Neuroimaging and Other Diagnostic Methods
Core concepts to master
Understand what each modality measures and its strengths and limits. CT is fast and best for acute hemorrhage and mass effect; MRI offers superior soft-tissue contrast, with sequences (T1, T2, FLAIR, DWI, GRE/SWI) each answering different questions. DWI detects acute ischemia; FLAIR shows edema and chronic changes; SWI detects microbleeds. Functional and metabolic methods (fMRI, PET, SPECT, MRS) and electrophysiology (EEG, evoked potentials) answer distinct questions about activity, metabolism, and conduction.
Know how structural findings relate to cognition: white-matter hyperintensities, atrophy patterns (medial temporal vs. frontal), and vascular burden. Understand that imaging is supportive, not diagnostic in isolation - many findings appear in asymptomatic individuals.
Traps
Assuming a normal scan excludes cognitive dysfunction (functional and microscopic disease may not show). Confusing modality purposes (e.g., using CT to characterize acute infarct vs. DWI). Treating incidental findings as causal. Forgetting that fMRI is correlational, not a direct measure of neuronal firing.
Rule of thumb
Match modality to question: Is there blood or mass? → CT. Is there acute infarct? → DWI. Is there atrophy or chronic change? → T1/FLAIR. Is there abnormal activity? → EEG. Imaging informs but does not replace clinical reasoning.
Worked example: A patient with acute-onset aphasia and a normal non-contrast CT should still be evaluated with DWI, since CT is often insensitive to early ischemia.