PET and SPECT Scans in Medical Imaging

Positron Emission Tomography (PET) Scan

• Uses a radioactive drug called a tracer to show both typical and atypical metabolic activity
• Positive findings indicate a tissue biopsy is necessary when cancer is suspected
• Primarily used to diagnose and track the progression of heart disease, Alzheimer's disease, and various psychological disorders

Single Photon Emission Computed Tomography (SPECT) Scan

• Provides 3D images of the distribution of radioactive tracer molecules in the body
• Uses gamma rays to diagnose and track the progression of heart disease, bone disorders, gallbladder disease, and intestinal bleeding
• Recently become available for diagnosing Parkinson's disease and dementias

SPECT Risks and Benefits

• Risks: radioactive tracer injection, bleeding, pain, or swelling at injection site, and possible allergic reaction in rare cases
• Benefits: small amount of radiation used, generally safe for most people, and no known long-term health risks associated with the test

PET Indications

• Alzheimer's disease: decreased brain metabolism of glucose and oxygen
• Neuropsychology: helps delineate a link between specific processes and brain activity
• Psychiatry: radiotracers binding dopamine, serotonin, opioid, and cholinergic receptors are used to study their roles in various psychological disorders
• Stereotactic surgery and radiosurgery: PET-image guided surgeries are now being done
• Cardiology: helps to identify hibernating myocardium, imaging of atherosclerosis to detect patients at risk of stroke, and detects inflammation early
• Myocardial perfusion tracers: visualize myocardial blood flow
• Myocardial metabolic tracers: assess myocardial viability and are the gold standard for this
• Infectious diseases: can identify bacterial infections
• Autoimmune diseases: efficient in the initial diagnosis and follow-up disease management
• Musculoskeletal system disease: provides muscle activation data about deep-lying muscle

PET Risks and Benefits

• Risks: patients should avoid drinking or eating anything with calories or sugar for several hours before the scan, radioactive tracers, and avoid close contact with pregnant women, babies, and young children for 6 hours after the scan
• Benefits: noninvasive, no recovery time, and radioactive tracers are safe to be in the body for a short time

Ultrasonography (US Imaging)

• Uses high-frequency sound waves to view inside the body
• Can show movement of the body's internal organs as well as blood flowing through the blood vessels
• No ionizing radiation exposure associated with US imaging
• Produced based on the reflection of the waves off of the body structures
• Evaluates for various conditions based on the region of the body, such as:
  • RUQ: free fluid, cholelithiasis, choledocholithiasis, hepatic abscess mass, and hydronephrosis
  • RLQ: appendicitis, intussusception, and psoas abscess
  • LUQ: free fluid, splenic pathology, stomach, and hydronephrosis
  • LLQ: diverticulitis and small bowel obstruction
  • Epigastric: pancreatic mass and abdominal aortic aneurysm
  • Pelvic: free fluid, urinary retention, pregnancy, and ectopic pregnancy

This quiz covers the principles and applications of Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) scans in medical imaging, including cancer diagnosis and heart disease tracking.