Physics II- Chapter 18 viewing the digital image

The AMLCD is a very inefficient device. Only approximately ___% of the backlight is transmitted through a monochrome monitor and half of that through a color monitor. This inefficiency is partly attributable to light absorption in the filters and polarizers. Because a substantial portion of each pixel is blocked by the TFT and the bus lines, efficiency is reduced still further.

10%

1 fc = _____ lux

10.8 lux

Medical flat panel digital display devices are identified by the number of pixels in the AMLCD. A 1-megapixel display will have a ____ x ______ pixel arrangement. A high-resolution monitor will have a 5-megapixel display, or a 2000- x 2500-pixel arrangement.

1000 x 1000

The maximum photopic eye response is at ______ nm.

555 nm

The principal disadvantage of an LCD is the ___________ dependence of viewing.

Angular

Aperture ratio is a measure of image ______________ of AMLCDs.

Aperture ratio is a measure of image luminance of AMLCDs.

Photopic is ______ light vision using cones.

Bright

______ and _____ represent the first widespread digital medical images.

CT and MRI. Computed tomography (CT) (1974) and magnetic resonance imaging (MRI) (1980) represent the first widespread digital medical images. However, until recently, even these digital images were interpreted from film placed on a lighted viewbox.

Scotopic is _____ light vision using rods.

Dim

Each type of digital image receptor generates an elec¬ tronic latent image that may not be made visible com¬ pletely. What remains is called _________.

Each type of digital image receptor generates an elec¬ tronic latent image that may not be made visible com¬ pletely. What remains is image lag, and this can be troublesome when one is switching from high-dose to low-dose techniques, such as switching from digital sub¬ traction angiography (DSA) to fluoroscopy. The solu¬ tion is application of an offset voltage before the next image is acquired.

An LED emits light when _______ stimulated.

Electrically

Gain images are generated when?

Every few months

Spatial resolution improves with the use of (higher/lower) megapixel digital display devices?

Higher

All video monitors today are actually ______ with a more intense backlight, the LED.

LCDs

_____ is superior to CRT displays.

LCDs

What does LED stand for?

Light Emitting Diode. Remember a diode allows current flow in one direction.

Fluorescence

Light emission during stimulation

Phosphorescence

Light emission following stimulation

The basic unit of photometry is the ________.

Lumen

Luminance intensity is measured in:

Lumens per steradian or candela

Luminance intensity - define

Luminance intensity is a property of the source of light, such as a viewbox or a digital display device. Luminance intensity is the luminous flux that is emitted into the entire viewing area; it is measured in lumens per steradian or candela. *Intensity of light on entire surface • Maxwhensurfaceis viewed straight on

Luminous flux- define

Luminous flux is the total intensity of light from a source. Household lamps are rated by the power they consume in watts. An equally important value found on each lamp package is its luminous flux in lumens. *Total intensity of light emitted from a source

How is the inverse square law applied in photometry?

Luminous intensity decreases in proportion to the inverse square of the distance from the source. This is the famous inverse square law. *As the intensity doubles, the distance is decreased to 1⁄4 the original distance. *As the intensity is cut in half, the distance is increased 4 times the original distance.

Offset images are generated when?

Many times each day

What are 0ffset images and gain images?

Offset images and gain images are automatic calibra¬ tion images designed to make the response of the image receptor uniform. Gain images are generated every few months, and offset images are generated many times each day.

Postprocessing of digital images requires __________.

Postprocessing of digital images requires operator manipulation.

Preprocessing is designed to produce _______________digital images.

Preprocessing actions are outlined in Table 18-5. Pre¬ processing is designed to produce artifact-free digital images. In this regard, preprocessing provides electronic calibration to reduce pixel-to-pixel, row-to-row, and column-to-column response differences. The processes of pixel interpolation, lag correction, and noise correc¬ tion are automatically applied with most systems.

Some voltage variations may be seen along the buses that drive each pixel. This defect is called what?

Some voltage variations may be seen along the buses that drive each pixel. This defect, called line noise, can cause linear artifacts to appear on the final image. The solution is to apply a voltage correction from a row or a column of pixels in a dark, unirradiated area of the image receptor.

The best viewing of a digital display device is _____ ___.

Straight on

Digital image receptors and display devices have millions of pixels; therefore, it is reasonable to expect some individual pixels to be defective and to respond differently or not at all. Such defects are corrected by _____________________.

Such defects are corrected by signal interpolation. The response of pixels surrounding the defective pixel is averaged, and that value is assigned to the defective pixel.

How is the cosine law important to photometry?

The cosine law is important when one is describing the luminous intensity of a digital display device. When a monitor is viewed straight on, the luminous intensity is maximum. When a monitor is viewed from an angle, the contrast and the luminous intensity, as seen in Figure 18-2, are reduced. This reduced projected surface area follows a mathematical function called a cosine. Luminous intensity falls off rapidly as one views a digital display device at larger angles from perpendicular.

Electroluminescence

The emission of light resulting from a high-frequency electric discharge.

What two fundamental laws are associated with photometry?

The inverse square law and the cosine law

The portion of the pixel face that is available to transmit light is the "_____________"

The portion of the pixel face that is available to transmit light is the "aperture ratio." Aperture ratio is to a digital display device as "fill factor" is to a digital radiographic detector. Aperture ratios of 50% to 80% are characteristic of medical AMLCDs.

Photometry

The science of the response of the human eye to visible light

What is a hard copy digital image?

Until the mid 1990s, essentially all medical images were "hard copy," that is, the images were presented to the radiologist on film.

Soft copy viewing is performed on what?

a digital cathode ray tube (CRT) or an active matrix liquid crystal display (LCD).

Preprocessing of digital images is largely _______.

automatic

Illuminance- defined

describes the intensity of light incident on a surface. One lumen of luminous flux incident on a single square foot is a fc. This English unit, the fc, is still in wide use. The metric equivalent is 1 lumen per square meter, which is 1 lux (lx) (1 fc = 10.8 lux). *Intensity of light hitting a surface

One lumen of luminous flux incident on a single square foot is a ____

fc. This English unit, the fc, is still in wide use. The metric equivalent is 1 lumen per square meter, which is 1 lux (lx) (1 fc = 10.8 lux).

Luminance- define

is a quantity that is similar to luminance intensity. Luminance is another measure of the brightness of a source such as a digital display device expressed as units of candela per square meter or nit.

Preprocessing calibration techniques are identified as _________

preprocessing calibration techniques are identified as flatfielding