18. Ultrasonography Flashcards
What is ultrasound?
Sound waves with frequencies higher than the human audible range, the upper limit is considered to be approximately 20kHz
What is the pulse echo principle?
- The ultrasound probe has 2 main functions, to first emit a sound wave and then to receive the echoes from the original wave. 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.
- 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 are some clinical applications of ultrasonography?
MAINLY:
- obstetrics
- gynaecology
- abdominal
- urinary
ALSO:
- trauma - POCUS
- testicular
- breast
- head/neck
- vascular
- cardiology
- musculo-skeletal (MSK)
- lungs
List the advantages and disdavantages of ultrasound.
PROS: - 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
CONS:
- No known side effects?
- Ultrasound image quality is highly dependant on patient habitus
- Training is more resource intensive for departments compared to other modalities
- Effectiveness and accuracy are highly operator dependent
Why do we have a selection of types of transducers?
Increased choice of technical variables allows for optimisation of your image.
Choice over sector width, scan depth (resolution), patient habitus, field of view etc.
Describe the obstetric (12 wees scan) ultrasound.
- Foetus is approximately 45-84mm in
Length (11+2wks – 14wks) - First routine scan offered to most low
Risk pregnancies - Detects ‘Viability’, number of foetus’,
Gross anatomy, detectable major abnormalities, morphology of ovaries and an accurate gestational age of the foetus.
How can the 12 weeks obstetric scan be used to screen for Down’s Syndrome?
Down’s syndrome is caused by a change in one of the genes in the egg before it is fertilised by the sperm (at the time of conception). This is usually a completely random happening, though it is more common in older mothers. Throughout the world, the frequency of DS is about 3 per 2000 births.
Fetal nuchal translucency (NT) screening uses ultrasound to measure the size of the nuchal pad at the nape of the fetal neck. It should be performed between 11 weeks and 13 weeks + 6 days
Describe the obstetric (20 week scan) ultrasound.
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
Other standard aims;
- Placenta localisation
- Fetal Biometry
- Fibroid Monitoring
- Liquor Assessment
List some abnormalities that can be detected at the 20 week scan.
- spina bifida
- achondroplasia: thickened soft tissue surrounding the long bones
- low-lying placenta
- talipes (club foot)
Describe how you can detect a low lying placenta at the 20 weeks scan.
- In England at the 20 week scan we measure the distance from the lowest edge of the placenta to the internal OS of the cervix.
- If the placenta is within 2.5cm of the cervix then future scans are required.
- If the placenta does not raise higher closer to the due date then a C-Section may be required.
What is the use of the umbilical artery doppler assessment?
Can be used to highlight the affects of pre-eclampsia and intrauterine growth restriction (IUGR)
Is used more frequently now as is being suggested we can improve perinatal mortality and morbidity.
What is an ectopic pregnancy?
When an egg implants outside of the uterine cavity it is know as an ectopic pregnancy
Associated with severe pain and also bleeding
- Can be caused by tubal damage (from surgery, PIDS, endometriosis)
- Treatment depends on the
Individual, Medical or surgical.
Describe how an early pregnancy is detected.
Pregnant women can be referred by their GPs in cases of lower abdominal/pelvic pain, bleeding, confirmed history of recurrent miscarriage and sometimes due to previous obstetric history issues.
- The fetal pole is detected as an area of thickening along the periphery of a yolk sac
- Minimum of 1-2mm in length for detection (5-6 wks)
- Cardiac Activity should be detected routinely from 4-5mm (6wks)
Describe multiple pregnancies
Multiple pregnancy usually caused by delays in the fertilized egg reaching the womb before implanting.
It can be dichronic or monochronic
Describe fibroids.
Fibroids consist of fibrous muscular tissue, many eventually grow until the
blood supply they receive can no longer support further growth, but others can
get very large and require surgical interventions ( myomectomy / uterine
embolisation / hysterectomy)
