Basics of ultrasound

1. ULTRASOUND
IMAGING
1

2. Learning objectives
• Present an introduction to medical
ultrasonography at the level of a third or
fourth year medical student.
• After the brief course, the student should be
able to:
– Understand basic physics and terminology of
ultrasound
– State the advantages and disadvantages of
ultrasound
– Understand how the images are obtained
– Begin to interpret simple ultrasound images.

3. Outline
• Brief history of ultrasound technology
• Advantages, disadvantages
• What is ultrasound?
• Physics
• Probes, controls, machine, Doppler
• Terminology
• What structures look like
• Abdominal ultrasound
• Example of liver/gallbladder
• Quick review questions

4. History
• Medical use – 1940s
• Developing technology – 1950s
• Advancements – 1960s/1970s
• Real time ultrasound – 1980s
• 3D and 4D images – 1990s

5. Advantages
• Lack of radiation
• Quick, adaptable
• Looking at different layers/planes
• High resolution in low fat areas
• Portable
• Less expensive

6. Disadvantages
• Operator-dependent
• Depends on area to view
• Depends on body habitus of patient
• Artifact
• Location

7. What is ultrasound?
• Sound waves
• Waves have amplitude and frequency
• Frequency – measured in Hz
• Pulse-echo principle – crystals respond to
sound waves
• Ultrasound waves – transmitted well through
fluids and poorly through gases

8. What is Ultrasound?
• Ultrasound or ultrasonography is a medical
imaging technique that uses high frequency
sound waves and their echoes. The technique
is similar to the echolocation used by bats,
whales and dolphins, as well as SONAR used
by submarines.

9. In ultrasound, the following events
happen:
• The ultrasound machine transmits high-frequency (1 to 5 megahertz)
sound pulses into your body using a probe.
• The sound waves travel into your body and hit a boundary between
tissues (e.g. between fluid and soft tissue, soft tissue and bone).
• Some of the sound waves get reflected back to the probe, while some
travel on further until they reach another boundary and get reflected.
• The reflected waves are picked up by the probe and relayed to the
machine.
• The machine calculates the distance from the probe to the tissue or organ
(boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s)
and the time of the each echo's return (usually on the order of millionths
of a second).
• The machine displays the distances and intensities of the echoes on the
screen, forming a two dimensional image like the one shown below.

10. The Ultrasound Machine
• Transducer probe - probe that sends and receives the sound waves
• Central processing unit (CPU) - computer that does all of the calculations
and contains the electrical power supplies for itself and the transducer
probe
• Transducer pulse controls - changes the amplitude, frequency and
duration of the pulses emitted from the transducer probe
• Display - displays the image from the ultrasound data processed by the
CPU
• Keyboard/cursor - inputs data and takes measurements from the display
• Disk storage device (hard, floppy, CD) - stores the acquired images
• Printer - prints the image from the displayed data

11. Transducer probe
• Is the main part of the ultrasound machine.
• The transducer probe makes the sound waves and receives the echoes.
• The mouth and ears of the ultrasound machine. The transducer probe
generates and receives sound waves using a principle called the
piezoelectric (pressure electricity) effect, which was discovered by Pierre
and Jacques Curie in 1880.
• In the probe, there are one or more quartz crystals called piezoelectric
crystals.
• When an electric current is applied to these crystals, they change shape
rapidly. The rapid shape changes, or vibrations, of the crystals produce
sound waves that travel outward. Conversely, when sound or pressure
waves hit the crystals, they emit electrical currents.
• Therefore, the same crystals can be used to send and receive sound
waves. The probe also has a sound absorbing substance to eliminate back
reflections from the probe itself, and an acoustic lens to help focus the
emitted sound waves.

15. Physics
• Speed of ultrasound – average 1,540
m/second, but depends on tissue
• Acoustic impedance – density of tissue
multiplied by velocity of sound; harder
substances (like bone) usually have higher
acoustic impedance (than substances like
water or fat)

16. Terminology
• Echogenicity – measure of jumps in
impedance of an organ (NOT density)
• Hyperechoic – bright; many echos
• Hypoechoic – dark; few echos
• Anechoic – black; no echoes
• Shadowing

17. Frequencies
• Higher frequencies – better resolution but less
penetration [useful for thyroid, testes,
superficial blood vessels]
• Lower frequencies – better penetration but
worse resolution [useful for the abdomen,
aorta]

18. Orientation of probe
Head Feet
Transverse/axial
Head
Feet
Feet
Head
Coronal Longitudinal

19. Different probes
Linear probes Convex probes
Marker on right side of screen used to show scale

20. Ultrasound probe
Where pizoelectric
crystal is internally
Connects probe to cable,
which is connected to
ultrasound machine

21. How to hold an ultrasound probe

22. Types of probes – linear

23. Linear probes
Probe
Direction of waves

24. Linear
Image from UCMC

25. Types of probes – convex

26. Convex probes (also known as
‘curved’)
Direction of waves
Probe

27. Large convex
Large curved probe
Images from UCMC

28. Small convex
Small curved probe – similar to sector probe; used to picture a baby’s head
Images from UCMC

29. Ultrasound machine

30. Ultrasound machine - portable

31. 4 main controls
Doppler
Freeze
Depth
Gain

32. How to operate machine

33. Doppler
Images from UCMC
Color Doppler – blue and red show
flow of blood
Spectral Doppler – waveform showing
flow (same as color, but quantitative)
• Tells you direction of flow, and its
magnitude

34. Doppler
Images from UCMC
Color Doppler – kidney , showing
segmental arteries and veins
Spectral Doppler – right testicle with
low impedance arterial waveform
• A little more detail

35. What structures look like. . .

36. Pleural effusion - anechoic
Image from UCMC

37. Pleural effusion - anechoic
Image from UCMC
Pleural
effusion
Liver
Skin/abdo
minal wall

38. Coronal view neonatal brain
hydrocephalus – anechoic
Image from UCMC

39. Coronal view neonatal brain
hydrocephalus – anechoic
Image from UCMC
Mid-line
Lateral ventricles
Third ventricle
Posterior lateral
horns
Skull
Sylvian fissure

40. Conus medullaris – hypoechoic
Image from UCMC

41. Conus medullaris – hypoechoic
Image from UCMC
Vertebral body
Spinal cord in spinal canal
Posterior process

42. Kidneys – parenchyma hypoechoic
to liver
Image from UCMC

43. Kidneys – parenchyma hypoechoic
to liver
Image from UCMC
Liver
Kidney
Liver-
kidney
interface
Calyx
Cortex
Fat

44. Gallstones – hyperechoic and
shadowing underneath
Image from UCMC

45. Gallstones – hyperechoic and
shadowing underneath
Image from UCMC
Kidney
Gallstone
Gallbladder
Shadowing
Liver

46. Liver/gallbladder example
• Now – try to think of an ultrasound from start
to finish; we will take the example of a
liver/gallbladder ultrasound
• Liver parenchyma
• Ducts
• Vascular system
• Gallbladder, stones

47. Indications
• Hernia
• Tumors/cancers/metastasis
• Ascites
• Organomegaly
• Free peritoneal fluid s/p trauma
• Gallbladder or kidney stones
• Evaluation of liver anatomy and ducts
• Pancreatitis
• Abscess
• Appendicitis
• Ultrasound guided biopsy

48. Liver/gallbladder example
• NPO 4-6 hours – gallbladder distended and
bowel gas minimal
• Longitudinal, transverse, and coronal scans in
supine and left posterior oblique positions
• Subcostal approach good for most of liver, but
may need intercostal approach for most
superior part
• Use Doppler to distinguish blood vessels and
ducts

49. Abdominal ultrasound
• Layperson description (what your patient gets
told):
http://www.nlm.nih.gov/medlineplus/ency/ar
ticle/003777.htm
• Example of how to do an abdominal
ultrasound:
http://www.youtube.com/watch?v=7Y6wFXf
muvg

50. Liver/gallbladder anatomy
Middle hepatic vein
Gallbladder
Small bowel with
contrast
Distended bladder
Stomach
Image from UCMC

51. Liver/gallbladder anatomy
IVC coursing
through liver
Aorta passing
anterior to IVC
and bifurcating
into right and left
common iliac
arteries
Portal vein
formed by
SMV and
splenic
vein, going
to liver
Branches of SMA
and SMV
Image from UCMC

52. Liver/gallbladder anatomy
Spleen
Bowel
Liver
Right kidney
Left kidney
Image from UCMC

53. Liver/gallbladder
CT – sagittal cut U/S – longitudinal orientation
Liver Gallbladder Right kidney Liver Right kidney
Images from UCMC

54. Liver/gallbladder
CT – axial cut
Right, middle, and left hepatic veins
Right, middle, and left hepatic veins
Draining into the IVC
Draining into the IVC
U/S – transverse orientation
Images from UCMC

55. Liver/gallbladder
Liver
CT – axial cut
Kidneys
Gallbladder
U/S – transverse orientation
Liver Right kidney
Gallbladder
Splenic vein
Images from UCMC

56. Liver/gallbladder
U/S – transverse orientation
IVC
Pancreas
Left lobe of liver
Left kidney
Spleen
Splenic vein
CT – axial cut
Right portal vein
IVC
Aorta
Images from UCMC

57. Summary
• You should now understand ultrasound basics
• Physics, orientation, probes
• Terms, anatomy
• Much more to learn

58. Quick review questions
1. What is ultrasound? What types of tissues
does it travel well through? Poorly through?

59. Quick review questions
2. How does the frequency of the ultrasound
affect resolution and penetration?

60. Quick review questions
3. Name some types of hyperechoic,
hypoechoic, and anechoic tissues. Can you
picture them as they would appear on an
ultrasound image?

61. Quick review questions
4. What are some pros and cons of using
ultrasound?

62. Quick review questions
5. What shapes do the probes come in? Can you
describe a few of the differences of the probe
types?

63. Quick review questions
6. What are the three main ways in which the
ultrasound probe can be held (i.e. the
orientations of the probes)?

64. Quick review questions
7. Name at least three indications for an
abdominal ultrasound.
What are some of the things you could tell a
patient when they are preparing for an
abdominal ultrasound and orders you might
need to write?

65. Quick review questions
8. (Difficult) What are these ultrasound images
of? What do they show?

66. References
• Pediatric Sonography, by Siegel, 4th edition
• Ultrasound Teaching Manual, by Hofer: Thieme medical
publishers
• Abdominal Ultrasound: Step by Step, by Block, Thieme
medical publishers
• ACS Ultrasound for Surgeons, 1998
• http://www.ultrasound-images.com/liver.htm
• http://www.ultrasoundcases.info/
• http://www.genesis.net.au/~ajs/projects/medical_physics/ult
rasound/index.html
• http://www.radiologytoday.net/archive/rt_120108p28.shtml
• http://www.ultrasoundpaedia.com/

67. Questions?