X RAY/CT

Question 1

what is x ray

Answer 1

cathode towards metal target plate anode
sheet of electrons
thermionic emission
in vacuum towards metal plate anode

Question 2

CT mechanism

Answer 2

gun fires electron beam
focus coil
deflection coil
target rings and detector rings
ring rotates round patient to fire sheet of electrons with no superimposition of structures like in x ray

In computed tomography, a transverse slice of the patient is imaged, avoiding the superimposition of adjacent structures that occurs in conventional radiography.
The slice is defined by a “sheet of x-rays” produced by a narrow, well-collimated, x-ray fan beam rotated around the patient.
The x-ray beam is attenuated by absorption and scatters as it passes through the patient.
Detectors on the other side of the patient measure the x-ray transmission through the patient. These measurements are repeated many times from different directions, whilst the tube is pulsed as it rotates 360° around the patient.

Question 3

GE CT scanner

Answer 3

64 detectors
detector and tube move around patient at the same time
4th generation x ray tube alone rotates with thousands of stationary detectors in a tube formation

Question 4

dual bolus CTU

Answer 4

initial bolus 50-75ml is administered at T0
5-7 mins later second bolus
patient scanned at 60-90 seconds
initial bolus in pyelographic phase
poportion in nephrogenic phase
second bolus is in vascular phase
2 scans - non contrast and then second scan 60-90 seconds after second bolus

Question 5

ultra low dose CT KUB

Answer 5

ultra low dose

lower current

Question 6

wavelength x ray

Answer 6

10-8 to 10-12 m
or 0.1 to 10nm
1nm = 10-9m

Question 7

visible light wavelength

Answer 7

380-700nm

Question 8

em spectrum
from <0.1nm 10 to -19 m
to 1000m

Answer 8

Gamma 10-19
x ray 10-9to12
UV 100nm
light 300-700nm
Infra red 10um
microwaves 1cm
radio 1m
long waves 1km

Question 9

what happens to x rays

Answer 9

X-rays may be:
Transmitted: pass through unaffected
Absorbed: transfer to the matter some or all of their energy
Scattered: diverted in a new direction, with or without loss of energy

Question 10

what is attenuation

Answer 10

Attenuation is the fractional reduction in the intensity of the primary x-ray beam as it passes through a medium.
Attenuation = absorption + scatter
The linear attenuation coefficient is related to the attenuating property of a material, i.e., how well it absorbs, scatters, or transmits x-rays.
Tissues of different density cause attenuation of x-rays at different rates.
For example, a higher proportion of x-rays will pass through a similar volume of lung than bone, and hence, a corresponding higher proportion of x-rays will reach the detector. This allows different tissue types to be differentiated in the final image

Question 11

how is image produced in x ray

Answer 11

screen composed of phosphors
x ray beams collides with this
light is emitted causing a reaction in x ray film
latent image produced
morden use a resuable plate
photostimulable phosphor
following exposure plate scanned laser beam and light emitted is measured to form a digital image

Question 12

how to minimise radiation with c arm

Answer 12

screening time, pulsed vs continuous fluro, low frame rate
use collimation for reagion of interest
reduce contrast of image
position patient as close to detector as possible

Question 13

omnipaque dose

Answer 13

300mg/mL
Excretory Urography
Omnipaque 300/350: 200-350 mgI/kg body weight
i.e. 50mls

Question 14

omnipaque dose
osmolality
ionic/monomer

Answer 14

300mg/mL
Excretory Urography
Omnipaque 300/350: 200-350 mgI/kg body weight
i.e. 50mls

LOCM - still higher than plasma 2-3 x i.e. 884 mOSM/kg
non ionic monomer

Question 15

HU units
water
air
fat
tissue
bone
stone

Answer 15

CT pixel numbers are proportional to the difference in average x-ray attenuation of the tissue within the voxel and that of water. A Hounsfield unit (HU) scale is used; water is assigned a value of 0; the scale extends from -1,000 HU for air to +3,000 HU for dense bone.
Soft tissue +100 to +300 HU
Fat -120 to -90 HU
Kidney stones 300 – over 1000HU

Question 16

split bolus technique

Answer 16

split bolus technique where an initial bolus of contrast (50–75 mL) is administered and a second bolus (50–75 mL) is administered 5–7 min later.
The patient is then scanned after a further 60–90 s. When this single post-contrast scan is obtained, the majority of the initial bolus is in the pyelographic phase with a proportion in the nephrogenic phase, and the second bolus is in the vascular phase; the maximal anatomical detail of the kidney and its collecting system can, thereby, be obtained

Question 17

cortico medullary vs nephrogenic phase

Answer 17

coricomedullary 25-40sec
diff tumour from pseudotumour based on enhancement, but not good if in renal medulla

nephrogenic 60-100s
most important for tumour detection
tumour thrombus

Question 18

contrast agents
based on iodine
classifications

Answer 18

Group of drugs used to improve visibility of internal organs in XR based imaging techniques due to high atomic weight of iodine = radiodensity
Based on the chemical modification of a 2,4,6-tri-iodinated benzene ring
Different types: ionic/nonionic and monomeric/dimeric
They do not differ greatly in their imaging capabilities
They do differ in their SE profile

iodine is water soluble

Question 19

LOCM vs HOCM toxicity profile

Answer 19

less nephrotoxic
LOCM still higher than plasma 2-3 x
visipaque is iso osmolar 290mosmol/kg but expensive

Question 20

side effect contrast agent

Answer 20

<3% mild hypersensitivity
flushing
uritcaria
retching
coughing
dizziness

mod severe <0.004% vomiting, headache, facial oedema, anaphylaxis

delayed allergic reaction >1 hr, rash, skin redness, swelling

CIN 2-5% peaking day 3-5 return to baseline 10-14days

Question 21

CIN peak incidence, when resolve

Answer 21

CIN 2-5% peaking day 3-5 return to baseline 10-14days

Question 22

mechanism of CIN

Answer 22

due to hypoxia
Despite extensive speculation, the actual occurrence of contrast-induced nephropathy has not been demonstrated in the literature.[4] The mechanism of contrast-induced nephropathy is not entirely understood, but is thought to include direct damage from reactive oxygen species, contrast-induced increase in urine output, increased oxygen consumption, changes in dilation and narrowing of the blood vessels to the kidneys, and changes in urine viscosity.[citation needed]

Question 23

voxel vs pixel

Answer 23

The slice is subdivided into a matrix of 512 × 512 volume elements (voxels). The image is reconstructed by a computer as a corresponding matrix of 512 × 512 picture elements (pixels).
A pixel is a representation of the average linear attenuation coefficient of a voxel. The image is displayed as a matrix of pixels; the brightness or greyscale value of each pixel represents the average linear attenuation coefficient of the contents of the corresponding voxel.

Question 24

voxel vs pixel

Answer 24

The slice is subdivided into a matrix of 512 × 512 volume elements (voxels). The image is reconstructed by a computer as a corresponding matrix of 512 × 512 picture elements (pixels).
A pixel is a representation of the average linear attenuation coefficient of a voxel. The image is displayed as a matrix of pixels; the brightness or greyscale value of each pixel represents the average linear attenuation coefficient of the contents of the corresponding voxel.

Question 25

linear attenuation coefficient

Answer 25

The linear attenuation coefficient is related to the attenuating property of a material, i.e., how well it absorbs, scatters, or transmits x-rays.

Question 26

mosmol/kg what is it

Answer 26

milliosmoles per kilogram
Some medical tests report results in milliosmoles per kilogram (mOsm/kg) of water. An osmole is an amount of a substance that contributes to the osmotic pressure of a solution. A milliosmole is one-thousandth of an osmole

Question 27

what are contrast agents

Answer 27

heterogenous group of radiopharmaceuticals used to enhance tissue definition

Question 28

iodinated agents

Answer 28

based on organic salts of iodine
high atomic / molecular weight of iodine 127
making it radiodense

Question 29

sievert vs gy

Answer 29

sievert is the measure of the health effect of low levels of ionizing radiation
a measure of the stochastic health risk

grey is the absorped dose of energy deposition of 1j/kg and is a measure of the deterministic effect, used in theraputic radiotherapy

Question 30

risk of anaphylaxis, risk of death

Answer 30

<0.001%

1 in 100,000 disk of death

Question 31

american college radiology defined post contrast AKI as

Answer 31

1.5 x or more increase in creatinine from baseline in 48-72 hours

Question 32

arterial phase
corticomedullary phase
nephrogenic phase
timings

Answer 32

15-20 sec
renal arteries
30-40sec
intense enhancement renal cortex, preferential arterial flow to cortex , glomerular filtration contrast, medulla less well enhanced, renal veins
80-120 sec
tubular filtration of contrast , subtle parenchymal lesions

Question 33

density on ct of renal masses
haemorrhagic cyst on unehanced
fat
equivocal enhancement

Answer 33

> 70 on unenhanced is haem cyst
fat is less than -20 HU
equivocal enhancement 10-20HU - seen in cyst due to beam hardening, or poorly enhancing papillary rcc

Question 34

oncocytoma characteristis

Answer 34

sharply demarcated
uniform enhancement
central scar

Question 35

clear cell rcc on ct

Answer 35

most strongly ehancing in CM phase

best seen in nephrogenic phase

Question 36

papillary rcc on ct

Answer 36

homogenous
hypovascular
can mimic cysts
enhancement can be 10-20
more likely bilateral and multifocal

Question 37

chromophobe rcc

Answer 37

sharply demarcted
slightly lobulated
can have central scar and spoke wheel pattern contrast similar to onc
often ehance less than ccrcc and more homogenous

Question 38

XGP

Answer 38

chronic granulomatous infection with accumulation of lipid laden macrophages
diffuse renal destruction
can be segmental
renal enlargement
can see macroscopic fat

Question 39

dual energy ct

Answer 39

two ct data sets acquired
correspond to x ray attenuation from
lower and higher energy x rays 
two data sets manipulated to extract information 
renal stone types
renal and adrenal masses

Question 40

what is attenuation

Answer 40

is the reduction in the energy of the primary x ray beam as it passes through a medium

Question 41

structure of hyperosmolar ionic monomer

Answer 41

has COO- as well as three iodine and two side units in heaxagonal ring

Question 42

anaphylaxis protocl

Answer 42

500mcg 0.5ml  IM adrenaline 1:1000, repeat 5 min if not better
chlorphenamine 10mg, IM or slow IV
hydrocoritsone 200mg IV
500ml to 1l fluid challenge
child 20ml/kg crystalloid

Question 43

CIN and IV contrast royal college radilogists

Answer 43

risk of IV contrast non existant for patients GFR more than 45
no precautions needed

risk of CI AKI low or non existant 30-45
may benefit hydration if acutely deteriorating, not recommended for all

GFR less than 30, or acutely deteriating, weigh risk vs benefit, can give periperocedural IV hdyration
but is not absolute CI to medically indicated iodinated contrast media administration

Question 44

x ray safety in theatres

lead gown thickness 8

Answer 44

IRMER trained
surgeon understanding equipment
all equipment tested and functioning correctly
tube close to patient
staff stand far away
lead aprons reduce dose 90%
0.35mm thickness lead apron
radiation dose to staff and patient justified
pregnancy test
screening - doors closed and signs
ALARA principle