Diagnostic Ultrasound

Farm Animal

How are ultrasound waves produced?

Running alternating current through special crystals causing the piezoelectric effect. This releases ultrasound waves in pulses.

How does depth of penetration of an ultrasound beam relate to frequency?

Penetration directly proportional to 1/frequency.

How does resolution (detail) relate to frequency?

Resolution directly proportional to frequency.

What are the types of probes in ultrasonography?

-Sector (crystals moving)

-Linear (crystals in line)

-Convex (linear bent into curve)

What is the benefit of sector ultrasound probes?

They have a smaller outlet and detector for ultrasound waves meaning they are useful for looking at small/hard to view structures (e.g. looking between ribs).

What is the limitation of sector ultrasound probes?

They contain moving parts within the probe that move the crystals, leaving them prone to damage.

Describe how the reverberation artefact occurs in ultrasonography and how it appears

Ultrasound waves hit objects and reflect back to the scanner head, these waves can then reflect off of the scanner head and then reflect off the tissue again, back to the scanner head. This leads to artefactual whitening in a linear pattern.

What ultrasound artefact is seen here?

Reverberation.

How is the reverberation artefact useful for follicles/vessels?

When the beam is perpendicular to a follicle or vessel, the reverberation artefact will consequentially cause the wall to become whiter.

Why does acoustic enhancement cause artefacts?

If ultrasound waves travel through a structure which is less attenuating (absorbing) or a more transparent structure, the tissue of interest behind it may be shrouded due to more waves being transmitted through and hence reflecting back and reaching the scanner head. This causes false hyperechoic (white) regions to form.

What structures can potentially cause acoustic enhancement artefacts?

-Cysts

-Urinary bladder

-Large blood vessels

(anything filled with fluid)

How can artefacts occur due to poor resolution?

If the resolution is poor, it will be difficult to differentiate between two separate structures which are small.

How can ultrasound be used to determine bloodflow?

doppler —> frequency of reflected wave changed by movement of structure as reflects the wave

will show higer frequency if blood moving towards scanner

How is ultrasound useful for large animals which are used for breeding?

Determining the stage of pregnancy or oestrus.

Label this ultrasound of the right ovary

A = Ovary

B = CL

C = Follicle

What are the uses of bovine reproductive ultrasonography?

Allows:

-Pregnancy determination

-Age determination

-Sex determination

How can you distinguish between a uterus in oestrus and a uterus in pregnancy?

Pregnancy:

-Fluid (circular)

-Heartbeat presence (day 26)

-Embryo presence

-Presence of CL (fluid in CL)

-Foetus presence

-Placentome presence (day 33)

-Pulse in the umbilical cord (day 110)

What are some signs that the foetus has miscarried?

no heart beat

membranes flaccid

allantochorion fluid

How would you age a foetus?

Mid-sagittal section for crown-rump length

Horizontal section for biparietal distance

Transverse section for trunk diameter

How would you sex a foetus?

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

What are some uterine abnormalities that can be identified on ultrasound?

Cloudy fluid

• Mucometra

• Endometritis

• Pyometra

Hard mass with bones

• Mummified fetus

What is an ovarian abnormality?

granulosa cell tumour

What routine should you use to pregnancy scan?

Evacuate faeces from rectum.

Insert protected and lubricated hand into rectum

• lubricated scanner head cupped in palm of hand.

Use fingers to identify cervix

• if necessary try to gently move tract back into the pelvic

Either move sideways from the cervix or follow the right horn round to identify the right ovary

• Start on right as has 60% of ovulations and pregnancies

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 the age the fetus

• assess its size and how it is lying

• decide best view to allow a measurement

• freeze a good quality image and estimate age (use callipers or grid on screen)

Sexing - if old enough and the client requires it

transverse cross-section image at the umbilicus

move back, is there a hyperechoic genital tubercle behind umbilicus ?

if not move back to examine below the tail

a longitudinal midline cross-section down the fetus can also be used if the fetus is lying appropriately

What should you do if there is fluid but no fetus?

recheck both horns

is uterus over pelvic brim?

put probe over brim

placentomes? diameter?

is fluid cloudy? flecky?

any masses?

What can you identify on ultrasound relating to tendons?

• injury

• Longitudinal – tissue architecture

• Cross-sectional – fluid accumulation

• Repeat to gauge progress / prognosis

• Skin preparation

What can you identify on ultrasound relating to cardiology?

• Valve incompetence

• Ventricular septal defects, PDA

• Doppler – see direction of flow as colour

• See valve motion and cardiac cycle – correlate with murmur

• Pericardial effusion

• Pleural fluid – U/S guided chest drain

What can you identify on ultrasound relating to the umbilical cord?

• Umbilical masses

  • Abscess or hernia ?

  • Identify before incising!

• Structure infected ?

  • Urachus – caudally

  • Umbilical arteries – caudally

  • Umbilical veins – cranially towards liver

What can you identify on ultrasound relating to the bladder and kidneys?

• Urolithiasis

• Is bladder intact ?

• Gut motility - peritonitis

• Ultrasound-guided paracentisis

• Hydronephrosis

• Pylonephritis

• Ultrasound-guided tube cystotomy