21 Intro to ultrasound imaging

Question 1

Diagnostic ultrasound

Answer 1

• Ultrasound uses short sound pulses that are transmitted into the body
• Sound pulses can be reflected, scattered, refracted or absorbed
• Combined effects of reflection, scattering and absorption result in attenuation in the intensity of the sound pulse as it travels through matter
• Attenuation limits the depth of imaging and is greater at higher transmit frequencies

Question 2

Advantages of ultrasound?

Answer 2

• Safe
• No ionising radiation
• Equipment required is portable, compact and relatively inexpensive

Question 3

Disadvantages of ultrasound?

Answer 3

• Highly operator dependent
• Structures surrounded by bone e.g. brain and spinal cord, don’t give clinically useful image
• Attenuation of ultrasound signal at air/ tissues boundaries means the technique is not suitable for imaging structures in the lung or abdominal organs obscured by gas in the overlying bowel
• Can heat tissues slightly
• In some cases, can produce small pockets of gas in body fluids or tissues (cavitation)

Question 4

Ultrasounds transducer

Answer 4

• Ultrasound is produced and detected using an ultrasound transducer
• Capable of sending an ultrasound and then the same transduce can detect the sounds and convert it to an electrical signal tube diagnosed

Question 5

What are piezoelectric crystals?

Answer 5

• Ceramic crystals that deform and vibrate when they are electronically stimulated generate the sound pulses used for diagnostic sonography
• Echoes that return to the transducer distort the crystal elements and generate an electric pulse that is processed into an image

Question 6

What are the types of transducers/ probes?

Answer 6

1. Linear array probe
2. Curved array probe
3. Phased array probe
4. Intraluminal probe

Question 7

Linear- array transducers

Answer 7

• Images obtained with linear arrays have a flat superficial surface
• High frequency probe - doesn’t penetrate deeply into tissues so only useful for superficial structures

Question 8

Curved-array transducers

Answer 8

• Images obtained with curved array have a curved superficial surface
• Probes with short radius of curvature used for endoluminal scanning and probes with a larger radius used for general abdomen and obstetrical scanning

Question 9

Phased-array transducer

Answer 9

• Because the sounds beams are steered at varying angles from one side of the transducer to the other, a sector image format is produced
• Probe is smaller and capable of scanning in areas where acoustic access is limited - e.g. ribs

Question 10

Intraluminal probes

Answer 10

• Small transducers that can be placed within various body lumens
• Images are higher quality
• Endovaginal and endorectal transducers commonly used

Question 11

What is the most commonly used ultrasound mode?

Answer 11

Brightness or B-mode

Question 12

Ultrasound probe manipulation manoeuvres “PART”

Answer 12

• Pressure
• Alignment
• Rotation
• Tilt

Question 13

What is lithotripsy?

Answer 13

• Stones present in urinary system are crushed into small sand like particles by vibratory impulses generated by biphasic, ultrasound shock waves
• Small particles then excreted in urine

Question 14

What is point-of-care ultrasound (POCUS)?

Answer 14

Defined as a goal-directed bedside ultrasound examination performed by a healthcare provider to answer a specific diagnostic question or to guide performance of an invasive procedure