Define:

Dynamic Range

The ratio of the largest to the smallest signal strength that each component processes.

Give an example of dynamic range

It is the number of choices. The dynamic range of the display indicates the number of gray shades.

Narrow dynamic range will have:

few choices

bistable (black and white)

high contrast

Wide dynamic range will have:

many choices

gray scale

low contrast

What are the units of dynamic range?

dB, a relative measurement

What are some typical values?

As a general rule the dynamic range of information decreases the more it is processed 

What is PACS?

Picture Archiving and Communications System

Digital lab, stores and displays data via a computer network. Stores and forwards teleradiology or telemedicine.

Typically, offsite.

What is DICOM?

Digital Imaging and Communications in Medicine

Provides standards or guidelines for imaging networks

What is NAS?

network storage devices

high storage capacity disc drives

economical

used in PACS systems

What are some magnetic type of recording and archiving?

videotape, computer discs, magnetic tape

Disadvantage for all magnetic media:

data can be disrupted by strong magnetic field.

What is harmonic imaging?

The creation of an image from sound reflections at twice the frequency of the transmitted sound.

What is a fundamental frequency?

The frequency of sound created by the transducer and transmitted into the body.

What is a harmonic frequency?

Twice the fundamental frequency (also called second harmonic frequency).

Give an example of how harmonics works:

A transducer transmits a sound pulse with a fundamental frequency of 2 MHz. In the harmonic mode, an image created from 4 MHz sound reflections is displayed

What is non-linear behavior?

Sound is a series of compressions and rarefactions. Sound moves slightly faster in regions of compressions (higher pressure). Sound travels slightly slower in regions of rarefaction (lower pressure). This small difference in the speeds, known as non-linear behavior, distorts the sound wave and creates harmonics.

Define non-linear behavior:

Irregular or disproportionate

Define linear behavior:

proportional or symmetrical

What is tissue harmonics?

As a sound wave travels in the body, a miniscule amount of energy is converted from the fundamental frequency to the harmonic frequency. This conversion creates tissue harmonics during transmission.

What is pulse inversion harmonic imaging?

A form of harmonic imaging where positive and negative pulses are transmitted down each scan line. The negative pulse is the 'inverse' of the positive pulse, thereby cancelling the fundamental reflections. Only the harmonic reflections remain and are used to create the image. Thus, harmonic images are created with this process.

What is the major disadvantage of pulse inversion imaging?

The frame rate is half that of fundamental imaging. Thus, pulsed inversion imaging degrades temporal resolution, while improving spatial resolution.

What are contrast agents and what are they used for?

Contrast agents, also called microbubbles, are gas bubbles encapsulated in a shell. They are injected in the circulation (usually by IV) or ingested (swallowed). Contrast agents have a different acoustic fingerprint than blood or tissue. They are designed to create strong reflections that actually "light up" blood chambers, vessels, or other anatomic regions.

What are the requirements for contrast agents?

Safe

Strong reflector of ultrasound

long persistence

small enough to pass through capillaries

metabolically inert