RAD-CONTRAST(PRELIM)

Radiographic contrast

difference in optical density between adjacent structures on an image

Contrast (degree)

degree of difference between black & white on a radiograph

Density (radiograph)

overall blackening of a radiograph

High contrast images

show greater distinction between light and dark areas

Low contrast images

feature a wider range of gray shades

Radiolucent

definition: permits X-rays to pass; appears dark/black on X-ray

Radiopaque

definition: absorbs X-rays; appears white/light on X-ray

Example of radiolucent

air, fat, most soft tissues

Example of radiopaque

bone, metal, calcifications, many contrast agents

Double contrast

definition: use of positive + negative contrast (e.g., iodine + air)

Intra-biliary (IB)

contrast route used to image the bile ducts

Oral (PO)

contrast given by mouth for gastrointestinal imaging

Rectal (PR)

contrast administered per rectum for lower GI imaging

Intravenous (IV)

contrast into a vein used for vascular imaging and CT

Intra-arterial (IA)

contrast injected directly into arteries for angiography

Intra-articular

contrast injected into a joint for arthrography

Topical

contrast applied to the skin or mucosal surface

Sublingual

contrast placed under the tongue for rapid absorption

Subcutaneous

contrast injected under the skin (subcutaneously)

Contrast for CT angiography

typically IV iodinated contrast

Positive contrast media

appears white on X-ray (radiopaque) — e.g., barium, iodine

Negative contrast media

appears black on X-ray (radiolucent) — e.g., air, CO₂

Barium sulfate

GI radiopaque contrast (BaSO₄); insoluble; coats mucosa; avoid if perforation

Iodinated contrast (water-soluble)

used for vascular, urinary, and CT studies; may cause allergic reactions

Gastrografin

water-soluble, hyperosmolar iodinated contrast used when perforation suspected

Gadolinium-based contrast agents (GBCAs)

MRI agents that alter proton relaxation times (T1 enhancement)

Air (negative contrast)

used as negative contrast in double-contrast GI studies

CO₂ contrast

negative contrast gas used in some vascular studies (alternative to iodine)

Ionic iodinated agents

older, high-osmolar agents with higher adverse reaction rates

Non-ionic iodinated agents

newer, low-osmolar agents with fewer reactions (e.g., iohexol)

Wilhelm Röntgen (1895)

discovered X-rays — foundation for radiologic imaging

Walter Cannon

early user of bismuth for GI contrast studies

Evarts Graham & Warren Cole (1924)

introduced clinical use of barium sulfate for GI studies

Moses Swick (1929)

introduced first organic iodinated contrast (Uroselectan) for urography

Ionic vs non-ionic

ionic = older and more reactive; non-ionic = safer, low-osmolar

Non-ionic development

major safety shift in 1970s–1980s toward low-osmolar agents

Examples of non-ionic agents

iohexol (Omnipaque), iopamidol (Isovue), ioversol (Optiray)

MRI pioneers (Lauterbur & Mansfield)

developed MRI technology (Nobel Prize 2003)

Gadolinium introduction

late 1980s — used for MRI contrast enhancement

Early toxic contrasts

heavy metals like bismuth, lead, mercury — abandoned due to toxicity

Perforation rule

do NOT use barium if perforation is suspected; use water-soluble iodine instead

Gold-standard GI contrast

(barring perforation) barium sulfate

Double-contrast barium enema

combines barium + air to enhance mucosal detail and detect polyps

Gadolinium property

paramagnetic agent that shortens T1 relaxation (bright on T1 MRI)

Advantage of non-ionic iodinated

lower osmolarity → fewer systemic reactions

BaSO4 formula

chemical formula: BaSO₄ (barium sulfate)

Barium atomic number

barium element Z = 56

Thin barium

use to evaluate esophageal motility and swallowing (flows easily)

Thick barium

use to coat mucosa, detect ulcers, aspiration — flows slowly

Thin barium consistency

like a milkshake (low viscosity)

Thick barium consistency

like pudding (high viscosity)

Thin barium best for

motility/peristalsis assessment; first in swallow studies

Thick barium best for

visualizing mucosal lesions, detecting aspiration, subtle leaks

Thin barium aspiration risk

higher aspiration risk due to low viscosity

Thick barium aspiration risk

lower aspiration risk; better mucosal coating

Contrast for suspected TEF in infants

use water-soluble iodinated contrast (not barium)

Barium solubility

insoluble; not absorbed systemically; passes through GI tract

Barium excretion

excreted unchanged in stool

When NOT to use barium

in suspected GI perforation or uncontrolled aspiration risk

Mnemonics for barium

“Thin to see it flow; Thick to catch it slow.”

Barium swallow (esophagogram)

evaluates esophagus for dysphagia, reflux, hiatal hernia

Upper GI series

examines esophagus, stomach, and duodenum with contrast

Small bowel follow-through (SBFT)

timed study to image small intestine transit

Barium enema

examines colon; can be single or double contrast

IVU / IVP (intravenous urography)

imaging of kidneys, ureters, bladder with iodinated contrast

Hysterosalpingography (HSG)

evaluates fallopian tube patency for infertility workup

Myelography

contrast into subarachnoid space to image spinal canal and nerve roots

Arthrography

contrast into joint space to evaluate ligaments, cartilage, menisci

Angiography

imaging of blood vessels using intra-arterial or IV contrast

CT with contrast

uses iodinated contrast to enhance vessels and soft tissues

MRI with contrast

uses gadolinium chelates to enhance lesion detection on MRI

Fluoroscopy

use for real-time dynamic contrast studies and procedures

Double-contrast esophagogram

barium + air to show mucosa and motility together

Erect chest X-ray

best plain film for detecting free intraperitoneal air

Contrast choice in trauma/w/ suspected perforation

water-soluble iodinated contrast

Mild contrast reaction symptoms

nausea, warmth, itching

Moderate contrast reaction symptoms

urticaria (hives), vomiting, bronchospasm

Severe contrast reaction

signs of anaphylaxis: hypotension, bronchospasm, collapse

Anaphylaxis treatment

first-line: intramuscular/intravenous epinephrine and emergency care

Urticaria definition

hives — itchy red raised welts

Pre-contrast renal check

assess renal function via serum creatinine/GFR

Important lab before contrast

serum creatinine or estimated GFR (eGFR)

Contrast-induced nephropathy (CIN)

acute kidney injury after iodinated contrast exposure

Safer contrast in renal impairment

iso-osmolar iodinated agents (lower nephrotoxicity risk)

Gadolinium risk in renal failure

possible nephrogenic systemic fibrosis (NSF) in severe renal impairment

Shellfish allergy = iodine allergy?

no — shellfish allergy is not the same as iodine allergy

Premedication for prior mild reaction

steroids and antihistamines per protocol

Hydration before/after contrast

helps reduce risk of contrast-induced nephropathy

Informed consent

for contrast administration; discuss risks and alternatives

Post-contrast observation

time to monitor: commonly 15–30 minutes post-injection

More radiopaque: metal or bone?

metal is more radiopaque than bone

More radiolucent: fat or air?

air is more radiolucent than fat

Swallowing studies in stroke patients

use thick barium to reduce aspiration risk

Imaging with no ionizing radiation that uses contrast

MRI (gadolinium-based contrast)

Exam using both positive & negative contrast

double-contrast studies (e.g., barium + air)

Osmolarity of older iodinated contrast

high osmolarity (HOCM)

Osmolarity of modern non-ionic iodinated contrast

low osmolarity (LOCM)

Iso-osmolar contrast example

iodixanol

Main purpose of contrast media

to make soft tissues and hollow organs more visible for diagnosis

Golden rule mnemonic about perforation

if perforation suspected → pick iodine (not barium)