Brain Scans vs. MRI: Understanding the Differences

"Brain scan" is an umbrella term for any neuroimaging technique. MRI is one specific type of brain scan.

Common Brain Scan Modalities

Modality	Principle	Key Uses	Radiation?
CT (Computed Tomography)	X-ray attenuation	Trauma (bleed, fracture), stroke (early), hydrocephalus, bone	Yes (ionizing)
MRI (Magnetic Resonance Imaging)	Nuclear magnetic resonance (H¹ protons in B₀ field + RF pulses)	Soft tissue detail: MS, tumors, stroke (subacute/chronic), epilepsy, pituitary, spine, joints	No
PET (Positron Emission Tomography)	γ-rays from positron annihilation (FDG, amyloid, dopamine tracers)	Cancer staging, dementia differentiation, epilepsy focus, cardiac viability	Yes (tracer)
SPECT	γ-rays from radiotracer (Tc-99m, I-123)	Perfusion (brain death, dementia), dopamine transporter (DaTscan)	Yes (tracer)
fMRI	BOLD contrast (deoxyhemoglobin)	Brain mapping (pre-surgical), research	No
MRS	Proton spectroscopy (metabolites: NAA, Cho, Cr, Lac)	Tumor grading, metabolic disorders, epilepsy	No
Ultrasound (cranial)	Sound waves	Neonates (open fontanelle): IVH, hydrocephalus	No

When Each Is Chosen

• Acute trauma/stroke: CT (speed, blood sensitivity).
• Soft tissue detail, no radiation: MRI.
• Metabolic/functional: PET, fMRI, MRS.
• Cost/availability: CT > MRI > PET/SPECT.

All are "brain scans." MRI is the premier non-ionizing structural/functional tool.