Lange Image Acquisition and Technical Evaluation

Spatial Resolution Direct Digital Factors

TFT and DEL size(inverse-smaller better); always fixed

Spatial Resolution Indirect Digital Factors

sampling frequency, laser scanner, PSP

Exit/Remnant X-Ray Subject Contrast Factors

kV and photon energy

Exit/Remnant X-Ray Image Contrast Factors

rescaling, windowing, LUT

Additive Osteo Pathologies

osteomyelitis, osteosclerosis, osteochondritis

Subtractive Osteo Pathologies

osteoporosis and osteomalacia

X-Ray Imaging Algorithm

series of variable instructions

Aliasing Artifact

moire effect with appearance of wavy linear lines with CR using stationary grids

Aliasing Cause

grid’s lead strip pattern(frequency) matches scanning(sampling) pattern of scanner/reader; decreased with decreased sampling frequency

Osteoporosis

increased porosity and softening of bone typically in elderly patients; bones more dense need to decrease exposure

Osteosclerosis

abnormal hardening of bone, increase in exposure factors required

DEL Components

sensing area(fill factor), TFT, and capacitor

DEL Fill Factor

largest portion, made of amorphous selenium in direct digital systems, 75%-80% good

Best Fill Factor

highest number; creates higher contrast resolution, spatial resolution, and SNR

DEL Capacitor

stores electrical charges

DEL TFT

acts as switch/gate to release charges for readout

CCD

charge coupled device coupled with an image intensifier

Geometric Sharpness Inverse Factors

OID because as it increases magnification increases

Geometric Sharpness Direct Factors

SID and SOD because as they increase magnification decreases

Exposure Artifact

motion, double exposure, and patient clothing/jewelry

Increase kVp Effect on Remnant Beam/Signal

1.increased exposure rate

2.increased production of scattered radiation

3.increased image noise

4.decreased visibility of image details

5.decreased radiographic contrast

Image Spatial Resolution/Image Sharpness Factors

patient factors, focal spot size(inverse), SID(direct), OID(inverse), SOD(direct), motion

NOT mA

Insufficient mAs Factors

cause quantum noise/mottle which is a grainy appearance that is spotted/freckled

Grid Cutoff

absorption of useful beam by grid and usually results in loss of signal and visibility of grid lines

Anode Heel Effect Greatest

1.short SID

2.large IRs

3.small anode angles(steep target)

4.parts with uneven tissue densities

AEC Backup Timer Function

prevent patient overexposure and prevent x-ray tube overheating; terminates exposure in case AEC fails

Photon Energy Factors

1.kVp(direct)

2.wavelength(inverse)

NO relation to mA

Magnification Factors

1.SID(inverse)

2.OID(direct and most significant)

NO relation to focal spot size

OID Correction

7in SID increase for every inch of OID

Off-Center Grid Error

overall loss of receptor exposure

Off-Center and Incorrect SID Grid Error

over or under exposure under anode

Low-Pass Filtering

postprocessing spatial frequency filtering that does image smoothing through removal of high-frequency noise by averaging the frequency of each pixel with that of surrounding pixels

Low-Pass Filtering Advantages

visualization of small fine anatomic details

Windowing

post-processing to adjust brightness and contrast of digital image

Edge Enhancement

averages fewer adjacent pixels, result in enhancement of interface between adjacent structures

AEC Needed Factors

proper positioning, centering, and photocell selection

Resolution

how closely fine details may be associated and still recognized as separate details(not blending and appearing as one)

Resolution Units

lp/mm, line-spread function(LSP), modulation transfer function(MTF)

Line Pairs per Millimeter Measurement

use resolution test pattern while using 10mm x-ray beam

MTF

measure amount of information lost between object and IR

Effective Focal Spot

foreshortened size of actual focal spot as it is projected down toward the IR

Line-Focus Principle

how the angled surface of the anode(target) creates smaller effective focal spot size from perspective of patient(looking up) while maintaining larger actual focal spot on anode

Foreshortening

improper part alignment; cause object projected on IR to be smaller than its original size

Elongation

improper tube or IR alignment

Shape Distortion

foreshortening or elongation caused by improper alignment of tube, part, and IR

Size Distortion

magnification caused by increased OID along with decreased SID

Minimize Motion Unsharpness Methods

suspend respiration, short exposure time, patient instruction, immobilization

kV Increase per Centimeter Thickness

2 kV added per each cm

Automatically Programmed Radiography(APR)

radiographer uses console graphics or touch screen to select anatomic part and its relative size(S/M/L) to be imaged; used in conjunction with AEC

Object within IP

creates sharply delineated edges

Object Not Within IP

blurred edges due to magnification from increased distance

Remnant Signal Factors

tissue density, pathology, beam restriction

Differential Attenuation Effect

impacts exit radiation signal reaching the IR

PA Chest EC

adequate penetration with faint visualization of t-spine through heart also lung vasculature, long scale contrast with many shades of gray, adequate inspiration with 10 pairs of posterior ribs above diaphragm

AEC

device that terminates exposure following ionization of a particular quantity of an air

Grid Ratio

height of lead strips/width(distance) between them

High Grid Ratio Advantages

absorb more scattered and primary radiation but require very accurate centering

Decrease kV Effects

1.decrease photon energy

2.decrease receptor exposure

NO effect on resolution

Lateral Soft Tissue Neck EC

air-filled airway demonstrated, no motion unsharpness, sufficient receptor exposure to visualize bony anatomy of c-spine

X-Ray Beam Filtration Function

reduce patient skin dose by removing low energy photons that could be absorbed by patient

kVp 15% Rule

increase in 15% kVp(x1.15) doubles exposure(1/2 mAs) and decrease in 15% kVp(x.85) halves exposure(x2 mAs)

Exposure Maintenance Formula

mAs₁/mAs₂=D₁²/D₂²

Magnification Factor

degree of magnification; SID/SOD

Magnification Equation

image size/object size

Law of Image Magnification

image size/object size=SID/SOD

Analog IVU Imaging Recommendations

use low kV to enhance photoelectric effect and provide better visualization of renal collecting system, use high mAs for short exposure time

Digital IVU Imaging Recommendations

can use high kV due to postprocessing capabilities, allows for reduced patient exposure, use high mAs for short exposure time

Primary Beam Exposure Rate Factors

mA, kV, and distance(NOT field size)

IR Exposure Biggest Determinant

SID due to inverse square law of radiation(DISTANCE)

Subject Contrast Factors

differential tissue absorption, atomic number of tissue being traversed, and pathology; NOT mAs

SOD

SID-OID

Contrast

difference between adjacent brightness levels; used to make details visible

Grayscale

number of brightness levels or shades of gray

Long Scale Contrast

low contrast, mangy shades of gray with little difference between them, high kVp

Short Scale Contrast

high contrast, few gray shades(black and white), low kVp

Pixel

two dimensional picture element; measured in XY direction

Voxel

three dimensional volume element; measured in Z direction; depth

Block Depth

number of bits required to describe gray level that each pixel can take on(bit depth)

FOV

describe how much of the patient is included in the matrix; increased in a fixed matrix increases size of pixels

Compensating Filter

device used to overcome severe variation in patient anatomy or tissue density providing more uniform receptor exposure

Collimator

used to decrease production of scattered radiation by limiting the volume of tissue irradiated

Dropout Artifacts

tiny areas of increased brightness; dust/dirt particles on PSP

CR PSP Backscatter

overall gray appearance of fog over image

CR PSP Phantom Image

caused by incomplete erasure of previous image

CR PSP Image Fading

caused by exposed image being left several hours without processing and causing blurring of entire image

Radiographic Image Requirements

1.patient name/identification number

2.correct left/right side marker

3.date of examination

4.identity of institution or office

Require Increase of Technical Factors

excessive BMI, additive pathologies(skeletal sclerosis, ascites, pulmonary edema)

Require Decrease in Technical Factors

asthenic patients, degenerative pathology(osteomalacia, osteoporosis, emphysema)

Matrix

number of pixels in XY direction, larger produce better resolution due to smaller pixels and pixel pitch

Anode Heel Effect

causes highest intensity at the cathode end of the beam due to beveled anode focal track facing the cathode allowing photon divergent towards it

Computed Radiography

use IP to enclose PSP, delayed image display, lower DQE and higher patient dose, require ADC

Digital Radiography

use IR detector, immediate image display, higher DQE and lower patient dose, direct or indirect conversion

Grid Conversion Formula

mAs 1/mAs 2=GF1/GF2

5:1 Grid Conversion

x2 mAs, +10 kVp

6:1 Grid Conversion

x3 mAs, +12 kVp

8:1 Grid Conversion

x4 mAs, +16 kVp

10:1 Grid Conversion

x5 mAs, +18 kVp

12:1 Grid Conversion

x5 mAs, +20 kVp

16:1 Grid Conversion

x6 mAs, +25 kVp