Advanced Biomedical Imaging
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Transcript of Advanced Biomedical Imaging
Advanced Biomedical Imaging
Dr. Azza HelalDr. Azza HelalA. Prof.A. Prof. of Medical Physics of Medical Physics
Faculty of MedicineFaculty of MedicineAlexandria UniversityAlexandria University
To understand physical principles of imaging
modalities.
Aiming to apply these modalities in a safe and
effective way.
Intended learning outcomes of the course (ILOS)Intended learning outcomes of the course (ILOS)
Imaging ModalitiesImaging Modalities
TechniquePhysical
principlesInstrument
Imaging parameters
Resolution
& speed
Advantages
&
HazardsArtifacts
Plain X-ray
CT
Isotope
scan
US
MRI
Plain x rayPlain x ray
Dr Azza Helal
Structure of the atomStructure of the atom
Electron mass 1800 time < p or n
a)Attractiona)Attraction
1.(+ve nuc. 1.(+ve nuc. & –ve e).& –ve e).
Prevent ele. Prevent ele. from from
leaving leaving atom atom
2. Neutron2. Neutron
b) b) repulsionrepulsion between pbetween p
+ve
-ve
nucleonsnucleons
ZZXXAA
2n2n22
Energy levels
potential energy
Binding energyBinding energy
K shell, L,M,N,O
Radiation Wave length Frequency
Radio waves 3x106cm – 0.01cm 104-1012
Infrared 0.01-7000Aº 1012-1014
Visible light 7000Aº-4000Aº 1014-1015
UV 4000Aº-100Aº 1014-1016
X & gammaX & gamma 100Aº-10-4Aº 1016-1022
10-12cm
Types of electromagnetic wavesTypes of electromagnetic waves
X Rays are high-energy EM radiation and part of EM spectrum
Dr Azza Helal
Production of X- Rays, X ray tubeProduction of X- Rays, X ray tube
High-speed electrons suddenly slowed down releasing part of their energy as X-Rays.
X-Ray tube consists of:
Evacuated tube Cathode (tungsten) Focusing cup Copper anode block Tungsten target (high Z material)
– high melting point high melting point
– high thermal conductivity high thermal conductivity
– More efficient X-Ray productionMore efficient X-Ray production
Interactions in a targetInteractions in a target
Characteristic radiationCharacteristic radiation
BremsstrahlungBremsstrahlung
•Therapeutic x-ray tubeTherapeutic x-ray tube:: Mega electron volts (MeV) are Mega electron volts (MeV) are used, a higher conversion of electrons into photons, high used, a higher conversion of electrons into photons, high KV, larger focal spot, longer duration & stationary anode.KV, larger focal spot, longer duration & stationary anode.
•Diagnostic x ray tube:Diagnostic x ray tube: (KeV), (KeV), there is more conversion of there is more conversion of the electrons to heat, low KV, small focal spot, short the electrons to heat, low KV, small focal spot, short duration & rotating anode.duration & rotating anode.
•Total number of electrons converted to heat is 99%.Total number of electrons converted to heat is 99%.
•Only 1% of the electrons are converted to photonsOnly 1% of the electrons are converted to photons
Probing patient from different directions during 360rotations with x-ray beam of known intensity (I0) & measuring it after it has passed the pt (I).Attenuation depends thickness and density of tissues
• Image displays on computer or multiple films
New technologies are
• Helical CT &• Multiple slice / detector arrays
Computed Axial Tomography (CT)Computed Axial Tomography (CT)
Ultrasound (US) Ultrasound machine transmits high-frequency sound
into body using a probe.
Sound waves travel into body & hit a boundary between tissues (fluid & soft tissue).
Some waves reflected back to the probe and are detected by probe while some travel on further until they reach another boundary and then reflect back to the probe.
So image depends on transmission characteristics of the interfaces.
Image display on computer or films.
DR Azza HelalDR Azza Helal
160Us
260Us
Reflection
Reflection
Time between pulse Time between pulse emission and echo emission and echo return determines return determines
depthdepth
12cm
20cm
Echo
Echo
Velocity =Distance/
Time
Magnetic Resonance ImagingMagnetic Resonance Imaging(MRI)(MRI)
•Image formed by transmitting and receiving radio waves Image formed by transmitting and receiving radio waves inside a high magnetic field.inside a high magnetic field.
•All routine MRI techniques are based on receiving and processing of the signals from protons of hydrogen atom.
•The image is mainly related to The image is mainly related to Patient hydrogen densityPatient hydrogen density
•MRI makes great pictures because of large no of protons in the body, primarily in water and fat.
•Image display on computer or multiple filmsImage display on computer or multiple films
AssignmentsAssignments
One student will be selected for assignmentOne student will be selected for assignment
Suggested ReadingsSuggested Readings
David Sutton’s RadiologyDavid Sutton’s Radiology
Physics for medical imaging by RF Fare & Physics for medical imaging by RF Fare & PJ Allisy-Roberts.PJ Allisy-Roberts.
QuestionQuestion
Mention different components of x ray Mention different components of x ray tube?tube?