How does ultrasound work to give information about organs?
The ultrasound machine (probe or scan head) generates sound waves of a particular frequency (which we cannot hear). These waves, when they pass through an organ, get reflected back to the scan head. Depending on the structure and texture of the organ (whether fluid or solid, dense or thin, transparent or opaque), the reflected waves form patterns on the screen which are then interpreted by the sonologist.
The images appear as grey dots of various brightness levels and these dots are known as ‘echoes’. A person has to be specially trained to be able to interpret these echoes.
Ultrasound seems to be the most commonly advised investigation these days. What are the uses of ultrasound in gynaecology and obstetrics?
Yes, ultrasound is probably one of the most important advances in the field of medicine in the past few years. It gives information about the structure of organs and their relationship to each other. Today, we can study blood flow patterns to various organs and also the ‘hardness’ and ‘elasticity’ of organs.
In gynaecology, ultrasound helps us to measure the size of the uterus, cervix and ovaries and to diagnose any abnormality in these organs. It can tell us if there is fluid or any tumour in the pelvis and also the relationship of the tumour to the various surrounding organs.
Normal fallopian tubes are not seen on ultrasound, however, thickened tubes or tubes filled with fluid or pus or blood; or ectopic pregnancy can be diagnosed by ultrasound.
In gynaecology, ultrasound is commonly used in the following conditions:
Fibroids – to assess the size, location and number
Ovarian cysts – to assess the size, number, type (simple, blood filled, benign or malignant)
Infertility – to assess development of the follicle (egg) throughout the menstrual cycle and also the development of the uterine lining and blood flow patterns to understand ovulation and implantation of the fertilised egg
Endometriosis – to diagnose chocolate cysts
Irregular/heavy periods – To measure the thickness of the uterine lining (endometrium) and diagnose polyps or any other abnormalities therein.
PCOS – To diagnose polycystic ovaries
In obstetrics, ultrasound is the single most important tool to study the foetus.
Using ultrasound, we can diagnose the following conditions:
- Foetal organs and any abnormality therein – such as heart, brain, kidney or skeletal defects
- Foetal growth – through serial measurements
- Amount of liquor amnii (fluid in the uterus)
- Placenta – whether it is low-lying or abnormal or blood flows are reduced
- Umbilical cord – whether there are loops of cord around the foetal neck or if there are any cord abnormalities
- Blood flow to the foetus can be studied in great details
- Oxygenation of the foetus (whether the foetus is receiving adequate oxygen for brain development and survival) can be studied in high risk pregnancies so that decision can be taken regarding timing of delivery and whether to permit normal vaginal delivery or perform caesarean section
- Assessing the risk for genetic abnormalities such as Down’s syndrome (nuchal translucency assessment)
- Premature shortening or opening of the cervix
Ultrasound is actually ‘seeing’ the organs in question. ‘Seeing is believing’. That means ultrasound is the ultimate tool. It cannot go wrong. Isn’t it?
Unfortunately, that is not true. Ultrasound imaging depends on image quality (which depends on various factors) and the interpretation of the image also depends on many aspects.
There is scope for errors due to various factors such as follows:
- The sonologist (the doctor performing the scan): Ultrasound imaging depends on the interpretation of the doctor. Two doctors may interpret the same image differently depending on their experience and expertise.
- The machine: More advanced machines give more accurate images and thus the chances of errors are minimised. However, the doctor has to be technically well-versed with the machine to be able to utilise all the faculties and get the best possible image.
- The patient: If the patient is very obese, the image quality is inferior as ultrasound waves do not pass well through fatty tissue and also the image quality deteriorates with increasing depth in the obese patient (increased distance between the probe and the organ).
- The organ: Certain organs are not viewed as clearly on ultrasound such as the normal fallopian tube or appendix. Similarly, normal intestine loops are not seen very clearly due to presence of gas in the abdomen as ultrasound waves do not pass very well through gas.
Deeply situated organs such as the pancreas or deeply situated lymph nodes are relatively difficult to study.
The uterus and ovaries cannot be seen on abdominal ultrasound unless the urinary bladder is filled with urine (fluid) because ultrasound waves pass easily through clear fluid. The bladder thus creates a window for viewing the pelvic organs. Hence, you are always asked to drink plenty of fluids before a pelvic scan.
- The type of imaging: In gynaecology and obstetrics, transvaginal sonography (internal sonography) is a very useful tool to view the uterus and ovaries clearly. The image quality is far better and larger and the study is harmless to the foetus too.
- The disease: Certain conditions such as reduced amniotic fluid (oligohydramnios) make it very difficult to study the foetal organs (as fluid is needed for ultrasound waves to pass through easily).
Thus ultrasound plays an invaluable role in the diagnosis of gynaecological diseases and pregnancy conditions. But you must understand its limitations as well.