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 SVOICE 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 withbright 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