High Yield Overview

Plain Radiography Principles

X-Ray Physics for Orthopaedic Surgeons

70-80kVp for Extremities

120kVp for Spine/Pelvis

1/d²Inverse Square Law

0.1mSvLimb X-ray Dose

Tissue Radiodensity

Air (Black)

PatternLowest density. No absorption.

Treatment-1000 HU

Fat (Dark Grey)

PatternLow density.

Treatment-100 HU

Soft Tissue (Grey)

PatternWater density.

Treatment0-80 HU

Bone (White)

PatternHigh density. High absorption.

Treatment+400-1000 HU

Metal (Bright White)

PatternHighest density.

Treatment+3000 HU

Critical Must-Knows

X-ray Production: Electrons accelerated across high voltage (kVp) strike tungsten anode → Bremsstrahlung (braking) + Characteristic radiation.
kVp controls penetration (quality): Higher kVp = more penetrating beam, lower contrast.
mAs controls quantity (exposure): Higher mAs = more photons, darker image, higher dose.
Inverse Square Law: Intensity ∝ 1/distance². Doubling distance quarters the dose.
Bone appears WHITE (radiopaque): High atomic number (Ca) absorbs more X-rays. Air appears BLACK (radiolucent).

Examiner's Pearls

"
Bremsstrahlung = 'braking radiation' = electron slows near nucleus = continuous spectrum.
"
ALARA principle: As Low As Reasonably Achievable - always minimize radiation exposure.
"
Lead apron attenuates approximately 95% of scatter radiation.
"
Pediatric patients require LOWER dose settings due to increased radiosensitivity.

Radiation Safety - ALARA Principle

Every X-ray examination must be justified (benefit outweighs risk) and optimized (minimum dose for diagnostic quality). The three cardinal principles of radiation protection are: Time (minimize exposure duration), Distance (maximize distance from source), and Shielding (use lead barriers).

X-Ray Physics

X-Ray Production

X-ray tube schematic showing cathode emitting electrons, high voltage accelerating them, and anode producing X-rays when electrons strike the tungsten target — X-ray tube schematic: Electrons are emitted from the heated cathode (C), accelerated by high voltage, and strike the rotating anode (A) producing X-rays. The copper anode (Cu) dissipates heat.Credit: OpenStax College Physics 2e, CC BY 4.0

X-rays are produced in an X-ray tube containing:

Cathode: Heated tungsten filament emits electrons (thermionic emission)
Anode: Rotating tungsten target where electrons strike
High Voltage (kVp): Accelerates electrons across the tube

Two Mechanisms of X-Ray Production

Bremsstrahlung vs Characteristic Radiation

Feature	Bremsstrahlung	Characteristic
Mechanism	Electron brakes near nucleus	Electron ejects inner shell electron
Spectrum	Continuous (all energies)	Discrete (specific energies)
Contribution	80-90% of X-ray beam	10-20% of X-ray beam
Depends on	Atomic number of target	Binding energy of shells

Technical Parameters

kVp (Kilovoltage Peak)

Controls PENETRATION (Quality)

Higher kVp = shorter wavelength = more penetrating
Higher kVp = lower contrast (more grey tones)
Extremities: 55-70 kVp
Chest: 120 kVp
Spine/Pelvis: 80-90 kVp

mAs (Milliampere-seconds)

Controls QUANTITY (Exposure)

mAs = mA × time
Higher mAs = more photons = darker image
Higher mAs = higher patient dose
Doubling mAs doubles dose

Image Formation

X-ray image contrast depends on differential absorption:

Photoelectric Effect: Complete absorption (dominates at low kVp, high atomic number)
- Proportional to Z³ (atomic number cubed)
- Responsible for bone-soft tissue contrast
Compton Scatter: Partial absorption with scattered photon
- Dominates at higher kVp
- Creates image fog (reduces contrast)
- Main source of radiation to staff

Systematic Interpretation

The ABCS Approach

Mnemonic

ABCSSystematic X-Ray Interpretation

Alignment

Joint congruity, subluxation, deformity

Bone

Fractures, lesions, density, cortex

Cartilage

Joint space, subchondral bone

Soft Tissue

Swelling, effusion, calcification, foreign body

Memory Hook:Always Be Checking Systematically

View Selection

Standard Orthopaedic Views

Region	Standard Views	Additional Views
Hand/Wrist	PA, Lateral, Oblique	Scaphoid, Carpal tunnel
Elbow	AP, Lateral	Radial head, Obliques
Shoulder	AP (IR/ER), Axillary	Scapular Y, West Point
Spine	AP, Lateral	Obliques, Flexion/Extension
Pelvis	AP	Inlet, Outlet, Judet
Hip	AP, Lateral (Cross-table)	Dunn view (for FAI)
Knee	AP (WB), Lateral	Sunrise, Rosenberg
Ankle	AP, Mortise, Lateral	Stress views

Radiation Safety

Comparison chart showing radiological exposure from various medical imaging sources including X-rays, CT, fluoroscopy — Medical radiation dose comparison chart. Note the significant difference between peripheral X-rays (0.001-0.1 mSv) and CT scans (2-20 mSv). Understanding these values is essential for informed consent and ALARA compliance.Credit: Wikimedia Commons - Wolfpaw98, CC BY-SA 4.0

Dose Reference

Typical Effective Doses

Examination	Effective Dose (mSv)	Equivalent Background
Limb X-ray	0.001-0.01	Few hours
Chest X-ray	0.02	3 days
Pelvis X-ray	0.7	4 months
Lumbar Spine	1.5	8 months
CT Abdomen	10	4.5 years

Protection Principles

Time

Minimize exposure duration. Use pulsed fluoroscopy. Last-image-hold.

Distance

Inverse Square Law: Doubling distance = 1/4 dose. Stand back during screening.

Shielding

Lead apron (0.5mm Pb), thyroid shield, lead glasses. Protect gonads in reproductive age.

Pregnancy Considerations

Fetal dose should be kept below 1 mGy throughout pregnancy
Limb X-rays pose negligible fetal risk (beam remote from uterus)
Abdominal/pelvic imaging requires careful justification and optimization
Lead shielding of abdomen does NOT protect from internal scatter
If imaging essential: use lowest dose settings, minimize field size, shield where possible

Image Quality

Factors Affecting Quality

Image Quality Parameters

Factor	Definition	Optimized By
Contrast	Difference in density between structures	Lower kVp, adequate mAs
Resolution	Ability to see fine detail	Small focal spot, minimize motion
Noise	Random fluctuation (graininess)	Adequate mAs (more photons)
Distortion	Magnification/shape change	Long SID, short OID

Common Artifacts

Motion blur: Patient/tube movement during exposure
Grid cutoff: Misaligned grid causes peripheral darkening
Scatter fog: Reduces contrast, worse with larger field size
Metal artifact: Streak artifact from implants/jewelry

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

X-Ray Physics Viva

EXAMINER

"How are X-rays produced and what determines the energy spectrum?"

EXCEPTIONAL ANSWER

X-rays are produced when high-energy electrons strike a tungsten anode. Two mechanisms: (1) Bremsstrahlung (80-90%) - electrons brake near nuclei producing continuous spectrum up to maximum keV = kVp; (2) Characteristic radiation (10-20%) - inner shell electron ejection produces discrete energy peaks. kVp determines maximum energy and penetration; mAs determines quantity of photons.

KEY POINTS TO SCORE

Bremsstrahlung = braking radiation = continuous spectrum

Characteristic = discrete peaks at specific energies

kVp controls penetration, mAs controls quantity

Tungsten used due to high melting point and atomic number

COMMON TRAPS

✗Confusing kVp with mAs effects

✗Forgetting the continuous nature of Bremsstrahlung

✗Not mentioning thermionic emission from cathode

LIKELY FOLLOW-UPS

"Why does higher kVp reduce contrast?"

"What is the inverse square law?"

"How would you reduce dose to a pediatric patient?"

VIVA SCENARIOStandard

Radiation Safety Viva

EXAMINER

"A 28-year-old woman requires a pelvic X-ray. She tells you she might be pregnant. How do you proceed?"

EXCEPTIONAL ANSWER

First, determine pregnancy status (LMP, pregnancy test if uncertain). If pregnant, assess if imaging is truly indicated - can it wait or can alternative imaging (US, MRI) provide the answer? If X-ray essential: counsel patient on low but non-zero fetal risk, use lowest dose technique, minimize field size, single AP view if sufficient. Document discussion and justification. Fetal dose from single pelvic X-ray approximately 1 mGy (well below 100 mGy threshold for deterministic effects).

KEY POINTS TO SCORE

Always ask about pregnancy in women of reproductive age

Determine if imaging can be deferred or alternative used

Fetal threshold for deterministic effects ~100 mGy

Single pelvic X-ray ~1 mGy - low but not zero risk

Lead shielding does not protect from internal scatter

COMMON TRAPS

✗Refusing all imaging in pregnancy (extremity X-rays are safe)

✗Thinking lead shielding fully protects the fetus

✗Not documenting the risk-benefit discussion

LIKELY FOLLOW-UPS

"What is the ALARA principle?"

"What are the risks of radiation in the first trimester?"

"How does dose compare between X-ray and CT?"

VIVA SCENARIOStandard

Image Interpretation Approach

EXAMINER

"Describe your systematic approach to interpreting a plain radiograph of a long bone."

EXCEPTIONAL ANSWER

I use the ABCS approach: A - Alignment: overall bone axis, joint congruity, any deformity or subluxation. B - Bone: cortical integrity (fracture lines), trabecular pattern, bone density, any focal lesions (lucent or scite), periosteal reaction. C - Cartilage/Joint: joint space width, subchondral bone, osteophytes, loose bodies. S - Soft tissues: swelling (joint effusion, soft tissue mass), calcification, foreign bodies, gas. I always ensure adequate views (minimum 2 at 90 degrees), check patient details match, and correlate with clinical findings.

KEY POINTS TO SCORE

Always use a systematic approach - never jump to obvious pathology

Two views at 90 degrees minimum for any long bone

Check entire image including edges

Correlate with clinical examination

Compare with previous imaging if available

COMMON TRAPS

✗Satisfaction of search - missing second pathology after finding first

✗Not checking patient demographics match

✗Ignoring soft tissues

LIKELY FOLLOW-UPS

"What additional views would you request for a scaphoid fracture?"

"How do you assess bone quality on X-ray?"

"What are the signs of a joint effusion on lateral knee X-ray?"

Evidence Base

Fundamental Physics and Safety

Image Quality Optimization

Australian Context

Key Evidence Points

Radiation Safety: ALARA principle mandatory in all radiographic examinations
Image Quality: Proper technique reduces repeat exposures and patient dose
DRLs: Benchmark doses help identify optimization opportunities
Quality Assurance: Regular calibration and maintenance ensure consistent image quality

Plain Radiography Exam Day Cheat Sheet

High-Yield Exam Summary

X-Ray Physics

•kVp = penetration (quality), mAs = quantity (exposure)
•Bremsstrahlung = continuous spectrum, Characteristic = discrete peaks
•Inverse Square Law: Intensity ∝ 1/d²
•Photoelectric effect: ∝ Z³, dominates at low kVp

ABCS Interpretation

•A = Alignment (joints, deformity)
•B = Bone (fracture, lesion, density)
•C = Cartilage (joint space, subchondral)
•S = Soft tissue (swelling, calcification)

Radiation Safety

•ALARA: Time, Distance, Shielding
•Limb X-ray ~0.01 mSv, Pelvis ~0.7 mSv, CT ~10 mSv
•Pregnancy: fetal threshold 100 mGy for deterministic effects
•Lead apron attenuates ~95% of scatter

Common Views

•Always minimum 2 views at 90 degrees
•WB views for arthritis assessment
•Stress views for ligament instability
•Comparison views in pediatrics

High Yield Overview

Plain Radiography Principles

X-Ray Physics for Orthopaedic Surgeons

70-80kVp for Extremities

120kVp for Spine/Pelvis

1/d²Inverse Square Law

0.1mSvLimb X-ray Dose

Tissue Radiodensity

Air (Black)

PatternLowest density. No absorption.

Treatment-1000 HU

Fat (Dark Grey)

PatternLow density.

Treatment-100 HU

Soft Tissue (Grey)

PatternWater density.

Treatment0-80 HU

Bone (White)

PatternHigh density. High absorption.

Treatment+400-1000 HU

Metal (Bright White)

PatternHighest density.

Treatment+3000 HU

Critical Must-Knows

X-ray Production: Electrons accelerated across high voltage (kVp) strike tungsten anode → Bremsstrahlung (braking) + Characteristic radiation.
kVp controls penetration (quality): Higher kVp = more penetrating beam, lower contrast.
mAs controls quantity (exposure): Higher mAs = more photons, darker image, higher dose.
Inverse Square Law: Intensity ∝ 1/distance². Doubling distance quarters the dose.
Bone appears WHITE (radiopaque): High atomic number (Ca) absorbs more X-rays. Air appears BLACK (radiolucent).

Examiner's Pearls

"
Bremsstrahlung = 'braking radiation' = electron slows near nucleus = continuous spectrum.
"
ALARA principle: As Low As Reasonably Achievable - always minimize radiation exposure.
"
Lead apron attenuates approximately 95% of scatter radiation.
"
Pediatric patients require LOWER dose settings due to increased radiosensitivity.

Radiation Safety - ALARA Principle

X-Ray Physics

X-Ray Production

X-rays are produced in an X-ray tube containing:

Cathode: Heated tungsten filament emits electrons (thermionic emission)
Anode: Rotating tungsten target where electrons strike
High Voltage (kVp): Accelerates electrons across the tube

Two Mechanisms of X-Ray Production

Bremsstrahlung vs Characteristic Radiation

Feature	Bremsstrahlung	Characteristic
Mechanism	Electron brakes near nucleus	Electron ejects inner shell electron
Spectrum	Continuous (all energies)	Discrete (specific energies)
Contribution	80-90% of X-ray beam	10-20% of X-ray beam
Depends on	Atomic number of target	Binding energy of shells

Technical Parameters

kVp (Kilovoltage Peak)

Controls PENETRATION (Quality)

Higher kVp = shorter wavelength = more penetrating
Higher kVp = lower contrast (more grey tones)
Extremities: 55-70 kVp
Chest: 120 kVp
Spine/Pelvis: 80-90 kVp

mAs (Milliampere-seconds)

Controls QUANTITY (Exposure)

mAs = mA × time
Higher mAs = more photons = darker image
Higher mAs = higher patient dose
Doubling mAs doubles dose

Image Formation

X-ray image contrast depends on differential absorption:

Photoelectric Effect: Complete absorption (dominates at low kVp, high atomic number)
- Proportional to Z³ (atomic number cubed)
- Responsible for bone-soft tissue contrast
Compton Scatter: Partial absorption with scattered photon
- Dominates at higher kVp
- Creates image fog (reduces contrast)
- Main source of radiation to staff

Systematic Interpretation

The ABCS Approach

Mnemonic

ABCSSystematic X-Ray Interpretation

Alignment

Joint congruity, subluxation, deformity

Bone

Fractures, lesions, density, cortex

Cartilage

Joint space, subchondral bone

Soft Tissue

Swelling, effusion, calcification, foreign body

Memory Hook:Always Be Checking Systematically

View Selection

Standard Orthopaedic Views

Region	Standard Views	Additional Views
Hand/Wrist	PA, Lateral, Oblique	Scaphoid, Carpal tunnel
Elbow	AP, Lateral	Radial head, Obliques
Shoulder	AP (IR/ER), Axillary	Scapular Y, West Point
Spine	AP, Lateral	Obliques, Flexion/Extension
Pelvis	AP	Inlet, Outlet, Judet
Hip	AP, Lateral (Cross-table)	Dunn view (for FAI)
Knee	AP (WB), Lateral	Sunrise, Rosenberg
Ankle	AP, Mortise, Lateral	Stress views

Radiation Safety

Dose Reference

Typical Effective Doses

Examination	Effective Dose (mSv)	Equivalent Background
Limb X-ray	0.001-0.01	Few hours
Chest X-ray	0.02	3 days
Pelvis X-ray	0.7	4 months
Lumbar Spine	1.5	8 months
CT Abdomen	10	4.5 years

Protection Principles

Time

Minimize exposure duration. Use pulsed fluoroscopy. Last-image-hold.

Distance

Inverse Square Law: Doubling distance = 1/4 dose. Stand back during screening.

Shielding

Lead apron (0.5mm Pb), thyroid shield, lead glasses. Protect gonads in reproductive age.

Pregnancy Considerations

Fetal dose should be kept below 1 mGy throughout pregnancy
Limb X-rays pose negligible fetal risk (beam remote from uterus)
Abdominal/pelvic imaging requires careful justification and optimization
Lead shielding of abdomen does NOT protect from internal scatter
If imaging essential: use lowest dose settings, minimize field size, shield where possible

Image Quality

Factors Affecting Quality

Image Quality Parameters

Factor	Definition	Optimized By
Contrast	Difference in density between structures	Lower kVp, adequate mAs
Resolution	Ability to see fine detail	Small focal spot, minimize motion
Noise	Random fluctuation (graininess)	Adequate mAs (more photons)
Distortion	Magnification/shape change	Long SID, short OID

Common Artifacts

Motion blur: Patient/tube movement during exposure
Grid cutoff: Misaligned grid causes peripheral darkening
Scatter fog: Reduces contrast, worse with larger field size
Metal artifact: Streak artifact from implants/jewelry

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

X-Ray Physics Viva

EXAMINER

"How are X-rays produced and what determines the energy spectrum?"

EXCEPTIONAL ANSWER

KEY POINTS TO SCORE

Bremsstrahlung = braking radiation = continuous spectrum

Characteristic = discrete peaks at specific energies

kVp controls penetration, mAs controls quantity

Tungsten used due to high melting point and atomic number

COMMON TRAPS

✗Confusing kVp with mAs effects

✗Forgetting the continuous nature of Bremsstrahlung

✗Not mentioning thermionic emission from cathode

LIKELY FOLLOW-UPS

"Why does higher kVp reduce contrast?"

"What is the inverse square law?"

"How would you reduce dose to a pediatric patient?"

VIVA SCENARIOStandard

Radiation Safety Viva

EXAMINER

"A 28-year-old woman requires a pelvic X-ray. She tells you she might be pregnant. How do you proceed?"

EXCEPTIONAL ANSWER

KEY POINTS TO SCORE

Always ask about pregnancy in women of reproductive age

Determine if imaging can be deferred or alternative used

Fetal threshold for deterministic effects ~100 mGy

Single pelvic X-ray ~1 mGy - low but not zero risk

Lead shielding does not protect from internal scatter

COMMON TRAPS

✗Refusing all imaging in pregnancy (extremity X-rays are safe)

✗Thinking lead shielding fully protects the fetus

✗Not documenting the risk-benefit discussion

LIKELY FOLLOW-UPS

"What is the ALARA principle?"

"What are the risks of radiation in the first trimester?"

"How does dose compare between X-ray and CT?"

VIVA SCENARIOStandard

Image Interpretation Approach

EXAMINER

"Describe your systematic approach to interpreting a plain radiograph of a long bone."

EXCEPTIONAL ANSWER

KEY POINTS TO SCORE

Always use a systematic approach - never jump to obvious pathology

Two views at 90 degrees minimum for any long bone

Check entire image including edges

Correlate with clinical examination

Compare with previous imaging if available

COMMON TRAPS

✗Satisfaction of search - missing second pathology after finding first

✗Not checking patient demographics match

✗Ignoring soft tissues

LIKELY FOLLOW-UPS

"What additional views would you request for a scaphoid fracture?"

"How do you assess bone quality on X-ray?"

"What are the signs of a joint effusion on lateral knee X-ray?"

Evidence Base

Fundamental Physics and Safety

Image Quality Optimization

Australian Context

Key Evidence Points

Radiation Safety: ALARA principle mandatory in all radiographic examinations
Image Quality: Proper technique reduces repeat exposures and patient dose
DRLs: Benchmark doses help identify optimization opportunities
Quality Assurance: Regular calibration and maintenance ensure consistent image quality

Plain Radiography Exam Day Cheat Sheet

High-Yield Exam Summary

X-Ray Physics

•kVp = penetration (quality), mAs = quantity (exposure)
•Bremsstrahlung = continuous spectrum, Characteristic = discrete peaks
•Inverse Square Law: Intensity ∝ 1/d²
•Photoelectric effect: ∝ Z³, dominates at low kVp

ABCS Interpretation

•A = Alignment (joints, deformity)
•B = Bone (fracture, lesion, density)
•C = Cartilage (joint space, subchondral)
•S = Soft tissue (swelling, calcification)

Radiation Safety

•ALARA: Time, Distance, Shielding
•Limb X-ray ~0.01 mSv, Pelvis ~0.7 mSv, CT ~10 mSv
•Pregnancy: fetal threshold 100 mGy for deterministic effects
•Lead apron attenuates ~95% of scatter

Common Views

•Always minimum 2 views at 90 degrees
•WB views for arthritis assessment
•Stress views for ligament instability
•Comparison views in pediatrics