Summary

Question 1

uses of auditory brainstem response?

Answer 1

newborn hearing screening
intra-operative monitoring
determining degree and type of hearing loss
vestibulocochlear nerve and brainstem lesion detection

Question 2

how can the performance of a test be evaluated?

Answer 2

impact on health: does it improve the health of the patient, hence is the subsequent management effective for the patient
therapeutic impact: contributes to planning and delivery of therapy, will management be altered?
diagnostic impact: will it replace other tests and will it improve the diagnostic confidence
diagnostic performance: does it allow accurate diagnoses to be made?
technical performance: what is the reliability of the test?- PPV, NPV, sensitivity, specificity

Question 3

what are we measuring when using radiography?

Answer 3

attenuation: tissues attenuate X-rays-so intensity gradually lost as it passes through a medium, depending on their density or atomic number

Question 4

why does CT have better contrast resolution than plain X-ray?

Answer 4

gets rid of overlapping structures

Question 5

how is a patient positioned when a CT scan is performed?

Answer 5

must lie down on a table which moves through the hole. The gantry contains an X-ray tube and X-ray detectors. The tube and detectors move around the patient gathering data which can make an image on a computer screen
Linear array of about 800 detectors, single X-ray tube, wide fan beam to cover whole patient

Question 6

what 2 things does CT (computed tomography) allow?

Answer 6

reduction in overlapping structures- better contrast resolution
calculation of attenuation coefficient of each voxel (each body part)- image intensity relates to a reproducible unit=hounsfield unit- goes from about -1000(air) to +1000(metal), HU of water is 0, depicted as shades of grey
so HU= measurement of radiodensity. concept of centre and windowing. width=black, centre=grey, +width=white

Question 7

4 types of resolution?

Answer 7

spatial
contrast
functional
temporal

Question 8

what is spatial resolution?

Answer 8

ability to distinguish between small objects, so size of the smallest structure that can be distinguished

Question 9

what is contrast resolution?

Answer 9

ability to distinguish between different objects

Question 10

what is functional resolution?

Answer 10

ability to tell the difference between things that work differently

Question 11

what is temporal resolution?

Answer 11

how quickly something can be measured so precision of measurement with respect to time

Question 12

what has the best spatial resolution?

Answer 12

chest X-ray

Question 13

what has the best contrast resolution?

Answer 13

MRI

Question 14

what has the best functional resolution?

Answer 14

PET scan

but this has the worst spatial resolution

Question 15

which scan is the best compromise for resolution?

Answer 15

CT

Question 16

why use contrast enhancement?

Answer 16

make structures/pathology visible
give functional info. relating to structures/pathology
types: intra-venous-focus
intra-arterial
oral
-ve (air/fat) or +ve (iodinated)

Question 17

mechanism of contrast action?

Answer 17

small molecule, quite a lot needs injecting, but doesn’t leak into brain as can’t cross BB barrier
EC, extravascular agent- relates to info gained
excreted by kidneys- can lead to renal failure if poor kidney function

Question 18

SEs/contraindications of contrast?

Answer 18

flushing
renal damage
if contrast could have further actions we could do more BUT would probably be more toxic

Question 19

2 different types of risk and what they mean?

Answer 19

stochastic risk: chance of effect increases with exposure, e.g. more exposure to UV light increases risk of skin cancer, so plays the odds- MAY occur and chance of occurrence increases with exposure. related to DNA and damage and failure to repair/repair properly-cancer, genetic
non stochastic risk: effect increases with exposure e.g. increased burning the more UV light expereinced. effect WILL occur if over a threshold e.g. cataracts, bone marrow failure, death.

Question 20

what is anatomical measurement?

Answer 20

size measurement, form of image based measurement. Measurement on CXR only works if all borders can be seen. Much easier and logically better on CT scan.
BUT inter and intra observer variability, indistinct borders and physiological changes
thickness of slice may be greater than what you think and will have an impact-partial volume effect
some things just too small to measure
AND technique can affect measurement e.g. contrast timing

Question 21

what are the margins for morphological measurements in cancer?

Answer 21

size change: response- >30% reduction in diameter required, progression- >20% increase in diameter
margins are wide to avoid intra and inter observer variability, indistinct borders and physiological changes.
also, things may get bigger eventhough they are getting better e.g. due to oedema or inflammation

Question 22

why can measuring contrast agent dynamics be very interesting in cancer?

Answer 22

tumour may be seen better following tment as there is reduced contrast enhancement, showing that tment is good

Question 23

describe the use of PET scan isotope uptake measurements

Answer 23

better spacial resolution: ability to distinguish between small objects
tracer= 18 flourine, and carbon and O2
so 18 fluro-deoxy glucose (FDG): mirrors high glucose turnover, tumours are highly metabolic and anaerobic so take up 18 FDG
also good for cardiac function and looking at the brain
not all tumours will take it up
sensitive test for detecting cancerous lymph nodes

Question 24

problems of PET scan isotope uptake measurements?

Answer 24

false -ve findings: lesions smaller than 8mm, diabetes/non-fasting patients, tumor histology
false +ve findings: normal physiology, granulomas and other infections, adenomas

Question 25

what is standard uptake value (SUV)?

Answer 25

standard amount of activity injected in PET scan isotope
PET camera assesses amount of activity per volume of tissue which can be expressed in SUV units
an SUV over 2.5 is considered suspicious of malignancy
BUT how good are cut offs- too much overlap!
depends on normal variation
variation in SUV is high
what is required to define response

Question 26

thin slice CT?

Answer 26

can make image ‘noisy’
necessary to see renal stones
may need to increase dose to increase precision of more complex measurements

Question 27

what tumour functional characteristics can be quantified using PET?

Answer 27

cellular proliferation
hypoxia
angiogenesis
apoptosis

Question 28

how can PET be used in molecular targeting to predict response?

Answer 28

label cell surface receptors

micro dosing- can label the drug to see its concentration in different parts of body