Archive for the ‘Radiation Physics’ Category
- Refers to procedures instituted to estimate the amount of radiation received by individuals who work in a radiation environment
- Personnel monitoring device simply measures the quantity of radiation to which the monitor was exposed and therefore is used as an indicator of the exposure of the wearer
1. Film Badges
- Film badges came into general use during the mid 1940’s
- Film badges are specially designed devices in which a small piece of film similar to dental radiographic film is sandwiched between metal filters inside a plastic holder
- The film incorporated into a film badge is special radiation dosimetery film that is particularly sensitive to ionizing radiation
- Exposure less than 10 mR (2.6 µC/Kg) are not measured by film badge monitors
- Film badge cannot be worn for long periods because of fogging cause by temperature and humidity
- Film badge monitors should be not worn for longer than 1 month
2. Thermoluminescence dosimeters (TLD’s) or OSL Dosimeter
- Lithium Flouride (LiF) in crystalline from – is the sensitive material of the TLD monitor
- When exposed to x-rays, the TLD absorbs energy and stores it in the form of excited electrons fall back to their normal orbital state with the emission of visible light
- Intensity of visible light – is measured with the photomultiplier tube (PM) and is proportional to the radiation dose receive by the crystal
- TLD monitoring device is more sensitive and more accurate than the film badge monitor
- TLD monitors can be worn for intervals up to 3 months at a time
- Optically Stimulated Luminescent Dosimeter method makes use of electrons trapped between the valence and conduction bands in the crystalline structure of certain types of matter (such as quartz, feldspar, and aluminum oxide).
- The ionizing radiation produces electron-hole pairs
- The electrons which have been excited to the conduction band may become entrapped in the electron or hole traps.
- Under stimulation of light the electrons may free themselves from the trap and get into the conduction band.
- From the conduction band they may recombine with holes trapped in hole traps. If the center with the hole is a luminescence center emission of light will occur.
- The photons are detected using a photomultiplier tube.
- The signal from the tube is then used to calculate the dose that the material had absorbed.
- The OSL dosimeter provides accurate reading as low as 1 mrem for x-ray and gamma ray photons with energies ranging from 5 keV to greater than 40 MeV.
3. Pocket ionization chamber
- Pocket ionization chambers are small devices measuring approximately 2cm by 10cm long and are designed to be clipped onto a wearing apparel
- Pocket ionization chamber that are usually use is diagnostic imaging has a range of 0 to 200 mR (0 to 50 µC/Kg)
This year, Radiology 101 is proud to say that it has published two informative/useful/helpful textbooks and workbooks which can be used both by Radiologic Technology teachers and students .
The Radiologic Physics Made Incredibly Easy Book 1 and Book 2 Textbook/Workbook is still available in all Jade Bookstores nationwide. National Bookstores also sell these books but in limited quantities. For those who can’t find Jade Bookstores in their respective areas, you can request these books or order them from National Bookstore. These books are sold for only P350.00 – P375.00.
These are also beneficial to all the resident doctors who are planning to specialize in Radiology and are planning to take the exam, as well as, for those who are reviewing for the board examinations and related licensure examinations, as well as, for those who just simply like to get “refreshed”.
For those who have already bought these books, thank you very much and I hope that it can help you to better understand Radiologic Physics.
There are three (3) x-ray tube rating charts that are very important in order to prolong tube life. They are listed below:
- Radiographic Tube Rating Charts
- Anode Cooling Chart
- Housing Cooling Chart
Radiographic Tube Rating Charts
- A guide regarding the most common technical factor combinations that can be used without overloading the tube.
- When you use the Radiographic Tube Rating Charts for the X-Ray machine you want to make sure that the kVp setting and the time of the exposure intersect below the mA reading.
- The mA is graphed as a curved line.
- Any combination of kVp and Time below the line should be safe for a single exposure.
Anode Cooling Chart
- Shows the thermal capacity of an anode and its heat dissipation characteristics
- Permits the calculation of the time necessary for the anode to cool enough for additional exposure to be taken.
- The anode has a limited capacity for storing heat.
- Thermal energy in x-ray is measured in Heat Units (HU)
- HU= kVp x mA x time (s)
- The cooling is rapid at first but slows as the anode cools. Usually, it take approximately 15 minutes to completely cool down the anode.
- When you need to find out how long it will take to cool the anode so that you can make more exposures you need to follow the instructions below.
1. Find the total heat units applied on the vertical scale.
2. Read from the heat units over to the cooling curve and then down to read the corresponding time.
3. Calculate the time necessary for the anode to cool to any desired level and subtract the corresponding time of the initial exposure.
Housing Cooling Chart
- It indicates the heat unit capacity and cooling characteristics of the housing.
- The tube housing cooling chart is very similar to the anode cooling chart.
- The tube housing will generally have a capacity of about 1 to 1.5 million HU.
- Complete cooling time may take 1 to 2 hours.
Photo credits: Stewart Bushong (^_^)