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Diagnostic Ultrasound for Postgraduates in Obstetrics and Gynaecology

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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


1
Diagnostic Ultrasound for Postgraduates in
Obstetrics and Gynaecology
  • Max Brinsmead PhD FRANZCOG
  • September 2008

2
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

3
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

4
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

5
But before you can do all this
  • You must know how to drive an ultrasound machine

6
What is Medical Ultrasound?
  • Sound waves whose frequency is beyond the human
    ear
  • That is gt20 kHz

7
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

8
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

9
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)

10
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

11
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

12
Disadvantages of Ultrasound
  • Travels poorly through gas
  • The amount reflected depends on the degree of
    acoustic mismatch
  • The piezoelectric crystals are quite delicate

13
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

14
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

15
Probe Types

16
Machine Controls

17
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

18
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

19
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

20
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)

21
Machine Controls

22
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

23
Machine Controls

24
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

25
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

26
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

27
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

28
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

29
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

30
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
    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

31

32
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

33
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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