Past paper Qs

Question 1

How does the X-ray spectrum vary with Kv and Ma changes. what is the characteristic peak of tungston.

Answer 1

Increases in Kv shift the peak to the right and increase area under the graph. Increases quality and quantity of the beam. If the max Kv includes the characteristic X-ray energy then that will be emitted. For tungston that is 60 and 70KeV.

Ma will increase only area under graph. i.e. quantity

Question 1

How do you increase X-ray tube efficiency

Answer 1

Increase the voltage

Question 2

Define absorbed dose, Equivalent Dose and Effective dose. Under what conditions would they be the same for the same exposure?

Answer 2

Absorbed - Energy deposited by ionising radiation

Equivalent - Includes a weighting factor to take into account the type of radiation and it’s ionising effect.

Effective - From equivalent takes into account the sensitivity of that type of tissue to radiation.

The same if radiation weighting factor = 1 (X-rays) and the entire body is uniformly irradiated.

Question 3

Summerise the main functions of a pacemaker

Question 4

Why is carbon not used for MRI but Hydrogen is?

Answer 4

It does not provide as good a nuclear magnetic resonance signal as hydrogen. because it has an even number of protons and neutrons.

Question 5

How do you change a spin echo pulse sequence to a gradient echo pulse sequence?

Question 6

Which are the two main categories of non-ionising radiation sources in healthcare. and which one has heating as it’s main health effect?

Answer 6

Radiofrequency radiation - MRI

Optical Radiation - UV. Main effect is heating

Question 7

Which are the three main health effects in the optical radiaition spectrum between 200-700nm.

Answer 7

Photochemical effects

Thermal effects

Photomechanical

Question 8

Distinguish between stochastic and deterministic effects of ionising radiation

Answer 8

Stochastic -

Deterministic -

Question 9

Explain how these principles of stochastic and deterministic radiation lead to the two principles of ionising radiatino protection

Answer 9

As low as reasonably Practicable.

Threshold of what exposures should not be more than

Question 10

Summerize with a diagram the main parts of an image intensifier and an X-ray tube

Answer 10

kjb

Question 11

Cacculate the spatial resolution of a CT scanner if the diameter of teh scanning field is….

Answer 11

,,,,

Question 12

Explain briefly blood pressure measurement

Answer 12

blah blah

Question 13

Describe the characteristics of laser radiation that differentiate it from other non-ionising EMF radiations

Answer 13

1. It uses visible light

2.

3.

Question 14

Describe the need of a common image format in PACS systems

Answer 14

5

Question 15

Identify an application where the hydrogen nucleus is not used for MRI

Answer 15

duh duh duhhhh

Question 16

Summerise the main sources of noise in ECG and briefly explain the main methods of minimising / eliminating them

Answer 16

many things

Question 17

Describe the major processes performed on a digital image during segmentation. Include pre-processing through object discrimination and morphological processing.

Answer 17

Pre-processing - Histogram equilisation

Object discrimination - Binary contrast enhancement

This produces an object with rough edges ill define and noisey.

Binary morphological processing. Erosion and dilation filters are used either in opening or closing ways. These smooth contours and removes either bright pixels or dark pixel areas respectively.

Question 18

Outline an example of a simple brightness / texture feature and of a shape feature which might be appropriate in identifying stained circular cells on histology slides

Answer 18

Mean brightness feature can help identify whether a pixels belong to an object or not.

Texture analysis can be completed by Fourier analysis. Completed in small sections this can help identify the object outlines according to local variance in spatial frequencies.

Various shape parameters can be used to identify a shape once it’s boundaries have been identified. icluding the objects area. In this case roundness: the ratiio of the object area to the area of it’s convex hull, close to 1 in circular objects.

Question 19

How might the features of of circular shape and edges be used in finally classifying the segmented objects.

Answer 19

Brightness/ Tesxture: Objects with similar brightness levels or texture patterns may belong to the same class.

Shape: Circular cells in histology slides can be identified based on their roundness

Classification: Cells may be classified based on a combination of brightness texture and shape. Neural networks and fuzzy logic can be employed to classify objects based on multiple features.

Question 20

Image data is often resampled or remapped prior to processing it further. Why and how is this done and what precautions should be taken to minimise errors and aretefacts?

Answer 20

Resampling and mapping is done for various reasons including correcting distortions alterting perspective or adjusting resolution. This process invovles repositioning pixels within an image according to mathematical transformations.

How its done:

Completed using affine transforms for translationg rotation and caling to reposition pixels without introducing curvature.
Warping: Non-linear transformations for complex distortions (barrel) involving polynomial equations with higher powers.

Control points: Selected points in the image define areas of pixels and their positions in the transformed image.

3. Precautions: Low-pass filtering for down-sampling: This avoids aliasing artefacts when reucing resolution.

Pixel interpolation for Up-sampling: During up-sampling, where the output resolution is higher than the input, pixel interpolation techniques are used to estimate pixel values between already known values. Nearest neighbour or bilinear or higher order interpolation. Avoids pixelation.

Question 21

Image processing may be classified into point local and global processes explain these and give practical examples

Answer 21

Pixel point

Question 22

Briefly describe Image re-sampling prior to spatial transformation

Answer 22

Spatial transformations include enlarging and distorting images and moving them in space. There is an issue with resampling as the new position is not an exact pixel shift. With rotations, the pixels will be in slightly more offset positions. Resampling is required on the original image to ensure that when you move something, you don’t result in issues with sharp edges. For example, scaling down - resampling is important to do before reducing the size as you might lose data. You begin by smoothing the image to avoid moire fringes / sampling errors.

Question 23

What is the equation to find max frame rate in ultrasound.

Answer 23

f = C / 2DN

Question 24

Why is ultrasound attenuated through bone

Answer 24

Bone has a high Z number compared to tissue. This causes high reflectivity and little transmission

Question 25

Why is distortion of displayed depth through fat?

Answer 25

Speed of sound is slow through fat, therefore signal arrives later than expected. This results in mapping the signal as coming from a deeper location than it actually does.

Question 26

Why do mirror images of ultrasound occur. e.g. whe nimaging the diaphragm or lung surface

Answer 26

At the lung/diaphragm surface there is a large change in impedance. Due to this, most of the ultrasound is reflected. The reflected part starts to image itself due to other scattering and reflections of surrounding tissues. Ultrasound assumes a linear propagation.

Question 27

In ultrasound energy is…

Answer 27

Conserved, reflected and transmitted

Question 28

Calculate the reduction in energy in dB through a barrier in ultrasound

Answer 28

Ir / Ii = (Z1 - Z2)^2 / (Z1 + Z2)^2

in dB = 10log_10(Ir/Ii) = should be a negative to indicate a reduction in energy.

Question 29

In ultrasound what is a shadow artefact and how does it occur?

Answer 29

wave passes through something very attenuating

Question 30

Ultrasound, enhancement artefact

Answer 30

Part below something appears brighter due to changes in impedance. e.g. below a blood vessel.

Question 31

Us reverberation artefact

Answer 31

Due to multiple unexpected reflections

Question 32

Us Ghost image artefact

Answer 32

Image appears in the wrong place due to reflection. If we have a different speed of sound. Wave might pass through faster and things appear closer. Speed variation causes depth variation .

Question 33

Summerise the principle of defibrillation, draw a diagram and explain how to estimate the power of the defibrilating pulse of an external defib

Question 34

Describe how an echo pulse is formed in a spin echo pulse sequence. Include accounts of the seperate contributions of the RF refocussing pulse and the imaging gradients on the frequency encoding axis

Question 35

Explain how non-laser radiation can induce skin damage if it has emissions in the UV range rather than the visible one

Answer 35

Higher energy photons allow it to penetrate the skin and cause damae to the cells and DNA. Causing protein and lipid damage.

Question 36

Why does colourflow imaging decrease maximum frame rate in ultrasound?

Answer 36

In doppler multiple scan lines are required in each frame. Computational demands of processing doppler data also reduce this.

Question 37

Equisation to calculate the loss of ultrasound amplitude through an attenuaing tissue

Answer 37

10 log_10(I2/I1) -> 10^(-attenuation coefficient / 10)

Question 38

Describe some image compression techniques

Question 39

What are the radiation weighting factors for alpha beta and gamma radiation?

Question 40

Why is NaTl suitable for for gamma camera single photons imaging ?

Answer 40

High light output
Good energy resolution
Efficient gamma ray absorption
Emission wavelength of 415nm is compatable with photomultiplier tubes
Fast response / decay time
Proven track record

Question 41

Describe and give the expression or a CT number in tissue

Answer 41

(u object - u water / u water) *1000

Question 42

Explain beam hardening and how it is acheived in CT

Answer 42

CT acheived thorugh a bowtiem filter. Removes lower energy componants of the brem. reducing dose. Bowtie helps give a uniform image as the patient is less attenuating at the sides.

Question 43

Define what is meant by spatial resolution and how it is measured. Explain if you can see an object 0.1mm when using an image intensified with limiting resolution of 6lp/mm.

Answer 43

Describes the smallest detail that can be visualised. Measured in line pairs / mm. to assess smallest point to be resolved inverse of the doubled limitation.

1 / 6*2 = 0.083mm.

Question 44

Describe the need for a common image format in the PACS system

Answer 44

DICOM. allows patients to be identified and relevent medical featres be viewed. And allows clincians to easily observe adice from radiologists.

Format dimensions, transfer, archive, print and management

Question 45

What display colour will the tissue from A be if window centre is +40 and window width is 100. CT number = +100

Answer 45

40-(100/2) = 40-50=-10. to
40+(100/2) = 40+50 = 90.

The tissue will be outside the window and therefore will be presented with a white colour

Question 46

three major types of nuclear medicine image acquisition and clinical examples

Answer 46

static - bone
dynmaic - renogram
tomographic - gated cardiac study