medical imaging overview—oleh tretiak, drexel university

MIPR Lecture 1Copyright Oleh Tretiak, 2004

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Medical Imaging and Pattern Recognition

Lecture 1 Medical Imaging Overview

Oleh Tretiak


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IntroductionThe first part of the course will provide an introduction to medical imaging modalities, on object-image relationship and the relationship between the state of the object and image features. The second part of the course will cover statistical pattern recognition methods and methodologies for performance evaluation.


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Course Outline

• Part 1: Imaging models and methods– Introduction– Linear system theory and Fourier analysis– Probability and random processes– Image acquisition and storage– Image processing operations. Unary operations. Linear and

nonlinear filtering. Morphological operations. Segmentation.– Laboratory 1. Introduction to ImageJ. Scanning.

Characterization of an imaging device.– Laboratory 2. Image processing. Experiments with standard

operations. Problem solving experiments.


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Course Outline: More

• Diagnostic Imaging Modalities– X-ray imaging: X-ray attenuation and scattering. Contrast

mechanisms. Dose. Three-dimensional imaging. – Computer tomography: Radon transform and its inversion.

X-ray, SPECT, and PET tomography.– Magnetic Resonance Imaging. Signal generation. Scanner

operation and inversion. Pulse sequences. – Laboratory 3. Medical image processing. Experiments with

CT image stacks and image subtraction.


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Course Outline: Yet more• Part 2: Statistical Pattern Recognition

– Foundations of statistical pattern recognition. Statistical estimation, hypothesis testing.

– Estimation problems in patter recognition. Linear classifiers. – Neural nets and training rules. Backpropagation.– Evaluation methods: resubstitution, leave-one-out. ROC

methods: parametric and ordinal dominance. Bootstrap and permutation.

– Review and overview: topics in medical image research.– Lab 4. Methods of data plotting and analysis. Pseudorandom

numbers and modeling. Bootstrap.– Lab 5. Classification with linear classifiers. Experiments on

neural-net training.


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Formal Details

• Instructor: Oleh Tretiak – [email protected]

• Course web site:– http://www.ece.drexel.edu/faculty/tretiak/KPI/

mailto:[email protected]

http://www.ece.drexel.edu/faculty/tretiak/KPI/


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This Lecture’s Outline

• Examples of medical images• The imaging triangle: object, image,

observer• Imaging categories in medicine• Physics, biology, and imaging


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Examples of Medical Images


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Questions

• What does the image show?• What good is it?• How is it made?


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X-ray Image


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X-ray Image of Hand


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What is it?

• Two X-ray views of the same hand are formed on an single film by exposing the hand onto half of the film while the other half is blocked by an opaque screen.


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What good is it?

• A fracture of the middle finger is seen on both views, though it is clearer on the view on the left. This image can be used for diagnosis - to distinguish between a sprain and a fracture, and to choose a course of treatment.


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X-ray Imaging: How it works.

X-ray shadow cast by an object Strength of shadow depends on composition and thickness.


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Summary: X-ray Imaging

• Oldest non-invasive imaging of internal structures

• Rapid, short exposure time, inexpensive• Unable to distinguish between soft tissues in

head, abdomen• Real time X-ray imaging is possible and used

during interventional procedures.• Ionizing radiation: risk of cancer.


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CT (Computed Tomography)

CT Image of plane throughliver and stomach Projection image

from CT scans


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What Is It?

• Computer Tomography image of section through upper abdomen of patient prior to abdominal surgery.

• Section shows ribs, vertebra, aorta, liver (image left), stomach (image right) partially filled with liquid (bottom).


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What Good Is It?

• The set of CT images, from the heart down to the coccyx, was used in planning surgery for the alleviation of intestinal blockage.

• The surgery was successful (I’m still here).


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Computer Tomography:How It Works

Only one plane is illuminated. Source-subject motion provides added information.


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Fan-Beam Computer Tomography


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Summary of X-Ray CT

• Images of sectional planes (tomography) are harder to interpret

• CT can visualize small density differences, e.g. grey matter, white matter, and CSF. CT can detect and diagnose disease that cannot be seen with X-ray.

• More expensive than X-ray, lower resolution.• Ionizing radiation.


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Functional Magnetic Resonance Imaging

From http://www.fmri.org/Picture naming task

Plane 3

Plane 6

http://www.fmri.org/


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What Is It?

• Two of sixteen planes through brain of subject participating in an image-naming experiment.

• Images are superposition of anatomical scans (gray) and functional scans (colored).

• Plane 3 shows functional activity in the visual cortex (bottom)

• Plane 5 shows activity in the speech area ( image right).


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What Good Is It?

• This set of images is part of research on brain function (good for publication).

• Functional imaging is used prior to brain surgery, to identify structures such as the motor areas that should be avoided, and focal areas for epilepsy, that should be resectioned.


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MRI Signal Source

ω0 = γH0

When a nuclear magnet is tilted away from the external magnetic field it rotates (precesses) at the Larmour frequency. For hydrogen, the Larmour frequency is 42.6 MHz per Tesla.

H0

ω0


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Detected Signal in MRI

Spinning magnetization induces a voltage in external coils, proportional to the size of magnetic moment and to the frequency.

H0

ω0

σ(τ)


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MRI Image Formation

• Magnetic field gradients cause signals from different parts of the body to have different frequencies.

• Signals collected with multiple gradients are processed by computer to produce an image, typically of a section through the body.


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Features of MRI

• No ionizing radiation – expected to not have any long-term or short-term harmful effects

• Many contrast mechanisms: contrast between tissues is determined by pulse sequences

• Can produce sectional as well as projection images.

• Slower and more expensive than X-ray


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Magnetic Resonance Summary

• No ionizing radiation (safe)• Tomography at arbitrary angle• Many imaging modes (water, T1, T2,

flow, neural activity)• Slow• Expensive


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Ultrasound Imaging

Twin pregnancy during week 10


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What Is It?

• Ultrasound image of a woman’s abdomen

• Image shows a section through the uterus. Two embryos in their amniotic sacs can be seen.


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What Good Is It?• This image allows a safe means for

early identification of a twin pregnancy.• Obstetric ultrasonography can be used

to monitor high-risk pregnancies to allow optimal treatment.

• Pre-natal scans are part of baby picture albums.


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Ultrasound Scanner• A picture is built up

from scanned lines. • Echosonography is

intrinsically tomographic.

• An image is acquired in milliseconds, so that real time imaging is the norm.

Transducer travel

Object

Image


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Ultrasound Imaging Overview

• Imaging is in real time - used for interventional procedures.

• Moving structures and flow (Doppler) can be seen. Used for heart imaging.

• Ultrasound has no known harmful effects (at levels used in clinical imaging)

• Ultrasound equipment is inexpensive• Many anatomical regions (for example, Head)

cannot be visualized with ultrasound.


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Single Photon Computed Tomography

Images on left show three sections through the heart.A radioactive tracer, Tc99m MIBI (2-methoxy isobutyl isonitride) is injected and goes to healthy heart tissue.


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What Is It?

• Three sectional (tomographic) images of a living heart. Colored areas are measures of metabolic activity of left ventricle muscle. Areas damaged by an infarct appear dark. This seems to be a normal heart.


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What Good Is It?

• Used for staging (choosing treatment before or after a heart attack), and monitoring the effectiveness of treatment.


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Radionuclide Imaging

• Basic Idea• Collimator• Tomography

Basic idea: A substance (drug) labeled with a radioactive isotope is ingested. The drug goes to selective sites.


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Collimator

Only rays that are normal to the camera surface are detected.


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SPECT

Single Photon Emission Computed Tomography. Shown here is a three-headed tomography system. The cameras rotate around the patient. A three-dimensional volume is imaged.

Gamma camera

Gamma camera

Gamma camera


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Features of Radionuclide Imaging

• The image is produced from an agent that is designed to monitor a physiological or pathological process– Blood flow– Profusion– Metabolic activity– Tumor– Brain receptor concentration


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Fluorescence MicroscopyImage of living tissue culture cells. Three agents are used to form this image. They bond to the nucleus (blue), cytoskeleton (green) and membrane (red).


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What Is It?

• Optical microscope image of tissue culture.

• Image is formed with fluorescent light.• Tree agents are used. They bond to

– DNA in nucleus, blue– Cytoskeleton, green– Lipid membranes, red


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What Good Is It?

• This image seems to be a demonstration of fluorescent agents.

• Tissue culture is used in pharmaceutical and physiological research, to monitor the effect of drugs at the cellular level.

• Fluorescent labeling and imaging allows in-vivo evaluation of the location and mechanism of a drug’s activity.


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Optical Imaging• Optical imaging (visible and near infrared) is

undergoing very rapid development.• Like radionuclide imaging, agents can be designed to

bind to almost any substrate. • Intrinsic contrast, such as oxy- vs. deoxy-hemoglobin

differential absorption are also exploited.• There has been a growth in new optical imaging

methods.


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Thoughts on Imaging

• Three entities in imaging– Object– Image– Observer


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Image vs. Object

• Images (and vision) are two-dimensional– Surface images– Projection images– Sectional images (tomograms)

• Image eliminates data– 3D object - 2D image– Moving object - still image


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Creative Imaging

• Imaging procedures create information– Functional MRI for the first time allows non-

invasive study of the brain– Doppler ultrasound for the study of flow– Agents for the study of gene expression,

in-vivo biochemistry


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End of First Lecture

More to Come!

medical imaging overview—oleh tretiak, drexel university

Documents

medical image processing

imaging models

medical imaging modalities

imaging device

threedimensional imaging

medical image research

image subtraction

image features