Ultrasonagraphy Flashcards
What is ultrasound?
They are 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..
E.g. 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 disadvantages of ultrasound.
PROS:
- no radiation
- no documented side effects in humans
- usually non-invasive
- results can be available immediately (bedside)
- widely accessible
- well-tolerated
- ‘real time’ imaging
CONS:
- ultrasound image quality is highly dependent on patient habitus
- no KNOWN side effects
- 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?
The increased choice of technical variables allows for optimisation of your image.
We have a choice over sector width, scan depth (resolution), patient habitus, field of view, etc.
Describe the obstetric (12 week scan) ultrasound.
The foetus is approximately 45-84mm in length (11+2wks – 14wks).
It is the first routine scan offered to most low risk pregnancies.
It detects the ‘viability’, number of fetus’, gross anatomy, detectable major abnormalities, morphology of ovaries, etc.
It also gets an accurate gestational age of the foetus.
How can the 12 weeks obstetrics 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.
Foetal nuchal translucency (NT) screening uses ultrasound to measure the size of the nuchal pad at the nape of the fetal neck. This should be performed between 11 weeks and 13 weeks + 6 days.
We take a small sample of fluid from the back of the neck. The more fluid there is, the more increased risk there is of the foetus developing Down’s.
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
- foetal 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 week 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?
It can be used to highlight the affects of pre-eclampsia and intrauterine growth restriction (IUGR).
It is used more frequently now as is being suggested we can improve perinatal mortality and morbidity.
What is an ectopic pregnancy?
It is when an egg implants outside of the uterine cavity; it is know as an ectopic pregnancy.
It is associated with severe pain and bleeding.
It can be caused by tubal damage (from surgery, PIDS, endometriosis).
Treatment depends on the individual (if it will be medical or surgical).
Describe how an early pregnancy (EPU) 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 foetal pole is detected as an area of thickening along the periphery of a yolk sac.
There should be a minimum of 1-2mm in length for detection (5-6 weeks)
The cardiac activity should also be detected routinely from 4-5mm (6 weeks).
Describe multiple pregnancies.
Multiple pregnancy are 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).
