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?