Diagnostic ultrasound Flashcards
How are ultrasound waves generated
Piezoelectric material – vibrates when a current is put across it, when it vibrates it generates a current as well
Wavelength (frequency) – determines how well it penetrates tissue
How are ultrasound waves propagated?
- The wave propagates through the tissue and is reflected by the tissue
- The amount of reflection depends on the echo-density of the tissue
- The time from when the pulse starts to when the reflection comes back is a measure of the distance from the probe and the object reflecting it
Which tissue completely reflects the wave?
Bone
How can artefacts occur?
- Reflection/reverberation
- Refraction
- Acoustic enhancement
- Poor resolution
What is the relationship between wave frequency and resolution?
What is the relationship between penetration and frequency?
shorter frequency = higher resolution
more detail can be seen in closer structures to the probe - less penetration = higher resolution = shorter frequency
When is the earliest that you can pd a cow?
25 days
Why is it beneficial to pd earlier?
Why is it beneficial to pd later?
Identify non-pregnant animals
Fetal loss over time - “accuracy”
A 37 day old foetus is how big?
1cm
When should you dry off a pregnant cow?
60 days before birth
How does the fluid appear on an ultrasound in a cow in oestrus compared to a pregnant cow?
- oestrus - star shaped fluid
- pregnant - circular fluid
what other things can be observed on ultrasound that indicate a cow may be pregnant?
CL present on the ovary that last ovulated - foetus is most likely to be in this uterine horn (60%+ time in R horn!!)
CL may:
- be fluid filled - if >35mm, luteal cyst?
- or solid
- appear to have a line through
Most of the time, cattle foetuses stay in the same horn as the CL - how do horses differ?
Horse foetuses migrate in the uterus so could be in either horn
What factors do we assess when determining if a cow is pregnant?
- position
- fluid
- CL
- foetus
- heartbeat
- placentomes
How does amniotic fluid appear on an ultrasound?
Cloudy
- Foetus discharges urate into it
How does Allantochorionic fluid appear on an ultrasound?
Black
- if it is cloudy it could be a sign of an infection
Can twins be detected on ultrasound?
yes, at any stage but easiest once floated off wall but small enough to be on a single image (30-40d)
counting CLs is usually best way to detect twins
What % of twins are bilateral and unilateral
40% of twins are bilateral and 60% unilateral
Are twin pregnancies most likely to be lost if they are unilateral or bilateral?
8% of bilateral
35% of unilateral
how can a foetus be aged on ultrasound?
- mid-sagittal section for crown-rump length
- horizontal section for biparietal distance (across the head)
- transverse section for trunk diameter
Why may some people want foetal sexing to be carried out?
- Sufficient male or female offspring for progeny testing
- Keep dams bearing heifer replacements
- Keep dams bearing bulls attracting subsidy
What is progeny testing?
Progeny Testing refers to evaluation of bulls on the basis of their daughter’s performance
How is foetal sexing done?
Genital tubercle migrates so that at about day 56 it is:
- Just behind the umbilicus in males
- Between the back of the hind legs and the tail in the female
Teats and scrotum can be identified from 70 to 120 days
uterine abnormalities:
- what could cloudy fluid in the uterus indicate?
- what could a hard mass with bones indicate?
- cloudy fluid - mucometra, endometritis, pyometra
2. hard mass - mummified foetus
Name an ovarian abnormality
Granulosa cell tumour
Describe some features of an ultrasound scanning routine up to finding an ovary
- logical and systematic
- clear decision making framework
- evacuate faeces from rectum
- insert protected and lubricated hand into rectum
- use fingers to identify cervix
- either move sideways from the cervix or follow the right horn round to identify the right ovary
Describe the scanning routine once the ovary has been identified
- Obtain an image of the ovary and see if it has a CL
- Scan horn towards uterine body - look for fluid, white line of amniotic vesicle and eventually fetus
- If no fetus repeat process on left ovary and horn
- Scan fetus from trunk towards head for heartbeat
- Estimate age, sex
What should you do if there is fluid present but no foetus?
- recheck both horns
- is uterus over pelvic brim?
- put probe over brim – placentomes? diameter?
- is fluid cloudy? flecky?
- any masses?
