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physics 3
| Question | Answer |
|---|---|
| A digital image always begins as an | analog signal |
| A __ matrix is determined by the hardware | fixed |
| the matrix exists in the | monitor. |
| contrast resolution is measured in | bit depth |
| spatial resolution is measured in | line pairs per mm |
| most systems use bit depth of ____ to ___ bits | 10 - 16 |
| if the matrix is fixed and the FOV is increased, there will be ___ spatial resolution bc | decreased ; pixels increased in size |
| A smaller pixel pitch means | smaller pixels and better resolution |
| typical DR detector DEL pitch | 0.1-0.2 mm |
| If matrix doubles the pixel size is | halved |
| pixel size formula | pixel size = FOV / matrix |
| in order for the Nyquist frequency to accurately sample the analog signal into digital, it must receive | twice the signal of the spatial resolution frequency |
| Lower than twice the amount of signal needed will cause ___ by the nyquist frequency | aliasing. Ex: moire effect. |
| Detail recorded ______ the Nyquist frequency is recorded correctly. Detail ____ recorded as aliasing | below;above |
| nyquist formula | n frequency = (1 / 2 x DEL pitch) |
| which grids are better for avoiding aliasing | moving grids, high frequency grids. |
| photodiodes are used in | indirect |
| photocathodes are used in | direct |
| the three chemicals that could be used in indirect conversion | CSi, gadolinium oxysulfide, and amorphous silicon |
| This holds the charge in the TFT | capacitor |
| Each pixel has these three things | sensing element, storage capacitor, TFT switch. |
| what part of the photodiode that causes current to flow in one direction by creating a charge gradient | p=n junction in the semiconductor |
| semiconductors are typically made of | silicon |
| p=type semiconductors are doped with n-type semiconductors are doped with | boron phosphorus |
| a missing line across the image could indicate | readout failure of the TFT in each pixel |
| two types of phosphor in the photodiode | turbid and structured. |
| Which strcture of phosphor had better spatial resolution due to less light spread | structured phosphor. uses CsI |
| If a tech wants to choose a mechanism that produces a fast image and noise is ok, should they get CCD or CMOS. | CMOS. it is cheaper, faster but has more noise. |
| If a tech wants to choose a mechanism that produces as little noise as possible and slow is ok, should they get CCD or CMOS. | CCD. it is slower but has less noise |
| the capability of the detector to show shades of gray | dynamic range |
| Having a wide dynamic range means the pt gets ___ dose. | less dose, bc you can use less exposure. |
| The room for error in exposure. the range of exposures that can create an image. | exposure latitude |
| A wide exposure latitude can create | dose creep bc many kvps can create an acceptable image. |
| The ADC converts ___ into ____ | analog (voltage) signal into 0 and 1s computer signal |
| when window width is narrowed | contrast is increased, more b and w |
| Rescaling corrections compare the raw data to the | selected look up table |
| dead pixels will appear | white |
| purpose of flat-fielding preprocessing | flat fielding evens out pixel to pixel response, gain uniformity |
| purpose of offset preprocessing | removes baseline electronic noise |
| incorrect brightness or contrast applied to an image is an error in which type f preprocessing | histogram error |
| the x axis of a histogram shows the y axis | pixel value number of pixels |
| Low energy (kVp) gives a ___ histogram. | wider histogram. more contrast, b and w are on either side of the histogram |
| A High energy (kVp) exposure gives a ___ histogram. | narrow. more grays, which are in the center of the graph. |
| What causes histogram analysis errors? | incorrect collimation, positioning, metal, wrong exam. |
| A histogram of the luminance values derived during image acquisition | look up table |
| The look up table is used to evaluate __ and to correct __ vlaues | raw data: luminance |
| The vertical axis of the LUT | the displayed pixel values |
| High pass filter is used for | sharpening the edges |
| downside to edge enhancement | increases noise and haloing |
| Smoothing is aka | low pass filter |
| compressing the range of grays so all regions are visible is called | equalization- preprocessing |
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user-1989152