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Diagnostic Ultrasound for Postgraduates in Obstetrics and Gynaecology


Diagnostic Ultrasound for Postgraduates in Obstetrics and Gynaecology Max Brinsmead PhD FRANZCOG September 2008 Potential uses for ultrasound in the 1st trimester of ... – PowerPoint PPT presentation

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Title: Diagnostic Ultrasound for Postgraduates in Obstetrics and Gynaecology

Diagnostic Ultrasound for Postgraduates in
Obstetrics and Gynaecology
  • Max Brinsmead PhD FRANZCOG
  • September 2008

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
  • That is gt20 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
  • The image is displayed on an oscilloscope (or TV

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

Maxs Maxim Number 17
  • Using an ultrasound machine without using a few
    of its knobs is like driving a car only in the
    first gear
  • Its a safe to go
  • But you dont get very far

Some tips
  • Dont 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
  • 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
  • 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
  • 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
  • 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
  • Can be /- 10 days based on HC, AC and FL in 2nd
  • Becomes increasingly unreliable after 22w
  • Identification of multiple pregnancy
  • Twins have a perinatal mortality that is 2-4x
  • 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

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
  • 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

Caring for your ultrasound machine
  • Treat your probes as if they were made of glass
  • Wash, clean and dry probes
  • Sterilisation options
  • Dont 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
  • Its not as far in as you think
  • Look for embryo at the edges of a sac lt7w
  • FH should be demonstrable when sac size is gt2 cm
  • Measure CRL up to 12w, thereafter BPD, HC, AC and
  • 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


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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