diagnostic imaging lecture 3

Question 0

principles of image formation? what is matter? 3 types of interaction? different tissues vary in x-ray absorption?
absorption depends on?

Answer 0

x-rays interact with matter (patient)
1. absorped
2. scattered
3. transmitted
relates to the type of tissue - amount of density (atomic number)3. bone, gas,, soft tissue, mineral.

Question 1

what is opacity? what is density?

Answer 1

opacity - the degree to which light is not allowed to travel through an object
density - mass per unit volume.

Question 2

what are the 5 types of tissue?

Answer 2

air, fat, soft tissue, bone, lead

Question 3

what is the photoelectric effect?

what is the Compton effect?

Answer 3

photoelectric - depends on atomic number - gives a good quality image.
compton - depends on density - want to keep this low.

want more of a photoelectric effect then compton. need to control the KV.

Question 4

what shows up dark on an xray? what shows up light? what cant you tell the difference between?

Answer 4

dark - gas (radiolucent) then fat, soft tissue or fluid, mineral, metallic (light - radiopaque)
cant tell the difference between soft tissue or fluid.

Question 5

what happens when you take an xray? a 3D image changes to what?

Answer 5

a 3D image turns into a 2D image!! but can use MRI or CT scans which are in 3d.

Question 6

how can you re-create a 3d image? depth perception!

Answer 6

reconstruct it mentally. take one later and one vetrodorsal projection and the put them togther. eg. with a joint you wouldtake many projections and see all the way around it. dont want to miss anything!! may look normal from one angle but not another.

Question 7

what are the 3 types of radiographic geometry?

Answer 7

magnfication
penumbra
distortion

Question 8

what is the magnification?

Answer 8

enlargement of the radiographoc image of an object relative to its actual size. . increased subject -film distance. image gets bigger closer to the tube.

Question 9

magnification - which leg would look bigger?

Answer 9

the leg frther from the X-ray tube…nearer the cassette. - will look smaller.
the leg on top = bigger.

Question 10

what is penumbra?

Answer 10

related to mignification. more mag = edges more blurred…dont want to much mag as this increases the width of the penumbra.

Question 11

what is distortion?

Answer 11

images are more distorted at the edges/periphery of the image. further from the middle of the cassette. (distortion at the edges. )

Question 12

what is summation?

Answer 12

all 2d images so can get summation of structures on top of each other. different opacities can help you interperate this. organs in different planes may add together. eg. kidneys. /intestines.

Question 13

what is border effacement?

Answer 13

if 2 sturctures of the same radiopacity in contact then their edges may look effaced. eg. if there is perfusion in the thorax. cant see the heart. lose cardiac silhouette. soft tissue and fluid.

Question 14

radiographic orientation. what is the conventional way? patient right = ? pateint cranial = ?

Answer 14

pateint right to image left.

patient rostral/cranial to image left.

Question 15

what are the ideal veiwing conditions?

Answer 15

quiet, dark, block out extra light, enough view boxes. not tired, stressy, busy.

Question 16

what is a good way to interperate the image? (6)

Answer 16

1. viewing conditions
2. radiograph quality
3. rontgen signs
4. examine systematically
5. apply knowledge of normal anatomy
6. form a differential list to explain any changes

Question 17

what are the roentgen signs?

Answer 17

a description of the abnormailites on x-ray of a tissue/organ. eg. may use contrast studies eg. barium for assessing the fuction of an organ. kidney?

Question 18

what is collimation?

Answer 18

reduces penetration to other areas. reduces scatter and improves image quiality. mean light exposure is confined to just one area.

Question 19

what is the ideal exposure factors?

Answer 19

decrease exposure time. over exposed = high kv .

under = too birght, low kv

Question 20

what is the effect of motion on x-rays?

Answer 20

decrease exposure time to avoid motion artefacts. eg. respiration/heart beat.

Question 21

what is kv? and mAs?

Answer 21

kv - penetrating power. if too low then under exposed and too bright.
mAs - no of x-rays. if use to much then can burn out detail eg in the abdomen. (too dark)
air = very good contrast and so dont need high mAs.

Question 22

how should you position the patient?

Answer 22

avoid rotation - distorts everything. needs to be straight.

Question 23

how does the respiratory phase matter?

Answer 23

if you are looking at the lung field - want on inspiratory phase to get a good details.
if you are looking at the abdomen then want on expiratory phase - see more of guts.

Question 24

what are the 6 roentgen signs? used for?

Answer 24

size, shape, number, location, margination, radiopacity

used as a checklist when looking at a structure.

Question 25

how would you determine the size of a structure?
shape?
opacity?
location?
number?
margination?

Answer 25

size - can measure it eg. by intercostal spaces (all relative!)
shape - eg. may see new bone frmation
opacity - eg. increased in bone - may be a medullary cavity.
location - which hip? where is the mass? eg. caudla left lateral lung lobe.
number - eg, egges in tortoise? kidney stones? may just say multiple.
margnations - alignment?

Question 26

always have a systematic approach to xrays?

Answer 26

may look at whole thign first then different areas then individual organs.

Question 27

why does body condition matter?

Answer 27

if obese- hard to get a good image with lots of subcutaneous fat.
if emaciated - also difficult to position etc.

Question 28

how can breed and conformation matter?

Answer 28

eg. small bone length in some dogs? malformed bones may actually be normal!!!

Question 29

what may you see in arthritis?

Answer 29

new bone formation!!! - blurry joint.

Question 30

radiography can be? soppy analogy.

Answer 30

a window to the past (may not be relevant)
a mirror to the present (reflection of todays problem)
picture of the future (predict future outcomes)