Transcript ImageModalities

The University of Louisville
CVIP Lab
Medical Image Processing
M. Sabry Hassouna
Ph.D.
Computer Vision & Image Processing Laboratory (CVIP)
Louisville, Kentucky
Medical Imaging
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.
X-Ray
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.
Nov 8, 1895
Wilhelm Konrad Röntgen
reported discovery of new “rays”
(Nobel Prize in physics in 1901).
Jan 13, 1896
First clinical use of X-rays by 2
British doctors to find a needle
in a hand.
+ Excellent for imaging bones.
- No depth information, bad for soft tissue, excessive radiation
Sample X-Ray Slices
Computed Tomography (CT)
Image Formation
The object is viewed from a number of different angles and then a crosssectional image of it can be computed (reconstructed).
Nov 8, 1895
G. Hounsfield (computer expert)
and A.M Cormack (physicist)
(Nobel Prize in Medicine in 1979).
+ Provide 3D anatomical information
+ Preserves topology (bones)
- Excessive radiation
- Not good for all soft tissues
Sample CT Slices
CT Acquisition Techniques
slice-by-slice scanning
Spiral (volume) scanning
(Very Fast)
3D Reconstruction
Magnetic Resonance Imaging (MRI)
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.
1952
F. Bloch and E. Purcel, extended by R. Ernst)
(Bloch & Purcel: Nobel Prize in Physics in 1952)
(Ernst: Nobel Prize in Chemistry in 1991)
+ 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 Slices
Ultrasound (US)
Image Formation
An 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.
1979: Samuel H. Maslak
+ Noninvasive
+ Clean & safe
+ In-expensive
- Noisy
- Gas filled and bony structures cannot be imaged
because they absorb ultrasound waves.
Positron Emission Tomography (PET)
Image Formation
- Detection of radiation from the emission of positrons.
1998-2001:
Dr. David Townsend and Dr. Ron Nutt.
+ Valuable technique for some diseases
and disorders.
+ Amount of radiation is small
- Invasive (inject radioactive material)
Magnetic Resonance Angiography (MRA)
Image Formation
Imaging the blood vessels (moving spins) using MRI scanner.
TOF (time-of-flight)
PCA (phase contract angiography)
(CEA) (contrast enhanced angiography)
(CTA) (computer tomography angiography)
(DSA) (digital subtraction angiography)
DSA
CTA
TOF
Medical Image Processing
Data 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
Preprocessing
Original
Enhanced
Detection
Find location of objects of interest without prior knowledge
about their location/existence
• Bones
• Organs
• Polyps in colon
• Nodules in lungs
Segmentation
Exactly delimitate objects, once they are detected.
- Vessels
- Liver
- Cardiac imaging (left ventricle)
- Brain
Analysis
• Measurement
Volume - growth
Vessel stenosis
• Functional imaging
Stroke
Cardiac perfusion
Tumor perfusion
• Cardiac function
LV motion
Injection fraction
Classification / Diagnoses
• Comparison to developed atlases
• Use of knowledge databases
• Classify as normal/abnormal (brain)
• Classify lung nodules as benign/malignant
• Determine cancer/non-cancer