Lesson 14

Diagnostic Procedures and Nuclear Medicine

Diagnostic medicine encompasses radiology, nuclear medicine, laboratory testing, and complementary/alternative medicine. From plain x-rays to MRI, PET scans, and molecular diagnostics, modern medicine has extraordinary tools for visualizing anatomy and physiology. This lesson covers the major imaging modalities, their indications, and the terminology of the diagnostic process.

60 min4 sections5 objectives

Learning Objectives

1Distinguish between different imaging modalities and their uses
2Identify combining forms for diagnostic procedures
3Understand the principles of nuclear medicine and radiation therapy
4Recognize common laboratory tests and their significance
5Apply diagnostic terminology in clinical contexts

1Radiology: X-ray and CT

Plain Radiograph (X-ray):

First-line imaging; uses ionizing radiation

Excellent for: Bones (fractures), lungs, foreign bodies

Dense structures (bone, metal) appear white; air appears black

Standard views: AP (anteroposterior), PA (posteroanterior), lateral

Fluoroscopy: Real-time x-ray; used for barium swallow/enema (GI studies), cardiac cath

CT (Computed Tomography):

Multiple x-ray slices → cross-sectional images

With/without contrast (iodinated dye)

Best for: Head trauma, pulmonary embolism (CT angiography), abdominal emergencies

Hounsfield units (HU): Scale of radiodensity

Radiation exposure: CT = ~100-200× plain x-ray; use ALARA principle (As Low As Reasonably Achievable)

2MRI and Ultrasound

MRI (Magnetic Resonance Imaging):

Uses magnetic field + radiofrequency waves; NO ionizing radiation

Excellent for: Brain, spinal cord, soft tissues, joints, cartilage

T1-weighted: Fat bright, water dark (good for anatomy)

T2-weighted: Water bright (good for edema, pathology)

Contraindications: Metallic implants (pacemakers), claustrophobia

Gadolinium contrast used for enhancement

Ultrasound (US):

High-frequency sound waves; NO ionizing radiation; real-time; bedside available

Best for: Pregnancy, gallbladder (gallstones), thyroid, FAST exam (trauma), vascular

Doppler: Measures blood flow velocity

Limitations: Operator-dependent; poor penetration through bone/gas

3Nuclear Medicine

Principles: Radioactive tracers (radiopharmaceuticals) injected → taken up by specific tissues → gamma camera detects emissions → functional imaging

Common Studies:

Bone scan: Technetium-99m; detects metastases, osteomyelitis, fractures

Thyroid scan: I-131 or Tc-99m; evaluates function, detects nodules

MUGA scan: Evaluates left ventricular ejection fraction

VQ scan (Ventilation-Perfusion): Diagnoses pulmonary embolism

PET Scan (Positron Emission Tomography):

FDG (fluorodeoxyglucose) tracer; cancer cells have high glucose metabolism → "light up"

PET/CT combination: Functional + anatomical imaging

Used for: Cancer staging, cardiac viability, neurological assessment

Radiation Therapy:

External beam radiation therapy (EBRT): Linear accelerator delivers focused radiation

Brachytherapy: Radioactive seeds placed inside/near tumor

4Laboratory Diagnostics

Complete Blood Count (CBC):

WBC, RBC, Hemoglobin, Hematocrit, Platelets, Differential (neutrophils, lymphocytes, etc.)

Basic Metabolic Panel (BMP): Sodium, potassium, chloride, CO2, glucose, BUN, creatinine, calcium

Liver Function Tests (LFTs): ALT, AST, ALP, GGT, bilirubin, albumin

Coagulation studies: PT/INR, aPTT, thrombin time; assess clotting

Urinalysis: pH, specific gravity, glucose, protein, blood, nitrites, leukocyte esterase

Cultures: Blood, urine, CSF, sputum, wound → identify organism + sensitivity

Biopsy types: Fine needle aspiration (FNA), core needle biopsy, excisional biopsy

Complementary Medicine: Acupuncture, chiropractic, naturopathy, homeopathy, herbal medicine

Clinical Connections

►MRI is preferred over CT for neurological conditions to avoid radiation exposure
►PET scans are the gold standard for cancer staging and detecting occult metastases
►Point-of-care ultrasound (POCUS) has transformed emergency and critical care medicine

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