Advanced Physics Unit 2

What is numerical values able to be stored in computer memory

Matrix

For a given FOV, the larger the matrix

smaller the pixels

What is the equation for pixel size:

Pixel size= Image Size (mm)/Matrix Size (pixels)

What does spatial domain control?

pixel location (X & Y coordinates)

What does frequency domain control?

resolution

What does high frequency mean

smaller structures with higher contrast

What is the Fourier transformation

Spatial location to spatial frequency (detector to computer)

What is the equation for spatial frequency:

SF=1/2(PS)

What does SNR stand for?

signal to nosie ratio

Is 1000/1 a good SNR

yes low noise

What does AMA stand for?

Active Matrix Array

What modality has the best spatial resolution

DR & CR

What are the pros to Direct systems

higher image resolution

What are the pros to indirect systems

less patient dose

What does the PSP plate in CR consist of

PSP crystals

How is the maximum spatial resolution determine in DR systems

Del pitch/pixel pitch

What does DQE stand for?

Detective quantum efficiency

What is the DQE measure?

measure of the system’s overall efficiency (detectors ability to take xrays, Quantify to image “electrical”)

Why does indirect have less dose

absorbed by the phosphor layer

What is window width?

Shades of grey (contrast)

What is window level?

Brightness (density)

The sensing area of a single DEL is referred to as the ______________ and is expressed as a percentage. How is it calculated?

fill factor

sensing area of the DEL/area of the DEL

Before a flat panel detector can be exposed for acquisition, it is first must be __________________ by placing a small negative voltage on the switching element, placing it in an “off-state”. X-ray exposure changes the voltage to a positive value and the data is readout line-by-line.

initialized

The direct flat panel detectors lack a _____ layer and possess a higher _________________ value when compared to other digital technologies

scintillation, MTF

The ____ is the range of grey values per pixel

Bit depth

_____ allows for consistency of image quality, exposure technique aside in DR

Automatic rescaling

The process of assigning “bins” to pixel data regardless of their original value

Normalization

Digital imaging allows for a greater _____ in image production compared to film

latitude

What is happening during sampling?

measuring each pixel

What is happen during quantization?

digital value given to pixel from each measurement

Dynamic range

number of gray shades, which each pixel can be represented (what is available)

Gray scale

range of pixel values actually represented (not using full potential range)