Microscopy & Medical Imaging Techniques: Tissue Prep, Light vs. Electron, and Modalities

Light Microscopy

Uses a beam of light; provides lower magnification.

Electron Microscopy

Uses beams of electrons; provides much higher magnification.

Scanning Electron Microscopy (SEM)

Specifically provides 3D images of whole, unsectioned surfaces.

Fixation

Preserving the tissue specimen.

Sectioning

Slicing the specimen thin enough for light/electrons to pass through.

Staining

Applying dye to distinguish cellular structures.

Acidic stains

Have negatively charged dye molecules (bind to positively charged cellular components).

Basic stains

Have positively charged dye molecules (bind to negatively charged components like nucleic acids).

Artifacts

Minor distortions introduced during tissue preservation and processing; important because they mean the slide is not 100% identical to living tissue.

Standard X-Ray (Radiograph)

Uses short-wavelength electromagnetic waves.

Computed Tomography (CT / CAT Scan)

Takes successive X-rays around the body's full circumference to reconstruct a cross-sectional (transverse) slice via computer.

Digital Subtraction Angiography (DSA)

Involves injecting a contrast medium into blood vessels.

Positron Emission Tomography (PET Scan)

Detects radioactive isotopes (tracers) injected into the body.

Ultrasound / Sonography

Uses high-frequency sound wave pulses that echo off tissues.

Magnetic Resonance Imaging (MRI)

Uses magnetic fields to detect relative water (hydrogen) content across tissues.

Best for dense structures

Bones, tumors/masses and finding abnormal dense tissue.

Great for soft-tissue and bony details

In cross-section.

Highlights vessel blockages

Aneurysms, or narrowing (especially coronary and cerebral arteries).

Evaluates cellular metabolic activity

Frequently used to spot active tumors/metastases and assess cancer treatment.

Safe, non-invasive, radiation-free method

Primarily used for fetal monitoring and soft tissue evaluation.

Produces high-contrast images

Of soft tissues (muscles, brain, ligaments, cartilage/meniscus tears).