medical image processing

CVIP LabThe University of Louisville

Medical Image Processing

M. Sabry HassounaM. Sabry Hassouna

Ph.D.Ph.D.Computer Vision & Image Processing Laboratory (CVIP)

Louisville, Kentucky

The study of medical imaging is concerned with

Interaction of all forms of radiation with tissue.

The development of appropriate technology to extract clinically useful information, usually in the form of an image from the observed technology.

Medical ImagingMedical Imaging

X-RayX-Ray

Nov 8, 1895 Wilhelm Konrad Röntgen reported discovery of new “rays” (Nobel Prize in physics in 1901).

Jan 13, 1896First clinical use of X-rays by 2 First clinical use of X-rays by 2 British doctors to find a needle British doctors to find a needle in a hand.in a hand.

Image Formation A beam of X-rays is directed through a patient

onto a film. The film provides a measure of the ray

attenuation in tissue.

+ Excellent for imaging bones.+ Excellent for imaging bones.

- No depth information, bad for soft tissue, excessive radiation- No depth information, bad for soft tissue, excessive radiation

Sample X-Ray SlicesSample X-Ray Slices

Computed Tomography (CT)Computed Tomography (CT)

Nov 8, 1895 G. Hounsfield (computer expert) and A.M Cormack (physicist)(Nobel Prize in Medicine in 1979).

Image FormationThe object is viewed from a number of different angles and then a cross-sectional image of it can be computed (reconstructed).

+ Provide 3D anatomical information+ Provide 3D anatomical information

+ Preserves topology (bones)+ Preserves topology (bones)

- Excessive radiation- Excessive radiation

- Not good for all soft tissues- Not good for all soft tissues

Sample CT SlicesSample CT Slices

CT Acquisition TechniquesCT Acquisition Techniques

slice-by-slice scanning

Spiral (volume) scanning (Very Fast) 3D Reconstruction

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI)

1952F. Bloch and E. Purcel, extended by R. Ernst)(Bloch & Purcel: Nobel Prize in Physics in 1952)(Ernst: Nobel Prize in Chemistry in 1991)

Image Formation- Hydrogen nuclei (protons) under a strong magnetic field spin in phase with one another and align with the field.- Relaxed protons induce a measurable radio signal.

+ Main modality for image guided surgery.+ Superb ability to discriminate between subtle differences in tissue characteristics.+ Very safe.- Less accurate for bone scanning.

Sample MRI SlicesSample MRI Slices

Ultrasound (US)Ultrasound (US)

1979: Samuel H. Maslak

Image FormationAn ultrasonic energy is propagated into the patient from a transducer placed on the skin and back-scattered echo signal is recorded by the same transducer.

+ Noninvasive+ Clean & safe+ In-expensive- Noisy- Gas filled and bony structures cannot be imaged because they absorb ultrasound waves.

Positron Emission Tomography (PET)Positron Emission Tomography (PET)

1998-2001: Dr. David Townsend and Dr. Ron Nutt.

Image Formation- Detection of radiation from the emission of positrons.

+ Valuable technique for some diseases and disorders.+ Amount of radiation is small- Invasive (inject radioactive material)

Magnetic Resonance Angiography (MRA)

Magnetic Resonance Angiography (MRA)

Image FormationImaging the blood vessels (moving spins) using MRI scanner.

TOF (time-of-flight)TOF (time-of-flight)

PCA (phase contract angiography)PCA (phase contract angiography)

(CEA) (contrast enhanced angiography)(CEA) (contrast enhanced angiography)

(CTA) (computer tomography angiography)(CTA) (computer tomography angiography)

(DSA) (digital subtraction angiography)(DSA) (digital subtraction angiography)

DSADSA CTACTA TOFTOF

Medical Image ProcessingMedical Image Processing

Data ProcessingData Processing

1. Preprocessing

Filtering, registration

2. Detection

Finding objects (nodules, polyps, organs)

3. Segmentation

Exact delimitation of objects

4. Analysis

Measurement (volume, curvature)

5. Classification/diagnoses

PreprocessingPreprocessing

Original Enhanced

DetectionDetectionFind location of objects of interest without prior knowledge about their location/existence

• Bones• Organs• Polyps in colon• Nodules in lungs

SegmentationSegmentationExactly delimitate objects, once they are detected.

- Vessels- Liver- Cardiac imaging (left ventricle)- Brain

AnalysisAnalysis

• Measurement Volume - growth Vessel stenosis

• Functional imaging Stroke Cardiac perfusion Tumor perfusion

• Cardiac function LV motion Injection fraction

Classification / DiagnosesClassification / Diagnoses

• Comparison to developed atlases• Use of knowledge databases• Classify as normal/abnormal (brain) • Classify lung nodules as benign/malignant• Determine cancer/non-cancer