USG Colour Doppler



Doppler Ultrasound

The doppler shift principle has been used for a long time in fetal heart rate detectors. Further developments in doppler ultrasound technology in recent years have enabled a great expansion in it"s application in Obstetrics, particularly in the area of assessing and monitoring the well-being of the fetus, its progression in the face of intrauterine growth restriction, and the diagnosis of cardiac malformations.
Doppler ultrasound is presently most widely employed in the detection of fetal cardiac pulsations and pulsations in the various fetal blood vessels. The "Doptone" fetal pulse detector is a commonly used handheld device to detect fetal heartbeat using the same doppler principle.
Blood flow characteristics in the fetal blood vessels can be assessed with Doppler "flow velocity waveforms". Diminished flow, particularly in the diastolic phase of a pulse cycle is associated with compromise in the fetus. Various ratios of the systolic to diastolic flow are used as a measure of this compromise. The blood vessels commonly interrogated include the umbilical artery, the aorta, the middle cerebral arteries, the uterine arcuate arteries, and the inferior vena cava.
The use of color flow mapping can clearly depict the flow of blood in fetal blood vessels in a realtime scan, the direction of the flow being represented by different colors. Color doppler is particularly indispensible in the diagnosis of fetal cardiac and blood vessel defects, and in the assessment of the hemodynamic responses to fetal hypoxia and anemia.
Blood flow characteristics in the fetal blood vessels can be assessed with Doppler "flow velocity waveforms". Diminished flow, particularly in the diastolic phase of a pulse cycle is associated with compromise in the fetus. Various ratios of the systolic to diastolic flow are used as a measure of this compromise. The blood vessels commonly interrogated include the umbilical artery, the aorta, the middle cerebral arteries, the uterine arcuate arteries, and the inferior vena cava.
The use of color flow mapping can clearly depict the flow of blood in fetal blood vessels in a realtime scan, the direction of the flow being represented by different colors. Color doppler is particularly indispensible in the diagnosis of fetal cardiac and blood vessel defects, and in the assessment of the hemodynamic responses to fetal hypoxia and anemia.
A more recent development is the Power Doppler (Doppler angiography). It uses amplitude information from doppler signals rather than flow velocity information to visualize slow flow in smaller blood vessels. A color perfusion-like display of a particular organ such as the placenta overlapping on the 2-D image can be very nicely depicted. Doppler examinations can be performed abdominally and via the transvaginal route. The power emitted by a doppler device is greater than that used in a conventional 2-D scan. Its use in early pregnancy is therefore cautioned.
Doppler facilities are generally an integral part of modern ultrasound scanners. They merely would need to be switched on to function. One does not need to "go" to another machine for the doppler investigations.

3-D and 4-D Ultrasound

3-D ultrasound can furnish us with a 3 dimensional image of what we are scanning. The transducer takes a series of images, thin slices, of the subject, and the computer processes these images and presents them as a 3 dimensional image. Using computer controls, the operator can obtain views that might not be available using ordinary 2-D ultrasound scan. 3-dimensional ultrasound is quickly moving out of the research and development stages and is now widely employed in a clinical setting. It too, is very much in the News. Faster and more advanced commercial models are coming into the market. The scans requires special probes and software to accumulate and render the images, and the rendering time has been reduced from minutes to fractions of a seconds.
A good 3-D image is often very impressive to the parents. Further 2-D scans may be extracted from 3-D blocks of scanned information. Volumetric measurements are more accurate and both doctors and parents can better appreciate a certain abnormality or the absence of a certain abnormality in a 3-D scan than a 2-D one and there is the possibility of increasing psychological bonding between the parents and the baby.
An increasing volume of literature is accumulating on the usefulness of 3-D scans and the diagnosis of congenital anomalies could receive revived attention. Present evidence has already suggested that smaller defects such as spina bifida, cleft lips/palate, and polydactyl may be more lucidly demonstrated. Other more subtle features such as low-set ears, facial dysmorphia or clubbing of feet can be better assessed, leading to more effective diagnosis of chromosomal abnormalities. The study of fetal cardiac malformations is also receiving attention. The ability to obtain a good 3-D picture is nevertheless still very much dependent on operator skill, the amount of liquor (amniotic fluid) around the fetus, it"s position and the degree of maternal obesity, so that a good image is not always readily obtainable.

 


Obstetric Ultrasound


Obstetric Ultrasound is the use of ultrasound scans in pregnancy. The information obtained from different reflections are recomposed back into a picture on the monitor screen (a sonogram, or ultrasonogram). Movements such as fetal heart beat and malformations in the feus can be assessed and measurements can be made accurately on the images displayed on the screen. Such measurements form the cornerstone in the assessment of gestational age, size and growth in the fetus.
A full bladder is often required for the procedure when abdominal scanning is done in early pregnency. There may be some discomfort from pressure on the full bladder. The conducting gel is non-staining but may feel slightly cold and wet. There is no sensation at all from the ultrasound waves.


Transvaginal Scans

With specially designed probes, ultrasound scanning can be done with the probe placed in the vagina of the patient. This method usually provides better images (and therefore more information) in patients who are obese and/ or in the early stages of pregnancy. The better images are the result of the scanhead"s closer proximity to the uterus and the higher frequency used in the transducer array resulting in higher resolving power. Fetal cardiac pulsation can be clearly observed as early as 6 weeks of gestation.
Vaginal scans are also becoming indispensible in the early diagnosis of ectopic pregnancies. An increasing number of fetal abnormalities are also being diagnosed in the first trimester using the vaginal scan. Transvaginal scans are also useful in the second trimester in the diagnosis of congenital anomalies.