In this segment we will try and cover important viva topics for a postgraduate examination (MD/DMRD/DNB). Most of these relate to physics, contrast agents and procedures; we will post short sessions covering these topics on a fortnightly basis. A lot of these might well be a little boring. But rest assured , they are hugely important for the exam. Lets start with radiation protection and hazards. The first two segments deal with personal dosimeters.
Q & A SESSIONS 1 - PERSONAL DOSIMETRY – FILM BADGE
Q. What are the commonly used devices for personal dosimetry ?
A. Film badge, thermoluminescent dosimeter (TLD), electronic dosimeter
Q. What type of film is used in a film badge?
A. Double coated, about same size as dental film
Has 2 emulsions, one fast to detect occupational exposure ; second slow to detect accidental exposure
Q. What are the parts of a film badge ?
A. Consists of three parts : -
- plastic holder made of a material with low atomic number to filter low energy x rays
- assortment of filters / windows
- film packet and film
Q. What are the different filters/windows in a film badge and what are their uses?
A. Allow measurement of different types of radiation reaching the monitoring device eg,
Open window – measurement of xrays
Plastic ( grey colour) – beta rays
Cadmium (yellow) – slow neutrons
Thin copper (green) – diagnostic xrays
Thick copper (pink) – gamma rays
Lead (black) – fast neutrons and gamma rays
All filters except forthin copper are 1mm thick, thin copper is 0.25 mm
Q. What parameters can be assessed by processing the badge ?
A. a) Amount of radiation exposure –
Calibration films exposed to known quantities of radiation are used to generate density – dose graphs. Films worn by personnel are developed , densities are measured and the dose is then read from the density – dose graph
b) Different types of radiation – by use of different filters
c) Occupational/accidental exposure – using 2 different emulsions
d) Differentiating direct / scatter radiation – direct exposure has a sharp edge, scatter exposure ahs blurred edges, spots on intense blackening may result from a radioactive spill
Q. What are the advantages of film badges ?
A. Provides a permanent record
Inexpensive
Measure a wide range of exposure ( 0.2 – 1000 mSv)
Can differentiate btw diff types of radiation and accidental/occupational exposure, quantity and direction of radiation
Q. What are the disadvantages of film badges ?
A. Affected by heat, humidity, inadequate storage conditions
Requires dark room and wet processing
Have to changed on a monthly basis
Exposure cannot be determined on the day of occurrence
Accuracy +/- 20%
The next segment will deal with TLD badges and electronic dosemeters
Inspite of all radiological wisdom available to us on internet, we feel there is dearth of platforms focussing on radiologists preparing for examinations - whether post graduate courses or post PG fellow ships. As radiologists who have taken MD and FRCR exams in the past, we can empathise with a budding radiologist who feels a little lost amidst the sea of non exam oriented radiology education. This site aims to provide the training radiologists with the right set of tools which will help them in an exam setting.
