Doppler sonography (2. LF UK)

Introduction
Doppler Sonography is a non-invasive imagery method used in medicine to assess the movement velocity of static as well as moving components of the body, i.e tissue and blood.

The doppler sonography technique, as its name indicates, is based on two physical principles: ultrasound and the doppler effect.

The term ultrasound refers to a high frequency sound wave outside the human hearing range. Consecutives ultrasound pulses are transmitted by a transducer towards a target before they are, in turn, reflected by this target. The reflected waves are detected by the transducer which acts as the transmitter and recipient of the ultrasound waves.

However, the emitted and reflected waves differ in wavelength and frequency. This phenomenon is described by the doppler frequency shift, characteristic for the doppler effect.

The frequency of sound waves, hence the sound pitch, changes according to the movement of the source which emits the waves. If the movements effects towards the detector, the frequency is higher -  from the detector the frequency is lower.

Therefore the emitted waves have a higher frequency than the reflected ones, detected by the transducer. The recorded signal is then translated into a graph which can be analyzed under different aspects.

Importance in clinical medicine
In clinical medicine doppler sonography mainly serves a diagnostic and preventive role and is used in almost all fields.

An analysis of the doppler spectrum, i.e the recorded signal, enables to detect any potential abnormalities. In vascular medicine, it is used to determine the state of the vessels, which allows to diagnose anomalies including stenosis, a peripheral occlusion of arteries and veins. In gynecology and obstetrics, doppler sonography is used for prenatal screening. This analysis is not only crucial to monitor the development of the fetus, but mostly to detect risk factors that can lead to stillbirths or obstructed labor, which can favor perinatal mortality.

Neurologists utilize sonography to prevent brain damage by recognizing cerebral occlusions, clots, bleeds and blockages of peripheral nerves.

Changes in perfusion of tissue can indicate to an oncologist, that a tumor is present. In this case doppler sonography is used to assess the extent of spread and whether the tumor is malicious or benign. By analyzing the blood flow  of an artery in terms of blood flow velocity, resistance and flow volume heart valve defects and congenital disorders in fetuses can be diagnosed by cardiologists.

Furthermore, doppler sonography is used to plan and monitoring interventions.

Literature Review
There are several advantages attributed to Doppler Sonography, the major one being offering information about the qualitative function of an organ in form of real time pictures, thus being a time effective method. Furthermore and most importantly it is non-invasive and pain free to the patient’s body. As very little to no harmful radiation is involved, the patient, as well as the health care practitioner are not likely to suffer from damages, in contrast to other frequently used diagnostic methods like the X-ray or the CT scan.

On the other hand, are there are four major disadvantages that can not be left unmentioned. First and foremost, the patient’s physical status influences the flow pattern, which makes a correct diagnosis more difficult, i.e if the patient is obese as the ultrasound waves have a limited reach. Moreover in the case of an abnormal narrowing of blood vessels, a condition known as stenosis, the device only displays changes in flow patterns if the stenosis is significantly prominent. Another hindering factor is the fact that bones do not allow the ultrasound beams to pass through. The aforementioned facts but also motion stemming from the patient not staying still can lead to a blurred image resolution.

In the medical field Doppler sonography is generally considered safe, even though it is not completely risk free to the human body. Due to absorption of the ultrasound energy in the body tissue, heat is produced on and inside the skin of the patient. The longer the same region is exposed to the sound waves the higher the temperature. During pregnancy this may have biological effects on the fetus’s developing brain and sensory organs, leading to birth defects. Furthermore, the waves can also cause cavitation in gas-filled tissue, which means that spaces of gas are enlarged. For the patient this can lead to mechanical stress in organs such as lungs and bowel. As a conclusion of these effects, the duration and also the number of examinations using this imaging method should be limited and especially during pregnancy.

From an ethical point of view concerns must be voiced in relation to obstetrics, where doppler sonography is part of the standard examination to assess the unborn’s health status and to detect possible fetal anomalies, as aforementioned. On the other hand, results obtained from the scan can lead to a dilemma, when indicating conflicting interests regarding maternal and fetal health. The challenge for the professional then consists in deciding on whose health to prioritize, naturally considering the mother’s wish, but especially basing their decision on their medical knowledge and ethical values.

The Equipment

 * 1) Conducting medium: Ultrasound gel
 * 2) Doppler-Sonography device
 * 3) Probe
 * 4) BiDop operating software

Methodology

 * 1) Turn on device and operating software
 * 2) Palpate optimal spot for examination
 * 3) Apply ultrasound gel to the to be examined area
 * 4) Choose a measuring angle and look for the optimal signal (all the selected categories should display data, systole and diastole should be clearly recognisable)
 * 5) Modification can be achieved by
 * 6) scaling the vertical axis
 * 7) changing the angle
 * 8) reversing the displayed direction of blood flow
 * 9) Analyse the obtained graph under different parameters: i.e Heart rate, blood flow velocity, 	 resistance, ratio of systole to diastole

Conclusion
Over the course of the last half decade the development on the field of diagnostic ultrasound has been rapid, the newest technology being 3D-imaging.

The development has not come to an end, au contraire; new techniques for volume blood flow estimation have emerged. Based on Gauss’s theorem, an angle-independent measurement is now possible; the theorem is based on the relation of the integrated flux of a vector field through a surface, and the divergence of the vector field in the closed surface, i.e the inside of the surface.

Doppler sonography improves diagnosis due to provision of immediate clinical information through imagery, hence the reduction of wrong diagnosis consequently a reduction of harm to the patient which could be caused by wrong treatments. On the financial side the immediate result reduce overall healthcare costs.