Basic Physics of Digital Radiography/Quiz2

A quiz on Radiation Biology & Dosimetry is available below for those who wish to test their knowledge and understanding of these topics.

Additional quizzes are also available on:

• X-ray Production & Interactions with Matter
• Technology of Radiographic Imaging

Radiation Biology & Dosimetry

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1 Deterministic effects of radiation are those for which:

	The severity of the effect varies with dose, but there is no threshold.
	The probability of the effect varies with dose, but there is no threshold.
	The probability of the effect varies with dose, and there is a threshold.
	The severity of effect varies with dose, and there is a threshold.

2 The annual effective dose limit for occupationally exposed workers is:

	1 mSv.
	5 mSv.
	20 mSv.
	50 mSv.

3 The entrance skin dose from a lateral lumbar sacral spine examination is about:

	0.5 mGy.
	1.5 mGy.
	5 mGy.
	15 mGy.

4 The latent period for radiation-induced carcinogenesis (solid tumors) is about:

	2 years.
	5 years.
	20 years.
	50 years.

5 Carcinogenesis is considered to be 'stochastic' effect. Is this statement:

	TRUE.
	FALSE.

6 Which of the following would be more suitable for measuring the absorbed dose to the fingers during fluoroscopy?

	Film badge.
	Thermoluminescent Dosimeters (TLD).
	Scintillation detector.
	Ionisation Chamber.

7 The entrance skin dose to the patient per abdominal radiograph is approximately:

	10 mGy.
	5 mGy.
	1 mGy.
	0.5 mGy.

8 In the context of radiobiology which is false?

	Cells tend to be more radiosensitive when young.
	Greater metabolic activity increases radiation resistance.
	Cells which divide rapidly are more radiation sensitive.
	The radiation sensitivity of cells can be increased by certain drugs.

9 For a given total dose of X-rays, a low dose rate (less than 1 Gy/h) is less effective at killing mammalian cells than a high dose rate (greater than 1 Gy/min). The principal reason is likely to be:

	Fewer free radicals are produced at low dose rate.
	The mitotic cycle is shortened by the low dose rate.
	Repair of sublethal damage occurs during the low dose rate irradiation.
	Ion pairs can recombine during a long exposure.

10 1 mSv is the annual effective dose limit for occupationally exposed personnel. Is this statement:

	TRUE.
	FALSE.

11 The law which states that radiation intensity is inversely proportional to the square of the distance between the radiation source and the point of interest is called:

	Ohm's law.
	Inverse square law.
	Law of conservation of energy.
	Proportionality law.

12 Photoelectric interactions from 15 keV photons, per unit mass, are how likely in calcium (Z = 20) than in carbon (Z = 6)?

	~3 times less likely.
	~3 times more likely.
	no different.
	about 11 times more likely.
	about 37 times more likely.

13 Which one the following is in increasing order of entrance skin dose?

	AP abdomen, PA chest, lateral pelvis, lateral skull.
	PA chest, lateral pelvis, AP abdomen, lateral skull.
	Lateral skull, AP abdomen, PA chest, lateral pelvis.
	AP abdomen, PA chest, lateral skull, lateral pelvis.
	PA chest, lateral skull, AP abdomen, lateral pelvis.

14 According to the ICRP dose limits, the maximum permissible dose per annum to the lens of the eyes of persons occupationally exposed is:

	1 mSv.
	20 mSv.
	50 mSv.
	150 mSv.

15 A narrow beam of monoenergetic X-ray photons is directed from an XRT located 50 cm above the surface of a water-filled container 20 cm thick. The HVL is 10 cm of water at the photon energy. The exposure at the bottom of the container relative to that incident on the surface is about:

	50%.
	25%.
	17%.
	13%.
	6%.

16 The annual effective dose limit for persons other than designated workers is:

	1 mSv.
	5 mSv.
	20 mSv.
	50 mSv.

17 An apron with a 0.5 mm lead equivalent thickness typically attenuates the scattered X-rays for tube potentials around 100 kVp by how much:

	25%.
	50%.
	75%.
	95%.

18 For diagnostic X-ray tubes operated above 70 kVp, the minimum total filtration in the beam is:

	1.5 mm Al.
	2.0 mm Al.
	2.5 mm Al.
	3.0 mm Al.

19 The recommended annual equivalent dose limit for prevention of radiation damage to the lens of the eye is:

	5 mSv.
	30 mSv.
	100 mSv.
	150 mSv.
	500 mSv.

20 A hypothetical patient receives an entrance skin dose of 20 Gy after a cardiac pacemaker insertion in which prolonged screening was used with a grossly inadequate X-ray machine. The most likely effects are:

	None or insignificant.
	Early symptoms of damage to the GI tract followed by a temporary recovery and death after about 2 weeks from irreversible damage to the blood-forming organs.
	Skin damage over the irradiated area with no healing after several months.
	Early symptoms of damage to the GI tract followed by a temporary recovery and symptoms of damage to the blood-forming organs after about 2 weeks. Recovery after a few months with nursing care.

21 Non-malignant damage to skin is considered to be a 'stochastic' effect. Is this statement:

	TRUE.
	FALSE.

22 Which of the following dose reduction techniques will improve image quality?

	Increasing the kV.
	Increasing the beam filtration.
	Gonad shielding.
	Collimating to minimum field size.

23 The radiation risk to a patient can be reduced by using a grid. Is this statement:

	TRUE.
	FALSE.

24 Skin damage following irradiation is an example of an early somatic effect. This means:

	The severity of erythema occurring is dependent on dose to the patient and it occurs in the irradiated area after a few days to a few weeks.
	The severity of the erythema occurring is not dependent on dose to the patient but it occurs in the area irradiated a few days to a few weeks after irradiation.
	The severity is not dependent on dose to the patient, but occurs in the area of the body irradiated within a few minutes.
	The severity is not dependent on dose to the patient but occurs in the area of the body irradiated after a few minutes.

25 A staff member standing 1 m from a patient in a field of scattered radiation experiences an air kerma of 630 mGy/h. If they move back to 3 m from the patient, they will experience a dose reading of approximately:

	70 mGy/h.
	210 mGy/h.
	1,890 mGy/h.
	6,300 mGy/h.

26 Which one of the following is a stochastic effect?

	Genetic defects.
	Erythema.
	Epilation.
	Reduced blood cell count.

27 Cells which undergo rapid division are:

	More sensitive to radiation.
	Less sensitive to radiation.
	Insensitive to radiation.
	None of the above.

28 The radiation risk to a patient can be reduced by using collimation. Is this statement:

	TRUE.
	FALSE.

29 Radiation dose limits set by bodies such as the ICRP are set at such levels that, if all personnel were exposed at these levels for a 50 year working life:

	About 5% of the personnel exposed would die due to radiation.
	We could expect detrimental effects in about 5% of the exposed personnel.
	The risk of death or injury is comparable to that from any other risk of life.
	The risk of death or injury would be very much greater than the risk of death or injury from other occupations.

30 The appropriate unit for the measurement of absorbed dose in SI units is:

	The gray.
	The rad.
	Coulombs per kilogram of dry air.
	Watts per square meter.

31 A kilogram cube of water is uniformly irradiated so that it receives an absorbed dose of 500 mGy. The absorbed dose in 1 cubic centimetre of this water is therefore:

	0.5 mGy.
	0.5 Joules/gm.
	0.5 Gy.
	500 Gy.
	cannot be determined from the information given.

32 The radiation risk to a patient can be reduced by decreasing the kV. Is this statement:

	TRUE.
	FALSE.

33 For an X-ray tube the radiation output at a position 1 m from the focus is 36 &mu:Gy/mAs when the X-ray tube current is 200 mA. If the X-ray tube kV remains constant, which ONE of the following statement is false?

	The output measured at a position 2 m from the focus is 18 μGy/mAs.
	The output measured at a position 0.5 m from the focus is 144 μGy/mAs.
	If the HVL of the X-ray beam was 2.5 mm Al and if another 2.5 mm Al was added to the beam, the output at 1 m from the focus would be 18 μGy/mAs.
	If the X-ray tube current was reduced to 100 mA the output at a position 1 m from the focus would be 36 μGy/mAs.

34 Cataract production in the lens of the eye is considered to be a 'stochastic' effect. Is this statement:

	TRUE.
	FALSE.

35 For radiation protection purposes the radiation weighting factor for X-rays is:

	1.
	2.
	5.
	10.

36 With regard to the use of TLDs, which ONE of the following statements is false?

	Dosimeters can be made quite small.
	Dosimeters are tissue equivalent at all X-ray energies.
	The TLDs retain the dose information for later readout.
	Doses at a relatively large number of points in or on the patient may be measured simultaneously.

37 The radiation risk to a patient can be reduced by increased beam filtration. Is this statement:

	TRUE.
	FALSE.

38 The DNA molecule may be damaged by:

	Being directly hit by a photon.
	By reaction with free radicals.
	By reaction with other toxic substances resulting from irradiation.
	All of the above.

39 The Dose-Area Product (DAP) meter:

	Measures integral dose to the patient.
	Measures the product of X-ray output and X-ray beam cross-sectional area.
	Is useful to determine accurately incident area-exposure product for examination of the knee, cervical spine, wrist and fingers etc.
	May be used to estimate effective dose.

40 The annual effective dose to an individual due to natural background radiation is of the order of:

	1.5 mSv.
	2.5 mSv.
	15 mSv.
	25 mSv.

41 0.25 to 0.5 mm lead equivalence at 100 kV is used in protective lead aprons. Is this statement:

	TRUE.
	FALSE.

42 An occupationally exposed person undergoing fluoroscopy of their abdomen has inadvertently left their personnel dosimeter on in such a way that it is at the point of entry of the primary beam. It would take how many minutes of screening time for the dosimeter to record his annual maximum permissible whole body dose?

	less than 5.
	~10.
	~20.
	~40.
	more than 60.

43 A fluoroscopic system has automatic brightness control in which the kV is adjusted manually and the mA varies as a function of patient thickness. For a given patient thickness, as the kV is decreased:

	The mA decreases and patient entrance skin dose increases.
	The mA increases and patient entrance skin dose is constant.
	The mA increases and patient entrance skin dose increases.
	The mA increases and patient entrance skin dose decreases.

44 The radiation risk to a patient can be reduced by using a smaller focal spot. Is this statement:

	TRUE.
	FALSE.

45 The sievert is a unit of:

	Intensity.
	Exposure.
	Absorbed dose.
	Effective dose.

46 An individual receives a radiation effective dose of 200 Sv of penetrating radiation during the detonation of a nearby nuclear device. The most likely effects are:

	None or insignificant.
	Damage to central nervous system resulting in death within 48 hours.
	Early symptoms of damage to the GI tract followed by a temporary recovery and death after about 2 weeks from irreversible damage to the blood forming organs.
	Skin erythema, depilation and permanent sterility for males. Not life threatening.

47 The inverse square law applies well in the primary beam. In regard to radiation scattered from the patient the inverse square law:

	Applies approximately only at distances greater than 5 m from the patient.
	Applies approximately only at distances greater than 10 m from the patient.
	Applies approximately at distances greater than 1 m from the patient.
	Applies approximately as an inverse cube law for up to 2 m, then as the inverse square law thereafter.

48 One gray is defined as:

	100 J/kg.
	1 J/kg.
	0.01 J/kg.
	1 mJ/kg.

49 The effective dose a patient receives from a single PA chest X-ray is about:

	0.02 mSv.
	0.2 mSv.
	2 mSv.
	20 mSv.

50 Which one of the following has minimal effect on the patient's skin dose?

	The size of the focal spot.
	The irradiated field size.
	The grid ratio.
	The beam filtration.