Imaging

Question 1

what does X ray use

Answer 1

uses an heterogenous beam of x rays

Question 2

describe how an X ray works

Answer 2

• Based on the density and composition of the structure some of the x rays will be absorbed
• The x rays that pass through are black and these are the less dense tissues
• Grey and white areas are areas that have absorbed more x rays and are therefore white

Question 3

what are the advantages of plain radiograph

Answer 3

• Cheap
• Readily available
• Uses ionising radiation
  not catastrophic
• come portable if the patient can’t get to the suite and can take into the operating theatres
• can find some diseases in soft tissue but you need a contrast medium

Question 4

what are the disadvantages of plain radiographs

Answer 4

• Only calcified tissue shows up clearly
• Soft tissues don’t show up very well
• Not sensitive – have to loose 30% of bone mass before it shows up on an x ray
• Things in front can obscure structures behind
• Processes taking place inside the bone cannot be seen
• 2D representation of a 3D object

Question 5

what does radio-opaque mean

Answer 5

white - areas that block the x rays

Question 6

what does radio-lucent mean

Answer 6

black - areas that did not stop the x rays

Question 7

what does a dexa scan do

Answer 7

• Two different low energy X ray sources

- The denser the bone the fewer x rays that get to the detector

Question 8

what does 2 different x ray sources do in the DEXA scan

Answer 8

• provides and improves higher accuracy

Question 9

What is the DEXA scan used for

Answer 9

• Used for body mass calculations

- Used for diagnosis and following of bone density changes in osteoporosis

Question 10

what does contrast media do

Answer 10

show differences

• barium and iodine issued with contrast
• gadolinium is used in MRI

Question 11

what does CT do

Answer 11

• Uses multiple x ray beams at different angles to build up a cross section of the bodies organs and tissues

Question 12

what are the advantages of CT

Answer 12

• Cross sectional images and other planes can be reconstructed afterwards or 3D reconstructiosn
• Good high contrast bone detail
• Well tolerated
• Radily available

Question 13

what are the disadvantages of CT

Answer 13

• Ionising radiation dose
• Metallic artefacts cause loss of detail
• Soft tissue surrounded closely by bond difficult to image
• Respiratory movement artefact

Question 14

how does MRI work

Answer 14

• Uses non-iosning radiation – 10,000-30,000 times the earths magnetic field

Question 15

what are the advantages of MRI

Answer 15

• Very high soft tissue contrast
• Images acquired in transverse plane – can be reconstructed in any plane
• Can get both structural and functional information
• Safe during fetal development as no radiation
• Cheap
• Readily available
• common for both diagnosis and therapeutic imaging

Question 16

what are the disadvantages of MRI

Answer 16

• does not image bone directly
• difficult to interpret whats going on
• noisy
• catastrophic

Question 17

how does MRI work

Answer 17

• Based on sound waves with frequencies usually in rnage of 1-18megahertz

Question 18

what does PA stand for

Answer 18

posterior to anterior

Question 19

what do you always show in radiographs

Answer 19

always show the image from the front

Question 20

describe the view in PA

Answer 20

1. Clavicle in lung field
2. Ribs slanted (posterior ribs distinct)
3. Scapula outwards from lung field
4. Heart shadow smaller
5. Usual view for the chest as it does not show the heart being magnified

Question 21

describe the view in AP

Answer 21

1. Clavicle remains at top of lung field
2. Ribs lie more horizontal (anterior ribs more distinct)
3. Scapula comes in the lung field
4. Heart shadow looks larger
5. Usually bedridden and infants

Question 22

for the appendicular skeleton…

Answer 22

AP and lateral views are most common

Question 23

why are AP and Lateral views used in the appendicular skeleton

Answer 23

Need two view to be able to get view

Need AP to get a head on view and lateral view to see if you can see anything that you can see from the front

Question 24

what is a difference in children X rays

Answer 24

different cartilage isn’t calcififed, if the cartailage plate is not calficided appears as a radiolucent line that appears in childrens x rays, this is where the bone is growing and is a growth plate, not a fractured

Question 25

Define contrast media

Answer 25

these are solutions of non toxic substances that contain elements of high atomic number

Question 26

what do you do in order to increase the average atomic number of a hollow structure

Answer 26

• you fill the cavities with a liquid with a much higher average atomic number

Question 27

describe the difference in densities in contrast media

Answer 27

• large difference in densities of two organs show up such as the solid muscle in the heart and the airs in the lungs
• if two organs have similar densities then they do not show up such as the small intestine and large intestine

Question 28

how do you reduce the density of a hollow organ

Answer 28

• fill it with gas or air

Question 29

how do you give barium

Answer 29

Barium is non toxic – give it in differnte ways
Swallow – looks at the oseophogus and goes down to the stomach after time and the small insteine
Rectum – becomes an enema – jiggles the person around as your working against the normal flow, takes 30 minutes to jiggle the person around to get to the colon
Will be excreted and go back out
Few people that asparate it – goes into the lungs instead of the osphogus

Question 30

how do you give iodine

Answer 30

• non toxic

- inject it into the vascular system either in the arteries or the veins

Question 31

describe the radiation in CT

Answer 31

Normal background radiation per year is around 3.0 mSv, coast to coast flight across US adds 0.03 mSv
CT of abdo and pelvis = 10 mSv versus radiograph 8 mSv
Radiograph of arms or legs 1.5 mSv bone DEXA 0.001 mSV
Chest x-ray 0.1 whereas mSV chest CT 7 mSv, therefore it is higher, as your taking multiple x ray images down the chest

Question 32

when looking at axial scans how do you look at them

Answer 32

• look at them as if your standing from the head of the individual

Question 33

MRI what is T1 and what is T2

Answer 33

T1 – fat white

T2 – high free water white (oedema) – sees pathological process and measures water

Question 34

what does gadolinium do

Answer 34

goes across the blood brain barrier

- contrast enhancemnet