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The Essential Physics Of Medical Imaging 3rd Edition > Chapter 7: Radiography > Flashcards

Chapter 7: Radiography Flashcards

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1
Q

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

A

Object Magnification

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2
Q

parameter that is kept consistent during xray

A

Source to image distance

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3
Q

General SID and upright Chest SID

A

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

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4
Q

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

A

Screen film radiography

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5
Q

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

A

Scintillator

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6
Q

material used in scintillator

A

Gd2O2S

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7
Q

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

A

Extremities and Mammo

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8
Q

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

A

Ag halide crystals (95% AgBr/AgI)

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9
Q

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

A

Sensitivity Speck

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10
Q

Reducing Agent and Oxidizing Agent

A

Reducing Agent - Developer

Oxidizing Agent - Fixer

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11
Q

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

A

Hurler and Driffield (H&D Curve)

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12
Q

A low contrast and wide latitide is required in _____.

A high contrast and narrow latitude is required in ______.

A

Chest xray and Mammography

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13
Q

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.

A

Computed Radiography

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14
Q

Phosphors usually composed of

A

BaFBr or other Ba Fluorohalides

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15
Q

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

A

Vertically and horizontally

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16
Q

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

A

85% BaFBr/15%BaFl
Europium
Doping

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17
Q

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

A

Charge couple device (CCD)

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18
Q

stage where the # of quanta is lowest

A

Quantum sink

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19
Q

optically couples to an xray scintillator by fiberoptic channel plates.

A

Linear CCS arrays

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20
Q

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

A

Linear CCD Arrays

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21
Q

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

A

Linear CCD arrays

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22
Q

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

A

CMOS

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23
Q

Major issue of CMOS

Limitation of CMOS

A

Electronic noise

Small FOV

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24
Q

Signal modulates light transmitter from a backlit liquid crystal display element

A

Thin film transistor (tft) array

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25
Q

TFT charge collection electrode + storage capacitor

A

Dexel

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26
Q

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

A

Indirect Detection TFT arrays

27
Q

Scintillator use in Indirect TFT

A

CsI

28
Q

Disadvantage of Indirect TFT

A

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

29
Q

Percent of each dexel taht is photosensitive

A

Fill factor

30
Q

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

A

Direct detection TFT arrays

31
Q

Widely used conductor for DIrect Detection TFT arrays

A

Amorphous Selenium

32
Q

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

A

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)

33
Q

In CXR is the kV low or high?

A

HIGH

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

34
Q

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

A

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

35
Q

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

A

scintillator

36
Q

thicker/thinner phosphor screen, more spreading of light.

A

THICKER

Called lateral light propagation.
CsI has less lateral light propagation

37
Q

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

A

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

38
Q

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

A

Quantum detection efficiency

39
Q

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

A

Conversion efficiency

40
Q

phenomenon whereby technologists tendto use unnecessary high exposures

A

dose creep

41
Q

indicates amount of radiation reaching the detector

If this a indicator of dose to patient?

A

Exposure index

NO.

42
Q

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

A

Dual Energy Radiography

43
Q

Refers to the amt of scatter in an image

A

Scatter to primary ratio (SPR) or scatter fraction

44
Q

Scatter fraction INC or DEC in relation to

volume of tissue irradiated, field size and patient thickness

A

INCREASES in ALL

45
Q

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

A

Antiscatter grid

46
Q

most fundamental descriptor of the grid’s construction

A

grid ratio

47
Q

ratio of the height of the interspace material to its width

A

grid ratio

Lower in mammo

48
Q

Grid septa is usually made up of ____

A

Lead

49
Q

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

A

Al - low cost

Carbon fiber grids - more common

50
Q

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

A

Dx xrays - linear grid

Mammo - crossed grid

51
Q

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.

A

Bucky grid

52
Q

Refers to the relative increase in x ray intensity or equivalent mA needed when a grid is used

typically, 3-8

A

Bucky factor

53
Q

fraction of primary photons transmitted thru the grid

A

Primary transmission factor

Ideally 1
Usually 0.5 to 0.75

54
Q

Fraction scattered radiation that penetrates the grid

A

ideally 0

usually 0.05 to 0.2

55
Q

Gold standard in scatter radiation reduction methods

A

Scan slot system

56
Q

One gray is equal to

A

100 rads

57
Q

Xray tube output:air kerma

A

mGy per 100mAs at 100cm

58
Q

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

A

Source to skin distance (SSD)

59
Q

Free in air measurements

A

Without backscatter

60
Q

Surrogate measure of the dose used in projection radiography

A

ESK

61
Q

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

A

Monte Carlo procedures

62
Q

Compute the 3D dose distribution for a given exposure geometry

A

Monte Carlo calculations

63
Q

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

A

Monte Carlo dosimetry

The Essential Physics Of Medical Imaging 3rd Edition (13 decks)

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