Advanced Biomedical Imaging Dr. Azza Helal A. Prof. of Medical Physics Faculty of Medicine Alexandria 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)

Imaging Modalities

Technique Physical principles Instrument Imaging parameters Resolution & speed Advantages & Hazards Artifacts Plain X-ray CT Isotope scan US MRI

Plain x ray

Dr Azza Helal Structure of the atom Electron mass 1800 time < p or n a)Attraction 1.(+ve nuc. & –ve e). Prevent ele. from leaving atom 2. Neutron b) repulsion between p +ve -ve nucleons ZXAZXAZXAZXA 2n 2 Energy levels potential energy Binding energy K shell, L,M,N,O

FrequencyWave lengthRadiation x10 6 cm – 0.01cmRadio waves AºInfrared Aº-4000AºVisible light Aº-100AºUV Aº Aº X & gamma cm Types of electromagnetic waves X Rays are high-energy EM radiation and part of EM spectrum

Dr Azza Helal Production 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 thermal conductivity – More efficient X-Ray production

Interactions in a target Characteristic radiation Bremsstrahlung

Therapeutic x-ray tube: Mega electron volts (MeV) are used, a higher conversion of electrons into photons, high KV, larger focal spot, longer duration & stationary anode. Therapeutic x-ray tube: Mega electron volts (MeV) are used, a higher conversion of electrons into photons, high KV, larger focal spot, longer duration & stationary anode. Diagnostic x ray tube: (KeV), there is more conversion of the electrons to heat, low KV, small focal spot, short duration & rotating anode. Diagnostic x ray tube: (KeV), there is more conversion of the electrons to heat, low KV, small focal spot, short 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 photons Only 1% of the electrons are converted to photons

Probing patient from different directions during 360 rotations with x-ray beam of known intensity (I 0 ) & 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)

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 Helal 160Us 260Us Reflection Time between pulse emission and echo return determines depth 12cm 20cm Echo Velocity =Distance/ Time

Magnetic Resonance Imaging (MRI) Image formed by transmitting and receiving radio waves inside a high magnetic field.Image formed by transmitting and receiving radio waves 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 Patient hydrogen densityThe image is mainly related to Patient 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

Assignments One student will be selected for assignment One student will be selected for assignment

Suggested Readings David Sutton’s Radiology David Sutton’s Radiology Physics for medical imaging by RF Fare & PJ Allisy-Roberts. Physics for medical imaging by RF Fare & PJ Allisy-Roberts.

Question Mention different components of x ray tube? Mention different components of x ray tube?