Doppler ultrasonography

SOME DETAILS ABOUT THE DOPPLER ULTRASONOGRAPHY AND ITS TYPES IN DIAGNOSTIC RADIOLOGY

1. DOPPLER ULTRASONOGRAPHY MAAJID MOHI UD DIN MALIK LECTURER COPMS ADESH UNIVERSITY BATHINDA PUNJAB

2. DOPPLER ULTRASONOGRAPHY Doppler ultrasonography is a non-invasive procedure that uses detectable changes in high frequency sound waves (2-20 MHz), based on the Doppler effect, to create clear digital images in real time. As a medical imagery method it is used for diagnostics, during medical procedures or for pathology research. It has been in medical use for several decades with no or little report of long-term side effects.

3. Thus is characterized as harmless, painless, cost-effective and generally widely available. It requires little or no prior patients’ preparation or aftercare. Predominantly, it is used to monitor the circulatory system by detecting direction, velocity and turbulence of blood flow, in order to provide information on possible blood clots, blocked vessels, cardiac or valve insufficiency.

4. PHYSICAL PRINCIPLES Doppler ultrasonography is based on two basic principles: Ultrasound principle High-frequency sound wave aimed at a target will be reflected back and detected.

5. DOPPLER PRINCIPLE Effect of changes in the sound pitch depending on the movement of the object in relation to the detector (positive or negative shift - the speed of sound in blood is 1570 m/s).

6. Piezoelectric crystals within the transducer or probe produce electrical pulses when vibrated by the returning wave (as with all ultrasonography gel medium is used). The transducer will send thousands of series of waves, which may be continuous or pulsed. If pulsed then pauses for detection of the returning waves are necessary. Upon detection, ultrasonograph calculates and determines the direction and depth of each returning sound wave. 

7. Thousands of such pulses sent and detected are computed and displayed in order to produce an image of the studied object, each detected wave displayed as pixel on the screen. Use of color helps in depicting direction and rate of blood flow, assisting the physician interpreting the results. It is important to note that there is no standard on colors used for depiction of effect or type of vessel, thus colors vary between manufactures or operating modes.

8. TYPES Color flow Doppler ultrasound Continuous wave Doppler ultrasound Duplex Doppler ultrasound

9. COLOR FLOW DOPPLER ULTRASOUND The use of color flow Doppler (CFD) or color Doppler imaging (CDI) (or simply color Doppler) sonography allows the visualization of flow direction and velocity within a user defined area. A region of interest is defined by the sonographer, and the Doppler shifts of returning ultrasound waves within are color-coded based on average velocity and direction.

10. CLINICAL USE Color flow Doppler is used frequently in sonography to semi quantitate overall blood flow to a region of interest. Depiction of the general velocity and direction of blood flow within the heart and blood vessels is of primary importance in  echocardiography  and vascular ultrasound respectively. It also allows the generation of unique phenomena such as the fluid color sign or the twinkling artifact, and allows the targeting of spectral Doppler for a quantitative assessment of blood flow.

11. CONTINUOUS WAVE DOPPLER ULTRASOUND With continuous-wave Doppler ultrasound, the emitting and receiving crystals function continuously and display information representative of all moving targets in the ultrasound beam. The continuous mode has no limitation of recordable velocities and therefore allows accurate measurement of high velocities. The signal, however, is not gated (it receives all underlying velocities); thus, spatial localization of the abnormal velocities is lacking.

12. DUPLEX DOPPLER ULTRASOUND A duplex ultrasound is a test to see how blood moves through your arteries and veins .

13. HOW THE TEST IS PERFORMED A duplex ultrasound combines: Traditional ultrasound: This uses sound waves that bounce off blood vessels to create pictures. Doppler ultrasound: This records sound waves reflecting off moving objects, such as blood, to measure their speed and other aspects of how they flow.

14. There are different types of duplex ultrasound exams. Some include: Arterial and venous duplex ultrasound of the abdomen. This test examines blood vessels and blood flow in the abdominal area. Carotid duplex ultrasound looks at the carotid artery in the neck. Duplex ultrasound of the extremities looks at the arms or legs. Renal duplex ultrasound examines the kidneys and their blood vessels.

15. PROCEDURE You may need to wear a medical gown. You will lie down on a table, and the ultrasound technician will spread a gel over the area being tested. The gel helps the sound waves get into your tissues. A wand, called a transducer, is moved over the area being tested. This wand sends out the sound waves. A computer measures how the sound waves reflect back, and changes the sound waves into pictures. The Doppler creates a "swishing" sound, which is the sound of your blood moving through the arteries and veins.

16. You need to stay still during the exam. You may be asked to lie in different body positions, or to take a deep breath and hold it. Sometimes during a duplex ultrasound of the legs, the health care provider may calculate an ankle-brachial index (ABI). You will need to wear blood pressure cuffs on your arms and legs for this test. The ABI number is obtained by dividing the blood pressure in the ankle by the blood pressure in the arm. A value of 0.9 or greater is normal.

17. A-MODE  A-mode is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy.

18. B-MODE In B-mode ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen.

19. M-MODE M stands for motion. In m-mode a rapid sequence of B-mode scans whose images follow each other in sequence on screen enables doctors to see and measure range of motion, as the organ boundaries that produce reflections move relative to the probe.

20. THE NATURE OF ULTRASOUND Ultrasonic waves are waves of frequency above the audible frequencies the human ear. In medical diagnostics are used ultrasound frequencies between 1 and 2 0 MHz The most important parameters describing the wave are : Wavelength Frequency Velocity Intensity

21. The first three characteristics are linked together by the formula: v = fl v–Velocity of ultrasound (approximately 1540 m/s in the soft tissues), f–Frequency in Hz l–Wavelength in m

22. THE MAIN COMPONENTS OF THE ULTRASONIC DEVICES Ultrasound device, essentially, consists of a transducer, transmitter pulse generator, compensating amplifiers, the control unit for focusing, digital processors and systems for display. It is used in cases of: abdominal, cardiac, maternity, gynecological, urological, cerebrovascular examination, breast examination, and small pieces of tissue as well as in pediatric and operational review.

23. THE INVERTER AND THE ULTRASOUND BEAM The inverter is a device that converts electrical signals into mechanical (ultrasonic vibrations), and vice versa. When activated inverter is leaned on the body, it emits an ultrasonic beam. Ultrasonic waves are focused by lenses, ultrasonic mirrors and by electronic means.

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