lecture 5 fluoroscope and digital imaging

Because of its relatively poor contrast resolution, film based radiography requires a subject contrast difference of at least [...] to enable perception of structures

10%

Because of the contrast enhancing capability of digital imaging software, perception of adjacent structures with a subject contrast _______ is made possible

as low as 1%

Bit depths correspond to different 

levels of brightness

Digital image receptors are either _____________ or direct digital capture

computed radiography

Digital image receptors are either computed radiography or 

direct digital capture

Digital Radiography approximate spatial resolution is 

6 - 8 lp/mm

Digital Units

• Gray tones are based upon

• attenuation coefficients

DR Direct FP uses what capture element? 

Amorphous Selenium

Each cell is called a picture element, or aka 

pixel

Film and comptued radiography are both 

latent image

For radiographic images, ____________ stored in each cell represents ______

numeric value, brightness

Increasing the displayed field of view generally ________ resolution

decreases

Increasing the number of pixels decreases the pixel size leading to 

increased resolution

Larger the matrix, greater the number of pixels = Sharper the image

Sharper the image

More radiation will absorb more light therefore it will be

lighter

Photodectector converts light into 

electrical charge

Pixel value is calculated by ___
n represents the bit depth

2^n

Quantizing values assigned to each pixel is pre-designated for a 

gray level

Smaller pixel size =

higher resolution

Spatial frequency can also be derived from __________that can be imaged

minimum object size

Standard Radiography approximate spatial resolution is 

8 - 12 lp/mm

The ability of the system to resolve small high contrast objects describe? 

Spatial Resolution

The measurement of image resolution given in LPs/mm of length? 

Spatial Frequency

The original Fuji digital receptor was known as 

computed radiography

The range of gray levels made available to construct images = 

dynamic range

The scintillator is found in the ____________ and is responsible for converting x-ray photons into ______

Indirect Conversion Detectors, light

The smallest absolute object size that can be reproduced is

inversely proportional to 1/2 the spatial frequency

What are the smallest absolute object sizes that can be resolved by units with spatial frequency of 3.0?

• OS = 0.17 mm 

What are the two components that make up the basic fluoroscope that we care about? 

The image intensifier and xray tube

What are the two different types of Direct Digital Radiography?

Indirect and Direct Conversion Detectors

What is a special factor that can be done in digital radiology? 

The ability to change contrast and exposure after the xray has been taken

What is function of the photocathode and image intensifier? 

Works like film screens, amplifies light photons creation per xray incident

What is the most common photoconductor in digital radiation? 

Selenium

What is the units for spatial frequency? 

line pairs per millimeter

Wheras the response to x-rays in screen film systems is the ____________ by the intensifying screens. The response to x-ray interaction in computed radiology is both immediate release of the ________________

release of light, light and trapping of electrons.

With digital imaging, one major change is the 

image receptor

X-ray directly converted to electrical charges describes 

direct conversion detectors

_____________ - The maximum range of pixel values the computer can store 

Bit depth

_______________ - The portion of imaging plate that contains relevant anatomic information and is displayed at the monitor screen

Displayed Field of View

_________ is a pattern of cells laid out in rows and columns

Matrix

__________ - number assigned to each pixel representing discrete, pre-designated gray value

Quantization

____________ - intensity of light or radiation measured at each pixel

Sampling

___________ - field of the image is divided up into an array of small cells

Scanning