Radiation Units And Its Application

  1. Units of measurements, but first let's look at the prefixes associated with the different types of units
    Tera (T) = 10 12
    Giga (G) = 109
    Mega (M) = 10 6
    kilo (k) = 103
    hecto (h) = 102
    deca (da) = 101
    deci (di) = 10-1
    centi (c) = 10-2
    milli (m) = 10-3
    micro (    µ) = 10-6
    nano (n) = 10-9
    pico (p) = 10-12
    femto (f) = 10-15
    atto (a) = 10-18

    You must be able to move between these values as if it's second nature to you.

    Point of interest: When working with Ci we tend to use milli and micro and when working with Bq we tend to use Mega and Giga.

    Example 1 nanos = 10-15 Mega Example 1 gigas = 1021 pico?
    2.3 M = _______ f 1.5 x 1025 = _______ k

    Remember - when you are working with exponents and applying division subtract and when multiplying exponents you add!

     

    Next we need to look at how radiation is measured. There are different types of units that need to be considered. They are noted below in the table. As a student you must be able to define each unit, understand both the English and SI values, and be able to convert between English and SI.

    2. English Unit

    SI Unit
    Roentgen (R) = 2.58 * 10-4 C/kg (coulomb per kilogram)

    Coulomb/kg (C/kg)
    Radiation Absorbed Dose (RAD) = 100 erg/gm Gray (Gy) = 100 RAD
    Relative biological effectiveness (RBE)=Dose in rad to produce same effect with x or gamma ray/ Dose in rad to produce same effect with radiation under investigation Becquerel (Bq) = 1 dps
    Roentgen equivalent man (REM) = RBE*RAD Sievert (Sv) = 100 REM
    curie (Ci) = 2.2 * 1012 dpm
    Ci =3.7*1010 dps    		 Becquerel (Bq) = 1 dps

  2. Here are some examples on how to work with these different radiation units
  • Convert RAD to Gray to RAD (think 102)
    •
  • Convert 2 mCi to Bq (think 37 or 3.7 x 1010 dps = 1 Ci)
  • 2 x 3.7 x 107 = 7.4 x 107 or 74 MBq
  • Calculate: 120 MBq = ______ mCi
  • Calculate: 250 mCi = ______GBq
  • Remember to think 37
    •

    More information on units of measurement in radiation

    Disintegrations Per Minute (dpm)

    Remember that 1 Bq is equal to 1 disintegration per second (dsp). For every disintegration that is measured a gamma ray is detected. Likewise, if a group of atoms decayed and emit 1000 gamma rays in a second then the amount recorded would be 1000 dps.

    Usually, the two units used when detecting radiation in this manner is either in dps or dpm. Note the value of these units as they relate to a Ci.

    Here are two ways radiation is recorded. Prior to injecting a patient a dose calibrator is used to measure the amount of activity (radiation) that will be injected into a patient. This unit usually used to record the patient dose is usually in mCi or μCi. Once the activity is injected into a patient a gamma camera or scintillation detector is used to measure the distribution of the radioactive compound. This device records counts over time, not disintegrations. Any idea as to why? The images below there are the two types of instruments under discussion. On the left is a dose calibrator and on the right is a two-headed gamma camera.

     

    As mentioned, a dose calibrator measures the radioactive dose (radiopharmaceutical) being administered to the patient. As an example, a syringe is placed into the the dose calibrator and measures 25 mCi of 99mTcMDP. What is this equivalent to in Bq? Answer After the patient is injected the activity being emitted from the patient is acquired on the gamma camera. The gamma camera detects the gamma rays, either in total counts. While we are recording the amount of counts the image displays distribution of MDP within the skeletal system
    https://www.lhsc.on.ca/thoracic-surgery/bone-scan (above image)

    An Important difference between dps/dpm and cps/cpm

    Uptake probes, well counters, and gamma cameras actually record counts in counts [not disintegration] per minute or seconds (cpm or cps). If any of these instruments were able to count 100% of all the radiation being emitted, then we could say it records in dps/dpm. However, this can never happen because NO system has 100% counting efficiency. Therefore, a technologist must be able to convert cps/cpm to dps/dpm.

    The key to determining the total disintegration from total counts is to know the efficiency of your counting system. Follow the example given and example given on converting counts to disintegrations.