image processing and display ch13

Raw data - pres processing

Fixes:

Noise

Dead pixels

Evens out brightness

Quantization - pre processing

Converts analog signal to grey values

Flat fielding - pre processing

Corrects detector inconsistencies and removes shading

Dead pixel correction- pre processing

Replaces malfunctioning pixels before image display

Nyquist theorem

How raw data is sampled by detector.

Detector catches enough info = more image detail

Electronic cropping - post processing

Removes unwanted black edges

Look up table LUT

Substitutes new values for each pixel improving contrast and brightness

Histogram

Evaluates exposure and image quality without modifying the image

Kvp calibration- QC testing

KVp must be within -4 / +4 anual check

mA linearity - QC testing

Constant radiation output mA + exposure time

Timer accuracy- QC

Pre mature = under exposed

Exposed delay = over exposed

Beam/collimation restriction - post processing

Check beam alignment to IR

Reproducibility- post processing

Successful exposures of at least 5 times

KVp + mA + time

Filtration- QC testing

Measure half value layer/beam quality

Focal spot size - QC testing

Measures image sharpness

PSP testing for CR

Uniformity = over all signal from exposed IP

IP erasure = tests white light when deleting trapped energy in IP

Display monitor QC

AAPM/TG 18 uses a pattern calibration

Cosine law

Better view of image straight on than from an angled view