Comprehensive Radiographic Image Production

Increase SID Geometric Effect

1.decrease magnification and distortion

2.increase recorded detail

3.require increased exposure

Increased OID Geometric Factors

1.increase magnification

2.decrease spatial resolution

3.air gap technique decrease scatter but also decrease IR exposure

Focal Spot Size Geometric Factors

smaller size provide better recorded detail due to decreased penumbra(blur)

Motion Geometric Factors

voluntary and involuntary reduce recorded detail; controlled through short exposure time and immobilization

Alignment Geometric Factors

x-ray tube, anatomy, and IR need proper arrangement together to avoid shape distortion(foreshortening/elongation)

Shape Distortion

foreshortening(improper part alignment) and elongation(improper tube/IR alignment)

Brightness vs Density

digital use term brightness but film use term density

Digital Brightness Control

LUT and window level

Film Density Control

mAs

mAs

control quantity of x-rays; directly impact IR exposure and density in film; NO effect on contrast

kVp

control quality and penetration of beam

1.increases IR exposure

2.decrease image/subject contrast

3.increase beam penetration

kVp and Image Contrast Relationship

inverse

Inverse Square Law

doubling the distance decreases exposure to 1/4; halving it increases exposure 4x

15% Rule

15% increase in kVp doubles exposure(same as ½ mAs) or 15% decrease in kVp halves exposure(same as 2x mAs)

Grid

1.remove scatter radiation to improve image contrast

2.increase patient dose

3.require increase exposure factors

Grid Ratio

height of lead strips/distance between them; higher reduce more scatter but require more exposure factors

Grid Frequency

number of lead lines per in/cm; higher produce less visible grid lines but more scatter to IR

Grid Types

parallel and focused

Grid Cutoff Cause

improper alignment; types include off-center, off-level, off-focus, and upside-down

Contrast Improvement Factor

radiographic contrast with grid/radiographic contrast without grid; 1.5-3.5x; better with more lead content and higher grid ratio

Grid Selectivity

percent of primary radiation/percent of scatter radiation reaching IR; better with higher grid lead content

Grid Conversion Formula

mAs 1/mAs 2=GF1/GF2

5:1 Conversion

x2 mAs, +10 kVp

6:1 Conversion

x3 mAs, +12 kVp

8:1 Conversion

x4 mAs, +16 kVp

10:1 Conversion

x5 mAs, +18 kVp

12:1 Conversion

x5 mAs, +20 kVp

16:1 Conversion

x6 mAs, +25 kVp

Computed Radiography(CR)

use photostimulable phosphor(PSP) plates composed of barium fluorohalide; require scanning by laser and emits blue-violet light(PSL)

Indirect DR

1.scintillator(cesium iodide or gadolinium oxysulfide) convert x-ray to light

2.photodiode(amorphous silicon) convert light to electrical signal

Direct DR

amorphous selenium directly convert x-rays into electrical charge without scintillator

Alternative Indirect Detectors

CCD(bucket brigade architecture) and CMOS(more power efficient but more noise)

Signal to Noise Ratio(SNR)

higher produce better image quality and low cause quantum mottle

Contrast to Noise Ratio(CNR)

measure contrast in presence of noise, digital have higher than film

Detective Quantum Efficiency(DQE)

indicate how efficiently a detector converts incoming x-ray to output image; higher creates better image at lower dose

Spatial Resolution Factors

matrix size, pixel size(DEL), and sampling frequency

Spatial Resolution Measurement

line pairs per mm

Bit Depth

controls gray scale levels; higher allows more shades of gray(14 bit=16,384 shades)

Pre-Processing

happens automatically and includes histogram creation, LUT application, and flat-field corrections

Post-Processing

windowing(level and width), filtering(high-pass and low-pass), and equalization

Histogram Analysis

maps pixel intensity values; errors occur due to poor collimation or incorrect algorithm selection

Look-Up-Table(LUT)

alters brightness and contrast by adjusting the input-output pixel value relationships

Flat-Fielding

corrects pixel-to-pixel sensitivity variations using gain and offset images and interpolation to reduce artifacts and make IR response uniform

Offset Images

correct for image lag(image not made completely visible)

Gain Images

corrects for line noise(variations in buses that drive each DEL)

Regular QC

ensure consistency and safety in imaging performance; tests include detector calibration, erasure checks, uniformity, and spatial resolution

Plate Reader Calibration

ensure accurate exposure indicator values in CR

Detector Uniformity

check for consistent response across IR

Linearity and Slope

asses relationship between exposure and pixel value

Dark Noise

evaluates inherent noise in detectors without exposure

Ghosting and Image Retention

residual image from previous exposure due to incomplete erasure

Long Scale Contrast

low contrast, many shades of gray, high kVp

Short Scale Contrast

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

Air Gap Technique

increase contrast by removing scatter reaching the IR

Fixed kVp Charts

maintain constant kVp and adjust mAs for part thickness

Fixed kVp Chart Advantages

more consistent contrast and lower dose

Variable kVp Charts

adjust kVp by 2 per cm thickness while keeping mAs constant

Variable kVp Chart Advantages

best for small anatomy changes

Additive Pathologies

require increase technique due to increased tissue density

Additive Pathology Examples

pneumonia, CHF, ascites, atelectasis, tumor, edema, empyema, pleural effusions(hemothorax), cirrhosis, acromegaly, osteomyelitis, rheumatoid arthritis, Paget’s, edematous tissue

Destructive Pathologies

decrease technique due to reduced tissue density

Destructive Pathology Examples

emphysema, osteoporosis, osteoarthritis, osteomalacia, necrosis, atrophy, osteomyelitis, degenerative arthritis, pneumoperitoneum

Cast/Splint Adjustments

fiberglass(rarely require changes), plaster(requires increase of technique especially wet); use calipers to measure thickness than adjust technique

Picture Archiving and Communication System(PACS)

manages image storage, retrieval, distribution, and display

Digital Imaging and Communications in Medicine(DICOM)

standard that ensures interoperability between imaging systems; includes GSDF for consistent grayscale

Hospital Information System(HIS)

manages patient records

Radiology Information System(RIS)

handles imaging workflow and scheduling

Deviation Index(DI)

indicate exposure accuracy; 0 ideal; +1=25% overexposed, -1=20% underexposed

Quantum Mottle

grainy image, due to low mAs or poor signal

Moire Effect

interference pattern from grid frequency aligning with scanning laser

Dead Pixels

result in permanent image dropout; fixed by interpolation

Halo Effect

occur from excessive equalization; appears as bright glow around structures

Increase SID

1.decrease magnification

2.increase resolution

3.decrease exposure(inverse square law)

Increase OID

1.increase magnification

2.decrease resolution

3.increase contrast(air-gap)

Decrease Focal Spot Size

increase resolution(smaller penumbra)

Increase mAs

increase exposure(brightness), NO effect on contrast

Increase kVp

1.increase exposure

2.decrease contrast

3.increase scatter

Increase Grid Ratio

1.decrease scatter

2.increase contrast

3.increase technical factors

Increase Bit Depth

1.increase gray scale

2.increase contrast resolution

Increase Matrix Size

1.increase spatial resolution

2.decrease pixel size

Increase Sampling Frequency

1.increase MTF

2.increase spatial resolution