14 Medical Ultrasonography

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MEDICAL

ULTRASONOGRAPHY

CHAPTER 13


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Introduction

Ultrasonography is a noninvasive technique

that uses a skin probe emitting sound waves

(ultrasound) .

Thus, visual images of the internal organs, e.g.,

the urinary tract, can be obtained for the

purpose of assessing its position .


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Audible Sound

Humans can hear only a limited range of

frequencies that are called the audible spectrum.

The frequncy range of audible sound is

appropriately 20 Hz to 20 kHz


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Ultrasound

Frequncies higher than the 20KHz are calledultraound.

Ultrasound is sound with a frequency greater

than the upper limit of human hearing,approximately 20 kilohertz/20,000 Hertz.

Some animals, such as dogs, dolphins, bats, and

mice have an upper limit that is greater than thatof the human ear and thus can hear ultrasound.
http://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Doghttp://en.wikipedia.org/wiki/Dolphinshttp://en.wikipedia.org/wiki/Bathttp://en.wikipedia.org/wiki/Micehttp://en.wikipedia.org/wiki/Earhttp://en.wikipedia.org/wiki/Earhttp://en.wikipedia.org/wiki/Micehttp://en.wikipedia.org/wiki/Bathttp://en.wikipedia.org/wiki/Dolphinshttp://en.wikipedia.org/wiki/Doghttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Sound


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Sonography

Medical ultrasonography (sonography) is an

ultrasound-based diagnostic imaging technique used to

visualize internal organs, their size, structure and any

pathological lesions.
http://en.wikipedia.org/wiki/Ultrasoundhttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Lesionhttp://en.wikipedia.org/wiki/Image:Baby_in_ultrasound.jpghttp://en.wikipedia.org/wiki/Lesionhttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Ultrasound


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Working

Ultrasonography (sonography) uses a probecontaining one or more acoustic transducers tosend pulses of sound into a material.

Whenever a sound wave encounters a materialwith a different acoustical impedance, part ofthe sound wave is reflected, which the probedetects as an echo.
http://en.wikipedia.org/wiki/Sonographyhttp://en.wikipedia.org/wiki/Transducerhttp://en.wikipedia.org/wiki/Transducerhttp://en.wikipedia.org/wiki/Sonography


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Working

The time it takes for the echo to travel back tothe probe is measured and used to calculate thedepth of the tissue interface causing the echo.

The greater the difference between acousticimpedences, the larger the echo is.

The difference between gases and solids is sogreat that most of the acoustic energy is

reflected, and so imaging of objects beyond thatregion is not possible.
http://en.wikipedia.org/wiki/Echohttp://en.wikipedia.org/wiki/Echo


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To generate a 2D-image

The probe is swivelled, either mechanically or

electronically through a phased array of acoustic

transducers.

The data is analyzed by computer and used to

construct the image.

In a similar way, 3D images can be generated

by computer using a specialised probe.
http://en.wikipedia.org/wiki/2Dhttp://en.wikipedia.org/wiki/Phased_arrayhttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/Phased_arrayhttp://en.wikipedia.org/wiki/2D


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Display mode

A- mode

B- mode

M- Mode


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A mode :


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B MODE

The B mode stands for brightness.

Shifting the position of ultrasound transmision& reception results in scanning.

Echo signals received undergo intensitymodulation, so that a cross sectional image canbe diaplyed on the CRT.

Using this display method, we can see internalstructures in patient safety .


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M MODE

M mode stands for motion.

This display mode is useful for studying moving

tragets such as the anterior mitral valves.

The transducer position remain fixed when using thismode while the display moves across the monitor

screen ina movemt called scroling.

Scrolling allows movement of a vale to be displayedas an image


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ULTRASOUND EQUIPMENT


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PRINCIPLES OF ULTRASOUND EQUIPMENT

Ultrasound Diagnostic equipment uses a pulsereflection system.

The pulse generation circuit generates high volatgepulses.

Then the T delay line circuit applies appropiate delaytime for each transmitted pulse for electronicfocussing for the ultrasound beam.

When the ultarsound probe touches the patients skin

surface, ultrsound waves are transmittable to thepatinet.


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The delayed high volateg pulses are applied to thepiezo electric transducer elements

They produce the ultarsound waves, which will enter

to the patiinet & will be reflected back by internalstructures. The reflected echo signals are received bythe same probe.

Then theay are input the R delay line circuit to

compensate for the trasnmission delay factor of thepulses & mix the echo signals


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Then the receiver circuits ampliier the mixedecho signasl from R delay line

In new equipment, the echo signals are

produced using a digital scan converter so thattehimage data is stored into the frame memory& read sequentilaly out in a format for displayon the TV monitor.

The result is real time imaging .


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DOPPLER SONOGRAPHY

Ultrasonography can be enhanced with Dopplermeasurements, which employ the Doppler effectto assess whether structures (usually blood) aremoving towards or away from the probe, and itsrelative velocity.

By calculating the frequency shift of aparticular sample volume, for example a jet of

blood flow over a heart valve, its speed anddirection can be determined and visualised.
http://en.wikipedia.org/wiki/Doppler_effecthttp://en.wikipedia.org/wiki/Doppler_effect


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DOPPLER SONOGRAPHY

This is particularly useful in cardiovascularstudies (ultrasonography of the vasculature andheart) and essential in many areas such asdetermining reverse blood flow in the livervasculature in portal hypertension.

The Doppler information is displayedgraphically using spectral Doppler, or as an

image using colour Doppler or power Doppler. It is often presented audibly using stereo speakers: this

produces a very distinctive, although synthetic, sound.
http://en.wikipedia.org/wiki/Portal_hypertensionhttp://en.wikipedia.org/wiki/Portal_hypertension


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APPLICATIONS:

It images muscle and soft tissue very well and is particularlyuseful for delineating the interfaces between solid and fluid-filled spaces.

It renders "live" images, where the operator can dynamically

select the most useful section for diagnosing and documentingchanges, often enabling rapid diagnoses.

It shows the structure as well as some aspects of the function oforgans.

It has no known long-term side effects and rarely causes anydiscomfort to the patient.
http://en.wikipedia.org/wiki/Musclehttp://en.wikipedia.org/wiki/Soft_tissuehttp://en.wikipedia.org/wiki/Soft_tissuehttp://en.wikipedia.org/wiki/Muscle


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APPLICATIONS:

Equipment is widely available andcomparatively flexible.

Small, easily carried scanners are available;

examinations can be performed at the bedside. Relatively inexpensive compared to other

modes of investigation (e.g. computed X-ray

tomography, DEXA or magnetic resonanceimaging).
http://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Dual_energy_X-ray_absorptiometryhttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Dual_energy_X-ray_absorptiometryhttp://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Computed_tomography


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DISADVANTAGES

Classical ultrasound devices have troublepenetrating bone but current research onultrasound bone imaging will make it possible

with dedicated devices in the future. Ultrasound performs very poorly when there is

a gas between the scan head and the organ ofinterest, due to the extreme differences inacoustical impedance .
http://en.wikipedia.org/wiki/Bonehttp://en.wikipedia.org/w/index.php?title=Ultrasound_bone_imaging&action=edithttp://en.wikipedia.org/w/index.php?title=Ultrasound_bone_imaging&action=edithttp://en.wikipedia.org/wiki/Bone


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DISADVANTAGES

Even in the absence of bone or air, the depth

penetration of ultrasound is limited, making it

difficult to image structures that are far removed

from the body surface, especially in obese patients. The method is operator-dependent. A high level of

skill and experience is needed to acquire good-quality

images and make accurate diagnoses.


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MAINTENANCE

Make sure to check the system daily before starting to examinepatinets

Daily check will help dicover a malfunction at the earliestpossible stage.

Before deciding on the malfucntion , check whethr the power isturned ON, whether the chracters are displaying. Etc.

If charcaters are diaplyed & no ultrasound image then set thegain knob t themaximum positions.

If this operation do not correct the problem, confirm that theprobe is connected correctly.

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14 Medical Ultrasonography