Diagnostic Ultrasound for

Postgraduates in Obstetrics and Gynaecology

Max Brinsmead MB BS PhDMay 2015

Potential uses for ultrasound in the 1st trimester of pregnancy:

Locate the pregnancy – exclude ectopic Assessment of viability Diagnosis of molar pregnancy Determining gestational age Diagnosis of multiple pregnancy Assessment of other pelvic masses Screening for fetal abnormalities Assisting CVS and amniocentesis

Other uses for ultrasound in obstetrics:

Screening for placenta previa Assessment of APH Cervical length monitoring Assessment of fetal growth Evaluation of polyhydramnios and hydrops Diagnosis and management of malpresentation Assessment of fetal welfare Assessment of the postpartum uterus Directing intrauterine interventions

Potential uses for ultrasound in gynaecology:

Assessment of adnexal pelvic masses IUCD and Implanon location Treatment of ovarian cysts (aspiration) and ectopic

pregnancy (methotrexate) Investigation of postmenopausal bleeding Evaluation of pelvic pain Investigation of menorrhagia Diagnosis of polycystic ovaries Tubal patency studies in infertility Evaluation of primary amenorrhoea Screening for ovarian cancer Monitoring of follicle number and growth for IVF Egg recovery for IVF and ICSI

But before you can do all this…

You must know how to drive an ultrasound machine

What is Medical Ultrasound?

Sound waves whose frequency is beyond the human ear

That is >20 kHz

Advantages of Ultrasound:

Can be directed in a beam Obeys the laws of reflection and refraction Reflected by objects of quite small size Can be converted to analogue or digital signals for

image production

An ultrasound image is produced by:

Producing a beam of sound waves Transmitting this through the object of interest Receiving echoes Converting the echoes into electric signals Interpreting and displaying those signals Can be snapshot or in real time

The ultrasound beam AND the receipt of echoes is achieved by piezoelectric crystals:

Mounted in an array on a probe The probe can be fixed or oscillating The wave of sound can be focused to a point of interest The image is displayed on an oscilloscope (or TV

screen)

The image is formed by:

The direction of the echo The strength of the echo The time taken for the echo to return These 3 characteristics determine which pixels on

the screen will light up And with what intensity

So the ultrasound image will be:

White = Area of high acoustic impedance e.g. bone Black = Areas of low acoustic impedance e.g fluid All shades of grey in between Shadowed by area of non penetration or areas

behind those of high acoustic impedance e.g. behind bone

Disadvantages of Ultrasound:

Travels poorly through gas

The amount reflected depends on the degree of acoustic mismatch

The piezoelectric crystals are quite delicate

Diagnostic ultrasound:

Typically involves frequencies of 2 – 15 mHz Lower frequencies will give greater penetration And thereby you can see further Higher frequencies allow you to see more detail But the penetration is less And very high frequencies have the potential for

adverse biological effects

Types of Probes: A linear array of crystals

Produces parallel sound waves And a rectangular image Good for surface structures

A sector scanning probe Produces a fan-like image Can fit ito narrow spaces Has poor near-field resolution

A curved array of crystals Will fit curved surfaces of the body The density of scan decreases proportionally to the distance

from the transducer

Probe Types

Machine Controls

Max’s Maxim Number 17

Using an ultrasound machine without using a few of its knobs is like driving a car only in the first gear

It’s a safe to go…

But you don’t get very far

Some tips: Don’t be intimidated by all the knobs Just like driving a car, You only need to know a few

basic controls Practice and play! The first challenge is to find the switch to turn it on

There may be more than one Next find the machine pre set for the exam you are

about to do And do all this before you get to the patient

Some more tips: Ultrasound is no substitute for a good history ALWAYS do an abdominal scan before using the

vaginal probe Know how to switch probes

Is it safe to “hot wire”? The trick is to build up a 3-dimensional picture in your

mind using real-time imaging You will always be better than sonographers because

you know the anatomy and pathology Or you will get to see it! So beware of premature conclusions

Machine Controls:

Gain Controls brightness or “contrast” Also in a array of sliding levers Use maximum gain and minimum power

Depth Reach to the area of interest then…

Zoom To enlarge your view then…

Freeze For measurements (or stored image)

Machine Controls

Machine Controls 2:

Tracker Ball This is the “mouse” for your computer, usually with right

and left click buttons to execute functions Used to superimpose things on the screen May have several functions

Calipers To measure distance between 2 points

Ellipse To measure area

Machine Controls

Some more tips: Use a low light but make sure you can see all the

controls Adjust contrast on your screen before you start Make yourself and the patient comfortable Use a good quality transducer gel - SPARINGLY Remember the prime purpose of the exam Make sure that always follow a routine and do it all Scroll-back and cine re-loop can be very useful Look for acoustic enhancement on the other side of

fluid Look for shadowing on the other side of bone

Some traps: Doing patients in succession when data from one is

carried forward onto the next When you find a fetal heart make sure that it inside a

uterus Pseudo sac within the uterus with an ectopic Measuring the yolk sac as a part of the CRL Image duplication resulting in the false diagnosis of

twin sacs A small amount of free fluid in the pelvis can be

normal Know the many variations of a corpus luteum Using a too-narrow field of view

Proven uses for ultrasound in pregnancy:

Dating the gestation Many women cannot provide a reliable LMP Should be +/- 7 days based on CRL in the 1st trimester Can be +/- 10 days based on HC, AC and FL in 2nd trimester Becomes increasingly unreliable after 22w

Identification of multiple pregnancy Twins have a perinatal mortality that is 2-4x singletons Monitoring for discordant growth with Doppler reduces risk Important to diagnose zygosity

Identification of breech in the third trimester ECV reduces the rate of Caesarean section

Few RCTs of routine ultrasound have shown any effect on overall perinatal mortality and morbidity

Unproven uses for ultrasound in pregnancy:

Screening for Aneuploidy Cost effectiveness of universal screening debated Ethical issues and patient choice involved

Screening for structural malformations Sensitivity is 13 – 50% depending on expertise & equipment And only half of these before 20 w gestation False positives occur

Screening for IUGR in the 3rd trimester Sensitivity is 80-90% But the positive predictive value of neonatal morbidity is only 25-

50% The rest have constitutional smallness

Harmful Effects of ultrasound in pregnancy:

It is not ionising radiation However, thermal effects and cavitation can occur

in tissues exposed to high power ultrasound One RCT of repeated routine ultrasound with

Dopplers in the 3rd trimester found a small but significant decrease in birth weight in the exposed cohort

A meta analysis showed males exposed to ultrasound in uterus are more likely to be left-handed

Caring for your ultrasound machine:

Treat your probes as if they were made of glass Wash, clean and dry probes Sterilisation options Don’t use oil or alcohol Transport probes safely stowed If you changed the machine defaults set them back

to the original

Ultrasound in the first trimester of pregnancy:

Start with the abdominal probe Counsel the patient about your expected findings

and expertise First find the cervix and/or uterine body

It’s not as far in as you think Look for embryo at the edges of a sac <7w FH should be demonstrable when sac size is >2 cm Measure CRL up to 12w, thereafter BPD, HC, AC

and FL Remember ectopic and multiple pregnancy If you are not sure say so…

Exclude ectopic and recheck in 7 – 14 days Check the POD and ovaries before you finish

Assume ectopic & proceed accordingly

>1000 iu/L

Diagnostic laparoscopy if clinically suspicious

500 - 1000 iu/L

Observe

Repeat HCG in 24 - 48 hrsRescan when >1000 iu/L

or follow to <10 iu/L if EP possible

<500 iu/L

Quantified beta HCG

Inconclusive Vaginal Scan = Empty uterus

Pain & Bleeding in Pregnancy

Emergency Management

Ultrasound in the third trimester of pregnancy:

Start with abdominal palpation Tell patient purpose of examination Quick scan for presentation and lie Measure BPD, HC, AC and FL Remember that this does not predict dates Liquor volume Find placenta and examine lower edge in relationship

to the presenting part Suspected placenta previa best evaluated by PV or TV

scan Ovaries virtually never seen

Ultrasound for the non pregnant woman:

Start with abdominal probe Preferably with a full bladder I measure uterine dimensions in two planes Then send patient to empty bladder…

And switch to vaginal probe First find the cervix Acutely anteverted/flexed uterus is tricky Find and measure endometrium Then evaluate myometrium Ovaries can be anywhere

And cannot be found 25 – 30% of the time I measure ovaries in two dimensions

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