MEDICAL IMAGING: The techniquesand processes used to create image ofthe internal as well as external humanbody parts for clinical purpose .
why medical imaging is required?Medical imaging provides a pictorial statusof particular organ which is to be treatedIt makes a surgical targets more clear andpreciseIt provides a pictorial status of fetusdevelopment right from 4th weak to 36th- 38thweekIt make therapeutic targets easy to detect
TYPES OF MEDICAL IMAGING WIDELYUSEDX-RAYMAMOGRAPHYCONTRAST RADIOGRAPHYULTRA SOUNDCT SCANMRISPECT(SINGLE PHOTON EMMISIONTOMOGRAPHY)PET(POSITRON EMISSIONTOMOGRAPHY)
HISTORY OFULTRASOUND……………..PIZOELECTRIC IS DEVELOPED BY THECURIES IN 1880 USING NATURALQUARTZSONAR was first time used inwar time 1940Diagnosis medical
ULTRA SOUND : PHYSICAL DEFINATION !!!!!!!!! • Sound waves greater than 20,000 Hertz or cycles per secondInfrasoun <20 Hz (ACOUSTIC) >20 KHZ Ultrasound
ULTRA SOUND : MEDICALDEFINATION!!!DIGNOSTIC MEDICALULTRASOUND IS THE USE OF HIGHFREQUENCY SOUND TO AID INDIGNOSIS AND TREATMENT OFPATIENT.FREQUENCY RANGES USED INMEDICAL ULTRASOUND ARE 2-15 MHZ
Piezoelectric Effect The principle Definition: ofconverting energy by applyingpressure to a crystal .The reverse of the piezoelectriceffect converts the energy back to itsoriginal form
piezoelectric effect Ultrasound Transducers•A transducer converts one typeof energy into another• Based upon :pulse-echo principle occurring with ultrasoundthe crystals, ultrasound transducers piezoelectric convert: – Electricity into sound = pulse – Sound into electricity = echo
Transducer 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 softtissues•Sound interaction with soft tissues=bio effect•Pulsing is determined by transduceror probe crystal and ins not operatedor control
ECHOECHO IS PRODUCED BY SOFT TISSUESTISSUE INTRACTION WITH SOUND =ACOUSTIC PROPAGATION PROPERTIESECHOES ARE RECEIVED BY THETRANSDUCER CRYSTALECHOES ARE INTRPRETED AND PROCESSEDBY ULTRA SOUND MACHINE
reflective refractionScatteredechoes Incident Angle of incidence = angle of reflection
Reflected 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 AFFECTINGULTRASOUNDFREQUENCYWAVELENGTHBANDWIDTHATTENUATIONTIME GAIN COMPENSATION
The thickness of the crystal determines the frequency of the scan head Low High Frequency Frequency 3 MHz 10 MHz
FREQUENCY AND RESOLUTIONHIGH FREQUENCY = HIGH RESOLUTION 3.5 MHz(sector) 7.5 MHz(linear)
Size, design andfrequencydepend upon theexamination
Electrical 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 bytravel time. The velocity in tissue is assumed constant at 1540m/sec Distance = Velocity Time
Interactions of Ultrasound with Tissue • 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 Transducer • works both ways (send and receive directions) Medium 1 Medium 2 Medium 3
Sound is attenuated by tissue More tissue to penetrate = more attenuation of signalCompensate by adjusting gain based on depth near field / far field AKA: TGC
Gain controls receiver gain only does NOT change power output think: stereo volumeIncrease gain = brighter Decrease gain = darker
Gain settings are important to obtaining adequate images. bad farbad near field field balanced
Strong Reflections = White dots Diaphragm, tendons, bone „Hyperechoic‟
No Reflections = Black dotsFluid within a cyst, urine, blood „Hypoechoic‟ or echofree
Beam comes out as a slice Beam Profile Approx. 1 mm thickDepth displayed – user controlled Image produced is “ 2D ” tomographic slice assumes no thickness You control the aim 1mm
The ultimate goal of any ultrasoundsystem is to make like tissues look thesame and unlike tissues look different
Resolving capability of the system axial/lateral resolution spatial resolution contrast resolution temporal resolution Processing Powerability to capture, preserve and display the information
Ultrasound ApplicationsVisualisation Tool:Nerves, soft tissue massesVessels - assessment of position, size,patencyUltrasound Guided Procedures in realtime – dynamic imaging; central venousaccess, nerve blocks
ImagingKnow your anatomy – Skin, muscle,tendons, nerves and vesselsRecognise normal appearances –compare sides!
Skin, subcutaneoustissue Epidermis Loose connective tissue and subcutaneous fat is hypoechoic Muscle interface Muscle fibres interface Bone
Summary • Resolution determines image clarity • Electronic Arrays may be sector or linear• Frequency & wavelength are inversely proportional • Attenuation & frequency are inversely related • Display mode chosen determines how image is registered• Diagnostic Medical Ultrasound is safe!
conclusion•Imaging tool – Must have the knowledge tounderstand how the image is formed•Dynamic technique•Acquisition and interpretation dependantupon the skills of the operator.