Ultrasonagraphy Flashcards
What are ultrasounds?
Sound waves with frequencies higher than the human audible range,
The upper limit is considered to be approximately 20kHz
What are the functions of the ultrasound probe?
The ultrasound probe has 2 main functions
- Emit a sound wave
- Receive echoes from the original wave
What is the pulse echo principle?
This is the foundation principle of all Ultrasound applications and technology
Whenever the ultrasound wave passes through a tissue boundary it can be reflected or will pass through and continue propogating
Describe how tissue density affects the amount of sound wave reflected
Adjacent tissues with varying densities will reflect more of the sound wave, adjacent tissues with similar densities will reflect less..
Eg Air in lungs creates a poor image
What does an ultrasound image look like?
Gray scale is traditional for ultrasound
Dense bone reflects back at higher altitudes than less dense tissues ∴ denser areas shown in white
How is fluid shown in ultrasound images?
Fluid (e.g. urine, bile, cysts, amniotic fluid) doesn’t contain v. dense materials for ultrasound to reflect back off so produces a dark black image
What are the clinical applications of ultrasound?
Obstetrics Gynaecology Abdominal Urinary Trauma - POCUS Testicular Breast Head / neck Vascular Cardiology Musculoskeletal (MSK) Lungs
Outline the pros of using ultrasound
🗸 No radiation 🗸 No documented side effects in humans 🗸 Usually non invasive 🗸 Well tolerated 🗸 “real time” imaging 🗸 Results can often be available immediately – Bedside 🗸 Widely Accessible
What are the cons of ultrasound use?
⨯ Ultrasound image quality is highly dependant on patient habitus
⨯ No known side effects?
⨯ Training is more resource intensive for departments compared to other modalities
⨯ Effectiveness and accuracy are highly operator dependant
Why is there a variety of transducers available?
Important to have a selection as an increased choice of technical variables allows for optimisation of your image
Choice over sector width, scan depth (resolution), patient habitus, field of view..
What is the major advantage of Ultrasound over X-ray / CT in obstetric imaging?
All women in the UK are offered ultrasound Screening during pregnancy (12/20 weeks)
Scan Preparation?
If there is a problem, what happens?
How big is a fetus typically at 12 wk scan?
Fetus is approximately 45-84mm in length (11+2wks – 14wks)
What is the purpose of the 12 week scan?
First routine scan offered to most low risk pregnancies
Detects ‘Viability’, number of fetus’,
What can we identify at the 12 week scan?
Gross anatomy, detectable major abnormalities, morphology of ovaries and an accurate gestational age of the fetus
What are common abnormalities detected at 12 weeks?
- Body Stalk Defect 1:14-30,000
- Blighted Ovum / Missed
- Cystic Hygroma
10% survival rate - Molar Pregnancy 1:1000
What are the chances of miscarriage throughout a pregnancy?
1 / 4 pregnancies from the start will result in miscarriage
After 12 weeks of pregnancy the chances of miscarriage decrease
What causes downs syndrome (DS)?
Down’s syndrome is caused by a change in one of the genes in the egg before fertilisation (at the time of conception); Usually completely random, though more common in older mothers
What is the frequency of DS around the world?
Throughout the world, the frequency of DS is ~3 per 2000 births.
Outline incidence rates of DS
1: 1500 at 20 years
1: 800 at 30 years
1: 270 at 35 years
1: 100 at 40 years
1: 50 at 45 years and over
How is DS detected using ultrasound?
Fetal nuchal translucency (NT) screening uses ultrasound to measure size of nuchal pad at nape of fetal neck
It should be performed between 11 weeks and 13 weeks + 6 days
What physical changes can we identify using ultrasound in DS babies?
In DS, NT is much thicker around 3mm
Also have lack of nasal bone (soft marker for DS)
How can a maternal blood test help identify DS?
Maternal blood test can identify different DS markers e.g enzyme gene mutations
Can be tweaked to optimize chances of healthy baby
What is the purpose of the 20 week scan?
The purpose of the 20 week scan in England is to identify abnormalities which:
- may indicate the baby has a life-limiting condition
- may benefit from antenatal treatment
- may require early intervention following delivery
What are other aims of the 20 week scan?
Other standard aims;
- Placenta localisation
- Fetal Biometry
- Fibroid Monitoring
- Liquor Assessment
