BASICS OF RADIOLOGY🗸

BASICS OF RADIOLOGY

Types of Radiation

• Electromagnetic radiation
• Travel as photons like light.
• Light is not used for imaging due to poor penetration.
• X-rays.
• Gamma rays.
• Have maximum penetration power (out of alpha, beta, X-rays).
• Mnemonic: Penetrate → Game over (Gamma)

• Particulate radiation
• Alpha.
• Most damaging.
• Most ionizing.
• Maximum linear energy transfer (LET).
• Mnemonic: Alpha has maximum energy (LET) → and most damaging ()
• Beta.
• Neutrons.
• The above are called Ionizing radiation.

Damage and Penetration

• Damage and penetration are inversely related.
• Decreased penetration means increased damage.

• Damage Caused:
• Alpha > Beta > X-ray > Gamma.

• Penetration Caused:
• Neutrons > Gamma > X-ray > Beta > Alpha.

• Neutrons:
• Penetrating power > Gamma.

No radiation in

• No radiation → non-ionizing.

• USG
• Uses sound waves.
• FAST.
• Doppler: An ultrasound for blood flow.

• MRI
• Uses Radio waves.
• MRCP (Magnetic Resonance Cholangio pancreatography).

Radiation is seen in

• X-rays (not produced from the nucleus)
• Used in radiography.
• CT scan (3D X-ray).

• Gamma rays
• Comes from the nucleus of the atom.
• Used in nuclear medicine.
• Nuclear medicine modalities include:
• Scintigraphy.
• Radioisotope scan.
• PET.
• SPECT scan.

Note

• ERCP:
• Is a contrast X-ray (Dye study).
• Has radiation exposure.
• Procedure:
• Endoscope goes to duodenum.
• Into the duct.
• Contrast is put.
• X-ray images are taken.

• Intravenous Pyelogram:
• Contrast X-ray.
• For kidney, ureter, bladder.

• HSG (Hysterosalpingography):
• Contrast X-ray.
• For uterus and Fallopian tubes.

CT Scan in Females:

• LMP should be asked.

• To rule out pregnancy.

• Rule of 10:
• Investigations with radiation exposure.
• Should be done within ten days of LMP.
• This ensures no ovulation/fertilization/pregnancy.

Machine /Equipment identification

X-ray Machine

• This is a digital X-ray machine.

• Advantage: digital image.

• The X-ray beam is detected by an electronic detector, image appears on the screen.

• Can be accessed by anyone in the hospital with a PACS system
• (Picture Archiving and Communication system).

USG

• Uses sound waves.

• Frequency is outside the human audible range (2 -20 Megahertz's).

CT vs MRI

• CT Machine:
• Tunnel is absent.

• MRI Machine:
• Tunnel is present.

• MRI and Claustrophobia:
• Contraindicated in claustrophobic patients.
• Can be done using sedation.

• MRI Magnet Strength:
• Unit is Tesla.

Room Walls:

• CT room:
• Coated with Lead.

• MRI room:
• Have a Faraday's cage.
• Prevents disturbance from outside radiowaves with MRI radiowaves.

Speed:

• CT is always faster.
• Example:
• CT brain: 2 mins vs
• MRI brain: 20 mins.

• CT is preferred in emergencies.

Principles of Various Modalities

1. X-ray

• X-ray tube is the source.

• Electrons come from cathode to anode.

• Anode has Tungsten.
• Incoming electrons are deflected by the anode nucleus.
• This is Bremsstrahlung radiation.

• Another method of producing radiation is
• Characteristic radiation.
• Characteristic of the anode material.

• Mnemonic: Xray → Electron → Anayude (Anode) tongue (Tungsten) vazhi straw itt Lungsilott (Brem staw Lung radiation)

2. CT scan

• X-ray tube rotates around the patient, taking images from all angles.
• Continuous rotation by slip ring technology (Spiral CT).

3. Ultrasound

• Based on the Piezoelectric effect.

• In the probe, a crystal converts electricity into sound
• 2 -20 MHz

• Sound goes into the body, returns, and is converted back into electricity.

• Crystal is made of Lead Zirconium Titanate.
• Mnemonic: Piezo → Pb, Z, T → Lead Zirconium Titanate

4. MRI

• Based on the gyromagnetic property of moving protons.
• 1.5, 3 tesla

• Based on H+.

• Best Constrast

• Takes 20 - 30 mins → Not useful in emergencies

• NMR (Nuclear magnetic resonance) is the principle.

• Mnemonic: MRI to Protect (Proton) Neymer (NMR)

5. PET

• Positron Emission Tomography.

• Principle is annihilation coincidence circuit.

• 18F-FDG is used.

• Mnemonic: Put Pet (PET) in AC (ACC → Annihilation coincidence circuit)

Terminologies - Black and White

X-ray Tube Construction

• Cathode:
• Electrons are produced at the cathode.
• By Thermionic emission (in a vacuum).
• Made of Tungsten (W).

• Anode:
• Made of Tungsten (W).

• X-ray Tube:
• Must have a vacuum.
• No gas should be present.
• To interact with moving electrons.

• X-ray Production:
• Occurs when the fast-moving electron beam is suddenly stopped.

Normal vs Mammography X-ray tube

• Mammography is the X-ray of the breast.

• Requires a different machine due to different X-ray tube construction and potential.

X-ray tube in mammography:

• Anode - Molybdenum.
• Mnemonic: Moly de Mammogram

• Has a lower atomic number than Tungsten.

• Produces low energy X-rays (low kV).
• Low kV- improves image contrast (to see microcalcifications).

• Machine has a compression plate.
• Compression is a must for mammography.

Five basic densities on X-ray

Lesser density leads to:

• More X-ray penetration.

• Blacker appearance.

Appearance by Density:

• Air:
• Appears black.
• Least dense.

• Metal:
• Appears white.
• Most dense.

• Fat:
• Appears dark.
• Less dense than water.

Order of Increasing Density and Whiteness:

• Air < Fat < Water/soft tissue < Bone < Metal.

Clinical Examples:

• Consolidation of lungs:
• Appears white.

• Collapse of lung (no air):
• Appears white.

• Pneumothorax:
• Appears black.

HU value

• HU - Hounsfield units
• Used in CT scans.
• After Godfrey Hounsfield.

• Depends on attenuation coefficient/electron density.

High attenuation coefficient → high HU value.

• Mnemonic: Beware → Be (Bone) Wa (water) AIR

• Fat-containing lesion:
• Angiomyolipoma
• A/w Tuberous sclerosis

Image 1

• CT showing Metallic foreign body
• streak artifact.

• Image 3: Kidney has the same density as subcutaneous fat.
• Dirty black appearance.
• Fat containing Angiomyolipoma

Image 2

• CT showing white

• acute hemorrhage
• Hyperdense on Non-contrast CT.

• Chronic hemorrhage:
• RBC lysis,
• density decreases,
• becomes hypodense.

Image 4:

• Jet black color surrounding the lung
• Pneumothorax.

NCCT vs CECT

• CECT (Contrast-Enhanced CT):
• Contrast: Important if lesions are suspected.
• Uses IV iodinated contrast.
• A white aorta identifies it as a contrast scan.
• Contrast shows how lesions take up contrast.
• Compared to normal liver.
• Early/more contrast → appear more white.

• NCCT (Non-Contrast CT):
• Lesions with the same density as adjacent parenchyma get camouflaged.

Indications

Indications for Contrast:

• Lesion/Tumour.

• Infections/Inflammation.

Indications for NCCT:

• Calcifications.

• Renal stones:
• Calcified stones.

• Acute hemorrhage.

• Chronic hemorrhage:
• SWI MRI picks up hemosiderin well.

• Exception: NOT Gall bladder stones:
• Non-calcified.
• Seen on USG.

MCU Indications

• PUV

• VUR

MRI Indications:

MRI Contraindications:

• Metallic foreign body.

• Pacemaker.

• Cochlear implant.

• Knee implant.

• Note: MRI compatible implants are now available.

Contraindications of Mammography

• Breast abscess.

• Young females.
• Have dense breasts.
• White calcifications are not seen in dense breasts.

• Female with a breast implant.
• Compression can rupture the implant.
• MRI is done in this case.
• Intracapsular rupture:
• Ruptured membranes are seen.
• Linguine sign.

IOC - General Principles

CT vs MRI

• White skull bone cortex → CT.

• Black skull bone cortex → MRI.

• White outline seen is outermost fat in the scalp.
• Fat appears white on MRI.

• Knee image:
• Bone cortex is white → CT.

• Marrow with fat:
• black on CT.
• white on MRI.

• Always look for the bone cortex.

Posterior Acoustic Shadowing and Enhancement

• Shadow:
• Appears black.

• Enhancement:
• Appears white.

Posterior Acoustic Shadowing:

• Is given by:
• Gall stones.
• Renal stones.
• Calcifications of bones.
• Air.

• Mechanism for Gall stones:
• Sound reaches the calculus (hyperechoic/white).
• Bad conductor of sound.
• Stones do not transmit sound.
• Area behind is black (Posterior acoustic shadowing).

• Bile:
• Is a good conductor of sound.
• Doesn't give shadowing.
• Leads to enhanced sound -> more sound echoed -> appears white.

Posterior Acoustic Enhancement:

• Cystic lesions.
• Anechoic + Posterior acoustic enhancement

Fluid:

• Appears black.

• Is called anechoic.

• It transmits sound but produces no echo.

Doppler

Doppler:

• Is an ultrasound for blood flow.

• Based on the principle of doppler shift.

• Doppler Shift:
• Change in sound frequency by moving blood.
• Shows color in the doppler.

Color in Doppler:

• Indicates the direction of blood flow.

• Red:
• Flow towards transducer.

• Blue:
• Flow away from transducer.

• Mnemonic: Red Tower (Towards) Blows Away (Away).

Spectral Doppler:

• A graph/Duplex doppler.

• Velocity of blood flow can be quantitatively measured.

Peripheral Vessel Doppler/ Duplex

• 1st IOC
• POVD
• Aneurysm

Vessel	Flow	Notes
Peripheral artery	Triphasic waveform	Triphasic EEG → Hep Enceph
Visceral artery	Monophasic with pulsations	ㅤ
Veins	Monophasic with respiratory phasicity. without pulsations	ㅤ

Elastography

• Study of elasticity or loss of elasticity (fibrosis).

• Helps identify:
• Malignant thyroid nodules.
• Liver fibrosis (cirrhosis).

• Pressure is given with a probe;
• values in kPa.

• B mode ultrasound:
• black and white.

Contrast-enhanced ultrasound (CEUS):

• Orange color.

• Ultrasound contrast: microbubbles.

• CEUS is common for liver lesion characterization.

• Advantage: microbubbles are excreted by the lungs, not kidneys.
• Safe in renal failure.
• Can be given when CT/MRI contrast (renal excretion) cannot.

Investigations for Vascular Pathologies

• Pathologies:
• Thrombosis,
• Embolism,
• Aneurysm,
• Aortic dissection.

Doppler:

• First investigation for peripheral vessels.

• Done for intermittent claudication.

CT angio:

• Identified by white bone and IV contrast.

• Faster than MR angio.

• Preferred in emergencies like
• Aortic dissection,
• Pulmonary embolism.

MR angio:

• White blood vessels, no white bone.

• Can be done with or without contrast.

• Can be done in Renal failure.

DSA (Digital Subtraction Angiography):

• Gold standard investigation.

• Blood vessels can appear black or white.

• Done by Fluoroscopy (video X-ray).

• Contrast given by Intraarterial technique (more invasive).

• Advantage of DSA:
• Therapeutic potential.
• Thrombus can be removed.
• Aneurysm: Coiling can be done (Embolization).
• Other treatment for Aneurysm is clipping.

Contrast Media

• Contrast helps in better evaluation and visualization.

• Positive contrast:
• makes it appear white.
• Examples:
• Iodinated,
• Gadolinium,
• Barium.
• Mnemonic: Positive → Believe () In () God (Gadolinium)

• Negative contrast:
• makes it appear black.
• Example: Air.

1. IODINATED contrast media

Other Contrasts

• Ionic dimer:
• Ioxaglate.
• Io di () sajil ate (Xaglate)

• Diatrizoate: •
• brand name Gastrografin.

• Isosmolar.
• Non-ionic dimer: Iodixanol
• Mnemonic: iso nonidi = non-ionic dimer.

• High osmolar.
• Ionic monomers
• Mnemonic: IM (Ionic, Monomeric) high (high osmolar).

• Low osmolar.
• Rest of the groups

Iohexol

• Iodinated, water-soluble contrast.

• Used for X-ray studies needing contrast (HSG, IVP, CECT).

• Most commonly used.

• Low osmolar, renal safe.

• Most common side effect:
• Anaphylactoid reaction
• not IgE mediated

• Kidney assesment
• KFT/RFT must be done before giving contrast.
• Renal function must be normal (check Serum creatinine).

2. Gadolinium

• Non-iodinated.

• Used for T1 weighted MRI.

• A paramagnetic substance.
• Has magnetic properties.

• Nephrotoxic. → Nephrogenic systemic fibrosis

3. Sonovue

• Orange color image

• Ultrasound contrast.

• Microbubbles of sulfur hexafluoride gas.
• R/o Sulfa allergy

• Excreted from the body via lungs.

• Safe in renal failure.

4. Barium SULFATE

• Barium sulfate is the contrast.

• Given via oral or rectal route.
• For GIT only.
• Not given IV (water-insoluble).

• Contraindicated → Leakage causes Peritonitis.
• Perforation
• Obstruction
• TEF
• Post Operative

• Iodinated contrast is used when Barium Contrindicated

• Barium studies are done under Fluoroscopy
• Fluoroscopy is a video X-ray for moving structures.
• Has more radiation exposure.
• Lead apron is important.

Radiation Units

• Conventional units → begin with R.

• SI units → don't begin with 'R'.

• Conversions:
• 1 Gray = 100 Rad.
• 1 Sv = 100 Rem.

Examination Typical Effective Dose

Relative Radiation Doses

• Radionuclide studies (Isotope scans, PET) have radiation exposure.
• Radionuclide scans use Tc-99.
• PET scans use F-18 FDG.

Investigation	Radiation Dose (mSv)
Chest X-ray	0.02
Mamography	0.5 - 0.7 msv
CT Head	2
Bone scan	4
CT Chest	8
CT Abdomen	10
PET	25

Radiation Hazards

Stochastic effects

• Occur by chance.

• Due to DNA damage.

• Occur at any dose of radiation (low or high).
• As dose increases, probability of occurrence increases.
• No dose threshold.
• Severity is dose independent.

• e.g., Radiation-induced cancer/mutations.

Deterministic effects

• Have a determinable threshold.
• Have a dose threshold (typically several Gy).
• As dose increases, severity increases.

• e.g., Bone marrow suppression, skin erythema (m/c), Alopecia, Cataract, Epilation

• Due to cell killing.
• Proliferating cells are more sensitive:
• Bone marrow,
• Gonads,
• Intestinal epithelium.
• Neurons are the least sensitive (most resistant).

Acute Radiation Syndrome

• Seen with exposure to high radiation > 1 gray.

• Phases: Prodromal → Incubation → Onset → Convalescent (or death).

• Prodromal Phase (first 48 hours):
• Nausea and vomiting (≥ 1 Gy).
• Skin injury (≥ 3 Gy).
• Headache (≥ 4 Gy).

• Onset Phase (0-3 weeks):
• In the onset phase, systems affected first are:
• Bone marrow (> 1-2 Gy) > GIT (> 8 Gy) > Nervous system (>20 Gy).
• Hematopoietic disorder (infection, bleeding) (≥ 3 Gy).
• Diarrhea (≥ 4 Gy).
• Gastrointestinal tract disorder (≥ 8 Gy [800-1000rads]).
• Disturbance of consciousness (≥ 8 Gy).
• Nerve and blood vessel disorders (≥ 30 Gy [3000 rads]).

AERB Guidelines for Personal Protection

• Lead Aprons and Gloves:
• Minimum thickness
• = 0.25 mm (Indian guideline).
• = 0.5 mm (International guideline)
• Most commonly used in India = 0.5 mm.

• Gonadal Shield:
• Minimum thickness = 0.5 mm.

TLD (Thermoluminiscent dosimeter)

• Measures dose of radiation exposure in occupational workers.

• It checks if the radiation is within limits.

• This is monitored every 3 months (Quarterly).

• The substance in the TLD badge
• Calcium sulphate dysprosium in India.
• Lithium Fluoride is used outside India.

• TLD should be worn below the apron to get the actual exposure value.
• If worn above, it measures a false high dose.

• Mnemonic: TLD → L, D → Lithium Fluoride, Dysprosium

Q. The monitoring of the equipment shown in the photograph is done every

DOSE Limitations Set by AERB

NCRP guidelines for mother:

• 5 mSv = 0.5 rad.