ULTRA SOUNDIN

MEDICAL IMAGING

Mohammad AmirFinal Year MBBSJJMMC

WHAT IS MEDICAL IMAGING

?

MEDICAL IMAGING: The techniques and processes used to create image of the internal as well as external human body parts for clinical purpose .

Why medical imaging is required?Medical imaging provides a pictorial status of

particular organ which is to be treated

It makes a surgical targets more clear and precise

It provides a pictorial status of fetus

development right from 4th weak to 36th- 38th week

It make therapeutic targets easy to detect and treat

TYPES OF MEDICAL IMAGING WIDELY USED

X-RAYMAMOGRAPHYCONTRAST RADIOGRAPHYULTRA SOUNDCT SCANMRISPECT(SINGLE PHOTON EMMISION TOMOGRAPHY)

PET(POSITRON EMISSION TOMOGRAPHY)

PIZOELECTRIC IS DEVELOPED BY THE CURIES IN 1880 USING NATURAL QUARTZ

SONAR was first time used in war time 1940

Diagnosis medical application in use since late 1950’s

WHAT IS ULTRA SOUND

?

ULTRA SOUND : MEDICAL DEFINATION!!!DIGNOSTIC MEDICAL

ULTRASOUND IS THE USE OF HIGH FREQUENCY SOUND TO AID IN DIGNOSIS AND TREATMENT OF PATIENT.

FREQUENCY RANGES USED IN MEDICAL ULTRASOUND ARE 2-15 MHZ

Piezoelectric Effect

Definition: The principle of converting energy by applying pressure to a crystal.

The reverse of the piezoelectric effect converts the energy back to its original form

piezoelectric effect Ultrasound Transducers

•A transducer converts one type of energy into another

• Based upon the

:pulse-echo principleoccurring with ultrasound piezoelectriccrystals, ultrasound transducers convert:

– Electricity into sound = pulse– Sound into electricity = echo

Ultrasound ProductionTransducer contains piezoelectric

elements/crystals which produce the ultrasound pulses (transmit 1% of the time)

These elements convert electrical energy into a mechanical ultrasound wave

PULSE• Pulse of sounds is send to soft tissues

•Sound interaction with soft tissues= bio effect

•Pulsing is determined by transducer or probe crystal and ins not operated or control

ECHOECHO IS PRODUCED BY SOFT TISSUESTISSUE INTRACTION WITH SOUND = ACOUSTIC PROPAGATION PROPERTIES

ECHOES ARE RECEIVED BY THE TRANSDUCER CRYSTAL

ECHOES ARE INTRPRETED AND PROCESSED BY ULTRA SOUND MACHINE

Refraction

Incident

reflective

refraction

Angle of incidence = angle of reflection

Scattered

echoes

The Returning EchoReflected echoes return to the scan head where the piezoelectric elements convert the ultrasound wave back into an electrical signal

The electrical signal is then processed by the ultrasound system

FACTORS AFFECTING ULTRASOUNDFREQUENCYWAVELENGTHBANDWIDTHATTENUATIONTIME GAIN COMPENSATION

Piezoelectric Crystals

The thickness of the crystal determines the frequency of the scan head

Low Frequenc

y3 MHz

High Frequency

10 MHz

FREQUENCY AND RESOLUTION

HIGH FREQUENCY = HIGH RESOLUTION

3.5 MHz(sector)

7.5 MHz(linear)

DYNAMIC RANGEDecreased DR Increased DR

B-MODE M-MODE

Color Doppler Power Doppler

MACHINE COMPONENTTransducer probe

CPU(central processing unit)Transducer pulse

controlDisplay Keyboard /cursor

Disk storage device Printer

Transducer Design

Size, design and frequencydepend upon theexamination

Image FormationElectrical signal produces ‘dots’ on the

screen

Brightness of the dots is proportional to the strength of the returning echoes

Location of the dots is determined by travel time. The velocity in tissue is

assumed constant at 1540m/sec Distance = Velocity

Time

‘B’ mode

Image Formation

• Acoustic impedance (AI) is dependent on the density of the material in which sound is propagated

- the greater the impedance the denser the material.

• Reflections comes from the interface of

different AI’s• greater of the AI = more signal

reflected• works both ways (send and receive

directions)

Interactions of Ultrasound with Tissue

Attenuation & GainSound is attenuated by tissue

More tissue to penetrate = more attenuation of signal

Compensate by adjusting gain based on depthnear field / far field

AKA: TGC

Ultrasound Gain

Gain controlsreceiver gain only

does NOT change power output

think: stereo volumeIncrease gain =

brighterDecrease gain = darker

Balanced Gain

Gain settings are important to obtaining adequate images.

balancedbalanced

bad near fieldbad near field bad far fieldbad far field

Reflected Echo’sStrong Reflections = White dots

Diaphragm, tendons, bone

‘Hyperechoic’

Weaker Reflections =

Grey dots

Most solid organs,

thick fluid – ‘isoechoic’

Reflected Echo’s

Reflected Echo’sNo Reflections = Black dots

Fluid within a cyst, urine, blood‘Hypoechoic’ or echofree

Ultrasound Beam Profile

Beam comes out as a sliceBeam ProfileApprox. 1 mm thick

Depth displayed – user controlled

Image produced is “2D”tomographic slice

assumes no thicknessYou control the aim

1mm

Goal of an Ultrasound System

The ultimate goal of any ultrasound system is to make like tissues look the same and unlike

tissues look different

Accomplishing this goal depends upon...

Resolving capability of the systemaxial/lateral resolution

spatial resolutioncontrast resolutiontemporal resolution

Processing Powerability to capture, preserve and display

the information

Ultrasound Applications

Visualisation Tool:

Nerves, soft tissue masses

Vessels - assessment of position, size, patency

Ultrasound Guided Procedures in real time – dynamic imaging; central venous access, nerve blocks

Imaging

Know your anatomy – Skin, muscle, tendons, nerves and vessels

Recognise normal appearances – compare sides!

Epidermis

Loose connective tissue and subcutaneous fat is hypoechoic

Muscle interface

Muscle fibres interface

Bone

Skin, subcutaneous tissue

Summary

• Frequency & wavelength are inversely proportional

• Attenuation & frequency are inversely related

• Resolution determines image clarity

• Electronic Arrays may be sector or linear

• Display mode chosen determines how image is registered

• Diagnostic Medical Ultrasound is safe!

conclusion

• Imaging tool – Must have the knowledge to understand how the image is formed

• Dynamic technique

• Acquisition and interpretation dependant upon the skills of the operator.