ULTRASOUND – THE BASICS Dr. S. Parthasarathy MD, DA, DNB, Dip Diab.MD ,DCA, Dip software based statistics, PhD (physiology) FICA

Echo IF WE GO TO A BAD HALL , THE SPEAKER ‘S VOICE WILL COME BACK TO YOU WE CANT HEAR ANY THING WHAT DO WE CALL THIS ? Echo

In ultrasound The same thing The machine sends waves , it echoes from our tissues Comes back to the machine Converted to digital display for us to see But it is ultrasound waves – not sound

Pulse echo principle

Frequency 20 KHz – man Just above range – cats , dolphins hear ?? frequencies used clinically lie largely between 3 MHz and 15 MHz. There are no naturally occurring sources or detectors of such waves

Two main uses Regional anesthesia Vascular access Safety Efficacy

To generate the ultrasound an electrical current is applied to the crystal (piezo electric) component within the transducer face. current is then converted to mechanical (ultrasound) energy and transmitted to the tissues at very high (megahertz) frequencies. The ultrasound energy produced then travels through the tissues as pulsed, longitudinal, mechanical waves

In echo Mouth speaks and ears hear the reflected waves One machine part does it Transducer One reflector and one receiver – not enough So waves are continuously sent from many transducers !! – ARRAY

Phased - Linear –curvilinear- arrays

Phased Phased arrays are ideally suited to applications with small access windows, e.g., scanning the heart while avoiding the lung field.

linear, curvilinear, and phased Linear arrays - rectangular field of view suited to applications with reasonable access and a need to cover a lot of tissue close to the surface. Curvilinear arrays rely on being able to apply some pressure to the skin surface in order to make it deform to their shape. Once done , a very wide field of view can be obtained.

A single probe from 3 – 13 Mhz Patient mode Vascular Nerves Small parts

3 - 10 MHz 8- 10 – superficial structures 5- 8 – medium distance 3 – 5 – deeper structures

Sound travels –speed m/s 1540 for all scanners

Higher frequency energy is ‘lost’ to the tissues to a greater extent than lower frequency energy with progressive tissue penetration. Irrespective of frequency, lateral and axial resolution always decrease with increasing tissue depth Lateral – perpendicular to the USG beam Axial – parallel to USG beam

Selecting transducer Probes Frequency Array Foot print or the diameter of the transducer Attenuation ?

Hyperechoic - solids – liver – stones Hypoechoic – vessels Continuous echoes 20 frames /second

Hypo and hyper echoic

Anechoic and iso echoic

Artifacts Something is there but not seen Some thing is not there but seen Acoustic Enhancement Reverberation Three types

Acoustic Shadowing occurs when structures that are highly attenuating of ultrasound energy (such as bone)

Nerves !! Near subclavian or enhancement artifact Passes through structures of different attenuation The deeper one may show more reflections and enhanced image Nerves !! Near subclavian or enhancement artifact

Reverberation artifact Each successive ultrasound pulse emitted from the transducer produces a temporal ‘echo’ resulting in a series of parallel lines both above and below the actual object. commonly seen with highly attenuating wide-bore needles

Beyond the transducer From the transducer – we have to get the image Which is meaningful !! Put the probe – assess the image – assess which is marker side Use gain and depth !!

Low gain

Brightens everything to compensate resolution Medium and high gain Brightens everything to compensate resolution

Time gain compensation

Depth Interscalene – 2 cm Femoral 4 cm The resolution will decrease as soon as the depth goes

B and M modes A and B are static C and D are moving B = brightness M = motion (cardiac)

Why use gel ?? Coupling Agent Ultrasound does not travel through air Gel provides medium for sound wave into the body by removing air gap Povidone-iodine, surgical spirit

Colour doppler Select doppler and select site

In Colour Doppler mode, blood flow towards the transducer will be red on screen, flow away from the transducer will be blue on screen. It must be emphasized that colour does not necessarily characterize arterial or venous flow.

Anechoic lumen, non-pulsatile, compressible Anechoic lumen, non-pulsatile, compressible. Valsalva effect, doppler - continuous flow Short axis

Anechoic lumen , pulsatile, non-compressible. Doppler - pulsatile flow Long axis

Tendon Hyperechoic with bright lines longitudinally or bright dots at right angles -fibrillary pattern

Hypoechoic with multiple hyperechoic lines muscle

Nerve

Liver normal and cirrhosis

Normal kidney and kidney stone

Save clip , record , patient ,type Name Age sex Type of scan ---- done Save clip , photo , Review , list

Caliper This is used to measure a distance (eg kidney length). It is used by selecting a starting spot by pressing a kidney key and using the trackball to measure to a second mark. The distance between the two marks will then be displayed on screen measured in cm. This can be used with other functions such as Res/Freeze. Freeze – caliper – mouse fix point – mouse another point – distance will be shown.

Knobology Trackball ( mouse with select buttons)

Zoom magnification of areas of the ultrasound picture. Looking at Res/Zoomed areas of interest has the advantage of a more detailed view drawback of less anatomy visible

Movements of the transducer sliding, tilting, rotating, angling. To create an image

orient the transducer such that the left and right sides are consistent with the left and right sides of the ultrasound screen, position the plane of the screen similar to the plane of the transducer Sample survey of the area

Tilting, rotating and angling

Slightly give tilting motion to the transducer – get the target to 90* Anisotropy

Rotation from short axis to long axis

Angling Gentle pressure may be applied to one side of the transducer to maintain full contact along the skin surface in concave or confined fields, or when attempting to direct the beam under a superficial highly attenuating structure such as bone.

Focus Lateral resolution better Different echoic structures – better seen Some machines if we adjust depth focus is automatically changed Beam width decreased

Future developments

Two probes in one

Three-dimensional probes . Needle tips which emit an ultrasound signal that is detected by the probe and visualized as a pulsating spot

Summary Ultrasound –echo , array , types frequency , speed, focus Depth Movements of the transducer Artifacts gain and TGC– B and M modes freeze , caliper , trackball Future developments