Physics - Digital Image Acquisition and Display (ASRT Outline)

What is commonly used as the phosphor material in conventional intensifying screens of film-screen systems?

Gadolinium

Which has significantly more light spread than the other: Gadolinium oxysulfide or Cesium iodide?

Gadolinium oxysulfide

The principal descriptor for contrast resolution is ____, also called _______.

Grayscale, dynamic range

Greater matrix = (lesser/greater) amount of pixels & (lesser/greater) resolution

Greater, Greater

Larger matrix = (lesser/greater) amount of pixels & (lesser/greater) resolution

Greater, Greater

Bone trabeculae, breast miccrocalcifications, and contrast filled vessels have (low/high) spatial frequency and are therefore (easy/hard) to image.

High, Hard

What is the relationship between pixel size and resolution?

Inverse relationship

If dots were not high contrast, the spatial resolution of the eye would require (smaller/larger) dots.

Larger

Does a scintillator result in a gain or loss of resolution?

Loss

Dots of shades of gray = (low/high) contrast

Low

Large soft tissues, such as the liver, kidneys, and brain, has (low/high) spatial frequency and are therefore (easy/hard) to image.

Low, Easy

What is a combination of rows & columns that give form to the image (layout & brightness of pixels) called?

Matrix

The minicomputers used in radiology have capacities measured in ______.

Megabytes

Does direct-capture method use a scintillator?

NO

What is a single recorded numerical brightness level for one shade of gray called?

Pixel

What is the cell of a digital image matrix called?

Pixel

The distance between the center of one pixel and the center of a adjeacent pixel is called ______ and is measured in ______.

Pixel pitch, microns

Digital images are made of discrete picture elements, ___, arranged in a ____.

Pixels, Matrix

In many cases digital images do not achieve the ____ of coventional film images.

Resolution

The size of the matrix determines the _____.

Resolution

What do the number of pixels (pixels/mm) determine?

Resolution

The matrix size is dependent upon what 2 things?

Sample frequency & size of IR

What is the frequency at which data sample is acquired from the decector called?

Sampling frequency

What describes how digital detectors sample the x-ray exposure? (They do so discretely - that is, at specific locations seperated by specific intervals)

Sampling pitch

What is expressed as sampling pitch?

Sampling pitch

Amorphous selenium layers have the same single-crystal layer structure across (short/long) distances, but are less ordered across (shorter/longer) distances, thereby performing uniform detection ability across large aurface areas needed by flat-panel detectors.

Short, longer

Spatial resolution refers not to ___ but to the ____.

Size, line pair

Larger spatial frequency = (smaller/larger) objects

Smaller

Spatial resolution is described by ________.

Spatial frequency

The matrix size is dependent upon what 2 things?

Ssample frequency & size of IR

True or False: No matter how you change the technique or latitude, still no more than 30 shades of gray will be viewed because of the limitations of the human visual system.

True

True or False: With the post processing exercise of window and level, each grayscale can be visualized - not just 30 or so.

True

The detector size or field of view desccribes the ___________.

Useful imaging area of the digital receptor

If the DQE is too high, the patient dose will be (very low, high), but the image will also be ______.

Very low, very noise (grainy)

If the exposure indicator value is OUTSIDE the acceptable range, attempting to adjust the image data with post processing functions (will/will not) correct for proper receptor exposure and may result in noisy or suboptimal images that should not be submitted for interpretration.

Will not

If the exposure indicator value is WITHIN the acceptable range, then adjustments can be made for contrast and brightness (density) with postprocessing functions and (will/will not) degrade the image.

Will not

Two bytes usually constitutes a "_____".

Word

What is a pixel measured in?

um

What binary number system will give you a pixel size of the following: - 32 - 128 - 1024 - 16,384

- 2(^5) - 2(^7) - 2(^10) - 2(^14)

A system with 3 orders of magnitude, has an optical density of near __ to ___. This represents a dynamic range of ______, but the viewer can visualize only about ___ shades of gray.

0 to 3.0, 1000, 30

1. CT and MRI generally hace a __-bit dynamic range. 2. DR may have a __-bit dynamic range. 3. Mammography needs contrast resolution of __-bit dynamic range.

1. 12 2. 14 3. 16

One kilobyte (kB) is equal to ____ bytes.

1024

What is the matrix size for digital fluoroscopy?

1024x1024 (2^10)

With spatial resolution, dots range from ____ down to ___.

10mm to 50um

A "word" would consist of ___ consecutive bits.

16

Spatial resolution of the eye is described as ___ um.

200

What is the matrix size for digital radiography?

2048x2048 (2^11) & 4096x4096 (2^12)

What is the matrix size(s) for CT & MRI?

256x256 (2^8) & 1024x1024 (2^10)

A digital radiographic imaging system has a spatial resolution of 3.5 lp/mm. How small an object can it resolve?

3.5 lp/mm = 7 objects in 1 mm or 7/mm; 1/7mm = 0.143mm = 143 um

Digital imaging system is __ to __ orders of magnitude.

4 to 5

Bit depth is in strings of __, __ or __ that are manipulated simultaneously.

8, 16 or 32

With direct capture, the photodetector is ______.

Amorphous selenium (a-Se)

With indirect capture, the photodetector is generally an __________ photodiode.

Amorphous silicon (a-Si)

_________ is a liquid that can be painted onto a substrate (foundationn or underlying layer) and is the material that makes _____ detectors possible.

Amorphous silicon (a-Si), flat-panel

The size of the image is described in the ____ ____ ____ by power of ___ equivalents.

Binary Number System, 2

What is the smallest unit of measure in computer storage capacity, and are a single binary digit (0 or 1) called?

Bit

What is the number of bits used to reproduce image gray levels called?

Bit Depth

The dynamic range is identified by the ______ of each pixel.

Bit capacity

Bits are often grouped into bunches of eight called _____.

Bytes

Computer capacity is expressed by the number of _____ that can be accommodated.

Bytes

The other indirect capture method also uses a scintillator with _____ or ____ as the phosphor, photodetectors, and a thin-film transistor (TFT) array.

Cesium iodide or gadolinium oxysulfide

A system that can display a greater number of shades of gray has better ___________.

Contrast resolution

Increased pixel size = (increased/decreased) resolution

Decreased

What does the Detective Quantum Efficiency (DQE) predict?

Dose Efficiency

One problem with the indirect-capture methods is that there is an _______ during which x-rays are converted to light, and then to electrons, which causes a loss of ______.

Extra step, resolution