axial stack obtained from a CT exam to create obtained from a CT exam to create projections of what various anatomical projections of what various anatomical structures would look like from many structures would look like from many different anglesdifferent angles


Axial MRI of the circle Axial MRI of the circle of willis has been of willis has been subjected to a subjected to a projective imaging projective imaging technique.technique.


Central kangaroo is Central kangaroo is projected at several projected at several different angles into different angles into the 2D viewing spacethe 2D viewing space

Volume ImagingVolume Imaging

Volume imaging should not be confused Volume imaging should not be confused with Volume renderingwith Volume rendering

Volume rendering (often seen in MRI and Volume rendering (often seen in MRI and CT) is a class of projective imagingCT) is a class of projective imaging

Volume imaging produces a true 3D Volume imaging produces a true 3D visualization modevisualization mode

Volume ImagingVolume Imaging

Various methods of volume imaging Various methods of volume imaging includeinclude– HolographyHolography– Stereoscopic displaysStereoscopic displays– Anaglyphic methodsAnaglyphic methods– Varifocal mirrorsVarifocal mirrors– SynthanalyzerSynthanalyzer– Rotating multidiode arraysRotating multidiode arrays

Picture of a HologramPicture of a Hologram

Generic 3D Imaging SystemGeneric 3D Imaging System

Four major elements are noted for any 3D Four major elements are noted for any 3D imaging systemimaging system– InputInput– WorkstationWorkstation– OutputOutput– UserUser

InputInput

Devices that acquire the dataDevices that acquire the data– CT scanner, MR scannerCT scanner, MR scanner

The acquired data is sent to a workstationThe acquired data is sent to a workstation

WorkstationWorkstation

The workstation is the heart of the 3D The workstation is the heart of the 3D systemsystem

The workstation is a powerful computed The workstation is a powerful computed that handles the various 3D imaging that handles the various 3D imaging operationsoperations– PreprocessingPreprocessing– VisualizationVisualization– ManipulationManipulation– AnalysisAnalysis

OutputOutput

Once processing is completed, the results Once processing is completed, the results are displayed for viewing and recordingare displayed for viewing and recording

UserUser

The user interacts with each of the three The user interacts with each of the three components to optimize use of the systemcomponents to optimize use of the system

4 Steps to Create 3D Images4 Steps to Create 3D Images1. Data acquisition – slices, or sectional 1. Data acquisition – slices, or sectional images, of the patient’s anatomy are images, of the patient’s anatomy are produced. Methods of data acquisition in produced. Methods of data acquisition in radiology include CT, MRI, ultrasound, PET, radiology include CT, MRI, ultrasound, PET, SPECT, and digital radiographySPECT, and digital radiography

2. Creation of 3D space or scene space. 2. Creation of 3D space or scene space. The voxel information from the sectional The voxel information from the sectional images is stored in the computerimages is stored in the computer– Scene is defined as a multidimensional image; Scene is defined as a multidimensional image;

rectangular array of voxels with assigned values rectangular array of voxels with assigned values

4 Steps to Create 3D Images4 Steps to Create 3D Images

3. Processing for 3D image display. This 3. Processing for 3D image display. This is a function of the workstation and is a function of the workstation and includes the four operation listed aboveincludes the four operation listed above

4. 3D image display. The simulation 3D 4. 3D image display. The simulation 3D image is displayed on the 2D computer image is displayed on the 2D computer screenscreen

Maximum Intensity ProjectionMaximum Intensity Projection

Maximum Intensity Projection (MIP) is a Maximum Intensity Projection (MIP) is a volume rendering technique that originated volume rendering technique that originated in magnetic resonance angiography and is in magnetic resonance angiography and is now used frequently in computed now used frequently in computed tomography angiography. MIP does not tomography angiography. MIP does not require sophisticated computer hardware require sophisticated computer hardware because, like surface rendering, it makes because, like surface rendering, it makes use of less than 10% of the data in 3D use of less than 10% of the data in 3D spacespace

Steps Involved in MIPSteps Involved in MIP

A mathematical ray is projected from the A mathematical ray is projected from the viewer’s eye through the 3D spaceviewer’s eye through the 3D space

This ray passes through a set of voxels in This ray passes through a set of voxels in its pathits path

The MIP program allows only the voxel The MIP program allows only the voxel with the maximum intensity to be selectedwith the maximum intensity to be selected

Stand Alone WorkstationsStand Alone Workstations

Picker, Siemens, General Electric, and Picker, Siemens, General Electric, and several other manufacturers provide 3D several other manufacturers provide 3D packages. Most workstations offer a packages. Most workstations offer a variety of 3D processing featuresvariety of 3D processing features

3D Processing Features3D Processing Features

Multiplanar Reconstruction (MPR)Multiplanar Reconstruction (MPR)– Can demonstrate the entirety of a curved Can demonstrate the entirety of a curved

anatomical structured in one image. This anatomical structured in one image. This feature could be useful in demonstrating the feature could be useful in demonstrating the entire length of the descending aorta in one viewentire length of the descending aorta in one view

Surface RenderingSurface Rendering

Slice Plane MappingSlice Plane Mapping– Allows two tissue types to be viewed at the Allows two tissue types to be viewed at the

same timesame time


Slice Cube CutsSlice Cube Cuts– This is a processing technique that allows the This is a processing technique that allows the

operator to slice through any plane to operator to slice through any plane to demonstrate internal anatomydemonstrate internal anatomy

Transparency VisualizationTransparency Visualization– This technique allows the operator to view This technique allows the operator to view

both surface and internal structures at the both surface and internal structures at the same timesame time


Maximum Intensity ProjectionMaximum Intensity Projection

4D Angiography4D Angiography– This shows bone, soft tissue, and blood This shows bone, soft tissue, and blood

vessels at the same time to allows the viewer vessels at the same time to allows the viewer to see tortuous vessels with respect to boneto see tortuous vessels with respect to bone

DisarticulationDisarticulation– This shaded surface display technique allows This shaded surface display technique allows

the viewer to enhance the visualization of the viewer to enhance the visualization of certain structures by removing otherscertain structures by removing others


Virtual Reality ImagingVirtual Reality Imaging– Some workstations are capable of virtual Some workstations are capable of virtual

endoscopy. This allows the viewer to “fly endoscopy. This allows the viewer to “fly through” various anatomical structures through” various anatomical structures including the colon and bronchusincluding the colon and bronchus

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Three Dimensional Computed Tomography: Basic Concepts Chapter 17 Seeram