Medical Imaging - Ultrasound Flashcards

Flashcards based on Medical Imaging Lecture Notes about Ultrasound

How does sound transfer energy, and what medium does it require?

Sound is a physical phenomenon that transfers energy from one point to another, and it can only pass through matter.

What is a key characteristic of sound, how is it measured, and what range can humans hear?

The significant characteristic is frequency, measured in Hertz (Hz), cycles/sec, or vibrations/sec. Human ear can hear frequencies ranging from 20Hz - 20kHz.

How does a pulse generator create ultrasound pulses?

Pulse generator and transmitter produces short, identical pulses of high frequency (0.8-15 MHz) at a rate of 1000 per second, with a duration of about a microsecond.

How does a transducer work, and how is depth determined in ultrasound?

The transducer transforms electric pulses into mechanic vibrations, and reflection occurs at tissue boundaries. The lapse of time is proportional to the depth.

Name different diagnostic imaging modes and which ones are combined in duplex scanners.

Spatial information, velocity information. A-mode, B-mode, C-mode, M-mode, C.W. Doppler. B-mode imagers and pulsed Doppler imagers are the most expensive. Duplex scanners combine B-mode and pulsed Doppler.

Name two behaviors of a US beam within Tissue

Exponential attenuation of US beam intensity within a homogeneous material, Reflection and transmission at interface

What is the relationship between wave length, frequency, and speed of sound?

Wavelength * Frequency = sound of speed

What is the relationship between Axial and Lateral resolution ?

Axial resolution is proportional to wavelength, Lateral resolution is proportional to diameter.

What are longitudinal and shear waves?

Longitudinal waves have vibrations in the same direction as sound moves, while shear waves have vibrations at right angles.

What is the frequency that the pulse contains

It contains packets of frequency (vibration) in the range of (0.8-15 MHz).

What determines the velocity with which sound travels through a medium

Characteristics of the medium and not the sound

What is the standard relative measure for comparing the intensities of two signals?

The decibel (dB) is the standard measure for comparing the intensities of two signals.

What happens to Reflection and Refraction in image formation?

Reflection allows for US image formation, refraction causes image distortion.

How do the reflection and incidence angles relate, and what influences the amount of reflection?

The angle of reflectance is equal to the angle of incidence. Amount of reflection depends on the acoustic impedance of the two media.

How is acoustic impedance calculated?

Z = r*c (units of Z = kg/m2.sec also called RAYL)

What is Snell's Law?

sinq1/sinq2 = c1/c2

What are US transducers made of?

US transducers are made of piezoelectric crystal such as PZT (lead zirconate titanate).

How is Q defined?

Q is defined as fres/FWHM or resonance frequency over the full width at half maximum.

What determines the resonant frequency of the piezoelectric crystal in the transducer?

The thickness of the piezoelectric crystal determines its resonant frequency. Thickness equals one-half the wavelength.

What is Fresnel Zone?

The region where the US beam retains the shape of the crystal is known as the ‘Fresnel’ or the ‘near’ zone. This zone extends a distance of D2/4l, where D is the diameter of the transducer.

What is ZMatching formula?

ZMatching = (ZTissue x ZCrystal)-1/2

How do A-mode Scanners Work?

Short pulses of ultrasound are transmitted. Reflections are returned when the pulse strikes an interface between tissues. Distances are measured by timing echoes.

What is B-Mode known for?

Light intensity V.S. time display

How does C-Mode work?

Through-transmission imaging using separate transducers, Scanned by translating the Xducers and 2-D images are obtained

What is M-Mode used for?

Analysis of heart valve motion by varying the positions of a brightness-modulated dot.

How does direction and speed of blood flow relate to Doppler Ultrasound?

Reflected Sound waves increased frequency when they echo from red blood cells moving toward the transducer.

What does red and blue indicate on a color flow?

red: blood flow toward the xducer, blue: blood flow away from the xducer

What is are the characteristics of Convex array

Good penetration, Fan shaped large field of view and Large foot-print