RANZCR – 2004 AIT

April 2004

Question 1

1. List the current effective and equivalent dose limits applicable to radiation workers and to the general population and discuss the reasons why these limits are different
2. Discuss any added restrictions that are applicable to the pregnant radiation worker
3. Describe the possible risks to the foetus following the inadvertent irradiation of the maternal abdomen and relate these to the stage of the pregnancy. At what radiation dose limit would the possibility of therapeutic abortion be considered? Discuss whether it is conceivable that this limit could ever be approached or even exceeded with routine diagnostic examinations before the pregnancy is actually identified

Question 2

1. Describe the composition of the intensifying screen in an X-ray film cassette and discuss the physical principles underlying its use. What factors affect the efficiency of the screen?
2. Describe the factors which influence high contrast resolution in a film-screen system
3. A low contrast CT image, say of lung nodes, is found to be too noisy. Explain what scanner factors may be altered to reduce the noise and the likely trade-offs involved with changing these factors
4. “Computed Radiography (CR) has a large dynamic range compared with film-screen radiography”. Describe what you understand by this statement and its implications for work practice

Question 3

1. Describe how CT fluoroscopy differs from conventional CT imaging. In particular discuss issues associated with:
   1. image reconstruction
   2. patient and operator dose
   3. any special technological requirements on hardware
2. Describe the physical principles behind pulse-echo imaging using ultrasound. Your answer should include a brief discussion of the following:
   1. Transducer design and the temporal characteristics of the ultrasound pulse
   2. Image formation including signal processing needed for a satisfactory image
   3. Image storage and post-processing
3. The basic spin echo pulse sequence is frequently employed in MRI to produce high quality images.
   1. Draw a diagram illustrating the essential features of this pulse sequence.
   2. Describe how and why you would select the parameters (TR, TE) to ensure T1 and T2 weighted images, respectively. In both instances indicate, with reasons, whether tissues with short or long relaxation times will appear brightest in the images
   3. Briefly explain how the gradient (recalled) echo pulse sequence differs from the spin echo one. What are the disadvantages/advantages of using the gradient echo versus the spin echo technique?

September 2004

Question 1

1. In the context of radiation effects explain the terms stochastic and deterministic and give two examples of each.
2. Define the terms absorbed dose and effective dose and indicate the usual units used to quantify them. Discuss the relevance of each dose term in the context of determining the likelihood and/or severity of deterministic and stochastic effects from the use of X-rays.
3. Image intensifier based fluoroscopy is to be undertaken using a fixed under table X-ray tube with an overtable, variable field, image intensifier. The unit also offers automatic brightness control (ABC) with a range of dose rate options, including pulsed fluoroscopy. Discuss practical procedural measures that you might implement to ensure that both the patient and operator doses are minimised without compromising the diagnostic information obtained. Where necessary supplement your answer with reasons for your actions.Contrast is arguably the most important factor determining image quality in medical imaging. Describe how the attenuation processes affect contrast in X-ray imaging. Outline the equipment and operational factors of importance to achieve maximal contrast for a routine abdominal radiograph.

Question 2

1. Discuss the impact of these parameters on patient dose
2. With the aid of a diagram explain what is meant by ‘apparent focal spot size’? Explain why the apparent focal spot size is larger when the tube is operated at 60 kVp, 400 mA compared with 90 kVp and 200 mA.

Question 3

1. For images obtained using CT scanning, discuss factors that affect the following parameters
   1. Spatial resolution
   2. Image noise
   3. iii Image artifacts
2. Why is knowledge of the speed of sound and its variation important for diagnostic (including Doppler) ultrasound techniques?
3. Briefly discuss the principle of Positron Emission Tomography (PET) paying particular attention to the properties of the radionuclides that are used and the method of determining the line along which each annihilation event occurred. Give one example of a radionuclide commonly used as well as one advantage and one limitation (or disadvantage) of PET imaging.