Radiologic Procedures & Imaging Modalities – Comprehensive Exam Notes

Radiologic Technology: Scope & Importance

• Radiologic technology (diagnostic imaging) is fundamental for:
  • Routine screenings (e.g., mammograms, chest X-rays).
  • Targeted diagnostic evaluations to confirm or rule out disease/injury.
• Imaging can also monitor disease progression, guide therapy, and assess treatment response (e.g., MRI follow-up for tumor shrinkage).

Radiation Safety & Occupational Precautions

• All personnel in radiology settings risk excessive radiation exposure; strict precautions are mandatory.
• Protective protocols include:
  • Wearing a personnel-monitoring device (film badge or digital dosimeter) at all times.
  • Each worker has an age-dependent maximum permissible dose (MPD)—regulatory cap on cumulative exposure.
  • Adhering to ALARA (As-Low-As-Reasonably-Achievable) principles: time, distance, shielding.
• Film badge specifics:
  • Contains a sensitized film that darkens proportionally to radiation received.
  • Badges are evaluated periodically to document exposure history.

X-Rays (Roentgen Rays)

• Definition: High-energy electromagnetic radiation produced when a beam of electrons collides with a metal target inside an X-ray tube.
• Historical note: Discovered in 1895 by Wilhelm Conrad Roentgen (1845-1923).
• Chest X-ray protocol:
  • Patient must remain motionless in prescribed positions.
  • Radiologist generally renders the official interpretation, though ordering providers may preview images.

Radiation Therapy (Therapeutic Radiology)

• Goal: Destroy or inhibit cancer cells by preventing cellular reproduction.
• Two principal modalities:
  • Teletherapy – External-beam radiation; deep tissue penetration; typically outpatient.
  • Brachytherapy – Placement of radioactive implants inside or adjacent to tumor tissue for highly localized dosing.
• Ethical/practical note: Balances tumor control with minimization of collateral tissue damage.

General Patient Preparation Principles

• Preparation varies by study & facility; always verify up-to-date instructions when scheduling.
• Key elements: fasting, bowel cleansing, medication adjustments, contrast-related allergies.

Contrast Agents & Media

• Purpose: Increase density differences to enhance visualization.
• Common types:
  • Barium sulfate – GI tract studies.
  • Iodine-based compounds – IVP, CT, angiography.
  • Gas/air – Double-contrast colon studies.
• Risk considerations: allergic reactions, nephrotoxicity (especially iodine), patient hydration status.

Gallbladder Imaging: Cholecystogram

• Gallbladder function: Stores bile from liver for fat digestion.
• Indications: Abdominal pain, nausea, suspected gallstones/dysfunction.
• Imaging outcome: Provider can pinpoint etiology of symptoms.

Abdominal Ultrasound (Sonogram)

• Ultrasound basics: Utilizes sound waves > $20\,000$ vibrations/sec to create images.
• Benefits over cholecystogram:
  • No radiation.
  • Real-time visualization of gallbladder, liver, ducts.
• Process: Continuous waves emitted → reflected echoes captured by transducer → converted to screen image.
• Clinical relevance: First-line test for biliary colic, pregnancy, pediatric cases.

Upper GI Series (Barium Swallow)

• Procedure steps:
  • Patient drinks a milkshake-like barium suspension under fluoroscopy.
  • Radiologist tracks passage through esophagus, stomach, duodenum, small intestine.
• Diagnostic yield: Detects hiatal hernia, peptic/duodenal ulcers, tumors, motility disorders.

Lower GI Series (Barium Enema)

• Technique:
  • Barium sulfate introduced into colon via enema tube.
  • Fluoroscopic observation + multiple radiographs.
• Double-Contrast Study: After draining most barium, air is insufflated → colon distends → mucosal detail sharpened.
• Uses: Identify polyps, tumors, inflammatory bowel disease, diverticula.

Standard Bowel Prep (Example)

• Transition to all-liquid diet morning before exam.
• NPO after midnight (no food/drink).
• Take cathartic (e.g., $2$ Dulcolax (5\,\text{mg}) tablets) with water night prior.
• OTC enema may be required night before or hours before.
• Verify medication restrictions ≥ 1 week prior (anticoagulants, metformin, etc.).

Urinary Tract Imaging

Intravenous Pyelogram (IVP)

• IV iodinated contrast highlights kidneys → ureters → bladder.
• Variants: Retrograde pyelogram via catheter up ureters; contrast flows retrograde into kidneys.
• Applications: Stones, obstruction, congenital anomalies.

KUB (Kidneys, Ureters, Bladder) X-Ray

• Plain abdominal film; no prep needed.
• Uses:
  • Detect urinary calculi, GI foreign bodies.
  • Confirm intrauterine device (IUD) placement.

Breast Imaging

Standard Mammography

• Detects masses ≤ $1\,\text{cm}$.
• ACS guideline: Baseline at $40$ yr; annual if in good health.
• Technique: Multiple angles with breast compression → lowers radiation & improves clarity.
• Immediate follow-up required if palpable lump found.

3D Mammography (Breast Tomosynthesis)

• Acquires images at multiple angles → reconstructed into 3-D slices.
• Advantages: Better visualization in dense breasts, improved small cancer detection.

Computed Tomography (CT) Scans

• Produces cross-sectional “slices” ≈ $1\,\text{cm}$ thick within seconds.
• Former term: Computerized Transverse Axial Tomography (CTAT).
• Widely used for breast, brain, thoracic & abdominal pathology; rapid trauma assessment.

Nuclear Medicine & Radionuclide Studies

• Patient ingests or receives IV radiopharmaceuticals; gamma camera records emitted radiation.
• Uptake studies: Quantify tracer concentration in an organ after ~$24$ h (e.g., thyroid iodine uptake).
• Strengths: Functional information (perfusion, metabolism) beyond structural imaging.

Sonographic (Ultrasound) Studies – Technical Overview

• Transducer emits & receives high-frequency waves.
• Echo pattern converted into electrical signal → real-time image or printout.
• Depicts cross-sections; safe during pregnancy.

Magnetic Resonance Imaging (MRI)

• Uses strong electromagnetic fields + radiofrequency pulses; no ionizing radiation.
• Exam time: $30$–$60$ min; patient lies on table slid into bore.
• Multi-planar capability without repositioning.
• Contraindications:
  • Pacemakers, cochlear/metallic implants.
  • First-trimester pregnancy.
  • Severe claustrophobia, extreme obesity.
• Pre-scan requirements: Remove all metallic objects (jewelry, hairpins, dentures).
• Utility: Neurology, musculoskeletal, cardiac, tumor staging, therapy monitoring.

Positron Emission Tomography (PET) Scan

• Involves IV injection of radioactive tracer; distributes via bloodstream, accumulates in metabolically active tissue.
• Wait period: ~$60$ min post-injection before scan.
• Patient lies on narrow table sliding into tunnel-shaped detector.
• Computer reconstructs tracer signals into 3-D images displaying metabolic activity.
• Combines with CT (PET/CT) or MRI (PET/MRI) for fused functional + anatomical detail.

Ethical, Philosophical & Practical Implications

• Balancing diagnostic yield vs. radiation risk—especially in pediatric & pregnant populations.
• Informed consent: Patients must understand contrast risks, radiation exposure, alternatives (e.g., ultrasound vs. CT).
• Equity & access: Advanced modalities (MRI, PET) are costly; insurance coverage and geographic availability affect patient care.
• Technologic evolution: Improvements (3D mammography, rapid CT) continually change prep protocols and diagnostic algorithms; clinicians must stay updated.

Quick Reference: Numerical & Technical Facts

• Ultrasound frequency: >20\,000\,\text{Hz} (above audible range).
• Breast mass detection threshold (mammography): $\le1\,\text{cm}$ diameter.
• CT slice thickness: $\approx1\,\text{cm}$.
• Dulcolax laxative dose (prep example): $2$ tablets, $5\,\text{mg}$ each.
• IVP contrast: Iodine-based; monitor for renal function & allergy.

Study Connections & Integration

• Many organs can be imaged by multiple modalities; choice depends on diagnostic question, patient factors, safety, and resource availability.
  • Gallbladder: Ultrasound (first-line) vs. cholecystogram.
  • Colon: CT colonography vs. barium enema vs. colonoscopy.
  • Oncology: PET assesses metabolism; MRI evaluates extent; CT monitors size.
• Sequential imaging may track disease (e.g., baseline CT, follow-up MRI; PET for therapy response).

Summary Cheat-Sheet

• X-ray = quick structure; CT = detailed cross-sections; MRI = high-resolution soft tissue without radiation; Ultrasound = safe sound-based; Nuclear/PET = physiology & metabolism; Mammography = breast screening; Barium studies = GI tract contour; IVP = urinary outline; Safety first: MPD, shielding, metal-free MRI.