RANZCR – 2015 AIT

March 2015

Section 1 – Radiation Biology and Safety 

Question 1 

The ICRP system of radiation protection is founded on the twin tenets of Justification and Optimization backed up by the application of dose limits. 

1. In the specific context of the medical use of ionising radiation discuss what is meant by Justification and Optimisation and give examples of how these principles might be applied in practice. (6 marks) 
2. Dose limits do not apply to patient exposures but increasingly Diagnostic Reference Levels (DRLs) do. What are DRLs, and how can they be used to optimise imaging procedures in diagnostic radiology? (4 marks) 

Question 2 

A female patient of child bearing age presents for an abdo-pelvic CT examination but states that she may be pregnant. 

In responding to this situation discuss: 

1. Decisions about your immediate management of the patient that might be taken; (4 marks) 
2. Information that you might give to the patient about magnitude of the foetal dose and risks assuming that the procedure is to go ahead; and (4 marks) 
3. Any practical measures that you might take to help minimise the dose to the foetus and information that you might record to aid in retrospective estimate of the foetal dose. (2 marks) 

Question 3 

In the context of the biological effects of ionising radiation on human tissue, discuss the following: 

1. Radiation weighting factors and their relationship to the linear energy transfer (LET) of radiation. Provide the values of the radiation weighting factors for x-rays and for gamma-rays. (3 marks) 
2. Tissue weighting factors and how are they used. Provide the values of the radiation weighting factors recommended by the ICRP in Publication 103 for the breast and gonads. (3 marks) 
3. The linear-quadratic dose response model. (3 marks) 
4. The term Latent Period. (1 mark) 

Section 2 – Basic Physics & Technology 

Question 1 – Fluoroscopy 

A patient is undergoing an interventional Posterior Anterior (PA) fluoroscopic investigation, under automatic brightness control, with the initial acquisition beam geometry giving a focal spot to entrance skin distance of 70 cm and a focal spot to image receptor distance of 100 cm. 

1. Explain, with reasons, any changes to the skin entrance dose rate and image quality if the original acquisition beam geometry is changed to each of the following situations: 
   1. The focal spot to patient distance is unchanged but the focal spot to image receptor distance is increased to 110 cm; (3 marks) 
   2. The gantry is rotated 90 degrees to give a lateral projection; (3 marks) 
   3. The image receptor field size diameter is doubled. (2 marks) 
2. The radiographer records two dose indicators for the procedure. Specify two fluoroscopic dose indicators, which the fluoroscopic equipment should provide, used for best dose audit practice and briefly explain what they measure. (2 marks) 

Question 2 – Mammography 

The Mean glandular dose (MGD) is a common dose metric in x-ray breast imaging: 

1. Define the term and indicate its units. (1 mark) 
2. List the patient and equipment variables that influence the MGD. (4 marks) 
3. What is the expected range of the MGD per image for a breast of average size and composition that undergoes contact imaging with a grid in screening mammography? (1 mark) 
4. If the breast is imaged in magnification mode, describe the changes to the image acquisition technique that are required. Indicate with reasons how you expect these will affect the MGD. (4 marks) 

Question 3 – Basic Physics & Technology 

1. The exit x-ray beam from a patient undergoing a radiological examination has both primary and scatter x-ray components. 
   1. Identify and describe the principal atomic interaction responsible for the scatter x-ray component. (2 marks) 
   2. Identify the factors that contribute to the magnitude of the relative scatter component exiting the patient. (2 marks) 
   3. What is the effect on image quality as the amount of scatter radiation exiting a patient increases when compared to the primary exit radiation? (1 mark) 
2. A grid is a device commonly used to reduce the impact of scatter radiation in image formation. Briefly describe the components and construction of a grid as well as its principle of operation. (3 marks) 
3. A digital image receptor is typically composed of detector elements or ‘dels’ grouped to form pixels in an image matrix. Assuming the input beam quality and dose to the image receptor is unchanged, and the system resolution is limited by the del size, discuss the possible impact on image quality resulting from the linear dimension of the dels (image pixels) being halved. (2 marks) 

Section 3

Question 1 – CT 

In CT scanning, the mAs per rotation is arguably the most important operator adjustable factor with respect to the patient’s effective dose. Discuss the impact that mAs and two other operator adjustable factors that have a substantial impact on effective dose to the patient. For each factor describe methods that can be used to minimise the dose when scanning, and any consequent impact on image quality. (10 marks) 

Question 2 – MRI 

Briefly explain the following terms and their relevance in Magnetic Resonance Imaging: 

1. The Larmor frequency. (2 marks) 
2. The spin-lattice relaxation time constant (T1). (2 marks) 
3. The transverse relaxation time constant (T2). (2 marks) 
4. Spin echo pulse sequence. (2 marks) 
5. Magnetic field gradients. (2 marks) 

Question 3 – US 

1. Discuss the factors affecting the axial and lateral spatial resolution in real-time ultrasound imaging. (4 marks) 
2. State ONE way by which the axial resolution can be improved. (1 mark) 
3. Two pulsed Doppler spectral displays of the same vascular region are shown in images A and B (see DopplerSpectrum.jpg). One was obtained using a lower pulse repetition frequency (PRF) than the other. All other imaging parameters were the same. 
   1. Which spectral display contains an artifact, what is the name of this artifact, and how was it produced? (3 marks) 
   2. Discuss TWO methods by which this artifact might be eliminated. (2 marks) 

Question 4 – Nuclear Medicine 

In nuclear medicine imaging CT is commonly used in combination with PET examinations using PET/CT cameras. 

1. Briefly describe the physical principles of image acquisition in PET imaging. (Note: do not describe methods of PET radioisotope production). (6 marks) 
2. Give the two main reasons why the CT part of a PET/CT examination is performed. (2 marks) 
3. In PET imaging there are two fundamental physical factors that limit the ultimate spatial resolution achievable by any PET camera. State ONE of these factors and briefly explain how it limits the spatial resolution achievable. (2 marks) 

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September 2015

Section 1 – Radiation Biology and Safety 

Question 1 

The ICRP has developed a system of dose limits for the protection of individuals and populations. 

1. What are the dose limits that apply for the prevention of stochastic effects to (i) occupationally exposed individuals and (ii) members of the public? Why is there a difference? (4 marks) 
2. What is the dose limit that applies once a female employee becomes pregnant? (1 mark) 
3. Briefly discuss why the effective dose may be a useful dose metric but also indicate its limitations. (3 marks) 
4. For occupationally exposed individuals what are the dose limits that apply to the skin and the lens of the eye, respectively for the prevention of tissue reactions (deterministic effects)? (2 marks) 

Question 2 

A pregnant woman undergoes the following examinations at 14 weeks of her pregnancy: 

1. 1. CT of the abdomen and pelvis with and without contrast. 
   2. Mammography. 
   3. Plain abdominal radiography – single AP view. 
   4. Ventilation/perfusion lung scan. 

1. Provide an estimate of the magnitude of any foetal radiation doses involved from each procedure. (2 marks) 
2. Discuss any possible risks to the foetus from these procedures when considered collectively. (4 marks) 
3. Indicate what you might say to the concerned patient to allay any fears she may have. (4 marks) 

Question 3 

An obese patient presents for an abdominal interventional examination to be conducted on a C-arm X-ray fluoroscopy system. The X-ray unit has automatic brightness control (ABC) with a range of dose rate options, including pulsed fluoroscopy, and an image intensifier with variable field size. You anticipate that the procedure will be difficult and may require considerable fluoroscopy time. In order to minimise the severity of any tissue reactions occurring in the patient’s skin you need to optimise your procedure. 

1. Discuss the impact of choice of the following system operating parameters and factors on the patient skin dose. Provide reasons for your answer where applicable. (8 marks):
   1. Dose rate, 
   2. Field size (magnification), 
   3. Collimation, and 
   4. Radiographic geometry 
2. After the procedure is completed the fluoroscopy unit indicates that the skin exposure received by the patient may be about 5 Gy. What possible tissue reactions might you expect and what advice might you offer to the referring physician? (2 marks) 

Section 2 – Basic Physics & Technology including Mammography, Fluoroscopy & DSA 

Question 1 

1. Describe the electromagnetic spectrum paying particular attention to the radiations used in medical imaging. The perspective from a frequency, wavelength and/or photon energy should be used. (3 marks) 
2. Distinguish between characteristic X-ray production and the photoelectric effect. (4 marks) 
3. A high voltage of 70 kVp is applied to an X-ray tube. What is the impact of adding a small amount of filtration (e.g. 2.5 mm Al) on such an X-ray spectrum and why is this beneficial? (1.5 marks) 
4. Relatively large amounts of filtration (e.g. 0.1 mm Cu + 1 mm Al) may be used when performing barium enemas. Why is it not appropriate to do this routinely for all radiological studies? (1.5 marks) 

Question 2 

1. Fluoroscopy based on X-ray image intensifiers is currently being superseded by two types of digital radiography-based detectors. Compare all three types of image receptor in terms of their construction and operation. (6 marks) 
2. Modern fluoroscopy systems can be operated in both continuous and pulsed exposure modes. Explain the difference between these two modes of operation and indicate the major advantages and disadvantages of each. (2 marks) 
3. Modern interventional and digital subtraction angiography (DSA) systems can be operated in both screening and acquisition modes. What is the difference between these two modes of operation? (2 marks)

Question 3 

1. Breast compression is useful for optimising X-ray mammographic imaging. Describe how such compression is generally applied in practice and discuss four advantages of the technique. (5 marks) 
2. Explain the reasons for the anode-cathode orientation and the anode’s focal spot placement for the X-ray tube used in contact mammography. (4 marks) 
3. What is the major difference between primary diagnosis monitors used for mammographic imaging viewing and those used for plain radiographic viewing in terms of pixel resolution? (1 mark) 

Section 3 – Advanced Technology 

Question 1 

1. Describe what is meant by CT-AEC, sometimes referred to as “tube current modulation”, in CT scanning. (2.5 marks) 
2. What is the effect of tube current modulation on patient effective dose and how is this change in dose accomplished? (2.5 marks) 
3. When a CT scanner is operating under tube current modulation how are dose and image quality affected by changes in: 
   1. Pitch (2.5 marks) 
   2. Tube rotation time (2.5 marks) 
   3. bearing in mind that the effective mAs (mAs/pitch) remains unchanged? In each case give an explanation for what causes the observed changes. 

Question 2 

With respect to magnetic resonance imaging, describe the role of the following in producing an image: 

1. Fixed magnetic field (2 marks) 
2. Magnetic field gradients (2 marks) 
3. Radiofrequency field (2 marks) 
4. Flip angles of less than 90⁰ (2 marks) 
5. Head coil. (2 marks) 

Question 3 

1. Real time ultrasound instruments make a number of basic assumptions in order to produce an image. State 3 of these assumptions. (3 marks) 
2. When performing real-time imaging using linear or phased array transducers the axial and lateral spatial resolution both contribute to the overall image spatial resolution. Explain how each can be optimised, how the optimisation is achieved and stating any trade-offs associated in achieving higher spatial resolution. (7 marks) 

Question 4 

1. Gamma cameras are the basic imaging device for much of nuclear medicine imaging. The diagram depicts a schematic of the major components of a gamma camera detector head. For each of the components labelled A to C in the diagram, name the component and briefly describe its function in the detector head’s operation. (5 marks) 
2. Suppose your nuclear medicine practice routinely performs a planar imaging study but you notice that most patient images appear to have quite a lot of noise that makes them difficult to interpret. Discuss how the image noise can be reduced without compromising image spatial resolution and give details of how this can be achieved. (2 marks) 
3. Technetium-99m is often described as an ideal isotope for nuclear medicine SPECT and planar imaging. State six (6) desirable physical and chemical characteristics a radioisotope suitable for nuclear medicine imaging will possess. (3 marks)