ULTRASOUND IN MEDICAL DIAGNOSTICS

Prof. Ivo Hrazdira, MD., DSc.

WHAT IS ULTRASOUND?

• Acoustic vibrations of frequencies higher than 20 kHz, non audible by human ear

• According to the type of interaction with cells and tissues: - ACTIVE ULTRASOUND – high intensity (applications in physical therapy and surgery) - PASSIVE ULTRASOUND – low intensity (applications in medical diagnostics)

ACOUSTIC PARAMETERS

• Source:

- FREQUENCY - INTENSITY

• Medium: - SPEED OF PROPAGATION - ACOUSTIC IMPEDANCE - ATTENUATION: - absorption . - scattering

DIAGNOSTIC ULTRASOUND

• PHYSICAL PRINCIPLE ULTRASONIC WAVES PASSING THROUGH THE BODY ARE PARTIALLY REFLECTED ON TISSUE INTERFACES. REFLECTIONS (ECHOES) ARE RECEIVED, PROCESSED AND DISPLAYED

HISTORY OF ULTRASOUND

PREPARATORY PERIOD• 1842 - DOPPLER: PRINCIPLE OF FREQUENCY SHIFT• 1880 - BROTHERS CURIE: DISCOVERY OF PIEZOELECTRIC PHENOMENON• 1916 - LANGEVIN AND CHILOWSKI: CONSTRUCTION OF THE FIRST ULTRASOUND GENERATOR (SONAR)• 1929 - SOKOLOV: BASIS OF NON-DESTRUCTIVE ULTRASOUND MATERIAL TESTING

HISTORY OF DIAGNOSTIC ULTRASOUND

FIRST ATTEMPS

• 1942 - DUSSIK: HYPERPHONOGRAPIE (TRANSMISSION METHOD)

• 1949 - KEIDEL: HEART VOLUME MEASUREMENT

• 1949 - UCHIDA: A-MODE ENCEPHALOGRAPHY

• 1950 - WILD: TISSUE DIFFERENTIATION

• 1951 - WAGAI: BILL STONE DETECTION

HISTORY OF DIAGNOSTIC ULTRASOUND

• 1942 - FIRST ATTEMP - UNSUCCESSFUL

CLINICAL APPLICATIONS• 1950 - 1D IMAGING (A- MODE)• 1954 - ECHOCARDIOGRAPHY (M-MODE)• 1955 - 2D - IMAGE OF ABDOMEN (B - MODE)• 1958 - 2D - IMAGING IN OBSTETRICS• 1958 - 2D - IMAGING IN OPHTHALMOLOGY• 1968 - TRANSRECTAL EXAMINATION• 1968 - FIRST CONTRAST IMAGING (SALINE)

HISTORY OF DIAGNOSTIC ULTRASOUND

CLINICAL APPLICATIONS (CONTINUED)• 1978 - TRANSESOPHAGEAL EXAMINATION• 1990 - BROAD-BAND TRANSDUCERS• 1992 - 3D IMAGING IN OB/GYN• 1992 - TRANSPULMONARY ECHOCONTRAST

AGENTS• 1996 - NATIVE HARMONIC IMAGING• 1998 – 4D (3D imaging in real time)

DIAGNOSTIC DEVICE

• MAIN PARTS OF A DIAGNOSTIC DEVICE

• ELECTROACOUTIC TRANSDUCER

• GENERATOR OF ELECTRIC IMPULSES

• PROCESSING OF RECEIVED ECHOES

• DISPLAY

• RECORDING SYSTEM

DIAGNOSTIC DEVICES

TRANSDUCERS (imaging lines)

TRANSDUCERS sector convex linear

transvaginal/transrectal transesophageal

DIAGNOSTIC ULTRASOUND

• IMAGING METHODS: - A MODE (one-dimensional) - B MODE (two-dimensional,

three-dimensional)

• DOPPLER METHODS: - CW - PULSED - COLOUR

• COMBINED METHODS (duplex, triplex)

PRINCIPLE OF A- AND B- IMAGING

DIAGNOSTIC FREQUENCIES

• 2 - 6 MHz abdominal ultrasound, obstetrical and gynaecological exam, echocardiography, transcranial Doppler

• 7.5 - 14 MHz small parts, vascular Doppler, musculoskelatal ultrasound

DIAGNOSTIC FREQUENCIES

• 10 - 20 MHz ophthalmology, special vascular exam

• 20 - 50 MHz endoluminal exam, ultrasound biomicroscopy (ophthalmology, dermatology)

A- AND B- MODE IN OPHTHALMOLOGY

B- MODE IN ABDOMINAL REGION

B- MODE IN OBSTETRICS

B- MODE IN MUSCULOSKELETAL ULTRASOUND

Meniscal TearMeniscal Tear

B- AND M- MODE IN CARDIOLOGY

PROGRESS IN ULTRASONOGRAPHY

• IMPROVED IMAGE DISPLAY

- digital technology

- 3D/4D imaging IMPROVED SIGNAL DETECTION

- echo-enhancing agents

- harmonic imaging

PROGRESS IN ULTRASONOGRAPHY

• NOVEL METHODS

- anisotropic imaging

- perfusion imaging

- elastography• NOVEL APPLICATIONS

- intraoperative

- intraluminal

DIGITAL TECHNOLOGY

• BROADBAND SCANHEADS/ BROADBAND BEAMFORMING

- captures full tissue signature• EXTENDED SIGNAL PROCESSING - digitally preserves entire signal• TISSUE SPECIFIC IMAGING - improves signal/noise ratio for detection of small, low-contrast lesions

DIGITAL TECHNOLOGY

BROADBAND TECHNOLOGY

BROADBAND TECHNOLOGY IMAGES

WHAT ARE ECHOCONTRAST AGENTS?

• AIR OR GAS MICROBUBBLES, FREE OR INCAPSULATED IN A POLYMER COVER

• ACCORDING TO THEIR HIGHER DIFFERENCE IN ACOUSTIC IMPEDANCE, CONTRAST AGENTS ENHANCE THE ECHOGENICITY OF THE BODY SPACE IN WHICH THEY WERE INTRODUCED

ECHOCONTRAST AGENTS

CATEGORY OF ECHOCONTRAST AGENTS:

• GAS BUBBLES INTRODUCED INTO THE ORGANISM (ECHOVIST, LEVOVIST, ALBUNEX, ECHOVIEW)

• GAS BUBBLES FORMED IN THE ORGANISM (ECHOGEN)

ECHOCONTRAST AGENTS

• IN VASCULAR IMAGING

- enhance weak signals resulting from deep vessels or slow flow (hyperaemia, ischaemia)

- improve signals from malignant neovascularization

• IN NON-VASCULAR IMAGING

- increase the reflectivity of particular normal or pathologic tissues (targeted agents)

- delineate body cavities and communications

INCAPSULATED BUBBLES(scanning electronmicrograph)

HARMONIC IMAGING

NEW MODE OF ULTRASOUND IMAGING, IN WHICH THE FUNDAMENTAL FREQUENCY OF RETOURNING ECHOES IS SUPPRESSED AND SIGNALS OF HARMONIC FREQUENCY ARE RECEIVED, PROCESSED AND DISPLEYED

FORMS OF HARMONIC IMAGING

• CONTRAST HARMONIC IMAGING

microbubbles of echo enhancing agents are able to resonate and emit harmonic signal

• NATIVE HARMONIC IMAGING

harmonic signal is produced by oscillation of tissue structures due to the non-linear propagation of ultrasound

PRINCIPLE OF HARMONIC IMAGING

transmission

2.5 MHz

5 MHz

receiving

5 2.5

supression

HARMONIC IMAGING

FUNDAMENTAL HARMONIC

stone

3-D IMAGING

• 3-D IMAGING TECHNOLOGY ALLOWS PHYSICIANS TO VIEW PATIENT´S NORMAL AND PATHOLOGIC ANATOMY AS A VOLUME IMAGE

• IT IS SUGGESTED THAT 3-D IMAGING WILL PROVIDE A CENTRAL INTEGRATING FOCUS IN ULTRASOUND DIAGNOSTICS

3-D IMAGING

PHYSICAL PRINCIPLE:

• THE TRANSDUCER IS MOVED DURING EXPOSURE (linear shift, swinging, rotation)

• RECEIVED ECHOES ARE STORED IN THE MEMORY

• THE IMAGE IN THE CHOSEN PLAIN IS RECONSTRUCTED MATHEMATICALY

3D IMAGING

3-D COLOUR DOPPLER SONOGRAPHY

• REPRESENTS A COMBINATION OF 3-D AND POWER DOPPLER TECHNOLOGY: transducer elements are electronically or manually sectored during exposure

• 3D CDS ALLOWS DEPICTION OF THE OVERALL VASCULARITY IN THE AREA OF INTEREST (esp. tumours)

3D COLOUR DOPPLER IMAGING

ANISOTROPIC IMAGING

PHYSICAL PRINCIPLE

• IN ULTRASOUND TECHNOLOGY, ANISOTROPY REPRESENTS A DIRECTIONAL DEPENDENCY OF BACKSCATTERED WAVES

• THIS MODALITY CAN BE USED FOR DIFFERENTIATING NORMAL ANISOTROPIC TISSUES FROM ISOTROPIC ABNORMALITIES

ANISOTROPIC IMAGING

AREAS OF CLINICAL APPLICATIONS

• CARDIOLOGY: MYOCARDIUM EXAMINATION

• NEPHROLOGY: EXAMINATION OF RENAL CORTEX

• MUSCULOSKELETAL ULTRASOUND: EXAMINATIONS OF TENDONS AND CARTILAGES

ELASTOGRAPHY

METHOD FOR IMAGING THE ELASTIC PROPERTIES OF TISSUES

• REPRESENTS AN IMAGING ANALOGY TO PHYSICAL EXAMINATION BY TOUCH

• DIFFERENCES IN MECHANICAL PROPERTIES OF TISSUES CAN BE IMAGED IN 2D- OR 3D- COLOUR-SCALE MANNER

ELASTOGRAPHY

MODEL MIMICING CONTRAST LESION IN PROSTATEMODEL MIMICING CONTRAST LESION IN PROSTATE

ELASTOGRAPHY(benign and malignant lesion of the breast)

ENDOLUMINAL IMAGINGTransversal view of oesophageal sphincter

1 mucosa, 2 submucosa, 3 circular muscle,4 intermuscular connective tissue,5 longitudinal muscle, 6 adventitia

2D and 3D image of advancedoesophageal cancer

DOPPLER ULTRASOUND

• A.Ch. Doppler (1803-1853)

• DOPPLER PRINCIPLE (1842) - frequency shift due to the movement of the source or reflector

• DOPPLER METHODS SERVE IN MEDICINE FOR: - DETECTION OF TISSUE MOVEMENTS - MEASUREMENT OF BLOOD FLOW VELOCITY AND DIRECTION

MILESTONES OF DOPPLER ULTRASOUND

• 1960 - CONTINUOUS WAVE DOPPLER (CWD)• 1974 - PULSE WAVE DOPPLER (PWD)• 1982 - TRANSCRANIAL DOPPLER (TCD)• 1986 - COLOUR FLOW MAPPING (CFM)• 1992 - CONTRAST HARMONIC IMAGING (CHI)• 1994 - POWER DOPPLER (PD)• 1996 - TISSUE DOPPLER IMAGING (TDI)

DOPPLER EQUATION 1 (Doppler shift)

c

vffD

cos2 0

DOPPLER EQUATION 2 (velocity)

cos2 0f

cfv D

CONVENTIONAL DOPPLER METHODS

FLOW DIRECTION

MAIN VELOCITY CURVES

Low vascular impedance

High vascular impedance

COLOUR FLOW MAPPING(right renal artery)

COLOUR FLOW MAPPING(common carotid artery)

COLOUR FLOW MAPPING

NEW COLOUR DOPPLER IMAGING MODALITIES

• POWER DOPPLER (Colour Doppler Energy, Colour Doppler Angio)

• TISSUE DOPPLER IMAGING (TDI)

• 3-D COLOUR DOPPLER SONOGRAPHY (3D CDS)

POWER DOPPLER

• NEW TECHNOLOGY OF DOPPLER SIGNAL PROCESSING, IN WHICH ITS ENERGY ISTEAD OF ITS AMPLITUDE IS RECORDED

• THE ENERGY IS RELATED TO THE SQUARE OF THE AMPLITUDE OF THE SIGNAL

• USING THIS TECHNOLOGY, EVEN WEAK SIGNALS (CORRESPONDING TO LOW FLOW RATES) CAN BE RECORDED

DOPPLER SIGNAL ENERGY

POWER DOPPLER(renal perfusion)

POWER DOPPLER(increased thyroid perfusion)

POWER DOPPLER(kinking of internal carotid artery)

POWER DOPPLER

• ADVANTAGE

- detection of very low blood flow - more complete displaying of the vascular bed - absence of aliasing and only little angle dependence• DISADVANTAGE

- loss of directional and partial loss of velocity information

TISSUE DOPPLER IMAGING

• NEW COLOUR DOPPLER IMAGING MODALITY IN WHICH THE DOPPLER SIGNAL IS DERIVED FROM SLOW TISSUE MOVEMENTS

• THE SYSTEM SUPRESSES FAST VELOCITIES OF BLOOD FLOW AND RECORDS ONLY SLOW MOVEMENTS IN THE RANGE 1 - 10mm/s

CLINICAL IMPORTANCE OF TDI

• ASSESSMENT OF MYOCARDIUM MOVEMENTS DURING HEART CONTRACTION

• ASSESSMENT OF DISTENSIBILITYAND COMPLIANCE OF VESSEL WALL

• ASSESSMENT OF SKELETAL MUSCLES CONTRACTIBILITY AND TENDON MOVEMENTS

TDI - HEART

Colour imaging of blood flow

TDI- Colour imaging of heart movements

TDI - ARTERY

FUTURE OF ULTRASONOGRAPHY

In the medical imaging world, it is hard to beat ultrasound in following terms:

• COST - EFFECTIVENESS

• RANGE OF APPLICATIONS

• SAFETY

FUTURE OF ULTRASONOGRAPHY

ACCORDING TO RECENT ADVANCES IN POWER DOPPLER, 3-D IMAGING, CONTRAST AGENTS, HARMONIC IMAGING AND INTERVENTIONAL APPLICATIONS, ULTRASONOGRAPHY BECOMES THE PREFERRED DIAGNOSTIC IMAGING MODALITY OF THE 21TH CENTURY