PRE clinical exam 3

digital image composed of

matrix, FOV, pixel, matrix, Grayscale bit depth

pixel

smallest unit of a digital image. individual matrix boxes

what do pixels represent

brightness value and tissue attenuation

if pixel size decreases what happens to spatial resolution

it increases

matrix

rectangular array of pixels, rows and columns

matrix sizes

512×512 1024×1024 2048×2048

if matrix size increases (FOV constant) what happens to pixel size

pixels decrease in size. so spatial resolution increases

field of view

anatomical area included in the image

what happens to pixel size if FOV decreases (matrix constant)

pixels get smaller. better spatial resolution

what happens to pixel size and spatial resolution when FOV increases

pixels get larger and spatial resolution decreases

pixel size formula

FOV/Matrix

grayscale formula

2^n (n represents number of bits per pixel)

increasing bit depth increases? _____ _____

contrast resolution. we get better visibility of soft tissue detail

detector element DEL

size of detector sampling area. (rhinehart said think of it like pixel size at the detector)

increasing DEL size does what to spatial resolution? decreasing it?

increasing it reduces resolution. decreasing it makes resolution better.

what does computed radiography use? _____ _____ ______

photostimulable phosphor plate

what is required in CR to get the image?

a laser reader

is CR direct or indirect

indirect.

CR workflow

cassette → placed in reader → stored energy is released as light → light is converted into signal, then into digital image

does direct radiography use a phosphor plate

no. uses a flat panel detector

indirect digital vs direct digital workflow

indirect x-ray → light → electrical signal

direct x-ray → electrical signal

two materials used for indirect digital

cesium iodide, and gadolinium oxysulfide

this measure how efficiently IR converts incoming x-ray photons into useful signal with minimal noise

DQE. detective quantum efficiency (you want it high)

four steps of digital imaging chain

acquisition, processing, display, storage

segmentation

system identifies anatomy of interest and separates exposure field from background

window level

controls image brightness. higher means it gets darker. lower makes it brighter

window width

controls image contrast. increasing this makes long scale contrast. decreasing makes it short scale

quantum mottle is caused by insufficient ______ reaching the image receptor

photons

fluoroscopy

dynamic imaging used primarily for functional studies

fluoroscopic tube current is ____ to ____ mA

.5 to 5 mA

fixed fluoroscopy units minimum SSD is?

38cm or 15 inches

mobile fluoroscopy units minimum SSD is

30 cm or 12 inches

minimum SSD in fluoroscopy is used to reduce?

patient ESE

what is the fluoroscopic imaging chain

tube → patient → input phosphor → photocathode → electrostatic lenses → accelerating anode → output phosphor → camera/adc → processor → monitor

input phosphor in fluoroscopy image intensifier made of? what does it convert?

.1-.2mm cesium iodide. converts x-ray photons into light

the columnar cystal structure of fluoroscopy input phosphor does what?

reduces lateral light spread.

what does the photocathode convert? (What to what)

converts lights into electrons

what is the primary contributor to flux gain

the electrostatic lenses (the lenses increase kinetic energy)

purpose of fluoroscopy accelerating anode

increases electron kinetic energy before they reach the output phosphor

what is the charge of the accelerating anode in fluoroscopy? and has accelerating potential of ____ kVp?

positive. 25 kVp

what is the output phosphor material in fluoroscopy? what does it convert?

zinc cadmium sulfide. converts electrons into light.

flux gain

increase in brightness due to electron acceleration across an image intensifier in fluoroscopy. represents the number of light photons produced per electron

typical flux gain value

50

minification gain

increase in brightness in fluoroscopy due to output phosphor being smaller than input phosphor. electron image is focused onto smaller output phosphor.

minification gain formula

(input phosphor diameter / output phosphor diameter)²

what is the brightness gain formula

flux gain x minification gain

multifield image intensifier (dual field)

23/15

multifield image intensifier triple field

12/9/6

in fluoro a smaller field size does what to dose and what to spatial resolution

better resolution. more dose

automatic brightness controls compensates for changes in? to maintain brightness in fluoro

kVp, mA, pulse width, pulse rate

scintillator converts ____ into ____

x-rays into light

photodiodes convert _____ into ______

light into electrical signal

typical detector element size

100-200 microns

benefits of flat panel detector in fluoro

eliminates vignetting, pincushion, magnification does not increase dose

pincushion

outward edge curvature distortion

vignetting

distortion with edge brightness loss

flat panel resolution vs Csi

3 lp/mm vs 2

pulse width

in fluoro this controls the amount of time per pulse. more dose the longer it is, and less temporal resolution. also more motion blur.

pulse rate

number of pulses per second in fluoro. lower patient gets less dose but also more motion blur.

maximum tabletop exposure rate in flouro

10 R/min

typical tabletop exposure rate in flouro

1-3 R/min

tomography

creates section images. blurs structures above and below a focal plane

tomographic principle

involves tube, ir, and object.

the tube and the IR have synchronous movement. moving contralaterally

fulcrum

pivot point in which IR and image receptor move. object in the plane of this are sharp. above or below are blurred. greater distance from this the more blurred they are.

tomographic amplitude

distance tube travels. if this is larger there is more blur

exposure amplitude (angle)

distance tube travels in tomo during exposure. if this is increased the thickness is less. zonography uses a short exposure amplitude for thicker “slice”