Basic Ultrasound

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Introduction and Basic

Obsterics Ultrasound



►Ultrasound imaging, also called ultrasoundscanning or sonography, is a method of obtaining images from inside the human

body through the use of high frequencysound waves



►Ultrasound = sound with a frequency over20,000 Hz

►Medical ultrasound generally uses

frequencies between one and 10 millionhertz (1-10 MHz).

► Higher frequency ultrasound waves

produce more detailed images, but are alsomore readily absorbed and so cannotpenetrate as deeply into the body.



► An ultrasound machine consists of twoparts: the transducer and the analyzer.

►The transducer both produces the soundwaves that penetrate the body and receivesthe reflected echoes



► transducer thenreceives the returningechoes, translates

them back into electricpulses and sends themto the analyzer--acomputer that

organizes the data intoan image on atelevision screen



screen

transducer

console

printer



►Four different modes of ultrasound are usedin medical imaging A-mode

►a single transducer scans a line through the bodywith the echoes plotted on screen as a function of depth

B-mode►a linear array of transducers simultaneously scans a

plane through the body that can be viewed as a two-dimensional image on screen



M-Mode

►M stands for motion



Doppler mode

►capability of accurately measuring velocities of moving material, such as blood in arteries and veins

►most often combined with B-mode scanning toproduce images of blood vessels from which bloodflow can be directly measured







Obstetric Ultrasound

►Obstetrics USG provide enough benefits, inenough pregnancies to support itswidespread use

►USG has different role in different stages of pregnancies



►Prerequisites

Details of history, examination andinvestigations

Relevant risk factors identified

Relevant serology and genetic concerns



►Preparation

High resolution real time gray-scale USGmachine

Experienced sonographer

Comfortable mother

Screen visible to mother (optional) and

sonographer



First Trimester Scan

►Comment

Complimentary to mid trimester scan

►Content

Establishing date (CRL)

Number of fetuses and chorionicity

Establish viability

Evaluate gross fetal anatomy



Examine uterus and adnexal structures

Specific examinations with indications

Nuchal translucency *



18-22 week scan

►Content

Confirm viability

Check dating/gestational age

Confirm fetal number

Examine fetal anatomy

►Head & neck

►Thorax► Abdomen

► Axial skelelton



Amniotic fluid

Placenta

Uterus & adnexal structures



Third Trimester Scan

►Comment

Generally targeted scan

►Content

Depend on indication

► Anatomy

►Growth/Doppler/BPP

► Amniotic fluid



►Presentation

►Placenta

►Uterus & adnexa



Technique

►Know what’s the reason

►Know the machine capability and limitation



►Comfortable position for bothsonographer and patient



•Adequate exposure



Technique

►Orientation

Screen menu

Image orientation

►Longitudinal scan: as if from the left side of patient

►Transverse scan: as if from the foot of the patient

►

No agreed orientation for the display of TVS







►General overview of the fetus Number of fetus

Presentation & lie

Attitude

Liquor

Placenta



Technique

►Show to the patient (esp the viability)





► GS Visible from 5 to 6 weeks POA

Shape: uniform round or oval

Rim of chorionic decidual reaction

Measurements:1. Diameter

2. Volume

- Accuracy of sac vol: + 1 week



Volume : GSV (ml3) = L (cm) X AP (cm) X T(cm) X 0.5



►GS

Shape distortion,angulation and irregularmargin may indicatemissed abortion

Abortion may showchoriodecidualhaemorrhage



Measurements

►CRL

First described by Robinson in 1975

Most accurate mean of estimating gest age

But depends on the ability to obtain a treulongitudinal section of unflexed embryo withend points clearly seen



►Spine can be visualised from 9 weeksonward; a guide to obtain the truelongitudinal view

►Maybe difficult to obtain after 10 weeks – fetus often curved





►BPD

The maximum diameter of the skull at the levelof parietal eminences.

Correct section:►Oval shape head

►Short midline in the anterior half of the head

►

Cavum septum pellucidum



Measurement: from the outer table of theproximal surface of the skull to the inner tableof the distal surface





Problems:

►Breech/transverse : may lead to underestimation (indolicocephalic shape); due to maternal breathingmovements and pressure from transducer

►OP/OA : landmarks may not be visualised clearly

- press to rotate the fetal head or tilt the patienthead down



►HC

Not a routine

Same plane as BPD

Measure the outer circumference of the skull





Content:►Liver

►Stomach bubble

►Intrahepatic potion of umbilical vein (anteriorthird of the AC)

• AC•The best parameter reflecting fetal sizeand growth

• Taken at the level of liver; 4% of bodyweight and increases steadily with gestage







►FL

Highly reproducible because of the preciselydefined end points

Both ends should be visualised

Measurements made from the centre o the U-shape at the ends of the bone (length of

diaphysis)







► Liquor

1. Amniotic fluid index

2. Single quadrant measurement



► AFI

Measurements of 4 quadrants

Pools of free liquor

Perpendicular to maternal sagital plane

Normal range = depend on gestational age

At term

►<8 olighydramnios►> 20 polyhydramnios





►Single pocket measurement

Largest pocket of liquor

Measurements of 2 perpendicular plane

Oligohydramnios = <2 cm

Polyhydramnios = > 8 cm



► Anatomy scan

Detailed morphology scan is best done 18-22weeks gestation

Screening or confirmatory

Case selected on risk factors (age, previoushistory, teratogen exposure etc)



►Systematic appropach

Number of fetus

Presentation

Fetal activity

liquor volume

Placental site

Number of cord vessels



►Begin with the head, progressing caudally tothe thorax, abdomen, urogenital system andspino-skeletal system

► A checklist may be required

►Examination in 3 basic planes

Coronal

Sagital

Axial





►Head

Cranial vault

Intracranial contents

Soft tissue of the face











►Thorax

Heart

►4 chamber view

► A third of thorax►Both chambers of equal

sizes





Lungs

►Right lobe bigger than the left

►Left lobe behind the heart



► Abdomen

Liver occupies the upper third

Prior to the junction with the portal vein,

umbilical vein will take a J-shaped turn(AC measurement)



►Genitourinary

Kidneys

►Seen lateral to the spine

►Below the level of AC

Bladder

►

Cyctic mass at the centre of pelvis►Umbilical artery on both side







►Spine

Observed in 3 basic planes

Completeness should be examined

►Limbs and digit







►Placenta

Low lying placenta detected in second trimestershould have a repeat scan at 32-34 weeks

gestation Marginal placenta may require TVS

Lower segment = 5 cm from internal os





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Basic Ultrasound