1. Department of radiology divided into
1.Radiography
2.CT SCAN
3.US
4.Doppler & Color Doppler
5.MRI
6.Nuclear medicine
7. Interventional radiology

2. PRODUCTION OF X-RAY -X-ray used for all conventional radiography & CT
-produced by passing a high voltage across two terminals placed in an evacuated tube ( cathode & anode ).
- Usually a high Kv ( 50 to 150 kv), is applied across the two terminals.
-The electrons are attracted towards the anode at a high speed. They hit the tungsten target and x-ray are produced, 99%of its energy will be converted into heat &only 1% is converted to useful x-ray

3. ABSORPTION OF X-RAY
image in radiography &CT depend on the fact that the x-ray are absorbed to variable extent as they pass through the body (x-ray attenuation )
With conventional radiography there are four basic densities :
1- gas does not attenuate any x-ray so appear black.
2- fat less radiolucent
3- soft tissues(gray)
4- calcified structures &bone (white)

4. CONVENTIONAL RADIOGRAPHY PROJECTIONS :
1-Frontal views(AP, PA).
2-Lateral view
3-oblique.
Precise localization of a shadow requires more than one view, usually at right angle to one another ( AP & LAT. ) , oblique views may be required.

5. CONVENTIONAL TOMOGRAPHY
The aim of a tomography is to blur out overlying structures ,but to keep a selected plane of interest in sharp focus , this is achieved by moving the X-RAY tube &film about an axis at level of interest.
Now days computed tomography has replaced conventional tomographic examination .

6. COMPUTED TOMOGRAPHY
Depend on the principle of x-ray absorption, CT uses a more sensitive X-RAY detection system than photographic film ,namely gas or crystal detectors ,&manipulate the data using a computer .
X-RAY tube and detectors rotate around the patient .
2 types of CT :
A-conventional (take axial section but there is interval)
B-spiral
Advantage of spiral CT :
1. reduction in time
2. no gap between the section
3.better reconstruction to other planes ( sagital & coronal)
CT NO. (attenuation value )

8. ULTRASOUND (US) The principle in diagnostic US examination
very high frequency sound (3-10MHZ)is directed into the body from a transducer placed in contact with the skin in order to make good acoustic contact ,the skin is smeared with a jelly-like substance .
Sound travels through the body ,is reflected by the tissue interfaces to produce echoes which are picked up by the same transducer and converted into an electrical signal .

9. ULTRASOUND (US)
-US plays little role in diagnosis of lung or bone disease(total reflection of US beam ) .
Fluid is a good conductor of sound . so US very useful in examination of UB &cyst .
The fetus in its amniotic sac surrounding by fluid and containing no air can be well demonstrated by US .

10. DOPPLER EFFECT
Sound reflected from mobile structures shows a variation in frequency which corresponding to the speed of movement of structure .
This shift in frequency can be converted to an audible signal (sonicaid) , the is principle that the Doppler probe used in obstetric to listen to the fetal heart .

11. COLOR DOPLLER US
-if blood flow toward the transducer , then the received signal (red in color )
-if reverses true (blue color )
Image similar to an arteriogram can be produced ,on which atherosclerotic plaque may be visible .

12. RADIONUCLIDE IMAGING
The radionuclide isotopes emit gamma rays are electromagnetic radiation similar to x-ray , produced by radioactive decay of the nucleus .
Radionuclide imaging depend on the fact that certain substance concentrate selectively in different part of body .
Radionuclide can be chemically tagged to these substances.
Most commonly radio used is technetium-99m .

13. MAGNETIC RESONANCE IMAGING
It differ from CT :
I. can directly image in any plane (sagittal , coronal and axial)
2. longer scanning time
3. MRI involve no ionizing radiation
4.CM in MRI is gadolinium which produced very high signal intensity in T1 weighted images .

14. MAGNETIC RESONANCE IMAGING
How to get MRI image ?
-Strong magnetic field
-Radio frequency pulse
Certain hydrogen protons ( H+) change their alignment according to received freq.
Stopping the radio freq so H+ return to it's state & loses energy.
Energy is converted into signal.

15. Contraindication to MRI
Absolute
1.cardiac pacemaker
2.metalic stent
3.shell or retained bullet
Relative
1.1st.&2nd trimester of pregnancy .
2.claustrophobia
3.obesity

16. Risk of ionizing radiation
acute effect : occur in high doses
ulceration,desequmation,damage to old blood vessels .
B.chronic effect : increase incidence of cancer , leukemia & genetic effect .
Radiation protection :
1.limit size of x-ray beam to required area .
2.limit number of films.
3.keeping repeated examination to minimum.

17. Thank you