Diagnostic Ultrasound. Sutiporn Khampunnip, M.D.

Transcription

1 Diagnostic Ultrasound Sutiporn Khampunnip, M.D.

2 Definition of Ultrasound Ultrasound is simply sound waves, like audible sound. High-frequency sound and refers to mechanical vibrations above 20 khz. Human ears can hear sounds with frequencies between 20 Hz and 20 khz.

3 Ultrasound frequencies commonly used for medical diagnosis are between 2 MHz and 15 MHz.

4 Generation of ultrasound pulse Ultrasound transducers (or probes) contain multiple piezoelectric crystals which are interconnected electronically and vibrate in response to an applied electric current.

5 Imaging by ultrasound Ultrasound imaging is performed by emitting a pulse, which is partly reflected from a boundary between two tissue structures, and partly transmitted The reflection depends on the difference in impedance of the two tissues. Different structures will reflect different amount of the emitted energy, and thus the reflected signal from different depths will have different amplitudes as shown below. The time before a new pulse is sent out, is dependent of the maximum desired depth that is desired to image.

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7 Ultrasound wave length and frequency Proper selection of transducer frequency is an important concept for providing optimal image resolution in diagnostic and procedural US. High-frequency ultrasound waves (short wavelength) generate images of high axial resolution. Low-frequency waves (long wavelength) offer images of lower resolution but can penetrate to deeper structures due to a lower degree of attenuation

8 Ultrasound Instruments Ultrasound machines convert the echoes received by the transducer into visible dots, which form the anatomic image on ultrasound screen A linear transducer can produce parallel scan lines and rectangular display, called a linear scan Curved transducer yields a curvilinear scan and arcshaped image

9 Bioeffect and Safety Ultrasound application could produce a biologic effect can be characterized into two aspects: heating and mechanical. The generation of heat increases as ultrasound intensity or frequency is increased.

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11 Curved transducer

12 linear transducer

13 Transvaginal transducer

14 4 4 D transducer

15 Ultrasound mode A mode is the oldest ultrasound modality Simple one-dimensional ultrasound image is generated

16 B mode Two-dimensional image of the area B mode can provide a cross sectional image through the area of interest

17 Doppler mode Produces a color-coded map of Doppler shifts superimposed onto a B-mode ultrasound image Blood flow direction depends on whether the motion is toward or away from the transducer. Selected by convention, red and blue colors provide information about the direction and velocity of the blood flow.

18 Power Doppler mode Up to five times more sensitive in detecting blood flow than color Doppler and it is less dependent on the scanning angle. Not provide any information on the direction and speed of blood flow

19 M mode A single beam in an ultrasound scan can be used to produce a picture with a motion signal Movement of a structure such as a heart valve can be depicted in a wave-like manner.

20 Liver abscess Liver abscesses are typically poorly demarcated with a variable appearance, ranging from predominantly hypoechoic (still with some internal echoes however) to hyperechoic. Gas bubbles may also be seen. Doppler will demonstrate absence of central perfusion.

21 Cirrhosis

22 Acute cholecystitis

23 Pancreatitis

24 Renal calculi and hydronephrosis

25 Appendicitis

26 Torsion testis VS orchitis

27 Urinary bladder lesion

28 Other bowel lesion