Introduction of Medical Imaging

What are the five Diagnostic Imaging techniques used and their function

Detect and diagnose diseases, determine disease severity

X-ray radiography
Computed tomography (CT)
Magnetic resonance imaging (MRI)
Ultrasound (US)
Nuclear medicine

What are the three Therapeutic imaging techniques used and their function

Guide procedures such as surgery or radiation therapy

Fluoroscopy
Angiography
Interventional radiology

General concept, Key concepts, Clinical Strengths, Limitations of X rays

Principle: Uses external X-rays that are differently absorbed (attenuated) by tissues.

X-ray: Single burst of X-rays creates a 2D shadowgram

Key concepts:

• Radiodensity (Air<Fat<Water/Soft tissue<Bone<Metal)

• Superimposition of structures

• Contrast agents (Barium, Iodinated)
  

Clinical strengths (High-yield uses)

• Skeletal: Fractures, dislocations, arthritis

• Chest (CXR): Pneumonia, pneumothorax, heart failure, lung masses

• Abdomen (KUB): bowel obstruction, free air (perforation)

• Screening: Mammography
  

Limitations: Poor soft tissue detail, radiation dose (low), 2D view

What do we use contrast materials for? Examples of procedure used? Examples of compounds used?

Used to enhance plain radiography:

• Angiography, urography, upper and lower GI studies

• We use Barium or Iodine containing compounds

General concept, Key concepts, Clinical Strengths, Limitations of Computed Tomography (CT)

Rotating X-ray gantry and detectors create cross-sectional “slices”, computer reconstructs 3D data

Key Concepts:

• Hounsfield Units (HU) for quantitative density

• Use multi-slice detector which can acquire multiple images

• IV contrast (Iodinated): Assesses vascularity, organ perfusion, inflammation

• CT Angiography (CTS) and Venography (CTV)
  

Clinical strengths (The “Workhorse”)

• Emergency/Trauma: Head injury, internal hemorrhage, aortic dissection

• Oncology: Cancer staging, detecting metastases, treatment response

• Vascular: Pulmonary embolism (PE), aneurysm, stroke evaluation

• Abdomen/Pelvis: Appendicitis, diverticulitis, kidney stones, pancreatitis
  

Limitations: Significant radiation dose, risks of IV contrast (nephropathy, allergy), metal artifacts

General concept, Key concepts, Clinical Strengths, Limitations of Imaging with Sound waves

Principle: Non-ionizing; uses high frequency sound waves and their echoes to create images

• Transducer sends/receives sound waves; image is generated in real-time
  

Key concepts:

• Echogenicity (hyperechoic, hypoechoic, anechoic)

• Acoustic shadowing (e.g. by gallstones) and enhancement

• Doppler: Assesses presence, direction and velocity of blood flow
  

Clinical strengths (Safe and Dynamic):

• Obstetrics/Gynecology: fetal assessment, ovarian/uterine pathology

• Cardiology: echocardiography (cardiac structure and function)

• Abdomen: Gallbladder, liver, kidneys, aorta

• Vascular: Deep vein thrombosis (DVT), Carotid Stenosis

• Point-of-care (POCUS): FAST exam (trauma), guiding procedures (central lines, biopsies)
  

Limitations: Highly operator-dependent, limited by bone and gas, poor penetration in obese patients

What are the advantages of Ultrasounds? Which frequencies do we use?

Advantages:

• portable

• real-time

• no ionizing radiation

• fetal imaging

• inexpensive

• Produces images via backscattering of mechanical energy from boundaries between tissues
  

Frequency: typically 1 to 10 MHz

• Use lower frequencies for deep-lying structures

• Higher frequencies for superficial structures

General concept, Key concepts, Clinical Strengths, Limitations of Imaging with MRIs

Principle: Non-ionizing; uses a powerful magnet and radio waves to
manipulate body protons to generate images

• Protons align in magnetic field radiofrequency pulse knocks them out of alignment → signal is emitted as they relax → computer creates detailed image
  

Key concepts:

• T1 vs T2 weighting: The fundamental contrast mechanisms (T1: fat is bright; T2: water/pathology is bright)

• Gadolinium (IV contrast): shortens T1, highlights vascularity, inflammation

• Functional MRI (fMRI): measures brain activity via blood flow changes
  

Clinical strengths (The Soft Tissue Specialist):

• Neurology: Brain tumors, stroke, spinal cord injury, multiple sclerosis

• Musculoskeletal (MSK): ligament/ tendon tears, cartilage, joint pathology

• Abdomen/Pelvis: Liver/biliary characterization, female pelvic pathology
  

Limitations: Slow, expensive, contraindications (pacemakers, certain metal implants), claustrophobia, noise, NSF risk with gadolinium

General concept, Key concepts, Clinical Strengths, Limitations of Imaging with Nuclear Medicine (Planar scintigraphy, SPECT, PET)

Principle:

• Patient is given a radioactive tracer, a detector captures radiation emitted from the body to show physiological processes

• Radiopharmaceutical is designed to accumulate in a target organ or tissue based on its metabolic activity

• Over time the radioactive isotope will decay, emitting gamma radiation, which is then detected with a gamma camera  increased uptake in areas with increased metabolic activity

• SPECT: Single photon emission computed tomography (3D view)

• PET: Positron emission tomography (higher resolution, quantitative)

• Hybrid imaging (PET/CT, SPECT/CT): fuses

• Functional data with anatomical CT data for precise localization

Clinical strengths (The "How is it working " scan)

• Oncology (PET/CT): The standard for cancer staging, restaging and assessing treatment response

• Cardiology (SPECT): Myocardial perfusion scans (stress tests)

• Endocrinology: Thyroid scan, parathyroid scan

• Skeletal: Bone scan for metastases, infection, osteomyelitis

• Neurology (PET): Dementia evaluation (e.g. Alzheimer’s vs FTD)
  

Limitations: High radiation dose (internal) low spatial resolution, expensive, limited availability

Compare and contrast CT and MRI

Discuss the use of Anatomical information (CT, MRI) VS
Functional/Physiological information (PET, SPECT)

What are some factors in choosing the right test