ULTRASOUND.

Question 1

Define ultrasound scanning

Answer 1

Ultrasound involves exposing part of the body to high frequency sounds waves to produce pictures of the inside of the body

Question 2

What kind of waves does US create?

Answer 2

SONAR

Question 3

What is the range of US probe frequencies used in medical diagnostics?

Answer 3

2mHz - 10mHz

Question 4

How does US work?

Answer 4

US waves are created by passing an electric current through a crystal (contained within a ceramic probe), causing it to vibrate.
The US waves then travel through bodily tissues where they are partially reflected at each tissue interface.
Each returning reflection hits the crystal and causes it to vibrate creating a current.
Echoes have discrete amplitudes which are assigned a specific brightness (using a finite gray scale) and subsequent location on the screen – the image on the screen is a plot of all the reflection returned

Question 5

How frequently is an US plot refreshed?

Answer 5

25-50 times a second

Question 6

Probe frequency determines…?

Answer 6

Optimal depth of penetration
Higher frequency (>5.0mHz) have less depth of penetration but provide a higher resolution – good for vascular structures
Lower frequency (<5.0mHZ) are good for deeper depths – good for visualising the abdomen and heart

Question 7

What causes different brightness levels in US scanning?

Answer 7

Time taken for the wave to return to the probe and the direction from which it came from

Question 8

What do the following colours represent on US?

White
Black
Grey

Answer 8

White: soft tissue (echogenic structures) – muscle, fat, vessels, nodes, masses
Black: fluid (anechoic structures) – blood, CSF
Grey: somewhere in between

Question 9

When would the use of a transvaginal probe be indicated?

Answer 9

Investigating infertility disorders
Diagnosis of ectopic pregnancy
Differentiation of normal and abnormal pregnancies in the 1st trimester
Diagnosis of congenital abnormalities in the 2nd trimester

Question 10

Name 3 advantages of TVUS

Answer 10

Specially designed high frequency transducers
Higher resolution images
Favorable for obese patients in the early stages of pregnancy

Question 11

Name 2 disadvantages of TVUS

Answer 11

More invasive procedure

Reduced beam penetration

Question 12

At what point can the following structures be expected to be seen?

Gestational sac
Yolk sac
Embryo

Answer 12

Gestational sac seen at 4 weeks – fluid filled with an echogenic border
Yolk sac seen at 33 days
Embryonic echoes seen at 38 days

Question 13

How much daily growth does a gestational sac undergo?

Answer 13

0.6mm

Question 14

In a normal pregnancy at what point should the gestational sac be visible on US?

Answer 14

If 25mm or larger in diameter

Question 15

How is gestational age calculated using crown rump lenght?

Answer 15

CRL + 6.5 = gestational age in weeks

Question 16

What tests are used to screen for T21 (between 11-13+6 weeks)? What is the sensitivity of these tests? What is the false positive rate?

Answer 16

Fetal nuchal translucency
b-hCG
PAPPA

60-85% sensitivity
5% false positive rate

Question 17

What is considered an abnormal nuchal translucency measurement?

Answer 17

> 3.5mm

Question 18

What two criteria must be fulfilled when calculated fetal nuchal translucency?

Answer 18

The fetus must be in a neutral position

The measurement must be taken in a sagittal view

Question 19

What is the change of having a pregnancy affected by T21 at the following ages:

20 years
30 years
40 years

Answer 19

20 years: 1 in 1500
30 years: 1 in 900
40 years: 1 in 100

Question 20

What is a normal cervix length from 10-36 weeks gestation?

Answer 20

> 2.5cm or more

Question 21

What should the width of the cervical canal be at the level of the internal os?

Answer 21

<4mm

Question 22

Define the following views in US scaning:

Transverse

Longitudinal

Answer 22

Transverse: perpendicular to long axis of patient
Longitudinal: parallel to long axis of patient

Question 23

Which 3 structures need to be included when measuring bi-parietal diameter?

Answer 23

Cavum septum pellucidum
Thalamus
Choroid plexus

Question 24

What is the most sensitive marker of macrosomnia / IUGR?

Answer 24

Abdominal circumference

Question 25

Why does placental echogenecity increase with gestational age?

Answer 25

Increased fibrosis and calcium content

Question 26

Name 3 conditions that placentolmegaly is associated with

Answer 26

Diabetes
Fetal hydrops
Rh isoimmunisation

Question 27

Name the 3 different types of Doppler and their characteristic features

Answer 27

Colour Doppler: uses a computer to convert Doppler measurements into an array of colors to visualize the speed and direction of blood flow through a blood vessel.
Power Doppler: newer technique that is more sensitive than color Doppler, however, does not help the radiologist determine the direction of blood flow, which may be important in some situations.
Spectral Doppler - measurements are displayed graphically rather than visually

Question 28

How does 3D US work?

Answer 28

The transducer captures a series of images which are then processed into a 3D display by a computer

Question 29

Name four advantages of 3D US

Answer 29

Displays multiple longitudinal, transverse and coronal images
Images may improve the accuracy of anomaly detection of the fetal face, ears and distal extremeties
Provides a ‘cleaner’ image
Significantly improve the ability to identify cleft lips, spina bifida and polydactyl

Question 30

Name 5 advantages of US

Answer 30

Easily available
Can be performed quickly
Low cost (once the machine has been purchased)
Doesn’t utilise ionizing radiation – patient acceptability
Captured in real time and therefore can show the structure and movement of the body’s internal organs as well as blood flow measurements

Question 31

Name 5 limitations of US

Answer 31

Gestational age can affect what it is that is able to be seen
Assess structure not function
Difficult to distinguish between abnormal and normal variant
Ability to see things properly can be affected by a number of factors – high BMI, foetal position, uterine abnormalities, reduced amniotic fluid
Operator depedent