Chapter 7: Radiography Flashcards by Aileen Castillo

(a+b)/a
a = src to obj distance
b = obj to detector distance

Object Magnification

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parameter that is kept consistent during xray

Source to image distance

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General SID and upright Chest SID

100 cm (40 inches) and 183 cm (72 inches)

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types of radiography where a sheet of film with light sensitive emulsion on both sides sandwiched between 2 intensifying screens

Screen film radiography

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converts incident xray photons to visible light which exposes the Ag halide emulsion of the film

Scintillator

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material used in scintillator

Gd2O2S

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In screen film radiography, only one screen with single emulsion film is used

Extremities and Mammo

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The film is a thin plastic base coated on one or both sides with a layer of light sensitive emulsion, consisting of _____ held in water soluble gelatin

Ag halide crystals (95% AgBr/AgI)

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AgS introduces defects producing a protrusion of the (+) charge that reaches the surface of the crystal, which is called _______.

Sensitivity Speck

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Reducing Agent and Oxidizing Agent

Reducing Agent - Developer

Oxidizing Agent - Fixer

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This corresponds to the non linear change of the Optical density (OD) with respect to the xray exposure.

Hurler and Driffield (H&D Curve)

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A low contrast and wide latitide is required in _____.

A high contrast and narrow latitude is required in ______.

Chest xray and Mammography

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Xrays are absorbed by PSP, some light is emitted but a fraction is trapped in the PSP screen and can be read out later using laser light. these systems are housed in cassette.

Computed Radiography

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Phosphors usually composed of

BaFBr or other Ba Fluorohalides

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CR Reader translate the image plate _______ by rollers across the moving stage, then scans ______ by a laser beam

Vertically and horizontally

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typical imaging plates are usually composed of ______ and is activated with _____. The activation is called ____.

85% BaFBr/15%BaFl
Europium
Doping

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Form image using visible light, using an integrated circuit using crystalline silicon

Charge couple device (CCD)

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stage where the # of quanta is lowest

Quantum sink

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optically couples to an xray scintillator by fiberoptic channel plates.

Linear CCS arrays

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used is slot scan systems and use a narrow xray fan beam

Linear CCD Arrays

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This type of xray is useful in examinations of chest and in full body trauma imaging

Linear CCD arrays

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based on crystalline silicon matrix. These are RAM chips with built in photosensitive detectors, storage capacitors and active readout electronics

CMOS

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Major issue of CMOS

Limitation of CMOS

Electronic noise

Small FOV

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Signal modulates light transmitter from a backlit liquid crystal display element

Thin film transistor (tft) array

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TFT charge collection electrode + storage capacitor

Dexel

USe a scintillator to convert xrays to light with optical coupling of the scintillator to the active matrix

Indirect Detection TFT arrays

Scintillator use in Indirect TFT

CsI

Disadvantage of Indirect TFT

light released inthe scintillator layer has to propagate large distances and may cause blurring and loss of spatial resolution

Percent of each dexel taht is photosensitive

Fill factor

Use a semiconductor material that produces electron hole pairs in proportion to incident xray intensity

Direct detection TFT arrays

Widely used conductor for DIrect Detection TFT arrays

Amorphous Selenium

Relate the relationship of kV in relation to the Patient Dose Contrast resolution (and why and where is it used?)

Low kV Inc Px Dose but Inc Contrast resolution Lower kV emphasize contrast due to PE effect on px which is impt for high z materials (bone)

In CXR is the kV low or high?

HIGH High kV is used (120kV) to decrease conspicuity of the ribs by reducing PE effect

High mA allows exposure time to be (shorter/longer).

High mA allows exposure time to be SHORTER -> Freezes px motion mA is set at high value (500( and exp time is determined by the AEC

converts xray to visible light which exposes the film emulsion or photoconductor

scintillator

thicker/thinner phosphor screen, more spreading of light.

THICKER Called lateral light propagation. CsI has less lateral light propagation

One factor of xray detectors (phosphor layer) | It is determined by the phosphor composition (z and density) and screen thickness, as well as, the xray beam energy

Absorption efficiency NOTE: Thicker, denser phosphor layer absorb more of the incident xray beam but concomitant incin blurring and loss of spatial resolution has to be considered

This described how well xray detectors capture the incident photom beam but does not include xray fluorescence (from reemission of photon energy)

Quantum detection efficiency

Describes how efficiently the optical signal is conveyed from the scintillator to the photodetector and subsequently amplified and converted to signal in the image

Conversion efficiency

phenomenon whereby technologists tendto use unnecessary high exposures

dose creep

indicates amount of radiation reaching the detector If this a indicator of dose to patient?

Exposure index NO.

reduces anatomical noise and produces imagewithbetter information content. acquires 2 radiographic images at 2 different effective energy levels (kV) enable either the bone/ST component to be removed by image post processing

Dual Energy Radiography

Refers to the amt of scatter in an image

Scatter to primary ratio (SPR) or scatter fraction

Scatter fraction INC or DEC in relation to | volume of tissue irradiated, field size and patient thickness

INCREASES in ALL

most widely used technology to reduce scatter in radio, fluoro and mammo

Antiscatter grid

most fundamental descriptor of the grid's construction

grid ratio

ratio of the height of the interspace material to its width

grid ratio Lower in mammo

Grid septa is usually made up of ____

Lead

Solid interspace material should be used to keep the malleable septa aligned, which is made up of

Al - low cost | Carbon fiber grids - more common

What is the grid type used in diagnostic xrays and mammo?

Dx xrays - linear grid | Mammo - crossed grid

this is a moving grid whichs moves with a reciprocating motion during exposure causing the grid bars to be blurred and not visible on the image. Movement is perpendicular to the long axis of the septa.

Bucky grid

Refers to the relative increase in x ray intensity or equivalent mA needed when a grid is used typically, 3-8

Bucky factor

fraction of primary photons transmitted thru the grid

Primary transmission factor Ideally 1 Usually 0.5 to 0.75

Fraction scattered radiation that penetrates the grid

ideally 0 | usually 0.05 to 0.2

Gold standard in scatter radiation reduction methods

Scan slot system

One gray is equal to

100 rads

Xray tube output:air kerma

mGy per 100mAs at 100cm

Distance from the xray tubes focal spot to the entrance skin layer

Source to skin distance (SSD)

Free in air measurements

Without backscatter

Surrogate measure of the dose used in projection radiography

ESK

Use computer simulation to study the dose deposition during an xray exposure

Monte Carlo procedures

Compute the 3D dose distribution for a given exposure geometry

Monte Carlo calculations

Based on tracking the trajectory and energy deposition of xray photons through a mathematical phantom with a defined geomatery and composition

Monte Carlo dosimetry